National Ambient Air Quality Standards for Ozone: Final Response to Remand

Note: EPA no longer updates this information, but it may be useful as a reference or resource.
  [Federal Register: January 6, 2003 (Volume 68, Number 3)]
[Rules and Regulations]
[Page 613-645]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr06ja03-24]

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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 50
[FRL-7428-7]
RIN 2060-ZA11
 
National Ambient Air Quality Standards for Ozone: Final Response 
to Remand

AGENCY: Environmental Protection Agency (EPA).
ACTION: Final response to remand.

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SUMMARY: On July 18, 1997, in accordance with sections 108 and 109 of 
the Clean Air Act (Act), EPA completed its review of the national 
ambient air quality standards (NAAQS) for ozone (O₃) by 
promulgating revised primary and secondary standards (62 FR 38856; 
henceforth, ``1997 final rule''). On May 14, 1999, the United States 
Court of Appeals for the District of Columbia Circuit (``D.C. 
Circuit'') remanded the O₃ NAAQS to EPA to consider, among 
other things, any potential beneficial health effects of O₃ 
pollution in shielding the public from the ``harmful effects of the 
sun's ultraviolet rays.'' 175 F.3d 1027 (D.C. Cir., 1999). Today's 
action provides EPA's final response to that aspect of the Court's 
remand. Based on its review of the air quality criteria and NAAQS for 
O₃ completed in 1997, its additional assessment of potential 
beneficial effects of tropospheric O₃, and taking into 
account public comments, EPA has determined that information linking 
(a) changes in patterns of ground-level O₃ concentrations 
likely to occur as a result of programs implemented to attain the 1997 
O₃ NAAQS to (b) changes in relevant patterns of exposures to 
ultraviolet (UV-B) radiation of concern to public health is too 
uncertain at this time to warrant any relaxation in the level of public 
health protection previously determined to be requisite to protect 
against demonstrated direct adverse respiratory effects of exposure to 
O₃ in the ambient air. Further, it is the Agency's view that 
associated changes in UV-B radiation exposures of concern, using 
plausible but highly uncertain assumptions about likely changes in 
patterns of ground-level ozone concentrations, would likely be very 
small from a public health perspective. As a result, the revised 
O₃ NAAQS will remain set 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. No other issues 
related to the 1997 O₃ NAAQS remain before the Court, and 
other remanded issues related to implementation of the O₃ 
NAAQS are not addressed by today's action.

EFFECTIVE DATE: March 7, 2003.

ADDRESSES: A docket containing information relating to EPA's review of 
the O₃ primary and secondary standards and this response to 
the D.C. Circuit remand (Docket No. A-95-58) is available for public 
inspection at the EPA's Air Docket Center, 1301 Constitution Avenue, 
N.W., Room B108, Washington, DC 20460, Mail code 6102T. This docket 
incorporates the docket from the previous review of the O₃ 
standards (Docket No. A-92-17) and the docket established for the ozone 
air quality criteria document (Docket No. ECAO-CD-92-0786). The docket 
may be inspected between 8:30 a.m. and 4:30 p.m. on weekdays, excluding 
legal holidays. A reasonable fee may be charged for copying. The 
information in the docket constitutes the complete basis for the 
decision announced in this final response to the remand. For the 
availability of related information, see SUPPLEMENTARY INFORMATION.

FOR FURTHER INFORMATION CONTACT: Susan Lyon Stone, Office of Air 
Quality Planning and Standards, U.S. Environmental Protection Agency 
(C539-01), Research Triangle Park, NC 27711; e-mail 
stone.susan@epa.gov; telephone (919) 541-1146.

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) The Review of the National Ambient Air Quality Standards for 
Ozone: 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).
    (2) Air Quality Criteria for Ozone 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 and $58.00 microfiche).
    A limited number of copies of other documents generated in 
connection with the review of the standard, such as documents 
pertaining to human exposure and health risk assessments and the 
relationships between ground-level O₃, UV-B radiation, and 
health effects, can be obtained from: U.S. Environmental Protection 
Agency Library (C267-01), 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.

Electronic Availability

    The Staff Paper and documents pertaining to human health risk and 
exposure assessments are available on the Office of Air and Radiation, 
Policy and Guidance Web site at: http://www.epa.gov/ttn/oarpg/t1sp.html.
 The O₃ NAAQS 1996 proposal and 1997 final rule 
are available at the same Web site, at: http://www.epa.gov/ttn/oarpg/
t1pfpr.html.

Children's Environmental Health

    This final response to the Court's remand, reaffirming the 1997 8-
hour O₃ NAAQS, specifically takes into account children as 
the group most at risk to the direct inhalation-related effects of 
O₃ exposure, and was based on studies of effects on 
children's health (U.S. EPA, 1996a; U.S. EPA, 1996b) and assessments of 
children's exposure and risk (Johnson, 1994; Johnson et al., 1996 a,b; 
Whitfield et al., 1996; Richmond, 1997). The 8-hour O₃ 
primary standard protects children's health with an adequate margin of 
safety from the direct adverse effects associated with inhalation 
exposures to ground-level O₃, after considering potential 
indirect beneficial effects of ground-level O₃ related to 
its attenuation of UV-B radiation and any associated adverse health 
effects.

Implementation Activities

    When the 8-hour primary and secondary O₃ standards are 
implemented by the States, the power generation, automobile, petroleum, 
and chemical industries are likely to be affected, as well as other 
manufacturing concerns that emit volatile organic compounds (VOC) or 
nitrogen oxides (NO_X). The extent of such effects will 
depend on implementation policies and control strategies adopted by 
States to assure attainment and maintenance of the standards.
    The EPA is now developing appropriate policies and control 
strategies to assist States in the implementation of the 8-hour primary 
and secondary O₃ NAAQS. The EPA now expects to propose an 
implementation strategy for public comment early in 2003.

Table of Contents

    The following topics are discussed in today's preamble:

[[Page 615]]

I. Background
    A. 1997 Revision of the O₃ NAAQS
    1. Legislative Requirements
    2. Review of Air Quality Criteria and Standards for 
O₃
    B. Ozone NAAQS Litigation and Remand
    1. Litigation Summary
    2. Remand on Health Benefits Issue
    C. Atmospheric Distribution of O₃ and UV-B Radiation
    D. Related Stratospheric O₃ Program
    E. Summary of Proposed Response to Remand
II. Rationale for Final Response to Remand on the Primary 
O₃ Standard
    A. Direct Adverse Health Effects from Breathing O₃ in 
the Ambient Air
    1. Health Effects Associated with O₃ Inhalation 
Exposures
    2. Human Exposure and Risk Assessments
    B. Potential Indirect Beneficial Health Effects Associated with 
Ground-level O₃
    1. Health Effects Associated with UV-B Radiation Exposure
    2. Relationship Between Ground-level O₃ and UV-B 
Radiation Exposure
    3. Evaluation of UV-B Radiation-related Risk Estimates for 
Ground-level O₃ Changes
    C. Consideration of Net Adverse Health Effects of Ground-level 
O₃
    D. Final Response to Remand on the Primary O₃ NAAQS
III. Rationale for Final Response to Remand on the Secondary 
O₃ Standard
    A. Direct Adverse Welfare Effects
    B. Potential Indirect Beneficial Welfare Effects
    C. Final Response to Remand on the Secondary O₃ NAAQS
IV. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination with 
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children from 
Environmental Health and Safety Risks
    H. Executive Order 13211: Actions that Significantly Affect 
Energy Supply, Distribution, or Use
    I. National Technology Transfer Advancement Act
    J. Congressional Review Act
V. References

I. Background

A. 1997 Revision of the O₃ NAAQS

    On July 18, 1997, in accordance with sections 108 and 109 of the 
Act, EPA completed its review of the NAAQS for O₃ by 
promulgating revised primary and secondary standards (1997 final rule). 
These standards were based on EPA's review of the available scientific 
evidence linking direct exposures to ambient O₃ to adverse 
health and welfare effects at levels allowed by the then current 
O₃ standards. The revised primary and secondary standards 
were each set at a level of 0.08 ppm, with an 8-hour averaging time and 
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.\1\ The new primary standard was established to 
provide increased protection to the public, especially children and 
other at-risk populations, against a wide range of O₃-
induced respiratory health effects due to inhalation exposures, 
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 new secondary standard was 
established to provide increased protection to the public welfare 
against direct O₃-induced effects on vegetation, such as 
agricultural crop loss, damage to forests and ecosystems, and visible 
foliar injury to sensitive species.
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    \1\ The form of a standard refers to the air quality statistic 
that is used to determine whether an area attains the standard.
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1. 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.'' 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.'' \2\
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    \2\ 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, man-made 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.''
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    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.
2. Review of Air Quality Criteria and Standards for O₃
    An overview of the last review of the O₃ air quality 
criteria and standards is presented in section I.C of the preamble to 
the 1997 final rule. In summary, the 1997 review was initiated in 
August 1992 with the development of a revised Air Quality Criteria 
Document for Ozone and Other Photochemical Oxidants (henceforth, the 
``Criteria Document''). Multiple drafts of the Criteria Document were 
reviewed by CASAC and the public, resulting in a final Criteria 
Document (U.S. EPA, 1996a) that reflected CASAC and public comments.\3\ 
The EPA also prepared a staff paper, Review of National Ambient Air 
Quality Standards for Ozone: Assessment of Scientific and Technical 
Information (henceforth, the ``Staff Paper'').\4\ Multiple drafts of 
the Staff Paper were also reviewed by CASAC and the public, resulting 
in a final Staff Paper (U.S. EPA, 1996b) that reflected CASAC and 
public comments.\5\
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    \3\ 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 ozone and related photochemical oxidants'' 
(Wolff, 1995a).
    \4\ 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.
    \5\ In separate letters from the CASAC chair to the 
Administrator, CASAC advised that the primary standard and secondary 
standard sections of the final draft Staff Paper provide ``an 
adequate scientific basis for making regulatory decisions'' 
concerning the O₃ standards (Wolff, 1995b, 1996).
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    On November 27, 1996 EPA announced its proposed decision to

[[Page 616]]

revise the NAAQS for O₃ (61 FR 65716, December 13, 1996; 
henceforth, ``1996 proposal''), as well as its proposed decision to 
revise the NAAQS for particulate matter (PM). To ensure the broadest 
possible public input on these proposals, EPA took extensive and 
unprecedented steps to facilitate the public comment process, including 
the establishment of a national toll-free telephone hotline and 
provisions for electronic submission of comments. The EPA also held 
several public hearings, participated in numerous meetings across the 
country, and held two national satellite telecasts to provide direct 
opportunities for public comment and to disseminate information to the 
public about the proposed standard revisions. As a result of this 
intensive effort to solicit public input, more than 50,000 comments 
were received on the proposed revisions to the O₃ NAAQS by 
the close of the public comment period on March 12, 1997.
    The final rule, published on July 18, 1997, presented EPA's 
rationale for its final decision, and addressed the major issues raised 
in comments on the 1996 proposal. A comprehensive summary of all 
significant comments, along with EPA's response to such comments (U.S. 
EPA, 1997; henceforth, ``Response to Comments''), can be found in the 
docket for the 1997 rulemaking (Docket No. A-95-58).\6\ The 1997 final 
rule presented EPA's decision to replace the existing 1-hour primary 
and secondary standards \7\ (each set at a level of 0.12 ppm, with a 1-
expected-exceedance form, averaged over 3 years \8\ with 8-hour 
standards, each set at a level of 0.08 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 
(as determined by 40 CFR part 50, appendix I).
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    \6\ This docket incorporates by reference the docket from the 
previous O₃ NAAQS review (Docket No. A-92-17) and the 
docket established for the Criteria Document (Docket No. ECAO-CD-92-
0876).
    \7\ These 1-hour O₃ standards were originally set in 
1979 (44 FR 8202, February 8, 1979) and reaffirmed in 1993 (58 FR 
13008, March 9, 1993).
    \8\ The 1-hour 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 one, averaged over 3 years 
(as determined by 40 CFR part 50, appendix H).
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B. Ozone NAAQS Litigation and Remand

1. Litigation Summary
    Following promulgation of the revised 8-hour O₃ NAAQS, 
numerous petitions for review of the standards were filed in the D.C. 
Circuit. American Trucking Associations v. EPA, No. 97-1441. Oral 
argument was held on December 17, 1998 and the Court rendered its 
opinion on May 14, 1999. American Trucking Associations v. EPA (``ATA 
I''), 175 F.3d 1027 (D.C. Cir., 1999). A divided panel found that 
section 109 of the Act, 42 U.S.C. Sec.  7409, as interpreted by EPA in 
setting the revised O₃ (and PM) NAAQS, effected an 
unconstitutional delegation of legislative authority. Id. at 1033-1040. 
The Court remanded the O₃ standards with instructions that 
EPA should articulate an ``intelligible principle'' for determining the 
degree of residual risk to public health permissible in setting revised 
NAAQS. Id. In addition, the Court also directed that, in responding to 
the remand, EPA should consider the potential beneficial health effects 
of O₃ pollution in shielding the public from the ``harmful 
effects of the sun's ultraviolet rays.'' Id. at 1051-1053.
    In 1999, EPA petitioned the D.C. Circuit for rehearing en banc on 
several aspects of that Court's decision in ATA I. Although the 
petition for rehearing was granted in part and denied in part, the 
Court declined to review its ruling with regard to the potential 
beneficial effects of O₃ pollution. American Trucking 
Associations v. EPA (``ATA II''), 195 F.3d 4, 10 (D.C. Cir., 1999). The 
Court did note, however, that it ``expressed[ed]
no opinion, of course, 
upon the effect, if any, that studies showing the beneficial effects of 
tropospheric ozone * * * might have upon any ozone standards * * *'' 
Id.
    On January 27, 2000, EPA petitioned the U.S. Supreme Court for 
certiorari on the constitutional issue and two other issues, but did 
not request review of the D.C. Circuit ruling regarding the potential 
beneficial health effects of O₃. The EPA's petition for 
certiorari was granted on May 22, 2000; oral argument was subsequently 
held on November 7, 2000; and an opinion was issued on February 27, 
2001. Whitman v. American Trucking Associations (``Whitman''), 531 U.S. 
457 (2001). The U.S. Supreme Court reversed the judgment of the D.C. 
Circuit on the constitutional issue, holding that section 109 of the 
Act does not delegate legislative power to the EPA in contravention of 
the Constitution, and remanded the case to the D.C. Circuit to consider 
challenges to the O₃ (and PM) NAAQS that had not been 
addressed by that Court's earlier decisions.
    Oral argument was held on December 18, 2001, and on March 26, 2002, 
the D.C. Circuit issued its final decision finding the 1997 
O₃ (and PM) NAAQS to be ``neither arbitrary nor 
capricious,'' and denied the remaining petitions for review. American 
Trucking Associations v. EPA (``ATA III''), 283 F.3d 355, (D.C. Cir. 
2002). Thus, today's final response to the Court's 1999 remand 
regarding the potential beneficial health effects of O₃ 
constitutes EPA's final response to challenges to the 1997 
O₃ NAAQS. Other remanded issues, relating to implementation 
of the O₃ NAAQS, are not addressed by today's action.
2. Remand on Health Benefits Issue
    The D.C. Circuit's 1999 ruling concludes that ``EPA cannot ignore 
the possible health benefits of ozone.'' \9\ ATA I, 175 F.3d at 1033. 
According to the Court ``[p]etitioners presented evidence that, 
according to them, shows the health benefits of tropospheric ozone as a 
shield from the harmful effects of the sun's ultraviolet rays--
including cataracts and both melanoma and non-melanoma skin cancer.'' 
Id. at 1051. In rejecting EPA's view that Congress did not intend it to 
consider potential indirect beneficial effects of tropospheric 
O₃ in shielding the public from potentially harmful, but 
naturally occurring, UV-B radiation from the sun, the Court concluded 
that ``legally * * * EPA must consider the positive identifiable 
effects of a pollutant's presence in the ambient air in formulating air 
quality criteria under section 108 and NAAQS under section 109.'' Id. 
at 1052. As a result, the Court directed EPA to ``determine whether * * 
* tropospheric ozone has a beneficent effect and, if so, then to assess 
ozone's net adverse health effect.'' Id. at 1053. Today's action sets 
forth EPA's final response in that regard.
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    \9\ For the reasons discussed in the Response to Comments (U.S. 
EPA, 1997, pp. 128-135), EPA did not consider in the 1997 review 
adverse health effects that might be caused by the potential 
increase in UV-B radiation that could result from reductions in 
ground-level O₃ brought about by control programs 
implemented to attain a revised O₃ NAAQS.
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C. Atmospheric Distribution of O₃ and UV-B Radiation

    The focus of the 1997 review of the air quality criteria and 
standards for O₃ and related photochemical oxidants was on 
public health and welfare effects associated with direct exposure to 
ambient levels of O₃ in the lower troposphere, essentially 
at ground level. People are directly exposed to ground-level 
O₃ simply by breathing ambient air; similarly, plants are 
directly exposed through their respiratory processes. Ground-level 
O₃ is not emitted directly from mobile or stationary sources 
but, like other photochemical oxidants, commonly exists in the ambient 
air as an

[[Page 617]]

atmospheric transformation product. Ground-level O₃ 
formation is the result of chemical reactions of VOC, NO_X, 
and oxygen in the presence of sunlight and generally at elevated 
temperatures. As a principal ingredient in photochemical smog, elevated 
episodic concentrations of ground-level O₃ typically occur 
in the summertime. High concentrations may be found in and downwind of 
major urban centers as well as across broad regions of elevated 
precursor emissions. A detailed discussion of atmospheric formation, 
ambient concentrations, and health and welfare effects associated with 
direct exposure to O₃ can be found in the Criteria Document 
and Staff Paper.
    Naturally occurring O₃ is found in two sections of the 
earth's atmosphere, the stratosphere and the troposphere. The 
demarcation between these two layers varies between about 8 and 18 
kilometers (km) above the earth's surface. As illustrated in Figure 1, 
depicting the vertical profile of O₃, most naturally 
occurring O₃ (£ 90 percent) resides in the 
stratosphere, with the remaining O₃ (< 10 percent) in the 
troposphere. The band of O₃ between about 15 and 30 km is 
commonly known as the ``ozone layer.''
    Man-made air pollution has significantly perturbed the natural 
distribution of O₃ in both layers. It is now widely accepted 
that emissions of long-lived chlorofluorocarbons (CFCs) and other 
compounds can deplete the natural O₃ layer in the 
stratosphere. And, as summarized above, much shorter lived emissions of 
VOC and NO_X can markedly increase ``smog'' O₃ in 
the lowest portion of the troposphere, which is termed the planetary 
boundary layer. This fluctuating planetary boundary or ``mixing'' layer 
of the troposphere can extend as high as 1 to 3 km above the ground. 
Assuming a fairly high summertime O₃ pollution reservoir of 
65 parts per billion (ppb) in a typical 1 km mixing layer, Cupitt 
(1994) estimated that pollution would add less than 1 percent to the 
expected total vertical profile of tropospheric and stratospheric 
O₃ (i.e., ``total column'' O₃) that would occur 
in the natural environment.
[GRAPHIC]
[TIFF OMITTED]
TR06JA03.000

    Ozone at ground level and throughout the troposphere is chemically 
identical to stratospheric O₃. Stratospheric O₃ 
occurs far too high to present any threat of direct respiratory-related 
adverse effects to people or plants from ambient ground-level 
exposures, but is known to provide a natural protective shield from 
excess radiation from the sun by absorbing UV-B radiation \10\ before 
it penetrates to ground level. Recognizing that exposure to UV-B 
radiation has been associated with adverse health and welfare effects, 
EPA and international scientific, regulatory, and legislative 
organizations have for some time focused on understanding the effects 
of UV-B radiation and on controlling the man-made pollution that is 
causing the depletion of the O₃ layer in the stratosphere, 
as discussed in section I.D below.\11\
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    \10\ UV-B radiation refers to the region of the solar spectrum 
within the range of wavelengths generally from 280-290 nanometers 
(nm) at the lower end, to 315-320 nm at the upper end.
    \11\ For example, in 1977 and again in 1990, Congress added 
provisions to the Act to address stratospheric O₃ 
depletion and the resultant increase in exposure to UV-B radiation.
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    During the 1997 review, EPA recognized that tropospheric 
O₃ also absorbs UV-B radiation (U.S. EPA, 1996a, p. 5-79), 
such that ground-level O₃ formed by man-made pollution has 
the potential to provide some degree of additional shielding beyond the 
natural

[[Page 618]]

levels that would otherwise occur in the absence of man-made pollution. 
The relationship between ground-level O₃ and UV-B radiation, 
as well as the health effects associated with exposure to UV-B 
radiation and consideration of the UV-B radiation-related health risks 
associated with changes in ground-level O₃ are discussed in 
section II.B below. In response to the remand on the health benefits 
issue, EPA's assessment of the net adverse health effects of ground-
level O₃ is discussed in section II.C below, as a basis for 
today's decision on the primary O₃ NAAQS, summarized in 
section II.D below.

D. Related Stratospheric O₃ Program

    In the 1970s, scientists first grew concerned that certain 
chemicals could damage the earth's protective stratospheric 
O₃ layer, and these concerns were validated by the discovery 
of thinning of the O₃ layer over Antarctica in the southern 
hemisphere. Because of the risks posed by stratospheric O₃ 
depletion and the global nature of the problem, leaders from many 
countries decided to work together to craft a workable solution. Since 
1987, over 175 nations have signed a landmark environmental treaty, the 
Montreal Protocol on Substances that Deplete the Ozone Layer. The 
Protocol's chief aim is to reduce and eventually eliminate the 
production and use of man-made O₃ depleting substances, such 
as CFCs. By agreeing to the terms of the Montreal Protocol, signatory 
nations ratifying the Protocol--including the United States--commit to 
take actions to protect the stratospheric O₃ layer and to 
reverse the damage due to the use of O₃ depleting 
substances.
    In 1990, Congress amended the Act by adding title VI (sections 601-
618) to address the issue of stratospheric O₃ depletion.\12\ 
Most importantly, the amended Act required the gradual end to the 
production of certain chemicals that deplete the O₃ 
layer.\13\ In addition, the Act requires EPA to develop and implement 
regulations for the responsible management of O₃ depleting 
substances in the United States. The EPA has developed several 
regulatory programs under these authorities that include: ending the 
production and import of O₃ depleting substances (57 FR 
33754, July 30, 1992) and identifying safe and effective alternatives 
(59 FR 13044, March 18, 1994), ensuring that refrigerants and halon 
fire extinguishing agents are recycled properly (58 FR 28660, May 14, 
1993), banning the release of O₃ depleting refrigerants 
during the service, maintenance, and disposal of air conditioners and 
other refrigeration equipment (60 FR 40420, August 8, 1995), and 
requiring that manufacturers label products either containing or made 
with the most harmful O₃ depleting substances (58 FR 8136, 
February 11, 1993). Because of their relatively high O₃ 
depletion potential, several man-made compounds, including CFCs, carbon 
tetrachloride, methyl chloroform, and halons were targeted first for 
phaseout. The EPA continues to develop additional regulations for the 
protection of public health and the environment from effects associated 
with the depletion of the stratospheric O₃ layer.
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    \12\ Title VI replaced the provisions regarding stratospheric 
O₃ depletion enacted in 1977. 42 U.S.C. 7671.
    \13\ Both the Act and the Montreal Protocol, however, provide 
for limited ``essential use exemptions'' for the continued 
production and import of very small quantities of CFCs and other 
O₃ depleting substances needed for certain essential 
uses, for example, for metered dose inhalers used by people with 
asthma and other respiratory diseases.
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    Besides implementing and enforcing stratospheric O₃ 
protection regulations in the U.S., EPA continues to work with other 
U.S. government agencies and international governments to pursue 
ongoing changes to the Montreal Protocol and other treaties. These 
refinements to the Protocol and other treaties are based on ongoing 
scientific assessments of O₃ depletion that are coordinated 
by the United Nations Environment Programme (UNEP) and the World 
Meteorological Organization (WMO), with cooperation from EPA and other 
agencies around the globe (UNEP, 1998; and WMO, 1998).
    In addition to these regulatory and scientific activities, EPA 
maintains several education and outreach projects to help protect the 
American public from the health effects of overexposure to ultraviolet 
(UV) radiation. Chief among these projects is the UV Index, a tool that 
provides a daily forecast of the next day's likely UV levels across the 
United States.\14\ The UV Index, which EPA launched in partnership with 
the National Weather Service, serves as the cornerstone of EPA's 
SunWise School Program, the goal of which is to educate young children 
and their caregivers about the health effects of overexposure to the 
sun, as well as simple steps that people can take to avoid 
overexposure.\15\
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    \14\ Information about the UV Index is available from the EPA 
Stratospheric Ozone Hotline at (800) 296-1996 or at 
http://www.epa.gov/sunwise/uvindex.html.
    \15\ Information about EPA's SunWise School Program is available 
at http://www.epa.gov/sunwise/.
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E. Summary of Proposed Response to Remand

    On November 14, 2001, EPA proposed a response to the D.C. Circuit 
remand (66 FR 52768; henceforth, ``proposed response'') to consider any 
potential beneficial effects of ground-level O₃ in shielding 
the public from potentially harmful, but naturally occurring, UV-B 
radiation from the sun. ATA I, 175 F.3d at 1051-53. Based on its review 
of the air quality criteria and NAAQS for O₃ completed in 
1997, and its additional assessment of potential beneficial effects of 
ground-level O₃, EPA provisionally determined that the 
information linking (a) Changes in patterns of ground-level 
O₃ concentrations likely to occur as a result of programs 
implemented to attain the 1997 O₃ NAAQS to (b) changes in 
relevant patterns of exposure to UV-B radiation of concern to public 
health is too uncertain at this time to warrant any relaxation in the 
level of public health protection previously determined to be requisite 
to protect against the demonstrated adverse respiratory effects of 
direct inhalation exposure to O₃ in the ambient air.\16\ 
Further, the proposed response presented the Agency's view that even 
when using plausible but highly uncertain assumptions about likely 
changes in patterns of ground-level O₃ concentrations, 
associated changes in UV-B radiation exposures of concern would likely 
be very small from a public health perspective. Thus, EPA proposed not 
to change the O₃ NAAQS set in 1997 at a level of 0.08 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.
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    \16\ The D.C. Circuit upheld EPA's determination that the 1997 
O₃ NAAQS was requisite to protect against demonstrated 
adverse respiratory effects in ATA III.
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    The proposed response solicited public comments on EPA's proposed 
decision not to change the 1997 O₃ NAAQS, and on various 
specific aspects of EPA's review and rationale. The EPA received ten 
comments on the proposed response from industry, public interest 
groups, and local and State governments. Significant comments are 
addressed throughout section II below and more fully in a separate 
Response to Comments (U.S. EPA, 2002).

