Federal Register / Vol. 73, No. 60 / Thursday, March 27, 2008 / Rules and Regulations

ENVIRONMENTAL PROTECTION

AGENCY

40 CFR Parts 50 and 58

[EPA-H Q-OAR-2005-0172; FRL-8544-3]

RIN 2060-AN24

National Ambient Air Quality

Standards for Ozone

AGENCY: Environmental Protection

Agency (EPA).

ACTION: Final rule.

SUMMARY: Based on its review of the air

quality criteria for ozone (03) and

related photochemical oxidants and

national ambient air quality standards

(NAAQS) for 03, EPA is making

revisions to the primary and secondary

NAAQS for 03 to provide requisite

protection of public health and welfare,

respectively. With regard to the primary

standard for 03, EPA is revising the

level of the 8-hour standard to 0.075

parts per million (ppm), expressed to

three decimal places. With regard to the

secondary standard for 03, EPA is

revising the current 8-hour standard by

making it identical to the revised

primary standard. EPA is also making

conforming changes to the Air Quality

Index (AQI) for 03, setting an-AQI value

of 100 equal to 0.075 ppm, 8-hour

average, and making proportional

changes to the AQI values of 50, 150

and 200.

DATES: This final rule is effective on

May 27, 2008.

ADDRESSES: EPA has established a

docket for this action under Docket ID

No. EPA-HQ-OAR-2005-0172. All

documents in the docket are listed on

the www.regulations.gov Web site.

Although listed in the index, some

information is not publicly available,

e.g., confidential business information

or other information whose disclosure is

restricted by statute. Certain other

material, such as copyrighted material,

is not placed on the Internel and will be

publicly available only in hard copy

form. Publicly available docket

materials are available either

electronically through

www.regulations.gov or in hard copy at

the Air and Radiation Docket and

Information Center, EPA/DC, EPA West,

Room 3334, 1301 Constitution Ave.,

NW., Washington, DC. This Docket

Facility is open from 8:30 a.m. to 4:30

p.m., Monday through Friday, excluding

legal holidays. The Docket telephone

number is 202-566-1742. The

telephone number for the Public

Reading Room is 202-566-1744.

FOR FURTHER INFORMATION CONTACT: Dr.

David J. McKee, Health and

Environmental Impacts Division, Office

of Air Quality Planning and Standards,

U.S. Environmental Protection Agency,

Mail Code C504-06, Research Triangle

Park, NC 27711; telephone: 919-541-

5288; fax: 919-541-0237; e-mail:

mckee.dave@epa.gov.

SUPPLEMENTARY INFORMATION:

Table of Contents

The following topics are discussed in this

preamble:

I. Background

A. Summary of Revisions to the 03 NAAQS

B. Legislative Requirements

C. Review of Air Quality Criteria and

Standards for 03

D. Summary of Proposed Revisions to the

03 NAAQS

E. Organization and Approach to Final

Decision on 03 NAAQS

II. Rationale for Final Decision on the

Primary 03 Standard

A. Introduction

1. Overview

2. Overview of Health Effects

3. Overview of Human Exposure and

Health Risk Assessments

B. Need for Revision of the Current

Primary 03 Standard

1. Introduction

2. Comments on the Need for Revision

3. Conclusions Regarding the Need for

Revision

C. Conclusions on the Elements of the

Primary 03 Standard

1. Indicator

2. Averaging Time

3. Form

4. Level

D. Final Decision on the Primary 03

Standard

IlI. Communication of Public Health

Information

IV. Rationale for Final Decision on the

Secondary 03 Standard

A. Introduction

1. Overview

2. Overview of Vegetation Effects Evidence

3. Overview of Biologically Relevant

Exposure Indices

4. Overview of Vegetation Exposure and

Risk Assessments

B. Need for Revision of the Current

Secondary 03 Standard

1. Introduction

2. Comments on the Need for Revision

3. Conclusion's Regarding the Need for

Revision

C. Conclusions on the Secondary 03

Standard

1. Staff Paper Evaluation

2. CASAC Views

3. Administrator's Proposed Conclusions

4. Comments on the Secondary Standard

Options

5. Administrator's Final Conclusions

D. Final Decision on the Secondary 03

Standard

V. Creation of Appendix P-Interpretation of

the NAAQS for 03

A. General

B. Data Completeness

C. Data Reporting and Handling and

Rounding Conventions

VI. Ambient Monitoring Related to Revised

03 Standards

VII. Implementation and Related Control

Requirements

A. Future Implementation Steps

1. Designations

2. State Implementation Plans

3. Trans-boundary Emissions

4. Monitoring Requirements

B. Related Control Requirements

VIII. Statutory and Executive Order Reviews

A. Executive'Order 12866: Regulatory

Planning and Review

B. Paperwork Reduction Act

C. Regulatory Flexibility Act

D. Unfunded Mandates Reform Act

E. Executive Order 13132: Federalism

F. Executive Order 13175: Consultation

and Coordination With Indian Tribal

Governments

G. Executive Order 13045: Protection of

Children From Environmental Health &

Safety Risks

H. Executive Order 13211: Actions That

Significantly Affect Energy Supply,

Distribution or Use

I. National Technology Transfer and

Advancement Act

J. Executive Order 12898: Federal Actions

to Address Environmental Justice in

Minority Populations and Low-Income

Populations

K. Congressional Review Act

References

I..Background

A. Summary of Revisions to the 03

NAAQS

Based on its review of the air quality

criteria for 03 and related

photochemical oxidants and national

ambient air quality standards (NAAQS)

for 03, EPA is making revisions to the

primary and secondary NAAQS for 03

to provide protection of public health

and welfare, respectively, that is

appropriate under section 109, and is

making corresponding revisions in data

handling conventions for 03.

With regard to the primary standard

for 03, EPA is revising the level of the

8-hour standard to a level of 0.075 parts

per million (ppm), to provide increased

protection for children and other "at

risk" populations against an array of 03-

related adverse health effects that range

from decreased lung function and

increased respiratory symptoms to

serious indicators of respiratory

morbidity including emergency

department visits and hospital

admissions for respiratory causes, and

possibly cardiovascular-related

morbidity as well as total nonaccidental

and cardiorespiratory mortality. EPA is

specifying the level of the primary

standard to the nearest thousandth ppm.

With regard to the secondary standard

for 03, EPA is revising the standard by

making it identical to the revised

primary standard.

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B. Legislative Requirements

Two sections of the Clean Air Act

(CAA) govern the establishment and

revision of the NAAQS. Section 108 (42

U.S.C. 7408) directs the Administrator

to identify and list "air pollutants"

emissions of which "in his judgment,

cause or contribute to air pollution

which may reasonably be anticipated to

endanger public health or welfare,"

whose "presence * * * in the ambient

air results from numerous or diverse

mobile or stationary sources," and for

which the Administrator plans to issue

air quality criteria, and to issue air

quality criteria for those that are listed.

Air quality criteria are to "accurately

reflect the latest scientific knowledge

useful in indicating the kind and extent

of identifiable effects on public health

or welfare which may be expected from

the presence of [a] pollutant in ambient

air, in varying quantities * * *."

Sedtion 109 (42 U.S.C. 7409) directs the

Administrator to propose and

promulgate "primary" and "secondary"

NAAQS for pollutants listed under

section 108. Section 109(b)(1) defines a

primary standard as one "the attainment

and maintenance of which in the

judgment of the Administrator, based on

such criteria and allowing an adequate

margin of safety, are requisite to protect

the public health."' A secondary

standard, as defined in section

109(b)(2), must "specify a level of air

quality the attainment and maintenance

of which in the judgment of the

Administrator, based on such criteria, is

requisite to protect the public welfare

from any known or anticipated adverse

effects associated with the presence of

[the] pollutant in the ambient air." 2

The requirement that primary

standards provide an adequate margin

of safety was intended to address

uncertainties associated with

inconclusive scientific and technical

information available at the time of

standard setting. It was also intended to

provide a reasonable degree of

protection against hazards that research

has not yet identified. Lead Industries

'The legislative history of section 109 indicates

that a primary standard is to be set at "th&

maximum permissible ambient air level * * *

which will protect the health of any [sensitive]

group of the population," and that for this purpose

"reference should be made to a representative

sample of persons comprising the sensiti ,e group

rather than to a single person in such a group" [S.

