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Citation: 62 Fed. Reg. 38852 1997

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### Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations



# FIGURE5- Isolated Area NetworkDesign 

# 4
3)

U2

U1 Urbanized Fringe



# U3

LEGEND:
(O

-Acircle denotes aPAMS Site. Thenumberinsidedescribes theSitenumber.
U1
-Highozonedaypredominant morningwinddirection U2
-Secondmostpredominanthighozonedaymorningwinddirection U3
-Highozonedaypredominantafternoonwinddirection 38852

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### Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations



# FIGURE6

-Multi-Area and TransportAreaNetworkDesign 

# 4Z 3Z

-oMSA Z MSA Y

Central BusinessDistrict

Fringe 

# U

x



# Ul 

# U3

LEGEND:

oX

-A circledenotes aPAMS Site. Thenumberinside describesthe Sitenumber andthe letterindicatestheassociatedMSA/CMSA, e.g.,acirclewithIXindicates

aSite#1 forMSAX. SincePAMS canserve multiplepurposes formorethan

oneMSA/CMSA, Siteswithmutipleassociations areidentifiedwith multiple number andletteridentifiers. U1

-Highozone daypredominantmorningwinddirection U2

- Secondmostpredominant highozone daymorningwinddirection U3

- Highozone daypredominantafternoonwind direction 

## 38853

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## 38854 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

3SeeFigure 5. applicable for SLAMS and the required
4.4Minimum Monitoring Network t t t t t spatial scales for NAMS. There may also be Requirements. 5. Summary. some situations, as discussed later in

t t t t t Table 6 ofthis Appendix shows by Appendix E ofthis part, where additional Table 2 t t t pollutant, all ofthe spatial scales that are scales maybe allowed for NAMS purposes.

TABLE 6.-SUMMARY OF SPATIAL SCALES FOR 

## SLAMS AND REQUIRED SCALES FOR 

## NAMS

Scales Applicablefor SLAMS Spatial Scale SO2 CO 03 NO 2 Pb PM10 PM2.5

Micro

......................................................................... ............. IV V Middle

.................................................................................... V V V V V V N

eighborhood

...................................................................... g V V V V Urban ................................................................................. ...

. V V V V Regional

................................................................................ S e V f N Scales Required for NAMS
Micro
................................................................................. . .... . . . . . . . M

iddle

.................................................................................... N

eighborhood

...................................................................... V V V V V Urban

.................................................................................. / 2 Region al

................................................................................ / 2

1Only permitted if representative of many such micro-scale environments in a residential district (formiddle scale,at leasttwo). 2 Either urban or regional scalefor regional transport sites.

6. References.

18. Watson et al. Guidance for Network Design and Optimum Site Exposure for PM2.5 and PM 10. Prepared for U.S. Environmental Protection Agency, Research Triangle Park, NC.

o. Appendix Eis amended byrevising the entry for 8. in the table ofcontents, by revising theheading to section 8., adding a sentence at the end ofthe first paragraph of section 8.1, and in section 8.3 removing the term "PM10"wherever it appears and adding in its place "PM"
to read as follows: Appendix E-Probe and Monitoring Path Siting CriteriaforAmbient AirQuality Monitoring

t t t t t 8. Particulate Matter (PMlo and PM2 . 5)

8. Particulate Matter(PMioandPM2 .5).
8.1 Vertical Placement * * *Although microscale or middle scale stations are not the preferred spatial scale for PM2 .5sites, there are situations where such sites are representative ofseveral locations within an

area where large segments ofthepopulation may live or work (e.g., central business district ofMetropolitan area). In these cases, the sampler inlet for such microscale PM2.5 stations must alsobe 2-7 meters above ground level.

p. Appendix F is amended by revising in the table ofcontents the entry for 2.7.3 and adding a new entry for 2.7.4, by redesignating section 2.7.3 as section 2.7.4 and adding a new section 2.7.3 to read as follows: Appendix F-Annual SLAMS AirQuality Information

2.7.3 Annual Summary Statistics

2.7.4 Episode and Other Unscheduled Sampling Data

t t t t t 2.7.3 Annual Summary Statistics. Annual arithmetic mean (gg/m3) as specified in 40 CFRpart 50, Appendix N. All daily PM-fine values above the level ofthe 24 hour PMfine NAAQS and dates ofoccurrence. Sampling schedule used such as once every 6days, everyday, etc. Number of24 hour
average concentrations in ranges:

Number of Range Values

0 to 15 (gg/m 3)

......................... 1 6 to 30

..................................... 31to 50

..................................... 51to 70

..................................... 71to 90

..................................... 91to 11 0

................................... Greaterthan 110

......................

[FR Doc. 97 18579 Filed 7 17 97; 8:45 am]
BILLING CODE 6560-50-F

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38855 

## Friday July 18, 1997



# Part V


# Environmental Protection Agency

40 CFR Part 50 National Ambient Air Quality Standards for Ozone; Final Rule

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ENVIRONMENTAL PROTECTION
AGENCY
40 CFR Part 50 [ADA-95-58; FRL-5725-3]
RIN-2060-AE57

National Ambient AirQuality Standards forOzone
AGENCY: Environmental Protection Agency (EPA). ACTION: Finalrule.
SUMMARY: This document describes EPA's decision torevise the national ambient airquality standards (NAAQS) for ozone (03)based on its review ofthe 

### available scientific evidence linking exposures to ambient 03to adverse health and welfare effects at levels allowed by the current 03 standards. The current 1-hour primary standard is replaced by an 8-hour standard at a level of0.08 parts permillion (ppm) with a form based on the 3-year average ofthe annual fourth-highest daily maximum 8-hour average 03 concentrations measured at each monitor within an area. The new primary standard will provide increased protection to thepublic, especially children and other at-riskpopulations, against a wide range of03-induced health effects, including decreased lung function, primarily in children active outdoors; increased respiratory symptoms, particularly in highly sensitiveindividuals; hospital admissions and emergency room visits for respiratory causes, among children and adults with pre-existingrespiratory disease such as asthma; inflammation of the lung,and possible long-term damage to thelungs. Thecurrent 1-hour secondary standard is replacedby an 8- hour standard identical tothe new primary standard. Thenew secondary standard willprovide increased protection to thepublic welfare against 03-induced effects on vegetation, such

as agricultural crop loss, damage to forests and ecosystems, and visible foliar injuryto sensitive species. EFFECTIVE DATE: This rule is effective September 16, 1997. ADDRESSES: A docket containing information relating totheEPA's review ofthe03primary and secondary standards (DocketNo. A-95-58)is available forpublic inspection in the Central Docket Section oftheU.S. Environmental Protection Agency, South Conference Center, Room 4,401 M St., SW., Washington, DC.This docket incorporates the docket from the previous review ofthe03 standards (DocketNo. A-92-17) and the docket established for the air quality criteria document (DocketNo. ECAO-CD-92- 0786). The docket may be inspected between 8 a.m. and 3 p.m. on weekdays, and areasonable fee may be charged for copying. The information in the docket constitutes the complete basis for the decision announced in this final rule. For the availability ofrelated information, see "SUPPLEMENTARY INFORMATION." FOR FURTHER INFORMATION CONTACT: David McKee, MD-15, Air Quality Standards and Strategies Division, Office ofAir Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC27711; telephone: (919) 541- 5288; e-mail: mckee.dave @epamail.epa.gov. SUPPLEMENTARY INFORMATION: Availability ofRelated Information

Certain documents are available from the U.S. Department ofCommerce, National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161. Available documents include: (1) Air Quality Criteria for 03 and Other Photochemical Oxidants ("Criteria Document") (three volumes, EPA/600/P-93-004aF through EPA/600/ P-93-004cF, July 1996, NTIS # PB-96- 185574, $169.50 paper copy, $58.00 microfiche). (2) The Review ofthe National Ambient Air Quality Standards for 03: Assessment ofScientific and Technical Information ("StaffPaper")(EPA-452/R96-007, June 1996, NTIS # PB-96- 203435, $67.00 paper copy and $21.50 microfiche). (Add a $3.00 handling charge per order.)

A limited number ofcopies ofother documents generated in connection with this standard review, such as documents pertaining to human exposure and health risk assessments, and vegetation exposure, risk,and benefits analyses can be obtained from: U.S. Environmental Protection Agency Library (MD-35), Research Triangle Park, NC27711, telephone (919) 541- 2777. These and other related documents are also available for inspection and copying in the EPA docket identified under "ADDRESSES".

Electronic Availability

The StaffPaper and human exposure and health risk assessment support documents are now available on the Agency's Office ofAir Quality Planning and Standards (OAQPS) Technology Transfer Network (TTN) Bulletin Board System (BBS) in the Clean Air Act Amendments area,under Title I, Policy/ Guidance Documents. To access the bulletin board, a modem and communications software are necessary. To dial up, set your communications software to 8 data bits, no parity and

one stop bit. Dial (919) 541-5742 and follow the on-screen instructions to register for access. After registering, proceed to choice "<T> Gateway to TTN Technical Areas", then choose "<E> CAAA BBS". From the main menu, choose "<1> Title I: Attain/Maint of NAAQS", then "<P> Policy Guidance Documents." To access these documents through the World Wide Web, click on "TTN BBSWeb", then proceed to the Gateway to TTN Technical areas, as above. Ifassistance is needed in accessing the system, call the help desk
at (919) 541-5384 in Research Triangle Park, NC. Implementation Strategy for Revised Air Quality Standards

On Wednesday, July 16, 1997, President Clinton signed a memorandum to the Administrator specifying his goals for the implementation ofthe 03 and PM standards. Attached to the President's memorandum is a strategy prepared by

an interagency Administration group outlining the next steps that would be necessary for implementing these standards. The EPA willprepare guidance and proposed rules consistent with the President's memorandum. Copies ofthe Presidential document are available in paper copy by contacting the U.S. Environmental Protection Agency Library atthe address under "Availability ofRelated Information" and in electronic form as discussed above in "Electronic Availability."

The following topics are discussed in thispreamble: I.Background

A. Legislative Requirements B.Related Control Requirements C.Review ofAirQuality Criteria and

Standards for03 D. Summary ofProposed Revisions tothe

03Standards II.Rationale for thePrimary 03 Standard

A. Introduction B.Elements ofthePrimary Standard C.Communication ofPublic Health

Information III. Rationale forthe Secondary 03 Standard

A. Introduction B.Need forRevision ofCurrent Secondary

Standard C.Final Decision onthe Secondary

Standard IV. Other Issues

A. Cost Considerations B.Margin ofSafety C.Comment Period D. 1990 ActAmendments V. Technical Changes to Part 50 VI.Revisions toAppendices D,E,and H VII.Regulatory and Environmental Impact Analyses 

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A. Executive Order 12866 B. Regulatory FlexibilityAnalysis C. Impact ofReporting Requirements D.Unfunded Mandates Reform Act E.Environmental Justice F. Submission toCongress and Comptroller

General VIII. Response to Petition forAdministrator Browner's Recusal IX. References

I. Background

A. LegislativeRequirements

Two sections ofthe 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 ofall identifiable effects on public health or welfare which maybe expected from the presence of [a] pollutant in the ambient air ***""

Section 109 (42U.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 ofwhich in the judgment ofthe Administrator, based on [the] criteria and allowing an adequate margin ofsafety, are requisite to protect the public health." The margin ofsafety requirement was intended to address uncertainties associated with inconclusive scientific and technical information available atthe time of standard setting, as well as to provide a reasonable degree ofprotection against hazards thatresearch has not yet identified. Both kinds ofuncertainties

are components oftherisk associated with pollution at levels below those at which human health effects can be said
to occur with reasonable scientific certainty. Thus, by selecting primary standards that provide an adequate margin ofsafety, the Administrator is seeking not only to prevent pollution levels that have been demonstrated to be harmful but also to prevent lower pollutant levels that she finds maypose

an unacceptable risk ofharm, even ifthe risk is not precisely identified as to nature or degree. The Act does not require the Administrator to establish a primary NAAQS at a zero-risk level but rather at alevel that reduces risk sufficiently so as to protect public health with an adequate margin of safety. The selection ofany particular approach to providing an adequate margin ofsafety is a policy choice left specifically to the Administrator's judgment.LeadIndustries Association

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

A secondary standard, as defined in section 109(b)(2), must "specify alevel ofair quality the attainment and maintenance ofwhich in thejudgment ofthe Administrator, based on [the] criteria, [are] requisite to protect the public welfare from any known or anticipated adverse effects associated with thepresence of [the] pollutant in the ambient air." Welfare effects as defined in section 302(h) (42 U.S.C. 7602(h)) include, but are not limited to, "effects on soils, water, crops, vegetation, manmade materials, animals, wildlife, weather, visibility, and climate, damage to and deterioration ofproperty, and hazards to transportation, as well as effects on economic values and on personal comfort and well-being."
Section 109(d)(1) ofthe Act requires periodic review and, if appropriate, revision ofexisting air quality criteria and NAAQS. Section 109(d)(2) requires appointment ofan independent scientific review committee to review criteria and standards and recommend

new standards or revisions ofexisting criteria and standards, as appropriate. The committee established under section 109(d)(2) is known as the Clean Air Scientific Advisory Committee (CASAC), a standing committee of EPA's Science Advisory Board.

B. Related ControlRequirements

States areprimarily responsible for ensuring attainment and maintenance of ambient air quality standards once EPA has established them. Under section 110 ofthe Act (42U.S.C.7410) and related provisions, States are to submit, for EPA approval, State implementation plans (SIP's)that provide for the attainment and maintenance ofsuch standards through controlprograms directed to

sources ofthe pollutants involved. The States, in conjunction with EPA, also administer the prevention ofsignificant deterioration programs (42U.S.C.7470- 7479) for these pollutants. In addition, Federal programs provide for nationwide reductions in emissions of these and other air pollutants under Title II ofthe Act (42U.S.C. 7521-7574), which involves controls for automobile, truck, bus, motorcycle, nonroad engine, and aircraft emissions; the new source performance standards under section 111 (42U.S.C. 7411); and the national emission standards for hazardous air pollutants under section 112 (42U.S.C. 7412). C.Review of Air QualityCriteria and Standards for03
The last review of03 air quality criteria and standards was completed in March 1993 with notice ofa final decision not to revise the existing primary and secondary standards (58 FR 13008). The current primary and secondary standards are each set at a level of0.12 ppm, with a 1-hour averaging time and a 1-expectedexceedance form, such that the standards are attained when the expected number ofdays per calendar year with maximum hourly average concentrations above 0.12ppm is equal
to or less than 1, averaged over 3 years (as determined by 40CFRpart 50, Appendix H). 1

The EPA initiated this current review ofthe air quality criteria and standards in August 1992 with the development of

arevised Air Quality Criteria Document for 03 and Other Photochemical Oxidants, henceforth the "Criteria Document." Several workshops were held by EPA's National Center for Environmental Assessment (NCEA) to discuss health and welfare effects information during the summer and fall of 1993. An external review draft ofthe Criteria Document made available to the public and to the CASACin the spring of 1994was reviewed at apublic CASACmeeting held on July 20-21, 1994. Based on comments made at the meeting,NCEA staffprepared a second external review draft, which was reviewed at a public CASAC meeting on March 21-22, 1995. At the same meeting, the CASAC also reviewed draft portions ofa staffpaper prepared by the OAQPS, Review ofNational Ambient AirQuality Standards for 03: Assessment ofScientific and Technical Information (henceforth, the "Staff Paper"), focusing on health effects and the primary NAAQS. 2 Taking into
account CASAC and public comments, staffrevised both documents and made

new drafts available for public and CASACreview during the summer of 1995. The OAQPS staffalso prepared and made available draft portions ofthe StaffPaper focusing on welfare effects and the secondary standard.

1A more complete history ofthe 03 NAAQS is presented in section II.B. ofthe Office ofAir QualityPlanning and Standards StaffPaper, Review ofNational Ambient Air Quality Standards for 03: Assessment ofScientific and Technical Information (U.S. EPA, 1996b).

2The StaffPaper evaluates policy implications of
thekey studies and scientific information in the CriteriaDocument, identifies critical elements that EPA staffbelieves should be considered, and presents staff conclusions and recommendations of suggested options forthe Administrator's consideration. 

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A public CASAC meeting was held on September 19-20, 1995, at which time CASAC came to closure in its review of the draft Criteria Document and the primary standard sections ofthe draft StaffPaper. In a November 28, 1995 letter from the CASAC chairto the Administrator, CASAC advised that the final draft Criteria Document "provides

an adequate review ofthe available scientific data and relevant studies of03 and related photochemical oxidants" (Wolff, 1995a). Further, in aNovember 30, 1995 letter, CASAC advised the Administrator that the primary standard portion ofthe draft Staff Paper "provides an adequate scientific basis for making regulatory decisions concerning a primary 03 standard" (Wolff, 1995b). The final Criteria Document (U.S. EPA, 1996a) reflects CASAC and public comments received at and subsequent to the September 1995 CASAC meeting.

Based on comments on the StaffPaper from the September 1995 CASAC meeting, revisions were made to the secondary standard sections ofthe Staff Paper, which were reviewed at a public CASAC meeting held on March 21, 1996. At that meeting and in a subsequent letter to the Administrator, CASAC concluded that the secondary standard sections ofthe draft StaffPaper "provide an appropriate scientific basis for making regulatory decisions concerning a secondary 03 standard" (Wolff, 1996). The final Staff Paper (U.S. EPA, 1996b) reflects CASAC and public comments received at and subsequent to the September 1995 and March 1996 meetings on theprimary standard and secondary standard sections, respectively.

On November 27, 1996 EPA announced its proposed decision to revise the NAAQS for 03 (61 FR 65716, December 13, 1996, hereinafter "proposal") as well as its proposed decision to revise the NAAQS for particulate matter (PM). In the proposal, EPA identified proposed revisions, based on the air quality criteria for 03, and solicited public comments on alternative primary and secondary standards and on the proposed forms of the standards.

To ensure thebroadest possible public input on the 03 and PM proposals, EPA tookextensive and unprecedented steps to facilitate the public comment process beyond the normal process ofproviding an opportunity to request a hearing and receiving written comments submitted to therulemaking docket. The EPA established anational toll-free telephone hotline to facilitate public
comments on the proposed revisions to 

### the 03 and PMNAAQS, and onrelated notices dealing with theimplementation ofrevised 03 and PM standards, as well

as asystem for thepublic to submit comments on the proposals electronically viathe Internet. Over 14,000 calls and over4,000 electronic mail messages were received through these channels. The public could also

access key supporting documents (includingtheCriteria Document, Staff Paper, related technical documents and fact sheets) via theInternet.

The EPA alsoheld several public hearings and meetings acrossthe country toprovide direct opportunities for public comment on the proposed revisions to the03 and PM NAAQS and to disseminate information to thepublic about theproposed standard revisions. On January 14 and 15, 1997, EPAheld concurrent, 2-day public hearings in Boston, MA,Chicago, IL, and SaltLake City, UT. A fourth public hearing, which focused primarily on PM monitoring issues, washeld in Durham, NC on January 14, 1997. Over400 citizens and organizations testified duringthese public hearings. EPA also held two national satellite telecasts to
answerquestions on the standards and participated in meetings sponsored by the Air and WasteManagement Association on the proposed revisions to the standards at morethan 10 locations acrossthe country. Beyond that, several EPAregional offices held public meetings and workshops and participated in hearings that States and cities held around thecountry.

As a result ofthis intensive effortto solicitpublic input, over50,000 written and verbal comments were received on the proposed revisions tothe 03 

### NAAQS by theclose ofthe public comment period on March 12, 1997. The major issuesraised in the comments arediscussed throughout the preamble ofthis finalrule. A comprehensive summary ofall significantcomments, along with EPA's response to such comments (hereafter "Response toComments"), can befound in the docket for this rulemaking (DocketNo. A-95-58).

The focus ofthis current review ofthe airquality criteria and standards for 03 

### and related photochemical oxidants is

on public health and welfare effects associated with exposure to ambient levels oftropospheric 03. Tropospheric 03 is chemically identical to stratospheric 03, which is produced 

### miles above theearth's surface and provides a protective shield from excess ultraviolet radiation. In contrast, tropospheric 03 at sufficient 

### concentrations hasbeen associated with harmful effects due toits oxidative properties and its presence in the air that people and plants take up during respiratory processes. Ozone is not emitted directly from mobile or stationary sources but, like other photochemical oxidants, commonly exists in the ambient air as an atmospheric transformation product. Ozone formation is theresult of chemical reactions ofvolatile organic compounds (VOC), nitrogen oxides (NO.),and oxygen in thepresence of sunlight and generally atelevated temperatures. A detailed discussion of atmospheric formation, ambient concentrations, and health and welfare effects associated with exposure to 03

can be found in the Criteria Document and in the StaffPaper.

D. Summary ofProposedRevisionsto the 03 Standards

For reasons discussed in the proposal, the Administrator proposed to replace the current 1-hour primary standard for 03 with an 8-hour standard set at 0.08
ppm, which would be met at an ambient air quality monitoring site when the 3-
year average ofthe annual third-highest daily maximum 8-hour average 03 concentration is less than or equal to 0.08ppm. The proposal solicited
comments on alternative 8-hour standards set at 0.09 ppm, which generally represents the continuation of the present level ofprotection, and 0.07 ppm, which would be highly precautionary in nature, as well as on retaining the current primary standard. The proposal also solicited comments

on alternative forms ofthe standard, specific data handling and rounding conventions used in determining attainment with the standard, and issues related to the communication ofpublic health information.

With regard to the secondary standard, the Administrator proposed to replace the current 1-hour secondary standard with one oftwo alternative standards: either one set identical to the proposed primary standard or a new seasonal standard expressed as a sum of hourly 03 concentrations greater than or equal to 0.06 ppm, cumulated over 12 hours per day during the consecutive 3- month period ofmaximum concentrations during the 03 monitoring
season, set at a level of25 ppm-hour. The proposal solicited comments on these two alternatives, aswell as on specific issues related to the form ofa seasonal standard and on an enhanced rural air quality monitoring network. 

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II. Rationale for the PrimaryStandard

A. Introduction

1. Overview

.This notice presents the Administrator's final decision regarding the need to revise the current primary 03 standard, and, more specifically, regarding the averaging time, level, and form ofa new primary standard to replace the current 1-hour standard. This decision isbased on a thorough review, in the Criteria Document, ofthe scientific information on human health effects associated with exposure to ambient levels of03, including evaluation ofkey studies published through 1995. This decision also takes into account:

(1) StaffPaper assessments ofthe most policy-relevant information in the Criteria Document and analyses of human exposure and risk, presented in the StaffPaper and supporting technical reports.

(2) CASAC advice and recommendations, asreflected in discussions ofdrafts ofthe Criteria Document and StaffPaper atpublic meetings, in separate written comments, and in CASAC's letters to the Administrator.

(3) Public comments received during the development ofthese documents, either in connection with CASAC meetings or separately.

(4) Extensive public comments received on the proposal regarding the primary 03 standard.

After taking this information and
comments into account and for the

reasons discussed below in this unit, the Administrator concludes that revisions
to the current primary standard to provide increased public health protection are appropriate at this time to protect public health with an adequate margin ofsafety. Further, the Administrator determines that it is appropriate to establish a revised 8- hour, 0.08 ppm primary standard with

aform based on the 3-year average of the annual fourth-highest daily maximum 8-hour average 03 concentrations measured at each monitor within an area.

As discussed more fully below in this unit, the rationale for the final decision regarding the 03 primary NAAQS includes consideration of:

(1) Health effects information to inform judgments as to the likelihood that exposures to ambient 03 result in adverse health effects for exposed individuals.

(2) Insights gained from human exposure and risk assessments to provide abroader perspective for judgments about protecting public health from the risks associated with 03 exposure. (3) Specific conclusions with regard
to the elements ofa standard (i.e., averaging time, level, and form) that, taken together, would be appropriate to protect public health with an adequate margin ofsafety. (4) Alternative views ofthe significance ofthe effects and factors to be considered in policyjudgments about the appropriate elements ofthe standard.

The health effects information and human exposure and risk assessments

were summarized in the proposal and

are only briefly outlined below. More fully discussed in the followingunits of this preamble is the Administrator's rationale, in light ofkey issues raised in public comments, for concluding that it is appropriate to revise the specific elements ofthe current standard including averaging time (Unit II.B.I.), level (Unit II.B.2.), and form (Unit II.B.3.). Finally, the related subject of the communication ofpublic health information, and the public comments received on this subject, are summarized in Unit II.C.

2. Health effects information.The last review ofthe air quality criteria for 03 included an evaluation ofkey studies published through early 1989 and was the basis for EPA's 1993 decision not to revise the primary standard at thattime. However, in recognition ofthe large number ofnew studies, particularly on 6- to 8-hourexposures to 03,that had become available since early 1989 but had not undergone rigorous assessment and review by CASAC, the EPA made clear in the 1993 final decision notice that it would proceed with the next review as rapidly aspossible to consider this new information. Thus, the current review ofhealth effects information focused on a large body ofinformation published since 1989 that would lead to

amore informed decision than was possible in 1993 asto whether an 03 primary standard with a longer averaging time was appropriate to protect public health.

The proposal reviewed thehuman health effects associated with exposure to ambient levels of03based on an integrative assessment ofhuman clinical, epidemiological, and animal toxicological studies available through 1995, as assessed in the Criteria Document and StaffPaper. Based on this information, an array ofhealth effects has been attributed to short-term (I to 3 hours),prolonged (6 to 8 hours), and long-term (months to years) exposures to 03. Acute health effects 3 are induced by short-term exposures to 03 (observed at concentrations as low as 0.12 ppm), generally while individuals are engaged in moderate or heavy exertion, and by prolonged exposures to 03 (observed at concentrations as low as 0.08 ppm), typically while individuals are engaged in moderate exertion. Moderate exertion levels are more frequently experienced by individuals than heavy exertion levels. The acute health effects include transient pulmonary function responses, transient respiratory symptoms, effects

on exercise performance, increased airway responsiveness, increased susceptibility to respiratory infection, increased hospital admissions and emergency room visits, and transient pulmonary inflammation. Based in particular on new information available since the last review ofthe air quality criteria for03 was completed, such
acute health effects have been observed followingprolonged exposures at moderate levels ofexertion at concentrations of03 as low as 0.08 ppm. Groups at increased risk of experiencing such effects include active children and outdoor workers who regularly engage in outdoor activities and individuals with preexisting respiratory disease (e.g., asthma, chronic obstructive lung disease). Further, it is recognized that some individuals are unusually responsive to 03 and may experience much greater functional and symptomatic effects from exposure to 03 than the average individual.

With regard to chronic health effects4

, the collective data from studies of laboratory animals and human populations have many ambiguities, but provide suggestive evidence ofsuch effects in humans. It is clear from toxicological data that 03-induced lung injury isroughly similar across species (includingmonkeys, rats, and mice) with responses that are concentration dependent. The currently available information provides atleast a biologically plausible basis for consideringthe possibility thatrepeated inflammation associated with exposure to 03 over alifetime may result in sufficient damage to respiratory tissue such that individuals later in life may experience a reduced quality oflife,

3 "Acute health effects" of03 are defined as those effects induced by short-term and prolonged
exposures to 03. Examples ofthese effects are functional, symptomatic, biochemical, and physiologic changes.

4 "Chronic health effects" of03 are defined as those effects induced by long-term exposures to 02. Examples ofthese effects are structural damage to lung tissue and accelerated decline in baseline lung function. 

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although such relationships remain highly uncertain.

EPA's consideration ofthishealth effects information necessarily included judgments with respect to when these physiological effects become so significant that they should be regarded

as adverse to the health ofindividuals experiencing the effects. In making thesejudgments, the Administrator looked to guidelines published by the American Thoracic Society (1985) and the advice ofCASAC. The proposal summarized the criteria and reasoning for EPA'sjudgments on this issue,upon which the CASAC panel expressed a

consensus view that these "criteria for the determination ofan adverse physiological response was reasonable" (Wolff, 1995b). The criteria take into
account the degree ofseverity ofthe effects; the likelihood that the effects would interfere with normal activity for individuals with impaired respiratory systems or active healthy individuals; the likelihood that the effects would result in additional or more frequent use ofmedication, medical treatment, or emergency room visits for individuals with impaired respiratory systems; and the implications ofsingle orrepeated

occurrences ofthe effects for an individual.

Some commenters raised concerns regarding the criteria used byEPA to make determinations as to when effects become adverse, citing CASAC's closure letter (Wolff, 1995b) stating that "there

was considerable concern that the criteria for grading physiological and clinical responses to 03 was confusing if not misleading." These concerns with the draft criteria were discussed at length during apublic CASAC meeting, resulting in very specific agreements as to how to revise the draft criteria so as to be consistent with CASAC's advice (Transcript ofCASAC meeting, September 19-20, 1995, pp. 242-248). Having reached such specific agreement, CASAC advised that further review ofthe final version ofthese criteria, subsequently incorporated in both the final Criteria Document and StaffPaper, was unnecessary.

Other commenters have questioned whetherjudgments made in this review

are consistent with those made in the last review with regard to when physiological and clinical effects become adverse to individuals experiencing such effects. Specifically, the commenters focused on the judgment stated in the 1993 final decision notice (58 FR 13008, March 9, 1993) that "lesser effects associated with [1-to 3-hour] exposure to 03 in the range of0.12 ppm to 0.15ppm observed in the controlled human studies did not constitute adverse effects forpurposes ofsection 109 ofthe Act." The "lesser effects" referred to in that notice involved responses ofa maximum decrease in lung function [as measured by forced expiratory volume in 1 second (FEV)] offrom 9 percent to 16 percent for the most sensitive individuals exposed in this range, with few, if any, symptoms. The EPA notes that this judgment is, in fact, consistent with judgments presented in the 1996 proposal, which identify moderate and large lung function decrements (as reflected in EPA's risk assessment by FEV1 decreases of> 15 percent and > 20 percent, respectively, with the most sensitive individuals experiencing FEV1 decreases as large as 40percent to 50 percent at 6-to 8-hour exposures in the range of0.08 ppm to 0.10 ppm in controlled human studies), and moderate to severe symptoms asbeing adverse.

3. Exposureand risk assessments.To putjudgments about health effects that

are adverse for individuals into a broader public health context, EPA conducted quantitative assessments to estimate 03 exposures and related risks for the general population and two atrisk groups, "outdoor children" and "outdoor workers," livingin nine representative U.S. urban areas. This broader context included consideration,
to the extent possible, ofthe size ofthe particular population groups identified

as atrisk for various effects, the estimated number ofpeople within atrisk groups likely to experience 03- related adverse effects, the estimated number ofoccurrences ofsuch effects, and the estimated number ofpeople who would experience exposures of

concern5 associated with various air quality scenarios representing attainment ofthe current and alternative 8-hour standards. Consideration was also given to thekind and degree of uncertainties inherent in assessing such exposures and risks. Such considerations provided abasis for judgments discussed in the proposal about the levels ofexposure and risk associated with the current and alternative standards, which helped inform judgments about the adequacy of public health protection afforded bythe
current and alternative standards.