II. Rationale for Final Response To Remand on the Primary O₃ 
Standard

    Today's action presents the Administrator's final response to the 
remand, in which the Court directed EPA to determine ozone's net 
adverse effect on public health and not

[[Page 619]]

``disregard the studies'' upon which the petitioners primarily relied 
in their challenge. ATA I, 175 F.3d at 1053. Today's action reaffirms 
the 8-hour O₃ primary standard promulgated in 1997, based 
on:
    (1) Information from the 1997 criteria and standards review that 
served as the basis for the 1997 primary O₃ standard, 
including the scientific information on health effects associated with 
direct inhalation exposures to O₃ in the ambient air, 
consideration of the adversity of such effects for individuals, and 
human exposure and risk assessments (section II.A below);
    (2) A review of scientific information in the record of the 1997 
review (but not considered as part of the basis for the 1997 standard) 
on potential health effects associated with changes in UV-B radiation, 
the association between changes in ground-level O₃ and 
potential changes in UV-B radiation, and predictions of changes in 
ground-level O₃ levels likely to result from attainment of 
alternative O₃ standards (section II.B below);
    (3) Consideration of the net adverse effects of ground-level 
O₃, taking into account both direct adverse inhalation-
related health effects and potential indirect beneficial health effects 
associated with the shielding of UV-B radiation by ground-level 
O₃ (section II.C below); and
    (4) Consideration of the comments received on the proposed 
response.
    A number of commenters focused on various aspects of EPA's 
decision-making process and the timing of EPA's final response. A few 
such commenters expressed the view that EPA's proposed response to the 
remand was procedurally inadequate in that in reviewing information in 
the record on ozone's potential beneficial effects, EPA did not 
supplement the air quality criteria or consult with CASAC. These 
commenters also asserted that EPA should reopen the record to include 
new studies and analyses regarding ozone's potential beneficial effects 
that were not available for inclusion in the 1997 rulemaking record. 
These commenters thus argued that EPA should supplement the air quality 
criteria with information on ozone's potential beneficial effects, 
including both new and record information, consult with CASAC, and re-
propose a response to the remand.\17\
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    \17\ Some commenters also expressed the view that EPA's proposed 
response to the remand was premature since the D.C. Circuit had not 
yet decided other related issues. These comments are now moot since 
the D.C. Circuit issued its final opinion on March 26, 2002, denying 
all remaining challenges to the 1997 O₃ NAAQS.
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    Other commenters expressed the opposite view, agreeing with EPA's 
reliance on the rulemaking record that was before the Court in the ATA 
litigation as the basis for EPA's proposed response, and urging EPA to 
conclude its response as expeditiously as possible. These commenters 
argued that to reopen the record would require consideration not only 
of new information on potential beneficial effects, but also new 
information on adverse respiratory effects, and that to do so would 
effectively erase the previous review cycle. These commenters also 
asserted that the analyses of ozone's potential beneficial effects that 
were included in the record fail to meet minimum standards of 
reliability and scientific adequacy, that failure by EPA to 
expeditiously conclude the review that began in 1992 would represent 
unreasonable delay, and that any associated delay in implementing the 
1997 O₃ NAAQS would be at the expense of public health.
    Having considered these procedural comments, EPA continues to 
believe it is appropriate to base its response to the remand on the 
large amount of relevant information in the 1997 rulemaking record that 
was before the Court in ATA I, taking into account as well the 
substantive comments received on the proposed response. The EPA also 
believes it is unnecessary to supplement the air quality criteria with 
the draft, preliminary analyses relied on by commenters and by some 
petitioners in the ATA I litigation, or to undertake a more formal 
CASAC review. As more fully discussed in the Response to Comments, EPA 
took note of the following in reaching these conclusions:
    (1) This action responds to a remand from the D.C. Circuit and 
addresses the only remaining issue regarding the setting of the 1997 
O₃ standard.\18\ It is not a new, separate review of air 
quality criteria and NAAQS under sections 108 and 109. In these 
circumstances, it is appropriate for EPA to base its response on the 
record associated with the prior NAAQS review and court decisions. The 
EPA recognizes that new studies and related information relevant to 
further assessment of ozone's net adverse effects may now be available 
that were not part of the 1997 rulemaking record.
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    \18\ As noted earlier, this action does not address 
implementation of the O₃ NAAQS.
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    Such information is likely available not only on indirect 
potentially beneficial effects of O₃, but also on direct 
adverse respiratory-related effects of O₃. Taking into 
account the 5-year periodic review requirements of section 109 of the 
Act, and noting that this review already extended a decade since it was 
initiated (57 FR 38832; August 27, 1992), EPA believes that any such 
new information should be considered in the next periodic review. The 
EPA has already initiated the next periodic review. Preparation of a 
revised O₃ Criteria Document that will incorporate all such 
relevant information is well underway (65 FR 57810; September 26, 
2000).
    (2) Limiting its consideration to information that was part of the 
1997 record, as well as comments on the proposed response, is 
consistent with EPA's prior exercise of its discretion to decide 
whether new studies or analyses cited during a public comment period 
are of such potential significance that a final decision should be 
postponed so they can be assessed in supplemental air quality criteria 
and considered before concluding a NAAQS review. See 58 FR 12008, 13014 
n.2 (1993) (ozone NAAQS). In prior reviews, after an extended review of 
relevant scientific information, EPA has been aware of yet additional 
relevant information, but determined that the information would be more 
appropriately considered in its next periodic review.\19\ See, e.g., 62 
FR 38652, 38662 (1997) (PM NAAQS).
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    \19\ As in other instances where EPA has received additional 
studies during public comment, EPA provisionally examined a 1997 
draft analysis conducted by Madronich and determined that it did not 
warrant supplementing the air quality criteria at this time. See, 
e.g., 62 FR 38652, 38662 (1997) (PM NAAQS).
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    (3) The record includes relevant information on indirect 
potentially beneficial effects of O₃. The public has been 
afforded two opportunities to submit comments and relevant information 
on this issue, through EPA's solicitation of public comments on both 
the 1996 proposal and the 2001 proposed response.
    (4) The documents in the 1997 record cited by some commenters--and 
upon which certain petitioners primarily relied in their challenge of 
EPA's 1997 decision--(Cupitt, 1994; DOE, 1995; Lutter and Wolz, 1997) 
do not generally meet the minimum standards that EPA and CASAC have 
historically maintained for inclusion of health-related information in 
air quality criteria. The documents in question are either draft, 
unpublished analyses or, in the case of the one paper that was 
published, characterized by the authors as a ``preliminary analysis,'' 
which generally relied upon the assumptions in the other unpublished 
analyses. Consistent with its practice in other NAAQS reviews, the EPA 
judges these

[[Page 620]]

draft, unpublished or preliminary analyses to be inappropriate for 
inclusion in air quality criteria, and concludes that supplementing the 
1996 O₃ criteria is not warranted.
    (5) As discussed in more detail in section II.B.2, EPA also 
determined that it was not in a position to supplement the air quality 
criteria by developing its own more extensive analysis because 
information essential to the development of such an analysis (e.g., 
behavioral patterns related to potential UV-B radiation exposure) is 
not available at this time.
    (6) The EPA has appropriately consulted CASAC by providing for its 
review and comment the proposed response, as well as the key documents 
from the record upon which EPA's response is based.\20\ The CASAC has 
expressed no concern with this procedure nor indicated that any further 
CASAC involvement was necessary or appropriate. Indeed, only one member 
of CASAC chose to comment at all, and that member likewise expressed no 
concern with the method by which EPA consulted with CASAC on the 
response to the remand. Finally, the commenters have not provided any 
reason to believe that additional review by CASAC would have affected 
the outcome of this action in any way.
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    \20\ The EPA's request for comments, together with copies of the 
proposed response and key documents, was transmitted to CASAC in a 
letter to Dr. Philip Hopke from Dr. Karen Martin, January 14, 2002, 
which is available in the docket. The EPA had previously provided an 
earlier draft of the proposed response, together with copies of key 
documents, to CASAC members in January 2001, ten months before the 
proposed response was published. See letter to Dr. Philip Hopke from 
Dr. Karen Martin, January 22, 2001 (available in the docket).
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    In view of the above factors, in particular the quality and type of 
analyses relied on by commenters and the fact that CASAC had the 
opportunity to review those analyses as well as other information in 
the record, EPA believes its approach to this response represents a 
reasonable exercise of its discretion to decide when to supplement the 
review process and fulfills the Agency's responsibilities under the 
Act. The EPA's response fully complies with the direction of the Court 
that EPA determine ozone's net adverse effect on public health and not 
``disregard the studies'' upon which the petitioners primarily relied 
in their challenge. ATA I, 175 F.3d at 1053. Nothing in the Court's 
remand purports to require EPA to reopen the air quality criteria, or 
indeed the entire review process, before concluding this aspect of the 
1997 review. For the reasons discussed above, EPA also believes it 
would be inappropriate to do so.
    Accordingly, the EPA concludes that any further extension of this 
review, through reopening the rulemaking record or review process, 
would represent an unwarranted delay in completing this review cycle, 
which began in 1992 and originally concluded in 1997. Any further 
extension of this review would also delay Agency and State actions to 
implement the 8-hour O₃ NAAQS, which EPA believes would be 
inappropriate and contrary to the purpose of the Act, in that it would 
impede the important public health protections afforded by the 8-hour 
ozone NAAQS.

A. Direct Adverse Health Effects From Breathing O₃ in the 
Ambient Air

    This section briefly summarizes information on the direct adverse 
health effects from breathing O₃ in the ambient air, 
information as to when those effects become adverse to individuals, and 
insights gained from human exposure and risk assessments intended to 
provide a broader perspective for judgments about protecting public 
health from the risks associated with direct O₃ inhalation 
exposures.\21\
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    \21\ See the 1996 proposal and 1997 final rule for more complete 
summaries and the Criteria Document and Staff Paper for more 
detailed discussion.
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1. Health Effects Associated With O₃ Inhalation Exposures
    Based on information from human clinical, epidemiological, and 
animal toxicological studies, 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. Long-
established acute health effects \22\ induced by short-term exposures 
to O₃, generally while individuals were engaged in heavy 
exertion, include transient pulmonary function responses, transient 
respiratory symptoms, and effects on exercise performance.\23\ The 1997 
review included substantial new information on similar effects 
associated with prolonged exposures at concentrations as low as 0.08 
ppm and at moderate levels of exertion. Other health effects associated 
with short-term or prolonged O₃ exposures include increased 
airway responsiveness, susceptibility to respiratory infection, 
increased hospital admissions and emergency room visits, and transient 
pulmonary inflammation. The 1997 review also included new information 
on chronic health effects \24\ associated with long-term exposures. 
This array of effects is briefly summarized below, followed by 
considerations as to when these physiological effects could become 
medically significant such that they should be regarded as adverse to 
the health of individuals experiencing them.
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    \22\ ``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.
    \23\ The 1-hour O₃ primary NAAQS set in 1979 was 
generally based on these acute effects associated with heavy 
exercise and short-term exposures.
    \24\ ``Chronic'' health effects of O₃ are defined as 
those effects induced by long-term exposures to O₃. 
Examples of these effects are structural damage to lung tissue and 
accelerated decline in baseline lung function.
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a. Effects of Short-term and Prolonged O₃ Exposures

    (i) Pulmonary function responses. Transient reductions in pulmonary 
function have been observed in healthy individuals and those with 
impaired respiratory systems (e.g., asthmatic individuals) as a result 
of both short-term and prolonged exposures to O₃. The 
strongest and most quantifiable exposure-response information on such 
responses has come from controlled human exposure studies, which 
clearly show that reductions in lung function are enhanced by increased 
levels of activity involving exertion and by increased O₃ 
concentrations. Numerous such studies of exercising adults have 
demonstrated decrements in lung function both for exposures of 1-3 
hours at £= 0.12 ppm O₃ and for exposures of 6.6 
hours at £= 0.08 ppm O₃, providing conclusive 
evidence that O₃ levels commonly monitored in the ambient 
air induce lung function decrements in exercising adults. Further, 
numerous summer camp studies provide an extensive and reliable data 
base on comparable lung function responses to ambient O₃ and 
other pollutants in children and adolescents. The extent of pulmonary 
function decrements varies considerably among individuals, pulmonary 
function generally tends to return to baseline levels shortly after 
short-term exposure, and effects are typically attenuated upon repeated 
short-term exposures over several days.
    (ii) Respiratory symptoms and effects on exercise performance. 
Various transient respiratory symptoms, including cough, throat 
irritation, chest pain on deep inspiration, and shortness of breath, 
have been induced by O₃ exposures of both healthy 
individuals and those with impaired respiratory systems. Increasing 
O₃ exposure durations and levels have been shown to elicit 
increasingly more severe symptoms that persist for longer periods

[[Page 621]]

in increasingly larger numbers of individuals. Symptomatic and 
pulmonary function responses follow a similar time course during an 
acute exposure and the subsequent recovery, as well as over the course 
of several days during repeated exposures. As with pulmonary function 
responses, the severity of symptomatic responses varies considerably 
among subjects. For some outdoor workers or active people who are 
highly responsive to ambient O₃, respiratory symptoms may 
cause reduced productivity, may curb the ability or desire to engage in 
normal activities, and may interfere with maximal exercise performance.
    (iii) Increased airway responsiveness. Increased airway 
responsiveness is an indication that the airways are predisposed to 
bronchoconstriction, with a high level of bronchial responsiveness 
being characteristic of asthma. As a result of increased airway 
responsiveness induced by O₃ exposure, human airways may be 
more susceptible to a variety of stimuli, including antigens, 
chemicals, and particles. Because enhanced response to antigens in 
asthmatics could lead to increased morbidity (i.e., medical treatment, 
emergency room visits, hospital admissions) or to more persistent 
alterations in airway responsiveness, these health endpoints raise 
concern for public health, particularly for individuals with impaired 
respiratory systems.
    (iv) Increased susceptibility to respiratory infection. When 
functioning normally, the human respiratory tract, like that of other 
mammals, has numerous closely integrated defense mechanisms that 
provide protection from the adverse effects of a wide variety of 
inhaled particles and microbes. Evidence that inhalation of 
O₃ may break down or impair these defense mechanisms comes 
primarily from a very large number of laboratory animal studies with 
generally consistent results. One of the few studies of moderately 
exercising human subjects exposed to 0.08 ppm O₃ for 6.6 
hours reported decrements in alveolar macrophage function, the first 
line of defense against inhaled microorganisms and particles in the 
lower airways and air sacs. While no single experimental human study or 
group of animal studies conclusively demonstrates that human 
susceptibility to respiratory infection is increased by exposure to 
O₃, taken as a whole, the data suggest that acute 
O₃ exposures can impair the host defense capability of both 
humans and animals, potentially resulting in a predisposition to 
bacterial infections in the lower respiratory tract.
    (v) Hospital admissions and emergency room visits. Increased 
summertime hospital admissions and emergency room visits for 
respiratory causes have been associated with ambient exposures to 
O₃ and other environmental factors. Numerous studies 
consistently have shown such a relationship, even after controlling for 
modifying factors, as well as when considering only O₃ 
concentrations < 0.12 ppm. Individuals with preexisting respiratory 
disease (e.g., asthma, chronic obstructive pulmonary disease) may 
generally be at increased risk of such effects, and some individuals 
with respiratory disease may have an inherently greater sensitivity to 
O₃. On the other hand, individuals with more severe 
respiratory disease are less likely to engage in the level of exertion 
associated with provoking responses to O₃ exposures in 
healthy humans. On balance, it is reasonable to conclude that evidence 
of O₃-induced increased airway resistance, nonspecific 
bronchial responsiveness, susceptibility to respiratory infection, 
increased airway permeability, airway inflammation, and incidence of 
asthma attacks suggests that ambient O₃ exposure could be a 
cause of increased hospital admissions, particularly for asthmatics.
    (vi) Pulmonary inflammation. Respiratory inflammation can be 
considered to be a host response to injury and indicators of 
inflammation as evidence that respiratory cell damage has occurred. 
Inflammation induced by exposure of humans to O₃ may have 
several potential outcomes: (1) Inflammation induced by a single 
exposure (or even several exposures over the course of a season) could 
resolve entirely; (2) repeated acute inflammation could develop into a 
chronic inflammatory state; (3) continued inflammation could alter the 
structure and function of other pulmonary tissue, leading to disease 
processes such as fibrosis; (4) inflammation could interfere with the 
body's host defense response to particles and inhaled microorganisms, 
particularly in potentially vulnerable populations such as children and 
older individuals; and (5) inflammation could amplify the lung's 
response to other agents such as allergens or toxins. Exposures of 
laboratory animals to O₃ for periods <=8 hours have been 
shown to result in cell damage, inflammation, and increased leakage of 
proteins from blood into the air spaces of the respiratory tract. In 
humans, the extent and course of inflammation and its constitutive 
elements have been evaluated by using bronchoalveolar lavage (BAL) to 
sample cells and fluid from the lung and lower airways. Several such 
studies have shown that exercising humans exposed (1 to 4 hours) to 0.2 
to 0.6 ppm O₃ had O₃-induced markers of 
inflammation and cell damage, with the lowest concentration of 
prolonged O₃ exposure tested in humans, 0.08 ppm for 6.6 
hours with moderate exercise, inducing small but statistically 
significant increases in these endpoints. Thus, it is reasonable to 
conclude that repeated acute inflammatory response and cellular damage 
is potentially a matter of public health concern; however, it is also 
recognized that most, if not all, of these effects begin to resolve in 
most individuals within 24 hours if the exposure to O₃ is 
not repeated. Of possibly greater public health concern is the 
potential for chronic respiratory damage that could be the result of 
repeated O₃ exposures occurring over a season or a lifetime.

b. Potential Effects of Long-term O₃ Exposures

    Epidemiologic studies that have investigated potential associations 
between long-term O₃ exposures and chronic respiratory 
effects in humans thus far have provided only suggestive evidence of 
such a relationship. Most studies investigating this association have 
been cross-sectional in design and have been compromised by incomplete 
control of confounding variables and inadequate exposure information. 
Other studies have attempted to follow variably exposed groups 
prospectively. The findings from such studies conducted in southern 
California and Canada suggest small, but consistent, decrements in lung 
function among inhabitants of the more highly polluted communities; 
however, associations between O₃ and other copollutants and 
problems with study population loss have reduced the level of 
confidence in these conclusions. Other epidemiologic studies have 
attempted to find associations between daily mortality and 
O₃ concentrations in various cities around the United 
States. Although an association between ambient O₃ exposure 
in areas with very high O₃ levels and daily mortality has 
been suggested by these studies, the data are limited.
    In a large number of animal toxicology studies, ``lesions'' \25\ 
in the

[[Page 622]]

centriacinar regions of the lung (i.e., the portion of the lung where 
the region that conducts air and the region that exchanges gas are 
joined) are well established as one of the hallmarks of O₃ 
toxicity. Under certain conditions, some of the structural changes seen 
in these studies may become irreversible. It is unclear, however, 
whether ambient exposure scenarios encountered by humans result in 
similar ``lesions'' or whether there are resultant functional or 
impaired health outcomes in humans chronically exposed to 
O₃.
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    \25\ Differing views have been expressed by CASAC panel members 
regarding the use of the term ``lesion'' to describe the 
O₃-induced morphological (i.e., structural) abnormalities 
observed in toxicological studies. Section V.C.8 of the Staff Paper 
describes and discusses these degenerative changes in more detail.
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    The epidemiologic lung function studies generally parallel those of 
the animal studies, but lack good information on individual 
O₃ exposure history and are frequently confounded by 
personal or copollutant variables. Thus, the Administrator recognizes 
that there is a lack of a clear understanding of the significance of 
repeated, long-term inflammatory responses, and that there is a need 
for continued research in this important area. In summary, the 
collective data on long-term exposure to O₃ garnered in 
studies of laboratory animals and human populations have many 
ambiguities. Nevertheless, the currently available information provides 
at least a biologically plausible basis for considering 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, 
although such relationships remain highly uncertain.

c. Adversity of Effects for Individuals

    Some population groups have been identified as being sensitive to 
effects associated with exposures to ambient O₃ levels, such 
that individuals within these groups are at increased risk of 
experiencing such effects. Population groups at increased risk include: 
(1) Active children and outdoor workers who regularly engage in outdoor 
activities; \26\ (2) individuals with preexisting respiratory disease 
(e.g., asthma or chronic obstructive lung disease); \27\ and (3) some 
individuals, referred to as ``hyperresponders,'' who are unusually 
responsive to O₃ relative to other individuals with similar 
levels of activity or with a similar health status and may experience 
much greater functional and symptomatic effects from exposure to 
O₃ than the average individual response.
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    \26\ Exertion increases the amount of O₃ entering the 
airways and can cause O₃ to penetrate to peripheral 
regions of the lung where lung tissue is more likely to be damaged.
    \27\ While not necessarily more responsive than healthy 
individuals in terms of the magnitude of pulmonary function 
decrements or symptomatic responses, these individuals may be at 
increased risk since the impact of O₃-induced responses 
on already-compromised respiratory systems may more noticeably 
impair an individual's ability to engage in normal activity or may 
be more likely to result in increased self-medication or medical 
treatment.
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    In making judgments as to when the effects discussed above become 
significant enough that they should be regarded as adverse to the 
health of individuals in these sensitive populations, the Administrator 
has looked to guidelines published by the American Thoracic Society 
(ATS) and the advice of CASAC. Based on these guidelines, with CASAC 
concurrence, gradations of individual functional responses (e.g., 
decrements in forced expiratory volume (FEV₁), increased 
airway responsiveness) and symptomatic responses (e.g., cough, chest 
pain, wheeze) were defined, together with judgments as to the potential 
impact on individuals experiencing varying degrees of severity of these 
responses.\28\
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    \28\ These gradations and impacts are summarized in the 1996 
proposal and discussed in the Criteria Document (Chapter 9) and 
Staff Paper (section V.F, Tables V-4 and V-5).
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    In judging the extent to which such impacts represent effects that 
should be regarded as adverse to the health status of individuals, an 
additional factor considered is whether such effects are experienced 
repeatedly by an individual during the course of a year or only on a 
single occasion. While some experts would judge single occurrences of 
moderate responses to be a ``nuisance,'' especially for healthy 
individuals, a more general consensus view of the adversity of such 
moderate responses emerges as the frequency of occurrence increases. 
Thus, EPA has concluded that repeated occurrences of moderate 
responses, even in otherwise healthy individuals, may be considered to 
be adverse since they could well set the stage for more serious 
illness.
2. Human Exposure and Risk Assessments
    To put judgments about respiratory health effects that are adverse 
for individuals into a broader public health context, the Administrator 
has taken into account the results of human exposure and risk 
assessments.\29\ This broader context includes consideration, to the 
extent possible, of the particular population groups at risk for 
various health effects, the number of people in at-risk groups likely 
to be exposed to O₃ concentrations shown to cause health 
effects, the number of people likely to experience certain adverse 
health effects under varying air quality scenarios, and the kind and 
degree of uncertainties inherent in these assessments. These 
quantitative assessments add to our understanding of the overall body 
of evidence linking O₃ inhalation exposures to adverse 
health effects. The models used in these assessments were appropriate 
and the methods used represent the state of the art.
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    \29\ See the 1996 proposal (61 FR 65723-6) and 1997 final rule 
(62 FR 38860-1) for a more complete summary of these assessments. A 
detailed description of the exposure and risk models and their 
application at the time of the 1996 proposal are presented in the 
Staff Paper and associated technical support documents (Johnson, 
1994; Johnson et al., 1996 a,b; Whitfield et al., 1996). Following 
proposal, supplemental exposure and risk analyses were done to 
analyze the specific standard proposed and alternative standards on 
which comment was solicited, as well as to refine the procedures 
used to simulate O₃ concentrations upon attainment of 
alternative standards (Richmond, 1997).
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a. Exposure Analyses