Rep. No. 91-1196, 91st Cong., 2d Sess. 10 (1970)].

2Welfare effects as defined in section 302(h) (42

U.S.C. 7602(h)) include, but are not limited to,

"effects on soils, water, crops, vegetation, manmade

materials, animals, wildlife, weather, visibility and

climate, damage to and deterioration of property,

and hazards to transportation, as well as effects on

economic values and on personal comfort and wellbeing."

Association v. EPA, 647 F.2d 1130, 1154

(DC Cir 1980), cert. denied, 449 U.S.

1042 (1980); American Petroleum

Institute v. Castle, 665 F.2d 1176, 1186

(DC Cir. 1981), cert. denied, 455 U.S.

'1034 (1982). Both kinds of uncertainties

are components of the risk associated

with pollution at levels below those at

which human health effects can be said

to occur with reasonable scientific

certainty. Thus, in selecting primary

standards that provide an adequate

margin of safety, the Administrator is

seeking not only to prevent pollution

levels that have been demonstrated to be

harmful but also to prevent lower

pollutant levels that may pose an

unacceptable risk of harm, even if the

risk is not precisely identified as to

nature or degree. The CAA does not

require the Administrator to establish a

primary NAAQ$ at a zero-risk level or

at background concentration levels, see

Lead Industries Association v. EPA, 647

F.2d at 1156 n. 51, but rather at a level

that reduces risk sufficiently so as to

protect public health with an adequate

margin of safety.

The selection of any particular

approach to providing an adequate

margin of safety is a policy choice left

specifically to the Administrator's

judgment. Lead Industries Association

v. EPA, 647 F.2d at 1161-62. In

addressing the requirement for an

adequate margin of safety, EPA

considers such factors as the nature and

severity of the health effects involved,

the size of the population(s) at risk, and

the kind and degree of the uncertainties

that must be addressed.

In setting standards that are "requisite" to protect public health and

welfare, as provided in section 109(b),

EPA's task is to establish standards that

are neither more nor less stringent than

necessary for these purposes. Whitman

v. America Trucking Associations, 531

U.S. 457, 473. Further the Supreme

Court ruled that "[t]he text of § 109(b),

interpreted in its statutory and historical

context and with appreciation for its

importance to the CAA as a whole,

unambiguously bars cost considerations

from the NAAQS-setting process

. * Id. at 472.3

Section 109(d)(1) of the CAA requires

that "not later than December 31, 1980,

and at 5-year intervals thereafter, the

Administrator shall complete a

3

In considering whether the CAA allowed for

economic considerations to play a role in the

promulgation of the NAAQS, the Supreme Court

rejected arguments that because many more factors

than air pollution might affect public health, EPA

should consider compliance costs that produce

health losses in setting the NAAQS. 531 U.S. at 466.

Thus, EPA may not take into account possible

public health impacts from the economic cost of

implementation. Id.

thorough review of the criteria

published under section 108 and the

national ambient air quality standards * * * and shall make such revisions in

such criteria and standards and

promulgate such new standards as may

be appropriate in accordance with

section 108 and [109(b)]." Section

109(d)(2) requires that an independent

scientific review committee "shall

complete a review of the criteria * * *

and the national primary and secondary

ambient air quality standards * * * and

shall recommend to the Administrator

any new * * * standards and revisions

of existing criteria and standards as may

be appropriate under section 108 and

[section 109(b)]." This independent

review function is performed by the

Clean Air Scientific Advisory

Committee (CASAC) of EPA's Science

Advisory Board.

C. Review of Air Quality Criteria and

Standards for 03

Grpund-level 03 is formed from

biogenic and anthropogenic precursor

emissions. Naturally occurring 03 in the

troposphere can result from biogenic

organic precursors reacting with

naturally occurring nitrogen oxides

(NOx) and by stratospheric 03 intrusion

into the troposphere. Anthropogenic

precursors of 03, specifically NOx and

volatile organic compounds (VOC),

originate from a wide variety of

stationary and mobile sources. Ambient

03 concentrations produced by these

emissions are directly affected by

temperature, solar radiation, wind speed

and other meteorological factors.

The last review of the 03 NAAQS was

completed on July 18, 1997, based on

the 1996 03 Air Quality Criteria

Document (EPA, 1996a) and 1996 03

Staff Paper (EPA, 1996b). EPA revised

thePprimary and secondary 03 standards

on the basis of the then latest scientific

evidence linking exposures to anibient

03 to adverse health and welfare effects

at levels allowed by the 1-hour average

standards (62 FR 38856). The 03

standards were revised by replacing the

existing primary 1-hour average

standard with an 8-hour average 03

standard set at a level of 0.08 ppm,

which is equivalent to 0.084 ppm using

the standard rounding conventions. The

form of the primary standard was

changed to the annual fourth-highest

daily maximum 8-hour average

concentration, averaged over 3 years.

The secondary 03 standard was changed

by making it identical in all respects to

the revised prim ary standard.

EPA initiated this current review in

September 2000 with a call for

information (65 FR 57810) for the

development of a revised Air Quality

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Criteria Document for 03 and Other

Photochemical Oxidants (henceforth the

"Criteria Document"). A project work

plan (EPA, 2002) for the preparation of

the Criteria Document was released in

November 2002 for CASAC 03 Panel 4

-(henceforth, "CASAC Panel") and

public review. EPA held a series of

workshops in mid-2003 on several draft

chapters of the Criteria Document to

obtain broad input from the relevant

scientific communities. These

workshops helped to inform the

preparation of the first draft Criteria

Document (EPA, 2005a), which was

released for CASAC Panel and public

review on January 31, 2005; a CASAC

Panel meeting was held on May 4-5,

2005 to review the first draft Criteria

Document. A second draft Criteria

Document (EPA, 2005b) was released for

CASAC Panel and public review on

August 31, 2005, and was discussed

along with a first draft Staff Paper (EPA,

2005c) at a CASAC Panel meeting held

on December 6-8, 2005. In a February

16, 2006 letter to the Administrator, the

CASAC Panel offered final comments on

all chapters of the Criteria Document

(Henderson, 2006a), and the final

Criteria Document (EPA, 2006a) was

released on March 21, 2006. In a June

8, 2006 letter (Henderson, 2006b) to the

Administrator, the CASAC Panel offered

additional advice to the Agency

concerning chapter 8 of the final Criteria

Document (Integrative Synthesis) to

help inform the second draft Staff Paper.

A second draft Staff Paper (EPA,

2006b) was released on July 17, 2006

and reviewed by the CASAC Panel on

August 24 and 25, 2006. In an October

24, 2006 letter to the Administrator,

CASAC Panel provided advice and

recommendations to the Agency

concerning the second draft Staff Paper

(Henderson, 2006c). A final Staff Paper

(EPA, 2007a) was released on January

31, 2007. Around the time of the release

of the final Staff Paper in January 2007,

EPA discovered a small error in the

exposure model that when corrected

resulted in slight increases in the

human exposure estimates. Since the

exposure estimates are an input to the

lung function portion of the health risk

assessment, this correction also resulted

in slight increases in the lung function

risk estimates as well. The exposure and

risk estimates discussed in this final

rule reflect the corrected estimates, and

thus are slightly different than the

exposure and risk estimates cited in the

4 The CASAC 03 Review Panel includes the seven

members of the chartered CASAC, supplemented by

fifteen subject-matter experts appointed by the

Administrator to provide additional scientific

expertise relevant to this review of the 03 NAAQS.