Risk estimates were developed for those effects for which sufficient concentration-response information was available from studies evaluated in the

5"Exposures ofconcern" refer throughout to exposures atand above 0.08 ppm, 8 hour average, at which a range ofhealth effects have been observed in controlled human studies, butfor which data were too limited to allow for quantitative risk assessment. Criteria Document, including adverse lungfunction and respiratory symptom responses. In a separate analysis, excess respiratory hospital admissions for individuals with asthma associated with attainment ofalternative standards were also estimated, using arisk model for thishealth endpoint based on the results ofan epidemiological study in New York City (Thurston et al., 1992) for which adequate air quality information was available to assess population risk6

. These quantitative risk estimates (forthat subset ofO3-related effects for which information is sufficient to conduct such quantitative analyses) add to our understanding of the broader array ofhealth effects that

are associated with exposure to 03but for which quantitative risk estimates could notbe developed.

The methodology, results, and key observations from these assessments

were presented in theproposal. The EPA believes, and CASAC concurred, that the models selected to estimate exposure and risk were appropriate and that the methods used to conduct the health risk assessment for adverse lung function and respiratory symptom responses represent the state ofthe art. Nevertheless, the Administrator and CASACrecognized thatthere are many uncertainties inherent in such analyses, and that not all uncertainties inherent in such analyses could be quantified and reflected in ranges ofrisk estimates (Wolff, 1995b), as discussed in the proposal and thereferenced technical support documents.

The exposure and risk assessments available at the time ofproposal had been conducted to evaluate the 03 exposures and risks associated with attainment ofthe current 1-hour standard and various alternative 8-hour standards under consideration early in the standards review process when the
assessments were initiated. The EPA and CASACrecognized at that timethat additional alternative standards might need to be analyzed later in the review process. Upon deciding to propose a standard with a concentration-based form in the Fall of 1996, EPA staff initiated supplemental analyses to estimate exposures and risks7 for the

6This study is one ofseveral studies, mainly
conducted in the northeastern portion ofthe United States and southeastern Canada, reporting excess daily respiratory-related hospital admissions associated with elevated 03 levels within the general population and, more specifically, for individuals with asthma.

7The analyses were conducted for the at-risk population ofoutdoor children, the group with the highest exposures and risks. Outdoor children are the subset ofchildren between the ages of6 and 18
years old who tend to be active outdoors, and include approximately over 30 percent to 45 

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specific standard to be proposed and alternative standards on which the proposal solicited comment. In conducting these supplemental analyses, several technical changes were made based on insights gained from the initial analyses. 8 The supplemental
assessment (Richmond, 1997) was placed in the docket and on the TTN on February 12, 1997, and its availability

was announced in the Federal Register notice extending thepublic comment period on the proposal, providing the public the opportunity to comment on the supplemental assessment (61 FR 7743, February 20, 1997).

Key observations and results from the initial and supplemental exposure and risk assessments that are most pertinent
to the decision to revise the current primary standard arehighlighted in the following unit, together with discussion ofthekey issues raised in public
comments on the methodology and public health implications ofthese
assessments.

B. ElementsofthePrimaryStandard

In selecting a primary standard for 03, the Administrator must specify: Averaging time, 03 concentration (i.e., level), and form (i.e., the air quality statistic to be used as a basis for determining compliance with the standard). 9 All three ofthese elements

are necessary to define a standard and
to determine the degree ofpublichealth protection afforded by the standard. The proposal outlined the key factors considered in selecting each ofthese elements for theproposed standard, as well as the range ofoptions for each element on which the EPA solicited
comment. The factors reflect an integration ofinformation on acute and chronic health effects associated with exposure to ambient 03;expert judgments on the adversity ofsuch effects for individuals; and policy judgments, informed by air quality and exposure analyses and quantitative risk assessment when possible, as to the point at which risks would be reduced sufficiently to achieve protection of public health with an adequate margin ofsafety.

This approach to selecting aprimary standard was endorsed by CASAC (Wolff, 1995b), particularly through its

percent ofall children in this age group in the nine urban areas analyzed.

8These changes primarily focused on the air quality dataused in the exposure analysis and on the air quality adjustment procedures used to simulate ambient 03 concentrations upon attainment ofalternative standards.

9Thisreview focused onlyon a standard for 03,

as themostappropriate surrogate for photochemical oxidants. advice to the Administrator that "EPA's risk assessments must play a central role in identifying an appropriate level" and its recognition that "the selection ofa specific level and [form] is a policy judgment." Further, it was the

consensus view ofCASAC that the ranges of8-hour average levels (0.07 to 0.09 ppm) and forms (concentrationbased forms that generally allow for I to 5 exceedances) on which the proposal solicited comment were appropriate.

The following discussion focuses primarily on those considerations that

were most influential in the Administrator's final decisions on these elements, taking into account the
comments received on therange of options identified in the proposal. 1.Averagingtime. In proposing to change the averaging time ofthe primary standard from 1to 8 hours, the Administrator was concurring with the unanimous recommendation ofCASAC (Wolff, 1995b) "that the present i-hour standard be eliminated and replaced with an 8-hour standard," and that

more research is needed to resolve uncertainties about potential chronic effects before appropriate consideration

can be given to establishing a long-term (e.g., seasonal or annual) primary standard. The Administrator's proposed decision was supported bythe following key observations and conclusions: (1) The i-hour averaging time specified in the current NAAQS was originally selected primarily on the basis ofhealth effects associated with short-term (i.e., 1- to 3-hour)exposures, with qualitative consideration given to preliminary information on potential associations with longer exposure periods. (2) Substantial new health effects information available for consideration in this review demonstrates associations between awide range ofhealth effects and prolonged (i.e., 6- to 8-hour) exposures below the level ofthe current 1-hour NAAQS.

(3) Results from the quantitative risk analyses show that attaining a standard with a i-hour averaging time reduces the risk ofexperiencing health effects associated with both i-hour and 8-hour exposures. Likewise, attaining an 8- hour standard reduces the risk of experiencing health effects associated with both 8-hour and i-hour exposures. Thus, reductions in risks from both short-term and prolonged exposures can be achieved through a primary standard with an averaging time ofeither 1 or 8 hours. As a result, establishment ofboth i-hour and 8- hour standards would not be necessary to reduce risks associated with the full range ofobserved acute health effects. (4) The 8-hour averaging timeis more directly associated with health effects of

concern at lower 03 concentrations than is the 1-hour averaging time. It was thus the consensus ofCASAC "that an 8- hour standard was more appropriate for

ahuman health-based standard than a 1-hour standard." (Wolff, 1995b)

(5) While there is alarge animal toxicology database providing clear evidence ofassociations between long

### term (e.g., from several months toyears) exposures and lungtissue damage, with additional evidence ofreduced lung 

### elasticity and accelerated loss oflung function, there is no corresponding evidence for humans. Moreover, the 

### state ofthe science hasnotprogressed sufficiently topermit quantitative extrapolation ofthe animal-study findings tohumans. Thus,the Administrator concluded that consideration ofa separate long-term primary 03 standard is not appropriate
atthis time. As discussed below, however, the Administrator considered the possibility oflong-term effects in selecting the level ofan 8-hour standard, which will provide protection against such effects to the extent they may occur in humans, bylowering overall air quality distributions and, thus,reducing cumulative long-term exposures.

The public comments reflect broad support for a standard with an 8-hour averaging time, either alone or in conjunction with a 1-hour standard. This support was typically based on references to: (1) Evidence ofhealth effects from 6-
to 8-hour exposures to 03 concentrations down to 0.08 ppm, which are lower than those concentrations thathave induced such effects after 1- to 3-hour exposures, and which are lower than the 0.12 ppm level ofthe current standard.

(2) Analyses indicating that an 8-hour standard would limitboth 1- and 8- hour exposures. (3) CASAC's unanimous agreement that the current 1-hour standard should be replaced by an 8-hour standard. In consideringthe adequacy ofthe current 1-hour standard alone in light ofthe health effects evidence, some commenters have highlighted the
statement in the Criteria Document that there is "strong evidence that ambient exposures to 03 can cause significant exacerbations ofpreexisting respiratory disease in the general public at concentrations below 0.12ppm." (U.S. EPA, 1996a, p. 7-171)

Commenters expressing support for

an 8-hour averaging time included not onlythose who supported a level of public health protection consistent with 

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or greater than that reflected by EPA's proposed standard, but also many who disagreed for various reasons with the need for increased public health protection beyond that provided by the
current standard. Ofthose supporting an 8-hour averaging time but not supporting the need for increased protection, some expressed the view that the averaging time ofahealth-based standard should be consistent with the exposures ofmost concern, while others

were simply neutral between the choices ofretaining the current 1-hour standard and replacing it with an "equivalent" 8-hour standard.

The EPA agrees with the considerations raised by those commenters who favor an 8-hour standard. Further, in considering the appropriateness ofan 8-hour standard

as compared to a 1-hour standard, EPA also notes the results ofits exposure and risk assessments which show variability

across the nineurban areas analyzed with regard to the extent to which the
current 1-hour standard, and alternative 8-hour standards, limit 8-hour exposures ofconcern and associated risks ofadverse health effects. As noted in the proposal and in the supplemental risk assessment, there is much greater variability across urban areas, particularly in looking at the seven current nonattainment areas examined, in the extent to which the current 1- hour standard limits such exposures of

concern and risks than for the alternative 8-hour standards. For example, the updated assessment estimates that the current 1-hour standard results in 8-hour exposures of

concern at and above 0.08 ppm'0 that vary by almost two orders ofmagnitude

across these areas. In contrast, alternative 8-hour standards atthe proposed level of0.08 ppm result in estimated 8-hour exposures ofconcern and risks that are much more consistent." In EPA's view, the fact that

an averaging time of8hours results in

a significantly more uniformly protective national standard than the
current 1-hour standard is an important

10Moreprecisely, exposures at and above 0.08

ppm refers to estimates ofexposures to 03 concentrations >0.081 ppm from the exposure assessment.

11In terms ofthe percent ofoutdoor children estimated to be exposed to 03 concentrations at and above 0.08 ppm while engaged in moderate exertion, the current 1 hour standard results in a range across the seven nonattainment areas of approximately 0.3percent to 24percent of such children, whereas alternative 8 hour standards, at the proposed level of0.08 ppm, result in a significantly more uniform degree ofprotection, with ranges of approximately 2 percent to 9 percent, third-highest concentration form, and 3 percent to 11 percent, fifth-highest concentration form, across the areas. public health policy consideration that supports the selection ofan 8-hour averaging time.

Those commenters who did not support EPA's proposal for an 8-hour averaging time generally did not support any revision to the current standard. These commenters predominantly focused on two basicpoints: The generally improvingtrends in air quality under the current standard and associated air quality management programs, which, commenters argued, suggest that there is no need forEPA to adopt any more stringent standard; and observations made in CASAC's closure letter (Wolff, 1995b) with regard to EPA's risk assessment not demonstrating any "bright line" threshold ofeffects or acceptable risk. With regard to the first issue,EPA agrees that air quality trends are improving as a consequence ofongoing control programs designed to attain the
current NAAQS. The EPA does not, however, believe that these trends relieve the Agency ofits statutory mandate to review and, ifappropriate, revise the NAAQS on the basis ofthe best available scientific evidence to establish standards that protect public health with an adequate margin of safety. The fact that current control programs areresulting in progress toward improving air quality does suggest that it is important to ensure that such progress is maintained during any transition to a revised standard.

With regard to the second issue,
commenters very frequently quoted from the CASAC closure letter (Wolff, 1995b) stating "that there is no bright line' which distinguishes any ofthe proposed standards (eitherthe level or the number ofallowable exceedances)

asbeing significantly more protective of public health" and that "the selection of

a specific level and number ofallowable exceedances is a policyjudgment." These commenters have variously interpreted these statements as a CASAC consensus that the differences in the public health protection afforded by any ofthe alternative standards were too small to be important from a public health perspective, not statistically significantly different, or simply not different atall. Based on these interpretations, the commenters argued that itis not appropriate to revise the standard in any way, because arevised standard would result in disruption to ongoing programs, additional planning requirements, and increased implementation costs, but would provide no or only very little improvement in public health protection. The EPAbelieves that these commenters have misconstrued or too narrowly interpreted CASAC's advice to the Administrator bynot considering the entire range ofviews and recommendations included in its closure letter. Specifically, CASAC began its summary ofrecommendations
to the Administrator (Wolff, 1995b) by stating that "[t]he Panel was in unanimous agreement that thepresent 1-hour standard be eliminated and replaced with an 8-hour standard." This agreement was based on "the

consensus ofthe Panel that an 8-hour standard was more appropriate for a human health-based standard than a 1- hour standard." Thus, CASAC was unequivocal in its advice to the Administrator with regard to which averaging timethe health effects evidence more strongly supports. While

some commenters have also quoted
statements byindividual Panel members atCASAC meetings suggesting that choosing between a 1- or 8-hour averaging timeis a "policy" choice, these individual statements during the

course ofCASAC's review do not contradict nor supersede the clear and unanimous agreement ofCASAC on averaging time as conveyed to the Administrator in its closure letter.

In considering these comments, EPA also believes itis important to put into

apublic health perspective CASAC's observations about the differences among alternative standards in protecting thepublic from the health effects that were quantitatively estimated in EPA's risk assessment. In the closure letter (Wolff, 1995b), CASAC observed that "the differences in the percent ofoutdoor children *** responding between the present standard and the most stringent proposal *** are small and their ranges overlap for all health endpoints." Most importantly, EPA notes that the primary standard would provide protection from

abroader array ofhealth effects than it

was possible to consider in its quantitative risk assessment. This perspective is clearly shared in particular by those CASACpanel members who personally favored alevel

orrange oflevels that included the proposed level of0.08ppm, in that the closure letter characterizes their views

asreflecting, in part, their "concern over the evidence forchronic deep lung inflammation from the controlled human and animal exposure studies." While therisk ofthis effect, as well as other effects related to 6- to 8-hour exposures in the Criteria Document and StaffPaper (includingincreased airway responsiveness, impairment ofhost 

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defenses suggesting an increased susceptibility to respiratory infection, and increased emergency room visits, doctor visits, and frequency of medication useby individuals with impaired respiratory systems) could not be quantitatively estimated in EPA's risk assessment, EPAbelieves that consideration ofthese effects is nevertheless important in makingpublic health policyjudgments.

Further, in interpreting CASAC's statements on EPA's risk assessment report (Whitfield et al., 1996) that there is no "bright line" which distinguishes any ofthe standards as being "significantly" more protective, and that the "ranges overlap," EPA notes that there are statistically significant differences in the estimated risks for the standards analyzed with 1-and 5- exceedance forms. This information was presented to CASAC at its September 1995 meeting (CASAC meeting transcript, September 19-20, 1995, pp. 108-109). Further, EPA again notes that whether onejudges the differences to be significant or small can depend on whether one focuses on percentages, as CASAC's letter did, or on total numbers oftimes that children or other at-risk individuals experience such effects. The overlap in the ranges ofrisk referred to in the CASAC letterreflect differences amongurban areas used in EPA's risk analysis (e.g., air quality, exposure patterns, environmental factors), not random uncertainties in risk estimates within any given urban area. Thus, the fact thattheranges overlap does not

mean that there are no real or statistically significant differences in protection among alternative standards. To the extent that the quoted statements from CASAC's closure letter are read as implying that CASAC considered the differences not to be statistically significant (or that there are no differences at all in the protection afforded by the alternative standards), EPA disagrees with that reading.

Another group ofcommenters, while supporting an 8-hour standard, specifically opposed replacing the
current i-hour standard with an 8-hour standard, but favored instead both 8- hour and i-hour standards. These
commenters generally felt that agreater degree ofpublic health protection than that provided by the proposed standard

was warranted, and that standards based

on both averaging times were necessary to provide the requisite protection from 1- and 8-hour exposures ofconcern. These commenters generally argued that

an 8-hour standard alone could still allow forhigh i-hour exposures of
concern, or that the retention ofthe
current i-hour standard was critical to maintaining current pollution control

measures. As an initial matter, EPA is delaying revocation ofthe i-hour standard to ensure an effective transition to the 8-hour standard, as discussed in Unit II.B.4 ofthis preamble. While EPA agrees that it is possible that an 8-hour standard alone could allow for high i-hour exposures ofconcern, at and above 0.12 ppm,' 2

EPA's exposure assessments estimate that alternative 8-hour standards, atthe proposed level of0.08 ppm but with different forms, would be very effective in limiting i-hour exposures, and generally even more effective in limiting i-hour exposures ofconcern than is the
current i-hour standard. More specifically, theupdated assessment estimates that upon attainment of alternative 8-hour, 0.08 ppm standards, with forms rangingup to the fifthhighest concentration form, less than 0.1 percent ofoutdoor children are likely to experience any i-hour exposures greater than 0.12 ppm while atheavy exertion levels in four to seven ofthe nine urban areas analyzed, whereas this is true for only two ofthe nine areas upon attainment ofthe current i-hour standard. In allnine areas both the
current and alternative 8-hour, 0.08 ppm standards are estimated to limit such exposures to less than 1percent of the outdoor children. Thus, EPA concludes that an 8-hour averaging time does effectively limit both 1- and 8- hour exposures ofconcern.

For the reasons discussed above in this unit, and aftertaking into account the range ofviews expressed in the public comments, the Administrator finds that replacing the current i-hour standard with an 8-hour standard, in combination with the decisions on level and form described below, is appropriate to provide adequate and

more uniform protection ofpublic health from both short-term (1 to 3 hours) and prolonged (6 to 8 hours) exposures to 03 in the ambient air.

2. Level. Taken together, the level and form ofthe standard, for a given averaging time, determine the degree of public health protection afforded bythe standard. Consideration ofthe level of the standard discussed in this unit of the preamble reflects arecognition of this linkage between level and form (discussed separately below in Unit II.B.3).

The Administrator's decision to propose the level ofan 8-hour primary 03 standard at 0.08 ppm, and to solicit

12

TheEPA recognizes this possibility exists especially in the very few areas with unusually "peaky" air qualitypatterns (i.e., in which theratio ofthe 1 and 8 hour average design values for the current andproposed standardsis greater than 1.5). comment on alternative levels, necessarily reflected arecognition, as emphasized by CASAC, that it is likely that "03 may elicit acontinuum of biological responses down to background concentrations" (Wolff, 1995b). Thus, in the absence ofany discernible threshold, it is not possible
to select a level below which absolutely

no effects are likely to occur. Nor does it seem possible, in the Administrator's judgment, to identify a level atwhich it

can be concluded with confidence that

no "adverse" effects are likely to occur. In such acase, as CASAC has advised, the traditional paradigm for standardsetting cannot be applied in the usual way, and assessments ofrisk "must play

a centralrole in identifying an appropriate level" (Wolff, 1995b). Thus, the Administrator's taskbecame one of attempting to select a standard level that would reduce risks sufficiently to protect public health with an adequate margin ofsafety, since azero-risk standard is neitherpossible norrequired by the Act. In this and other NAAQS reviews the CASAChas generally recognized that the selection ofspecific standards requires that the Administrator make public health policyjudgments in addition to determinations ofa strictly scientific
nature. The Administrator's public health policyjudgment on the level of the proposed standard was framed by the considerations discussed above in thisunit and informed by the following key observations and conclusions: (1) During the last review ofthe 03 criteria and standards, CASAC concluded that the existing 1-hour standard set at 0.12 ppm 03provided "little, if any, margin ofsafety," and that the upper end ofthe range of consideration for a 1-hour standard should be 0.12ppm (McClellan, 1989). In addition, several members ofthe CASACpanel recommended that consideration should be given to a lower 1-hour level of0.10 ppm to offer some protection against effects for which there was preliminary information at that time ofassociations with 8-hour exposures to 03.

Regarding currently available evidence of (3-related effects:

(2) Based on a significant body of information available since the last review, there is now clear evidence from human clinical studies that 03 effects of

concern are associated with the 6- to 8- hour exposures tested. Studies were done at 6- to 8-hour exposure levels of 0.12, 0.10, and 0.08 ppm. This includes evidence ofthe following statistically significant responses at 6- to 8-hour exposures to the lowest concentration evaluated, 0.08 ppm 03, atmoderate 

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

on deep inspiration), nonspecific bronchial responsiveness, and biochemical indicators ofpulmonary inflammation. Field studies provide evidence ofsimilar functional and symptomatic effects at ambient 03 exposures that are consistent with the clinical findings. Laboratory animal studies provide supporting evidence of 03-induced biochemical indicators of inflammation and functional changes.

(3) Numerous epidemiological studies have reported excess hospital admissions and emergency department visits for respiratory causes (for asthmatic individuals and the general population) attributed primarily to ambient 03 exposures, including 03 concentrations below the level ofthe
current standard, with no discernible threshold at or below this level. The biological plausibility ofattributing such effects to ambient 03 exposures is supported byhuman studies showing increased nonspecific bronchial responsiveness, laboratory animal studies showingpulmonary changes that decrease the effectiveness ofthe lung's defenses against bacterial respiratory infections, and the reasonable anticipation that 03 exposures also increase the risk of respiratory infections in humans, based

on the many similarities between animal and human defense mechanisms.

(4) Long-term laboratory animal studies suggest that changes in lung biochemistry and structure may, under certain circumstances, become irreversible, although it is unclear whether long-term exposures to ambient 03 levels result in similar chronic health effects in humans.

Regarding the types and severity of 03-induced physiological effects that are considered to be adverse to thehealth
status ofindividuals experiencing such effects:

(5) With regard to lung function decrements and respiratory symptoms, the Administrator recognized that these 03-induced effects are transient and reversible, and concluded that the
extent to which such effects are adverse to thehealth status ofan individual depends upon the severity, duration, and frequency with which an individual experiences such effects throughout the 03 season. While group mean responses in clinical studies at the lowest exposure level tested of0.08 ppm are typically small or mild in nature, responses ofsome sensitive individuals

are sufficiently severe and extended in duration to be considered adverse. This would especially be true to the extent that those individuals likely to experience such effects would, on average, experience them several times

ayear.

(6) With regard to increased hospital admissions and emergency room visits, the Administratorjudged that such effects are clearly adverse to individuals. (7) With regard to pulmonary inflammation, the Administrator recognized that singular occurrences of inflammation are likely reversible and potentially oflittle health significance. On the other hand, based on laboratory animal studies, repeated inflammatory responses associated with exposure to 03 over a lifetime have the potential to result in damage to respiratory tissue such that individuals later in life may experience a reduced quality oflife. Furthermore, there is the possibility that repeated pulmonary inflammatory responses could adversely affect asthmatic individuals byresulting in increased medication use, medical treatment, and/or emergency room visits and hospital admission. Such effects in asthmatics are ofspecial concern particularly in light ofthe growing asthma problem in the United States and the increasing rates ofasthmarelated mortality and hospitalizations, especially amongchildren in general and black children in particular. While 03 has not been shown to cause asthma, the available evidence suggests that 03 may exacerbate asthma. Accordingly, the Administratorjudged that repeated exposures to 03 levels that produce inflammation ofthe lungs are adverse to individuals likely to experience such exposures over longperiods oftime.

The Administrator considered the results ofthe exposure and risk analyses and the following key observations and conclusions from these analyses in putting effects considered to be adverse
to individuals into a broaderpublic health perspective and in making judgments about the level ofa standard that would reduce risk sufficiently to protect public health with an adequate margin ofsafety: (8) The median risk estimates for respiratory functional and symptomatic effects, as well asfor excess hospital admissions ofasthmatics for respiratory
causes, are approximately the same or only marginally smaller for some ofthe 8-hour, 0.09 ppm standard options evaluated (includingthose with forms ranging from 1-to 3-expectedexceedances' 3) as compared to the

13The upper end ofthis range, 3-expectedexceedances, was based on air quality comparisons, since risk estimates were only available atthe time ofproposal for the 1 and 5-expected -exceedance 

### current 1-hour, 0.12ppm NAAQS (risk estimates are somewhat larger for an 8- hour, 0.09 ppm, 5-expected-exceedance standard as compared to those forthe current NAAQS).

(9) Within any given urban area, statistically significantreductions in exposure andrisk associated with respiratory functional and symptomatic effectsresult from alternative 8-hour standards as thelevel changes from 0.09 ppm to 0.08ppm to 0.07 ppm. These reductions represent differences of hundreds ofthousands oftimes that children in thenine urban areas included in the analysis would likely experience such effects undertherange ofalternative standards considered relative to thecurrent standard. There

are significantuncertainties in such quantitative estimates, however, and there isno breakpoint orbright linethat differentiates between acceptable and unacceptable risks within thisrange. (10) Similarly, reductions in hospital admissions forrespiratory causes for asthmatic individuals and the general population areestimated to occurwith each change in the levelofthe standard from0.09 ppm to 0.08ppm to 0.07 ppm. However,hospital admissions for asthmatic individuals associated with ambient 03 exposures within the range ofstandard levels under consideration represent arelatively small fraction of thetotal respiratory-related hospital admissions for asthmatics overthe 03

season.

(11) Estimated exposures to 03 

### concentrations at and above 0.08 ppm (at which increased nonspecific bronchial responsiveness, decreased pulmonary defense mechanisms, and indicators ofpulmonary inflammation have been observed in humans) while engaged inmoderate exertion are essentially zero at the 0.07ppm standard level (with a 1-expectedexceedance form)forthe seven nonattainment areas evaluated in the exposure analyses for the at-risk population ofoutdoor children. Such exposures ofoutdoor children increase to approximately 0to 1percent atthe 0.08ppm standard level,while the estimated range at the0.09 ppm standard level increases to approximately 3to 7percent ofoutdoor children for these areas.

(12) Whilerecognizing that sensitive individuals mayexperience adverse but transienteffects with a standard set at 0.08ppm, noCASAC panel member supported selection of0.07 ppm asthe levelofaprimary standard. Ofthe

forms ofa 0.09 ppm standard. This range is consistent with the results ofthe updated risk
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members who expressed their personal views, three indicated a preference for

alevel of0.08 ppm, one for arange of 0.08 to 0.09 ppm, three for a level of 0.09 ppm (with one ofthe three expressing apreference for selecting a form that would result in equivalent protection to the current standard), and

one for a range of0.09 to 0.10ppm, associated with public advisories for 03 levels at and above 0.07 ppm. Other CASAC panel members also expressed support for such public notices or advisories reflectingpotential effects for extremely sensitive individuals associated with 03 levels as low as 0.07 ppm.

These observations and conclusions resulted in the Administrator focusing in particular on the alternative levels of 0.08 ppm and 0.09 ppm, havingplaced great weight on the fact that none ofthe CASAC panel members expressed support for a standard set below 0.08 ppm. In deciding between these two levels, the Administrator took into
account quantitative estimates ofthe risks associated with attaining standards
set atthese levels for those effects for which such quantitative risk estimates could be developed. Other factors that

were important in the Administrator's proposed decision include:

(1) Quantitative estimates of8-hour exposures ofconcern (i.e., at and above 0.08 ppm) associated with these standard levels.

(2) The consistency ofthe clinical, field, and epidemiological studies, in which effects were seen not only from controlled exposures to 0.08ppm, but also in ambient environments in which 8-hour average 03 concentrations ranged from above to below the 0.08 ppm level.

(3) The importance ofincreased protection for those sensitive individuals who may experience respiratory symptomatic and functional effects at lower 03 concentrations than the population as a whole.

(4) The uncertainties in considering the potentially more serious but as yet uncertain chronic effects.

As discussed above in Unit II.A.3., EPA completed and made available for public comment supplemental exposure and risk assessments subsequent to the proposal. For any ofthe alternative standards considered in the assessment, the new estimates ofexposures at and above 0.08ppm are somewhat higher than those available atthe time of proposal, while the new estimates of risks, for adverse effects including moderate and large decreases in lung function, moderate to severe respiratory symptoms, and hospital admissions for asthmatics, are lower. However, the 

### relative differences in estimated exposures andrisksbetween alternative standard levels remain about the same
as atthe time ofproposal. Thus, while the Administrator's final decision takes into accountthe morerecent assessments, the differences in the quantitative results between the initial and supplemental assessments do not fundamentally alterthe basis for the judgments expressed atthe time of proposal.

To aid in comparing thepublic health protection associated with 8-hour standards at the0.08 ppm and 0.09 ppm levels, observations from theupdated exposure andrisk assessments for all nine urban areas evaluated are summarized below (assumingthethirdhighest concentration form, which was the upper end ofthe range of consideration forforms for the 0.09 ppm level). (1)Thepercentages ofoutdoor children exposed to 03 concentrations 

### at and above 0.08 ppm (at which increased nonspecific bronchial responsiveness, decreased pulmonary defense mechanisms, and indicators of pulmonary inflammation have been observed in humans)while engaged in moderate exertion are estimated to be approximately 3percent at the0.08 ppm standard level, rangingfrom approximately 2percent to 10percent in the nine areas, increasing to approximately 11 percent at a standard level of0.09 ppm, ranging from approximately 7percent to 29percent in the nine areas.

Updated riskestimates in terms ofthe percentages 14 

### and numbers ofoutdoor children estimated to experience various health effects, and the total numbers ofoccurrences ofthese effects in outdoor children, upon attainment of these two alternative standards forall nine urban areas combined 15

### are as follows: (2) Formoderate lung function (FEVI) decreases > 

### 15 percent, approximately 6 percent ofoutdoor children (180,000 children) would experience this effect

one or moretimes peryear (650,000 occurrences) atthe 0.08 ppm standard level, increasing to approximately 8 percent ofoutdoor children (250,000 children and 1,100,000 occurrences) at the 0.09 ppm standard level. (3)Forlarge lung function (FEVI) decreases >20percent, approximately 2

14These updated risk estimates in terms of the percentage ofoutdoor children in the nine urban

areas areroughly comparable to therange of original estimates presented in Table 1 ofthe proposal for 1-and 5-expected -exceedance forms of the standards.

15Approximately 3.1 million outdoor children
reside in these nineurban areas. percent ofoutdoor children (58,000 children) would experience this effect

one or more times per year (100,000 occurrences) at the 0.08 ppm standard level, increasingto approximately 3 percent ofoutdoor children (97,000 children and 220,000 occurrences) at the 0.09 ppm standard level.

(4) Formoderate or severe pain on deep inspiration, approximately 0.9 percent ofoutdoor children (27,000 children) would experience this effect

one or more times per year (120,000 occurrences) at the 0.08 ppm standard level, increasingto over 1percent of outdoor children (41,000 children and 220,000 occurrences) atthe 0.09 ppm standard level.

Many public commenters supported EPA's proposed level of0.08 ppm for an 8-hour standard, including most public health associations and groups of medical professionals, many citizens, and some States and regional associations. There were also large numbers ofcommenters who expressed strongviews in opposition to the proposed level. Ofthose who did not support the proposed 8-hour level, almost all commenters representing businesses and industry associations, many local governmental groups and private citizens, and some States either supported no change to the current standard or,if EPA were to replace the
current 1-hour standard with an 8-hour standard, supported a level of0.09 ppm directly or simply one that would be "equivalent" to the current standard. On the other hand, environmental groups, 

### many citizens, and some medical professionals andresearchers supported

a level of0.07 ppm for an 8-hour standard.



### In general, theissuesraised bythese
groups ofcommenters can be addressed in three categories: Comments on the strength and adequacy ofthe health effects evidence upon which the proposed decision was based, comments

on the quantitative exposure and risk 

### assessments and the extentto which the assessments either over-or underpredict exposures andrisks among sensitivepopulations, andjudgments as to whetherthe differences in public health protection provided by 

### alternative standards are significant from apublic health perspective. Each ofthese categories ofkey issues is discussed separately below.