    The EPA conducted exposure analyses to estimate O₃ 
exposures for the general population and two at-risk populations, 
active children who regularly engage in outdoor activity (i.e., 
``outdoor children'') and ``outdoor workers,'' living in nine 
representative U.S. urban areas.\30\ Exposure estimates were developed 
for a baseline year (e.g., 1993, 1994), using monitored O₃ 
air quality data (i.e., the ``as is'' scenario), as well as for 
simulated air quality conditions reflecting attainment of the 1-hour 
NAAQS and various alternative standards. The exposure analyses provide: 
(1) Estimates of the number of people exposed in each of these 
population groups to various O₃ concentrations, and the 
number of occurrences of such exposures, under different regulatory 
scenarios,\31\ which are an important input to the risk assessment 
conducted for certain adverse health effects (summarized in the next 
section); and (2) estimates of the frequency of occurrences of 
O₃ ``exposures of concern,'' \32\ which help

[[Page 623]]

to put into broader perspective other O₃-related health 
effects that could not be included in the risk assessment (summarized 
below).
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    \30\ The areas include a significant fraction of the U.S. urban 
population, 41.7 million people, the largest urban areas with major 
O3 nonattainment problems, and two large urban areas that are in 
attainment with the 1-hour NAAQS.
    \31\ Estimates of ``people exposed'' reflect the number of 
people who experience exposures to a given concentration of 
O₃, or higher, at least one time during the period of 
analysis, and estimates of ``occurrences of exposure'' reflect the 
number of times a given O₃ concentration is experienced 
by the population of interest.
    \32\ ``Exposures of concern'' refer throughout to O₃ 
exposures at and above 0.08 ppm, 8-hour average, at moderate 
exertion. Such exposures are particularly relevant to a 
consideration of a number of health effects, discussed in section 
I.A.1 above, that have been observed in controlled human studies 
under these exposure conditions, but for which data were too limited 
to allow for quantitative risk assessment. Exposures at and above 
0.12 ppm, 1-hour average, at heavy exertion, are also of concern; 
however, the focus here is on 8-hour average exposures since 
exposure estimates are higher for the 8-hour average effects level 
of 0.08 ppm at moderate exertion than for the 1-hour average effects 
level of 0.12 ppm at heavy exertion.
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    The computer model used in these analyses, the probabilistic NAAQS 
exposure model for O₃ (pNEM/O₃), combines 
information on O₃ air quality with information on patterns 
of human activity to produce estimates of O₃ inhalation 
exposures. This model has been developed to take into account the most 
significant factors contributing to total O₃ inhalation 
exposure including: The temporal and spatial patterns of ground-level 
O₃ concentrations throughout an urban area; the variations 
of O₃ levels within a comprehensive set of 
``microenvironments;'' \33\ the temporal and spatial patterns of the 
movement of people throughout an urban area; and the effects of 
variable exertion levels (represented by ventilation rates), associated 
with a range of activities that people regularly engage in, on 
O₃ uptake in exposed individuals. The analysis of these key 
factors incorporated extensive data bases, including, for example, data 
from ground-level O₃ monitoring networks in these areas, 
data from numerous research studies that characterized the activity 
patterns of the general population and at-risk groups as they go about 
their daily activities (e.g., from indoors to outdoors, moving from 
place to place, and engaging in activities at different exertion 
levels),\34\ and census data on relevant factors such as age, work 
status, home location and type of air conditioning system present, and 
work place location.
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    \33\ The five indoor and two outdoor microenvironments included 
in this exposure model account for the highly localized variations 
in O₃ concentrations to which people are exposed that are 
not directly reflected in the concentrations measured at ambient 
ground-level O₃ monitoring sites.
    \34\ See, for example, Tables V-8 and V-9 in the Staff Paper, 
pp. 83-84.
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    The regulatory scenarios examined in the exposure analyses include 
both 1-hour O₃ standards, at levels of 0.12 ppm (the 1979 
NAAQS) and 0.10 ppm, and 8-hour standards, at levels of 0.07, 0.08, and 
0.09 ppm, with 1- and 5-expected exceedance forms, i.e., the range of 
alternative 8-hour standards recommended in the Staff Paper and 
supported by CASAC as the appropriate range for consideration in this 
review. These estimates were also used to roughly bound exposure 
estimates for concentration-based forms of the standards under 
consideration (e.g., the second- and fifth-highest daily maximum 8-hour 
average O₃ concentration, averaged over a 3-year 
period).\35\ The estimated exposures are based on a single year of air 
quality data and reflect what would be expected in a typical or average 
year in an area just attaining a given standard over a 3-year 
compliance period; additional analyses were done to estimate exposures 
that would be expected in the worst year of a 3-year compliance period.
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    \35\ As discussed in section IV and appendix A of the Staff 
Paper.
-----------------------------------------------------------------------

    Based on the results of the exposure analyses, children who are 
active outdoors (representing approximately 7 percent of the population 
in the study areas) appear to be the at-risk population group examined 
with the highest percentage and number of individuals likely to 
experience exposures of concern. Estimated exposures of concern varied 
significantly across the urban areas examined in this analysis, with 
far greater variability associated with the 1-hour NAAQS in contrast to 
the more consistent results associated with alternative 8-hour 
standards.\36\ Despite this variability across areas, general patterns 
can be seen in comparing alternative standards. For example, for 
aggregate estimates of the mean percent of outdoor children likely to 
experience exposures of concern within the seven nonattainment areas: 
The range of estimates associated with the 1-hour NAAQS is 
approximately 0.3-24 percent, whereas for alternative 8-hour standards 
(of the same 1-expected-exceedance form as the 1-hour NAAQS), the 
ranges are approximately 3-7 percent for a 0.09 ppm standard, 0-1 
percent for a 0.08 ppm standard, and essentially zero for a 0.07 ppm 
standard. Within any given urban area, these differences in estimated 
exposures of concern between alternative standards are statistically 
significant.
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    \36\ The observed area-to-area variability reflects differences 
in the shape of air quality distributions and differences in the 
relationships between 1-hour and 8-hour peak concentrations across 
urban areas, as well as differences in the percentage of homes with 
air conditioning (which impacts exposure estimates when individuals 
are indoors) and the frequency of warm versus cool days (which 
impacts exposure estimates because different sets of human activity 
patterns are used for warm versus cool days in the exposure model) 
across the nine urban areas (Richmond, 1997).
-----------------------------------------------------------------------

    In looking more specifically at a comparison between 8-hour 
standards at the 0.09 ppm and 0.08 ppm levels, aggregate estimates of 
the mean percentage of outdoor children likely to experience exposures 
of concern are estimated to be approximately 3 percent at the 0.08 ppm 
level (ranging from 2-10 percent in the nine areas), increasing to 
approximately 11 percent at the 0.09 ppm level (ranging from 7-29 
percent in the nine areas).\37\ Thus, based on these analyses, a 
standard set at 0.09 ppm would allow more than three times as many 
children to experience exposures of concern as would a 0.08 ppm 
standard, with the number of children likely to experience such 
exposures increasing from approximately 100,000 to more than 300,000 in 
these nine areas alone. 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 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).
-----------------------------------------------------------------------

    \37\ Based on the supplemental analyses that used the third-
highest concentration-based form of the standards (Richmond, 1997).
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    In taking these observations into account, the Administrator and 
CASAC recognized the uncertainties and limitations associated with such 
analyses, including the considerable, but unquantifiable, degree of 
uncertainty associated with a number of important inputs to the 
exposure model. A key uncertainty in model inputs results from 
limitations in the human activity data base that may not adequately 
account for day-to-day repetition of activities common to children, 
such that the number of people who experience multiple occurrences of 
high exposure levels may be underestimated. Small sample size also 
limits the extent to which ventilation rates associated with various 
activities may be representative of the population group to which they 
are applied in the model. In addition, the air quality adjustment 
procedure used to simulate air quality distributions associated with 
attaining alternative standards, while based on generalized models 
intended to reflect patterns of air quality changes that have 
historically been observed, contains significant uncertainty, 
especially when applied to areas requiring very large reductions in air 
quality to attain alternative standards

[[Page 624]]

or to areas that are now in attainment with the 1-hour NAAQS.\38\
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    \38\ A more complete discussion of uncertainties and limitations 
is presented in the Staff Paper and technical support documents 
(Johnson et al., 1996a,b; Richmond, 1997).
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b. Risk Assessments

    The EPA conducted an assessment of health risks for several 
categories of respiratory effects considering the same population 
groups, alternative air quality scenarios, and urban areas that were 
examined in the human exposure analyses described above. The objective 
of the risk assessment was to estimate to the extent possible the 
magnitude of risks to population groups believed to be at greatest risk 
either due to increased exposures (i.e., outdoor children and outdoor 
workers) or increased susceptibility (e.g., asthmatics) while 
characterizing, as explicitly as possible, the uncertainties inherent 
in the assessment. While different risk measures are provided by the 
assessment, EPA has focused on ``headcount risk'' estimates which 
include: (1) Estimates of the number of people likely to experience a 
given health effect and (2) estimates of the number of incidences of a 
given health effect likely to be experienced by the population group of 
interest (n.b., some individuals likely experience that given health 
effect more than once in a year). While the estimates of numbers of 
people and incidences of effects are subject to uncertainties and 
should not be viewed as demonstrated health impacts, EPA believes they 
do represent reasonable estimates of the likely extent of these effects 
on public health given the available information.
    This risk assessment builds upon earlier O₃ risk 
assessment approaches developed during the previous O₃ NAAQS 
review. The risk models produce estimates of risk by taking into 
account: (1) Exposure-response or concentration-response relationships 
used to characterize various respiratory effects of O₃ 
exposure; (2) distributions of population exposures upon attainment of 
alternative standards resulting from the exposure analyses described 
above; and (3) distributions of 1-hour and 8-hour daily maximum 
O₃ concentrations upon attainment of alternative standards, 
developed as part of the exposure analyses. The assessment addresses a 
number of adverse lung function and respiratory symptom effects as well 
as increased hospital admissions, as discussed below.
    (i) Adverse lung function and respiratory symptom effects. Risk 
estimates have been developed for several of the respiratory effects 
observed in controlled human exposure studies to be associated with 
O₃ exposure for which sufficient quantitative dose-response 
information was available. These effects include lung function 
decrements (measured as changes in FEV₁) and pain on deep 
inspiration (PDI).\39\ More specifically, these effects, or health 
endpoints, are defined not only in terms of physiological responses, 
but also the amount of change in that response judged to be of medical 
significance (as discussed in section II.A.3 above). For decrements in 
FEV₁ responses, risk estimates are provided for the lower 
end, midpoint, and upper end of the range of response considered to be 
an adverse health effect (i.e., £= 10, 15, or 20 percent 
FEV₁ decrements), while for PDI responses, risk estimates 
are provided for moderate and severe responses. Although some 
individuals may experience a combination of responses, risk estimates 
could only be provided for each individual health endpoint rather than 
various combinations of functional and symptomatic responses.
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    \39\ Each of the effects is associated with a particular 
averaging time and, for most of the acute (1- to 8-hour) responses, 
effects also are estimated separately for specific ventilation 
ranges [measured as equivalent ventilation rate (EVR)]
that 
correspond to the EVR ranges observed in the studies used to derive 
exposure-response relationships.
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    The exposure-response relationships used to characterize these 
functional and symptomatic effects were based on the controlled human 
exposure studies, and were applied to ``outdoor children,'' ``outdoor 
workers,'' and the general population.\40\ These exposure-response 
relationships were combined with the results of the exposure analyses, 
which provided distributions of population exposures estimated to occur 
upon attainment of alternative standards, in terms of both the number 
of individuals in the general population, outdoor workers, and outdoor 
children exposed and the number of occurrences of exposure.
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    \40\ While these studies only included adults aged 18-35, 
findings from other clinical studies and summer camp field studies 
in several locations across the U.S. and Canada indicate changes in 
lung function in healthy children similar to those observed in 
healthy adults exposed to O₃ under controlled laboratory 
conditions.
-----------------------------------------------------------------------

    Following from the results of the exposure analyses showing outdoor 
children to be the population group experiencing the greatest 
exposures, this population group also has the highest estimated risk in 
terms of the percent of the population, and the numbers of children, 
likely to experience the health effects included in the assessment. As 
expected, the risk estimates exhibit the same general patterns in 
comparing alternative standards as was observed in the results of the 
exposure analyses. Estimated risk varied significantly across the urban 
areas examined, with greater variability associated with the 1-hour 
NAAQS than with alternative 8-hour standards, and, within any given 
urban area, the differences in risk estimated for the various 1-hour 
and 8-hour standards analyzed were statistically significant.
    In looking more specifically at a comparison between 8-hour 
standards at the 0.09 ppm and 0.08 ppm levels, aggregate estimates of 
the number of outdoor children in the nine areas likely to experience 
moderate (£= 15 percent) and large (£= 20 percent) 
FEV₁ decreases and moderate or severe PDI are summarized in 
the 1997 final rule.\41\ For example, for large FEV₁ 
decreases (£= 20 percent), approximately 2 percent of outdoor 
children (58,000 children) would likely 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. Based on this assessment, a standard set at 0.09 ppm would allow 
approximately 40-65 percent more outdoor children to experience these 
functional and symptomatic effects than would a 0.08 ppm standard, and 
approximately 70-120 percent more occurrences of such effects in 
outdoor children per year.
-----------------------------------------------------------------------

    \41\ Based on the supplemental analyses that used the third-
highest concentration-based form of the standards (Richmond, 1997).
-----------------------------------------------------------------------

    In considering these observations, the Administrator and CASAC have 
recognized that there are many uncertainties inherent in such 
assessments, not all of which can be quantified. Some of the most 
important caveats and limitations in this assessment include: (1) The 
uncertainties and limitations associated with the exposure analyses 
discussed above; (2) the extrapolation of exposure-response functions, 
consistent with CASAC's recommendation, that projects some biological 
responses below the lowest-observed-effects levels to an estimated 
background level of 0.04 ppm; and (3) the inability to account for some 
factors which are known to affect the exposure-response relationships 
(e.g., assigning children the same symptomatic response rates as 
observed for adults and not adjusting response rates to reflect the 
increase and attenuation of responses that have been

[[Page 625]]

observed in studies of lung function and symptoms upon repeated 
exposures).\42\
-----------------------------------------------------------------------

    \42\ A more complete discussion of assumptions and uncertainties 
is presented in the Staff Paper and the technical support documents 
(Whitfield et al., 1996; Richmond, 1997).
-----------------------------------------------------------------------

    (ii) Excess respiratory-related hospital admissions. A separate 
risk assessment was done for increased respiratory-related hospital 
admissions as reported in several epidemiologic studies.\43\ The 
assessment looked only at one urban area, New York City, for which 
adequate air quality information also was available to assess 
population risk. Increased respiratory-related hospital admissions for 
individuals with asthma were modeled using a probabilistic 
concentration-response function based on the results of an 
epidemiologic study in New York City (Thurston et al., 1992) and 
estimated distributions of daily maximum 1-hour average O₃ 
concentrations upon attainment of alternative standards at various 
monitors in New York City (developed as part of the exposure analysis 
discussed above).\44\ The resulting risk estimates are for excess 
respiratory-related hospital admissions (i.e., those attributable to 
O₃ concentrations above an estimated background 
O₃ level of 0.04 ppm) for asthmatic individuals over an 
O₃ season.
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    \43\ Several studies, mainly conducted in the northeastern U.S. 
and southeastern Canada have reported excess daily respiratory-
related hospital admissions associated with elevated O₃ 
levels within the general population and, more specifically, for 
individuals with asthma.
    \44\ The model is described in more detail in Whitfield et al. 
(1996) and results from the supplemental analysis are presented in 
Richmond (1997).
-----------------------------------------------------------------------

    Similar to the risk assessment discussed above for lung function 
and respiratory symptom effects, 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 alternative 8-
hour standards from 0.09 ppm to 0.07 ppm. In looking more specifically 
at a comparison between 8-hour standards at 0.09 ppm and 0.08 ppm 
levels, a standard set at 0.09 ppm is estimated to 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.
    In taking these observations into account, the Administrator 
recognizes the uncertainties and limitations associated with this 
assessment. These include: (1) The inability at this time to 
quantitatively extrapolate the risk estimates for New York City to 
other urban areas; (2) uncertainty associated with the underlying 
epidemiologic study from which the concentration-response relationship 
used in the analysis was drawn; and (3) uncertainties associated with 
the air quality adjustment procedure used to simulate attainment of 
alternative standards for the New York City area.\45\
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    \45\ A more complete discussion of these uncertainties and 
limitations is presented in the Staff Paper and technical support 
documents (Whitfield et al., 1996; Richmond, 1997).
-----------------------------------------------------------------------

B. Potential Indirect Beneficial Health Effects Associated with Ground-
level O₃

    This section is drawn from information in the record of the 1997 
review with regard to the effect of ground-level O₃ on the 
attenuation of UV-B radiation and potential associated health benefits. 
All relevant record information was reviewed, including EPA documents, 
published articles, oral testimony at public meetings, and written 
comments submitted during the rulemaking and on the proposed response. 
This section summarizes information on the health effects associated 
with UV-B radiation exposure (section B.1) and the relationship between 
ground-level O₃ and UV-B radiation (section B.2), and 
evaluates estimates of UV-B radiation risks that have been attributed 
to reductions in ground-level O₃ projected to result from 
attainment of the 1997 O₃ NAAQS (section B.3). This section 
also responds to a number of technical comments on the proposed 
response relating to (i) the distinctions that EPA has drawn between 
assessing the public health impacts of changes in stratospheric versus 
ground-level O₃, (ii) the distinctions between assessing the 
public health impacts of changes in inhalation-related exposures to 
ground-level O₃ versus the impacts of changes in dermal-
related exposures to UV-B radiation as mediated by changes in ground-
level O₃, and (iii) the appropriate weight to give to 
analyses in the record that provide quantitative estimates of the 
public health impacts of changes in dermal-related exposures to UV-B 
radiation as mediated by changes in ground-level O₃.
1. Health Effects Associated with UV-B Radiation Exposure
    The following short summary of information \46\ on the adverse 
human health effects associated with exposure to UV-B radiation focuses 
on the three major organ systems whose tissues are commonly exposed to 
solar radiation: the skin, eyes, and immune system.\47\ It is these 
three systems that are potentially subject to damage from increased UV-
B radiation as a result of the absorption of solar energy by molecules 
present in the cells and tissues of these organs. The biologically 
effective dose of radiation that actually reaches target molecules 
generally depends on the duration of exposure at particular locations, 
time of day, time of year, behavior (i.e., ``sun avoidance'' and ``sun 
seeking'' behavior \48\), and, for the skin, characteristics that 
include pigmentation and temporal variations (e.g., changes in the 
pigmentation due to tanning).
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    \46\ More detailed information about the health effects 
associated with UV-B radiation exposure may be found in the proposed 
response to the remand (66 FR 57278-57280).
    \47\ The reference document available in the record for the 
information in this section is the EPA document ``Assessing the Risk 
of Trace Gasses that Can Modify the Stratosphere'' (U.S. EPA, 1987).
    \48\ Sun avoidance is an intentional decrease in exposure, for 
example, by using clothing, sunscreens, and sunglasses to shield the 
body from solar radiation. Sun seeking behavior is an intentional 
increase in exposure to solar radiation, for example, by sunbathing.
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a. Effects on the Skin

    The most common form of solar damage to the skin is sunburn. 
Susceptibility to sunburn and the ability to tan are the basis for a 
classification system of six skin phenotypes. The most sensitive 
individuals (skin type I) are very light-skinned, with red or blonde 
hair and blue or green eyes (U.S. EPA, 1987, ES-33). The most resistant 
individuals (skin type VI) are darkly pigmented even without exposure 
to solar radiation. Susceptibility to sunburn may be a risk factor for 
skin cancer.
    Among light-skinned populations, skin cancer is among the most 
common kinds of cancer. The three types of skin cancer that have been 
associated with exposure to solar radiation include two common types of 
nonmelanoma skin cancers (NMSC), squamous cell carcinoma (SCC) and 
basal cell carcinoma (BCC), and melanoma, a far less common form of 
cancer.

[[Page 626]]

    Prolonged exposure to the sun is considered to be the dominant risk 
factor for NMSC (U.S. EPA, 1987, ES-33). It has been observed that NMSC 
tends to develop on sites that are most frequently exposed to the sun 
(e.g., head, face, and neck). Outdoor workers, who are subject to 
greater exposure to solar radiation, tend to have higher incidence 
rates of NMSC. A latitudinal gradient exists for the flux of UV-B 
radiation (i.e., the amount of radiation transmitted through the 
atmosphere), with fluxes generally higher in lower latitudes. A similar 
latitudinal gradient is generally seen in incidence rates of NMSC. Skin 
pigmentation provides a protective barrier that reduces the risk of 
developing NMSC, such that light-skinned individuals, who are more 
susceptible to sunburn and have blue or green eyes, are more likely to 
develop NMSC.
    Both types of NMSC result from the malignant transformation of 
keratinocytes, the major structural cells of the skin. Cumulative long-
term exposure to UV radiation is the exposure of concern for both types 
of NMSC. More specifically, the incremental increase in cumulative 
lifetime exposure to UV-B radiation is the metric used to estimate the 
risk of increased incidence of NMSC (U.S. EPA, 1987, ES-3). 
Epidemiological evidence, however, also indicates that exposure to 
solar radiation may play different roles in the etiology of SCC and 
BCC. In particular, SCC is more likely to develop on sites receiving 
the highest cumulative UV radiation doses (e.g., nose), and the 
development of SCC is more strongly associated with cumulative exposure 
to UV radiation. Relative to SCC, BCC is more likely to develop on 
sites that are not normally exposed to the sun, such as the trunk. For 
a given cumulative level of exposure to solar radiation, the risk of 
developing SCC may be greater than the risk of developing BCC.
    Dose-response relationships for NMSC are generally estimated in 
terms of a biological amplification factor (BAF), which is defined as 
the percent change in tumor incidence that results from a 1 percent 
change in UV-B radiation. While there is considerable uncertainty in 
such estimates, results from several studies have produced an overall 
BAF range that is 1.8 to 2.85 for all nonmelanoma skin tumors (U.S. 
EPA, 1987, ES-34). The BAF estimates are generally higher for males 
than females and for SCC than BCC, and generally increase with 
decreasing latitude. Key uncertainties in these estimates include, for 
example, uncertainties in the actual doses of UV-B radiation received 
and in the underlying baseline incidence rates in populations. 
Additional uncertainty is introduced in estimating the change in 
mortality from NMSC associated with changes in UV-B radiation, 
reflecting in part discrepancies of reporting between death 
certificates and hospital diagnoses. Based on published estimates, 
rates of metastasis among SCCs and BCCs varied by one to two orders of 
magnitude, with rates estimated to be approximately 2 to 20 percent for 
SCC and 0.0028 to 0.55 percent for BCC. The overall fatality rate for 
NMSC has been estimated to be approximately 1 to 2 percent, with three-
fourths to four-fifths of the deaths attributable to SCC (U.S. EPA, 
1987, ES-34).\49\
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    \49\ More recent estimates of mortality rates from NMSC may be 
found on the American Cancer Society's Web site http://www.cancer.org, 
 under cancer type ``Skin, Nonmelanoma,'' then under 
``Nonmelanoma Skin Cancer--Overview.''
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    Melanoma is a serious, life-threatening skin cancer that is far 
rarer and generally much more aggressive than NMSC. The relationship 
between exposure to UV-B radiation and melanoma is not as clear as the 
relationship between exposure to UV-B radiation and NMSC. The EPA 
(1987) noted limitations in the evidence linking solar radiation to 
melanoma. For example, no animal models were identified in which 
exposure to UV-B radiation experimentally induces melanoma, and no in 
vitro models for malignant transformation of melanocytes. Despite these 
limitations, EPA (1987) recognizes that a large array of evidence does 
support the conclusion that solar radiation is one of the causes of 
melanoma. Melanin, the principal pigment in the skin, effectively 
absorbs UV radiation, such that darker skin provides more protection 
from UV radiation. Lighter-skinned individuals, whose skin contains 
less protective melanin, have higher incidence and mortality rates from 
melanoma than do darker-skinned individuals.
    Sun exposure seems to induce freckling, which is an important risk 
factor for melanoma, and sun exposure leading to sunburn apparently 
induces melanocytic moles, which are also a risk factor for melanoma. 
Additional evidence suggests that melanoma risk may be associated with 
childhood sunburn. However, other evidence suggests that childhood 
sunburn may be a surrogate for an individual's pigmentation 
characteristics or be related to mole development, rather than being a 
separate risk factor (U.S. EPA, 1987, ES-37).
    Most studies that have used latitude as a surrogate for sunlight or 
UV-B exposure have found an increase in melanoma incidence or mortality 
correlated with proximity to the equator. Other evidence, however, 
creates uncertainty about the relationship between solar radiation and 
melanoma. Some ecologic epidemiology studies, conducted primarily in 
Europe or in countries close to the equator, have failed to find a 
latitudinal gradient for melanoma. In addition, outdoor workers 
generally have lower incidence and mortality rates from melanoma than 
indoor workers, which appears to be incompatible with the hypothesis 
that the cumulative dose from exposure to solar radiation causes 
melanoma. Unlike NMSC, most melanoma occurs on sites of the body that 
are not habitually exposed to sunlight. This evidence suggests that 
exposure to solar radiation, or UV-B, is not solely responsible for 
variations in the incidence and mortality from melanoma (U.S. EPA 1987, 
ES-37).
    Considering the available evidence, EPA (1987) concluded that UV-B 
radiation is a likely component of solar radiation that causes 
melanoma, either through the initiation of tumors or through 
suppression of the immune system. The EPA (1987) also recognized that 
significant uncertainties exist in characterizing associations between 
solar radiation and melanoma, including the appropriate action spectrum 
to be used in estimating doses, the best functional form for a dose-
response relationship, and the best way to characterize dose (e.g., 
peak value, cumulative summer exposure).