January 31, 2007 Staff Paper.5 In a

March 26, 2007 letter (Henderson,

2007), the CASAC Panel offered

additional advice to the Administrator

with regard to recommendations and

revisions to the primary and secondary

03 NAAQS.

The schedule for completion of this

review has been governed by a consent

decree resolving a lawsuit filed in

March 2003 by a group of plaintiffs

representing national environmental

and public health organizations,

alleging that EPA had failed to complete

the current review within the period

provided by statute.6 The modified

consent decree that currently governs

this review provides that EPA sign for

publication notices of proposed and

final rulemaking concerning its review

of the 03 NAAQS no later than June 20,

2007 and March 12, 2008, respectively.

The proposed decision (henceforth "proposal") was signed on June 20,

2007 and published in the Federal

Register on July 11, 2007.

A large number of comments were

received from various commenters on

the proposed revisions to the 03

NAAQS. Significant issues raised in the

public comments are discussed

throughout the preamble of this final

action. A comprehensive summary of all

significant comments, along with EPA's

responses (henceforth "Response to

Comments"), can be found in the docket

for this rulemaking.

Various commenters have referred to

and discussed a number of new

scientific studies on the health effects of

03 that had been published recently and

therefore were not included in the

Criteria Document (EPA, 2006a,

henceforth "Criteria Document). 7 EPA

has provisionally considered any

significant "new" studies, including

those submitted during -the public

comment period. The purpose of this

effort was to ensure that the

Administrator was fully aware of the

"new" science before making a final

5 EPA made available corrected versions of the

final Staff Paper (EPA, 2007b, henceforth, "Staff

Paper") and the human exposure and health risk

assessment technical support documents on July 31,

2007 on the EPA Web site http://www.epa.govlttnl

naaqs.

"American Lung Association v. Whitman (No.

1:03CV00778, D.D.C. 2003).

7 For ease of reference, these studies will be

referred to as "new" studies or "new" science,

using quotation marks around the word new.

Referring to studies that were published too

recently to have been included in the 2004 Criteria

Document as "new" studies is intended to clearly

differentiate such studies from those that have been

published since the last review and are included in

the 2004 Criteria Document (these studies are

sometimes referred to as new (without quotation

marks) or more recent studies, to indicate that they

were not included in the 1996 Criteria Document

and thus are newly available in this review.

decision on whether to revise the

current 03 NAAQS. EPA provisionally

considered these studies to place their

results in the context of the findings of

the Criteria Document.

As in prior NAAQS reviews, EPA is

basing its decision in this review on

studies and related information

included in the Criteria Document and

Staff Paper, which have undergone

CASAC and public review. The studies

assessed in the Criteria Document, and

the integration of the scientific evidence

presented in that document, have

undergone extensive critical review by

EPA, CASAC, and the public during the

development of the Criteria Document.

The rigor of that review makes these

studies, and their integrative

assessment, the most reliable source of

scientific information on which to base

decisions on the NAAQS, decisions that

all parties recognize as of great import.

NAAQS decisions can have profound

impacts on public health and welfare,

and NAAQS decisions should be based

on studies that have been rigorously

assessed in an integrative manner not

only by EPA but also by the statutorily

mandated independent advisory

committee, as well as the public review

that accompanies this process. As

described above, EPA's provisional

consideration of these studies did not

and could not provide that kind of indepth critical review.

This decision is consistent with EPA's

practice in prior NAAQS reviews. Since

the 1970 amendments, the EPA has

taken the view that NAAQS decisions

are to be based on scientific studies and

related information that have been

assessed as a part of the pertinent air

quality criteria, and has consistently

followed this approach. See 71 FR

61144, 61148 (October 17, 2006) (final

decision on review of PM NAAQS) for

a detailed discussion of this issue and

EPA's past practice.

As discussed in EPA's 1993 decision

not to revise the NAAQS for 03 "new"

studies may sometimes be of such

significance that it is appropriate to

delay a decision on revision of a

NAAQS and to supplement the

pertinent air quality criteria so the

studies can be taken into account (58 FR

at 13013-13014, March 9, 1993). In the

present case, EPA's provisional

consideration of "new" studies

concludes that, taken in context, the

"new" information and findings do not

materially change any of the broad

scientific conclusions regarding the

health effects of 03 exposure made in

the Criteria Document. For this reason,

reopening the air quality criteria review

would not be warranted even if there

were time to do so under the court order

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governing the schedule for this

rulemaking. Accordingly, EPA is basing

the final decisions in this review on the

studies and related information

included in the 03 air quality criteria

that have undergone CASAC and public

review. EPA will consider the newly

published studies for purposes of

decision making in the next periodic

review of the 03 NAAQS, which will

provide the opportunity to fully assess

them through a more rigorous review

process involving EPA, CASAC, and the

public. Further discussion of these "new" studies can be found in the

Response to Comments document.

This action presents the

Administrator's final decisions on the

review of the current primary and

secondary 03 standards. Throughout

this preamble a number of conclusions,

findings, and determinations made by

the Administrator are noted. They

identify the reasoning that supports this

final decision and are intended to be

final and conclusive.

D. Summary of Proposed Revisions to

the 03 NAAQS

For reasons discussed in the proposal,

the Administrator proposed to revise the

current primary and secondary 03

standards. With regard to the primary

03 standard, the Administrator

proposed to revise the level of the 8-

hour 03 standard to a level within the

range of 0.070 ppm to 0.075 ppm, based

on a 3-year average of the fourth-highest

maximum 8-hour average concentration.

Related revisions for 03 data handling

conventions and for the reference

method for monitoring 03 were also

proposed. These revisions were

proposed to provide increased

protection for children and other "at

risk" populations against an array of 03-

related adverse health effects that range

from decreased lung function and

increased respiratory symptoms to

serious indicators of respiratory

morbidity, including emergency

department visits and hospital

admissions for respiratory causes, and

possibly cardiovascular-related

morbidity, as well as total nonaccidental

and cardiorespiratory mortality. EPA

also proposed to specify the level of the

primary standard to the nearest

thousandth ppm. EPA solicited

comment on alternative levels down to

0.060 ppm and up to and including

retaining the current 8-hour standard of

0.08 ppm (effectively 0.084 ppm using

current data rounding conventions).

With regard to the secondary standard

for 03, EPA proposed to revise the

current 8-hour standard with one of two

options to provide increased protection

against 0 3-related adverse impacts on

vegetation and forested ecosystems. One

option. was to replace the current

standard with a cumilative, seasonal

standard expressed as an index of the

annual sum of weighted hourly

concentrations, cumulated over 12

hours per day (8 am to 8 pm) during the

consecutive 3-month period within the

03 season with the maximum index

value, set at a level within the range of

7 to 21 ppm-hours. The other option

was to make the secondary standard

identical to the proposed primary 8-

hour standard. EPA solicited comment

on specifying a cumulative, seasonal

standard in terms of a 3-year average of

the annual sums of weighted hourly

concentrations; on the range of

alternative 8-hour standard levels for

which comment was being solicited for

the primary standard, including

retaining the current secondary

standard, which is identical to the

current primary standard; and on an

alternative approach to setting a

cumulative, seasonal secondary

standard.

E. Organization and Approach to Final

03 NAAQS Decisions

This action presents the

Administrator's final decisions

regarding the need to revise the current

primary and secondary 03 standards.

Revisions to the primary standard for 03

are addressed below in section II, and a

discussion on communication of public

health information regarding revisions

to the primary 03 standard is presented

in section III. The secondary 03

standard is addressed below in section

IV. Related data completeness and data

handling and rounding conventions are

addressed in section V, and federal

reference methods for monitoring 03 are

addressed below in section VI. Future

implementation steps and related

control requirements are discussed in

section VII. A discussion of statutory

and executive order reviews is provided

in section VIII.