With regard tothe first category of comments, on the strength and adequacy ofthe health effects evidence,
commenters who did not support the need for any increased protection beyond that provided by the current standard questioned the adequacy or highlighted the limitations ofthe

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various types ofhealth effects studies that haverelated 03 exposures to adverse effects. For example, some commenters questioned the controlled human exposure studies, arguing that: Many such studies used patterns of exposures and exercise levels that are not representative ofnormalpopulation exposures to ambient 03; some exposure chambers using artificially generated 03 may have been contaminated with other pollutants that could have accounted for

some ofthe observed effects; and responses to elevated 03 levels were compared to responses to air with essentially no 03rather than to background levels typical ofambient air. Some commenters argued that these flaws in the study designs would result in overestimating responses to nonbackground levels ofambient 03 or in

erroneous findings ofstatistical significance. In contrast, others commented that because the chambers did not contain other pollutants and natural pulmonary irritants (e.g., pollens, dust)or a full range of environmental conditions (e.g., high temperatures and humidity) typical of ambient air,the results may underestimate the true impact of 03 in the ambient air.

Some commenters also questioned the

summer camp and other field studies and epidemiological studies reporting increased hospital admissions and emergency room visits, arguing that: The responses in these studies were inherently confounded byexposures to other pollutants, the camp studies did
not differentiate activity levels ofthe participants, and linear regression down
to orbelow background levels was unjustifiably used to analyze the results ofthehospital admission studies. These
commenters expressed the view that these and other flaws call into question any conclusions about whether the reported associations are causal. In contrast, other commenters argued that the hospital admissions reported in these studies are indicative ofapyramid ofadverse health effects, including increased mortality, increased visits to emergency and outpatient departments and physicians, increased numbers of asthma attacks resulting in increased medication use, and increased numbers ofrestricted activity days and acute respiratory symptom days, that EPA has
not adequately taken into account. The EPA notes that these comments are consistent with statistics published by the U.S. Department ofHealth and Human Services, which indicate that for every hospital admission ofan individual with asthma forrespiratory
causes, there are more than five emergency and outpatient department visits and more than 20 office-based physician visits (U.S. DHHS, 1996).

With regard to studies related to pulmonary inflammation and chronic respiratory damage, some commenters argued that the linkage between repeated inflammatory responses and chronic respiratory damage was merely speculation, and, therefore, should not be considered as part ofthe basis for decisions on the primary standard. In contrast, others commented that animal studies had demonstrated that repeated pulmonary inflammation leads to degenerative or irreversible lung damage, that these studies are consistent with observations in human exposure studies, and, therefore, that they should be considered in decisions on the standard.

The EPA notes that many ofthese comments did not reflect an integrative
assessment ofthe evidence-the approach CASAChas historically urged EPA to follow-but rather a piecemeal look at each individual study or type of study, which tends to miss the strength ofthe entire body ofevidence taken together. Other commenters did consider the body ofevidence in a more integrative manner, and many ofthese
commenters expressed the view that the body ofevidence as a whole provided clear evidence of03-related effects at and below 03 concentrations allowed by the current standard. Some commenters highlighted the large number ofstudies that demonstrate evidence ofeffects for prolonged exposures at and below 0.08 ppm, and criticized EPA for giving too little weight to those studies which reported serious effects, but for which the data were not sufficient to do quantitative risk assessments.

With regard to the second category of comments, on the exposure and risk assessments, anumber ofcommenters raised concerns about key aspects ofthe assessments, including the exposure model, the development of concentration-response functions, the application ofthe risk model, and the

measures ofrisk used to characterize the results ofthe assessments. With regard
to the exposure model, anumber of
commenters claimed that: The model overestimates the exertion level that can be achieved bymost children and outdoor workers and the fraction oftime that these groups spend in moderate or heavy exertion; the model overestimates outdoor ambient exposures because fixed-site monitors overestimate outdoor personal exposures; and the air quality adjustment procedures used to simulate attainment ofthe standards are inappropriate orhighly uncertain. Other
commenters expressed concern that the exposure model may be significantly underestimating exposures for children and outdoor workers who repeatedly exercise due to limitations in the available human activity pattern data.

As discussed in theproposal, EPA recognizes that the exposure model necessarily contains many sources of uncertainty, although every effort has been made to account for such uncertainties to the extent possible. In particular, the model incorporates and is sensitive to analytical procedures used to simulate spatial and temporal distributions of03 concentrations that would occur as a result ofan areajust attaining any ofthe alternative standards addressed in the exposure assessment. These air quality adjustment procedures arebased on generalized models intended to reflect the patterns ofchanges in distributions of03 concentrations that have historically been observed in areas implementing control programs designed to attain the 03 NAAQS. The EPA recognizes that future changes in air quality distributions are areaspecific, and willbe affected by whatever specific control strategies are implemented in the future to attain the revised NAAQS. Thus, generalized models are expected to be more uncertain for any given area than when exposure results are aggregated across many areas (as was done across the nine urban areas analyzed in EPA's exposure 

### assessment).

Some commenters questioned the specific air quality adjustment procedure used in the initial and supplemental assessment 6

, and afew of these commenters recommended revisions or alternative procedures that they believed would be more representative ofhistorical or projected future air quality patterns. As discussed in more detail in the Response to Comments, EPA acknowledges that both procedures used in the assessments result inprojections ofair quality that deviate to some degree from historical patterns ofair quality changes observed in specific urban areas, and that other procedures may be more representative ofair quality patterns in specific areas. While EPA will take these comments into account as future refinements are made to the air quality adjustment

16The initial risk assessment used both
"Weibull" and "proportional" air quality adjustment procedures, whereas the supplemental risk assessment used a "proportional" airquality adjustment procedure for all nine urban areas. In responding to comments on the air quality adjustment procedures, EPA also evaluated an alternative "quadratic" procedure (asdiscussed in theResponse to Comments), which generally resulted in risk estimates between those from the Weibull and proportional procedures. 

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procedures used in the exposure model, EPA believes, and CASAC concurred, that the procedures used in the
assessments conducted as part ofthis review arereasonable given the uncertainties inherent in projecting future changes in air quality patterns.

In commenting on the air quality adjustment procedure used in the supplemental assessment, some commenters particularly focused on the results for two ofthe nine areas analyzed in which, contrary to results from the initial assessment, lower risks

were estimated for the current standard

as compared to the proposed standard. As discussed more fully in the Response to Comments, EPA believes that these results for each area cannot be distinguished within the sensitivity of the alternative air quality adjustment procedures used in the initial and supplemental assessments. Further, EPA
notes that these two areas have much higher ratios ofpeak 1-hour to 8-hour 03 concentrations than the vast majority ofareas in which 03 is monitored' 7

, and it is thus reasonable to expect that generalized air quality adjustment procedures would be particularly uncertain for such areas.

Comments focusing on the development ofconcentration- response functions for use in the risk model have included a number ofclaims. Some
commenters claimed that EPA inappropriately selected studies for developing the functions by excluding studies that reported lower response rates and byusing only studies conducted byEPA scientists. Some commenters asserted that contaminants in the controlled exposure chambers may be responsible for some ofthe effects incorporated into the concentration-response functions for 03. Further, some commenters asserted that it was inappropriate to extrapolate the concentration-response functions to background levels or to develop concentration-response functions for symptomatic responses in children based on studies ofsuch responses in adults.

Ofthe comments focusing on the application oftherisk model, some commenters claimed that the aggregate risk results were overstated because of: Many ofthe methodological problems noted in the above summary of comments, the failure to take into
account the known attenuation of effects, and the assumption ofan inappropriately low background

17The two areas are Houston and parts ofLos Angeles county, which are two ofonly six areas nationwide with peak 1 to 8 hour design value ratios greater than 1.5. concentration in calculating risks attributable to non-background sources of 03. On the other hand, other
commenters claimed that aggregate risk results were understated because of: Methodological problems, noted above, that underestimate exposures, limiting the analyses to only a subset ofadverse health effects rather than estimating the full range ofeffects that have been attributed to 03, and by focusing only

on nine urban areas rather than projecting risk reductions from alternative standards nationally.

While EPAhas included comprehensive responses to these
comments in the Response to Comments, most ofthe issues and

concerns raised by commenters concerning the health effects evidence and the methods used in the exposure and risk assessments are essentially
restatements ofconcerns raised during the review ofthe Criteria Document and the development and review ofthese quantitative assessments as part ofthe preparation and review ofthe Staff Paper. EPApresented and the CASAC reviewed in detail the approaches used
to assess exposure and health risk,the studies and health effect categories selected for which concentrationresponse functions were estimated, and the presentation ofthe exposure and risk results summarized in the Staff Paper. As stated in the proposal, EPA believes and CASAC concurred, that the general models selected to estimate exposure and risk are appropriate and that the methods used to conduct the exposure and risk assessments represent the state ofthe art. EPA does not believe that the exposure or risk assessments are fundamentally biased in one direction

or the other as claimed in some ofthe
comments.

The Administrator and CASAC have recognized, however, that there are many uncertainties inherent in such
assessments and that the resulting ranges ofquantitative risk estimates do
not reflect all ofthe uncertainties associated with the numerous assumptions inherent in such analyses (Wolff, 1995b). EPA summarized some ofthe most important caveats and limitations concerning both the exposure analyses and therisk
assessments for lung function changes, respiratory symptoms, and hospital admissions in the proposal. A more complete discussion ofassumptions and uncertainties is contained in the Staff Paper and technical support documents (Johnson et al., 1996 a,b; Whitfield et al., 1996; Richmond, 1997).

With regard to the third category of comments, reflecting commenters' judgments as to whether the differences in public health protection ofalternative standards are significant from a public health perspective, EPA notes that highly divergentjudgments were expressed by different groups of
commenters. A large number of
commenters who expressed the view that the differences in public health protection were not significant or important enough to warrant any standard more stringentthan the current standard used CASAC as the basis for theirposition, as discussed above in UnitII.B.I. on averaging time. Others cited smallpercentages ofoutdoor children and other sensitive groups likely to be affected based on EPA's assessment, or even smaller percentages

as modified by analyses conducted by the commenter to correct perceived

errors in the analyses. In contrast, other
commenters cited large total numbers of children likely to be affected, not only for the subset of03-related effects and the nine areas analyzed in EPA's assessments, but also for abroader array ofrelated effects projected nationally.

The core issue in this review ofthe primary 03 standard, as stated by the Administrator at the time ofproposal, is who is to be protected, and from what. Clearly, for pollutants, such as 03,that have no discernible thresholds for health effects, no standard can be riskfree. The Administrator's task is to select a standard level that will reduce risks sufficiently to protect public health with an adequate margin of safety since a zero-risk standard is neither possible norrequired by the Act. As CASAC and the Administrator recognize, the selection ofa specific standard level for such pollutants requires public health policyjudgments in addition to determinations ofa strictly scientific nature.

In making suchjudgments, the Administrator rejects the notion that because standards cannot be risk-free they should not be revised to provide increased protection for sensitive populations, particularly including children in this case, when available evidence points to greater impacts on public health than had previously been demonstrated. In carefully reassessing both those risks to public health that

can be quantified as well as those for which quantitative risk information is

more limited, the Administrator has focused on the following comparisons between the degree ofpublic health protection likely to be afforded by an 8- hour standard at theproposed level of 0.08ppm and an alternative standard
set at a level of0.09 ppm (assumingthe

same third-highest concentration form):

(1) Based on EPA's updated analyses ofestimated moderate or large decreases 

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in lung function and moderate to severe pain on deep inspiration in outdoor children in nineurban areas (Richmond, 1997), a standard set at 0.09ppm would allow approximately 40percent to 65 percent more outdoor children to experience such effects than would a 0.08 ppm standard, and approximately 70 percent to 120 percent more

occurrences ofsuch effects in outdoor children per year.

(2) While only relatively small percentages ofoutdoor children are estimated to experience such effects, the differences in these percentages between the two standard levels represent tens ofthousands more children, and hundreds ofthousands

more occurrences ofadverse effects in these children, in these nine urban areas alone, for a 0.09 ppm standard as compared to a0.08 ppm standard.

(3) Based on EPA'supdated risk
assessment ofincreased hospital admissions in New York City (Richmond, 1997), a standard set at 0.09 ppm would allow approximately 40

more excess hospital admissions of asthmatics within an 03 season in New York City for respiratory causes as compared to a0.08 ppm standard, which represents approximately a 40 percent increase in excess 03-related admissions,but only approximately a 0.3 percent increase in total admissions ofasthmatics. The EPA believes that while these numbers ofhospital admissions arerelatively small from a public health perspective, they are indicative ofa pyramid ofmuch larger numbers ofrelated 03-induced effects, including respiratory-related hospital admissions amongthe general population, emergency and outpatient department visits, doctors visits, and asthma attacks and related increased use ofmedication that are important public health considerations.

(4) Based on EPA's exposure analyses in the nineurban areas, a standard set at 0.09 ppm would allow more than three times as many children to experience 8-hour average exposures of

concern as would a 0.08ppm standard, with the number ofoutdoor children likely to experience such exposures increasing from approximately 100,000
to more than 300,000 in the nineurban

areas alone, representing an increase from approximately 3 percent to approximately 11 percent ofthe outdoor children likely to experience such exposures.

(5) These exposures ofconcern are judged byEPA to be an important indicator ofthe public health impacts of those 03-related effects for which information is too limited to develop quantitative estimates ofrisk,but which 

### have been observed in humans at alevel of0.08 ppm for 6- to 8-hourexposures. Such effects include thefollowing: increased nonspecific bronchial responsiveness (related, for example, to aggravation ofasthma), decreased pulmonary defense mechanisms (suggestive ofincreased susceptibility to respiratory infection), and indicators of pulmonary inflammation (related to potential aggravation ofchronic bronchitis orlong-term damage to the lungs). (6)Toput these risks and exposures into broaderperspective, EPAnotes that approximately 46million more people, including approximately 13 million

more children and 3million more individuals with asthma, live in areas that would not attain a 0.08 ppm standard compared to a 0.09 ppm standard. The generalpopulation as well as children and asthmatics would breathe cleaner air asa direct result of control measures designed tobring areas into attainment with theproposed standard. 18



### While recognizingthe inherent uncertainties in these estimates, and aftertakinginto accountthe range of views andjudgments expressed in the public comments, theAdministrator finds thepublic health impacts described in theproposal, asupdated above, tobeimportant and sufficiently large as towarrant a standard setat a level of0.08 ppm, asproposed.

The Administrator recognizes the views ofthose who arguethat similarly large improvements in public health protection would result from a standard set at0.07 ppm as compared to the proposed standard, such that, based on the same reasoning, the evidence warrants a standard set at0.07 ppm. In considering these views, the Administrator gives significant weight to thefollowing considerations: (1)Nomember oftheCASAC panel of experts supported astandard set lower than 0.08 ppm, specifically after considering arange ofalternative standards thatincluded 0.07ppm.

(2) Themost certain 03-related effects, whilejudged tobe adverse, are transient and reversible (particularly at03 exposures below 0.08 ppm), and the

more serious effects with greater immediate and potentiallong-term impacts on health are less certain, both

asto thepercentage ofindividuals exposed to various concentrations who

arelikely to experience such effects and

asto thelong-term medical significance ofthese effects.

18The EPA anticipates that additional people
would beprotected through regional measures adopted for purposes ofan 8 hour, 0.08 ppm standard. (3) As many commenters have noted, based on information in the Criteria Document with regard to ambient concentrations of03from background
sources, an 8-hour standard set at a0.07 ppm level would be closerto peak background levels that infrequently

occur in some areas due to nonanthropogenic sources of03 precursors, and thus more likely to be inappropriately targeted in some areas

on such sources.

After taking into account the public comments, and for the reasons outlined above, the Administrator finds that a standard set at a level of0.07 ppm is not requisite to protect public health with

an adequate margin ofsafety.

3. Form. The form ofthe current 1- hour, 0.12 ppm standard is a "- expected-exceedance" form. That is, the
current standard is based on the expected 19 number ofdays per year, on average over 3 years, on which the level ofthe standard is exceeded, and limits that number ofexpected exceedances to be less than or equalto 1.0.

In evaluating alternative forms for the primary standard, the adequacy ofthe public health protection provided was the Administrator's foremost consideration. The Administrator also recognized, however, that concerns have been raised with the current form since it was promulgated in 1979 due to the inherent lack ofyear-to-year stability in the measure ofair quality on which the 1-expected-exceedance form is based. 2 0
The CASAC specifically took such

concerns into account in recommending that the current form be revised and in noting that a more robust, concentration-based form would minimize such instability and provide

some insulation from the impacts of
extreme meteorological events that are conducive to 03formation (Wolff, 1995b). Such instability can have the effect ofreducing public health protection by disrupting ongoing implementation plans and associated controlprograms.

As discussed in theproposal, based

on information presented in sections IV. and V.1 ofthe StaffPaper and the advice ofCASAC, the Administrator focused her consideration on the following alternatives:

(1) Revising the current 1-expectedexceedance form ofthe standard to

19The term "expected" means that thenumbers ofexceedances peryear are averaged over 3years and may be calculated using specific adjustments
to account for missing data.

20The 1-expected-exceedance form essentially requires the fourth-highest air quality value in 3
years, based on adjustments for missing data, to be less than orequal to the level ofthe standard for the standard to bemet at an air quality monitoring site. 

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allow for multiple (up to five) expected exceedances per year, averaged over 3 years. A multiple-exceedance form would be based on aless extreme air quality statistic and, thus, would increase the stability ofthe expectedexceedance form.

(2) Adopting a concentration-based statistic, such as the 3-year average of the nth-highest daily maximum 8-hour average 03 concentration, as an alternative to an expected exceedance statistic. Air quality analyses presented in the StaffPaper indicate that the3- year averages ofthe annual third-, fourth-, and fifth-highest daily maximum 8-hour concentrations would provide approximately the same health protection as the 3-, 4-, and 5-expectedexceedance forms averaged over the

sameperiod, respectively.

It was the consensus ofthe CASAC Panel that this range ofallowable exceedances (i.e., up to 5 exceedances), and the consideration ofcomparable concentration-based forms, was appropriate. Further, CASAC acknowledged that selecting from within this range ofalternative forms is

apolicyjudgment, especially given the
nature ofthe health effects and the absence ofa "bright line" that clearly differentiates between acceptable and unacceptable risks within this range. All 10 CASAC Panel members who expressed specific opinions on the form ofthe standard favored one that would allow for multiple exceedances (Wolff, 1995b).

In reaching her proposed decision on the form ofan 8-hour standard set at 0.08 ppm, the Administratorhad to choose a specific form within the range ofup to 5 allowable exceedances orup to the comparable fifth-highest concentration, and either an exceedance-based or a concentrationbased form. As discussed in the proposal, in considering possible forms within the range of 1to 5 exceedances (ortheir concentration-based counterparts) the Administrator took into consideration aggregate risk estimates for those health effects for which quantitative risk analyses have been done; estimated exposures associated with those effects for which

no quantitative risk estimates could be developed; and the magnitude ofpeak
measurements of8-hour average 03 concentrations, and the number ofdays

on which the level ofthe standard would likely be exceeded, based on an analysis ofhistorical air quality data (Freas, 1996). In considering exposure and risk estimates available at the time ofproposal for 1- and 5-expectedexceedance forms, the Administrator noted that the level ofthe standard is a more dominant factor in determining the degree ofexposure and risk reductions achieved, with the form being associated with smaller differences in risk estimates within a continuum ofrisk.In considering air quality comparisons for standards

across the range offorms considered, the Administrator focused in particular

on the extent to which alternative forms would limit the number ofdays in which the level ofthe standard would be exceeded in areas thatjust attain the standard2

, and the magnitude ofpeak 

### 8-hour average 03 concentrations 22that would occur in such areas. 23More specifically, the Administrator took into consideration the percentage of monitoring sitesjust attaining an 8- hour, 0.08 ppm standard that would have 8-hourpeak 03 concentrations above a benchmark level of0.09 ppm. This benchmark level is theupper end oftherange oflevels endorsed by CASAC for an 8-hour 03 standard. The Administrator believes, given the uncertainties associated with this kind ofcomplex health decision, that itis an appropriate goalto limit the percentages ofareas experiencing such daily peaks.

In choosing to propose a concentration-based form, the Administrator recognized the advantages ofa concentration-based form over an exceedance-based form. As discussed in the proposal, the principal advantage ofa concentration-based form is that it is more directly related to the ambient 03 concentrations that are associated with health effects. That is, given that there is a continuum of effects associated with exposures to varying levels of03,the extent to which public health is affected by exposure to ambient 03 is related to the actual magnitude ofthe 03 concentration, not just whether the concentration is above

21Areas that "just attain the standard" are defined as those whose design value falls between 0.075 and 0.084 ppm.

22Peak 8 hour average concentrations are defined
in terms ofthe fourth-highest daily maximum concentration in 3 years (i.e., the design value for the current 1-expected-exceedance form ofthe standard).

23The results ofthese air quality analyses are presented in Freas (1996) and summarized in the proposal for the third- and fifth-highest concentration forms and the 3 and 5-expectedexceedance forms. Based on these considerations, and the air quality comparisons in particular, the Administratorjudged that the middle ofthe range of exceedances considered, three expected exceedances, or the comparable third-highest concentration, represented a reasonable policy choice, and proposed the 3 year average ofthe annual third-highest daily maximum 8 hour
average 03 concentrations as the form ofthe standard. In recognition of arangeofviews on the degree ofhealth protection that would be appropriate, she also solicited comment on other concentration -based forms, including the second-, fourth-, and fifth-highest concentration forms. a specified level. With an exceedancebased form, days on which the ambient 03 concentration is well above the level ofthe standard are given equal weight to those days on which the 03 concentration isjust above the standard (i.e., each day is counted as 1 exceedance), even though the public health impact on the two days is significantly different. With a concentration-based form, days on which higher 03 concentrations occur would weigh proportionally more than days with lower 03 concentrations, since the actual concentrations are used directly in determining whether the standard is attained. A concentrationbased form also has greater temporal stability than the expected-exceedance form and, thus, would facilitate the development ofmore stable implementation programs by the States.

As discussed above in Units II.A.3. and II.B.2., EPA completed and made available for public comment supplemental exposure and risk
assessments subsequent to the proposal. These updated assessments, which specifically analyzed the third- and fifth-highest concentration-based forms, aid in comparing the differences in public health protection among alternative concentration-based forms within the range considered in the proposal for 8-hour, 0.08 ppm standards. Based on theseupdated assessments, the Administrator again
notes that the level ofthe standard is the

more dominant factor in determining the degree ofrisk reduction achieved, with these alternative formsbeing associated with much smaller differences in risk estimates within a continuum ofrisk.For example, within the nine urban areas included in the risk assessment, approximately 180,000 outdoor children would experience moderate lung function (FEV) decreases > 15 percent upon attainment ofan 8-hour, 0.08 ppm standard with

a third-highest concentration form, compared to approximately 200,000 outdoor children with afourth-highest concentration form and 220,000 outdoor children with afifth-highest concentration form.

The public comments include a large number that specifically addressed the form ofthe standard. Those commenters who expressed views on the form ofthe standard can be divided into three groups, accordingto the level of8-hour standard and the relative degree of public health protection that the commenter supported. These groups include: Commenters who supported an 8-hour, 0.08 ppm standard to provide increased public health protection relative to the current standard; 

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commenters who supported either an 8- hour, 0.09 ppm standard, or simply an 8-hour standard "equivalent" to the
current standard; and commenters who supported an 8-hour, 0.07ppm standard to provide a greater margin of safety than that afforded by the proposed standard.

The first group included many private citizens, somemedical professionals and researchers, and some States and local governmental groups. While a number ofcommenters in the first group specifically supported theproposed third-highest concentration form, generally for the reasons presented in the proposal, others supported either a 1-expected-exceedance form or a concentration-based form in the upper part oftherange (i.e., the fourth- or fifth-highest forms). The second group ofcommenters, which included many local governmental groups and private citizens, some States, and most commenters representing businesses and industry associations, almost exclusively supported a concentrationbased form in general, and a form in the upper part ofthe range (or above the range) in particular. In sharp contrast, the third group ofcommenters, which included environmental groups, many private citizens, and some medical professionals and researchers, almost exclusively supported a 1-expectedexceedance form in conjunction with an 8-hour, 0.07 ppm standard to provide the largest margin ofsafety within the range ofalternative standards considered.

To the extent that the second and third groups ofcommenters argued for

adifferent level than the Agency adopts today, the Administrator disagrees with their comments for the reasons set forth in the discussion ofthe standard level above in Unit II.B.2. To the extent that they argued for more than 5 exceedances (orthe concentration-based equivalent), the Administrator disagrees with their views because such forms fall outside the range recommended by CASAC and would provide lesspublic health protection than she deems appropriate. To the extent that the second and third groups ofcommenters addressed the merits ofparticular forms within the range offorms considered in the proposal, they raised points similar
to those raised bycommenters in the first group. These points are discussed below.

Among the commenters in the first group (i.e., those supporting an 8-hour, 0.08 ppm standard to provide increased public health protection), many felt that there was no compelling basis for selecting the third-highest rather than the fourth- or fifth-highest concentration-based form. These commenters frequently quoted CASAC's closure letter (Wolff, 1995b) as stating "that there is no bright line' which distinguishes any ofthe proposed standards (eitherthe level or the number ofexceedances) as being significantly more protective ofpublic health," and that "the selection ofa specific level and number ofallowable exceedances is a policyjudgment." In general, these commenters did not give weight to the air quality comparisons that were amajor consideration in the Administrator's decision to propose the third-highest concentration form. Some
commenters seem to view such air quality comparisons, particularly with regard to pollutants such as 03 that have

no discernible threshold ofeffects, as relating more to people's perceptions of how well airpollution is controlled than to any objective measure ofactual risks to public health.

These commenters made anumber of points in questioning the need to specify an 8-hour, 0.08 ppm standard in
terms ofthe third-highest rather than the fourth- or fifth-highest concentration form. Many noted that achange to an 8- hour averaging time in and ofitself would appropriately focus air quality management programs on prolonged exposures ofmost concern. Further, many noted that alevel of0.08 ppm, regardless ofthe form within the range offorms considered in theproposal, would provide significantly increased protection from 03-related risks to public health associated with acute effects (i.e., those resulting from shortterm and prolonged exposures) for which they believe there is sufficient evidence to be used as abasis for a standard at this time. Some ofthese
commenters expressed the view that the potential for chronic effects (i.e., those resulting from long-term exposures) would be better addressed through continued research, rather than by adding agreater margin ofsafety to a revised standard based primarily on effects ofshort-term and prolonged exposures. Many ofthese commenters recognized, as did EPA in the proposal, that there is a continuum ofrisks associated with 03 exposures, that no standard can therefore be risk-free, and that there are large uncertainties in any estimates ofthe degree ofprotection associated with alternative forms. In general, these commenters also noted that, for the same reasons, CASAC advised thatthe selection ofa form from within the range considered in the proposal was apolicyjudgment, not one that could be decided on the basis of science alone. In essence, these commenters argued that a more restrictive form than the upper part of the range endorsed by CASAC is not requisite to protect public health.

In contrast, other commenters in the first group (i.e., those supporting an 8- hour, 0.08 ppm standard) supported either theproposed third-highest or second-highest concentration form or a 1-expected-exceedance form. These
commenters generally gave greater weight to limiting the magnitude of peak 03concentrations and the number ofdays on which the standard level would be exceeded in areas meeting such a standard, and, in some cases, to providing a greater margin ofsafety to account forpotential chronic effects. Such views suggest that limiting the number ofdays on which the standard level would be exceeded, for example, is an important factor in risk communication and in the public's understanding ofthe degree to which a standard protects people from exposures to 03 that may interfere with their ability to engage in normal activities or mayresult in the need for increased medication or medical treatment, especially forthose individuals with asthma or otherrespiratory diseases. As discussed above in this unit, although

some ofthese commenters felt that the third-highest concentration form would protect public health while also providing increased stability, others expressed concern that public health could be compromised by any form that allowed for multiple exceedances ofthe standard. The advantages offorms that allow for multiple exceedances, thus providing increased stability as discussed in the proposal, and the views ofthe CASACpanel members who expressed opinions, all ofwhom favored such forms, were notgiven weight by
commenters within this group who supported a 1-expected-exceedance form.

The Administrator has carefully reassessed therelative risks to public health ofspecific forms within the range ofthe second- to fifth-highest concentration forms or their exceedance-based equivalents, taking into account the public comments summarized above, and the advice from CASACPanel members that the current form be replaced by a form that allows multiple exceedances. In doing so, the Administrator focused on the following considerations:

(1) The CASAC advised that concentration-based forms, within the range considered up to the fifth-highest concentration form, are appropriate for

ahealth-based primary 03 standard, and that selection from within thisrange is

apolicyjudgment that cannot be based 

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on science alone. This advice reflects CASAC's recognition that 03 exhibits a continuum ofeffects, such that there is

no discernible threshold above which public health protection requires thatno exposures be allowed orbelow which allrisks to public health can be avoided. The CASAC also recognized that a concentration-based form would increase the stability ofthe standard by providing someinsulation from the impacts ofextreme meteorological
events (Wolff, 1995b).

(2) Estimates ofthe differences inrisk
to public health, for those effects that could be considered quantitatively, within arange of alternative forms from the second- to fifth-highest concentrations (for an 8-hour, 0.08ppm standard) are relatively small compared
to the differences between alternative levels. In other words, the choice of level is substantially more important to the degree ofpublichealth protection afforded by the standard than the choice ofform from within thisrange offorms.

(3) Measures that distinguish between the alternatives within therange ofthe second- to fifth-highest forms, based on air quality analyses, reflect considerations related to how some individuals understand the degree to which an air quality standard protects public health. These considerations are

adistinct aspect ofrisk communication
to individual citizens even though the days on which exceedances occur are accounted for in EPA's quantitative
assessments ofrisks to public health.

(4) To assess the comparative effect of allforms within the range ofthe secondto fifth-highest concentration forms, EPA considered air quality comparisons for all such forms (Freas, 1996). These comparisons (based on 1993 to 1995 data) show that 8-hour, 0.08ppm second- and third-highest concentration standards are very similar in that each standard limits the percent of monitoring sites that would experience peak days above the benchmark level of 0.09 ppm to 1percent ofsuch sites, and the number ofdays on which the standards would likely be exceeded in the worst of3 years would be no more than 6 and 7, respectively. While less restrictive than either ofthese standards, an 8-hour, 0.08 ppm fourthhighest concentration standard would be significantly more restrictive than a fifth-highest standard. For example, the 8-hour, 0.08 ppm fourth-highest concentration standard would limit the percent ofmonitoring sites that would experience peak days about the benchmark level of0.09ppm to 8 percent ofsuch sites, and the number of days on which the standards would likely be exceeded in the worst of3 years would be no more than nine. In comparison, the fifth-highest concentration standard would limit the percent ofmonitoring sites that would experience peak days about the benchmark level of0.09 ppm to 17 percent ofsuch sites, and the number of days on which the standards would likely be exceeded in the worst of3 years would be no more than 11. (5) The extent to which the alternatives within the range ofthe second- to fifth-highest concentration forms provide protection against the

more serious, but less certain effects that have been associated with exposure to 03, including potential chronic effects,
cannot be quantitatively assessed atthis time. Given that all such forms would result in significant reductions in exposures to 03 at and above 0.08 ppm (thelevel where suggestive evidence of such effects is available), any form within this range would provide some margin ofsafety against these effects.