b. Effects on the Eyes

    Evidence suggests that adverse effects on the eye are associated 
with exposure to UV-B radiation. Effects likely include increases in 
cataract incidence or severity and increased incidence of retinal 
disorders and retinal degeneration. Cataracts are characterized by the 
gradual loss of transparency of the lens due to the accumulation of 
oxidized lens proteins. Many possible mechanisms exist for the 
formation of cataracts, and UV-B radiation may play an important role 
in some mechanisms. Therefore, while epidemiological studies indicate 
that the prevalence of human cataracts varies with latitude and UV 
radiation in general (U.S. EPA, 1987, ES-40), significant uncertainty 
exists about the action spectrum to be used in any estimation of dose 
associated with variations in solar radiation. Epidemiological and 
laboratory evidence indicates that the exposure of

[[Page 627]]

concern in the development of cataracts is the cumulative lifetime 
exposure to UV-B radiation.

c. Effects on the Immune System

    Information on the effects of UV-B radiation on the immune system 
comes primarily from laboratory animal studies. High doses of UV 
radiation cause a depression in systemic hypersensitivity reactions, 
whereas relatively lower doses cause a depression in local contact 
hypersensitivity. Both of these immunosuppressive effects of UV 
radiation have been found to reside almost entirely in the UV-B portion 
of the solar spectrum (U.S. EPA, 1987, ES-39).
    Information about the effects of UV radiation on the human immune 
system, however, is very limited. Without more complete information 
from laboratory or epidemiological studies, the nature of an exposure 
of concern cannot be estimated. Immunologic studies have not assessed 
the effects of long-term, low-dose UV-B irradiation, such that the 
magnitude of risk from this type of exposure cannot be assessed (U.S. 
EPA, 1987, ES-40).
2. Relationship Between Ground-level O₃ and UV-B Radiation 
Exposure

a. Relevant Atmospheric Factors

    The relationships between ground-level O₃ and UV 
radiation occur in the context of a much larger dynamic of the earth's 
atmospheric systems. The sun is, of course, overwhelmingly the main 
source of a wide band of electromagnetic radiation, including the 
ultraviolet. The total atmosphere blocks a significant portion of the 
range of this incoming solar radiation before it reaches ground level, 
including much of the more energetic wavelengths that are shorter than 
visible light (400-900 nm). The UV spectrum (100-400 nm) is comprised 
of UV-C (100-280 nm), UV-B (280-320 nm), and UV-A (320-400 nm). 
Ultraviolet -B radiation is efficiently but not completely absorbed by 
total column O₃. Wavelengths above 350 nm, including visible 
light, are not absorbed by oxygen (O2) or O₃ (U.S. EPA, 
1987, ES 35). Because the amount of atmospheric O₃ traversed 
by sunlight varies with the sun angle, atmospheric absorption is more 
complete in winter months and both early and late in the day, as 
compared to the absorption around mid-day near the summertime solar 
zenith. Therefore, a decrease in total column O₃ from 
naturally occurring conditions is of greater concern during times of 
higher sun angles, and for the more energetic portion of the UV-B 
range.
    The underlying annual and diurnal patterns of UV-B penetration to 
the ground layer are driven primarily by three factors: (1) The change 
in apparent sun angle with the surface that occurs as the earth travels 
around the sun; (2) the diurnal change in apparent sun angle caused by 
the earth's rotation; and (3) the solar/meteorologically driven annual 
change in the amount of O₃ in the stratosphere. 
Stratospheric O₃ over U.S. latitudes shows a characteristic 
peak in the spring months, falling steadily thereafter through summer 
and fall (Fishman et al., 1990; Frederick et al., 1993). The 
combination of the annual sun cycle and the stratospheric O₃ 
cycle means that peak UV-B radiation reaching the troposphere tends to 
occur in late June to early July, and falls steadily thereafter 
(Frederick et al., 1993). The annual peak in ground-level O₃ 
concentrations, which extends in most areas from May through September, 
generally overlaps the UV-B radiation peak (e.g., U.S. EPA, 1996a, 
Figure 4-23). Diurnal patterns of ground-level O₃ vary, but 
in urban areas, summertime peaks tend to occur between noon and 4 pm 
(U.S. EPA, 1996a, section 4.4). This obviously overlaps with peak 
incoming UV-B radiation. The pattern of vertical mixing in the 
atmosphere is such that morning ground-level measurements probably do 
not accurately reflect ``mixing-layer'' concentrations (U.S. EPA, 
1996a, p. 3-44).\50\
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    \50\ The mixing layer (relevant to the vertical ``thickness'' of 
ground-level O₃) develops and grows in height through the 
day.
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    The relationship between ground-level O₃ and solar 
radiation, including UV-B radiation, is complex and mediated by a 
number of atmospheric factors. It is not limited to the simple 
absorption of energy. At a fundamental level, the variation in apparent 
solar radiation is a primary cause of meteorological fluctuations that 
strongly influence the build-up and transport of anthropogenic air 
pollution. Further, as discussed in Chapter 3 of the Criteria Document, 
UV-B radiation that penetrates the stratosphere to the mixing layer 
plays a key role in the processes leading to the formation of 
photochemical smog, including the formation of ground-level 
O₃. In fact, increased penetration of UV-B radiation to the 
troposphere due to stratospheric O₃ depletion would likely 
increase ground-level concentrations of O₃ in most urban and 
many rural areas of the U.S. (U.S. EPA, 1996a, p. 3-5). The chain of 
indirect events triggered by increased penetration of UV-B radiation 
can result in both increases and decreases in aerosol and acid rain 
formation (U.S. EPA, 1996a; pp. 3-38 to 39), with attendant further 
feedbacks through heterogeneous chemistry and aerosol scattering of UV-
B radiation. All of these complex processes could, under varying 
conditions, increase or decrease the amount of UV-B radiation that 
actually reaches ground level relative to an unperturbed case. The 
reactions can further affect the concentrations of radiatively 
important substances such as methane, O₃, and particles, and 
could affect local, regional, and global climate.
    Setting aside the direction and magnitude of these complex indirect 
effects of UV-B radiation penetration on ground-level air pollution, 
and assuming appropriate sun angles and cloud density, the marginal 
effect of ground-level O₃ on the absorption of UV-B 
radiation by the earth's atmosphere can be considered separately. 
Because of increased scattering of incident UV-B radiation by the 
denser layer air molecules, droplets, and particles nearer the surface, 
tropospheric O₃ can absorb somewhat more UV-B radiation than 
an equal amount of O₃ in the stratosphere (Br[uuml]hl and 
Creutzen, 1989). The extent to which this increase in unit effect 
occurs depends on the relative concentrations and character of aerosols 
in the troposphere as compared to the stratosphere.
    A further consideration is the relative effectiveness of ground-
level O₃ in absorbing those spectra of UV-B radiation 
wavelengths most likely to cause health effects. The ``effective dose'' 
of UV-B radiation can be expressed as a function of two factors, the 
intensity of radiation (by wavelength) reaching the earth's surface and 
the action spectrum. The wavelength-dependent effect of O₃ 
on reducing the intensity of radiation in the UV-B range is summarized 
above. The action spectrum describes how effective radiation at 
particular wavelengths is at causing a particular biological effect or 
a response in an instrument. Action spectra allow the estimation of the 
potential effects of simultaneously changing radiation at different 
wavelengths by different amounts, as happens with changing 
O₃ levels. Laboratory and field studies have been used to 
estimate and adopt action spectra conventions for various biological 
endpoints (e.g., Madronich, 1992). As noted above, uncertainty exists 
about the action spectra as well as how to specify appropriate dose 
metrics for particular health endpoints. Even estimates of the range of 
wavelengths

[[Page 628]]

considered to be generally biologically active vary within the UV-B 
radiation spectrum. These different action spectra have different 
sensitivities to changes in total column O₃, which are 
formalized as numerical radiation amplification factors (RAF).\51\ In 
general, a 1 percent change in total column O₃ will produce 
greater than a 1 percent change (e.g., 1.1 to 1.8 percent) in effective 
radiation dose for particular effects.
-----------------------------------------------------------------------

    \51\ The RAF is defined as the percent increase in effective 
dose divided by the percent decrease in total column O₃ 
(Madronich, 1992).
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    Nevertheless, as noted above, typical summertime ground-level 
O₃ pollution in the eastern U.S. is less than 1 percent of 
total column O₃. Even considering the relative effectiveness 
of ground-level O₃ in reducing UV-B radiation and the 
amplification of effective dose, such pollution could add a few percent 
at most to naturally occurring biologically effective UV-B radiation 
shielding.\52\ Viewed from one perspective and holding all other 
factors constant, the assumed typical O₃ pollution level is 
providing some ``improvement'' or incremental UV-B radiation shielding 
above the natural conditions that would otherwise exist in the mixing 
layer. It should also be noted that, if typical summertime 
O₃ levels were assumed to approximate the estimated 
continental background of about 40 ppb for daylight hours (U.S. EPA, 
1996b, p.p. 20-21), this too would represent an ``improvement'' over 
the natural conditions that would exist in the mixing layer without the 
influence of international transport of O₃.\53\
    The extent to which changes in ground-level O₃ 
concentrations would translate into changes in UV-B radiation-related 
health effects in various locations cannot, however, be adequately 
viewed by reference to uniform assumptions applicable for specific sun 
angle, latitude, time of day, cloud cover, and the presence of other 
pollutants.\54\ In the real world, all of these factors vary with 
location, season, meteorology, and time of day. Moreover, the complex 
causal relationships noted above among all of these factors mean that 
neither static calculations holding other factors constant (e.g., 
Cupitt, 1994) nor simple empirical associations between measured 
ground-level O₃ and UV-B radiation (e.g., Frederick et al., 
1993) provide an adequate basis for assessing the ``net'' shielding 
associated with control strategy driven changes in ground-level 
pollution in various locations over an extended time period. Moreover, 
as for the direct effects of O₃, the extent of resultant UV-
B radiation-related health effects is also heavily dependent on the 
variation of these physical changes superimposed on the activity 
patterns and other factors that determine population exposures and 
sensitivities to UV-B radiation, and on the extent to which significant 
biological responses can be attributed in part to episodic peak 
exposures as well as to long-term cumulative exposures.
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    \52\ For reasons discussed below, any such shielding would vary 
widely from day-to-day, even in the summer O₃ season.
    \53\ This estimated continental background is due in part to 
natural sources of emissions in North America and in part to the 
long-range transport of emissions from both anthropogenic and 
natural sources outside of North America.
    \54\ Adding to the complexity of understanding this relationship 
are the results of high-dose animal toxicology studies that suggest 
more research is needed into the direct effects of ground-level 
O₃ on the skin. Tests by Thiele et al. (1997) suggest 
that long-term exposure to O₃ can deplete vitamin E in 
the skin, and this could make the skin more susceptible to the 
effects of UV-B radiation (U.S. EPA, 1997). Therefore, reducing 
long-term ground-level O₃ exposure might serve to reduce 
skin problems. Even a relatively small O₃ effect here 
could partially or completely offset any small UV-B radiation 
mediated effect estimated based on O₃--UV-B interactions 
alone.
-----------------------------------------------------------------------

    Assessing the effective O₃ layer shielding is 
considerably more difficult for ground-level O₃ than for 
stratospheric O₃ because of its far greater spatial and 
temporal variability and the much smaller contribution to the total 
O₃ column made by ground-level O₃. Some insights 
into the relative variability of these two layers are provided in 
Fishman et al. (1990), which compares satellite measurements of 
stratospheric O₃ with ``residual'' tropospheric 
O₃, a measure that actually excludes the lowest portion of 
the ground-layer O₃ in the mixing layer. For the summer 
months, the long-term spatial variability in the amount of 
O₃ in the stratosphere across the lower 48 U.S. States is 
about 7 percent (Figure 8c), while the variability in the tropospheric 
``residual'' is nearly 4 times greater, at about 25 percent (Figure 
9c). By comparison, the spatial variability in ground-level 
O₃ measurements across regions and cities in the U.S. is far 
greater (U.S. EPA, 1996a, Chapter 4) reaching 200 percent and higher 
for comparable long-term measurements. Within an area as small as the 
Los Angeles basin alone, for example, the median ground-level 8-hour 
O₃ values in different locations varied by more than a 
factor of 2 (Table 28; Johnson et al., 1996c). The satellite 
information also shows a marked contrast in the seasonal variations in 
O₃ for these two layers. The variation in the summer/winter 
stratospheric O₃ column over the U.S. is only about 2 to 4 
percent, while the variation in seasonal ``residual'' tropospheric 
O₃ is about 50 to 80 percent (Figures 8a,c;9a,c; Fishman et 
al., 1990). Again, the variability is even greater for ground-level 
measurements (e.g., U.S. EPA, 1996a, Figure 4-23; Frederick et al., 
1993).
    Although Fishman et al. (1990) do not compare daily variations in 
stratospheric O₃ above the U.S., it is reasonable to 
conclude that the spatial and annual/seasonal temporal stability 
evidenced by this large stratospheric reservoir would result in far 
more stable day-to-day and diurnal patterns as compared to ground-level 
O₃. The high variability of daytime O₃ 
concentrations for these temporal scales is amply documented in the 
Criteria Document (U.S. EPA, 1996a, Figure 4-23).
    The spatial and temporal stability of the expansive and deep 
stratospheric O₃ reservoir means that assessments of the 
effects of long-term declines or restoration can reasonably assume that 
short-term and local-scale variations in important factors such as 
cloud cover, other pollutants, temperature, population demographics and 
activity patterns beneath this layer will tend to ``even out'' over 
time, permitting more confidence in the magnitude and direction of such 
assessments. In contrast to the stability of the stratospheric 
O₃ layer, the large spatial and day-to-day variability 
outlined above for ground-level O₃ means that geographical 
or temporal variations in other factors such as weather, other 
pollutants, sensitive population subgroups and human activity patterns 
may not ``even out'' in particular areas under assessment. Moreover, it 
is reasonable to assume that the variations in ground-level 
O₃ are not independent of the variations in many of these 
other factors. Such variability may have a substantial impact on the 
outcome of any assessment of the relative effects of a change in 
ground-level O₃ strategies or standards. This, combined with 
the many local- and regional-scale interactions among all of these 
factors, would complicate any such ground-level O₃ 
assessment.
    A few commenters expressed the view that since EPA, and other 
agencies such as UNEP, have developed quantitative estimates of the 
public health impacts of relatively large increases in incident UV-B 
radiation associated with projected changes in the global reservoir of 
stratospheric O₃, it is necessarily the case that EPA can 
now develop credible estimates of the public health impacts associated 
with the relatively very small increases in incident UV-B radiation 
that could result from changes in ground-level O₃ likely to 
occur as a

[[Page 629]]

result of programs implemented to attain an 8-hour O₃ NAAQS. 
These commenters further suggest that EPA, in concluding that such 
estimates can not now be developed with sufficient credibility to serve 
as a basis for setting a less stringent 8-hour O₃ NAAQS, is 
treating scientific uncertainty differently than it did when regulating 
substances that deplete O₃ in the stratosphere. The EPA 
believes that these commenters are ignoring fundamental differences, 
discussed above, in the nature and relative magnitude of the temporal 
and spatial variability of O₃ levels in the stratosphere and 
at ground-level in the troposphere. The EPA remains convinced that it 
is entirely reasonable to use available information to make estimates 
of broad-scale public health impacts in the context of the 
stratospheric O₃ program, while concluding that such broad-
scale analytic approaches necessarily obscure and assume away the 
localized and highly variable factors that are central to credibly 
estimating public health impacts in the context of programs designed to 
attain the O₃ NAAQS.
    More specifically, EPA notes that quantitative estimates of public 
health impacts associated with projected changes in stratospheric 
O₃ are based primarily on epidemiological studies designed 
to evaluate impacts of long-term UV-B radiation exposures over broad 
geographic regions (defined in terms of latitude bands) within which 
stratospheric O₃ levels exhibit relatively little 
variability. These types of epidemiological studies are not designed to 
discern impacts associated with much smaller, and much more highly 
variable, localized changes in ground-level O₃ that will 
likely result from programs implemented to attain an 8-hour 
O₃ NAAQS--such local variations are simply averaged out in 
these studies that compare average UV-B radiation penetration over 
broad geographic regions with regional average incidence rates of UV-B 
radiation-related effects. The EPA believes that in choosing not to 
apply the same type of approach used to assess stratospheric 
O₃ impacts to its assessment of NAAQS-related changes in 
ground-level O₃, that it is treating scientific uncertainty 
in an appropriate and consistent manner. To do otherwise, as some 
commenters urge, would be to disregard the uncertainties associated 
with localized and highly variable changes in UV-B radiation exposure 
patterns that are central to an assessment of NAAQS-related changes, 
but that are not relevant to the long-term, regional assessment of 
stratospheric O₃ impacts. Therefore, EPA rejects the notion 
advanced by these commenters that the simple application of a 
stratospheric O₃-type assessment would produce credible 
quantitative estimates of NAAQS-related impacts for the purpose of 
weighing against the adverse respiratory-related impacts of ground-
level O₃, for which EPA has applied state-of-the-art 
assessments that appropriately take into account the relevant, highly 
variable patterns of changes in exposures of concern to ground-level 
O₃ (as discussed more fully in the following section).

b. Factors Related to Area-Specific Assessment

    An enumeration of factors that would be important in assessing the 
potential UV-B radiation-related consequences of a more stringent 
O₃ NAAQS in any geographical area serves to illustrate the 
complexities discussed above. Such UV-B radiation-related factors are 
analogous, but not equivalent to the factors that were important in the 
respiratory effects exposure and risk assessments discussed above in 
section II.A.2. These UV-B radiation-related factors include: the 
temporal and spatial patterns of ground-level O₃ 
concentrations throughout a geographic area where reductions are likely 
to occur, and the variations in O₃ concentrations within a 
comprehensive set of ``microenvironments'' relevant to UV-B radiation 
exposures (which are generally different from the microenvironments 
relevant to O₃ inhalation exposures); the associated 
temporal and spatial patterns of UV-B radiation flux in such 
microenvironments; the temporal and spatial patterns of movement of 
people throughout the UV-B radiation-related microenvironments within 
the geographic area; and the effects of variable behaviors (e.g., the 
use of sunscreen, hats, sunglasses) within the range of activities that 
people regularly engage in, on the effective dose of UV-B radiation 
that reaches target organs such as the skin.
    While analogous to the respiratory-related factors, there are a 
number of important differences between these sets of factors that 
arise, for example, due to: (1) The indirect nature of the relationship 
between changes in ground-level O₃ and UV-B radiation-
related health effects (in contrast to the direct relationship between 
ground-level O₃ and inhalation-related health effects); (2) 
the long-term nature of the relevant exposures that are associated with 
UV-B radiation's chronic health effects (in contrast to the short-term 
exposures associated with acute inhalation effects); (3) the different 
types of parameters that are relevant to assessing dermal exposures (in 
contrast to those that are important in assessing inhalation 
exposures); and (4) the importance of skin type in characterizing the 
sensitive populations (in contrast to characterizing sensitive 
populations in terms of activity levels and respiratory health status). 
Further, as was done in EPA's assessment of respiratory effects, it is 
important to characterize the exposure-related factors specifically to 
address the relevant at-risk sensitive population groups. As noted in 
section II.B.1, the sensitivity to UV-B radiation effects varies among 
U.S. demographic groups, such that it would be important to incorporate 
census data on relevant characteristics (e.g., age at time of exposure, 
skin pigmentation) that affect an individual's susceptibility.
    Aspects of each of these factors (including areas where current 
information or modeling tools are insufficient to address these factors 
at this time), significant comments received on these factors, and 
EPA's general responses are discussed briefly below.
    (i) Estimation of area-specific and microenvironment changes in 
ground-level O₃. Implementation of a more stringent 
O₃ standard would, over time, further reduce O₃ 
concentrations across many areas within the U.S., but would affect 
various areas in different ways. Depending on the strategies adopted, 
in some locations peak concentrations would be reduced significantly 
during the O₃ season, while the lower concentrations that 
occur on far more numerous days could increase. In such areas, the 
long-term cumulative effect could be little net change, or even a small 
increase in cumulative shielding. In other areas, the entire 
distribution of O₃ could be reduced. The assessment of the 
acute respiratory health effects of O₃ appropriately focused 
on the higher portion of this distribution, using a simple roll-back 
approach discussed above (section II.A.2.a) to simulate changes in air 
quality patterns during the O₃ season based on available air 
quality monitoring data. For assessment of chronic effects such as 
those associated with UV-B radiation, however, where long-term 
cumulative exposures are of central importance, the mid to lower 
portion of the distribution would also be important. Also the 
distribution across the entire year, for which O₃ monitoring 
data is not generally available in many parts of the country, could 
potentially be important. The mid to lower portion of the