Today's final decisions are based on

a thorough review in the Criteria

Document of scientific information on

known and potential human health and

welfare effects associated with exposure

to 03 at levels typically found in the

ambient air. These final decisions also

take into account: (1) Staff assessments

in the Staff Paper of the most policyrelevant information in the Criteria

Document as well as quantitative

exposure and risk assessments based on

that information; (2) CASAC Panel

advice and recommendations, as

reflected in its letters to the

Administrator, its discussions of drafts

of the Criteria Document and Staff Paper

at public meetings, and separate written

comments prepared by individual

members of the CASAC Panel; (3) public

comments received during the

development of these documents, either

in connection with CASAC Panel

meetings or separately; and (4) extensive

public comments received on the

proposed rulemaking.

II. Rationale for Final Decisions on the

Primary 03 Standard

A. Introduction

1. Overview

This section presents the

Administrator's final decisions

regarding the need to revise the current

primary 03 NAAQS, and the

appropriate revision to the level of the

8-hour standard. As discussed more

fully below, the rationale for the final

decision on appropriate revisions to the

primary 03 NAAQS includes

consideration of: (1) Evidence of health

effects related to short-term exposures to

03; (2) insights gained from quantitative

exposure and health risk assessments;

(3) public and CASAC Panel comments

received during the development and

review of the Criteria Document, Staff

Paper, exposure and risk assessments

and on the proposal notice.

In developing this rationale, EPA has

drawn upon an integrative synthesis of

the entire body of evidence 8 relevant to

examining associations between

exposure to ambient 03 and a broad

range of health endpoints (EPA, 2006a,

Chapter 8), focusing on those health

endpoints for which the Criteria

Document concluded that the

associations are causal or likely to be

causal. This body of evidence includes

hundreds of studies conducted in many

countries around the world. In its

assessment of the evidence judged to be

most relevant to decisions on elements

of the primary 03 standards, EPA has

placed greater weight on U.S. and

Canadian studies, since studies

conducted in other countries may well

reflect different demographic and air

pollution characteristics.

As discussed below, a significant

amount of new research has been

conducted since the last review, with

important new information coming from

epidemiological, toxicological,

controlled human exposure, and

dosimetric studies. Moreover, the newly

available research studies evaluated in

the Criteria Document have undergone

intensive scrutiny through multiple

layers of peer review, with extended

"The word "evidence" is used in this notice to

refer to studies that provide information relevant to

an area of inquiry, which can include studies that

report positive or negative results or that provide

interpretative information.

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opportunities for review and comment

by CASAC Panel and the public. As

with virtually any policy-relevant

scientific research, there is uncertainty

in the characterization of health effects

attributable to exposure to ambient 03,

most generally with regard to whether

observed health effects and associations

are causal or likely causal in nature and,

if so, the certainty of causal associations

at various exposure levels. While

important uncertainties remain, the

review of the health effects information

has been extensive and deliberate. In the

judgment of the Administrator, this

intensive evaluation of the scientific

evidence provides an adequate basis for

regulatory decision making at this time.

This review also provides important

input to EPA's research plan for

improving our future understanding of

the relationships between exposures to

ambient 03 and health effects.

The health effects information and

quantitative exposure and health risk

assessment were summarized in

sections Il.A and II.B of the proposal (72

FR at 37824-37862) and are only briefly

outlined below in sections II.A.2 and

II.A.3. Subsequent sections of this

preamble provide a more.complete

discussion of the Administrator's

rationale, in light of key issues raised in

public comments, for concluding that

the current standard is not requisite to

protect public health with an adequate

margin of safety, and it is appropriate to

revise the current primary 03 standards

to provide additional public health

protection (section II.B), as well as a

more complete discussion of the

Administrator's rationale for retaining

or revising the specific elements of the

primary 03 standards (section ll.C),

namely the indicator (section II.C.1);

averaging time (section II.C.2); form

(sectionII.C.3); and level (section II.C.4).

A summary of the final decisions on

revisions to the primary 03 standards is

presented in section ll.D.

2. Overview of Health Effects

This section outlines the information

presented in Section II.A of the proposal

on known or potential effects on publiG

health which may be expected from the

presence of 03 in ambient air. The

decision in the last review focused

primarily on evidence from short-term

(e.g., 1 to 3 hours) and prolonged ( 6 to

8 hours) controlled-exposure studies

reporting lung function decrements,

respiratory symptoms, and respiratory

inflammation in humans, as well as

epidemiology studies reporting excess

hospital admissions and emergency

department visits for respiratory causes.

The Criteria Document prepared for this

review emphasizes a large number of,

epidemiological studies published since

the last review with these and

additional health endpoints, including

the effects of acute (short-term and

prolonged) and chronic exposures to 03

on lung function decrements and

enhanced respiratory -symptoms in

asthmatic individuals, school absences,

and premature mortality. It also

emphasizes important new information

from toxicology, dosimetry, and

controlled human exposure studies.

Highlights of the evidence include:

(1) Two new controlled humanexposure studies are now available that

ex amine respiratory effects associated

with prolonged 03 exposures at levels at

and below 0.080 ppm, which was the

lowest exposure level that had been

examined in the last review.

(2) Numerous recent controlled

human-exposure studies have examined

indicators of 0 3-induced inflammatory

response in both the upper respiratory

tract (URT) and lower respiratory tract

(LRT), while other studies have

examined changes in host defense

capability following 03 exposure of

healthy young adults and increased

airway responsiveness to allergens in

subjects with allergic asthma and

allergic rhinitis exposed to 03.

(3) New evidence from controlled

human exposure studies showing that

asthmatics have greater respiratoryrelated physiological responses than

healthy subjects and new evidence from

epidemiological studies showing

associations between 03 exposure and

lung function and respiratory symptom

responses; these findings differ from the

presumption in the last review that

people with asthma had generally the

same magnitude of respiratory

responses to 03 as those experienced by

healthy individuas.

(4) Animal toxicology studies provide

new inforiation regarding potential

mechanisms of action, increased

susceptibility to respiratory infection,

and biological plausibility of acute

effects as well as chronic, irreversible

respiratory damage observed in animals.

(5) Numerous epidemiological studies

published during the past decade offer

added evidence of associations between

acute ambient 03 exposures and lung

function decrements and respiratory

symptoms in physically active healthy

subjects and asthmatic subjects, as well

as new evidence regarding additional

health endpoints, including

relationships between ambient 03

concentrations and school absenteeism

and between ambient 03 and cardiacrelated physiological endpoints.

(6) Several additional studies have

been published over the last decade

examining the temporal associations

between acute 03 exposures and both

emergency department visits for

respiratory diseases and respiratoryrelated hospital admissions.

(7) A large number of newly available

epidemiological studies have examined

the effects of acute exposure to PM and

03 on premature mortality, notably

including large multi-city studies that

provide much more robust information

than was available in the last review, as

well as recent meta-analyses that have

evaluated potential sources of

heterogeneity in 0 3-mortality

associations.

Section II.A of the proposal provides

a detailed summary of key information

contained in the Criteria Document

(chapters 4-8) and in the Staff Paper

(chapter 3), on the known and potential

effects of 03 exposure and information

on the effects of 03 exposure in

combination with other pollutants that

are routinely present in the ambient air

(72 FR 37824-37851). The information

there summarizes:

(1) New information available on

potential mechanisms for morbidity and

mortality effects associated with

exposure to 03, including potential

mechanisms or pathways related to

direct effects on the respiratory system,

systemic effects that are secondary to

effects in the respiratory system (e.g.,

cardiovascular effects);

(2) The nature of effects that have

been associated directly with exposure

to 03 or indirectly with the presence of

03 in ambient air, including premature

mortality, aggravation of respiratory and

cardiovascular disease (as indicated by

increased hospital admissions and

emergency department visits), changes

in lung function and increased

respiratory symptoms, as well as new

evidence for more subtle indicators of

cardiovascular health;

(3) An integrative interpretation of the

health effects evidence, focusing on the

biological plausibility and coherence of

the evidence and key issues raised in

interpreting epidemiological studies,

along with supporting evidence from

experimental (e.g., dosimetric and

toxicological) studies as well as the

limitations of the evidence; and

(4) Considerations in characterizing

the public health impact of 03,

including the identification of sensitive

and vulnerable subpopulations that are

potentially at risk to such effects,

including active people, people with

pre-existing lung and heart diseases,

children and older adults, and people

with increased responsiveness to 03.