Based on these considerations, the available health effects evidence, the quantitative assessments contained in the Criteria Document, StaffPaper, and supplemental analyses and supporting documents, and the range ofviews and judgments expressed in the public
comments on the appropriate form, the Administrator has reconsidered the form ofthe standard that is requisite to protect public health with an adequate margin ofsafety. As an initial matter, the Administrator has decided to adopt

aconcentration-based form which allows for more than one exceedance. While the Adminstrator understands the views ofthe many citizens who are concerned about a standard that would allow for multiple days on which the level ofthe standard may be exceeded, the Administrator concludes that such

concerns are more relevant for pollutants that exhibit a clear threshold ofeffects than for pollutants such as 03 that exhibit acontinuum ofeffects. The Administrator believes that the public health risks associated with such pollutants can be appropriately addressed through a standard that allows for multiple exceedances to provide increased stability, but that also significantly limits both the number of days on which the level may be exceeded and the magnitude of such exceedances. This approach recognizes that exposures associated with such exceedances are already reflected in the exposure and risk assessments that were

an important consideration in selecting

a0.08 ppm level for the primary 03 standard, and that increased stability in the standard is important to avoid disruption to ongoingcontrol programs, and thus to maintain ongoingpublic health protection.

Having again concluded that a concentration-based 03 standard that allows for multiple exceedances is appropriate, the Administrator considered the extent to which the form ofan 8-hour standard should be selected so as to provide a margin of safety against possible, but uncertain chronic effects. The Administrator carefully considered the views ofthe many commenters who emphasized the uncertainties in the evidence, primarily from laboratory animal studies, that was available in this review ofthe criteria and standards to relate long-term exposures to ambient levels of03 to possible chronic effects in humans. These commenters, as did CASAC, advised that further research into potential chronic effects in humans should be continued, and the results considered in the next review ofthe 03 standard. The Administrator is persuaded thatthe difference between the margins ofsafety for these potential chronic effects afforded by the alternatives within the range ofthe second- to fifth-highest concentration forms is not well enough understood at this timeto use asthe basis for choosing the most restrictive forms (i.e., the second- or third-highest concentration form). On the other hand, the Administrator alsojudges that the relatively large percentage ofsites that would experience 03 peaks above a benchmark level of0.09 ppm even when attaining afifth-highest concentration standard and the number ofdays on which the level ofafifth-highest concentration standard maybe exceeded argue against choosing that form, which is the least restrictive within the range considered.

For the reasons outlined above, and takinginto account the range ofviews in the public comments, the Administrator concludes that an intermediate form, the fourth-highest concentration form, would serve to appropriately balance these public health considerations in conjunction with the 8-hour averaging time and 0.08 ppm level selected, as discussed above in Units II.B.I. and II.B.2., that are of primary importance in determining the degree ofpublic health protection afforded by the standard. In addition, the Administrator notes that based on

an analysis ofair quality in counties that would attain an 8-hour, 0.08 ppm fourth-highest concentration standard (based on 1993-1995 data), over 99 percent ofsuch counties would be expected to have four or fewer days on which the level ofthe standard is exceeded in an average year (Freas, 

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1997). This number ofexceedances is clearly within the range ofmultiple exceedances that CASACjudged to be appropriate for ahealth-based primary 03 standard. Thus, in the Administrator's judgment,based on the information currently available, an 8- hour, 0.08 ppm standard with a fourthhighest concentration form will protect public health with an adequate margin ofsafety.

In the proposal, which maintained the current approach ofusing air quality data from the monitor measuring the highest 03 concentrations in an area to determine whether the primary standard for 03 is attained, the Administrator solicited comment on the alternative of using someform ofaveraging across monitors. As discussed in theproposal, EPA recognized that during the review ofthe StaffPaper, a number of
commenters suggested that averaging

across monitors might be appropriate to increase the degree to which monitoring data used in determining attainment of the standard reflects population exposure and aggregate population health risk. Further, these commenters suggested that averaging data from multiple monitors in an area would produce a more stable measure ofair quality and would take into account broader population exposure patterns

across an area than would the current approach ofconsidering data from each monitor independently.

The Administrator did not propose the use ofspatial averaging because of

concerns outlined in the proposal including: The difficulty in determining

an appropriate level for a spatially averaged primary standard given that the bulk ofthe human health effects evidence supporting a decision on an appropriate 03 standard isbased on controlled human exposure studies that relate known 03 exposures directly to responses in individuals; and questions

as to whether adequate health protection would be provided to individuals within the populations that live or work in communities that routinely experience higher 03 concentrations within abroad metropolitan area.

To address these two concerns, it would be necessary to define criteria for geographic locations or communities (e.g., spatial averaging zones) within which theuse ofspatially averaged 03 data would be acceptable. Such criteria would be important since 03 air quality concentrations can vary significantly

across most urban areas. The lowest concentrations typically occur in the urban center and in locations near 03 precursor sources, mid-range concentrations in neighborhoods and locations surrounding theurban center, and peak concentrations are typically measured downwind alongthe
outermost suburban regions ofthe urban

area. Also, the location ofresidences, schools, parks, and other places where individuals might be exposed more frequently to ambient 03 concentrations ofconcern would be an important consideration. Unless the 03 concentration gradients within each spatial averaging zone were relatively homogeneous, there may be significant numbers ofsensitive individuals exposed to high 03 concentrations in

areas where the spatial average indicates that the overall air quality is acceptable.

In the proposal, EPA also noted the need to help State and local governments devise different 03 monitoring networks by revising relevant regulations and guidance, should spatial averaging be adopted. This would likely involve defining general criteria for monitoring network design, siting, and spatial averaging

zones in nationally implementable terms, with case-by-case evaluation of each monitoring network. The EPA recognized that this activity would place additional burdens on State and local air quality management districts.

In solicitingcomment on whether it would be desirable to adopt some form ofspatial air quality averaging for 03, the Administrator also solicited
comment on specific alternative approaches that could be used to address the issues ofconcern. In particular, the Administrator was interested in analyses that inform questions about monitoring network design, sitingrequirements, and approaches for specification ofspatial averaging zones; the distribution of public health protection that would result from such alternative approaches; and the extent to which the level ofthe standard would need to be adjusted, if any, to provide public health protection consistent with the level ofprotection contemplated in the proposal.

The EPAreceived many comments on the subject ofusing spatially averaged data to determine when theprimary standard for 03 is attained. Commenters from business and industry associations frequently supported the use ofspatially averaged data, as did many local governments and a small number of States, principally because it would provide a more stable air quality indicator and would better represent population exposure and risk. Some of these commenters felt that the use of spatial averaging would be consistent with theuse ofrisk assessment as a policy toolfor standard setting. Many of these commenters agreed that the heterogeneity of03 concentrations

across geographic areas would need to be addressed by network design, with a few expressing the opinion that this would notbe an insurmountable problem given that there is continual
movement ofmonitors within existing networks. Some commenters suggested averaging approaches that included the

use ofpopulation weighting of monitored data, and some supported the

use ofapublic health information system to allow individuals residing in "hot spot" areas to reduce their exposures to 03 concentrations of

concern.

In contrast, environmental associations, public health professionals, most States, and many individuals voiced strong concerns that the use ofspatially averaged data would routinely allow individuals who live or work in communities with consistently higher 03 levels than those occurring

across the broader urban area to be exposed to concentrations ofconcern. Many ofthese commenters raised the issue ofenvironmental equity, expressing the view that communities with consistently higher 03 concentrations typically are composed predominantly ofindividuals oflower socioeconomic status, or are composed ofa predominantly minority population. The EPA notes that this view is not consistent with the air quality data discussed earlier in this unit, in that 03 concentrations are typically lower in urban centers than in locations surrounding or downwind ofurban
centers. Some commenters also raised

concerns about the complexity and burdens associated with redesigning existing monitoring networks.

Taking into account the comments received, the Administrator does not find that the issues ofconcern, as outlined in the proposal and above, have been adequately addressed in this review ofthe 03 standard. In particular, whileEPA strongly agrees with the importance ofpublic health advisories in addition to adequately protective standards, relying on theuse ofpublic health advisories to provide information for at-risk populations who may consistently be exposed to localized 03 concentrations ofconcern is considered by the Administrator to be an insufficient approach to protecting public health with an adequate margin ofsafety. Further, the suggested use of population weighting ofmonitored data may, in many cases, be insufficiently sensitive to local 03 variations to ensure adequate protection ofthese populations from localized 03 concentrations. Thus, therevised 03 standard will maintain the current 

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approach ofusing air quality data from the monitor measuring the highest 03 concentrations in an area to determine whether the standard is attained within

an area.

The EPA has also considered spatial averaging in the context ofthe decision
to revise the PM NAAQS, in part,by adopting a form ofan annual standard for fine particles (i.e., PM 2.5) that allows for spatial averaging within appropriate criteria. Itis important to note that different considerations apply in these
two cases. One principal difference is the nature ofthehealth effects evidence for 03 and PM 2. 5. When considering averaging approaches for 03, it should be recognized that much ofthehuman health effects evidence supporting the 03 standard isbased on controlled human exposure studies that relate individual 03 exposures directly to responses in individuals, whereas the health effects evidence supporting the PM2.5 standards is from epidemiological studies relating community measures of PM 2.5 concentrations to populationwide responses. Thus, information available for determining an appropriate level ofa standard in these two cases is predominantly individual-oriented in the case of03 and community-oriented in the case ofPM 2.5. As aconsequence, additional research and exposure and risk assessments beyond those available in this review would be necessary to provide abasis for further consideration ofa spatially averaged standard for 03. The EPA will continue to explore this approach.

Another important difference between the 03 and PM standards is that the suite ofannual and 

### 24-hour PM2.5 standards permits theuse ofthe 24- hour PM 2. 5 standard, which would not be spatially averaged, as abackstop to control localized "hot spots," whereas a single 03 standard does not allow for such a dual approach. Also, EPA notes that the existence ofan established, extensive 03 monitoring network would require substantial redesigning and relocation ofmonitors for thepurpose of spatial averaging, in contrast to the
current absence ofsuch a network for PM 2.5 which can be newly designed to address community-oriented monitoring from the outset.

As discussed in the proposal, the Administrator recognizes that no standard within the range oflevels and forms considered in this review, including the selected standard, is risk free, due to the continuum ofrisk likely posed by exposures to ambient 03 potentially down to background levels. Accordingly, consistent with CASAC advice, the Administrator solicited
comment in the proposal on elements of an enhanced public health advisory system. The Administrator believes that the information that could be made available through such a publichealth advisory system would be particularly useful to extremely sensitive individuals in making personal decisions about avoiding exposures with thepotential to cause transient adverse effects on days when 8-hour average 03 concentrations arepredicted
to be at or near the level ofthe standard. Approaches to developing an enhanced system, and comments received on such approaches, are discussed in Unit II.C. ofthis preamble.

4. Finaldecision on theprimary standard.After carefully considering the information presented in the Criteria Document and the StaffPaper, the advice and recommendations of CASAC, public comments received on the proposal, and for thereasons discussed above, the Administrator is replacing the existing 1-hour, 0.12 ppm primary standard with a new 8-hour, 0.08 ppm primary standard. The new 8- hour standard will become effective September 16, 1997.

The 8-hour, 0.08 ppm primary standard will be met at an ambient air quality monitoring sitewhen the 3-year average ofthe annual fourth-highest daily maximum 8-hour average 03 concentration is less than or equal to 0.08 ppm. Data handling conventions

are specified in a new Appendix I to 40 CFRpart 50 as discussed in Unit VI below.

In the proposal, EPAproposed that the revocation ofthe existing 1-hour 03 standard be delayed for certain purposes until EPAhad approved State Implementation Plans to implement the

new 8-hour 03 standard. EPAhad proposed continuing the applicability of the 1-hour standard in this way in order
to facilitate continuity in public health protection during the transition to a new standard. (SeeMemorandum from John S. Seitz to Mary D.Nichols, November 20, 1996; Docket No. A-95-58, item IIB-3.) Also, atthe time ofthe proposal ofthe new 03 standard, EPAhad proposed an interpretation ofthe Act in the proposed Interim Implementation Policy (61 FR 65764, December 13, 1996) under which the provisions of subpart 2 ofpart D ofTitle I ofthe Act would not apply to existing 03 nonattainment areas once a new 03 standard becomes effective.

In light ofcomments received regarding the interpretation proposed in the Interim Implementation Policy, EPA has reconsidered that interpretation and

now believes that the Act should be interpreted such that the provisions of subpart 2 continue to apply to 03 nonattainment areas for purposes of achieving attainment ofthe current 1- hour standard. As a consequence, the provisions ofsubpart 2, which govern implementation ofthe i-hour 03 standard in 03 nonattainment areas, will continue to apply as a matter oflaw for

so long as an area is not attaining the 1- hour standard. Once an area attains that standard, however, thepurpose ofthe provisions ofsubpart 2 will have been achieved and those provisions willno longer apply. However, the provisions ofsubpart 1 ofpart D ofTitle Iofthe Act would apply to the implementation ofthe new 8-hour03 standards.

To facilitate the implementation of those provisions and to ensure a smooth transition to the implementation ofthe

new 8-hour standard, the i-hour standard should remain applicable to

areas that are not attainingthe i-hour standard. Therefore, the i-hour standard will remain applicable to an

area untilEPA determines that ithas attained the i-hour standard, at which point the i-hour standard will no longer apply to that area.
C. Cornm unicationofPublicHealth Information

Information on the public health implications ofambient concentrations ofcriteria pollutants is currently made available primarily through twoEPA programs. The firstprogram is designed to prevent ambient pollutant concentrations from reaching the significant harm level (i.e., an exposure level that constitutes an imminent and substantial endangerment to public health). The second program is the Pollutant Standards Index (PSI),24 which is ahealth advisory system. The proposal focused on the potentially expanded use ofthe PSIin regard to allowing sensitive individuals to reduce theirrisk ofexposure. Currently, EPA and local officials use the PSI as a public information tool to advise the public about the general health effects associated with different pollution levels and to describe whatever precautionary steps may need to be taken ifair pollution levels riseinto the unhealthful range. By notifying the public when a PSIvalue exceeds 100 (which corresponds to the NAAQS for each criteria pollutant)25

, citizens are given the opportunity to take appropriate steps to avoid exposures of

concern. Thisuse ofthe PSIcould be expanded to provide more specific health information for03 concentrations

24For a discussion ofthese programs, see the proposal.

25Currently, aPSI value of 100 for 03 corresponds to an ambient concentration of0.12
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close to the level ofthe primary standard. Given the continuum ofrisks associated with exposure to 03, this information, while perhaps ofinterest to allcitizens, would be particularly useful
to those individuals who are extremely sensitive to relatively low 03 concentrations. As an example, the proposal mentioned the possibility of expanding the PSIto include two new descriptive categories in the Index, one including concentrations within a range somewhat below the level ofthe new primary standard (with apossible descriptor of "moderately good"), the other including concentrations within a range somewhat above the level ofthe standard (with a possible descriptor of "moderately unhealthful"). Such an approach could better reflect the increased understanding ofhealth effects associated with 03 exposure developed during thisreview, and would be consistent with the recommendation ofa number ofCASAC panel members "that an expanded air pollution warning system be initiated so that sensitive individuals can take appropriate 'exposure avoidance' behavior" (Wolff, 1995b).

The proposal also discussed the use of forecasting in combination with this expanded use ofthe PSI. Fora health advisory system to be effective, citizens need to be notified as early as possible
to be able to avoid exposures ofconcern. The notice indicated that ifthe current 1-hour primary NAAQS for 03 is replaced with an 8-hour standard, there would clearly be increased value in using forecasted 03 concentrations in providing cautionary statements to the public. Currently, when ahealth advisory indicates that the 1-hour 03 PSI value of 100has been exceeded, citizens generally have time to avoid exposures ofconcern because 03 levels tend to remain elevated for several hours during the day. With the new 8- hour standard, however, this would likely not be the case, since by the time

aPSI value isreported, thepotential for prolonged exposures ofconcern would likely have passed for that day. Forecasting 8-hour maximum 03 concentrations would facilitate the riskreduction function ofthe PSI by giving citizens more time to limit or avoid exposures ofconcern.

The EPA did not formally propose revisions to the PSI in the proposal. Instead, the Administrator requested comment, and indicated that the Agency might propose revisions to the PSI in conjunction with future proposals associated with the implementation ofa revised NAAQS.

The EPA received a large number of
comments from awide variety of 

### commenters onthe usefulness ofboth

an expanded health advisory system and the forecasting of8-hour ambient 03 concentrations. Commenters 

### representing State and local agencies, business and industry associations, as well as environmental associations overwhelmingly endorsed theuse ofan expanded public health advisory system and many noted theimportance of forecasting 8-hour 03 concentrations in conjunction with thePSI,while recognizing a numberofissuesthat would need tobe addressed.

Comments from environmental associations endorsed increasing the specificity ofwarnings with regard to the health effects that could occur as a result ofexposure, and noted that citizens are capable ofdealing with complex information. These commenters alsotook exception to describing 03 levels around the levelof the standard thathave been shown to result in decreased lung function and increased respiratory symptoms, as "moderately good," statingthat this descriptor ismisleading and might not beheeded bypeople who could, ifthey fully understood thenature ofthehealth risk, take action to minimize their exposures. Other commenters felt that the descriptors "moderately good" and "moderately unhealthful" were unnecessarily confusing.

Industry commenters wereuniformly supportive ofenhancingthe risk reduction function ofthePSI byissuing health advisories with specific health information at and above the level ofthe standard. Several industry commenters alsorecommended thatthe function of the PSIbe combined with the function ofan 03

### action system, which would recommend voluntary actionsto reduce ambient 03 concentrations when the level ofthe standard is forecasted tobe exceeded. This would resultin a system that not only could provide accurate health effects information specific tothe members ofthepopulation likely to experience effects, but alsocould help prevent exposures to levels of03 at or above thelevel ofthe standard.

Commenters from State and local air pollution control authorities strongly endorsed expanding theuse ofthe PSI and the utilization offorecasted 8-hour 03 concentrations. These commenters encouraged EPA todevelop any such approaches torevise the PSIin consultation with State and local agencies, specifically in the areas of sharingreal-time 03 monitoringdata amongneighboring States, risk communication with the public, and coordination ofanational program. States alsoexpressed theneed for flexibility in the implementation ofsuch approaches and for guidance from EPA

on technical aspects such asforecasting.

The EPA will take all ofthese
comments into consideration when developing a proposal to revise the PSI (40CFR 58.50) for 03.The EPAplans
to propose these revisions, as well as revisions to the significant harm level program (40CFR 51.16), at alater date.

III.Rationale for the Secondary 03 Standard

A. Introduction
1. Overview. This notice presents the Administrator's final decision regarding the need to revise the current secondary 03 standard, and more specifically, to replace the existing 1-hour, 0.12 ppm 03 secondary NAAQS with a secondary standard equal in form, level, and averaging timeto the new 8-hour, 0.08 ppm primary standard. This decision is based on athorough review ofthe scientific information on vegetation effects associated with exposure to ambient levels of03 as assessed in the Criteria Document. This decision also takes into account:

(1) StaffPaper assessments ofthe most policy-relevant information in the Criteria Document and staffanalyses of air quality, vegetation exposure and risk, and economic values presented in the StaffPaper, upon which staff recommendations for a new 03 secondary standard were based.

(2) Consideration ofthe degree of protection to vegetation potentially afforded by the new 8-hour, 0.08 ppm primary standard compared to alternative secondary standards.

(3) CASAC advice and recommendations as reflected in discussion ofdrafts ofthe Criteria Document and StaffPaper at public meetings, in separate written comments, and in CASAC's letter to the Administrator (Wolff, 1996).

(4) Public comments received during development ofthese documents either in conjunction with CASAC meetings or separately.

(5) Extensive public comments received on theproposed decision regarding the secondary 03 standard. After taking this information into
account and for the reasons discussed in this Unit, the Administrator concludes that revisions to the current secondary standard are appropriate atthis time to provide increased protection against adverse effects to public welfare, and that itis appropriate to set the new secondary standard identical to the new primary standard.

This review has focused on 03 effects

on vegetation since these public welfare effects are ofmost concern at 03 

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concentrations typically occurring in the United States. By affecting commercial crops and natural vegetation, 03 may also indirectly affect natural ecosystem components such as soils, water, animals, and wildlife. Based on the scientific literature assessed in the Criteria Document, the Administrator believes it is reasonable
to conclude that a secondary standard that protects thepublic welfare categories ofcommercial crops and natural vegetation from known or anticipated adverse effects would also afford increased protection to these other related public welfare categories. With regard to 03 effects on manmade materials and deterioration ofproperty, the scientific literature assessed in the Criteria Document contains little new information since the last review. Accordingly, EPA again concludes for the reasons setforth in 1993 (58 FR 13008, March 9, 1993) that 03-related effects on materials do notprovide a basis for selecting an averaging time and level for a secondary standard. In addition, since the effects of03 on personal comfort and well-being (e.g.,

nose and throat irritation, chest discomfort, and cough) have been accounted for in the review ofthe primary standard, these effects are not considered in this review ofthe secondary standard.

The vegetation effects information, exposure and risk assessment, and economic analyses presented in the StaffPaper and proposal arebriefly outlined in the remainder ofUnit III.A. ofthispreamble. The key issues raised in public comments with regard to: Whether revisions to the current secondary standard are requisite to protect public welfare from adverse effects and the specific elements ofa revised secondary standard are discussed in Unit III.B. along with the Administrator's rationale for concluding that itis appropriate to revise the
current secondary standard to be identical to the new primary standard.

2. Vegetationeffects information. Exposures to 03 havebeen associated quantitatively and qualitatively with a wide range ofvegetation 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
atthe forest stand and ecosystem level. Summarized below are key findings for each ofthe above effects categories that

are discussed in more detail in the Criteria Document, StaffPaper, and proposal.

Visible foliar injury can represent a direct loss ofthe intended use ofthe plant, ranging from reduced yield and/ or marketability for some agricultural species to impairment ofthe aesthetic value ofurban ornamental species. On

alarger scale, foliar injury is occurring

on native vegetation in national parks, forests, and wilderness areas, and may be degrading the aesthetic quality ofthe natural landscape, a resource important
to public welfare.

Ozone can interfere with carbon gain (photosynthesis) and allocation of carbon with or without the presence of visible foliar injury. As aresult of decreased carbohydrate availability, remaining carbohydrates may be allocated to sites ofinjured tissue or employed in other repair or compensatory processes, thus reducing the carbohydrates available for plant growth and/or yield. Growth and yield effects of03 have been well documented for numerous species, including commodity crops, fruits and vegetables, and seedlings ofboth coniferous and deciduous tree species.

Due to a number ofdifferences between seedlings and mature trees in their responses to 03 exposures, data from tree seedling studies cannot, atthis time, be extrapolated to quantify responses to 03 in mature trees. However, long-term observational studies ofmature trees have shown growth reductions in the presence of elevated 03 concentrations. Where these growth reductions are not attributed to 03 alone, due to the presence ofmany other environmental variables, it has been reported that 03 is a significant contributor that potentially exacerbates the effects ofother environmental
stresses (e.g., pests). In addition, studies show that sensitivity to 03 with respect to visible foliar injury and growth and yield effects can vary significantly within and between species for both crops and trees.

Growth reductions can indicate that plant vigor isbeing compromised such that the plant can no longer compete effectively for essential nutrients, water, light, and space. When many 03- 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 ofenergy flow and nutrient cycling can alter ecosystem 

### succession.

In the CASAC closure letter, all CASAC panel members agreed that "damage is occurring to vegetation and natural resources at concentrations below thepresent 1-hour national ambient air quality standard (NAAQS) of0.12 ppm," and the vegetation experts agreed that "plants appear to be more sensitive to 03 than humans" (Wolff, 1996). Further, the CASAC panel agreed "that a secondary NAAQS, more stringent than the present primary standard, was necessary to protect vegetation from 03" (Wolff, 1996). The Administrator concurred in the proposal with theunanimous view ofCASAC that the current standard of0.12 ppm, i-hour average, does not provide adequate protection to vegetation from the adverse effects of03, based on the following specific observations that

were taken from key studies and other biological effects information reported in the 03 Criteria Document and Staff Paper:

(1) 03 concentrations > 0.10ppm can be phytotoxic to a large number ofplant species, and can produce acute foliar injury responses and reduced crop yield and biomass production.

(2) 03 concentrations within the range of0.05 to 0.10 ppm have the potential

over a longer duration ofcreating chronic stress on vegetation that can result inreduced plant growth and yield, shifts in competitive advantages in mixed populations, decreased vigor leadingto diminished resistance to pest and pathogens, and injury from other environmental stresses. Some sensitive species can experience foliarinjury and growth and yield effects even when concentrations never exceed 0.08ppm.

The Administrator further concluded that the available scientific information supports the conclusion that a cumulative seasonal exposure index, such asthe proposed SUM06 index,26is

more biologically relevant than a single
event or mean index.

3. Vegetationexposureand risk analyses.In reaching ajudgment in the proposal as to a standard requisite to protect crops and vegetation against the adverse effects of03,the Administrator took into account several additional considerations including the extentof exposure of03-sensitive species, potential risks ofadverse effects to such 

### species, and monetized and nonmonetized categories ofincreased 

### vegetation protection associated with reductions in 03 exposures. In so doing, the Administrator recognized that markedly improved air quality, and thus significant reductions in 03 exposures would result from attainment ofthe alternative 0.08 ppm, 8-hour primary standards within the range of 1- and 5- expected exceedance forms. Thus, as a matter ofpolicy, the Agency estimated the increased protection from 03-related

26The SUM06 exposure index cumulates over a given time period and diurnal window all hourly 03 concentrations greater than or equal to 0.06 ppm. 

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effects on vegetation associated with attainment ofalternative 8-hour, 0.08 ppm primary standards, and then considered the incremental protection associated with attainment ofa seasonal secondary standard.

The ability ofEPA to characterize 03 air quality in rural and remote sites was limited bythe available rural 03 monitoring network. Therefore, EPA conducted national analyses using geographic information systems (GIS) and data from existing air quality monitoring sites to estimate seasonal 03 air quality for the year 1990, in terms of the 3-month, 12-hour, SUM06 exposure index. The year 1990 was selected because it was afairly typical year in terms of03 air quality. The estimated 1990 air quality was then used as a baseline from which to rollback 03 concentrations to project 03 air quality that would be expected to occur when alternative standards werejust attained.

The regulatory scenarios examined included just attaining the existing 1- hour secondary standard, alternative 8- hour primary standards in the range of 0.07 to 0.09 ppm, including standards
set at0.08 ppm, with 1- and 5-expectedexceedance forms, and a range of seasonal standards usingthe SUM06 index, based on a single year ofdata. Estimates of air quality associated with alternative 8-hour primary standards with 1- and 5-expected-exceedance forms were used to roughly bound air quality estimates for 8-hour standards with concentration-based forms ranging from the annual second- to the fifthhighest concentration-based forms, and including the proposed third-highest concentration-based form.

By comparing these projected air quality scenarios for alternative standards with maps showing the growing regions for 03-sensitive crops and tree seedling species, estimates of exposures ofconcern and risks of adverse effects for various species were developed for alternative standards. Taking into account the body of information concerning 03 effects on vegetation, as presented in the Criteria Document and StaffPaper and summarized in theproposal, EPA considered both quantifiable risks (when exposure-response functions

were available) as well as those risks that could onlybe qualitatively characterized.

The Administrator concluded in the proposal that attaining a 8-hour, 0.08 ppm primary standard within therange offorms under consideration would provide substantially improved protection ofvegetation from seasonal 03 exposures ofconcern. The Administrator recognized, however, that some areas may continue to have elevated seasonal exposures, including forested park lands and other natural

areas and Class I areas that are federally mandated to preserve certain air quality related values.

In its discussions ofuncertainties, described in theproposal, the CASAC Panel members expressed concerns about the use ofthe GIS methodology to project national 03 air quality and exposures of03-sensitive species. As is the case with other analytic methods (e.g., Krieging, inverse distance weighting), the GIS methodology contains numerous assumptions and uncertainties, and incorporates various databases each with their own set of uncertainties. As noted in the Staff Paper and proposal, the EPA and CASAC recognized that the uncertainties in exposure and risk estimates derived from the GIS methodology are large and unquantifiable, but that the method provides useful information that is appropriate to consider in comparing the relative protection afforded by alternative standards. Further, EPA noted in the StaffPaper and proposal that the GIS-generated air quality estimates compare reasonably well with the limited available 03 monitoring data. In taking the results from these analyses into account, the Administrator recognized these inherent limitations and primarily considered the comparative results in assessing the degree ofprotection afforded by alternative standards.

While the analyses discussed above indicated that an 8-hour, 0.08 ppm primary standard within the range of alternatives considered, would provide increased protection for commercial and natural vegetation, itremained uncertain as to the extent to which air quality improvements designed to reduce 8-hour 03 concentrations would reduce 03 exposures measured by a seasonal SUM06 index. To further explore this question, EPA also examined the design values for alternative 8-hour, 0.08 ppm standards, within the range of1- and 5-expected exceedances, averaged over 3 years, and

a 3-month, 12-hour SUM06 standard for 581 counties (thosehaving sufficient monitoring data for theperiod 1991

- 1993). As discussed in the StaffPaper and proposal, this analysis revealed that almost all areas that are within or above

a SUM06 range of25-38 ppm-hours would also have an 8-hour daily maximum design value ofgreater than 0.08 ppm. Thus, in those areas in which air quality monitoring isbeing conducted, areas that would likely be of
most concern for effects on vegetation, as measured by the SUM06 exposure index, would also be addressed by an 8- hour primary standard set at a0.08 ppm level.

4. Monetizedestimatesofvegetation 

### protection.As discussed in section VII.F. ofthe StaffPaper and in the proposal, EPA developed monetized estimates ofincreased protection associated with several alternative standards for economically important commodity crops nation-wide 27 and for fruit and vegetable crops in California.28

These analyses were based on the GISgenerated projections of03 air quality for various alternative standards. Monetized estimates ofincreased protection could notbe developed for other important categories ofvegetation, such asurban ornamentals, Class I
areas, and commercial and other forests because ofa lack ofavailable concentration-response functions and appropriate economic valuation models. The available data suggested, however, that reductions in ambient 03 concentrations resulting from attainment ofalternative standards would confer increased protection for these categories as well by reducing biomass loss,protecting functional, aesthetic, and existing values, and by preserving biodiversity and native habitats.