[[Page 630]]

distribution is much more strongly influenced by complex atmospheric 
chemistry and nonanthropogenic sources, such that more sophisticated, 
area-specific modeling may be needed to estimate changes in this part 
of the distribution likely to occur as a result of programs designed to 
attain a more stringent O₃ NAAQS.
    In addition, although not relevant to assessing direct respiratory 
effects, the vertical distribution of O₃ concentrations up 
through the mixing layer becomes important in assessing the effect of 
O₃ in shielding UV-B radiation. The current lack of routine 
vertical profile measurements means that little is known about the 
relative effect of ground-level control strategies on O₃ in 
the mixing layer.
    With regard to characterizing changes in O₃ 
concentrations within microenvironments relevant to UV-B radiation 
exposure, it is clear that this set of microenvironments would differ 
in some respects from the set of microenvironments that were relevant 
for respiratory effects. For example, while indoor microenvironments 
can reduce exposure to both ambient O₃ and UV-B radiation, 
outdoor microenvironments that are relevant for inhalation exposure do 
not reflect the characteristics that are important for UV-B radiation 
exposure. Further, while not relevant to inhalation exposure, 
microenvironments shaded by the presence of trees, buildings, and other 
structures in many heavily occupied areas would be important to 
characterize for UV-B radiation analyses because these 
microenvironments would tend to have greatly reduced UV-B radiation 
exposures even when at the same ground-level O₃ 
concentration as a sunny microenvironment.
    A few commenters expressed the view that estimating area-specific 
changes and microenvironment changes in ground-level O₃ is 
just as important in conducting exposure and risk assessments for 
direct respiratory-related effects of ground-level O₃ as it 
would be in conducting such assessments for UV-B radiation-related 
effects mediated by changes in ground-level O₃. These 
commenters further asserted that since EPA was able to estimate area-
specific changes and microenvironment changes in ground-level 
O₃ to conduct the respiratory-related exposure and risk 
assessments discussed above (section II.A.2), then EPA should also be 
able to estimate such changes as part of an assessment of UV-B 
radiation-related exposure and risk. While EPA agrees that these 
factors are relevant for both types of assessments, EPA does not agree 
that the same information on area-specific and microenvironment changes 
is relevant for both types of assessments. The EPA believes that these 
commenters are ignoring both the important differences, discussed 
above, in the information needed on area-specific and microenvironment 
factors to conduct the two types of exposure and risk assessments, and 
the limitations in the available information.
    In particular, EPA's 9-city exposure and risk assessment of acute 
respiratory health effects of O₃ appropriately focused on 
the higher portion of the distribution of ground-level O₃ 
concentrations during the O₃ season, in contrast to an area-
specific assessment of chronic UV-B radiation-related effects that 
would need to focus on the entire distribution of O₃ 
concentrations, not only at ground-level but extending up throughout 
the vertical mixing layer, across the entire year. While EPA has 
available air quality monitoring data sufficient for simulating changes 
in ground-level O₃ concentrations within the O₃ 
season associated with attaining a more stringent O₃ NAAQS, 
data are not generally available for simulating changes throughout the 
vertical mixing layer (necessary for calculating changes in UV-B 
radiation penetration to the earth's surface as a function of changes 
in ground-level O₃ concentration patterns) or for simulating 
changes beyond the O₃ season (which is only 4 to 5 months in 
many parts of the country). Further, while data are available on 
microenvironments relevant to direct inhalation-related exposures, data 
are not yet available on the different microenvironments relevant to 
dermal UV-B radiation exposures. Thus, while methodologically 
analogous, sufficient information is simply not yet available to 
address these factors as part of an area-specific assessment of UV-B 
radiation-related exposure and risk mediated by changes in ground-level 
O₃ associated with programs designed to attain a more 
stringent O₃ NAAQS.
    (ii) Estimation of temporal and spatial patterns of UV-B radiation 
flux. Relative to the assessment of direct respiratory effects, the 
assessment of the indirect effect of O₃ shielding on UV-B 
radiation-related health effects requires the additional step of 
estimating how changes in the temporal and spatial patterns of 
O₃ concentrations result in changes in the patterns of UV-B 
radiation. Given a three-dimensional pattern of O₃ levels, a 
first-order approximation of UV-B penetration to the earth's surface 
can be readily made. The factors that influence radiation flux through 
the stratosphere are fairly well characterized, and most are directly 
related to the modest changes in stratospheric O₃ and large 
variations in sun angle that depend on latitude, time of year, and time 
of day (U.S. EPA, 1987). Nevertheless, beyond these factors, and in 
addition to changes in ground-level O₃, a number of other 
(second-order) factors in the boundary layer and the rest of the 
troposphere can affect the amount of UV-B radiation reaching 
potentially affected populations. One such factor is cloud cover, which 
can reduce UV-B radiation reaching the earth's surface by 50 percent or 
more (Cupitt, 1994). Another such factor is the presence of UV-B 
radiation scattering and absorbing aerosols. Depending on local 
circumstances and the NAAQS implementation strategy chosen, aerosol-
related UV-B radiation exposure might increase or decrease as a result 
of ground-level O₃ reductions (U.S. EPA, 1996a, Chapter 3). 
Both O₃ and aerosols can affect local climate as well as UV-
B radiation, and this could affect cloud cover as a further indirect 
consequence of a reduction strategy. While any such indirect effects 
might be expected to be small for modest O₃ changes, it is 
not currently possible to predict the magnitude or the sign of their 
net effect on UV-B radiation penetration.
    A few commenters expressed the view that these types of 
uncertainties do not preclude a quantitative assessment of exposure and 
risk related to UV-B radiation, because assessments of environmental 
risks always include simplifying assumptions. While EPA agrees that 
simplifying assumptions could be made about these types of second order 
uncertainties, EPA notes that there is little information available for 
judging whether any such assumptions were realistic or even plausible. 
Thus, EPA continues to maintain that having relevant information on 
these factors would be important in judging the credibility of any 
area-specific assessment of UV-B radiation-related exposure and risk 
mediated by changes in ground-level O₃.
    (iii) Estimation of temporal and spatial patterns of movement of 
people throughout microenvironments. While population densities are 
high in areas with the highest ground-level O₃ 
concentrations, people may not receive their highest exposure to UV-B 
radiation in such locations. Reductions in O₃ shielding 
would presumably be most significant in outdoor recreational areas such 
as the beach or rural open areas where many people likely receive a 
disproportionate share of their cumulative sun exposure. Local or

[[Page 631]]

regional meteorological factors can, however, cause ground-level 
O₃ concentrations to be lower in many such areas, 
particularly in the western United States. For example, O₃ 
concentrations in the heavily populated Los Angeles area tend to be 
lowest at the coast and increase inland; in this case, smog-related 
O₃ would be providing the least shielding where the 
potential for exposure to UV-B radiation is the highest. The extensive 
data base on human activity patterns, which was used in the assessment 
of respiratory effects, does not generally include parameters that 
relate to people's movement through the types of outdoor 
microenvironments that are relevant to the assessment of UV-B radiation 
exposure.
    One comment referenced specific EPA data bases that now contain 
activity pattern data for limited types of outdoor recreation 
locations, such as tennis courts and golf courses, suggesting that data 
are now available to better address human activity patterns in 
microenvironments relevant to assessing UV-B radiation-related 
exposures and risk. While EPA recognizes that data bases have recently 
expanded to include additional relevant human activity information, it 
also notes that the expanded data bases still fall far short of what 
would be needed to comprehensively project population activity patterns 
over time and space--in shaded, partially-shaded, and sunny 
environments. Additional data are still needed to conduct an exposure 
analysis that could account for the fraction of UV-B radiation exposure 
that is incurred, for example, during outdoor recreational activities 
in various non-shaded or partially-shaded microenvironments. The EPA 
continues to believe that sufficient data on relevant activity patterns 
are still not currently available, and that reliable estimation of the 
change in UV-B radiation exposure associated with reducing ground-level 
O₃ would be significantly hindered by not taking such 
factors into account.
    (iv) Effects of variable behaviors on effective dose of UV-B 
radiation. Another important factor to be considered in assessing the 
potential UV-B radiation-related effects of a change in ground-level 
O₃ is that human behavior affects UV-B radiation exposures. 
When people choose to shield themselves from UV-B radiation exposure 
with clothing and sunscreens, and by timing their outdoor activities to 
avoid peak sun conditions, they are affecting a parameter that is 
important in assessing UV-B radiation-related effects. The generally 
well-known risks associated with too much sun exposure are such that 
many people limit their own as well as their children's exposure 
through such measures, regardless of the status of the protective 
stratospheric O₃ layer or variable amounts of ground-level 
O₃ pollution. While some sun exposure is generally 
beneficial to health, limiting excessive sun exposure would remain 
important for a person's health even if the stratospheric O₃ 
layer were fully restored to its natural state.\55\
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    \55\ Because of the high baseline risk of effects under natural 
conditions, as well as the increased risk posed by stratospheric 
O₃ depletion, medical authorities and governmental bodies 
have developed campaigns to effect such changes in behavior. The EPA 
and the National Weather Service (NWS) developed the UV Index. The 
Index provides a forecast of the expected risk of overexposure to 
the sun and indicates the degree of caution that should be taken 
when working, playing, or exercising outdoors. The EPA also 
developed the SunWise School Program to be used in conjunction with 
the UV Index. This program is designed to educate the public, 
especially children and their care givers, about the health risks 
associated with overexposure to UV radiation and encourage simple 
and sensible behaviors that can reduce the risk of sun-related 
health problems later in life (U.S. EPA, 1995a, b).
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    Since sun-seeking or sun-avoidance behaviors can tend to maximize 
or minimize exposure to UV-B radiation, not factoring such behavioral 
data into an area-specific exposure assessment would hinder reliable 
estimation of the increased exposure associated with reducing ground-
level O₃. Changes in behavior in the past, specifically 
increases in sun-seeking behaviors, are believed to be the primary 
reason for the increases in skin cancer incidence and mortality 
observed in the U.S. by the 1980's (U.S. EPA, 1987). Conversely, future 
rates of skin cancer could be reduced to the extent that people choose 
to change their behavior by increasing sun-avoidance behaviors.
    Public awareness of the risks associated with overexposure to UV 
radiation seems to be having an effect on behavior. In 1987, EPA noted 
that behaviors causing increased UV-B radiation exposure were 
apparently reaching an upper limit (U.S. EPA, 1987, ES-35). The effect 
of increased awareness of the health consequences of UV-B radiation 
exposure on decreasing the number of harmful exposures is not likely to 
show up, in terms of reducing the incidence and mortality rates of skin 
cancers, for many years. Nevertheless, ignoring its effects would tend 
to bias exposure estimates in an area-specific assessment of the UV-B 
radiation-related effects of smog reduction strategies.
    A few commenters noted that variable behaviors would also affect 
the assessments of respiratory-related exposure and risk, and that not 
having such information to assess exposure and risk of UV-B radiation-
related effects would not introduce any additional uncertainty beyond 
what is incorporated in the assessments of respiratory effects. The EPA 
believes that these commenters are not taking into account the extent 
to which EPA's respiratory-related exposure and risk analyses did 
incorporate effects of variable respiratory-related behaviors of people 
as they move through space and time, and through different 
microenvironments, in that such behaviors are part of the human 
activity pattern data base used in those assessments. The human 
activity pattern data base incorporates respiratory-related parameters 
derived from human activity studies in which subjects report the types 
of activity they engage in as a function of location and time 
throughout the day, which are then linked to variable breathing rates 
that affect the likelihood that specific O₃ exposures are 
likely to result in adverse respiratory effects.\56\ In contrast, the 
available human activity pattern data base does not include parameters 
related to dermal exposures to UV-B radiation, such as time spent in 
sunny, partially shaded, and shaded locations, nor does it include 
parameters related to the likelihood that people in sensitive groups 
exhibit sun-avoidance or sun-seeking behaviors while in such 
microenvironments. Thus, EPA disagrees with comments asserting either 
that its respiratory-related exposure and risk analyses did not take 
into account relevant variable behavior patterns or that there is now 
sufficient information available on UV-B radiation-related variable 
behaviors to take such factors into account in an area-specific 
assessment of UV-B radiation-related exposure and risk mediated by 
changes in ground-level O₃.
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    \56\ The EPA recognizes that these data bases may not contain 
the most current information on respiratory-related avoidance 
behaviors that may now be occurring in response to EPA's new Air 
Quality Index health advisories or local community ozone action day 
programs. Any such updated information appropriately will be 
included in analyses conducted as part of the periodic review of the 
O₃ NAAQS that is now underway.
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    In the proposed response to the remand, EPA specifically solicited 
comment on the factors related to area-specific assessments of UV-B 
radiation-related effects that are discussed above (66 FR 57284). 
Beyond the specific comments on each factor noted above, commenters did 
not generally challenge the appropriateness of these factors in the 
development of such area-specific assessments, or the importance of

[[Page 632]]

conducting area-specific assessments. However, as noted above, a few 
commenters expressed the view that since EPA conducted area-specific 
quantitative assessments for the inhalation exposure and respiratory 
effects risk assessments discussed above (section II.A.2), it 
necessarily has sufficient information about these same factors to 
conduct such exposure and risk assessments of the potential UV-B 
radiation-related consequences of a more stringent O₃ NAAQS. 
These commenters also expressed the view that to the extent that EPA 
has incorporated these factors in quantitative area-specific 
assessments of respiratory effects, it should be possible to use the 
same information on these factors to conduct similar assessments of UV-
B radiation-related effects.
    While EPA clearly recognizes that the factors that are important in 
the inhalation exposure and respiratory effects risk assessments are 
analogous to the factors that would be important to conducting similar 
assessments of the UV-B radiation-related effects, as discussed above, 
EPA believes that these commenters are ignoring the important 
differences between these sets of factors. Although substantial 
information has been gathered over time regarding factors related to 
respiratory effects, no such similar research has as yet been done that 
would provide comparable information related to dermal exposure 
factors. For the reasons discussed above, EPA rejects the notion 
advanced by these commenters that simply because there is sufficient 
information to conduct area-specific quantitative assessments for the 
inhalation exposure and respiratory effects risk assessment, that such 
information would be sufficient to conduct exposure and risk 
assessments of the UV-B radiation-related effects of a more stringent 
O₃ NAAQS.
    Based on the discussion of factors above and consideration of the 
comments received, EPA continues to believe that more information is 
needed before credible area-specific quantitative analyses of potential 
UV-B radiation-related consequences of a more stringent O₃ 
NAAQS could be conducted.
3. Evaluation of UV-B Radiation-Related Risk Estimates for Ground-level 
O₃ Changes
    As should be clear from the discussion above, a full risk 
assessment of UV-B radiation-related effects resulting from a moderate 
change in ground-level O₃ would be an extremely challenging 
enterprise that appears to be beyond current data and modeling 
capabilities. Nevertheless, three analyses (Cupitt, 1994; U.S. DOE, 
1995; Lutter and Wolz, 1997) have developed estimates that attempt to 
bound the potential indirect UV-B radiation related effects associated 
with replacing the former 1-hour O₃ NAAQS with an 8-hour 
O₃ standard. All three analyses essentially reflect a static 
comparison of two separate O₃ concentrations on a national 
basis, and include, either explicitly or implicitly, numerous 
assumptions needed while excluding the important area-specific issues 
and factors outlined above.
    The most thoroughly documented calculations are those provided in 
Cupitt (1994), an EPA white paper developed as an initial scoping 
analysis of the issues, in preparation for potential consideration in 
the Regulatory Impact Analysis (RIA) that would accompany the 
O₃ NAAQS regulatory package. This paper discusses many of 
the important factors and uncertainties outlined above, summarizes key 
background information to provide perspective, and includes a 
discussion and table summarizing the many simplifying assumptions that 
were needed to permit the development of quantitative estimates. 
Cupitt's analysis evaluates changes resulting from cumulative exposures 
under two scenarios, including one that compares estimates of NMSC 
incidence associated with an assumed reduction of daytime summer 
O₃ of 10 ppb that would occur uniformly throughout 30 
eastern States and the District of Columbia and within an assumed 
atmospheric mixing layer that ranged up to 2 km in altitude. Assuming 
no other relevant factors changed over the several decade exposure 
period that would be required, the resulting increase in NMSC incidence 
for this extreme scenario was estimated eventually to reach ``between 
0.6% and 1%.'' While these percentages are small--indeed too small to 
be measurable (Cupitt, 1994)--if taken at face value, they would not 
necessarily be judged as trivial because of the large baseline of NMSC. 
For reasons outlined below, however, even these small percentage 
estimates appear to be substantially overstated and cannot be 
considered reliable.
    The Cupitt paper was never formally published, but it was subjected 
to internal agency peer review and commentary by experts at EPA's 
Office of Research and Development (ORD) (Childs, 1994; Altshuller, 
1994). While finding the exposition, including recognition of the 
difficulties in such an approach, to be ``very acceptable,'' the 
reviewers noted substantial uncertainties in basic data and expressed 
concerns about the numerous simplifying assumptions that called the 
numerical results into significant question. Examples of data 
uncertainties noted by the reviewers include: (1) The accuracy of 
column O₃ (in Dobson units) and UV measurements used; (2) 
the fact, recognized in Cupitt (1994), that the predicted UV-B 
radiation flux changes are at the ``noise'' level and could not be 
reliably detected statistically or attributed to the change in ground-
level O₃ concentration; (3) data on effects of aerosols are 
limited, yet ignoring such effects in estimating the O₃--UV-
B radiation relationship was ``erroneous;'' and (4) data to permit 
dynamic assessment of the feedback between increased UV radiation and 
increased O₃ is limited to uncertain models, and this 
potential feedback mechanism was ignored in the analysis (Childs, 
1994).
    Reviewers also questioned a number of the simplifying assumptions 
that could have ``substantial impact'' on the resulting risk estimates. 
Among these were: (1) The assumed mixing height of 2 km, which 
reviewers considered too high on average, especially for the eastern 
United States--by overstating the thickness of the pollution-related 
layer of the atmosphere that is the focus of the control strategies 
designed to attain the NAAQS, this factor would bias the estimates 
upwards by as much as a factor of 2; (2) the assumption that the 
O₃ mixing ratio is the same at the earth's surface as it is 
at 2 km, when the vertical profile varies through the diurnal cycle--
because vertical mixing increases through the day, this assumption 
would be most important in the earlier portion of daylight hours; (3) 
the assumption that neither aerosols nor O₃ production 
cycles themselves exert either positive or negative feedback on UV-B 
penetration--as noted in the previous section, a dynamic consideration 
of these factors could change the direction of the result in particular 
areas; (4) the assumption that NMSC might result from episodic 
exposures, when, in fact, NMSC results from cumulative doses--this 
assumption affects only separate and far smaller estimates Cupitt made 
for episodic changes, essentially invalidating those results; (5) the 
assumption that all people would be susceptible to NMSC based on 
assumed exposure factors; and (6) the assumption that behavioral 
patterns, demographic patterns, and meteorological factors and other 
factors related to actual exposures remain constant over time (Childs, 
1994; Altschuller, 1994).
    These reviewers capsulized their conclusions regarding the 
quantitative results of this analysis as follows:


[[Page 633]]


In summary, (1) the numbers resulting from these calculations are 
quite small, and (2) the limitations of the accuracy and reliability 
of the input to the calculations produces numbers that cannot be 
defended, whether large or small. (Childs, 1994).

    As noted in the discussion above, this is not simply a matter of 
uncertain and small risk estimates. On balance, several of the problems 
noted above served to inflate the overall estimates, and, depending 
upon local conditions and the implementation strategy assumed, could 
even call the direction of the results into question for some 
locations. Further, a significant bias, not highlighted in the cited 
reviews, is how well the assumed 10 ppb change in daytime O₃ 
levels averaged over an entire summer season (and over half the U.S.) 
reflects what might occur in response to the revised O₃ 
NAAQS.\57\ In fact, this assumed change, as well as the assumptions 
regarding its spatial and vertical extent, are significantly larger 
than could reasonably be expected based on the revisions to the 
O₃ standard promulgated in 1997.
-----------------------------------------------------------------------

    \57\ Cupitt provides no rationale for the selection for this 
value where it first appears in a Table, which is characterized as 
addressing ``questions from OMB.''
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    To provide a fair comparison, it is necessary to convert the 1-hour 
standard into its nearest 8-hour equivalent. As documented in the Staff 
Paper (U.S. EPA, 1996b), the nearest equivalent 8-hour standard would 
have a level of about 0.09 ppm. Superficially, this might appear to 
support a 10 ppb difference compared to the 0.08 ppm 8-hour standard 
set in 1997. The appropriateness of this comparison fades, however, 
when one considers that these standards are stated in reference to 
extreme high values in the distribution (e.g., the average of the 4th-
highest daily maximum concentrations). Cupitt's analysis assumed that a 
``mixing layer'' up to 2 km deep over a very large geographical region 
would experience a change of 10 ppb in daylight average O₃ 
for an entire O₃ season. This scenario would require a 
challenging regional strategy that would, on average, reduce each day 
for the over 150 day O₃ season by 10 ppb. Yet, the 0.08 ppm 
8-hour O3 standard would require that only the fourth-highest day of 
the O₃ season be reduced by about 10 ppb, as compared to the 
previous standard. Based on available O₃ trends information, 
strategies that reduce peak O₃ days would have far less 
effect on the far more numerous days toward the middle and lower-parts 
of the O₃ season distribution (e.g., U.S. EPA, 1996a, 
Figures 4-2, 4-3). In fact, as reported in the Response to Comments 
document, based on earlier RIA projections of long-term O₃ 
reductions that might occur as a result of efforts to meet the 0.08 ppm 
8-hour O₃ standard, the magnitude of the assumed average 
change appears to be overstated by more than a factor of 3 (U.S. EPA, 
1997). When considered with the excessively high assumed mixing layer, 
the overly large geographical area requiring reductions (over 30 
States), and the assumption that the entire population would be at the 
same risk as the more sensitive subpopulations, it is EPA's judgment, 
based on the record, that these readily identified biases could well be 
on the order of a factor of 10.
    More subtle are the uncertainties and potential bias inherent in an 
essentially static comparison of two different O₃ values 
that are assumed to be uniform over a very large area. Dynamic, real-
world implementation strategies would involve a number of alternative 
local and regional scale approaches that vary significantly in time and 
space, with a variety of possible outcomes with respect to the middle 
and lower portions of the O₃ distribution that are most 
relevant to estimating long-term summer averages over a period of 
decades into the future. An example of such local strategy-dependent 
outcomes would be control of NO_X emissions across a 
metropolitan area, which could reduce O₃ concentrations at 
downwind peak monitors, but also result in localized increases in lower 
concentrations in the center city area (National Academy of Sciences, 
1991, Figure 11-2). As noted in section II.B.2 above and in Altshuller 
(1994), the interrelated indirect results from reduced O₃ 
and UV-B radiation could trigger feedbacks through increased 
O₃, aerosol, or cloud cover that could partially or fully 
offset the initial O₃ effects on UV-B radiation. Available 
data and assessment tools do not permit a reasonable quantitative 
assessment of these second- and third-order indirect effects 
(Altshuller, 1994; Childs, 1994).
    Other potential problems associated with ignoring area-specific 
considerations in an O₃/UV-B risk analysis summarized in the 
previous section include: (1) The assessment of local physical factors 
(e.g., buildings) that reduce UV-B radiation exposure in outdoor 
microenvironments, (2) meteorological conditions (e.g., sea breeze) or 
local emissions patterns that reduce pollution in high UV-B radiation 
exposure microenvironments, (3) behavioral adjustments to information 
concerning UV-B radiation risk over time, and (4) local differences in 
the proportion of sensitive populations. Even Cupitt's assumption that 
90 percent of exposure occurs during the summer O₃ season 
embeds an additional assumption about long-term personal behavior for 
which little empirical evidence exists.
    In the proposed response, EPA solicited comment on the above 
discussion of the key assumptions used in the Cupitt analysis (66 FR 
57285). None of the commenters disagreed with any specific aspect of 
EPA's evaluation of these assumptions as outlined in the proposed 
response, nor did any commenter disagree with EPA's judgement that the 
assumptions described above could introduce biases on the order of a 
factor of 10 to Cupitt's estimates of changes in UV-B radiation-related 
effects resulting from changes in ground-level O₃ projected 
to occur upon attainment of a more stringent O₃ NAAQS.
    In summary, EPA continues to believe that the Cupitt (1994) white 
paper was useful for its intended purpose as a scoping analysis to 
identify the potential issues arising in any attempt to assess the 
potential shielding provided by changes in ground-level O₃. 
It established that any effects of even fairly large, long-term 
O₃ reductions in ground-level O₃ would be quite 
small, but as evidenced in the comments of the peer review and the 
discussion above, available data and modeling tools fall far short of 
permitting reliable quantitative risk estimates for consideration in 
standard setting or benefits assessments.
    The analysis of this issue by U.S. Department of Energy (DOE) staff 
(1995) is summarized in a statement submitted as a part of public 
comments at a CASAC meeting. The exposition is far less complete than 
that of Cupitt, and it is quite difficult to reconcile the range of 
estimates for possible increased occurrences of NMSC, the lower bound 
of which are less than Cupitt, while the upper bound estimates are more 
than double his. The analysis apparently starts with the same 
assumptions regarding a constant change in summertime O₃ of 
10 ppb through a 2 km mixing layer, but important information about the 
other assumptions is lacking. In any event, the paper does not appear 
to improve upon the methodology in the Cupitt analysis.\58\ Given that 
the DOE