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3. Overview of Human Exposure and

Health Risk Assessments

To put judgments about health effects

that are adverse for individuals into a

broader public health context, EPA

developed and applied models to

estimate human exposures and health

risks. This broader public health context

included consideration of the size 6f

particular population groups at risk for

various effects, the likelihood that

exposures of concern would occur for

individuals in such groups under

varying air quality scenarios, estimates

of the number of people likely to

experience 0 3-related effects, the

variability in estimated exposures and

risks, and the kind and degree of

uncertainties inherent in assessing the

exposures and risks involved.

As discussed in more detail in section

II.B of the proposal, there are a number

of important uncertainties that affect the

exposure and health risk estimates. It is

also important to note that there have

been significant improvements since the

last review in both the exposure and

health risk models. The CASAC Panel

expressed the view that the exposure

analysis represents a state-of-the-art

modeling approach and that the health

risk assessment was "well done,

balanced and reasonably

communicated" (Henderson, 2006c).

In modeling exposures and health

risks associated with just meeting the

6urrent and alternative 03 standards,

EPA simulated air quality just meeting

these standards based on 03 air quality

patterns in several recent years and on

how the shape of the 03 air quality

distributions has changed over time

based on historical trends in monitored

03 air quality data. As discussed in the

proposal notice and in the Staff Paper

(section 4.5.8), recent 03 air quality

distributions were statistically adjusted

to simulate just meeting the current and

selected alternative standards.

Specifically, the exposure and risk

assessment included estimates for a

recent year of air quality and for air

quality adjusted to simulate just meeting

the current and alternative standards

based on 03 season data from a recent

three-year period (2002-2004). The 03

season in each area included the period

of the year for which routine hourly 03

monitoring data are available. Typically

this period spans from March or April

through September or October, although

in some areas it includes the entire year.

Three years were modeled to reflect the

substantial year-to-year variability that

occurs in 03 levels and related

meteorological conditions, and because

the standard is specified in terms of a

three-year period. The year-to-year

variability .observed in 03 levels is due

to a combination of different weather

patterns and the variation in emissions

of 03 precursors. Nationally, 2002 was

a relatively high year with respect to the

4th highest daily maximum 8-hour 03

levels observed in urban areas across the

U.S. (see Staff Paper, Figure 2-16), with

the mean of the distribution of annual

4th highest daily maximum 8-hour 03

levels for urban monitors nationwide

being in the upper third among the

years 1990 through 2004. In contrast, on

a national basis, 2004 was the lowest "

year on record with respect to the mean

of the distribution of annual 4th highest

daily maximum 8-hour 03 levels for this

same 15 year period. The 4th highest

daily maximum 8-hour levels observedin most, but not all of the 12 urban areas

included in the exposure and risk

assessment, were relatively low in 2004

compared to other recent years. The 4th

highest daily maximum 8-hour 03 levels

observed in 2003 in the 12 urban areas

and nationally generally were between

those observed in 2002 and 2004. As a

result of the variability in air quality,

the exposure and risk estimates

associated with just meeting the current

or any alternative standard also will

vary depending on the year chosen for

the analysis. Thus, exposure and risk

estimates based on 2002 air quality

generally show relatively higher

numbers of children affected and the

estimates based on 2004 air quality

generally show relatively fewer numbers

of children affected.

These simulations do not reflect any

consideration of specific control

programs or strategies designed to

achieve the reductions in emissions

required to meet the specified -

standards. Further, these simulations do

not represent predictions of when,

whether, or how areas might meet the

specified standards." Instead these

simulations represent a projection of the

kind of air quality levels that would be

likely to occur in areas just attaining

various alternative standards, when

historical patterns of air quality,

reflecting averages over many areas, are

applied in the urban areas examined.

a. Exposure Analyses

As discussed in section 11.B.1 of the

ppoposal, EPA conducted human

exposure analyses using a simulation

model to estimate 03 exposures for the

general population, school age children

(ages 5-18), and school age children

5 For informational purposes only, modeling that

projects how areas might attain alternative

standards in a future year as a result of Federal,

State, local, and Tribal efforts is-presented in the

final Regulatory Impact Analysis being prepared in

connection with this decision.

with asthma living in 12 U.S.

metropolitan areas representing

different regions of the country where

the current 8-hour 03 standard is not

met. The emphasis on children reflected

the finding of the last review that

children are an. important at-risk group.

Exposure estimates were developed

using a probabilistic exposure model

that is designed to explicitly model the

numerous sources of variability that

affect people's exposures. This exposure

assessment is more fully described and

presented in the Staff Paper and in a

technical support document, Ozone

Population Exposure Analysis for

Selected Urban Areas (EPA, 2007c;

henceforth "Exposure Analysis TSD").

As noted in the proposal, the scope and

methodology for this exposure

assessment were developed over the last

few years with considerable input from

the CASAC Panel and the public.

As discussed in the proposal notice

and in greater detail in the Staff Paper

(chapter 4) and Exposure Analysis TSD,

EPA recognized that there are many

sources of variability and uncertainty

inherent in the input to this assessment

and that there was uncertainty in the

resulting 03 exposure estimates. In

EPA's judgment, the most important

uncertainties affecting the exposure

estimates are related to the modeling of

human activity patterns over an 03

season, the modeling of variations in

ambient concentrations near roadways,

and the modeling of air exchange rates

that affect the amount of 03 that

penetrates indoors. Another important

uncertainty that affects the estimation of

how many exposures are associated

with moderate or greater exertion is the

characterization of energy expenditure

for children engaged in various

activities. As discussed in more detail in

the Staff Paper (section 4.3.4.7), the

uncertainty in energy expenditure

values carries over to the uncertainty of

the modeled breathing rates, which are

important since they are used to classify

exposures occurring at moderate or

greater exertion. These are the relevarqt

exposures since 0 3-related effects

observed in clinical studies only are

observed when individuals are engaged

in some form of exercise. The

uncertainties in the exposure model

inputs and the estimated exposures

have been assessed using quantitative

uncertainty and sensitivity analyses.

Details are discussed in the Staff Paper

(section 4.6) and in a technical

memorandum describing the exposure

modeling uncertainty analysis

(Langstaff, 2007).

The exposure assessment, which

provided estimates of the number of

people exposed to different levels of

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ambient 03 while at elevated exertion 10,

served two purposes. First, the entire.

range of modeled personal exposures to

ambient 03 was an essential input to the

portion of the health risk assessment

based on exposure-response functions

from controlled human exposure

studies, discussed in the next section.

Second, estimates of personal exposures

to ambient 03 concentrations at and

above specified benchmark levels while

at elevated exertion provided some

perspective on the public health

impacts of health effects that we cannot

currently evaluate in quantitative risk

assessments but that may occur at

current air quality levels, and the extent

to which such impacts might be reduced

by meeting the current and alternative

standards. In the proposal, we referred

to exposures at and above these

benchmark levels while at elevated

exertion as "exposures of concern."

Based on the observation from the

exposure analyses conducted in the

prior review that children represented

the population subgroup with the

greatest exposure to ambient 03, EPA

chose to model 8-hour exposures at

elevated exertion for all school age

children, and separately for asthmatic

school age children, as well as for the

general population in the current

exposure assessment. While outdoor

workers and other adults who engage in

moderate or greater exertion for

prolonged periods while outdoors

during the day in areas experiencing

elevated 03 concentrations also are at

risk for 0 3-related health effects, EPA

did not focus on developing quantitative

exposure estimates for these population

subgroups due to the lack of information

about the number of individuals who

regularly work or exercise outdoors.