As summarized in the proposal, most ofthe monetized estimates ofincreased protection would accrue from attainment ofan 8-hour, 0.08 ppm primary standard, with a smaller incremental improvement obtained by the addition ofa seasonal secondary standard. In contrast, the incremental protection obtained from the addition of

a seasonal secondary standard would be considerably more significant when compared to an alternative 8-hour primary standard at a level of0.09 ppm.
B. Need forRevision ofthe Current SecondaryStandard



### Based on the above considerations and the rationale in theproposal, the Administrator proposed and sought
comment on two alternative standards, either ofwhich in herjudgment would be appropriate to protect public welfare from known or anticipated adverse effects given the available scientific knowledge. The two alternatives were setting the revised secondary standard

27Including 15 species, representing approximately 75% ofthe U.S. sales ofagricultural crops, evaluated in the National Crop Loss Assessment Network (NCLAN) studies undertaken in the early to mid-1980's, which provide the largest,most uniform database on the effects of03

on agricultural crop species.

28These fruit and vegetable crops constitute approximately 50% ofthe Nation's fruits and vegetable markets. 

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identical to the proposed 8-hour, 0.08 ppm primary standard, or establishing a 3-month, 12-hour, SUM06 seasonal secondary standard at the level of25 ppm-hours. The Administrator recognized that it would be areasonable policy choice to set the revised secondary standard identical to an 0.08, 8-hourppm primary standard, but also recognized that a SUM06 seasonal standard is more biologically relevant and, therefore, was also appropriate to consider.

In reaching her final decision on a revised secondary standard, the Administrator has taken into account several factors. First, she again concludes based on information presented in the Criteria Document and StaffPaper, and summarized in the proposal and in thispreamble, that the existing secondary standard does not provide adequate protection for vegetation against the adverse welfare effects of03.

Second, she has considered the
comments made by the CASAC Panel members during their reviews ofthese documents and in CASAC's closure letter, "that a secondary NAAQS, more stringent than thepresent primary standard, was necessary to protect vegetation from 03" (Wolff, 1996). These statements provide strong support to the Administrator's judgment that the body ofscientific evidence on 03 effects

on vegetation provides sufficient and compelling evidence that the current secondary standard is not adequately protective and should be revised.

Third, the Administrator recognizes that significant uncertainties remain with respect to exposure dynamics, air quality relationships, and estimates of increased vegetation protection which

are important factors in selecting an appropriate secondary standard, as described more fully in the Criteria Document, StaffPaper and proposal. The CASAC closure letter highlighted key uncertainties that hampered the Panel's ability to make any recommendations as to an appropriate form or level for a secondary standard that would be protective against adverse effects on vegetation from exposure to ambient levels of0 3. The Panel stated that "agreement on the level and form ofsuch a standard is still elusive" and "***there remain important limitations
to ourunderstanding ofthe extent ofthe response ofvegetation to 03 under field conditions" (Wolff, 1996). These uncertainties are largely a result of inadequate rural and remote 03 air quality data that would allow with greater certainty determination ofthe relationships between 03-related effects being observed in the field and ambient 03 exposures. Nevertheless, the alternative standards proposed by the Administrator are consistent with the range ofviews expressed bythe CASAC panel members, and CASAC recognized that choosing between the two alternatives is apolicy decision that
cannot be based solely on science (Wolff, 1996).

Fourth, the Administrator recognized thatjust attaining the 8-hour, 0.08 ppm, 1- and 5-expected exceedance alternatives results in markedly improved air quality when compared to just attaining the existing secondary standard, with only slight improvements associated with going from a5- to 1-expected exceedance form.

Fifth, the Administrator has carefully considered the information and views provided in the public comments. Though these comments yielded no new scientific information relevant to choosing between the two alternative proposed standards, many commenters repeated the CASAC's concerns over the significant uncertainties remaining in the database. Many ofthese commenters expressed the view that EPA should wait to set a seasonal secondary standard untilbetter rural air quality data were available, which would allow for better characterization ofthe magnitude ofimprovements in public welfare protection likely to be afforded by such a standard compared to a revised primary standard.

In sharp contrast, other commenters expressed the view that the available data were sufficient to demonstrate a need to set a seasonal secondary standard to protect vegetation against the adverse effects of03, and many such
commenters recommended the proposed SUM06 form for such a standard. A significant number ofthese
commenters also made recommendations on the appropriate level for a seasonal SUM06, generally recommending levels lower than the proposed 25 ppm-hours, ranging from 8
to 20 ppm-hours. The key source frequently cited in support ofthese recommendations is an article by Heck and Cowling (1997) which summarizes the outcome ofaconsensus-building workshop sponsored bythe Southern Oxidant Study group on the secondary standard held in January 1996.

This workshop was attended by 16 scientists with backgrounds in agricultural, managed forest, natural systems, and air quality, allofwhom are leaders in their fields and whose research formed the basis ofmuch ofthe research examined in the Criteria Document. These scientists expressed theirjudgements on what standard level(s) would provide vegetation with adequate protection from 03-related adverse effects.

Though the report identified no new data in support ofthe scientists' recommendations, the Administrator believes that the report lends important support to the view that the current secondary standard is not adequately protective ofvegetation. Further, the Administrator believes that the report foreshadows the direction offuture scientific research in this area, the results ofwhich could be important in future reviews ofthe 03 secondary standard.

As theresults ofsuch research become available, EPA will be in a better position to characterize rural air quality and the improvements in vegetation protection that would result from a seasonal secondary standard, and to select a standard level that would provide adequate protection for vegetation. However, given the present limits ofthe scientific evidence of03- related effects and ofrural air quality data, as discussed in the Criteria Document, StaffPaper, the proposal, and by CASAC, the Administrator has decided that itis not appropriate to

move forward with a seasonal secondary standard at this time for thereasons described below. In coming to this conclusion, the Administrator specifically considered the significant improvements inpublic welfare protection that are expected to be afforded by the new 8-hourprimary standard, as well as the value of obtaining additional information to better characterize 03-related effects on vegetation under field conditions.

C.FinalDecisionon theSecondary Standard

Based on the scientific evidence, CASAC advice and recommendations, comments received on the proposal, and the considerations summarized above, the Administrator isreplacing the current secondary 03 standard with an 8-hour standard, set at a level of0.08 ppm, identical in allrespects to the new primary standard. The Administrator judges that this standard willprovide substantially improved protection for vegetation from 03-related adverse effects as compared to that provided by the current 1-hour, 0.12 ppm secondary standard, while allowing time for additional research and the development ofa more complete rural monitoring network and air quality database from which to evaluate the elements ofan appropriate seasonal secondary standard.

The decision notto set a seasonal secondary standard atthis time is based 

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in large part on the Administrator's recognition that the exposure, risk, and monetized valuation analyses presented in the proposal contain substantial uncertainties, resulting in only rough estimates ofthe increased public welfare protection likely to be afforded by each ofthe proposed alternative standards. These uncertainties were discussed in theproposal and the Staff Paper and were noted byCASAC (Wolff, 1996). In light ofthese uncertainties, the Administrator has decided it is not appropriate at this time to establish a

new separate seasonal secondary standard given the potentially small incremental degree ofpublic welfare protection that such a standard may afford. Instead, the Administrator finds it areasonable policy choice to set a

new secondary standard identical to the

new primary standard, while focusing additional research on key areas for consideration in the next review ofthe 03 criteria and standards.

Continued research on the effects of 03 on vegetation under field conditions and on better characterizing the relationship between 03 exposure dynamics and plantresponse willbe important in the next review because:

(1) The available biological database highlights the importance of cumulative, seasonal exposures as a primary determinant ofplant responses.

(2) The association between daily maximum 8-hour 03 concentrations and plant responses has notbeen specifically examined in field tests.

(3) The impacts ofattaining an 8- hour, 0.08 ppm primary standard in upwind urban areas on rural air quality distributions cannot currently be characterized with confidence due to limited monitoring data and air quality modeling in rural and remote areas.

Setting the secondary standard equal
to theprimary standard will allow EPA the opportunity to evaluate more specifically the improvement in rural air quality and in 03-related vegetation effects resulting from measures designed
to attain the new primary standard. This information in turn will allow for better evaluation ofthe incremental need for a separate seasonal secondary standard in the next review ofthe 03 criteria and standards.

In the proposal, the Administrator solicited comment on the appropriate spatial scale ofan expanded rural monitoring network. Relatively few
comments were received regarding an expanded rural monitoring network, but those who did submit comments were generally in favor ofan expanded network to allow for improved modelling oflong-range transport of03 and its precursors and forbetter characterization of03 air quality in rural and remote areas. Those comments will serve to inform EPA's development ofrevised air quality surveillance requirements (40CFRpart 58) that will be proposed at alater date.

With respect to the proposed seasonal secondary standard only, theproposal sought comment on whether 03 concentrations from several monitors should be spatially integrated when determining compliance with the standard. Only afew comments were received, with some supporting and

some opposing spatial integration of03 concentrations from several monitors.

In view ofthe Administrator's decision to replace the current secondary standard with a secondary standard which is identical in form, level, and averaging time to the new 8- hour, 0.08 ppm primary standard, rather than with a seasonal standard, EPA is
not adoptingthe useofspatial averaging for the new secondary standard.

To decrease some ofthe uncertainties discussed above and to remedy the lack ofair quality data in rural and remote

areas ofcommercial or ecological importance for vegetation, the Administrator reiterates her intention, expressed in the proposal, to expand the rural 03 monitoring network. The EPA will propose revised 03 air quality surveillance requirements (40 CFRpart 58) at a later date. The EPA is exploring opportunities to work with other Federal agencies to develop a coordinated and long-term rural monitoring network. 

### IV. OtherIssues
Several commenters raised key legal and procedural issues that are discussed below. These include: (1) Whether EPA
must give consideration to costs and similar factors in settingNAAQS; (2) whether EPA erred in its selection ofa methodology for determining the level ofa NAAQS thatprotects public health with an adequate margin ofsafety; (3) 

### whether EPAcommitted aprocedural

error bynot extending the comment 

### period; and (4)whether the 1990 amendments to the Act preclude EPA from revising the 03 NAAQS to establish anew 8-hour standard. Responses to other legal and procedural issues are included in the Response-to

### Comments Document.

A. CostConsiderations



### For morethan aquarter ofa century, EPA has interpreted section 109 ofthe Act asprecluding consideration ofthe economic costs or technical feasibility ofimplementing NAAQS in setting them. As indicated in the proposal, a number of judicial decisions have confirmed this interpretation. Natural ResourcesDefense Councilv. Administrator, 902 F.2d 962, 972-73 (D.C. Cir. 1990)(PM NAAQS)("PM10"), vacated, in part, dismissed, 921 F.2d 326 (D.C. Cir.), certs. dismissed, 498 U.S. 1075, and cert. denied, 498 U.S. 1082 (1991); Natural ResourcesDefense Councilv. EPA,824 F.2d 1146,1157-59 (D.C. Cir. 1987)(en banc)(CAA section 112 standards for vinyl chloride)("Vinyl Chloride"); AmericanPetroleum Institutev. Costle, 665 F.2d 1176, 1185- 86 (D.C. Cir. 1981)(ozone NAAQS)("Ozone"), cert. denied, 455 U.S. 1034 (1982); LeadIndustriesAss'n

v.EPA, 647 F.2d 1130, 1148-51 (D.C. Cir.)(lead NAAQS)("Lead Industries"),
cert. denied, 449 U.S. 1042 (1980).

Some commenters have argued that
costs and similar factors should, nonetheless, be considered, both in this rulemaking and in the rulemaking on proposed revisions to the NAAQS for particulate matter. Although most ofthe commenters' arguments are inconsistent with thejudicialdecisions cited above, several commenters have argued that those decisions are not dispositive. For

reasons discussed below and in the Response-to-Comments Document, EPA disagrees with these comments and maintains its longstanding interpretation ofthe Act as precluding consideration ofcosts and similar factors in settingNAAQS.

1.Background.Given the nature of the points raised, abriefreview ofthe issue seems useful before addressingthe comments. The requirement that EPA establish national ambient air quality standards for certain pollutants, to be implemented bythe States, was enacted in 1970 as part of a setof comprehensive amendments that established the basic framework for Federal, State, and local airpollution control. When EPApromulgated the original NAAQS in 1971, its first Administrator, William D.Ruckelshaus, concluded that costs and similar factors could notbe considered in that decision. 29 This conclusion was not challenged in litigation on the original NAAQS. Ithas been confirmed since then, however, by everyjudicial decision that has considered the issue.

As discussed below, EPA's interpretation rests primarily on the language, structure, and legislative history ofthe statutory scheme adopted in 1970. It is also supported bythe judicialdecisions cited above, as well as by legislative developments since 1970 that reaffirm Congress' original approach to the issue.

2936FR 8186, Apr. 30, 1971. EPA has maintained
thisinterpretation consistently sincethen. 

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Without cataloguing allrelevant aspects ofthe 1970 amendments and their legislative history, several basic points should be noted. Under section 109(b) ofthe Act, NAAQS areto be "based on" the air quality criteria issued under section 108. Under section 108(a)(2), the kind ofinformation EPA is required to include in criteria documents is limited to information about health and welfare effects "which may be expected from the presence of [a] pollutant in the ambient air 

### ***."
There is no mention ofthe costs or difficulty ofimplementing the NAAQS,

nor of "effects" that might result from implementing the NAAQS (as opposed
to effects ofpollution in the air).30 By contrast, Congress explicitly provided for consideration ofcosts and similar factors in decisions under other sections ofthe Act.31Moreover, States were permitted to consider economic and technological feasibility in developing plans to implement the NAAQS to the extent such consideration did not interfere with meeting statutory deadlines for attainment ofthe standards. 32Finally, the legislative history indicated that Congress had considered the issue and had deliberately chosen to mandate NAAQS that would protect health regardless of

concerns about feasibility. 3 3
The firstjudicial decision on the issue

came in the Lead Industries case. An industry petitioner argued that EPA should have considered economic and technological feasibility in allowing a "margin ofsafety" in settingprimary

30Thatconsideration ofsuch factors was not intended in NAAQS decisions is also supported by section 109(a)(1). For pollutants for which air quality criteriahad been issued prior to the 1970 amendments, that provision required EPA to propose NAAQS within 30 days after enactment and to take final action 90 days later. The criteria issued previously did notinclude information on costs and similar factors, and it would have been difficult if notimpossible for EPA to supplement them in time to include meaningful consideration of such factors in NAAQS proposed 30 days after
enactment.

31See, e.g., sections 110(e)(1), I1 1(a)(1), 231 (b) (1970 Act); see also, e.g., sections 113(d)(4)(C)(ii), 125(a)(3), 202(a)(3)(C), 317 (1977 Act).

32 UnionElectric Co. v. EPA, 427 U.S. 246,257
58 (1976).

33The Senate report on the 1970 amendments stated: "In the Committee discussions, considerable

concern was expressed regarding the use ofthe concept of technical feasibility as thebasis of ambient air standards. The Committee determined that (1) the health ofpeople is more important than the question ofwhether the early achievement of ambient air quality standards protective ofhealth is technically feasible; and, (2) the growth ofpollution load in many areas, even with application of available technology, would still be deleterious to public health."

"Therefore, the Committee determined that existing sources ofpollutants either should meet the standard of the law orbe closed down

S. Rep. No. 91 1196, at 2-3 (1970). standards for lead. Based on adetailed review ofthe language, structure, and legislative history ofthe statutory scheme, the U.S. Court ofAppeals for the District ofColumbia Circuit concluded that:

This argument is totally without merit. [Thepetitioner] is unable topoint to anything in eitherthe language ofthe Actor its legislative history that offers any support for its claim ***. Tothe contrary, the statute and its legislative history make clear that economic considerations play no part in the promulgation ofambient air quality standards under section 109.
647 F.2d at 1148.

The Court cited anumber ofreasons for this conclusion. Id. at 1148-50. Among other things, it noted the
contrast between section 109(b) and other provisions in which Congress had explicitly provided for consideration of economic and technological feasibility,

aswell as therequirement that NAAQS be based on air quality criteria defined without reference to such factors. Id. at 1148-49 &n.37. The Court also noted that, in developing plans to implement NAAQS, States may consider economic and technological feasibility only to the
extent that this does not interfere with meeting the statutory deadlines for attainment ofthe standards; and that EPA may not consider such factors at all in deciding whether to approve State implementation plans. Id. at 1149 n.37 (citing UnionElectricCo. v. EPA, 427 U.S. 246, 257-58, 266 (1976)). 3 4

As to the legislative history ofthe 1970 amendments, the Court observed that:

[T]he absence ofanyprovision requiring consideration ofthese factors was no accident; itwas theresult ofadeliberate decision by Congress to subordinate such

concerns tothe achievement ofhealth goals.
Id. at 1149. Citing several leading Supreme Court decisions, as well as the Senate report quoted above, the Court noted that Congress had intended a drastic change in approach toward the control ofair pollution in the 1970 amendments and was well aware that sections 108-110 imposed requirements ofa "technology-forcing" character. Id. 35

The Court also noted that Congress had already acted, in further amendments adopted in 1977, to relieve

some oftheburdens imposed by the 1970 amendments. Id. at 1150 n.38.

34These limitations would, ofcourse, make little

sense if such factors could be considered in setting the NAAQS themselves.

35Such requirements " 'are expressly designed to force regulated sources to develop pollution control devices that mightat the time appear to be economically ortechnologically infeasible.' " Id. (quoting UnionElectric Co. v. EPA, 427 U.S. at257). Observing that Congress had, however, declined to amend section 109(b) to provide for consideration ofcosts and similar factors as requested by industrial interests, id. n.39, the Court concluded:

A policy choice such as this is one which onlyCongress, notthe courts and notEPA,

can make. Indeed, the debates onthe [1970 amendments] indicate thatCongress was quiteconscious ofthis fact***.

*** [I]fthere is aproblem with the economic or technological feasibility ofthe lead standards, [the petitioner], or anyother party affected bythe standards, musttake its

caseto Congress, the onlyinstitution with theauthority toremedy the problem.
Id. at 1150.

After the decision in Lead Industries, Supreme Court review was sought on the question whether costs and similar factors could be considered in setting NAAQS, among other issues. The Supreme Court declined to review the decision. LeadIndustries A ss'nv. EPA, 449 U.S. 1042 (1980). The subsequent decisions in Ozone, Vinyl Chloride, and PM10, cited above, strongly reaffirmed the interpretation adopted in Lead Industries.3 6 Supreme Court review of the Ozone and PM10 decisions was sought but denied. American Petroleum Institutev. Gorsuch,455 U.S. 1034 (1984);AmericanIronandSteel Institutev. EPA, 498 U.S. 1082 (1991).

The Lead Industries opinion focused largely, though not exclusively, on the 1970 amendments and theirlegislative history. Perhaps as a result, it did not

canvass all the factors that, in fact, supported its conclusions atthe time. For example, when Congress enacted major amendments to the Act in 1977, it was clearly aware that some areas of the country had experienced difficulty in attempting to attain some ofthe NAAQS.3 7 It was also aware that there might be no health-effects thresholds for the pollutants involved, and that significant uncertainties are inherent in settinghealth-based standards under the Act.38 In response, Congress made

36In thePM1 0 case, for example, the Court considered an argumentthatEPAshould have considered potentialhealth consequences of unemployment that mightresult fromrevision of theprimary NAAQS for PM:

"This claimis entirely withoutmerit.Inthree previous cases,thiscourthas emphatically stated thatsection 109 does notpermit EPAtoconsider such costsin promulgatingnationalambient air qualitystandards ***. Itis onlyhealtheffects relatingtopollutantsin the air thatEPAmay consider

.***Consideration ofcosts associated withalleged healthrisksfrom unemployment wouldbe flatlyinconsistentwith the statute, legislativehistory and caselaw on this point."

902F.2d at973 (emphasisin original; citations omitted).

37

See, e.g., H.R.Rep. No.95 294, at207 17 (1977).

38

See, e.g., id.at 110 12; id.at43 51. 

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significant changes in the provisions for implementation ofthe NAAQS, including changes intended to ease the burdens of attainment. It also amended sections 108 and 109 in several ways; for example, by requiring periodic review and, if appropriate, revision of air quality criteria and NAAQS and by establishing a special scientific advisory committee (CASAC) to advise EPA on such reviews. Notably, Congress recognized that implementation of NAAQS could cause "adverse public health, welfare, social, economic, or energy effects" and charged CASAC with advising EPA on such matters.3 9

Yet itmade no changes in sections 109(b) or 108(a)(2); that is, in the substantive criteria for setting or revising NAAQS. In other words, Congress chose to address economic and other difficulties associated with attainment ofthe NAAQS by adjusting the scheme for their implementation, rather than by changing the instructions for settingthem. 4 0 Congress enacted major amendments to the Act again in 1990, well after the Lead Industries and Ozone decisions that interpreted section 109 as precluding consideration ofcosts in NAAQS decisions. 4' In doing so, Congress was clearly aware of intervening developments such as EPA's decision to revise the PM NAAQS in 1987-the result ofan elaborate review

39Section 109(d)(2)(C)(iv). Some commenters have argued that thisprovision requires EPA to consider such effects in setting NAAQS. From the language and structure ofsection 109(d), however, it is clear that CASAC's responsibility to advise on these factors is separate from its responsibility to review and recommend revision ofair quality criteria and NAAQS, and that the advicepertains
to theimplementation ofNAAQS rather than to setting them. The legislative history confirms this view, indicating that the advice was intended for the benefit of the States and Congress. See H.R. Rep. No. 95 294, at 183 (1977).

40 The 1977 amendments alsorequired EPA to
prepare economic impact assessments forspecified actions but limited the requirement to non-healthbased standards, excluding decisions under sections 109 and 112. Section 317; H.R. Rep. No. 95 294, at 51 52 (1977). In this and other respects, Congress continued the approach it took in the 1970 amendments, making careful choices as to when consideration ofcosts and similar factors would be required and giving paramount priority to protection ofhealth. See 123 Cong. Rec. H8993 (daily ed. Aug.4, 1977) (Clean Air Conference Report (1977); Statement ofIntent; Clarification of Select Provisions), reprinted in 3 Senate Committee

on Environment and Public Works, 95th Cong., A Legislative History ofthe Clean AirAct Amendments of 1977, at 319 (1978).

41In the interim, the National Commission on Air Quality had also submitted its report to Congress as required by aprovision ofthe 1977 amendments. Among otherthings, the Commission recommended that the statutory approach ofrequiringNAAQS to be set atlevels necessary to protect public health, without consideration ofeconomic factors, be continued without change. National Commission on Air Quality,To Breathe Clean Air55 (1981).] in which the Administrator strongly underscored the scientific uncertainties involved 42 -and the Vinyl Chloride case drawing a sharp distinction between sections 109 and 112 with regard to consideration ofcosts and similar factors. 43 Indeed, the legislative history ofthe 1990 amendments reflects Congress' understanding that primary NAAQS were to be based on protection ofhealth "without regard to the economic or technical feasibility of attainment." 44 Again, however, Congress chose to respond to severe, widespread, and persistent problems with attaining the NAAQS by adjusting the scheme for their implementation rather than by changing thebasis for settingthem. See, e.g., sections 181-192.

2. Publiccomments. As noted previously, anumber ofcommenters have argued that costs and similar factors should be considered in EPA's final decisions on revision ofboth the

ozone and particulate NAAQS. Aside from arguments that are simply inconsistent with thejudicial decisions cited above, some ofthe commenters argue that those decisions are not dispositive for avariety ofreasons. One commenter submitted aparticularly comprehensive version ofthis argument in the rulemaking on proposed revisions to theparticulate NAAQS; the following discussion focuses primarily on points raised bythat commenter, among others. 45

As a general matter, the commenter acknowledges that Congress intended to

42 As the Administrator indicated in EPA's proposal to revise thePM standards:

"[T]hat review has revealed a highly limited data base-particularly where quantitative studies are concerned and a wide range ofviews among qualified professionals about the exact pollution levels at which health effects are likely to occur. The setting ofan 'adequate margin ofsafety' below these levels calls for a furtherjudgment-in an area for which the scientific data base is even more sparse and uncertain***."

"[L]ong and expert review ofpublic health issues has to date revealed no scientific method of assessing exactly what level ofstandards public health requires. The scientific review indicates substantial uncertainties concerning the health risks associated with lower levels ofparticulate matter."

49 FR 10408, 10409, Mar. 20, 1984. 43Congress was clearly aware ofthe 1987 decision torevise the PMNAAQS, which among other things involved changing the indicator for particulate matter from "total suspended particulate" to PM1 o,because it enacted special nonattainment provisions, as well as provisions for PSD increments, applicable to PM10. Sections 188 190; section 166(f). It was clearly aware ofthe Vinyl Chloride decision because it amended section 112 in response to that decision, essentially creating a

new scheme for setting emission standards for hazardous pollutants.

44H.R.Rep. No. 101 490, pt. 1, at 145 (1990). See also S. Rep. No. 101 228, at 5 (1989).

45Additional responses to points raised by this
commenter and others are included, as appropriate, in the Response-to-Comments document. preclude consideration ofeconomic costs and similar factors in setting NAAQS. The commenter argues, however, that thisis so onlywhen the scientific basis for NAAQS is "clear and compelling" or "unambiguous." From that premise, the commenter advances three key assertions:

(1) Where non-threshold pollutants

are involved and the health evidence is ambiguous, section 109 must be interpreted to allow consideration ofall relevant factors, including the practical consequences ofEPA's decisions;

(2) To the extent thejudicial decisions cited above are read as precluding this, they rest on afaulty analysis that predates and cannot survive scrutiny under Chevron, U.S.A. v. NaturalResources Defense Council,467 U.S. 837 (1984);46 and

(3) Because EPAhas discretion to consider costs and similar factors where the health evidence is ambiguous, it
must do so in light ofExecutive Order 12866, 58 FR51735, Oct. 4, 1993, and
tworecent statutes, the Unfunded Mandate Reform Actof 1995, 2 U.S.C.

secs. 1501-1571 (UMRA), and the Small Business Regulatory Enforcement Fairness Act of 1996, Pub. L.No. 104- 121, 110 Stat. 857 (SBREFA), which in part amended the Regulatory Flexibility Act, 5 U.S.C. secs. 601-808.

EPA believes all three assertions are clearly incorrect. Regarding the first point, it should be evident, both from previous NAAQS decisions and from the court opinions upholding them, that the scientific basis forNAAQS decisions has neverpointed clearly and unambiguously to a single "right answer." 47 This is inherent in the statutory scheme for the establishment and revision ofNAAQS, which in effect requires them to be based on the "latest

46 Several other commenters argue that the cited
decisions arenot dispositive because theyheld only that EPA is not required to consider costs and similar factors in setting NAAQS. As discussed below in connection with Chevron, however,the decisions clearly concluded that Congress intended
to preclude consideration ofsuch factors, and that EPA is notfree to alter that congressional choice. Although these conclusions are technically dicta, nothing in the Court's opinions suggests that it would have interpreted section 109 differently had EPA claimed authority to consider costs and similar factors in NAAQS decisions. Indeed, the tone ofthe opinions argues to the contrary. See, e.g., PM10,902 F.2d at 973. Cf.Ethyl Corp.v. EPA, 51 F.3d 1053 (D.C.Cir. 1995).

47See, e.g., Lead Industries, 647 F.2d at 1146 47, 1153 56, 1160 61, 1167 n.106. In enacting the 1970 amendments, Congress was aware that there were gaps in the scientific information available then as

abasis for establishing the original NAAQS. See,
e.g., S. Rep. No. 91 1196, at 9 11 (1970). If anything, Congress had an even greater understanding ofthe point when it enacted that 1977 amendments without changing the substantive criteria for setting NAAQS. See H.R.Rep. No. 95 294, at 43 51, 181 82 (1977). 

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scientific knowledge" on potential health and welfare effects ofthe pollutant in question. See sections 109(b), 108(a)(2). Although advances in science increase ourunderstanding of such effects, they also raise new questions. Forthis reason, the key studies for any given decision on revision ofaNAAQS are, almost by definition, "at the very 'frontiers of scientific knowledge.' "48 That is, studies that call into question the adequacy ofa standard are always those that gobeyond previous studies-by reporting new kinds ofeffects, for example, or effects atlower concentrations than those at which effects have been reported previously.

As with pioneering work in other fields, such studies may have a variety ofstrengths and limitations. 49 As a result, the validity and implications of such studies may be both uncertain and highly controversial. Given the precautionary nature ofsection 109, 50 however, itis precisely these kinds of studies that the Administrator must grapple with when advances in science suggest that revision ofaNAAQS is appropriate.

As aresult, the EPA stafftypically recommends for consideration, and the Administrator may propose for comment, a range ofalternatives based

on what the commenter would call "ambiguous" science. In this respect, the current reviews ofthe NAAQS for

ozone and particulate matter are not unusual and do not differ, for example, from the review that led to adoption of the PM10 NAAQS in 1987. 51Indeed, the NAAQS that were upheld in the Lead Industries, Ozone, and PM10 decisions

were allbased on highly controversial health evidence; the Lead Industries decision took note ofcongressional statements recognizing that there may be no thresholds for criteria pollutants; and the Ozone and PM1odecisions noted the Administrator's findings that

48Lead Industries, 647 F.2d at 1147 (quoting Ethyl Corp.v. EPA, 541 F.2d 1, 24 27 (D.C. Cir.) (en banc), cert. denied, 426 U.S. 941 (1976)).

49They mayhave methodological flaws, for example, but nonetheless report effects that are of serious medical significance; or theymay be of impeccable quality butinvolve effects ofuncertain significance. Others mayinvolve results that are striking buthard to explain in terms ofprevious knowledge, orresults that seem plausible and important butare notyet replicated by other studies.]

50See, e.g., Lead Industries, 647 F.2d at 1155 56;
H.R. Rep. No. 94 295, at 43 51 (1977).

51As previously discussed, the Administrator strongly emphasized the uncertainties involved in that review. As aresult of theuncertainties, he proposed "relatively broad" ranges for comment, though hefocused on lower levels within the ranges

as providing greater margins of safety against the health risks involved. See 49FR 10408, 10409, Mar. 20, 1984. 

### clear thresholds could notbeidentified for ozone andparticulate matter, respectively. 52

### Thus, the present decisions on revision ofthe NAAQS for

ozone andparticulate matter cannot be distinguished from those pastdecisions in terms ofthe nature ofthehealth evidence orpollutants involved. 53



### Regarding the second ofthe commenter's key assertions, EPA believes it isclear thatthejudicial decisions cited above were correctly decided and continue tobe good law under Chevron. In Chevron, the Supreme Courtessentially reaffirmed the principlethat courts must deferto reasonable agency interpretations ofthe statutes they administer where Congress has delegated authority to them to elucidate particular statutory provisions. Where the intent ofCongress

on an issueis clear, however, it must be given effect by the agency and the courts. See 467U.S. at 842-45. Thus, the first question on review ofan agency's interpretation under Chevron is "whether Congress has directly spoken to theprecise question atissue." Ifthecourt determines thatit hasnot, the remainingquestion for the court is "whether the agency's answer isbased

on apermissible construction ofthe statute." 467U.S. at 842-43 (footnote omitted). In determining whether Congress "had an intention on the precise question atissue," acourt employs "traditional tools ofstatutory construction." Id. at 843 n.9. 54



### In essence, thecommenter's argument here isthat theLead Industries decision did not address whetherCongress had "spoken directly" totheprecise issue posed by thecommenter; thatis, whether section 109must be interpreted differently forNAAQS decisions involving non-threshold pollutants and "ambiguous" health evidence. The Lead Industries opinion, which pre-dated Chevron, did notposethe question in those terms. Itsfocus, however, was clearly on what Congress intended tobe the basis for NAAQS decisions, in a context the Courtunderstood toinvolve considerable uncertainty and debate about thehealth evidence, as well asthe possibility that there was no threshold

52See, e.g., Lead Industries, 647 F.2d at 1152 53
&n. 43, 1159 60; Ozone, 665 F.2d at 1185, 1187; PM 1 0, 902 F.2d at969 71, 972. 53Indeed, the presentdecisions on the NAAQS for PM and ozone are based on some ofthe best scientific information the Agency has ever been able to rely on in NAAQS decision-making.In particular, the science underlying these decisions is much more extensive and ofmuch better quality than the science underlying the existing NAAQS for PM and ozone.