[[Page 634]]

statement must share the limitations outlined above for Cupitt and the 
fact that the analytical approach is neither well documented nor peer 
reviewed, no reliance is placed on the quantitative results presented 
in the DOE submission.
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    \58\ In addition to estimates for NMSC, the DOE statements also 
provided estimates for melanoma skin cancers and cataracts. As 
discussed above, the quantitative relationship between cumulative 
UV-B exposure and the latter effects are not as well established as 
for NMSC. Given the lack of documentation and the additional 
uncertainties over those for NMSC, neither the DOE estimates of such 
effects nor the uncritical reliance on them by Lutter and Wolz 
(1997) should be given quantitative credence.
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    The work of economic analysts Lutter and Wolz (1997) provides a 
self-described ``preliminary analysis'' of UV-B radiation screening by 
tropospheric O₃. Here, the exposition permits a more direct 
comparison with that of Cupitt, and it appears that many of the same 
simplifying assumptions were used--either explicitly or implicitly. 
This paper relied upon Cupitt's assumption that the NAAQS revision 
might bring about a summertime average of 10 ppb reduction in 
O₃ in areas not attaining the standard. As discussed above, 
based on the record, EPA believes this substantially overstates the 
likely effect of the NAAQS revision. Their assumption of a constant 
mixing ratio for the 10 ppb change that would extend well above the 
planetary boundary layer, up to 10 km, also introduces upward bias into 
their upper-bound risk estimates. The resultant apparent dose appears 
to be a factor of 4 larger than the upper bound used by Cupitt and DOE 
staff. The other quantitative inputs to the analysis differed to a more 
modest degree from those used by Cupitt. In the end, the upper bound 
estimate of possible increased occurrences of NMSC is more than double 
that of Cupitt, due largely to the unwarranted assumption of a 10 km 
mixing height.
    Again, because the quantitative assessment shares most of the 
limitations cited above for Cupitt, and actually adds substantial bias 
in a key assumption, EPA has appropriately placed no reliance on the 
quantitative risk estimates for NMSC from Lutter and Wolz (1997) or to 
the secondary estimates derived in the DOE analyses.
    In the proposed response to the remand, EPA solicited comment on 
its evaluation of the three analyses discussed above (66 FR 57286). No 
commenter offered specific challenges to any technical aspect of EPA's 
evaluations of the quantitative analyses by Cupitt (1994), DOE (1995), 
and Lutter and Wolz (1997), as discussed above. Some commenters, 
however, expressed the general view, presumably despite the limitations 
of these analyses, that EPA was not justified in ignoring or 
discounting such evidence of positive effects, or that such analyses 
could serve as an upper bound on estimated UV-B radiation-related 
impacts. In sharp contrast, other commenters expressed the view that 
these analyses were of questionable reliability and did not achieve 
minimum standards of scientific adequacy appropriate for information to 
be used as a basis for NAAQS decisions.
    In taking all these comments into account, EPA rejects the notion 
that it has ignored or completely discounted these analyses. On the 
contrary, EPA has thoroughly reviewed these analyses by examining the 
methodologies used, the nature and validity of the underlying 
assumptions, and the resultant uncertainties inherent in the UV-B 
radiation-related impacts estimated by these analyses. In so doing, EPA 
has concluded that (1) the methodologies used in these analyses 
inherently ignore area-specific factors that are important in 
estimating the extent to which small, variable changes in ground-level 
O₃ mediate long-term exposures to UV-B radiation (in 
contrast to the appropriate application of such methodologies that EPA 
and others have done in estimating the impact of relatively large 
changes in the stratospheric O₃ reservoir attributable to 
emissions of O₃-depleting substances); (2) the studies 
likely substantially overestimate UV-B radiation-related impacts as a 
result of the biases introduced by the use of specific underlying 
assumptions, as discussed above; and (3) as a consequence of the first 
two conclusions, the analyses are not scientifically adequate to be 
relied upon as a basis for making NAAQS decisions, and they do not 
provide credible quantitative estimates of UV-B radiation-related 
impacts that can appropriately be compared to the quantitative 
estimates of direct adverse respiratory-related impacts that EPA used 
in part as a basis for its initial NAAQS decision. The EPA believes 
that its examination of these analyses and their underlying 
assumptions, together with its examination of the basic science dealing 
with the atmospheric distribution of O3 and UV-B radiation (section I.C 
above) and information on the health effects associated with UV-B 
radiation and the relationship between ground-level O₃ and 
UV-B radiation exposure (sections II.B.1 and 2 above), does support the 
conclusion that UV-B radiation impacts mediated by changes in ground-
level O₃ associated with attaining a more stringent 
O₃ NAAQS are likely very small from a public health 
perspective.
    Beyond the comments submitted on the three analyses discussed 
above, a few commenters also contended that EPA's proposed response was 
incomplete because it did not consider another draft analysis by 
Madronich, referred to as a 1997 ``EPA staff assessment'' of UV-B 
radiation-related health benefits, that had been submitted by EPA to 
the Office of Management and Budget (OMB) in conjunction with OMB's 
review of the draft RIA for the O₃ NAAQS. These comments 
expressed the view that this draft analysis represented a substantial 
improvement over the earlier analyses of Cupitt (1994), DOE (1995), and 
Lutter and Wolz (1997) in its approach to estimating potential 
increases in NMSC associated with State-specific average changes in 
O₃ concentrations between baseline levels (i.e., ground-
level O₃ concentrations current at the time of the analysis) 
and full attainment of the 1996 proposed O₃ NAAQS. These 
commenters assert that EPA should now consider the results of this 
draft analysis, or the results of a new analysis that incorporates 
further refinements and extensions to the methodology and scope of the 
Madronich analysis, in its response.
    In considering this comment, EPA first notes that the Madronich 
analysis submitted with the comments has not been appropriately 
characterized in the comments. The Madronich analysis is not an ``EPA 
staff assessment,'' but rather it is a draft analysis prepared by a 
consultant at the request of EPA, to help inform EPA's preparation of 
the RIA. This draft analysis was not completed, published, or peer 
reviewed. Moreover, it was judged not to provide an adequate basis for 
quantifying potential UV-B radiation-related impacts as part of EPA's 
final RIA, a document that historically includes quantitative estimates 
of a more speculative nature than those thought to be adequate to 
consider as a basis for setting a NAAQS. In fact, the final RIA for the 
1997 O₃ NAAQS, which was reviewed by other Federal agencies 
and approved for release by OMB, concluded that the available 
scientific and technical information, which included the Madronich 
draft analysis, would not permit reliable quantitative estimates of any 
potential impact of the more stringent O₃ NAAQS on UV-B 
radiation-related effects.\59\ In summary, the Madronich draft analysis 
does not represent the type of peer-reviewed

[[Page 635]]

information that is appropriately relied upon as a basis for NAAQS 
rulemaking.
-----------------------------------------------------------------------

    \59\ The EPA also notes that this draft analysis was 
appropriately not part of the rulemaking record upon which EPA is 
basing its response. The fact that OMB staff placed this draft 
analysis in OMB's docket, which includes information related to 
OMB's review of the RIA, in no way implies that the draft analysis 
was or should have been part of EPA's rulemaking record.
-----------------------------------------------------------------------

    Although, for the reasons discussed above, EPA has not relied on 
the Madronich draft analysis in reaching this final response, the 
Agency nevertheless has conducted a provisional examination of this 
draft analysis to assess whether the results of the analysis call into 
question or are consistent with the conclusions reached in the proposed 
response. In this draft analysis, Madronich estimates the increases in 
NMSC that would result from changes in ground-level O₃ from 
1997 baseline values to full attainment of the 1996 proposed 
O₃ NAAQS (i.e., a standard set at 0.08 ppm O₃ 
with a form based on the 3-year average of the annual third-highest 
daily maximum 8-hour average concentrations). As an initial matter, and 
as recognized by some commenters, this draft analysis is based on an 
inappropriate comparison--then-current air quality versus attainment of 
the proposed NAAQS. The relevant comparison is between full attainment 
of the 1979 1-hour 0.12 ppm O₃ standard and full attainment 
of the 1997 final 8-hour O₃ NAAQS (with a somewhat less 
stringent form based on the fourth-highest daily maximum 8-hour average 
concentrations). Thus, the analysis by its design substantially 
overestimates the relevant projected decreases in O₃ levels 
likely to result from revising the 1979 O₃ standard (since 
baseline levels in some areas are substantially above levels that would 
attain the 1979 1-hour standard), and thus, substantially overestimates 
projected UV-B radiation-related impacts.
    Looking beyond this initial matter, EPA notes that this analysis is 
based on estimated statewide average changes in O₃ 
concentrations. Thus, like the three other analyses discussed above, 
this draft analysis incorporates none of the area-specific factors, 
discussed in section II.B.2.b above, that EPA considers to be important 
in developing credible estimates of UV-B radiation-related impacts 
mediated by the localized and highly variable changes in ground-level 
O₃ likely to result from attainment of a more stringent 
O₃ NAAQS. The EPA does not dispute that the draft analysis 
uses assumptions and models that may well be appropriate for developing 
credible estimates of UV-B radiation-related impacts mediated by large-
scale regional and relatively uniform changes in stratospheric 
O₃ likely to result from emissions of O₃-
depleting substances.\60\ But, EPA also recognizes and has fully 
explained (above in section II.B.2) the important differences in the 
factors that are central to analyses of UV-B radiation-related impacts 
that are mediated by changes in stratospheric O₃ versus 
ground-level O₃--differences that this analysis, and the 
commenters, simply ignore.
-----------------------------------------------------------------------

    \60\ The EPA notes that the draft analysis estimates changes in 
radiation levels using a radiative transfer model that has been 
previously used in a number of O₃ scientific studies and 
WMO/UNEP international assessments of stratospheric O₃ 
depletion, and NMSC incidences using information from epidemiologic 
studies and from studies of action spectrum for induction of skin 
cancer in mice. The draft analysis assumes national incidence rates 
of 500,000 BCC cases per year and 100,000 SCC cases per year for the 
baseline scenario.
-----------------------------------------------------------------------

    Apart from these area-specific methodological issues, EPA has also 
provisionally looked at the quantitative estimates of State-by-State 
annual incidences of NMSC that result from the Madronich draft 
analysis, yielding a nationwide aggregate estimate of an additional 696 
NMSC cases annually, with over half of this estimate coming from the 
State of California alone.\61\ Using the California estimate as an 
example, EPA has considered the potential impact of various assumptions 
used in the analysis on the estimated incidences. First, as discussed 
above, the use of a current baseline comparison would likely 
substantially overestimate incidences in California in particular, in 
light of the significant extent to which many areas in California 
continue to exceed the 1979 1-hour standard. That is, it is likely that 
decreases in ground-level O₃ from baseline levels to levels 
that would attain the 1979 1-hour standard would be greater, perhaps 
much greater, than the additional decreases needed to reach attainment 
of the 1997 8-hour standard. This bias would also likely affect 
estimates from other States that contribute a high proportion of the 
national incidence estimate and that have areas that exceed the 1-hour 
standard by a significant margin, including, for example, New Jersey, 
Georgia, and Texas, which together account for approximately 20 percent 
of the national estimate.
-----------------------------------------------------------------------

    \61\ Only point estimates are presented in the analysis; no 
quantitative estimates or even qualitative discussion of the 
uncertainties in these estimates are presented.
-----------------------------------------------------------------------

    Second, as in the Cupitt analysis, the Madronich analysis assumes 
that the entire population would be equally susceptible to NMSC based 
on assumed exposure factors. This assumption would also lead to 
substantial overestimation of effects, however, based on demographic 
data from the 2001 Statistical Abstract of the United States and 
information on sensitive populations (discussed above in section 
II.B.1).\62\
-----------------------------------------------------------------------

    \62\ According to the 2000 Census (U.S. Census Bureau, 2001), 
approximately 47 percent of the population of California is 
designated as ``white alone.'' While not all ``white'' people are 
susceptible to skin cancer, this proportion is probably a better 
estimate of the fairer members of all races and ethnic groups in 
California that would be more susceptible to NMSC than the entire 
population.
-----------------------------------------------------------------------

    Third, as noted above, the Madronich draft analysis assumes that 
attainment of a more stringent O₃ standard will decrease 
O₃ concentrations and increase UV-B radiation flux equally 
throughout the State, without taking into account the highly variable 
and localized patterns of changes in ground-level O₃ likely 
to result from attainment of the O₃ NAAQS, nor does it take 
into account the variable exposure patterns of people as they move 
through various microenvironments and exhibit varying degrees of sun-
seeking and sun-avoidance behaviors. However, attainment of a more 
stringent O₃ standard will not reduce O₃ 
concentrations equally everywhere, and may not reduce O₃ 
concentrations at all in locations where people receive their highest 
exposure to UV-B radiation. As noted above in section II.B.2.b, in the 
heavily populated Los Angeles area, ground-level O₃ is at 
its lowest levels thus providing the least shielding along the coast, 
where the potential for exposure to UV-B radiation is the highest, and 
it is unlikely that programs designed to bring Los Angeles into 
attainment with a more stringent standard will result in any 
significant reductions in coastal O₃ levels. In this regard, 
some commenters also note that the analysis may also underestimate 
incidences since the analysis assumes that the entire population of a 
State will experience changes in O₃ concentrations, and 
presumably resultant changes in UV-B radiation-related impacts, that 
reflect a statewide average, thus potentially underestimating changes 
to the large segments of the population that live in urban areas that 
would likely experience larger than average changes in ground-level 
O₃ concentrations. However, given the variable and localized 
patterns of changes in ground-level O₃ that have been 
monitored in urban areas, including in some cases significantly lower 
concentrations in inner cities and higher concentrations in downwind 
suburban areas, it is not clear the extent to which ignoring such area-
specific factors would bias resulting estimates for any given urban 
area either low or high. These considerations serve to demonstrate the

[[Page 636]]

importance of conducting area-specific assessments, as EPA did in 
evaluating the adverse respiratory-related impacts likely to result 
from attaining a more stringent O₃ standard.
    Finally, one comment also notes that the Madronich draft analysis 
considers NMSC, but not other UV-B radiation-related effects, and that 
EPA should extend this quantitative analysis to estimate incidences of 
such other effects. The EPA believes that quantitative risk estimates 
to be used as a basis for NAAQS decision making should not be made 
based on back-of-the-envelope type approaches, as offered in the 
comment. Consistent with this view, EPA refrained from developing 
quantitative risk estimates for a range of adverse respiratory-related 
effects when it judged that information needed to make credible 
quantitative estimates was not available.\63\ To do otherwise with 
regard to potential beneficial effects would be to apply a lower 
information standard than was used to assess adverse effects, which EPA 
declines to do, consistent with the direction from the Court in its 
remand to apply the ``same approach,'' including the same (neither 
higher nor lower) ``information threshold'' to either type of 
information.
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    \63\ In the 1997 final rule (62 FR 38868), EPA specifically 
noted that for many O₃ inhalation-related risks to public 
health, information was too limited to develop quantitative 
estimates of risk, including: 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).
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    Although the biases and uncertainties outlined above can not be 
reliably quantified, EPA believes that it is reasonable to presume that 
any increase in nationwide annual incidences of NMSC associated with 
attaining a more stringent O₃ standard would likely be 
substantially smaller than estimated by the draft Madronich analysis. 
Assuming that it's even as much as one-third of that estimated by 
Madronich, the EPA judges that a nationwide NMSC incidence rate of this 
approximate magnitude would be very small from a public health 
perspective, representing an increase of roughly 0.03 percent in the 
national baseline incidence rate assumed by Madronich.\64\ As to other 
UV-B radiation-related effects, the Madronich draft analysis provides 
no basis for the development of credible quantitative estimates of such 
effects. Having chosen not to rely upon simple ratios to develop 
quantitative estimates of the ``pyramid of effects'' related to the 
estimated number of hospital admissions of asthmatics that EPA did 
quantify in its risk assessment,\65\ EPA declines to use any lower 
information standard, as suggested by a few commenters, in its 
evaluation of potential beneficial effects.
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    \64\ This judgment is consistent with the judgment made by EPA 
with regard to its estimate of the incidence rate of O₃-
related hospital admissions of asthmatics in New York City, which 
was one of many adverse public health effects considered as part of 
the basis for its 1997 O₃ NAAQS decision. In its 1997 
final rule, EPA judged that an annual increase of approximately 40 
hospital admissions in New York City alone, representing an increase 
of about 0.3 percent in total hospital admissions of asthmatics, was 
``relatively small from a public health perspective'' (62 FR 38868). 
An increase in NMSC incidence of roughly 0.03 percent is an order of 
magnitude lower than the estimated rate of O₃-related 
hospital admissions of asthmatics, and such hospital admissions 
would generally represent a more serious health effect than an 
incidence of NMSC, which can generally be treated in a doctor's 
office or outpatient facility. The EPA also notes that based on 
baseline incidence rates reported on the Skin Cancer Foundation Web 
site, www.skincancer.org,  submitted by a commenter, this 
increase in NMSC incidence would be roughly only 0.02 percent.
    \65\ In its 1997 final rule (62 FR 38868), EPA noted that 
O₃-related hospital admissions of asthmatics 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.
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    In summary, EPA has conducted a provisional examination of the 
Madronich draft analysis, considering the underlying assumptions and 
methodology as well as the quantitative results and likely 
uncertainties and biases in the results. Based on this provisional 
examination, EPA does not believe that this analysis calls into 
question, but rather is generally consistent with the conclusions 
reached in its proposed response: That information is not available at 
this time that will allow for credible quantitative estimates of 
potential UV-B radiation-related impacts of attaining a more stringent 
O₃ standard, and that associated changes in UV-B radiation 
exposures of concern, using plausible but highly uncertain assumptions 
would likely be very small from a public health perspective.

C. Consideration of Net Adverse Health Effects of Ground-level 
O₃

    In considering the net adverse health effects of ground-level 
O₃, EPA has focused on characterizing and weighing the 
comparative importance of the potential indirect beneficial health 
effects associated with the attenuation of UV-B radiation by ground-
level O₃ (section II.B above) and the direct adverse health 
effects associated with breathing O₃ in the ambient air 
(section II.A above). The same key factors considered by EPA in its 
1997 review of the O₃ standard, and in the proposed 
response, are again considered here in characterizing the information 
on potential beneficial effects in the record of the 1997 review and in 
comments received on the proposed response, and in comparatively 
weighing this information relative to the direct adverse effects. 
Beyond quantitative assessments of exposure and risk that were central 
to EPA's 1997 review, these factors include the nature and severity of 
the effects, the types of available evidence, the size and nature of 
the sensitive populations at risk, and the kind and degree of 
uncertainties in the evidence and assessments. Because of the 
complexity and multidimensional nature of such a comparison, and 
because many of the effects, both adverse and beneficial, could not be 
characterized in terms of quantitative risk estimates, EPA has made no 
attempt to characterize all the relevant effects or associated risks to 
public health with a common metric.\66\
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    \66\ A commenter asserted that the Court's direction to consider 
O₃'s net adverse health effect in essence presumes the 
existence and use of a common metric. The EPA notes that while the 
Court identified the use of a common metric as one approach that EPA 
could use, in no way did the Court require EPA to use such an 
approach, nor does EPA believe that such an approach would provide a 
more meaningful basis on which to evaluate O₃'s net 
effects.
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    The available record information on the potential indirect 
beneficial health effects associated with ground-level O₃ 
includes information from studies of health effects caused by exposure 
to UV-B radiation and studies that focus on the consequences of 
unnaturally high exposures to UV-B radiation due to depletion of the 
stratospheric O₃ layer, as well as analyses that attempt to 
focus specifically on the consequences of assumed changes in 
tropospheric O₃ levels. The nature and severity of the 
effects of UV-B radiation exposure on the skin, eye, and immune system 
are discussed above (section II.B.1), as is the nature of sensitive 
populations at risk for these effects. These effects, especially on the 
skin and eye, are generally understood to be associated with long-term 
cumulative exposure to UV-B radiation and to have long latency periods 
from cumulative exposures, especially those early in life. People with 
light skin pigmentation make up the primary at-risk population for 
effects on the skin, especially for NMSC, while at-risk populations for 
other effects are not as well understood. For NMSC, uncertainties in 
the evidence generally

[[Page 637]]

relate to uncertainties in the relevant action spectra and BAFs, as 
well as in factors related to characterizing the severity of the 
different types of NMSC. Based on the record information, for the other 
effects, the role of UV-B radiation is less well understood (e.g., as 
to relevant action spectra, BAFs, the nature of exposures of concern), 
although cumulative exposure to UV-B radiation is thought to play a 
causal role. These characterizations are derived from the large body of 
epidemiologic and toxicologic evidence that served as the basis for the 
reference document by EPA (1987).
    The record includes a quantitative assessment conducted by EPA 
(1987, App. E) of the health risks associated with changes in exposure 
to UV-B radiation attributable to changes in the stratospheric 
O₃ layer. This assessment models the relationship between 
wide-scale changes in global/regional levels of stratospheric 
O_3, resulting from emissions of O₃ depleting 
substances with long-atmospheric lifetimes, and changes in UV-B 
radiation flux as a function of latitude for three broad regions across 
the United States.\67\ As discussed above (section II.B.2), because 
changes in the stratospheric O₃ layer are relatively uniform 
across broad regions, varying across the U.S. primarily with latitude, 
information on localized spatial and temporal patterns of exposure-
related variables (e.g., changes in ground-level O₃, 
meteorological conditions, human activity patterns) are not relevant in 
producing credible estimates of risk associated with changes in 
stratospheric O₃. This is in sharp contrast to the nature of 
the information necessary to produce credible estimates of risk 
associated with changes in exposures to UV-B radiation projected to 
result from changes in ground-level O₃ that would be 
associated with attainment of alternative 8-hour standards for 
O₃.
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    \67\ Since the EPA's 1987 risk assessment on stratospheric ozone 
depletion, numerous changes have been made to the model to reflect 
the commitments made since 1987 by the United States, under 
amendments to the Montreal Protocol, for reductions in production of 
various ozone depleting chemicals and to incorporate more accurately 
the latest scientific information.
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    An evaluation of the available analyses that have produced 
estimates of UV-B radiation-related health risks associated with 
changes in ground-level O₃ and the comments received on 
them, in section II.B.3 above, identifies major limitations in 
available information that resulted in the need for the analyses to 
incorporate broad and unsupportable assumptions. These limitations are 
particularly important with regard to information on spatial and 
temporal patterns of changes in ground-level O₃ (across the 
entire year and extending vertically up through the tropospheric mixing 
layer) likely to result from various future emission control 
strategies, relevant meteorological conditions and atmospheric 
chemistry leading to a cascade of broader indirect effects, and human 
demographic and activity patterns (e.g., the degree of shading within 
outdoor microenvironments, and the prevalence of sun-seeking and sun-
avoidance behaviors among sensitive groups) likely to affect UV-B 
radiation-related exposures of concern. For the reasons discussed 
above, these limitations are judged to be of central importance in any 
such analysis. Thus, in light of such limitations, and after careful 
consideration of the comments received, EPA continues to agree with 
internal and external reviewers, and some commenters, in concluding 
that the available scientific and technical information would not 
permit credible quantitative estimates of these potential beneficial 
effects.\68\ Thus, EPA concludes that available analyses based on such 
limited information cannot serve as credible estimates of potential 
beneficial effects associated with the presence of ground-level 
O₃ due to man-made emissions of O₃-forming 
substances.
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    \68\ This conclusion was also reached by the Health and 
Ecological Effects Subcommittee of the Advisory Council on Clean Air 
Compliance Analysis, a part of EPA's Science Advisory Board, in 
conjunction with their review of ``The Benefits and Costs of the 
Clean Air Act 1990 to 2010'' (EPA, 1999b), noting that the relevant 
information ``was very weak and more information is required'' (EPA, 
1999a). As one commenter noted, this SAB Council has more recently 
recommended that in EPA's next periodic prospective analysis of the 
Act, the Agency's analysis address this issue (Advisory Council for 
Clean Air Compliance Analysis, 2001).
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    Beyond the specific technical comments discussed above in section 
II.B, several commenters expressed the general view that EPA had 
inappropriately applied a ``double standard'' in its evaluation of the 
scientific evidence because it failed to evaluate the protective 
shielding effects of ground-level O₃ using the same criteria 
by which it evaluated the adverse respiratory effects. This viewpoint 
was specifically expressed by one commenter in stating that ``EPA has 
accepted, often without reservation, scientific evidence purporting to 
establish the adverse effects of ground-level ozone on respiratory 
effects. At the same time it has often discounted proffered scientific 
evidence of the potential benefits of ground-level ozone in screening 
harmful UV-B radiation.'' (Docket No. A-95-58, VI-C-8, pg. 28) As 
discussed below, EPA strongly rejects both aspects of this comment. 
Other commenters expressed the opposite view, finding EPA's approach to 
be evenhanded in its evaluation of the scientific evidence for 
potential beneficial and adverse effects, with one commenter noting 
that EPA ``has never concluded that any allegation or ``evidence'' [of 
adverse effects], regardless of its preliminary or speculative nature 
or degree of uncertainty, must be factored into NAAQS decisionmaking.'' 
(Docket No. A-95-58, VI-C-6, pg. 2)
    First, EPA believes that there is ample evidence in the record of 
the 1997 review of the O₃ NAAQS to invalidate the notion 
that the Agency uncritically accepts scientific evidence of adverse 
respiratory effects of ground-level ozone. For example, in considering 
evidence of adverse respiratory-related effects such as increases in 
bronchial responsiveness, decrements in alveolar macrophage function, 
and O₃-induced markers of inflammation and cell damage (as 
discussed in the 1996 proposed rule, 61 FR 65720-21), EPA judged that 
there was not sufficient information on dose-response relationships to 
develop quantitative risk estimates for these acute effects, even in 
light of the availability of peer-reviewed human exposure studies 
demonstrating indicators of these effects in humans at quantified 
exposure levels over quantified time periods (1997 final rule, 62 FR 
38868). Similarly, EPA limited the scope of its quantitative risk 
assessment of acute respiratory-related hospital admissions of 
asthmatics to just one city (New York City), despite the availability 
of peer-reviewed studies showing increased admissions in other cities, 
because it judged that there was not adequate city-specific 
concentration-response information from epidemiological studies in 
other cities, that applying the New York City concentration-response 
information to other cities would introduce too much uncertainty into 
any such quantitative estimates, or that adequate ambient O₃ 
monitoring data were not available for other study areas to produce 
credible estimates of this risk for those cities (EPA, 1996b, pp. 111-
112). Further, EPA did not rely on quantitative estimates of other 
adverse effects that have been related to hospital admissions of 
asthmatics in published documents submitted by commenters on the 1996 
proposed rule (e.g., the ``pyramid of effects'' including hospital 
admissions among the general population, visits to emergency 
departments and doctors'