Thus, as presented in the proposal and

in the Staff Paper the exposure estimates

are most useful for making relative

comparisons 9 f estimated exposures in

school age children across alternative

air quality scenarios. This assessment

does not provide, information on

exposures for adult subgroups within

the general population associated with

the air quality scenarios.

EPA noted in the proposal key

observations that were important to

consider in comparing exposure

estimates associated with just meeting

the current NAAQS and alternative

standards considered. These included:

10 As discussed in section lI.A of the proposal, 03

health responses observed in controlled human

exposure studies are associated with exposures

while subjects are engaged in moderate or greater

exertion on average over the exposure period

(hereafter referred to as "elevated exertion") and,

therefore, these are the exposures of interest.

(1) As shown in Table 6-1 of the Staff

Paper, the patterns of exposures in

terms of percentages of the population

exceeding given exposure levels were

very similar for the general population

and for asthmatic and all school age (5-

18) children, although children were

about twice as likely as the general

population to be exposed at any given

level.

(2) As shown in Table 1 in the

proposal (72 FR 37855), the number and

percentage of asthmatic and all school

age children aggregated across the 12

urban areas estimated to experience 1 or

more exposures of concern declined

from simulations of just meeting the

current standard to simulations of

alternative 8-hour standards by varying

amounts, depending on the benchmark

level, the population subgroup

considered, and the air quality year

chosen."

(3) Substantial year-to-year variability

in exposure estimates was observed over

the three-year modeling period.

(4) There was substantial variability

observed across the 12 urban areas in

the percent of the population subgroups

estimated to experience exposures at

and above specified benchmark levels

while at elevated exertion.

(5) Of particular note, there is high

inter-individual variability in

responsiveness such that only a subset

of individuals who were exposed at and

above a given benchmark level while at

elevated exertion would actually be

expected to experience any such

potential adverse health effects.

(6) In considering these observations,

it was important to take into account the

variability, uncertainties, and

limitations associated with this

assessment, including the degree of

uncertainty associated with a number of

model inputs and uncertainty in the

model itself.

b. Quantitative Health Risk Assessment

As discussed in section II.B.2 of the

proposal, the approach used to develop

quantitative risk estimates associated

with exposures to 03 builds upon the

risk assessment conducted during the

last review. 12 The expanded and

"While the proposal notice stated in the text that

"approximately 2 to 4 percent of all and asthmatic

children" were estimated to experience exposures

of concern at and above the 0.070 ppm benchmark

level for standards in the range of 0.070 to 0.075

ppm (72 FR 37879), the correct range is about 1 to

5 perecent consistent with the estimates provided

in Table 1 of the proposal (72 FR 37855).

12 The methodology, scope, and results from the

risk assessment conducted in the last review are

described in Chapter 6 of the 1996 Staff Paper (EPA,

1996) and in several technical reports (Whitfield et

al., 1996; Whitfield, 1997) and publication

(Whitfield et aL., 1998).

updated assessment conducted in this

review includes estimates of (1) risks of

lung function decrements in all and

asthmatic school age children,

respiratory symptoms in asthmatic

children, respiratory-related hospital

admissions, and non-accidental and

cardiorespiratory-related mortality

associated with recent short-term

ambient 03 levels; (2) risk reductions

and remaining risks associated with just

meeting the current 8-hour 03 NAAQS;

and (3) risk reductions and remaining

risks associated with just meeting

various alternative 8-hour 03 NAAQS in

a number of example urban areas. The

health risk assessment was discussed in

the Staff Paper (chapter 5) and

presented more fully in a technical

support document, Ozone Health Risk

Assessment for Selected Urban Areas

(Abt Associates, 2007a). As noted in the

proposal, the scope and methodology

for this risk assessment was developed

over several years with considerable

input from the CASAC Panel and the

public.

EPA recognized that there were many

sources of uncertainty and variability

inherent in the inputs to these

assessments and that there was a high

degree of uncertainty in the resulting 03

risk estimates. Such uncertainties

generally relate to a lack of clear

understanding of a number of important

factors, including, for example, the

shape of exposure-response and

concentration-response functions,

particularly when, as here, effect

thresholds can neither be discerned nor

determined not to exist; issues related to

selection of appropriate statistical

models for the analysis of the

epidemiologic data; the role of

potentially confounding and modifying

factors in the concentration-response

relationships; and issues related to

simulating how 03 air quality

distributions will likely change in any

given area upon attaining a particular

standard, since strategies to reduce

emissions are not yet fully defined.

While some of these uncertainties were

addressed quantitatively in the form of

estimated confidence ranges around

central risk estimates, other

uncertainties and the variability in key

inputs were not reflected in these

confidence ranges, but rather were

partially characterized through separate

sensitivity analyses or discussed

qualitatively.

Key observations and insights from

the 03 risk assessment, together with

important caveats and limitations, were

discussed in section H1.B of the proposal.

In general, estimated risk reductions

associated with going from current 03

levels to just meeting the current and

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alterhative 8-hour standards show

patterns of increasing estimated risk

reductions associated with just meeting

the lower alternative 8-hour standards

considered. Furthermore, the estimated

percentage reductions in risk were

strongly influenced by the baseline air

quality year used in the analysis (see

Staff Paper, Figures 6-1 through 6-6)

Key observations important in

comparing estimated health risks

associated with attainment of the

current NAAQS and alternative

standards included:

(1) As discussed in the Staff paper

(section 5.4.5), EPA has greater

confidence in relative comparisons in

risk estimates between alternative

standards than in the absolute

magnitude of risk estimates associated

with any particular standard.

(2) Significant year-to-year variability

in 03 concentrations combined with the use of a 3-year design value to

determine the amount of air quality

adjustment to be applied to each year

analyzed, results in significant year-toyear variability in the annual health risk

estimates upon just meeting the current

and potential alternative standards.

(3) There-is noticeable city-to-city

variability in estimated 0 3-related

incidence of morbidity and mortality

across the 12 urban areas analyzed for

both recent years of air quality and for

air quality adjusted to simulate just

meeting the current and selected

potential alternative standards. This

variability is likely due to differences in

air quality distributions, differences in

estimated exposure related to many

factors including varying activity

patterns and air exchange rates,

differences in baseline incidence rates,

and differences in susceptible

populations and age distributions across

the 12 urban areas. (4) With respect to the uncertainties

about estimated policy-relevant

background (PRB) concentrations, 13 as

13 PRB 03 concentrations used in the 03 risk

assessment were defined in chapter 2 of the Staff

Paper (EPA, 2007, pp. 2-48, 2-54) as the 03

concentrations that would be observed in the U.S.

in the absence of anthropogenic emissions of

precursors (e.g., VOC, NOx, and CO) in the U.S.,

Canada, and Mexico. Based on runs of the GEOSCHEM model (a global tropospheric 03 model)

applied for the 2001 warm season (i.e., April to

September), monthly background daily diurnal

profiles for each of the 12 urban areas for each

month of the 03 season were simulated using

meteorology for the year 2001. Based on these

model runs, the Criteria Document states that current estimates of PRB 03 concentrations are

generally in the range of 0.015 to 0.035 ppm in the

afternoon, and they are generally lower under

conditions conducive to high 03 episodes. They are

highest during spring due to contributions from

hemispheric pollution and stratospheric intrusions.

The Criteria Document states that the GEOS-CHEM

model applied for the 2001 warm season reports

discussed in the Staff Paper (section

5.4.3), alternative assumptions about

background levels had a variable impact

depending on the health effect

considered and the location and

standard analyzed in terms of the

absolute magnitude and relative changes

in the risk estimates. There was relatively little impact on either

absolute magnitude or relative changes

in lung function risk estimates due to

alternative assumptions about

background levels.14 With respect to 03-

related non-accidental mortality, while

notable differences (i.e., greater than 50

percent) were observed in some areas,

particularly for more stringent

standards, the overall pattern of

estimated reductions, expressed in

terms of percentage reduction relative to

the current standard, was significantly

less impacted.