54In practice, analysis ofthis question is sometimes referred to as a "Chevron step one" analysis. forhealth effects ofthe pollutant.55 In short, thehealth evidence was hardly "unambiguous," yet the Court interpreted section 109 asprecluding consideration ofcosts and similar factors even in allowing a margin of safety. Nothing in the Lead Industries decision or in the subsequent cases suggests in any way that section 109 should be interpreted differently based

on the nature ofthe pollutants or health evidence involved, and the Court's findings on congressional intent admit ofno exceptions:

[T]he statute and its legislative history makeclear that economic considerations play

nopart in thepromulgation ofambient air quality standards under section 109.
647 F.2d at 1148.

Alternatively, the commenter argues that the Lead Industries case decided the issue incorrectly in light ofthe principles announced subsequently in Chevron. In this context, the commenter essentially argues that the Lead Industries decision rested on two factors that are no longer probative: (1) That there was no indication that Congress
meantto allow consideration ofcosts in NAAQS decisions, and (2) that Congress specifically provided for such consideration in other sections ofthe Actbut not in section 109. On the first point, the commenter argues that EPA is freeunder Chevron to consider costs and similar factors (byreinterpreting section 109) unless there is evidence that Congress intended to restrict its discretion. As to the second point, the
commenter argues that similar reasoning

was rejected in Vinyl Chloride.

In Vinyl Chloride, however, an en banc decision that post-dated Chevron, the Court essentially underscored the point that such issues cannot be decided mechanically but must turn, instead, on

more analytical attention to relevant indicia ofcongressional intent. See, e.g., 824 F.2d at 1157 n.4; id. at 1157-63. With reference to NAAQS decisions in particular, the Court concluded that there were concrete indications of congressional intent to preclude consideration ofcosts and similar factors; for example, the fact that section 108 "enumerate[s] specific factors to consider and pointedly exclude[s] feasibility." 824 F.2d at 1159. In a later
case, moreover, the same Court held that EPA could not consider certain factors, in decisions under section 211(f)(4) of the Act, for reasons exactly parallel to those that the commenter criticizes in Lead Industries. SeeEthyl Corp.v. EPA, 51 F.3d 1053, 1057-63 (D.C.Cir. 1995).

55See, e.g., 647 F.2d at 1148 51, 1152 53 &n.43, 1160 61. 

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Beyond this, the commenter's characterization ofthe Lead Industries decision ignores or discounts much of the key evidence cited by the Court, including the language, structure, and legislative history ofthe statutory scheme established in 1970, for its conclusion that Congress intended to preclude consideration ofcosts and similar factors in NAAQS decisions. 56

As indicated above, the Vinyl Chloride and PM 10 cases, both ofwhich postdated Chevron, reached the same conclusion.

Moreover, this series ofdecisions
went farbeyond mere deference to an agency interpretation. As indicated in the Vinyl Chloride case, the Lead Industries court found "clear evidence" ofcongressional intent, which was to limit the factors EPA may consider under section 109. 824F.2d 1159. Consistent with Chevron, these findings

were based on traditional tools of statutory construction. See id. at 1157- 59; Lead Industries, 647 F.2d at 1148- 51. In terms ofthe analytical framework later established by Chevron, these were Chevron step one findings, meaning that the statute spoke directly to the issue and that the courts, as well as the agency, must give effect to Congress' intent as so ascertained. See467 U.S. at 842-43.57 Thus, absent amore recent

56See 647 F.2d at 1148 51. By contrast, the
commenter's argument that Congress actually intended EPA to consider such factors relies heavily

on (1) statements made in subsequent legislative history, mostofwhich were made in floor debate, that sought tojustify controversial amendments to establish a different program than the NAAQS and did notinvolve any proposed changes in section 109 orrelated provisions; and (2) statements in earlyjudicial decisions involvingprograms under other statutory provisions. In context, EPA believes these and other statements cited by the commenter

are consistent with and do not alter the conclusion that Congress intended to preclude consideration of
costs and similar factors under section 109.

57The commenter argues that the post-Chevron

cases accepted the Lead Industries analysis uncritically rather than re-examining it under Chevron. Clearly, this elevates form over substance. It is true that neither case referred to Chevron in discussing the point at issue. In Vinyl Chloride, however, the Courtretraced the steps in the Lead Industries analysis in some detail, characterized

some ofthe key evidence reviewed in that analysis in terms going beyond mererote repetition (e.g., "a far clearer statement than anything in the present

case that Congress considered the alternatives"), and used Chevron-like language in discussing the significance ofthat evidence; that is, that it demonstrated congressional intention on the point
at issue. E.g., 824 F.2d at 1159. Given that the Vinyl Chloride case was decided 3years after Chevron, that it was an en banc decision of theD.C. Circuit involving interpretation ofstatutory language very similar to that in Lead Industries, and that the Court cited Chevron twice in analyzing the language and history ofsection 112, it seems highly unlikely that the Court was unmindful ofChevron principles in concluding that Congress intended to preclude consideration ofcosts under section 109 but not under section 112. legislative enactment overriding that intent, EPA has no discretion to alter its longstanding interpretation that consideration ofcosts and similar factors is precluded in NAAQS decisions under section 109.58

As to the commenter's third key assertion, Executive Order 12866 (58 FR 51735, October 4, 1993) UMRA sections 202 and 205, and the Regulatory Flexibility Act (RFA), as amended by SBREFA, do not conflict with this interpretation or require a different result. Basically, the commenter argues that the Executive Order, UMRA, and the RFA (as amended by SBREFA) require agencies to use cost (or similar factors) as adecisional criterion in making regulatory decisions, and that this modifies the Clean Air Act's directive that EPA is precluded from 

### considering costs when setting a NAAQS. Thecommenter's argument is flawed on a numberofgrounds. First, UMRA and the RFA (as amended by SBREFA) do not conflict with section 109 because they do not apply to this decision, as discussed in Unit VIII of this preamble. Second, the Executive Order and both statutes are quite clear that they do not override the substantive provisions in an authorizing statute. Third, the commenter's premise that UMRA and the RFA (as amended by SBREFA) establish substantive decisional criteria that agencies are required to follow is wrong.

As a matter oflaw, the Executive Order cannot (and does not purport to) override the Clean Air Act. The Executive Order does not conflict with section 109 because the requirement that agencies "select approaches that maximize net benefits" does not apply if a "statute requires another regulatory approach." EO 12866, sec. (1)(a), 58 FR 51735, Oct. 4, 1993. More generally, the Executive Order provides that agencies

areto adhere to its regulatory principles only "to the extent permitted by law." Id., sec. (1)(b).

UMRA sections 202 and 205 do not apply to this decision, as discussed in

In the PM10 decision, the Courtconfirmed the sharp distinction it had drawn, based on such evidence ofcongressional intent, between sections 109 and 112in Vinyl Chloride. 902 F.2d at 972 73. Although discussion of the point was briefand did notmention Chevron, theindustry petitioner raising the point had cited Chevron in arguing that the Lead Industries interpretation was notbinding, and that EPA's decision on the PM10 standards should be reversed on the ground that it rested on

a legal position that EPAunjustifiably believed was mandated by Congress. Reply Briefofthe American Iron and Steel Institute at 11 &n.10, Natural ResourcesDefense Councilv.Administrator,902 F.2d 962 (D.C. Cir. 1990) (Nos. 87 1438 etal.). Thus, Chevron issues were properly before the Court and were brought squarely to its attention.

58 See also 52FR 24854, July 1, 1987. UnitVII ofthis preamble. Even when they do apply to aregulatory action, they do not establish decisional criteria that an agency must follow, much less override decisional criteria established in the statute authorizing theregulatory action. UMRA does not require an agency to select any particular alternative. Rather, an agency can select

an alternative that is not the least costly,
most cost-effective or least burdensome ifthe agency explains why, sec. 205(b)(1). Such an explanation is not required ifthe least costly, most costeffective or least burdensome alternative would have been "inconsistent with law," sec. 205(b)(2), and the only alternatives that an agency should consider are ones that "achieve[] the objectives ofthe rule," sec. 205(a). The UMRA Conference Report confirms that UMRA does not override the authorizing statute. "This section [202] does not require thepreparation ofany estimate or analysis ifthe agency is prohibited by law from consideringthe estimate or analysis in adopting the rule." 141 Cong.Rec. H3063 (daily ed. March 13, 1995).

The RFA (as amended by SBREFA) also does not apply to this decision, as discussed in UnitVII ofthis preamble. As is the case with UMRA, even when the RFA (as amended by SBREFA) does apply to a regulatory action, itdoes not establish decisional criteria that an agency must follow, much less override the underlying substantive statute. When the RFA was adopted in 1980, Congress made clear that itdid not alter the substantive standards contained in authorizing statutes: "The requirements ofsection 603 and 604 ofthis title [to prepare initial and final regulatory flexibility analyses] do not alter in any

manner standards otherwise applicable by law to agency action." Section 606 of the RFA. The legislative history further explains that section 606 "succinctly
states that thisbill does not alterthe substantive standard contained in underlying statutes which defines the agency's mandate. '59When Congress passed SBREFA in 1996 and amended parts ofthe RFA, itdid not amend section 606.

Even when a regulatory decision is subject to sections 603 and 604 and an agency is therefore required to analyze alternatives that minimize significant economic impacts on small entities, the RFA (as amended by SBREFA) does not establish decisional criteria that an agency is required to follow. Both section 603 and 604 provide thatthe

59

126 Cong. Rec. 21452, 21455 (1980) (Description ofMajor Issues and Section-By-Section Analysis ofSubstitute forS. 299). 

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alternatives an agency should consider

areto be "consistent with the stated objectives ofapplicable statutes." Sec. 603 and 604(a)(5). Furthermore, although the RFA (as amended by SBREFA) requires agencies to consider alternatives that minimize impacts on small entities subject to the rules' requirements and to explain their choice ofregulatory alternatives, it does not require agencies to select such alternatives. For thesereasons, the RFA (as amended by SBREFA) does not conflict with or override the Clean Air Act's preclusion ofconsidering costs and similar factors in settingNAAQS.

3. Conclusion.In summary, EPA believes that thejudicial decisions cited above areboth correct and dispositive

on the question ofconsidering costs in settingNAAQS, and that the Agency is
not free to reinterpret the Act on that question.

B. MarginofSafety

Several commenters questioned the approach used by the Administrator in specifying 03 standards that protect public health with an adequate margin ofsafety. Rather than the integrative approach applied by the Administrator, these commenters maintained that EPA
must employ a two-step process. The line ofargument was that the Administrator must first determine a "safe level" and then apply a margin of safety taking into account costs and societal impacts. Itwas argued that this

was the only approach that would enable the Administrator to reach a reasoned decision on a standard level that protects public health against unacceptable risk ofharm, such that any remaining risk was "acceptable." In effect, these commenters argued that the Administrator must adopt the two-step methodology endorsed in Vinyl Chloride, 824 F.2d 1146, for setting hazardous air pollutant standards under section 112.

In recognition ofthe complexities facing the Administrator in determining

a standard that protects public health with an adequate margin ofsafety, the
courts have declined to impose any specificrequirements on the Administrator's methodological approach. Thus, in Lead Industries the
court held that the selection ofany particular approach to providing an adequate margin ofsafety "is apolicy choice ofthe type Congress specifically left to the Administrator's judgment. This court must allow him the discretion to determine which approach will best fulfill the goals ofthe Act." 647 F.2d at 1161-62. As a result, the Administrator is not limited to any single approach to determining an adequate margin ofsafety and may, in the exercise ofherjudgment, choose an integrative approach, atwo-step approach, or perhaps some other approach, depending on the particular circumstances confronting her in a given NAAQS review.

With respect to the approach advanced in comment, the PM 10 case made clear thatthe two-step process endorsed in Vinyl Chloride was necessary because ofthe need under section 112 ofthe Act to "sever determinations that must be based solely on health considerations from those that may include economic and technical considerations." 902 F.2d at 973. Because the Administrator may not consider cost and technological feasibility under section 109, however, the court concluded that "the rationale for parsing the Administrator's determination into two steps is inapposite." Id.

Because such factors as the nature and severity ofthehealth effects involved, the size ofthe sensitive population(s) at risk, the types ofhealth information available, and the kind and degree of uncertainties that must be addressed will vary from one pollutant to another, the most appropriate approach to establishing aNAAQS with an adequate margin ofsafety may be different for each standard under review. Thus, no generalized paradigm such as that imbedded in EPA's cancer risk policy

can substitute for the Administrator's careful and reasoned assessment ofall relevant health factors in reaching such

ajudgment. As noted above, both Congress and the courts have left to the Administrator's discretion the choice of analytical approaches and tools, including risk assessments, rather than prescribing aparticular formula for reaching such determinations. Because ofthe inherent uncertainties that the Administrator must address in margin ofsafety determinations, they arelargely judgmental in nature, particularly with respect to non-threshold pollutants, and may not be amenable to quantification in terms ofwhat risk is "acceptable" or any other metric. In view ofthese considerations, the task ofthe Administrator is to select an approach that best takes into account the health effects and other information assessed in the air quality criteria for the pollutant in question and to apply appropriate and reasoned analysis to

ensure that the scientific uncertainties

are taken into account in an appropriate

manner.

In this instance, the Administrator has clearly articulated the factors shehas considered, thejudgments she has had
to make in the face ofuncertain and incomplete information, and alternative views as to how such information should be interpreted, in reaching her decision on standard specifications that willprotect public health with an adequate margin ofsafety. See Unit IIof thispreamble. Her conclusions on these
matters are fully supported by the record.

C. CommentPeriod

A number ofcommenters maintained that EPA erred by not extending the
comment period for the review ofthe 03 standards by atleast 60 days. The commenters further maintained there

was nojustification for keeping the 03 standard review on the same schedule

as the PM NAAQS, since the 03 review is not subject to a court-ordered deadline as is PM.

The EPAbelieves that there are benefits to reviewing the 03 and PM NAAQS on the same schedule, for the

reasons set forth in the proposal, and that the period available forpublic
comment was sufficient. All interested parties have had ample notice thatEPA intended to complete this review ofthe 03 standards on an expedited basis. The EPA first announced its intention in a March 9, 1993, Federal Register notice (58 FR 13008) when the Administrator announced her commitment to expedite the review in light ofnew scientific evidence ofthe effects of03 on human health. In aFebruary 3, 1994, Federal Register notice (59 FR5164), the Administrator announced a schedule for completion ofthe scientific assessment and review ofthe standards, including opportunities for public comment. This schedule called forproposal in mid1996 and a final decision as to whether
to revise the 03 standard bymid-1997. On June 12, 1996, in an advance notice ofproposed rulemaking (61 FR29719), the Administrator announced her decision to delay the 03 proposal schedule in order to place it on the same schedule as the PM standard review. In that notice, she explained her rationale forreviewing the 03 and PM NAAQS on the same schedule and pointed to the benefits ofdeveloping integrated implementation strategies. She also provided advance notice ofthe kinds of revisions to the primary and secondary 03NAAQS that she was considering proposing. In effect, the delay ofthe 03 proposal provided interested parties an additional 5 months to review EPA's
assessments ofthe scientific and technical information, as well as staff and CASACrecommendations as to whether revisions were appropriate. With thisbackground, EPAbelieves all interested parties had ample opportunity to develop specific 

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comments on the 03 proposal during the 89 days allotted for public comment. 6 0
Another commenterraised amore specific issue in requesting a 60-day extension ofthe public commentperiod. This commenter maintained that such

an extension was necessary because EPA did not make publicly available certain 03 exposure and health risk
assessment reports and an explanatory memoranda in a timely manner. In response, EPA notes that the documents in question were entered into the docket

on February 12, 1997, and placed on the OAQPS Technology Transfer Bulletin Board on February 13, 1997, so that they would have wide public circulation. Because this commenter's organization

was aware that the reports were under preparation and had expressed interest in receiving them, copies were sent directly to the responsible staffperson

on February 12, 1997. Given that these reports build on analyses and methodologies that were available to the public during the scientific phase ofthe 03 NAAQS review, well in advance of the proposal, and that the new analyses and explanatory memorandum were only 120 pages in length, EPAbelieves that this commenter had sufficient time
to review the material and prepare comments before the close ofthe
comment period on March 12, 1997.

D.1990ActAmendments

Contrary to the view expressed in

somepublic comments, EPA maintains that the provisions ofsubpart 2 ofPart D ofTitle Iofthe Clean Air Act, enacted in 1990, do not preclude EPA from revising the 03 standard. The provisions ofsubpart 2 simply do not limit EPA's clear authority under section 109 to revise the standard.

The basic contention ofthe
commenters is that because the provisions ofsubpart 2 are linked to the
current 1-hour, 0.12 ppm 03 standard, they prohibit EPA from revising the 03 standard. These provisions, however, do
not lead to such a conclusion. Moreover, the view expressed in these comments ignores provisions indicating that Congress believed thatEPA could revise the 03NAAQS.

At the outset, it should be noted that Congress expressly authorized EPA to revise any ambient air quality standard in section 109. That section, which requires EPA to review and revise, as appropriate, each NAAQS every 5 years, contains no language expressly or implicitly prohibiting EPA from revising

aNAAQS. IfCongress had intended to

60This comment period reflects an extension of
22 days beyond the 67 day comment period originally announced in theproposal. preclude EPA from reviewing and revising a NAAQS, which is one of EPA's fundamental functions, Congress would have specifically done so. Clearly, Congress knew how to preclude EPA from exercising otherwise existing regulatory authority and did so in other instances. See section 202(b)(1)(C)(expressly precludingEPA from modifying certain motor vehicle standards prior to model year 2004); section 112(b)(2)(preventing EPA from addingto the list ofhazardous air pollutants any air pollutants that are listed under section 108(a) unless they meet the specific exceptions ofsection 112(b)(2)); section 249(e)(3), (f) and section 250(b)(limiting EPA's authority regarding certain clean-fuel vehicle programs). No such language was included in either section 109 or elsewhere in the Act and no such implication may properly be based on the provisions ofsubpart 2 ofPart D of Title I. Second, other provisions ofthe Act expressly contemplate EPA's abilityto revise any NAAQS, and provide no indication that such ability is limited to standards other than those whose implementation is the subject of subparts 2, 3 and 4 ofPart D.For example, section 110(a)(2)(H)(i) provides that SIPs are to provide for revisions "from time to time as maybe necessary to take account ofrevisions of such national primary or secondary ambient air quality standard ***." Section 107(d)(1)(A) provides aprocess for designating areas as attainment, nonattainment, or unclassifiable "after promulgation ofanew or revised standard for any pollutant under section 109 ***." Section 172(e) addresses modifications ofnational primary ambient air quality standards. Finally, section 172(a)(1) expressly contemplates that EPA may revise a standard in effect atthe time ofenactment ofthe 1990 Clean Air Act Amendments. Section 172(a)(1)(A) provides EPA with authority to classify nonattainment

areas on or after the designation ofan

area as nonattainment with respect to "any revised standard, including a revision ofany standard in effect on the date ofthe enactment ofthe Clean Air Act Amendments of 1990." Plainly, Congress had no intention ofprohibiting EPA from revising any ofthe ambient standards in effect at the time ofthe
enactment ofthe 1990 amendments.

Third, the provisions ofsubpart 2 of Part D do not support the contention that they somehow preclude EPA from exercising its authority to revise the NAAQS under section 109. The fact that Congress laid out an implementation program for the 03 standard existing at 

### thetime ofthe 1990 amendments in no way suggests thatCongress intended to preclude EPA from exercising the authority itprovided EPA torevise the NAAQS when thehealth data on which EPA bases such decisions warranted a change in the standard. Contrary tothis contention, section 181(a) does not preclude the designation ofareas as nonattainment for 03 thathave design values lessthan 0.121 ppm. EPA has designated asnonattainment numerous
areas whose design value was less than 0.121 ppm, butwhich violated the existing 1-hour, 0.12 ppm 03 standard. These areas, referred to as "nonclassifiable nonattainment areas," include "submarginal" areas (i.e., 03 nonattainment areas with design values below 0.121 ppm), (See 57FR 13498, 13524-27, April 16, 1992). These areas include areas thatwere designated nonattainment prior tothe 1990 amendments and whose nonattainment designation Congress required tobe continued after 1990. See section 107(d)(1)(C)(i). Clearly, Congress did not prohibit the designation ofareas as nonattainment for 03 with design values below 0.121 ppm;in fact, in some cases, Congress required it.Furthermore, the position advanced by thecommenters would mean that,in effect, Congress in the 1990 amendments legislatively revised the then-existing 1-hour, 0.12 ppm 03 standard to a 0.121 ppm standard. There isno indication that Congress intended to do that.

In addition, thefactthat Congress directed EPAto use "the interpretation methodology issued by the Administrator mostrecently" before the date oftheenactment ofthe Clean Air Act Amendments of 1990 inthe context ofsubpart 2does not add any support tothe commenters' position; itmerely shows thatCongress intended the existing 1-hour, 0.12 ppm standard to be implemented in a specified way, not thatCongress intended topreclude EPA fromusingits otherwise applicable authority torevise the standard.

The EPA also disagrees with the contention that sections 172(a)(1)(C) and (a)(2)(D),which provide thatthe general classification and attainment date provisions ofsection 172do not apply to areas forwhich classifications or attainment dates "are specifically provided under otherprovisions ofthis part," support theconclusion that Congress intended toprohibitEPA from revising the03 standard. These provisions simply mean thatwhere Congress elsewhere provided for specific classifications and attainment dates, as in thecase ofsubpart 2 regarding the 1-hour, 0.12 ppm standard, EPA isnot to modify those 

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classifications or dates. The EPA is not purporting to do this. These provisions do not lead to the conclusion that because Congress established them for the 03 standard in effect at the time of the 1990 amendments, Congress meant that EPA could not revise that standard in order to appropriately protect public health.

EPA does not accept the thesis that revising the 03 standard forces EPA to violate other provisions ofthe Act and, therefore, is not an "appropriate" revision ofthe standard under section 109. Revising the 03 standard in accordance with the language ofsection 109 does not result in EPA violating any provision ofthe Act. On the other hand,

adetermination by EPAthat the 03 standard should not be revised, even though EPA concludes that it needs to be revised to protect publichealth with

an adequate margin ofsafety, would violate section 109.

Also, EPA does not believe that carrying out theprovisions ofsection 109 to set a new 03 standard to protect public health with an adequate margin ofsafety somehow "risks undermining both perceptions and reality ofthe functioning ofour democratic form of government." EPA is merely implementing the words ofthe Clean Air Act, a statute passed by the Congress and signed by the President. To refuse
to revise the standard notwithstanding the need to protect public health as enunciated in section 109 would thwart the objectives ofthose who passed and signed the Clean Air Act on behalfof the American public.

Finally, for the reasons stated above, EPA's analysis ofits ability to implement the revised 03 standard under the provisions ofsubpart 1 ofPart D ofTitle Idoes not support the view that Congress prohibited EPA from revising the standard. Congress clearly specified an approach to the implementation ofthe 1-hour, 0.12 ppm 03 standard in the provisions ofsubpart 2 ofPart D.EPA believes thatthe clear and express linkage ofthat approach to the 1-hour,0.12 ppm standard indicates that it may implement arevised 03 standard in accord with the general principles ofsubpart 1 ofPart D, as informed by the no-backsliding principle embodied in section 172(e). That Congress directed specifically how EPA and the States should implement the 1-hour,0.12 ppm 03 standard does
not carry with it the implication that Congress intended to prohibit EPA from exercising its otherwise clear and express authority to revise that standard in order to carry out one ofits fundamental missions, the establishment of ambient air quality standards to protect public health with

an ample margin ofsafety. IfCongress had intended to prohibit EPA from exercising such a fundamental authority it would have clearly specified (as it did in other instances) that EPA could not do so.

The EPA also disagrees with the contention that a revised 03 standard may not be implemented for so long as the current 1-hour, 0.12 ppm 03 standard remains in effect. The fact that the provisions ofsubpart 2 ofPart D are focused on the implementation ofthe
current standard does not mean that, if

anew or revised 03 standard is promulgated pursuant to section 109, the new standard could not simultaneously be implemented under the provisions ofsection 110 and subpart 1ofPart D, which apply regardless ofthe criteria pollutant of

concern. There is no language in sections 181 or 182that precludes the implementation ofadifferent standard under other authority; those provisions simply govern the implementation of the 1-hour,0.12 ppm 03 standard. EPA further notes that it has historically had

more than one primary standard for criteria pollutants (e.g., annual and 24- hour PM 10 and sulfur dioxide standards, and 8-hour and 1-hour CO standards) and believes that had Congress wanted
to preclude EPA from implementing two primary 03 standards simultaneously it would have expressly precluded EPA from doing so. Thus, EPA does not believe that it must repeal the 1-hour, 0.12 ppm 03 standard before it can promulgate and implement anew primary 03 standard.

V. Technical Changes to Part50

In the proposal, the EPA proposed two alternative secondary standards: (1) A secondary standard set identical to the proposed 0.08 ppm, 8-hour primary standard; or (2) a seasonal secondary standard expressed in the SUM06 form. For thereasons discussed in Unit III, the EPA has decided to promulgate a secondary ambient air quality standard for 03 that is identical to theprimary ambient air quality standard. Accordingly, the language adopted in the final regulation (40CFR 50.10) has been revised to reflect this change.

In the proposal, theregulatory text in §50.9 inadvertently included language about what it means when the standard is not met, that should have been discussed in 40 CFRpart 50, Appendix H. Therefore this sentence hasbeen removed from §50.10(b), and the discussion moved to the new Appendix I to 40 CFRpart 50, which now provides additional clarification on calculations for sites with less than complete data, as discussed in UnitVI. ofthis preamble.

VI. Revisions to Appendices D, E, and H
The EPA is finalizing the changes to Appendices D and Eto 40 CFRpart 50, that were proposed and described in the proposal. No adverse comments were received on these changes.

Because the revocation ofthe existing 1-hour standard will become effective
at alater date (as discussed above in UnitII.B.4.), EPA is retainingAppendix H in its current form. A new Appendix Iexplains the computations necessary for determining when the new 8-hour primary and secondary standards are met.

The new Appendix I addresses data completeness requirements, data reporting, handling, and rounding conventions, and example calculations. The discussion in this unit sometimes refers to the contents ofthe new Appendix Ias revisions to Appendix H,

so as to highlight how the new Appendix Idiffers from the current Appendix H. For example, the example calculations in Appendix Idiffer from those in Appendix H to reflect the final form ofthe new 8-hourprimary standard.

In the proposal, two alternative secondary standards were proposed, and the proposed changes to Appendix H addressed both alternatives: A secondary standard set identical to the proposed 0.08ppm, 8-hourprimary standard; or a seasonal secondary standard expressed in the SUM06 form. For thereasons discussed above, the Administrator has decided to set the secondary standard identical to the primary standard asreflected in Appendix I.

Key elements ofAppendix I, particularly as they differ from those of Appendix H, are outlined below.

A. DataCompleteness

One key change to Appendix H, incorporated into Appendix I, for the

new 0.08ppm, 8-hourprimary and secondary standards is that no numerical adjustment is made to the measured 8-hour concentrations to account for missing or incomplete data

as was the case with the 1-hour standard. Instead, the EPAhas decided
to replace the methodology used to adjust the computation ofestimated exceedances for missing data under the 1-hour standard with new data completeness requirements for the 8- hour standards.

The EPAproposed that, in order to determine that the 8-hour standards have been met at amonitoring site 

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during the current 3-year period, revisions to Appendix H would require 90 percent data completeness, on average, with no single year at the site having less than 75 percent data completeness. A site could be found not to have met the standards with less than complete data. Almost all commenters supported deleting the estimated exceedances missing data adjustment procedure ofthe current 1-hour standard and replacing it with minimum data completeness requirements. Several commenters felt that the proposed data completeness requirement might be too stringent and would be difficult to attain. Other
commenters recommended that some consideration be made for hours lost due to instrument calibration. A few
commenters thought that EPA should establish higher minimum data completeness requirements.

Based on its analysis ofavailable air quality data, the EPA believes that, with the changes to the proposal described below, the data completeness requirement in Appendix I isreasonable given that 90 percent ofall monitoring sites that currently operate on a continuous basis meet this objective. The EPA believes that a missinghour during the day resulting from instrument calibration should not negatively impact the ability ofa monitoring site to meet the data completeness requirements because data completeness isbased on the number of days with valid daily maximum 8-hour concentrations, not on the number of non-missing hours.

In the proposal, the EPA sought
comment on whether meteorological data could provide an objective basis for determining, on a day for which there is missing data, thatthe meteorological conditions were not conducive to high 03 concentrations, and therefore, that the day could be assumed to have an 8- hour daily maximum 03 concentration less than 0.08 ppm. Under the 0.12 ppm 1-hour standard, amissing day is assumed less than the level ofthe standard only ifthe two adjacent days

are non-missing, and the daily maximum 1-hour concentration on each ofthose days is less than or equal to 0.09 ppm. In the proposal, the EPA specifically requested comment on the appropriateness ofusing data on meteorological conditions, as well as on other information that would permit better definition ofthose necessary conditions likely to result in peak 8- hour 03 concentrations in the ranges of

concern. Most commenters expressing

an opinion supported the use of meteorological data, aswell as ambient data from nearby monitoring sites to establish that missinghours could be assumed less than the level ofthe standard. Days assumed less than the level ofthe standard would be counted

asnon-missing when computing whether the data completeness requirements have been met atthe site. Taking these comments into account, EPA hasrevised the proposed revisions
to Appendix H, as reflected in Appendix I, to count missing days assumed less than the standard when computing whether the data completeness requirement hasbeen met. EPA will develop guidance on methodologies necessary for using meteorological data and ambient
measurements to make such determinations. Several commenters expressed

concerns about the possibility that stratospheric 03 intrusion from aloft or forest fires may lead to exceedances of the level ofthe standard, particularly within the context ofpeak 03 concentrations thathave been observed
atbackground sites. Commenters expressed concern that such events could lead to violations ofthe 8-hour standard and, therefore, they questioned the attainability oftheproposed standard. Consistent with a forthcoming update to EPA's policy on natural events for the new 8-hour standard, EPA hasrevised Appendix H to specifically address this concern by statingthat whether to usedata affected by stratospheric 03 intrusion or other natural events when determining ifthe standards have been met is subject to the approval ofthe appropriate Regional Administrator.