[[Page 638]]

offices, and increased asthma attacks and use of medication), due to 
the substantial uncertainties inherent in such ratio-of-effects-based 
approaches to quantifying risk. Finally, with regard to chronic 
effects, EPA declined to rely on available evidence, or develop 
quantitative estimates, of the risk of chronic O₃ 
respiratory-related morbidity or mortality effects in its 1997 final 
rule, judging that the evidence was too limited or uncertain, despite 
arguments by commenters on the 1996 proposed rule that such available, 
peer-reviewed evidence should be used as a basis for setting a lower 8-
hour O₃ standard than the 0.08 ppm standard set by EPA in 
that rulemaking.
    Second, far from discounting proffered scientific evidence of the 
potential ground-level ozone in screening harmful UV-B radiation, EPA 
has fully considered all the record evidence on the beneficial 
shielding effects of ground-level O₃, as well as information 
received in public comments, as discussed in section II.B above. 
Moreover, EPA has taken the additional step of provisionally 
considering the unpublished, Madronich draft analysis (section II.B.3), 
as submitted by commenters and characterized by them as an improvement 
over other analyses in the record. Having provisionally considered this 
analysis, for the reasons discussed above in section II.B, EPA has 
found that this analysis does not call into question the Agency's 
conclusions with regard to the lack of credibility of such available 
analyses or the likelihood that any such beneficial UV-B radiation-
related effects are likely very small from a public health perspective. 
The fact that EPA does not agree with commenters' opinions on these 
issues does not in any way demonstrate that EPA has simply discounted 
their proffered evidence of the potential beneficial screening effects 
of ground-level O₃.
    Therefore, EPA rejects the view of some commenters that it applied 
a double standard in reaching its conclusions about potential UV-B 
radiation-related effects that may result from a more stringent 
O₃ NAAQS. In fact, EPA believes that were it to rely upon 
the available evidence of UV-B radiation-related effects to conclude 
otherwise, as urged by these commenters, that it then would be applying 
the very type of double standard that these commenters argue against. 
If EPA were to have relied upon quantitative risk estimates from draft 
or preliminary analyses that did not utilize appropriate methods or 
information to take into account relevant area-specific factors, and 
that had not been peer-reviewed, it would then be inappropriately 
applying a double standard in comparing any such UV-B radiation-related 
risk estimates to the adverse respiratory-related risks estimated in 
peer-reviewed analyses that were appropriately designed and limited by 
the availability of credible information and assessment methods.
    In setting aside the available quantitative risk analyses, EPA 
notes that our above evaluation of a number of critical factors in the 
analyses provides reasons for believing that the public health impacts 
of any potential beneficial effects associated with ground-level 
O₃ are likely very small, albeit unquantifiable at this time 
(sections II.B.2-3). In giving qualitative consideration to the 
available evidence on potential indirect beneficial effects of ground-
level O₃, EPA believes it is appropriate to weigh this 
information in the context of the body of evidence on adverse effects 
caused by direct inhalation exposures to ground-level O₃ 
that formed the basis for the 1997 O₃ primary standard.
    As an initial matter, as discussed in the 1997 final rule, the 
Administrator focused primarily on quantitative comparisons of risk, 
exposure, and air quality in selecting both the level (62 FR 38867-8) 
and form (62 FR 38869-72) of the 1997 O₃ primary standard. 
More specifically, she looked at comparisons of both those risks to 
public health that can be explicitly quantified in terms of estimated 
incidences and the size of the at-risk population (e.g., children) 
likely to experience adverse effects, as well as those for which 
quantitative risk information is more limited, but for which 
quantitative estimates of the number of children likely to experience 
exposures of concern could be developed (as discussed in section II.A.2 
above). In considering these comparisons, she recognized that although 
there were inherent uncertainties in these estimates, the underlying 
assessments took into account extensive data bases on the spatial and 
temporal patterns of air quality and directly relevant human activity 
patterns likely to result in inhalation exposures of concern. Further, 
the Administrator recognized that the assessment methods were 
appropriate and state-of-the-art, and that the results should play a 
central role in her decision.
    Beyond the quantitative information on direct adverse effects, with 
regard to the qualitative evidence suggestive of potential serious, 
chronic adverse effects on public health associated with long-term 
inhalation exposures, EPA judged that such information was too 
uncertain and not well enough understood at the time to serve as the 
basis for establishing a more restrictive 8-hour standard in terms of 
either level (62 FR 38868) or form (62 FR 38871). In so doing, EPA 
understood that further research into potential chronic adverse effects 
in humans would be continued, and the results considered in the next 
review (62 FR 38871).
    In weighing the available information on potential indirect 
beneficial effects of ground-level O₃, the EPA considers 
this information in the same light as the information on potential 
direct chronic adverse effects associated with long-term inhalation 
exposures to ground-level O₃. In both instances, the 
potential health effects are serious and likely to develop over many 
years, with important periods of exposure likely occurring in 
childhood. Different population groups are likely affected, however, by 
these potential adverse and beneficial effects. Urban populations and 
people with impaired respiratory systems (e.g., people with asthma), 
who are disproportionately from certain minority groups, are most at-
risk for the direct inhalation-related effects, whereas fair-skinned 
populations are most generally, but not exclusively, at-risk for the 
indirect beneficial effects related to exposure to UV-B radiation. 
Although different types of uncertainties are inherent in the record 
information on these effects, in both cases, the uncertainties related 
to ground-level O₃ are so great as to preclude the 
development of credible estimates of the size of the affected 
population or the probability of the occurrence of such effects.\69\ In 
the case of indirect effects related to ground-level O₃, EPA 
believes that the use of plausible but unsubstantiated assumptions 
would likely lead to the conclusion that the potential impacts on 
public health are likely very small; no such conclusions have yet been 
drawn with regard to the public health impacts of potential direct 
chronic adverse effects related to inhalation exposures. After 
considering these factors and the public comments received, EPA now

[[Page 639]]

concludes that, much like the qualitative evidence on direct adverse 
effects potentially associated with long-term inhalation exposures, the 
newly considered available evidence on potential indirect beneficial 
effects is not well enough understood at this time to serve as the 
basis for establishing a less restrictive 8-hour standard than was 
promulgated in 1997. Rather, EPA believes that the most recent evidence 
and credible analyses of potential long-term, indirect beneficial 
effects should be considered in the next review in conjunction with the 
most recent information on long-term, direct adverse effects.
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    \69\ Two commenters expressed the view that EPA's analogy of UV-
B radiation-related protective effects to chronic respiratory-
related adverse effects is flawed because the nature of the 
uncertainties associated with these two types of effects are 
different. As discussed more fully in its response to comments (EPA, 
2002), EPA explicitly recognizes here that there are different types 
of uncertainties inherent in the evidence of these effects, but 
disagrees with the commenter's characterization of these differences 
and with the view that any such differences in the nature of the 
uncertainties invalidate the weighing of these types of effects as 
EPA has done in reaching its conclusions.
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D. Final Response To Remand on the Primary O₃ NAAQS

    After carefully considering the scientific information available in 
the record on adverse effects on public health associated with direct 
inhalation exposures to O₃ in the ambient air and on the 
potential for indirect benefits to public health associated with the 
presence of ground-level O₃ and the resultant attenuation of 
naturally occurring UV-B radiation from the sun, taking into account 
the weight of that evidence in assessing the net adverse health effects 
of ground-level O₃, considering comments received on the 
proposed response, and for the reasons discussed above, the 
Administrator is now responding to the remand by reaffirming the 8-hour 
primary O₃ standard promulgated in 1997. In leaving 
unchanged the 1997 O₃ standard at this time, the 
Administrator has fully considered the available information in the 
record of the 1997 O₃ NAAQS review on potential beneficial 
health effects of ground-level O₃ using the same approach as 
for her consideration of the adverse respiratory-related effects, as 
directed by the Court's remand. Based on such consideration, she has 
determined that the information linking (a) changes in patterns of 
ground-level O₃ concentrations likely to occur as a result 
of programs implemented to attain the 1997 O₃ NAAQS to (b) 
changes in relevant exposures to UV-B radiation of concern to public 
health is too uncertain at this time to warrant any relaxation in the 
level of public health protection previously determined to be requisite 
to protect against the demonstrated direct adverse respiratory effects 
of exposure to O₃ in the ambient air.\70\ Further, it is the 
Agency's view that even when using plausible but highly uncertain 
assumptions about likely changes in patterns of ground-level ozone 
concentrations, associated changes in UV-B radiation exposures of 
concern would likely be very small from a public health perspective.
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    \70\ As noted above, the D.C. Circuit has already upheld EPA's 
determination that the 0.08 ppm 8-hour O₃ NAAQS was 
requisite to protect against adverse respiratory effects. See ATA 
III, 283 F.3d at 379.
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    In the past, the Administrator has been confronted with situations 
where there has been both quantifiable and unquantifiable evidence, and 
has moved forward with a NAAQS decision. The inability to quantify all 
related effects does not preclude the Agency from making a NAAQS 
decision, particularly in situations where there is strong quantifiable 
evidence of significant adverse health effects. Moreover, in this case, 
as noted above, EPA believes that while the potential beneficial 
effects are not quantifiable at this time, they are likely very small 
from a public health perspective. Accordingly, the Administrator 
believes it is inappropriate to wait for additional information on such 
effects prior to responding to this remand.
    In determining now that the 0.08 ppm, 8-hour O₃ standard 
set in 1997 is requisite to protect public health with an adequate 
margin of safety, the Administrator is finding that such a standard is 
both necessary and sufficient. Consideration of the potential 
beneficial effects of ground-level O₃ did not, of course, 
call into question whether this standard was sufficient to protect 
against the adverse respiratory-related effects of O₃ 
addressed in EPA's 1997 final rule. However, it did raise the question 
as to whether this standard was still necessary to protect against 
O₃'s net effects. Having determined that any potential UV-B 
radiation-related effects associated with this more stringent standard 
are likely very small from a public health perspective, and having 
judged that the evidence of any such effects should be weighed no more 
heavily in a determination of O₃'s net effects than the 
record evidence on O₃'s potential chronic adverse effects, 
the Administrator has concluded that O₃'s net adverse 
effects necessitate a standard no less stringent than the standard set 
in EPA's 1997 final rule.\71\
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    \71\ In so doing, EPA is applying the same decision making 
standard as it applied in its 1997 final rule, based on the plain 
meaning of the word ``requisite,'' consistent with the U.S. Supreme 
Court's decision in Whitman, 121 S. Ct. at 911-12, 914.
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    The 0.08 ppm, 8-hour primary standard is met at an ambient air 
quality monitoring site when the 3-year average of the annual fourth-
highest daily maximum 8-hour average O₃ concentration is 
less than or equal to 0.08 ppm. Data handling conventions are specified 
in a new appendix I to 40 CFR part 50, as discussed in the 1996 
proposal and 1997 final rule.\72\
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    \72\ Subsequent to the 1997 final rule, EPA has promulgated 
further revisions to 40 CFR part 50 with regard to the applicability 
of the 1-hour O₃ standards (65 FR 45182; July 20, 2000). 
In addition, EPA notes that recent legislation addresses the timing 
of future actions on nonattainment designations with regard to the 
8-hour O₃ standards (Pub. L. 106-377, 114 Stat. 1441 
(2000)).
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    As discussed previously, the Administrator recognizes that relevant 
information on indirect potentially beneficial health effects of 
ground-level O₃ (as well as information on direct adverse 
health effects of ground-level O₃) is now available that was 
not part of the 1997 rulemaking record. In that regard, she notes that 
the next periodic review of the O₃ NAAQS is now well 
underway, having been formally initiated by EPA's Office of Research 
and Development with a call for information (65 FR 57810; September 26, 
2000). To ensure that the current review of the O₃ criteria 
and standards now underway can be based on a comprehensive and current 
body of relevant scientific information, EPA continues to encourage the 
submission of new scientific information on the relationships between 
ground-level O₃, associated attenuation of UV-B radiation 
and other indirect effects of the presence of O₃ in the 
ambient air, and effects on public health such as those associated with 
changes in relevant exposures to UV-B radiation.
    The EPA's ongoing review and revision of the O₃ Criteria 
Document is addressing a number of issues related to indirect 
potentially beneficial health effects of ground-level O₃. In 
particular, available information on the role of ground-level 
O₃ in attenuating solar UV-B radiation is being considered. 
Attention will be focused on the gaps in information, identified above 
in section II.B.2, that precluded the development of area-specific 
quantitative assessments of potential beneficial effects of ground-
level O₃. For example, the review is considering the 
available information related to understanding relevant spatial and 
temporal patterns in changes in ground-level O₃, and 
associated spatial and temporal patterns in changes in solar UV-B 
radiation flux. The review will also consider available information on 
changes in human exposure to solar UV-B radiation as mediated by 
changes in ground-level O₃, including information related to 
characterizing how UV-B radiation exposures of sensitive populations 
may be affected by human activity patterns and variable sun-seeking and 
sun-avoidance behaviors. In addition, available information on the 
nature of health

[[Page 640]]

effects associated with changes in exposure to UV-B radiation mediated 
by changes in ground-level O₃ concentrations is being 
considered. As part of the O₃ Criteria Document, this 
information will be presented to CASAC and the public for review and 
comment. Based on the revised O₃ Criteria Document, and 
taking into account CASAC advice and public comments, EPA will consider 
the extent to which the available information provides an adequate 
basis for developing credible quantitative estimates of potential 
beneficial health effects of ground-level O₃. All such 
relevant information will be considered in EPA's review of the primary 
O₃ NAAQS.

III. Rationale for Final Response To Remand on the Secondary 
O₃ Standard

    This notice also presents the Administrator's final response to the 
remand, reaffirming the 8-hour O₃ secondary standard 
promulgated in 1997, based on:
    (1) Information from the 1997 criteria and standards review that 
served as the basis for the 1997 secondary O₃ standard, 
including the scientific information on welfare effects associated with 
direct exposures to O₃ in the ambient air, with a focus on 
vegetation effects, and assessments of vegetation exposure, risk, and 
economic values;
    (2) A review of the scientific information in the record of the 
1997 review (but not considered as part of the basis for the 1997 
standard) on the welfare effects associated with changes in UV-B 
radiation, the association between changes in ground-level 
O₃ and changes in UV-B radiation, and predictions of changes 
in ground-level O₃ levels likely to result from attainment 
of alternative O₃ standards; and
    (3) Consideration of the comments received on the proposed 
response.

A. Direct Adverse Welfare Effects

    As discussed in the 1997 final rule, direct exposures to 
O₃ have been associated quantitatively and qualitatively 
with a wide range of vegetation effects such as visible foliar injury, 
growth reductions and yield loss in annual crops, growth reductions in 
tree seedlings and mature trees, and effects that can have impacts at 
the forest stand and ecosystem level. Visible foliar injury can 
represent a direct loss of the intended use of the plant, ranging from 
reduced yield and/or marketability for some agricultural species to 
impairment of the aesthetic value of urban ornamental species. On a 
larger scale, foliar injury is occurring on native vegetation in 
national parks, forests, and wilderness areas, and may be degrading the 
aesthetic quality of the natural landscape, a resource important to 
public welfare. Growth and yield effects of O₃ have been 
well documented for numerous species, including commodity crops, fruits 
and vegetables, and seedlings of both coniferous and deciduous tree 
species. Although data from tree seedling studies could not be 
extrapolated to quantify responses to O₃ in mature trees, 
long-term observational studies of mature trees have shown growth 
reductions in the presence of elevated O₃ concentrations. 
Even where these growth reductions are not attributed to O₃ 
alone, it has been reported that O₃ is a significant 
contributor that potentially exacerbates the effects of other 
environmental stresses (e.g., pests). In addition, growth reductions 
can indicate that plant vigor is being compromised such that the plant 
can no longer compete effectively for essential nutrients, water, 
light, and space. When many O₃-sensitive individuals make up 
a population, the whole population may be affected. Changes occurring 
within sensitive populations, or stands, if they are severe enough, 
ultimately can change community and ecosystem structure. Structural 
changes that alter the ecosystem functions of energy flow and nutrient 
cycling can alter ecosystem succession.
    Based on key studies and other biological effects information 
reported in the Criteria Document and Staff Paper, it was recognized 
that peak O₃ concentrations equal to or greater than 0.10 
ppm can be phytotoxic to a large number of plant species, and can 
produce acute foliar injury and reduced crop yield and biomass 
production. In addition, O₃ concentrations within the range 
of 0.05 to 0.10 ppm have the potential over a longer duration of 
creating chronic stress on vegetation that can result in reduced plant 
growth and yield, shifts in competitive advantages in mixed 
populations, decreased vigor leading to diminished resistance to pest 
and pathogens, and injury from other environmental stresses. Some 
sensitive species can experience foliar injury and growth and yield 
effects even when O₃ concentrations never exceed 0.08 ppm. 
Further, the available scientific information supports the conclusion 
that a cumulative seasonal exposure index is more biologically relevant 
than a single event or mean index.
    To put judgments about these vegetation effects into a broader 
national perspective, the Administrator has taken into account the 
extent of exposure of O₃-sensitive species, potential risks 
of adverse effects to such species, and monetized and non-monetized 
categories of increased vegetation protection associated with 
reductions in O₃ exposures. In so doing, the Administrator 
recognized that markedly improved air quality, and thus significant 
reductions in O₃ exposures would result from attainment of 
the 0.08 ppm, 8-hour primary standard. In looking further at the 
incremental protection associated with attainment of a seasonal 
secondary standard, she recognized that areas that would likely be of 
most concern for effects on vegetation, as measured by the seasonal 
exposure index, would also be addressed by the 0.08 ppm, 8-hour primary 
standard.

B. Potential Indirect Beneficial Welfare Effects

    This section is drawn from the limited information in the record of 
the 1997 review with regard to the effect of ground-level O₃ 
on the attenuation of UV-B radiation and potential associated welfare 
benefits.\73\ While this information suggests the potential for effects 
on plants and aquatic organisms, EPA (1987, ES-40--ES-43) recognizes 
that relevant studies are limited and the uncertainties are great due 
in part to problems in study designs, such that quantitative 
conclusions cannot be drawn.
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    \73\ The information in this section is drawn primarily from the 
EPA document ``Assessing the Risk of Trace Gasses that Can Modify 
the Stratosphere'' (U.S. EPA, 1987).
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    With regard to effects on vegetation, while some plant cultivars 
tested in the laboratory were determined to be sensitive to UV-B 
radiation exposure, these experiments have been shown to inadequately 
replicate effects in the field, such that they do not reflect the 
complex interactions between plants and their environment. The only 
long-term field studies of crops involved soybeans, producing 
suggestive evidence of reduced yields under conditions simulating 
changes in total column O₃ over an order of magnitude 
greater than those projected to occur as a result of changes in ground-
level O₃ associated with attainment of the 1997 
O₃ NAAQS. Beyond the limited studies of crops, EPA (1987, 
ES-41) notes that little or no data exist on UV-B radiation effects on 
trees and other types of natural vegetation, or on possible 
interactions with pathogens. While it is noted that changes in UV-B 
radiation levels could alter the results of competition in natural 
ecosystems, no evidence is available to evaluate this

[[Page 641]]

effect. Further, it is recognized that UV-B radiation may both inhibit 
and stimulate plant flowering, depending on the species and growth 
conditions. Recognizing that interactions between UV-B radiation and 
other environmental factors are important in determining potential UV-B 
radiation effects on plants, EPA (1987, ES-42) notes that extensive, 
long-term studies would be required to address these interactions.
    With regard to effects on aquatic organisms, EPA (1987, ES-42) 
notes that while initial experiments show that increased UV-B radiation 
has the potential to harm aquatic life, difficulties in experimental 
designs and the limited scope of the studies prevent the quantification 
of potential risks. Some study results suggest that most zooplankton 
show no effect due to increased exposure to UV-B radiation up to some 
threshold exposure level, with exposures above such threshold levels 
eliciting notable effects. For species under UV-B stress, such effects 
could include reduced time spent at the surface of the water, which is 
critical for breeding in some species, possibly leading to changes in 
species diversity. It is also noted that, as do all other living 
organisms, aquatic biota cope with exposure to UV-B radiation by 
avoidance, shielding, and repair mechanisms, although uncertainty 
exists as to the extent to which such mitigation mechanisms would occur 
(U.S. EPA, 1987, ES-43). It is recognized that determination of UV-B 
radiation exposure in aquatic systems is complex because of the 
variable attenuation of UV-B radiation in the water column, and that 
further research is needed to improve our understanding of how UV-B 
radiation exposure affects marine species, particularly given their 
world-wide importance as a source of protein.
    With regard to EPA's characterization of UV-B radiation-related 
effects, one commenter noted that there is now more information about 
the welfare effects of UV-B radiation than there was in the record of 
the 1997 review,\74\ and asserted that this information is sufficient 
for the Agency to reach ``rough'' quantitative conclusions about some 
of these effects. The commenter further expressed the view that the 
relevant information on UV-B radiation-related effects should be 
evaluated as part of EPA's air quality criteria and be made subject to 
CASAC review. Moreover, this commenter suggested that EPA's calling the 
risks ``potential'' effects in the proposed response is inconsistent 
with its concluding that such effects are ``real'' in the context of 
stratospheric O₃ depletion.
-----------------------------------------------------------------------

    \74\ The commenter specifically cited an EPA Web site pertaining 
to stratospheric O₃ depletion (http://www.epa.gov/ozone/science/effects.
html), with information on the effects of UV-B 
radiation on plant growth, aquatic organisms and materials of 
commercial interest.
-----------------------------------------------------------------------

    The EPA agrees that there is now more information on the effects of 
UV-B radiation on plants, aquatic ecosystems and materials than was 
available in the 1997 review, and notes that there is also more 
information available now on the direct adverse effects of 
O₃ on vegetation and ecosystems. While EPA agrees that 
relevant information about the welfare effects of ground-level 
O₃, including both potential UV-B radiation-related 
beneficial effects and direct adverse effects, should be evaluated as 
part of updated air quality criteria, EPA believes that all such 
updated information should be evaluated during the periodic review of 
the O₃ criteria and standards that is now underway. A fuller 
discussion of EPA's procedural approach to responding to the remand, 
especially with regard to incorporating new information in updated air 
quality criteria and CASAC review, can be found in the introduction to 
section II above.
    Further, EPA strongly disagrees with the commenter's assertion that 
currently available information on the effects of stratospheric 
O₃ depletion is sufficient for developing credible 
quantitative estimates of UV-B radiation-related effects associated 
with changes in ground-level O₃ likely to result from 
attainment of a more stringent O₃ NAAQS. While EPA has 
developed quantitative estimates of the impacts of relatively large and 
broadly uniform increases in incident UV-B radiation associated with 
projected changes in the global reservoir of stratospheric 
O₃, it is not necessarily the case that EPA can now develop 
credible estimates of impacts associated with the relatively very small 
and locally variable increases in incident UV-B radiation that may 
result from future projected changes in ground-level O₃. The 
EPA believes that this commenter is ignoring both the fundamental 
differences in the nature and relative magnitude of the temporal and 
spatial variability of O₃ levels in the stratosphere and 
ground-level troposphere, and the importance of area-specific 
assessments for addressing impacts related to changes in ground-level 
O₃ that take into account relevant factors (as discussed in 
section II.B above). Area-specific factors that would be important in 
assessing the potential for UV-B radiation-related consequences of a 
more stringent O₃ NAAQS on plants, aquatic ecosystems, and 
materials in any geographical area are the same or analogous to factors 
that are important in assessing the impacts on human health. Such 
factors include the temporal and spatial patterns of ground-level 
O₃ throughout a geographic area where reductions are likely 
to occur, the associated temporal and spatial patterns in UV-B 
radiation flux, and the sensitivity and spatial and temporal exposure 
patterns of plants, aquatic systems and materials to the relatively 
very small and highly variable changes in UV-B radiation associated 
with relevant changes in ground-level O₃.
    For example, the commenter specifically noted that new information 
on the effects of stratospheric O₃ depletion finds that 
solar UV-B radiation can affect marine ecosystems by damaging the early 
developmental stages of some marine organisms that, in turn, can result 
in significant reductions in the size of the populations of larger 
animals that feed on these animals. Thus for marine ecosystems, 
increased UV-B radiation is most likely to have an effect over specific 
geographic areas and during specific periods of time in the life cycles 
of some marine organisms. This geographic and temporal specificity is 
not important in estimating the impacts associated with changes in 
stratospheric O₃, given its relative spatial and temporal 
stability. Such assessments of the effects of long-term declines or 
restoration can reasonably assume that short-term and local-scale 
variations in important factors, such as developmental stages of marine 
organisms, will tend to ``even out'' over time, permitting more 
confidence in the magnitude and direction of such assessments. In 
contrast, such geographic and temporal factors would have a major 
influence in estimating impacts associated with the localized and 
highly variable changes in ground-level O₃ associated with 
attaining a more stringent O₃ NAAQS. In particular, as 
discussed above in section II.B.2, coastal areas tend to have much 
lower ground-level O₃ levels relative to inland areas, and 
there is little evidence to indicate that attaining a more stringent 
O₃ NAAQS would appreciably change O₃ levels, and 
associated UV-B radiation penetration, at ground-level over marine 
ecosystems. Further, the seasonality of ground-level O₃ 
levels, and efforts to reduce ground-level O₃ to attain a 
more stringent O₃ NAAQS, would be important to take in 
account in any credible assessment of impacts of changes in ground-
level O₃ levels on the seasonal developmental stages of 
organisms in marine

[[Page 642]]

ecosystems. This example illustrates why broad-scale analytic 
approaches appropriately used to estimate stratospheric O₃ 
impacts are not appropriate for developing credible estimates of the 
impacts on public welfare of changes in tropospheric O₃ 
likely to result from attaining a more stringent O₃ NAAQS. 
Thus, EPA believes that it is not inconsistent to conclude that such 
quantifiable effects are ``real'' in relation to large, relatively 
uniform changes in the stratospheric O₃ reservoir, and to 
characterize effects that can not be credibly quantified in relation to 
relatively very small and highly variable changes in tropospheric 
O₃ associated with attaining a more stringent O₃ 
NAAQS as ``potential'' effects at this time.