(5) Concerning the part of the risk

assessment based on effects reported in

epidemiological studies,-important

uncertainties include uncertainties (1)

surrounding estimates of the 03

coefficients for concentration-response

relationships used in the assessment, (2)

involving the shape of the

concentration-response relationship and

whether or not a population threshold

or non-linear relationship exists within

the range of concentrations examined in

the studies, (3) related to the extent to

which concentration-response

relationships derived from studies in a

given location and time when 03 levels'

were higher or behavior and /or housing

conditions were different provide

accurate representations of the

relationships for the same locations

with lower air quality distributions and/

or different behavior and/or housing

conditions, and (4) concerning the

possible role of co-pollutants which also

may have varied between the time of the

studies and the current assessment

period. An important additional

uncertainty for the mortality risk

estimates is the extent to which the

associations reported between 03 and

non-accidental and cardiorespiratory

mortality actually reflect causal

relationships.

As discussed in the proposal, some of

these uncertainties have been addressed

quantitatively in the form of estimated

confidence ranges around central risk

estimatds; others are addressed through

separate sensitivity analyses (e.g., the

PRB 03 concentrations for afternoon surface air over

the United States that are likely 10 ppbv too high

in the southeast in summer, and apcurate within 5

ppbv in other regions and seasons. 14 Sensitivity analyses examining the impact of

alternative assumptions about PRB were only

conducted for lung function decrements and nonaccidental mortality.

influence of alternative estimates for

policy-relevant background levels) or

are characterized qualitatively. For both

parts of the health risk assessment,

statistical uncertainty due to sampling

error has been characterized and is

expressed in terms of 95 percent

credible intervals. EPA recognizes that

these credible intervals do not reflect all

of the uncertainties noted above.

B. Need for Revision of the Current

Primary 03 Standard

1. Introduction

The initial issue to be addressed in

this review-of the primary 03 standard

is whether, in view of the advances in -

scientific knowledge reflected in the

Criteria Document and Staff Paper, the

current standard should be revised. As

discussed in section I.C of the proposal,

in evaluating whether it was appropriate

to propose to retain or revisethe current

standard, the Administrator built upon

the last review and reflected the broader

body of evidence and information now available. In the proposal, EPA

presented information, judgments, and

conclusions from the last review, which

revised the level, averaging time, and

form of the standard, from the Staff

Paper's evaluation of the adequacy of

the current primary standard, including

both evidence- and exposure/risk-based

considerations, as well as from the

CASAC Panel's advice and

recommendations. The Staff Paper

evaluation, CASAC Panel's views, and

the Administrator's proposed

conclusions on the adequacy of the

current primary standard are presented

below..

a. Staff Paper Evaluation

The Staff Paper considered the

evidence presented in the Criteria

Document as a basis for evaluating the

adequacy of the current 03 standard,

recognizing that important uncertainties

remain. The exten~ive body of human

clinical, toxicological, and

epidemiological evidence, highlighted

above in section II.A.2 and discussed in

section I1.A of the proposal, serves as

the basis for judgments about 0 3-related

health effects, including judgments

about causal relationships with a range

of respiratory morbidity effects,

including lung function decrements,

increased respiratory symptoms, airway

inflammation, increased airway

responsiveness, and respiratory-related

hospitalizations and emergency

department visits in the warm season,

and about the evidence being highly

suggestive that 03 directly or indirectly

contributes to non-accidental and

cardiorespiratory-related mortality.

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These judgments take into account

important uncertainties that remain in

interpreting this evidence. For example,

with regard to the utility of time-series

epidemiological studies to inform

judgments about a NAAQS for an

individual pollutant, such as 03, within

a mix of highly correlated pollutants,

such as the mix of oxidants produced in

photochemical reactions in the

atmosphere, the Staff Paper noted that

there are limitations especially at

ambient 03 concentrations below levels

at which 0 3-related effects have been

observed in controlled human exposure

studies. The Staff Paper also recognized

that the available epidemiological

evidence neither supports nor refutes

the existence of thresholds at the

population level for effects such as increased hospital admissions and

premature mortality. There are

limitations in epidemiological studies

that make discerning thresholds in

populations difficult, including low

data density in the lower concentration

ranges, the possible influence of

exposure measurement error, and

variability in susceptibility to 0 3-related

effects in populations.

While noting these limitations in the

interpretation of the findings from the

epidemiological studies, the Staff Paper

concluded that if a population threshold

level does exist, it would likely be well

below the level of the current 03

standard and possibly within the range

of background levels. This conclusion is

supported by several epidemiological

studies that have explored the question

of potential thresholds either by using a statistical curve-fitting approach to

evaluate whether linear or non-linear

models fit the data better using, or by

analyzing, sub-sets of the data where

days over or under a specific cutpoint

(e.g., 0.080 ppm or even lower 03 levels)

were excluded and then evaluating the

association for statistical significance. In

addition to consideration of the

epidemiological studies, findings from

controlled human exposure studies

indicate that prolonged exposures

produced statistically significant group

mean FEV1 decrements and symptoms

in healthy adult subjects at levels down

to at least 0.060 ppm, with a small

percentage of subjects experiencing

notable effects (e.g., >10 percent FEVI

decrement, pain on deep inspiration).

Controlled human exposure studies

evaluated in the last review also found

significant responses in indicators of

lung inflammation and cell injury at

0.080 ppm in healthy adult subjects.

The effects in these controlled human

exposure studies were observed in

healthy young adult subjects, and it is

likely that more serious responses, and

responses at lowdr levels, would occur

in people with asthma and other

respiratory diseases. These

physiological effects can lead to

aggravation of asthma and increased

susceptibility to respiratory infection.

The observations provide support for

the conclusion in the Staff Paper that

the associations observed in the

epidemiological studies, particularly for

respiratory-related effects such as

increased medication use, increased

school and work absences, increased

visits to doctors' offices and emergency

departments, and increased hospital

admissions, extend down to 03 levels

well below the current standard (i.e.,

0.084 ppm) (p. 6-7).

The newly available information

reinforces the judgments in the Staff

Paper from the last review about the

likelihood of causal relationships

between 03 exposures and respiratory

effects and broadens the evidence of 0 3-

related associations to include

additional respiratory-related endpoints,

newly identified cardiovascular-related

health endpoints, and mortality. Newly

available evidence also led the Staff

Paper to conclude that people with

asthma are likely to experience more

serious effects than people who do not

have asthma. The Staff Paper also

concluded that substantial progress has

been made since the last review in

advancing the understanding of

potential mechanisms by which ambient

03, alone and in combination with other

pollutants, is causally linked to a range

of respiratory-related health endpoints,

- and may be causally linked to a range

of cardiovascular-related health

endpoints. Thus, the Staff Paper found

strong support in the evidence available

since the last review, for consideration

of an 03 standard that is at least as

protective as the current standard and

finds no support for consideration of an

03 standard that is less protective than

the current standard. This conclusion is

consistent with the advice and

recommendations of the CASAC Panel

and with the views expressed by all

interested parties who provided

comments on drafts of the Staff Paper.

While the CASAC Panel and some

commenters on drafts of the Staff Paper

supported revising the current standard

to provide increased public health

protection and other such commenters

supported retaining the current

standard, no one who provided

comments on drafts of the Staff Paper

supported a standard that would be'less

protective than the current standard.

i. Evidence-Based Considerations

In looking more specifically at the

controlled human exposure and

epidemiological evidence, the Staff

Paper first noted that controlled human

exposure studies provide the clearest

and most compelling evidence for an

array of human health effects that are

directly attributable to acute exposures

to 03 per se. Evidence from such human

studies, together with animal

toxicological studies, help to provide

biological plausibility for health effects

observed in epidemiological studies. In

considering the available evidence, the

Staff Paper focused on studies that

examined health effects that have been

demonstrated to be caused by exposure

to 03, or for which the Criteria

Document judges associations with 03

to be causal or likely causal, or for

which the evidence is highly suggestive

that 03 contributes to thb reported

effects.