B. DataHandlingandRounding Conventions

For the reasons cited above, and taking into account the advice of CASAC, the Administrator has set the level ofthe new 8-hour primary and secondary standards at0.08 ppm. As EPA explained in the proposal, the level ofthe 8-hour standard is expressed to the second decimal place, 0.08 ppm, with the support ofCASAC and in part to reflect uncertainties in the health effects evidence upon which the proposed standard is based. More specifically, these uncertainties include the measurement uncertainty and representativeness inherent in the reported ambient 03 concentrations used in field and epidemiological studies and the uncertainty in the exposure estimates upon which quantitative risk assessments havebeen based. In theproposal, EPA stated its beliefthat expressing the proposed standard to the second decimal place is also consistent with the quality assurance guidelines that indicate the precision 6' for such 03 measurements shall be within + 15 percent.

To determine whether the standard is met, EPAproposed that the calculated value ofthe third-highest maximum 8- hour average concentrations, averaged

over 3 years, is compared to the level of the standard. Itis the level ofthe standard, 0.08ppm, expressed to two decimal places that determines the number of significant digits to be used when comparing air quality
measurements to the standard. The EPA proposed that, forhourly data, 8-hour average 03 concentrations computed from such hourly data, and the 3-year averages ofthe third highest maximum 8-hour average concentrations, that the third decimal place is carried forward as the rounding digit, and the insignificant digits are truncated. To compare the calculated 3-year average 03 concentration to the level ofthe standard, the third decimal place ofthe calculated value is rounded. The current rounding convention is to round up digits equal to orgreater than 5.

In the proposal, EPArecognized that the level ofpublic health protection afforded by the use ofthe current rounding convention could be increased by replacing the current rounding convention with a convention that defined the smallest increment above the level ofthe standard to be 0.001 ppm for the purposes ofdetermining whether the standard has been met. The EPA solicited comment on theuse of such an alternative rounding convention, with regard to potential increased public health protection, as well as to potential effects on the probability ofattainment misclassifications and on the stability of the standard.

Ofthe many States that commented specifically on the rounding convention,
most State agencies cited concerns by theirmonitoring staffs about the precision and accuracy ofmeasured 03 concentrations in ambient environments and recommended maintaining the
current rounding convention. A tribal association also supported the current rounding convention. Other State agencies felt that newer instruments

were capable ofsupporting a rounding convention set at 0.001 ppm. Ofthose environmental and health associations that commented, all supported replacing the current rounding convention with

61The term precision isused to denote both the reproducibility ofameasurement under a constant setof conditions, as well as othercomponents of
measurement uncertainty such as instrument drift and relative bias. 

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the alternative 0.001 ppm convention. 62
All industry and trade associations that commented on rounding recommended that EPA retain the current rounding convention.

After taking these comments into account, EPAhas decided that the
current rounding approach is appropriate for comparing monitoring data to the level ofthe standard expressed to two decimal places. The
current roundingprocedure has the effect ofreducing the probability of misclassifying an attainment area as nonattainment and ofproducing a more stable attainment test. The EPA believes that measures thatpromote a stable control program will lead to greater long-term health protection and risk reduction. For the reasons stated above, and taking into account the uncertainty in the exposure estimates upon which quantitative risk assessments havebeen based, measurement uncertainty, data representativeness, and the desirability oftheseresulting effects, EPA is retaining the current rounding convention and finalizing the data handling and rounding conventions, in Appendix I, as proposed.

VII. Regulatory and Environmental ImpactAnalyses

As discussed in Unit IV ofthis preamble, the Clean Air Act andjudicial decisions make clear that the economic and technological feasibility ofattaining ambient standards are not to be considered in setting NAAQS, although such factors may be considered in the development ofState plans to implement the standards. Accordingly, although, as described below, a Regulatory Impact Analysis (RIA) has been prepared, neither the RIA nor the associated contractor reports have been considered in issuing this final rule.

A. Executive Order12866

Under Executive Order 12866, 58 FR 51735 (October 4, 1993), the Agency
must determine whether aregulatory action is "significant" and, therefore, subject to Office ofManagement and Budget (OMB) review and other requirements ofthe Executive Order. The order defines "significant regulatory action" as any regulatory action that is likely to result in arule that may:

62One individual commenter provided an analysis ofcurrent monitoringtechnology and suggested that theprecision and accuracy data supported setting the standard to three decimal places and rounding the annual average thirdhighest 8 hour averageconcentration up at 0.001
ppm. EPA believes that the precision and accuracy data cited by the commenter does not capture all of theuncertainty inherent in ambient air quality
measurements. (1) Have an annual effect on the economy of$100 million or more or adversely affect in a material way the economy, a sector ofthe 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 thebudgetary impact ofentitlements, grants, user fees,

or loan programs or therights and obligations ofrecipients thereof. (4) Raise novel legal or policy issues arising out oflegal mandates, the President's priorities, or the principles
setforth in the Executive Order.

In view ofits important policy implications, this action has been judged to be a "significant regulatory action" within the meaning ofthe Executive Order. As a result,under section 6 ofthe Executive Order, EPA has prepared an RIA, entitled "Regulatory Impact Analysis for Particulate Matter and Ozone National Ambient Air Quality Standards and Proposed Regional Haze Rule (July 1997)." This RIA assesses the costs, economic impacts, and benefits associated with potential State implementation strategies for attaining the PM and 03 NAAQS and the proposed Regional Haze Rule. Changes made in response to OMB suggestions or recommendations will be documented in the public docket and made available for public inspection atEPA's Air and Radiation Docket Information Center (DocketNo. A-95-58). The RIA will be publicly available in hard copy by contacting the U.S. Environmental Protection Agency Library atthe address under "Availability ofRelated Information" and in electronic form as discussed above in "Electronic Availability."

B. RegulatoryFlexibilityAnalysis

The Regulatory Flexibility Act (RFA), 5 U.S.C. 601 et seq., provides that, whenever an agency is required to publish ageneral notice ofrulemaking for aproposed rule, the agency must prepare an initial regulatory flexibility analysis for the proposed rule unless the head ofthe agency certifies that therule "will not, ifpromulgated, have a significant economic impact on a substantial number ofsmall entities" (section 605(b)). The EPA certified each oftheproposed NAAQS rules based on its conclusion that the rule would not establish requirements applicable to small entities and therefore would not have a significant economic impact on small entities within the meaning ofthe RFA. See 61 FR 65638, 65668 (PM proposal); 61 FR 65716, 65746 (ozone proposal), both published on December 13, 1996. Accordingly, the Agency did
notprepare an initial regulatory flexibility analysis forthe proposed rule, but it did conduct a more general analysis ofthepotential impact on small entities ofpossible State strategies for implementing any new orrevised NAAQS.

At theheart ofEPA's certification of the proposed NAAQS rule was the Agency's interpretation ofthe word "impact" as used in the RFA. Is the "impact" to be analyzed under the RFA

arule's impact on the small entities that willbe subject to the rule's requirements, or therule's impact on small entities in general, whether or not they will be subject to the rule? In the

case ofNAAQS rules, the question arises because ofthe congressionallydesigned mixture ofFederal and State responsibilities in setting and implementing the NAAQS.

As EPA explained in the proposal, NAAQS rules establish air quality standards that States areprimarily responsible formeeting. Under section 110 and part D ofTitleI ofthe CAA, every State develops a State Implementation Plan (SIP) containing the control measures that will achieve a newlypromulgated NAAQS. States have broad discretion in the choice ofcontrol

measures. As the U.S. Supreme Court noted in Trainv.NRDC:

[P]rimary [NAAQS] deal with thequality of outdoor air and are fixed on a nationwide basis at alevel which the agency determines willprotect the public health. It is the attainment and maintenance ofthese standards which section 110(a)(2)(A) requires that Stateplans provide. In complying with thisrequirement, aState's plan mustinclude "emission limitations" which are regulations ofthe composition ofsubstances emitted into theambient air from such sources as power plants, service stations and the like. They are the specific rules to which operators of pollution sources are subject and which, if enforced, should result in ambient air which meets the national standards.

TheAgency isplainly charged bytheAct with theresponsibility for settingthe national ambient air standards. Just as plainly, it isrelegated toa secondary rolein theprocess ofdetermining and enforcingthe specific, source-by-source emission limitations which arenecessary ifthe national standards aretobe met.Under 110(a)(2), theAgency is requiredto approve
aStateplan which provides for the timely attainment and maintenance ofthe ambient air standards, and which also satisfies that section's other general requirements. TheAct givesthe agency noauthority to question the wisdom ofa State's choices ofemission limitations ifthey arepart ofaplan which satisfies the standards of 110(a)(2) and the Agency may devise and promulgate aplan of 

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its own onlyifthe state failsto submit an implementation plan which satisfies those standards. Section 110(c).
421 U.S. 60, at 78-79 (1975) (emphasis in original). In short,NAAQS rules themselves do not establish any control requirements applicable to small entities. Staterules implementing the NAAQS may establish such requirements and the extent to which they do depends primarily on each State's strategy for meeting the NAAQS. 63

To determine the proper interpretation of "impact" under the RFA, EPA considered the RFA's stated purpose, its requirements for regulatory flexibility analyses, its legislative history, the amendments made by the Small Business Regulatory Enforcement Fairness Act of 1996 (SBREFA)(Pub. L. 104-121), and caselaw. The EPA concluded that all ofthese traditional tools ofstatutory construction point in

one direction-that an agency is required to assess the impact ofarule

on the small entities that will be subject
to therule's requirements, because the purpose ofaregulatory flexibility analysis is to consider ways ofeasing or

even waiving arule's requirements as they will apply to small entities, consistent with the statute authorizing the rule. That purpose cannot be served in the case ofthe rules like the NAAQS that do nothave requirements that apply to small entities.

More specifically, EPA noted that its interpretation of "impact" flows from the express purpose ofthe RFA itself. As the RFA's "Findings and Purposes" section (Pub.L. 96-354, section 2) makes clear, Congress enacted the RFA in 1980 out ofconcern that agencies

were writingone-size-fits-all regulations that in fact did not fitthe size and

resources ofsmall entities. Congress noted that itis generally easier forbig businesses to comply with regulations, and that small businesses are therefore
at a competitive disadvantage in complying with uniform rules. Congress also noted that small entities' relative contribution to theproblem a rule is supposed to solve may not warrant applyingthe same requirements to large and small entities alike. In the RFA itself, Congress therefore stated:

63Itis worth noting that Federal rules that apply nationally also play arolein reducing emissions governed byNAAQS. For instance, EPA rules under Title II ofthe CAA require reductions in ozoneforming emissions from on and off-road vehicles and the fuels that power them. When EPA issues such rules, it conducts the analysis required under the RFA. For example, EPA performed regulatory flexibility analyses for the reformulated gasoline rule issued under section 211(k) ofthe CAA. See 59 FR 7716, February 16, 1994. It isthe purpose ofthis Act toestablish as
aprinciple ofregulatoryissuance that agencies shall endeavor, consistent with the objectives ofthe rule and ofapplicable statutes, tofitregulatory and informational requirements tothe scale ofthe businesses, organizations, and governmental jurisdictions subject toregulation. [Pub. L. 96-354, section 2(b).]

The EPA further noted that the RFA sections governing initial and final regulatory flexibility analyses reflect this statement ofpurpose. RFA sections 603 and 604 require that initial and final regulatory flexibility analyses identify the types and estimate the numbers of small entities "to which the proposed rule will apply" (sections 603(b)(3) and 604(a)(3)). Similarly, they require a description ofthe "projected reporting, recordkeeping and other compliance requirements ofthe proposed rule, including an estimate ofthe classes of small entities which will be subject to the requirement" (sections 603(b)(4) and 604(a)(4)). At the core ofthe analyses is the requirement that agencies identify and consider "significant regulatory alternatives" that would "accomplish the stated objectives ofapplicable statutes and which minimize any significant economic impact ofthe proposed rule on small entities" (section 603(c) and 604(a)(5)). Among the types ofalternatives agencies are to consider are the establishment of different "compliance or reporting requirements or timetables" for small entities and the exemption ofsmall entities "from coverage ofthe rule, or any part" ofthe rule (section 603(c)(1) and (4)).The RFA thus makes clear that regulatory flexibility analyses areto focus on how to minimize rule requirements on smallentities.

As EPA further explained, since regulatory flexibility analyses arenot required for a rule that will not have a "significant economic impact on a substantial number ofsmall entities," it makes sense to interpret "impact" in light ofthe requirements for such analyses. Regulatory flexibility analyses,

as described above, are to consider how

arule will apply to small entities and how its requirements may be minimized with respect to small entities. In this context, "impact" is appropriately interpreted to mean the impact ofarule

on the small entities subject to therule's requirements.

The Agency cited two Federal court

cases in support ofits interpretation. In Mid-TexElec. Co-op v. FERC,773 F.2d 327, 342 (D.C. Cir. 1985), petitioners claimed that the RFArequired an agency to analyze the effects ofa rule on small entities that were not regulated by the rule but might be indirectly impacted by it. Petitioners noted that the Small Business Administration (SBA) also interpreted the RFAto require analysis ofa rule's impact on small entities not regulated by the rule, and argued that the court should defer
to the SBA's position in light ofits compliance monitoring role under the RFA. After reviewing the RFA's "Findings and Purposes" section, its legislative history, and its requirements forregulatory flexibility analyses, the Mid-Tex courtrejected petitioners' interpretation. As the court explained:

Theproblem Congress stated itdiscerned

was the highcost to small entities of compliance with uniform regulations, and theremedy Congress fashioned careful consideration ofthose costs inregulatory flexibility analyses is accordingly limited to small entities subject tothe proposed regulation. *** [W]e conclude that an agency mayproperly certify thatno regulatory flexibility analysis is necessary when it determines thatthe rule will nothavea significanteconomic impact on a substantial number ofsmall entities that are subject to therequirements ofthe rule.
Id. at 342. Notably, Congress let this interpretation stand when itrecently amended the RFAin enacting the SBREFA.

The EPA also cited arecent case affirming the Mid-Tex court's interpretation. In UnitedDistribution Companiesv. FERC,88 F.3d 1105, 1170 (D.C. Cir. 1996), the courtnoted that the Mid-Tex court:

*** conducted an extensive analysis ofthe RFAprovisions governing when aregulatory flexibility analysis isrequired and concluded thatnoanalysis is necessary when an agency determines "that the rule will nothave a significanteconomic impact on a substantial number ofsmall entities thataresubjectto the requirementsofthe rule". Id., citing and quoting Mid-Tex (emphasis added by United Distribution court).

The Agency went on to explain that given the Federal/State partnership for attaininghealthy air, theproposed NAAQS, if adopted, would not establish any requirements applicable to small entities. Instead, any new or revised standard would establish levels ofair quality that States would be primarily responsible for achieving by adopting plans containing specific control

measures for that purpose. The proposed NAAQS rule was thus not susceptible to regulatory flexibility analysis as prescribed by the amended RFA. Since it would establish no requirements applicable to small entities, it afforded no opportunity for EPA to fashion for smallentities less burdensome compliance orreporting requirements or timetables, or 

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exemptions from all orpart ofthe rule. For thesereasons, EPA certified that the proposed rule "will not, ifpromulgated, have a significant economic impact on
a substantial number ofsmall entities," within the meaning ofthe RFA. Because EPA was not required to prepare an initial regulatory flexibility analysis for the rule, it was also not required to

convene a Small Business Advocacy Review Panel for therule under RFA section 609(b) as added by SBREFA.

Notwithstanding its certification of the proposed rule,EPA recognized that the proposed NAAQS, if adopted, would begin a process ofState implementation that could eventually lead to small entities having to comply with new or different control measures, depending on the implementation plans developed by the States. EPA also recognized that the CAA does not allow EPA to dictate or second-guess how States should exercise their discretion in regulating to attain any new or revised NAAQS. Under those circumstances, EPA concluded that the best way to take account ofsmall entity

concerns regarding any new orrevised NAAQS was to work with small entity representatives and States to provide information and guidance on how States could address small entity concerns when they write their implementation plans.

In line with this approach, aspart of the RIA itprepared for theproposed NAAQS, EPA analyzed how hypothetical State plans for implementing the proposed rule might affect small entities. The analysis was necessarily speculative and limited, since it depended on projections about what States might do several years in the future and did not take into account any new strategies that might be developed and recommended by the FACA subcommittee formed to help devise potential strategies for implementing a new or revised NAAQS (see discussion ofRIA and FACA process in the previous Unit ofthis notice). Nevertheless, the analysis provided as much information on potential small entity impacts as was reasonably available at the time ofthe proposed rule.

The Agency also took steps to ensure that small entities' voices were heard in the NAAQS rulemaking itself.With Jere Glover, ChiefCounsel for Advocacy of the SBA, EPA convened outreach meetings modeled on the SBREFA panel process to solicit and convey small entities' concerns with theproposed NAAQS. Two meetings were held as part ofthatprocess, on January 7 and February 28, 1997, with a total attendance of41 representatives of smallbusinesses, small governments and small nonprofit organizations. Both meetings were attended by representatives ofSBA and the Office of Management and Budget, as well as of EPA. The key concerns raised by small entities atthose meetings related to the scientific foundation ofthe proposed NAAQS and the potential cost of implementing it, the same concerns raised byother industry commenters on the proposed rule.The Agency produced areport on the meetings to

ensure that small entity concerns were part oftherulemaking record when EPA made its final decision on theproposal.

In light ofStates' pivotal role in NAAQS implementation, EPA also undertook anumber ofadditional activities to assist and encourage the States to be sensitive to small entity impacts asthey implement any new or revised NAAQS. With the SBA, EPA began an interagency panelprocess to collect advice and recommendations from smallentity representatives on how States could lessen any impacts on small entities. The EPA plans to issue materials in two phases to help States develop their implementation plans. In view ofStates' discretion in implementing the NAAQS, these materials will mostly take the form of guidance, which is not subject to the RFA's requirement for initial regulatory flexibility analysis. (Under RFA section 603, that requirement applies only to binding rules that arerequired to undergo notice-and-comment rulemaking procedures.) But regardless ofthe form such materials take,EPA is employing panelprocedures to ensure that small entities have an opportunity to raise any concerns prior to the materials being issued in draft form.

To supplement the input the Agency receives from the ongoingCAAAC process (described earlier in this Unit of this preamble), EPA also added more small entity representatives to the subcommittee on implementation ofany

new or revised NAAQS. These representatives have formed a small entity caucus to develop and bring to the subcommittee afocused approach to small entity issues. These new subcommittee members are also part of the group in the aforementioned panel process. By means ofthese various processes, EPAhopes to promote the consideration ofsmall entity concerns and advice throughout the NAAQS implementation process.

In response to the proposed rule, a number ofcommenters questioned EPA's decision to certify that the proposed NAAQS willnot have a significant impact on a substantial number ofsmall entities. Some commenters disagreed with EPA's view that the proposed NAAQS would not establish regulatory requirements applicable to small entities. These commenters argued that a number of controlrequirements applicable to small entities would automatically result from promulgation ofthe proposed NAAQS, such asnew reasonable further progress, SIP and Federal Implementation Plan (FIP)requirements. Other commenters stated that itis possible for EPA to

assess the impacts ofthe NAAQS revision on small entities and that, to a limited extent, EPA has already done so. Further, a number ofcommenters argued that EPA has alegal obligation under the RFA, as amended by SBREFA,
to choose a NAAQS alternative that minimizes the impact on small entities. Some commenters questioned EPA's interpretations ofthe Mid-Tex and United Distribution cases. In addition, other commenters stated that EPA's position regarding the NAAQS and the RFAis inconsistent with its past practice and the legislative history of the RFA. Finally, a few commenters noted that the panel process EPA conducted for the proposed NAAQS did
not satisfythe requirements ofSBREFA.

EPA disagrees that promulgation of the NAAQS will automatically result in controlrequirements applicable to small entities that EPA can and must analyze under the RFA. As noted previously, a NAAQS rule onlyestablishes a standard ofair quality that other CAA provisions call on States (or in case ofState inaction, the Federal government) to achieve by adopting implementation plans containing specific control

measures for that purpose. Following promulgation ofanew or revised NAAQS, section 110ofthe CAA requires States and EPA to engage in a designation process to determine what

areas within each State's borders are attaining or not attainingthe NAAQS. Under section 110 and parts C and D of TitleI ofthe CAA, States then conduct

aplanning process to develop and adopt their SIPs. Depending on an area's designation for theparticular NAAQS, these and other TitleI provisions require a State's SIP to contain certain controlprograms in addition to the control measures that the State decides

are also needed to attain and maintain the NAAQS.

The fact that the CAA requires SIPs to contain certain control programs under certain circumstances does notmean that EPA either can or must conduct a regulatory flexibility analysis ofarule establishing aNAAQS. Just from the standpoint offeasibility, EPA cannot know which areas will be subject to what mandatory SIP programs until 

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afterthe designation process is completed. Beyond that, any mandatory SIPprograms are still implemented by the States, and States have considerable discretion in how they implement them. For instance, the reasonable further progress requirement under section 172 leaves States broad discretion to determine the rate ofprogress and the control measures to achieve that progress. 64 As aresult, EPA cannot be certain where and how any mandatory programs will be implemented with respect to small (or large) entities. Much less can EPA know about how States will exercise their discretion to develop additional controls needed to attain and maintain the NAAQS.

Even ifEPA could know exactlyhow any mandatory SIP programs would apply to small entities, thepurpose of the RFA is not served by attempting a regulatory flexibility analysis ofState implementation ofthose programs. As explained previously, the RFA and the caselaw interpreting it clearly establish that the purpose ofthe RFA is to promote Federal agency efforts to tailor

arule's requirements to the scale ofthe small entities that willbe subject to it. That purpose cannot be served in the

case ofa NAAQS rule since therule does not establish requirements applicable to small entities. In promulgating a NAAQS, the only choice before EPA concerns the level ofthe standard, not its implementation. While mandatory SIP programs mayultimately follow from promulgation ofthe NAAQS, there is nothingEPA can do in settingthe NAAQS to tailor those programs as they apply to small entities. Whether and how theprograms will apply in particular nonattainment areas is beyond the scope ofthe NAAQS rulemaking and, indeed, beyond EPA's reach in any rulemaking to the extent the applicability and terms ofthe programs are prescribed by statute. 65 Moreover, any mandatory SIPprograms

64Contrary to what some commenters assumed, the SIP requirements of subpart 2 ofpart D ofTitle Iwill not apply to SIPs to implement the revised

ozone NAAQS. Those requirements were enacted by Congress in 1990 to address nonattainment of a 0.12 ppm 1-hour ozone NAAQS. To the extent those requirements remain in effect, they apply only to SIPs for areas still in nonattainment with that standard; they do not apply to SIPs for areas in nonattainment only with respect to the ozone NAAQS adopted today. Further, to the extent SIPs for areas in nonattainment with the previous ozone standard remain subject to subpart 2 requirements, there willbeno incremental change in the impact

on sources regulated by the States' SIPs pursuant to therequirements as a result oftoday's promulgation.

65Ifand when the Agency issues any rules addressing Stateimplementation ofany statutorily required actions, EPA would analyze and address the impact of thoserules on small entities as appropriate under theRFA. are supplemented bydiscretionary State controls that EPA has no power to tailor under the RFA or the CAA (see Trainv. NRDC,quoted previously).

The commenters' suggestions for minimizing thepotential impact ofthe NAAQS rule on small entities run afoul ofboth the RFA and the CAA. Some suggested that EPA set a less stringent standard (or no standard at all in the

case ofPM2.5) to reduce the chance that small entities would become subject to

new or tighter SIP requirements. Others suggested that EPA require States to exempt small entities from new or tighter SIP requirements. However, as explained in a previous Unit ofthis notice addressingthe Agency's authority to consider factors other than public health in setting primary NAAQS, the RFA neither requires nor authorizes EPAto set a less stringent NAAQS than the applicable CAA provisions allow in order to reduce potential small entity impacts. Indeed, the RFA provides that any means of providing regulatory flexibility to small entities be consistent with the statute authorizingthe rule.Moreover, even if EPA set a less stringent standard, States could still exercise their discretion to obtain any needed emission reductions from smallentities. As the Supreme Court in Trainv. NRDCmade clear, EPA has no authority to forbid States from obtaining reductions from any particular category ofstationary sources, including small entities. See also, Virginiav. EPA, No. 108 F.3d 1397, 1408 (D.C.Cir. 1997), quoting UnionElectricv. EPA, 427 U.S. 246, 269 (1976) ("section 110 left to the states thepower to determine which sources would be burdened by regulations and to what extent").

EPA's approval ofSIPs for the new or revised NAAQS also will not establish

new requirements, but will instead simply approve requirements that a State is already imposing.And again, EPA does not have authority to disapprove a State's plan except to the
extent that theplan fails to demonstrate attainment and maintenance ofthe NAAQS as required by Title I ofthe CAA. In cases where EPApromulgates

aFIP, EPA might establish control requirements applicable to small entities, and in such a circumstance, EPA would conduct the analyses required bythe RFA. Some commenters argued that under the RFA as amended by SBREFA, EPA

now has an obligation to choose the alternative that minimizes the impact on 

### smallentities when setting theNAAQS. As indicated above, EPA disagrees with the commenters' argument for the


### reasons stated in theUnit ofthis notice discussing the Agency's authority to consider costs and other factors not related to public health in setting and revising primary NAAQS. In a nutshell, both the text and legislative history of the RFA make clear thatthe RFA does
notoverride the substantive provisions ofthe statute authorizingthe rule,but onlyrequires agencies to identify and consider ways ofminimizing the economic impact on small entities subject to the rule in a manner consistent with the authorizing statute.

Some commenters disagreed with EPA's interpretation ofthe Mid-Tex and United Distribution cases. In particular, these commenters noted that in those

cases the relevant regulatory agency, FERC, wholly lackedjurisdiction to regulate the small entities atissue. According to these commenters, EPA does have the ability andjurisdiction to regulate small entities in the case ofthe NAAQS, and therefore EPA's reliance

on Mid-Tex and United Distribution is misplaced.

The commenters' attempt to distinguish the FERC cases from the NAAQS rulemaking wholly overlooks the courts' reasoning, which in fact fully supports EPA's certification ofthe proposed NAAQS. As described above, the Mid-Tex court exhaustively reviewed the relevant sections ofthe RFA and its legislative history. Its analysis revealed that Congress passed the RFA out ofconcern with one-sizefits-allregulations and fashioned a remedy limited to regulations that apply
to small entities. This principle is fully applicable to the NAAQS, which creates

norule requirements that apply to small entities.

The fact that FERChad no regulatory authority over the small entities indirectly affected by its rules played no essential rolein the court's rationale. FERC could (and apparently did in the Mid-Tex rulemaking) estimate the potential indirect impact ofits rules on small entities. Presumably, FERC could have also mitigated any indirect impact by changing some aspect ofthe rule (or else the smallentities would have had

no incentive to sue the agency). The
court nevertheless found it unnecessary forFERC to doeither, based on its reading ofthe RFA as limited to analysis ofa rule's impact on the small entities subject to the rule's requirements. In reaching its decision, the court noted that requiring agencies to "consider every indirect effect that any regulation might have on small businesses *** is

a very broad and ambitious agenda, *** that Congress is unlikely to have embarked on *** without airing the matter." Mid-Tex, 773 F.d. at 343.

The commenters also overstate EPA's regulatory authority over small entities 

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with respect to the regulation ofcriteria pollutants. Various CAA provisions authorize EPA to regulate various types ofsources atthe Federal level to accomplish specified goals. However, EPA's authority to more generally regulate sources, including small entities, in the manner ofSIPs is limited
to instances ofState default ofSIP responsibilities. When that occurs, EPA may issue a FIP containing specific control measures, and to the extent a proposed FIP would establish control

measures applicable to small entities, EPA would analyze the small entity impact ofthose measures as required by the RFA. In 1994, for example, EPA prepared an initial regulatory flexibility analysis when itproposed a FIP forLos Angeles. See 59 FR23264, May 5, 1994.

As noted above, Congress let the MidTex interpretation stand when it recently amended the RFA in enacting SBREFA. Ifithad disagreed with the court's decision, itwould have revised the relevant statutory provisions or otherwise indicated its disagreement when it enacted SBREFA. Instead, Congress actually reinforced the MidTex court's interpretation ofthe RFA in enacting section 212(a) ofSBREFA. That section requires that an agency issue a "small entity compliance guide" for "each rule *** for which an agency is required to prepare a final regulatory flexibility analysis under section 604" ofthe RFA. The guide is "to assist small entities in complying with the rule" by "explain[ing] the actions a small entity is required to take to comply" with the rule (SBREFA section 212(a)). Obviously, it makes no sense to prepare

a small entity compliance guide for a rule that does not apply to small entities. SBREFA thus stands as further confirmation that Congress intended regulatory flexibility analyses to address only rules that establish requirements small entities must meet. Since SBREFA's passage, the United Distribution courthas affirmed the MidTex court's interpretation.

Some commenters noted thatEPA's informal panel process did not comply with therequirements ofSBREFA. The EPA did not convene a SBREFA panel because such a panel is not required for rules like the NAAQS that do not apply
to small entities. Under the RFA as amended by SBREFA, since the Agency certified the proposal, it was not required to convene apanel for it. Nevertheless, EPA conducted the voluntary panel process described above, as well as other voluntary small business outreach efforts. The process could not comply with the analytical requirements ofthe RFA for the reasons given above. However, it could and did ensure that EPA heard directly from small entities about the NAAQS proposals.

A few commenters stated that EPA's view ofthe NAAQS and the RFA is inconsistent with EPA's pastpositions regarding the RFA and NAAQS revisions. Some commenters also cited the Regulatory Impact Analysis for the proposed NAAQS and noted that this analysis demonstrates EPA's ability to estimate the impact ofthe NAAQS on small entities, thereby undercutting EPA's argument that it is not able to perform a regulatory flexibility analysis when setting the NAAQS.

Past Federal Register notices make 

### clear thatthe nature ofthe NAAQS makes a regulatory flexibility analysis inapplicable to NAAQS rulemakings. For instance, in 1984, EPA stated that a "NAAQS forNOx byitselfhas no direct impact on small entities. However, it forces each State to design and implement control strategies for areas not in attainment." 49 FR 6866, 6876, February 23, 1984; see also, 50 FR 37484, 37499, September 13, 1985; 50 FR25532, 25542, June 19, 1985 (NAAQS for NO2 do not impact small entities directly). EPA stated again in 1987 thatthe NAAQS "themselves do
not contain emission limits or other pollution controls. Rather, such controls



### arecontained in State implementation plans." 52 FR24634, 24654, July 1, 1987.

EPA has typically performed an analysis to assess, to the extent 

### practicable, thepotential impact of retaining or revisingthe NAAQS on small entities, depending on possible State strategies for implementing the NAAQS. These analyses have provided

asmuch insight into the potential small entity impacts ofimplementing revised NAAQS as could be provided atthe NAAQS rulemaking stage. In some instances, these preliminary "analyses"

were described as "regulatory flexibility analys[es]" or as analyses "pursuant to this [Regulatory Flexibility] Act." See, e.g., 52 FR24634, 24654, July 1, 1987; 50 FR 37484, 37499, September 13, 

### 1985.

However, these analyses were based

on hypothetical State control strategies, and EPA made the point on various occasions that any conclusions to be drawn from such analyses were "speculative," given that the NAAQS themselves do not impose requirements

on small entities. Although these past analyses reflected the Agency's best efforts to evaluate potential impacts, they were not regulatory flexibility analyses containing the necessary elements required by the RFA. These analyses, for example, did not describe the "reporting, recordkeeping and other compliance requirements" ofthe proposed NAAQS rules that would apply to small entities, since the NAAQS rules did not apply to small entities. Nor did they determine how the proposed NAAQS rules could be eased or waived for smallentities. Such

an analysis is not possible in the case of 

### theNAAQS. Totheextent EPA labeled these analyses regulatory flexibility analyses in the past, that label was inappropriate. EPA's current practice is to describe such an analysis more accurately as a "general analysis ofthe potential cost impacts on small entities." See, e.g., 61 FR 65638, 65669, 65747, December 13, 1996 (current 03 and PM NAAQS proposals). 66EPA's analytical approach to small entity impacts ofthe NAAQS has thus remained consistent overtime.