C. Final Response To Remand on the Secondary O₃ NAAQS

    After considering the scientific information available in the 
record on adverse welfare effects associated with direct exposure to 
O₃ in the ambient air and on the potential indirect benefits 
to public welfare related to attenuation of naturally occurring UV-B 
radiation, and the relevant comments received, the Administrator again 
concludes that there is insufficient information available on UV-B 
radiation-related effects that may result from attaining the 1997 
O₃ NAAQS to warrant any relaxation in the level of public 
welfare protection previously determined to be requisite to protect 
against the demonstrated direct adverse effects of exposure to 
O₃ in the ambient air. Thus, the Administrator responds to 
the remand by reaffirming the 8-hour secondary O₃ standard 
promulgated in 1997, which is identical to the 8-hour primary 
O₃ standard.
    In determining now that the 0.08 ppm, 8-hour O₃ standard 
set in 1997 is requisite to protect public welfare, the Administrator 
is finding that such a standard is both necessary and sufficient. While 
consideration of the potential beneficial effects of ground-level 
O₃ clearly did not call into question whether this standard 
was sufficient to protect against the direct adverse welfare effects of 
ground-level O₃ addressed in EPA's 1997 final rule, it did 
raise the question as to whether this standard was still necessary in 
light of potential UV-B radiation-related beneficial effects. Having 
determined that any potential UV-B radiation-related welfare effects 
associated with attaining the 1997 O₃ standard are too 
uncertain to be given any appreciable weight in balancing against the 
demonstrated direct adverse effects of ground-level O₃ on 
vegetation, for which information was sufficient for both quantitative 
and qualitative assessments that provided the basis for the 1997 
secondary O₃ standard, the Administrator has concluded that 
the weight of evidence of O₃'s adverse effects necessitates 
a standard no less stringent than the standard set in EPA's 1997 final 
rule.\75\
-----------------------------------------------------------------------

    \75\ In so doing, EPA is applying the same decision making 
standard as it applied in its 1997 final rule, as noted above in 
section II.D on the primary standard, based on the plain meaning of 
the word ``requisite,'' consistent with the U.S. Supreme Court's 
decision in Whitman, 121 S. Ct. at 911-12, 914.
-----------------------------------------------------------------------

    As recognized in section II.D with regard to consideration of 
health effects, the Administrator also recognizes that relevant 
information on indirect potentially beneficial welfare effects of 
ground-level O₃ is now available that was not part of this 
rulemaking record. As previously noted, the next periodic review of the 
O₃ NAAQS has already been initiated by EPA's ORD and 
preparation of a revised O₃ Criteria Document that will 
incorporate such relevant information is now underway. Thus, to ensure 
that the next review of the O₃ criteria and standards can be 
based on a comprehensive and current body of relevant scientific 
information, EPA continues to encourage the submission of new 
scientific information on the relationships between ground-level 
O₃, associated attenuation of UV-B radiation and other 
indirect effects of the presence of O₃ in the ambient air, 
and effects on public welfare such as those associated with changes in 
relevant exposures to UV-B radiation.
    As noted above in section II.D, EPA's ongoing review and revision 
of the O₃ Criteria Document is addressing a number of issues 
related to indirect potentially beneficial health effects of ground-
level O₃. In addition to the issues noted above, EPA's 
review will also consider the available information on the nature of 
environmental effects associated with changes in solar UV-B radiation 
mediated by changes in ground-level O₃ concentrations. Based 
on the revised O₃ Criteria Document, and taking into account 
CASAC and public comments, EPA also will consider the extent to which 
the available information provides an adequate basis for developing 
credible quantitative estimates of potential beneficial environmental 
effects of ground-level O₃. All such relevant information 
will be considered in EPA's review of the secondary O₃ 
NAAQS.

IV. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

    Under Executive Order 12866, the Agency must determine whether a 
regulatory action is ``significant'' and, therefore, subject to OMB 
review and the requirements of the Executive Order. The order defines 
``significant regulatory action'' as one that may:
    (1) Have an annual effect on the economy of $100 million or more or 
adversely affect in a material way the economy, a sector of the 
economy, productivity, competition, jobs, the environment, public 
health or safety, or State, local, or tribal governments or 
communities;
    (2) Create a serious inconsistency or otherwise interfere with an 
action taken or planned by another Agency;
    (3) Materially alter the budgetary impact of entitlements, grants, 
user fees, or loan programs or the rights and obligations or recipients 
thereof; or
    (4) Raise novel legal or policy issues arising out of legal 
mandates, the President's priorities, or the principles set forth in 
the Executive Order.
    Pursuant to the terms of Executive Order 12866, it has been 
determined that this response is a ``significant regulatory action'' 
because of its important national policy implications. As such, this 
action was submitted to OMB for review. Changes made in response to OMB 
suggestions or recommendations will be documented in the public record 
and made available for public inspection at EPA's Air Docket Center 
(Docket No. A-95-58).
    Since today's final response to the remand is a reaffirmation of 
the revisions to the O₃ NAAQS previously promulgated in 
1997, no new RIA has been prepared. The RIA (1997) prepared in 
conjunction with the 1997 revision to the O₃ NAAQS is 
available in the docket, from EPA at the address under ``Availability 
of Related Information,'' and in electronic form as discussed above in 
``Electronic Availability.''
    As a number of judicial decisions have made clear, the economic and 
technological feasibility of attaining ambient standards are not to be 
considered in setting NAAQS, although such factors may be considered in 
the development of State plans to implement the standards. E.g., 
Whitman, 531 U.S. at 471 (2001); ATA I, 175 F.3d at 1040-1043. 
Accordingly, although a RIA was prepared for the 1997 decision to 
revise the O₃ NAAQS, neither that RIA nor the associated 
contractor reports have been considered in issuing this final response.

[[Page 643]]

B. Paperwork Reduction Act

    This action does not impose an information collection burden under 
provisions of the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. 
because today's final response to the remand does not establish any new 
information collection requirements beyond those which are currently 
required under the Ambient Air Quality Surveillance Regulations in 40 
CFR part 58 (OMB #2060-0084, EPA ICR No. 0940.16). Therefore, 
the requirements of the Paperwork Reduction Act do not apply to today's 
final action. Burden means the total time, effort, or financial 
resources expended by persons to generate, maintain, retain, or 
disclose or provide information to or for a Federal agency. This 
includes the time needed to review instructions; develop, acquire, 
install, and utilize technology and systems for the purposes of 
collecting, validating, and verifying information, processing and 
maintaining information, and disclosing and providing information; 
adjust the existing ways to comply with any previously applicable 
instructions and requirements; train personnel to be able to respond to 
a collection of information; search data sources; complete and review 
the collection of information; and transmit or otherwise disclose the 
information. An agency may not conduct or sponsor, and a person is not 
required to respond to, a collection of information unless it displays 
a currently valid OMB control number. The OMB control numbers for EPA's 
regulations are listed in 40 CFR part 9 and 48 CFR chapter 15.

C. Regulatory Flexibility Act

    The RFA generally requires an agency to prepare a regulatory 
flexibility analysis of any rule subject to notice and comment 
rulemaking requirements under the Administrative Procedure Act or any 
other statute unless the agency certifies that the rule will not have a 
significant economic impact on a substantial number of small entities. 
Small entities include small businesses, small organizations, and small 
governmental jurisdictions.
    For purposes of assessing the impacts of today's rule on small 
entities, small entity is defined as: (1) Any small business, based on 
the Small Business Administration's size standards; (2) a small 
governmental jurisdiction that is a government of a city, county, town, 
school district or special district with a population of less than 
50,000; and (3) a small organization that is any not-for-profit 
enterprise which is independently owned and operated and is not 
dominant in its field.
    After considering the economic impacts of today's final rule on 
small entities, I certify that this action will not have a significant 
economic impact on a substantial number of small entities. On May 14, 
1999, the United States Court of Appeals for the District of Columbia 
Circuit (``D.C. Circuit'') remanded the O₃ NAAQS to EPA to 
consider, among other things, any potential beneficial health effects 
of O₃ pollution in shielding the public from the ``harmful 
effects of the sun's ultraviolet rays.'' 175 F.3d 1027 (D.C. Cir., 
1999). Today's action provides EPA's final response to that aspect of 
the Court's remand and reaffirms the 1997 primary O₃ NAAQS. 
Therefore, this rule does not establish any new regulatory requirements 
affecting small entities.

D. Unfunded Mandates Reform Act

    Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public 
Law 104-4, establishes requirements for Federal agencies to assess the 
effects of their regulatory actions on State, local, and tribal 
governments and the private sector. Under section 202 of the UMRA, EPA 
generally must prepare a written statement, including a cost-benefit 
analysis, for proposed and final rules with ``Federal mandates'' that 
may result in expenditures to State, local, and tribal governments, in 
the aggregate, or to the private sector, of $100 million or more in any 
one year. Before promulgating an EPA rule for which a written statement 
is needed, section 205 of the UMRA generally requires EPA to identify 
and consider a reasonable number of regulatory alternatives and adopt 
the least costly, most cost-effective or least burdensome alternative 
that achieves the objectives of the rule. The provisions of section 205 
do not apply when they are inconsistent with applicable law. Moreover, 
section 205 allows EPA to adopt an alternative other than the least 
costly, most cost-effective or least burdensome alternative if the 
Administrator publishes with the final rule an explanation why that 
alternative was not adopted. Before EPA establishes any regulatory 
requirements that may significantly or uniquely affect small 
governments, including tribal governments, it must have developed under 
section 203 of the UMRA a small government agency plan. The plan must 
provide for notifying potentially affected small governments, enabling 
officials of affected small governments to have meaningful and timely 
input in the development of EPA regulatory proposals with significant 
Federal intergovernmental mandates, and informing, educating, and 
advising small governments on compliance with the regulatory 
requirements.
    As noted above, EPA cannot consider in setting a NAAQS the economic 
or technological feasibility of attaining ambient air quality 
standards, although such factors may be considered to a degree in the 
development of State plans to implement the standards. See, e.g., 
Whitman, 531 U.S. at 471; ATA I, 175 F.3d at 1040-43. Accordingly, and 
for the reasons discussed in the 1996 proposal and 1997 final rule, EPA 
has determined that the provisions of sections 202, 203, and 205 of the 
UMRA do not apply to this final action. The EPA acknowledges, however, 
that any corresponding revisions to associated State implementation 
plan requirements and air quality surveillance requirements, 40 CFR 
part 51 and 40 CFR part 58, respectively, might result in such effects. 
Accordingly, EPA will address unfunded mandates as appropriate when it 
proposes any revisions to 40 CFR parts 51 and 58.

E. Executive Order 13132: Federalism

    Executive Order 13132, entitled ``Federalism'' (64 FR 43255, August 
10, 1999) requires EPA to develop an accountable process to ensure 
``meaningful and timely input by State and local officials in the 
development of regulatory policies that have federalism implications.'' 
``Policies that have federalism implications'' is defined in the 
Executive Order to include regulations that have ``substantial direct 
effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government.''
    Today's final response to the remand does not have federalism 
implications. It will not have substantial direct effects on the 
States, on the relationship between the national government and the 
States, or on the distribution of power and responsibilities among the 
various levels of government, as specified in Executive Order 13132. 
The final response to the remand only reaffirms the previously 
promulgated ozone standard and would not alter the relationship that 
has existed under the Clean Air Act for 30 years, in which EPA sets 
NAAQS and the States implement them through submission of SIPs, in 
accordance with the requirements of the Clean Air Act. Thus, Executive 
Order 13132 does not apply to this action.

[[Page 644]]

F. Executive Order 13175: Consultation and Coordination With Indian 
Tribal Governments

    Executive Order 13175, entitled ``Consultation and Coordination 
with Indian Tribal Governments'' (65 FR 67249, November 6, 2000), 
requires EPA to develop an accountable process to ensure ``meaningful 
and timely input by tribal officials in the development of regulatory 
policies that have tribal implications.'' ``Policies that have tribal 
implications'' is defined in the Executive Order to include regulations 
that have ``substantial direct effects on one or more Indian tribes, on 
the relationship between the Federal government and the Indian tribes, 
or on the distribution of power and responsibilities between the 
Federal government and Indian tribes.''
    This final response to the remand, which leaves unchanged the 1997 
final rule, does not have tribal implications. It will not have 
substantial direct effects on tribal governments, on the relationship 
between the Federal government and Indian tribes, or on the 
distribution of power and responsibilities between the Federal 
government and Indian tribes, as specified in Executive Order 13175. 
Thus, Executive Order 13175 does not apply to this rule.

G. Executive Order 13045: Protection of Children From Environmental 
Health and Safety Risks

    Executive Order 13045, entitled ``Protection of Children from 
Environmental Health Risks and Safety Risks'' (62 FR 19885, April 23, 
1997), requires Federal agencies to ensure that their policies, 
programs, activities, and standards identify and assess environmental 
health and safety risks that may disproportionately affect children. To 
respond to this order, agencies must explain why the regulation is 
preferable to other potentially effective and reasonably feasible 
alternatives considered by the agency.
    This final response is not subject to the Executive Order because 
it is not economically significant as defined in Executive Order 12866. 
However, today's final response to the remand, reaffirming the 1997 
primary O₃ NAAQS, specifically takes into account children 
as the group most at risk to the direct inhalation-related effects of 
O₃ exposure, and was based on studies of effects on 
children's health (U.S. EPA, 1996a; U.S. EPA, 1996b) and assessments of 
children's exposure and risk (Johnson et al., 1994; Johnson et al., 
1996a, b; Whitfield et al., 1996; Richmond, 1997). The 1997 revision to 
the primary O₃ NAAQS was promulgated to provide adequate 
protection to the public, especially children, against a wide range of 
direct O₃-induced health effects, including decreased lung 
function, primarily in children who are active outdoors; increased 
respiratory symptoms, primarily in highly sensitive individuals; 
hospital admissions and emergency room visits for respiratory causes, 
among children and adults with respiratory disease; inflammation of the 
lung and possible long-term damage to the lungs. This final response to 
the remand affirming the 1997 primary O₃ NAAQS maintains the 
level of protection of children's health established by the standard 
set in 1997. Therefore, today's final action does comply with the 
requirements of Executive Order 13045.

H. Executive Order 13211: Actions That Significantly Affect Energy 
Supply, Distribution, or Use

    This final response to the remand is not a ``significant energy 
action'' as defined in Executive Order 13211, ``Actions Concerning 
Regulations That Significantly Affect Energy Supply, Distribution, or 
Use'' (66 FR 28355, May 22, 2001) because it is not likely to have a 
significant adverse effect on the supply, distribution, or use of 
energy. This is because this final response to the remand leaves 
unchanged the 1997 final rule. Thus, Executive Order 13211 does not 
apply to this rule.

I. National Technology Transfer Advancement Act

    Section 12(d) of the National Technology Transfer and Advancement 
Act of 1995 (NTTAA), Public Law 104-113, section 12(d) (15 U.S.C. 272 
note) directs EPA to use voluntary consensus standards in its 
regulatory activities unless to do so would be inconsistent with 
applicable law or otherwise impractical. Voluntary consensus standards 
are technical standards (e.g., materials specifications, test methods, 
sampling procedures, and business practices) that are developed or 
adopted by voluntary consensus standards bodies. The NTTAA directs EPA 
to provide Congress, through OMB, explanations when the Agency decides 
not to use available and applicable voluntary consensus standards. 
Today's final response to the remand does not involve technical 
standards. Therefore, EPA did not consider the use of any voluntary 
consensus standards.

J. Congressional Review Act

    The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the 
Small Business Regulatory Enforcement Fairness Act of 1996, generally 
provides that before a rule may take effect, the agency promulgating 
the rule must submit a rule report, which includes a copy of the rule, 
to each House of the Congress and to the Comptroller General of the 
United States. This action is not a ``major rule'' as defined by 5 
U.S.C. 804(2) because it is a reaffirmation of the O₃ NAAQS 
promulgated in 1997. Nonetheless, EPA will submit a report containing 
this response and other information to the U.S. Senate, the U.S. House 
of Representatives, and the Comptroller General of the United States 
prior to publication of the response in the Federal Register. Although 
this final response is not a major rule, EPA will apply the ``major 
rule'' restrictions regarding the effective date; thus, the response 
will be effective 60 days after publication in the Federal Register.

V. References

Altschuller, A.P. (1994) Memorandum to L.T. Cupitt re: Addendum to My 
Review of Your Manuscript ``Calculations of the Impact of Tropospheric 
Ozone Changes On UV-B Flux and Potential Skin Cancers,'' EPA Docket A-
95-58, IV-D-2694, Appendix B 17.
American Thoracic Society. (1985) Guidelines as to what constitutes an 
adverse respiratory health effect, with special reference to 
epidemiologic studies of air pollution. American Review of Respiratory 
Disease. 131: 666-668.
Br[uuml]hl, C. and Creutzen, P.J. (1989) On the Disproportionate Role 
of Tropospheric Ozone as a Filter Against Solar UV-B Radiation. 
Geophys. Res. Letters, 16:703-706. Docket A-95-58, IV-D-2694, Appendix 
B 10.
Childs, N. (1994) Memorandum to L. Grant re: Relationships of 
Reductions in Tropospheric Ozone to UV-B Penetration to Earth's 
Surface, EPA Docket A-95-58, IV-D-2694, Appendix B 16.
Cupitt, L.T. (1994) Draft memorandum, Calculations of the Impact of 
Tropospheric Ozone Changes on UV-B Flux and Potential Skin Cancers, EPA 
ORD/AREAL Docket A-95-58, IV-D-2694, Appendix B 2.
Fishman, J.; Watson, C.E.; Larsen, J.C.; and Logan, J.A. (1990) 
Distribution of Tropospheric Ozone Determined From Satellite Data J. 
Geophys. Res. 95:3599-3617. Docket A-95-58, IV-D-2694, Appendix B 1.

[[Page 645]]

Frederick, J.E.; Koob, A.E.; Weatherhead, E.C. (1993) Empirical Studies 
of Tropospheric Transmission in the Ultraviolet: Broadband 
Measurements. J. Applied Meteorology 32:1883-1892. Docket A-95-58, IV-
D-2694, Appendix B 13.
Johnson, T. (1994) Letter report: Enhancements to the pNEM summer camp 
methodology. Prepared by IT/Air Quality Services for U.S. EPA, Office 
of Air Quality Planning and Standards (OAQPS); Research Triangle Park, 
NC, March.
Johnson, T.; Capel, J.; Mozier, J.; McCoy, M. (1996a) Estimation of 
ozone exposures experienced by outdoor children in nine urban areas 
using a probabilistic version of NEM. Prepared by IT/Air Quality 
Services for U.S. EPA, OAQPS; Research Triangle Park, NC, August.
Johnson, T.; Capel, J.; McCoy, M.; Mozier, J. (1996b) Estimation of 
ozone exposures experienced by outdoor workers in nine urban areas 
using a probabilistic version of NEM. Prepared by IT/Air Quality 
Services for U.S. EPA, OAQPS; Research Triangle Park, NC, August.
Johnson, T.; Capel, J.; McCoy, M. (1996c) Estimation of ozone exposures 
experienced by urban residents using a probabilistic version of NEM. 
Prepared by IT/Air Quality Services for U.S. EPA, OAQPS; Research 
Triangle Park, NC, April.
Lutter, R. and Wolz, C. (1997) UV-B Screening by Tropospheric Ozone: 
Implications for the National Ambient Air Quality Standard. Envir. Sci. 
Technol. 31:142A-146A. Docket A-95-58, IV-D-2694, Appendix B 7.
Madronich, S. (1992) Implications of Recent Total Atmospheric Ozone 
Measurements for Biologically Active Ultraviolet Radiation Reaching 
Earth's Surface, Geophys. Res. Letters 19:37-40. Docket A-95-58, IV-D-
2694, Appendix B 8.
Martin, K. (2001) U.S. EPA, OAQPS, Letter to Dr. Philip Hopke, Chairman 
of the Clean Air Scientific Advisory Committee, dated January 22, 2001. 
Docket A-95-58, VI-F-1.
Martin, K. (2002) U.S. EPA, OAQPS, Letter to Dr. Philip Hopke, Chairman 
of the Clean Air Scientific Advisory Committee, dated January 14, 2002. 
Docket A-95-58, VI-F-2.
National Academy of Sciences (1991) Rethinking the Ozone Problem in 
Urban and Regional Air Pollution, National Academy Press, Washington, 
District of Columbia.
Richmond (1997) Supplemental ozone exposure and health risk analyses. 
Internal memorandum from Harvey M. Richmond to Karen M. Martin, U.S. 
EPA, AQSSD/OAQPS/OAR, RTP, NC, dated February 11, 1997. Docket No. A-
95-58, IV-A-1.
Thiele, J. J.; Traber, M. G.; Tsang, K.; Cross, C. E.; Packer, L. 
(1997) In vivo exposure to ozone depletes vitamins C and E and induces 
lipid peroxidation in epidermal layers of murine skin. Free Radical 
Biol. Med. 23: 385-391.
Thurston, G.D.; Ito, K.; Kinney, P.L.; Lippmann, M. (1992) A multi-year 
study of air pollution and respiratory hospital admissions in three New 
York State metropolitan areas: results for 1988 and 1989 summers. 
Journal of Exposure Analysis and Environmental Epidemiology. 2:429-450.
UNEP (1998) Environmental Effects of Ozone Depletion; Elsevier Science 
S.A., The Netherlands.
U.S. Census Bureau (2001) Profiles of General Demographic 
Characteristics 2000. 2000 Census of Population and Housing United 
States. Table DP-1. Profile of General Demographic Characteristics: 
2000, Geographic Area: California, page 1030.
U.S. DOE (1995) Statement of Marvin Frazier at Clean Air Scientific 
Advisory Committee (CASAC) Ozone Review Panel, Public Meeting, March 
21, 1995, at 203-218 transcript. Docket A-95-58, IV-D-2694, Appendix B 
9.
U.S. EPA (1987) Assessing the Risk of Trace Gases That Can Modify the 
Stratosphere. Volume 1 Executive Summary, Docket A-95-58, IV-D-2694, 
Appendix B 4.
U.S. EPA (1995a) Fact sheet: Health Effects of Overexposure to the Sun, 
EPA 430-F-95-003, Office of Air and Radiation Docket A-95-58, IV-D-
2694, Appendix B 5.
U.S. EPA (1995b) Fact sheet: UV Radiation, EPA 430-F-95-003, Office of 
Air and Radiation Docket A-95-58, IV-D-2694, Appendix B 18.
U.S. EPA (1996a) Air quality criteria for ozone and related 
photochemical oxidants. Research Triangle Park, NC: Office of Health 
and Environmental Assessment, Environmental Criteria and Assessment 
Office; EPA report nos. EPA/600/AP-93/004a-c.
U.S. EPA (1996b) Review of the national ambient air quality standards 
for ozone: assessment of scientific and technical information. OAQPS 
staff paper. Research Triangle Park, NC: Office of Air Quality Planning 
and Standards; EPA report no. EPA-452/R-96-007. Available from: NTIS, 
Springfield, VA; PB96-203435.
U.S. EPA (1997) Responses to Significant Comments on the 1996 Proposed 
Rule on the National Ambient Air Quality Standards for Ozone, Office of 
Air and Radiation Docket A-95-58, V-C-1, July 1997.
U.S. EPA (2002) Responses to Significant Comments on the 2001 National 
Ambient Air Quality Standards for Ozone: Proposed Response to Remand, 
Office of Air and Radiation Docket A-95-58, August 2002.
Whitfield, R.G.; Biller, W.F.; Jusko, M.J.; Keisler, J.M. (1996) A 
probabilistic assessment of health risks associated with short-term 
exposure to tropospheric ozone. Report prepared for U.S. EPA, OAQPS. 
Argonne National Laboratory; Argonne, IL.
Wolff, G. T. (1995a) Letter from Chairman of the Clean Air Scientific 
Advisory Committee to the EPA Administrator, dated November 28, 1995. 
EPA-SAB-CASAC-LTR-96-002.
Wolff, G. T., (1995b) Letter from Chairman of the Clean Air Scientific 
Advisory Committee to the EPA Administrator, dated November 30, 1995. 
EPA-SAB-CASAC-LTR-96-002.
Wolff, G. T., (1996) Letter from Chairman of the Clean Air Scientific 
Advisory Committee to the EPA Administrator, dated April 4, 1996. EPA-
SAB-CASAC-LTR-96-006.
WMO (1998) Scientific Assessment of Ozone Depletion: 1998, Global Ozone 
Research and Monitoring Project--Report No. 44, published in 1999.

List of Subjects in 40 CFR Part 50

    Environmental protection, Air pollution control, Carbon monoxide, 
Lead, Nitrogen dioxide, Ozone, Particulate matter, Sulfur oxides.

    Dated: December 18, 2002.
Christine Todd Whitman,
Administrator.
[FR Doc. 03-56 Filed 1-3-03; 8:45 am]
BILLING CODE 6560-50-P
Notices For
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
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1997
1996
1995
1994
National Ambient Air Quality Standards for Ozone: Final Response to Remand

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