### One commenter noted that the legislative history ofthe RFA suggests that the RFA was intended to apply to the NAAQS. As noted previously, EPA's reading ofboth the RFA and SBREFA, based on the language ofthe statute as amended and its legislative histories and applicable caselaw, is that the RFA requirements at issue do not apply to the NAAQS. The legislative history cited by the commenter does not change this conclusion.

In fact,the statement by Senator Culver on which the commenter relies does not indicate that the NAAQS should be subject to regulatory flexibility analyses. Rather, Senator Culveruses the NAAQS as an example ofthe type ofstandard that agencies would notchange as a result ofthe Regulatory Flexibility Act. According to Senator Culver, Section 606 "succinctly
states that thisbill does not alterthe substantive standard contained in underlying statutes which defines the agency's mandate." 126 Cong. Rec. S 21455 (Aug. 6, 1980)daily ed. After citing CAA section 109, Senator Culver goes on to describe EPA's bubble policy

66As commenters pointed out, the RIA for the proposed PM NAAQS does state that "[t]he screening analysis ***provides enough information foran initial regulatory flexibility analysis (RFA)if such an analysis were to be done." That statement

was mistaken and was not madein the RIA for the proposed ozoneNAAQS. While both RIAs attempted to gauge the potential impact on small entities ofState implementation of theproposed NAAQS, neither could or did identify any specific control orinformation requirements contained in theNAAQS rule that would apply to small entities. Indeed, both RIAs made clearthat theimpact being analyzed was that ofpotential State measures to attain the NAAQS, and that such an analysis was inherently speculative and uncertain. Thus, the RIAs actually confirm EPA's statement in the preambles forthe proposed NAAQS that conducting a complete regulatory flexibility analysis is notfeasible forrules setting orrevising

aNAAQS. 

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(which addresses the limitson emissions from aparticular facility) as the type offlexibleregulation that agencies should consider, once EPAhas set aNAAQS. "The importantpoint for purposes ofthis discussion is thatthe 'bubble concept', atype offlexible regulation, in no manner altered the basic statutory substantive standard of theEPA ***

.No regulatory flexibility analysis alters the substantive standard otherwise applicableby law toagency action." Id. Thus, contrary to the suggestion ofthecommenter, Senator Culver's statement actually confirms that thetime to considerregulatory flexibility is when regulations applicable to sources are being established, not when a NAAQS itselfis being set.

Under section 604 oftheRFA, whenever an agency promulgates afinal rule under section 553 ofthe Administrative Procedure Act, after beingrequired bythat section or any other law topublish ageneral noticeof proposed rulemaking (NPRM), the agencyisrequired toprepare a final regulatory flexibility analysis. RFA section 605(b) provides,however, that section 603 (reinitialregulatory flexibility analyses) and section 604 do not apply ifthe agency certifies thatthe rule will not have a significant economic impact on a substantial number ofsmall entities and publishes such certification at thetime of publication oftheNPRM or at thetime ofthefinalrule.

As noted above, EPA certified today's rule atthe time oftheNPRM. After considering the public comments on the certification, EPA continues tobelieve that today's rule will nothave a significant economic impact on a substantial numberofsmall entities for thereasons explained above and that it therefore appropriately certified the rule.Further, as required by theCAA, EPA ispromulgating today's rule under CAA section 307(d). For all the foregoing reasons, EPA hasnotprepared

afinalregulatory flexibility analysis for therule. The Agency has nonetheless analyzed in thefinal RIA for therule the potential impact on small entities of hypothetical Stateplans for implementing theNAAQS. TheAgency alsoplans to issueguidance to the States on reducing thepotential impact

on smallentities ofimplementingthe NAAQS.
C.Impacton ReportingRequirements

There are noreporting requirements directly associated with the finalization ofambient airquality standards under section 109 ofthe Act (42U.S.C. 7409). There are, however, reporting requirements associated with related sections ofthe Act, particularly sections 107, 110, 160, and 317 (42U.S.C. 7407, 7410, 7460, and 7617).

D. UnfundedMandatesReform Act

Title II ofthe Unfunded Mandates Reform Act of 1995 (UMRA), Pub. L. 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 ofthe UMRA, EPA generally must prepare awritten statement, including a cost-benefit analysis, for proposed and final rules with "Federal mandates" that may result in expenditures by State, local, and tribal governments, in the aggregate,

or by theprivate sector, of$100 million

or more in any one year. This requirement does not apply ifEPA is prohibited by law from considering section 202 estimates and analyses in adoptingthe rule in question. Before promulgating an EPArule for which a written statement is needed, section 205 ofthe UMRA generally requires EPA to identify and consider areasonable number ofregulatory alternatives and adopt the least costly, most costeffective, or least burdensome alternative that achieves the objectives oftherule. These requirements 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 ifthe Administrator publishes with the final rule an explanation ofwhy 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 ofthe UMRA a small government agency plan. The plan must provide for notifying potentially affected smallgovernments, enabling officials of affected small governments to have meaningful and timely input in the development ofEPAregulatory proposals with significant Federal intergovernmental mandates, and informing, educating, and advising small governments on compliance with the regulatory requirements. Section 204 ofUMRA requires each agency to develop "an effective process to permit elected officers ofState, local and tribal governments *** to provide meaningful and timely input" in the development of regulatory proposals containing a significant Federal intergovernmental mandate. 67

67As noted in Unit VII.B. of this preamble, a NAAQS rule only establishes a standard ofair The EPAhas determined that the provisions ofsections 202 and 205 of the UMRA do not apply to this decision. "Unless otherwise prohibited bylaw," EPA is to prepare a written statement under Section 202 ofUMRA that is to contain assessments and estimates of the costs and benefits ofarule containing a Federal mandate. Congress clarified that "unless otherwise prohibited by law" referred to whether

an agency was prohibited from consideringthe information in the rulemaking process, not to whether an agency was prohibited from collecting the information. The Conference Report

on UMRA states, "This section [202] does not require thepreparation ofany estimate or analysis ifthe agency is prohibited by law from consideringthe estimate or analysis in adopting the rule." 141 Cong.Rec. H3063 (daily ed. March 13, 1995). Because the Clean Air Actprohibits EPA, when setting the NAAQS, from considering the types of estimates and assessments described in section 202,UMRA does not require EPA to prepare awritten statement under section 202.68 The requirements in section 205 do not apply because those requirements only apply to rules "for which a written statement is required under section 202 ***."

The EPAhas determined that the provisions ofsection 203 ofUMRA do
not apply to this decision. Section 203 onlyrequires the development ofa small government agency plan for requirements with which small governments might have to comply. Since setting the NAAQS does not establish requirements with which small governments might have to comply, section 203 does not apply. The

quality that other provisions ofthe Act call on States (orin the case ofStateinaction, the Federal government) to achieve by adopting implementation plans containing specific control

measures forthe purpose. Thus, it is questionable whether the NAAQS itselfimposes an enforceable duty and thus whether it is a significant Federal mandate within the meaning ofUMRA. EPA need
not and does notreach this issue today. For the

reasons given in thisunit, even ifthe NAAQS were determined to be a significant Federal mandate, EPA does nothave any obligations under sections 202 and 205 ofUMRA, and EPA hasmet any obligations it would have under section 204 of UMRA.

68In addition to the estimates and assessments described in section 202 ofUMRA, written
statements are also to include an identification of theFederal law under which the rule is promulgated (section 202(a)(1) ofUMRA) and a description ofoutreach efforts under section 204 of UMRA (section 202(a)(5) ofUMRA). Although these requirements do notapply here because a written
statementis notrequired under section 202 of UMRA, thispreamble identifies the Federal law under which thisrule is beingpromulgated and a written statement describing EPA's outreach efforts with State, local, and tribal governments will be placed in the docket. 

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EPA acknowledges, however, that any corresponding revisions to associated State implementation plan requirements and air quality surveillance requirements, 40 CFRpart 51 and 40 CFRpart 58, respectively, might result in such effects. Accordingly, EPA will address unfunded mandates as appropriate when itproposes any revisions to 40CFRparts 51 and 58.

With regard to the outreach described in UMRA section 204, EPA did follow

aprocess forproviding elected officials with an opportunity for meaningful and timely input into theproposed NAAQS revisions, although EPA did not describe this process in the proposal. The EPA conducted a series ofpreproposal outreach meetings with State and local officials and their representatives thatpermitted these officials to provide meaningful and timely input on issues related to the NAAQS and the monitoring issues associated with them. Beginning in January, 1996, EPAbriefed State and local airpollution control officials at national meetings with State and Territorial Air Pollution Program Administrators (STAPPA)/Association ofLocal Air Pollution Control Officials (ALAPCO) inWashington DC,North Carolina, Chicago and Nevada. The EPA also held briefings for the Washington DCrepresentatives ofseveral State and local organizations, including National Conference ofStateLegislators, U.S. Conference ofMayors, National Governors Association, and National League ofCities, and STAPPA/ ALAPCO. EPA also held separate briefings and discussions with State and local officials at meetings setup bythe National Governors Association, the U.S. Conference ofMayors and the Council ofState Governments. The EPA also conducted in-depth briefings at each EPA regional office and regional staffalso had several meetings and discussions with their State counterparts about the standards. The efforts described above, which provided elected officials with opportunity for meaningful and timely input into the proposed NAAQS revisions, met any requirements imposed by section 204. The docket will contain a written statement describing these outreach efforts, including a summary ofthe
comments and concerns presented by State, local, and tribal governments and

a summary ofEPA's evaluation ofthose
comments and concerns.

Several commenters disagreed with EPA that UMRA sections 202, 203 and 205 do not apply to this decision. These
commenters argued thatEPA is not prohibited from considering costs in settingNAAQS under the Clean Air Act 

### and applicablejudicial decisions. Some
commenters also expressed the view 

### that there is no conflict between UMRA and the Clean Air Act with regard to the NAAQS. These commenters argued that UMRA and the NAAQS can be "harmonized" by readingUMRA as an information gathering statute and that EPA should therefore perform the analyses required by UMRA, regardless ofwhether costs may be considered. Finally, at least one commenter argued that in pastNAAQS reviews, EPA did not dispute its UMRA obligations.

As discussed more fully in Unit IV of this preamble, EPA is prohibited from considering cost in settingthe NAAQS. Given that fact (as noted in Unit IV preamble), sections 202 and 205 do not apply.69 As the Conference Report clarifies, UMRA itself states that the section 202 estimates and analyses are not required in cases such as the NAAQS, where an agency is prohibited by law from considering section 202 estimates and analyses. Reading UMRA in the manner suggested by the commenters would effectively read this provision out ofUMRA; UMRA contains

an exception for rules like the NAAQS, it must be given effect.

With regard to EPA's position regarding UMRA in previous NAAQS review exercises, EPA simply made plain in those situations thatbecause it did not plan on revising the NAAQS, it determined, without further review, that UMRA sections 202, 203 and 205 did
not apply. EPA thus stated that:

Because the Administrator has decided not to revise the existingprimary NAAQS for SO 2,this action will notimpose anynew expenditures on governments oron the private sector, orestablish any new regulatory requirements affecting small governments. Accordingly, EPAhas determined thatthe provisions ofsection 202, 203 and 205 do not apply to thisfinal decision.
61 FR25566, 25577, May 22, 1996; See also 61 FR52852, 52856, October 8, 1996 (Same statement for NO2NAAQS). As this statement makes clear,EPA only

69One commenter argued thatinreviewing the S02 NAAQS, EPA determined thatitneed not revisethe S02NAAQS, butcould instead pursue
an alternative regulatory programunder other authority. Thiscommenter argued thatEPA has similar flexibilityin reviewing the PM and Ozone NAAQS, and thus UMRArequires EPAto identify the least burdensome alternative (such as retaining the current NAAQS) aspart ofthatprocess. As discussed morefully above atUnit IV ofthis preamble, EPA does notagree thatit has flexibility to choose such an alternative;nor does EPA agree with the commenter's characterization ofthe action it took in deciding not to revisethe S02NAAQS. In fact,in deciding notto revise the S02NAAQS, EPA determined, for reasons independent ofsection 303 ofthe Clean Air Actthat aNAAQS revision was not warranted. See 61 FR25566, 25575, May 22, 1996. determined that UMRA sections 202, 203 and 205 did not apply to the NAAQS when EPA fails to revise the standard. Having made that determination, EPAhad noreason to catalogue additional bases for finding UMRA inapplicable. Nothing in that
statement was intended to preclude EPA, orprecludes EPA, from concluding forother reasons (such as those discussed above) that UMRA also does not apply when EPA in fact revises

an applicable NAAQS.

E. EnvironmentalJustice

Executive Order 12848 requires that each Federal agency make achieving environmentaljustice part ofits mission by identifying and addressing, as appropriate, disproportionately high and adverse human health or environmental effects ofits programs, policies, and activities on minorities and low-income populations. These requirements have been addressed to the extent practicable in the RIA cited above.

F. Submission to Congressandthe ComptrollerGeneral

Under 5 U.S.C. 801(a)(1)(A), as added by the Small Business Regulatory Enforcement Fairness Act of 1996 (SBREFA), EPA submitted areport containing this rule and other required information to the U.S. Senate, the U.S. House ofRepresentatives, and the Comptroller General ofthe United States prior to publication ofthe rule in today's FederalRegister. This rule is a "major rule" forpurposes ofSBREFA.

VIII.Response to Petition for Administrator Browner's Recusal

On March 13, 1997, the Washington Legal Foundation (WLF),filed a petition with EPA askingthat I, Carol Browner, disqualify myselfin rulemaking regarding the NAAQS for PM and 03. The petition claims that mypublic
statements indicate a "clear and convincing showing" that Ihad "already decided to revise the NAAQS for PM and ozone" and that I therefore "could notgive meaningful consideration" to comments adverse to the proposed rule. OnMay 12, 1997, EPA's General Counsel, Jonathan Z. Cannon, sent a letter to WLF regarding the petition. This letter and the WLF petition were then placed in the dockets for the proposed 03 and PM standards pending "consideration and final response in connection with the Agency's final actions."

Contrary to WLF's assertions, Ihave maintained an open mind throughout theseproceedings, and have based today's decisions on the rulemaking 

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record-including consideration of comments opposed to the proposal. The law does not require the Administrator ofEPA to disqualifyherselfmerely for expressing views on aproposed regulation; in fact, it is part ofmy responsibility to engage in the public debate on the proposals. Moreover, the assertions in WLF's petition do not accurately represent my views. The petition takes quotes out ofcontext and repeatedly misinterprets my statements. For example, WLF quotes a statement that Imade at the Children's Environmental Health Network Research Conference as an indication that Ihad "prejudged the issue." However, my statement that "I will not be swayed" did not refer to adopting the NAAQS as proposed. Instead, as is clear from reviewing the entire speech, I was addressing my broader concern about children's health and therange ofEPA standards affecting children's health. I also appeared at several congressional hearings and testified before members of Congress, some ofwhom were strongly opposed to theproposals. Atthose hearings, I explained the basis for the proposals and put forward the reasons why Iconcluded theproposals were appropriate, given the information before me atthe time. At the same time, I made clear that Itook very seriously my obligation to keep an open mind, and to consider fully and fairly all significant comments that the Agency received. For these reasons and others,

as set forth inMr. Cannon's May 12, 1997 response to WLF, which Iadopt in full, Ihave decided not to recuse myself from any aspect ofconsideringrevisions
to the NAAQS for 03 and PM. Accordingly, I am hereby denying WLF's petition.

IX. References

(1)American Thoracic Society. (1985) Guidelines asto whatconstitutes an adverse respiratory health effect, with special reference to epidemiologic studies ofair pollution.AmericanReview ofRespiratory Disease.. 131: 666 668.

(2)Freas (1996) Ambient air quality relationships amongalternative ozone air quality standards. Internal memorandum from Warren P. Freas to file, U.S. EPA, EMAD/OAQPS/OAR, RTP,NC, dated October 30, 1996. DocketNo. A 95 58 Item I B 6.

(3)Freas (1997) Ambient air quality relationships forcounties meeting alternative air quality standards. Internal memorandum from Warren P. Freas to file, U.S.EPA, EMAD/OAQPS/OAR, RTP,NC, dated July 1, 1997. Docket No. A 95 58 Item xxx.

(4)Heck, Walter W.And Ellis B. Cowling. January, 1997. EMJournal. "The Need fora Long Term Cumulative Secondary Ozone Standard -An Ecological Perspective." Air and Waste Management Association, Pittsburgh, PA.;pp. 23 33.

(5) Johnson, T;Capel, J.;Mozier, J.;McCoy, M. (1996a) Estimation ofozone 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 TrianglePark, NC, August.

(6) Johnson, T.; Capel, J.;McCoy, M.; Mozier, J. (1996b) Estimation ofozone exposures experienced by outdoor workers in nine urban areas using a probabilistic version ofNEM. Prepared by IT/Air Quality Services for U.S. EPA, OAQPS; Research Triangle Park, NC, August.

(7) McClellan, R.0., (1989) Letter from Chairman ofClean Air Scientific Advisory Committee to the EPA Administrator, dated May 1, 1989. EPA SAB-CASAC-LTR 89 019.

(8) 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 Item IV A 1.

(9) Seitz (1996) Revocation date for the existing 1-hour ozone standards. Internal memorandum from John S. Seitz to Mary D. Nichols, U.S. EPA, OAQPS/OAR, RTP, NC, dated November 20, 1996. Docket No. A 95 59 Item I B 3.

(10) Thurston, G.D.; Ito, K.; Kinney, P.L.; Lippmann, M. (1992) A multi-year study of air pollution and respiratory hospital admissions in threeNew York State metropolitan areas: results for 1988 and 1989

summers. JournalofExposureAnalysisand EnvironmentalEpidemiology.2:429 450.

(11) U.S. Department ofHealth and Human Services (1996) Vital and health statistics:
current estimates from the national health interview survey, 1994. Hyattsville, MD: Public Health Service, National Center for Health Statistics; DHHS publication no. (PHS) 96 278.

(12) U.S. Environmental Protection Agency (1996a) Air quality criteria for Ozone and related photochemical oxidants. Research Triangle Park, NC: Office ofHealth and Environmental Assessment, Environmental Criteria and Assessment Office; EPA report

nos. EPA/600/AP 93/004a c.

(13) U.S. Environmental Protection Agency (1996b) Review ofthe national ambient air quality standards for ozone: assessment of scientific and technical information. OAQPS staffpaper. Research Triangle Park,NC: Office ofAir Quality Planning and Standards; EPA report no. EPA 452/R 96 007. Available from:NTIS, Springfield, VA; PB96 203435.

(14) Whitfield, R.G.; Biller, W.F.; Jusko, M.J.; Keisler, J.M. (1996) Aprobabilistic
assessment ofhealth risks associated with short-term exposure to tropospheric ozone. Report prepared for U.S. EPA, OAQPS. Argonne National Laboratory; Argonne, IEL, June. (Forcopies, contact Harvey M. Richmond, U.S. Environmental Protection Agency, OAQPS, MD 15, Research Triangle Park, N.C. 27711, (919) 541 5271.)

(15) Wolff, G. T., (1995a) Letter from Chairman ofClean Air Scientific Advisory Committee to the EPA Administrator, dated November 28, 1995. EPA SAB CASAC LTR 96 001.

(16) Wolff, G.T., (1995b) Letterfrom Chairman ofClean AirScientific Advisory Committee to the EPA Administrator, dated November 30, 1995. EPA SAB CASAC LTR 96 002.

(17) Wolff, G.T., (1996) Letter from Chairman ofClean AirScientific Advisory Committee to the EPA Administrator, dated April 4, 1996. EPA SAB CASAC LTR 96 006.

List ofSubjects in 40 CFRPart 50

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

Dated:July 16, 1997.

CarolM.Browner,
Administrator.

Therefore, for thereasons setforth in the preamble, title40, chapter I, part 50 ofthe Code ofFederal Regulations is amended as follows:

PART50-NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY
STANDARDS

1. The authority citation for part 50 continues to read as follows:

Authority: Secs. 109 and 301(a), Clean Air Act, as amended (42U.S.C. 7409, 7601(a)).

2. Section 50.9 is revised to read as follows:
§50.9 National 1-hour primaryand secondary ambient airqualitystandardsfor
ozone.

(a) The level ofthe national 1-hour primary and secondary ambient air quality standards for ozone measured by

areference method based on Appendix Dto this part and designated in accordance with part 53 ofthis chapter, is 0.12 parts per million (235 gg/m 3 ). The standard is attained when the expected number ofdays per calendar

year with maximum hourly average concentrations above 0.12parts per million (235 gg/m 3)is equal to or less than 1, as determined by Appendix H to this part.

(b) The 1-hour standards set forth in this section will no longer apply to an
area once EPA determines that the area has air quality meeting the 1-hour standard. Area designations are codified in 40 CFR part 81.

3. Section 50.10 is added to read as follows: §50.10 National 8-hour primary and secondary ambient airqualitystandardsfor
ozone.

(a) The level ofthe national 8-hour primary and secondary ambient air quality standards forozone, measured 

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by a reference method based on Appendix Dto thispart and designated in accordance with part 53 ofthis chapter, is 0.08parts per million (ppm), daily maximum 8-hour average.

(b) The 8-hour primary and secondary ozone ambient air quality standards are met at an ambient air quality monitoring sitewhen the average ofthe annual fourth-highest daily maximum 8-hour average ozone concentration is less than or equal to 0.08 ppm, as determined in accordance with Appendix Ito thispart.

4. Appendix D is amended by revising references 8 and 9 and by removing all ofthe text and figures immediately following "Figure 2, Schematic Diagram ofa Typical UV Photometric Calibration System (Option 1), through the end of Appendix D. 

### Appendix D toPart 50-Measurement Principleand Calibration Procedure for the Measurement ofOzone inthe Atmosphere

6. References.

8.Transfer Standards for Calibration of Ambient Air Monitoring Analyzers for Ozone, EPApublication numberEPA 600/4 79 056,EPA, NationalExposure Research Laboratory, Department E, (MD 77B), Research Triangle Park, NC 27711.

9. Technical Assistance Document for the Calibration ofAmbient Ozone Monitors, EPA publication numberEPA 600/4 79 057, EPA, NationalExposure Research Laboratory, Department E, (MD 77B), Research Triangle Park, NC 27711.



### Appendix E[Removed and Reserved]

5. Appendix E is removed and reserved.

6. Appendix H is amended by revising the appendix heading to read "Appendix H To Part 50-Interpretation ofThe 1-Hour Primary and Secondary National Ambient Air Quality Standards for Ozone".

7. Appendix I is added to read as follows: 

### Appendix Ito Part 50-Interpretation of the 8-Hour Primary and Secondary National Ambient AirQuality Standards forOzone

1. General. This appendix explains the data handling conventions and computations necessary for determining whether the national 8 hour primary and secondary ambient air quality standards for ozone specified in §50.10 are met at an ambient ozone air quality monitoring site. Ozone is measured inthe ambient air by areference method based on Appendix Dofthispart. Datareporting, data handling, and computation procedures tobe used in making comparisons between reported ozone concentrations and the level ofthe ozone standard are specified in the following sections. Whether to exclude, retain, or make adjustments to the data affected by stratospheric ozone intrusion or other natural events is subject to the approval ofthe appropriate Regional Administrator.

2. PrimaryandSecondaryAmbientAir QualityStandards forOzone. 2.1 DataReportingandHandling Conventions.

2.1.1 Computing8-hour averages.Hourly average concentrations shall bereported in parts per million (ppm)to the third decimal place, with additional digits to the right being truncated. Running 8 hour averages shallbe computed from thehourly ozone concentration data for each hour oftheyear and the result shallbe stored in thefirst, or start, hourofthe 8 hour period. An 8 hour average shall be considered valid if at least 75% ofthehourly averages for the 8 hour period are available. In the event that only 6 (or 7) hourly averages are available, the 8 hour average shall be computed on the basis ofthehours available using 6 (or 7) as the divisor. (8 hourperiods with three ormore missing hours shall not be ignored if, after substituting one-half the minimum detectable limit for the missinghourly concentrations, the 8 hour average concentration is greater than the level ofthe standard.) The computed 8 hour average ozone concentrations shall be reported to three decimal places (the insignificant digits to theright ofthe third decimal place are truncated, consistent with the data handling procedures for thereported data.)

2.1.2 Dailymaximum 8-houraverage concentrations.(a) There are 24 possible running 8 houraverage ozone concentrations for each calendar day during the ozone monitoring season. (Ozone monitoring

seasons vary by geographic location as designated in part 58, Appendix D to this chapter.) The daily maximum 8 hour concentration for a given calendar day is the highest ofthe 24 possible 8 hour average concentrations computed for that day. This process is repeated, yielding a daily maximum 8 hour average ozone concentration for each calendar day with ambient ozone monitoring data. Because the 8 hour averages are recorded in the start hour, the daily maximum 8 hour concentrations from two consecutive days may have some hourly concentrations in

common. Generally, overlapping daily maximum 8 hour averages are not likely, except in those non urban monitoring locations with less pronounced diurnal variation in hourly concentrations.

(b) An ozone monitoring day shallbe counted as a valid day ifvalid 8 hour averages are available for atleast 75% of possible hours in the day (i.e., at least 18 of the 24 averages). In the event that less than 75% ofthe 8 hour averages are available, a day shall also be counted as a valid day if the daily maximum 8 hour average concentration for that day is greater than the level ofthe ambient standard.

2.2 PrimaryandSecondaryStandardrelatedSummary Statistic.The standardrelated summary statistic is the annual fourth-highest daily maximum 8 hour ozone concentration, expressed in parts per million, averaged over three years. The 3 year average shall be computed using thethree most recent, consecutive calendar years of monitoring data meeting the data completeness requirements described in this appendix. The computed 3 year average of the annual fourth-highest daily maximum 8 hour average ozone concentrations shallbe expressed to three decimal places (the remaining digits to the right are truncated.)

2.3 Comparisonswith thePrimaryand SecondaryOzoneStandards.(a) The primary and secondary ozone ambient air quality standards are met atan ambient air quality monitoring site when the 3 year average of the annual fourth-highest daily maximum 8 hour average ozone concentration is less than

orequal to 0.08 ppm. The number of significant figures in the level ofthe standard dictates the rounding convention for comparing the computed 3 year average annual fourth-highest daily maximum 8 hour average ozone concentration with the level ofthe standard. The third decimal place ofthe computed value is rounded, with values equal to or greater than 5 rounding up. Thus, a computed 3 year average ozone concentration of0.085 ppm is the smallest value that is greater than 0.08 ppm.

(b) This comparison shall bebased on three consecutive, complete calendar years ofair qualitymonitoring data. This requirement is
metfor the threeyear period at a monitoring site ifdaily maximum 8 hour average concentrations are available for at least 90%,

on average, ofthe days during the designated

ozone monitoring season, with a minimum datacompleteness in any one year ofat least 75% ofthe designated sampling days. When computingwhether theminimum data completeness requirements have been met, meteorological or ambient data maybe sufficient to demonstrate that meteorological conditions on missing days were not conducive to concentrations above the level ofthe standard. Missing days assumed less than the level ofthe standard are counted for thepurpose ofmeeting the data completeness requirement, subject to the approval ofthe appropriate Regional Administrator.

(c) Years with concentrations greater than the level ofthe standard shall not be ignored

on the ground that they have less than complete data. Thus, in computing the 3 year average fourth maximum concentration, calendar years with less than 75% data completeness shall be included in the computation ifthe average annual fourth maximum 8 hour concentration is greater than the level ofthe standard.

(d) Comparisons with the primary and secondary ozone standards are demonstrated by examples 1 and 2 in paragraphs (d)(1) and (d) (2) respectively as follows:

(1) As shown in example 1, the primary and secondary standards are met at this monitoring site because the 3 year average of the annual fourth-highest daily maximum 8 hour average ozone concentrations (i.e., 0.084 ppm) is less than or equal to 0.08ppm. The datacompleteness requirement is also met because the average percent ofdays with valid ambient monitoring datais greater than 

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90%, and no single year has less than 75% data completeness.

EXAMPLE 

### 1.AMBIENT MONITORING SITE ATTAINING THE PRIMARY AND SECONDARY OZONE STANDARDS

1st Highest 2nd Highest 3rd Highest 4th Highest 5th Highest Year Percent Daily Max Daily Max Daily Max Daily Max Daily Max Valid Days 8-hour 8-hour 8-hour 8-hour 8-hour Conc. (ppm) Conc. (ppm) Conc. (ppm) Conc. (ppm) Conc. (ppm)

1993

.................................................................................. 100% 0.092 0.091 0.090 0.088 0.085

1994

.................................................................................. 96% 0.090 0.089 0.086 0.084 0.080

1995

.................................................................................. 98% 0.087 0.085 0.083 0.080 0.075

Average

...................................................................... 98% 0.084

(2) As shown in example 2, theprimary average ozone concentrations (i.e., 0.093 capture is less than 75%, because the average and secondary standards are not met at this ppm) is greater than 0.08 ppm. Note that the fourth-highest daily maximum 8 hour monitoring sitebecause the 3 year average of ozone concentration data for 1994 is used in average concentration is greater than 0.08 the fourth-highest daily maximum 8 hour these computations, even though the data ppm.

EXAMPLE 

## 2. AMBIENT MONITORING SITE FAILING TO MEET THE PRIMARY AND SECONDARY OZONE STANDARDS

1st Highest 2nd Highest 3rd Highest 4th Highest 5th Highest Year Percent Daily Max Daily Max Daily Max Daily Max Daily Max Valid Days 8-hour 8-hour 8-hour 8-hour 8-hour Conc. (ppm) Conc. (ppm) Conc. (ppm) Conc. (ppm) Conc. (ppm)

1993

.................................................................................. 96% 0.105 0.103 0.103 0.102 0.102

1994

.................................................................................. 74% 0.090 0.085 0.082 0.080 0.078

1995

.................................................................................. 98% 0.103 0.101 0.101 0.097 0.095

Average

...................................................................... 89% 0.093

3. Design Values forPrimaryand SecondaryAmbientAirQuality Standards forOzone. The air quality design value at a monitoring siteis defined as that concentration that when reduced to thelevel ofthe standard ensures that the site meets the standard. For a concentration-based standard, the air quality design value is simply the standard-related test statistic. Thus, for the primary and secondary ozone standards, the 3 year average annual fourth-highest daily maximum 8 hour average ozone concentration is also the air quality design value for the site. [FR Doc. 97 18580 Filed 7 17 97; 8:45 am]

BILLING CODE 6560-50-F

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