In considering the epidemiological

evidence as a basis for reaching

conclusions about the adequacy of the

current standard, the Staff Paper

focused on studies reporting effects in

the warm season, for which the effect

estimates are more consistently positive

and statistically significant than those

from all-year studies. The Staff Paper

considered the extent to which such

studies provide evidence of associations

that extend down to ambient 03

concentrations below the level of the

current standard, which would thereby

call-into question the adequacy of the

current standard. In so doing, the Staff

Paper noted that if a population

threshold level does exist for an effect

observed in such studies, it would likely

be at a level well below the level of the

current standard. The Staff Paper also

attempted to characterize whether the

area in which a study was conducted

likely would or would not have met the

current standard during the time of the

study, although it recognizes that the

confidence that would appropriately be

placed on the associations observed in

any given study, or on the extent to

which the association would likely

extend down to relatively low 03

concentrations, is not dependent on this

distinction. Further, the Staff Paper

considered studies that examined

subsets of data that include only days

with ambient 03 concentrations below

the level of the current 03 standard, or

below even lower 03 concentrations,

and continue to report statistically

significant associations. The Staff Paper

judged that such studies are directly

relevant to considering the adequacy of

the current standard, particularly in

light of reported responses to 03 at

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levels below the current standard found

in controlled human exposure studies.

The Staff Paper evaluation of such

studies is discussed below and in

section II.C.2.a of the proposal, focusing

in turn on studies of (1) lung function,

respiratory symptoms and other

respiratory-related physiological effects,

(2) respiratory hospital admissions and

emergency department visits, and (3)

mortality.

(1) Lung function, respiratory

symptoms and other respiratory-related

physiological effects. Health effects for

which the Criteria Document continued

to find clear evidence of causal

associations with short-term 03

exposures include lung function

decrements, respiratory sympfoms,

pulmonary inflammation, and increased

airway responsiveness. In the last

review, these 0 3-induced effects were

demonstrated with statistical*

significance down to the lowest level

tested in controlled human exposure

studies at that time (i.e., 0.080 ppm).

Two new studies are notable in that

they are the only controlled human

exposure studies that examined

respiratory effects, including lung

function decrements and respiratory

symptoms, in healthy adults at lower

exposure levels than had previously

been examined. EPA's reanalysis of the

data from the most recent study shows

small group mean decrements in lung

function responses to be statistically

significant at the 0.060 ppm exposure

level, while the author's analysis did

not yield statistically significant lung

function responses but did yield some

statistically significant respiratory

symptom responses toward the end of

the exposure period. These studies

report a small percentage of subjects

experiencing lung function decrements

( 10 percent) at the 0.060 ppm

exposure level. These studies provide

very limited evidence of 0 3-related lung

function decrements and respiratory

symptoms at this lower exposure level.

The Staff Paper noted that evidence

from controlled human exposures

studies indicates that people with

moderate-to-severe asthma have

somewhat larger decreases in lung

function in response to 03 relative to

healthy individuals. In addition, lung

function responses in people with

asthma appear to be affected by baseline

lung function (i.e., magnitude of

responses increases with increasing

disease severity). This newer

information expands our understanding

of the physiological basis for increased

sensitivity in people with asthma and

other airway diseases, recognizing that

people with asthma present a different

response profile for cellular, molecular,

and biochemical responses than people

who do not have asthma. New evidence

indicates that some people with asthma

have increased occurrence and duration

of nonspecific airway responsiveness,

which is an increased

bronchoconstrictive response to airway

irritants. Controlled human exposure

studies also indicate that some people

with allergic asthma and rhinitis have

increased airway responsiveness to

allergens following 03 exposure.

Exposures to 03 exacerbated lung

function decrements in people with preexisting allergic airway disease, with

and without asthma. Ozone-induced

exacerbation of airway responsiveness

persists longer and attenuates more

slowly than 0 3-induced lung function

decrements and respiratory symptom

responses and can have important

clinical implications for asthmatics.

The Staff Paper also concluded that

newly available human exposure

studies suggest that some people with

asthma also have increased

inflammatory responses, relative to nonasthmatic subjects, and that this

inflammation may take longer to

resolve. The new data on airway

responsiveness, inflammation, and

various molecular markers of

inflammation and bronchoconstriction

indicate that people with asthma and

allergic rhinitis (with or without

asthma) comprise susceptible groups for

0 3-induced adverse effects. This body of

evidence qualitatively informs the Staff

Paper's evaluation of the adequacy of

the current 03 standard in that it

indicates that controlled human

exposure and epidemiological panel

studies of lung function decrements and

respiratory symptoms that evaluate only

healthy, non-asthmatic subjects likely

underestimate the effects of 03 exposure

on asthmatics and other susceptible

populations.

The Staff Paper noted that in addition

to the experimental evidence of lung

function decrements, respiratory

symptoms, and other respiratory effects

in healthy and asthmatic populations

discussed above, epidemiological -

studies have reported associations of

lung function decrements and

respiratory symptoms in several

locations. Two large U.S. panel studies

which together followed over 1,000

asthmatic children on a daily basis

(Mortimer et al., 2002, the National

Cooperative Inner-City Asthma Study,

or NCICAS; and Gent et al., 2003), as

well as several smaller U.S. and

international studies, have reported

robust associations between ambient 03

concentrations and measures of lung

function, daily respiratory symptoms

(e.g., chest tightness, wheeze, shortness

of breath), and increased asthma

medication use in children with

moderate to severe asthma. Mortimer et

al. (2002) found that of the pollutants

measured (including 03, NO2, SO2 and

PM10 ), 03 was the only one that had a

statistically significant effect on lung

function. (Mortimer et a." 2002) also

found associations between NO2, SO 2

and PM10 and respiratory symptoms that

were stronger than those between 03

and respiratory symptoms. Gent et al.

(2003) found that in co-pollutant

models, 03 but not PM2.

5 significantly

predicted increased risk of respiratory

symptoms and rescue medication use

among children using asthma

maintenance medication. Overall, the

multi-city NCICAS (Mortimer et al.,

2002), (Gent et al. 2003), and several

other single-city studies indicate a

robust positive association between

ambient 03 concentrations and

increased respiratory symptoms and

increased medication use in asthmatic

children.

In considering the large number of

single-city epidemiological studies

reporting lung function or respiratory

symptoms effects in healthy or

asthmatic populations, the Staff Paper

noted that most such studies that

reported positive and often statistically

significant associations in the warm

season were donducted in areas that

likely would not have met the current

standard. In considering the large multicity NCICAS (Mortimer et al., 2002), the

Staff Paper noted that the 98th

percentile 8-hour daily maximum 03

concentrations at the monitor reporting

the highest 03 concentrations in each of

the study areas ranged from 0.084 ppm*

to > 0.10 ppm. However, the authors

indicate that less than 5 percent of the

days in the eight urban areas had 8-hour

daily 03 concentrations exceeding 0.080

ppm. Moreover, the authors observed

that when days with 8-hour average 03

levels greater than 0.080 ppm were

excluded, similar effect estimates were

seen compared to estimates that

included all of the days. There are also

a few other studies in which the

relevant air quality statistics provide

some indication that lung function and

respiratory symptom effects may be

occurring in areas that likely would

have met the current standard (EPA,

2007b, p. 6-12).

(2) Respiratory hospital admissions

and emergency department visits. At the

time of the last review, many time-series

studies indicated positive associations

between ambient 03 and increased

respiratory hospital admissions and

emergency room visits, providing strong

evidence for a relationship between Q3

exposure and increased exacerbations of

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preexisting lung disease extending

below the level of the then current 1-

hour 03 standard (EPA 2007b, section

3.3.1.1.6). Analyses of data from studies

conducted in the northeastern U.S.

indicated that 03 air pollution was

consistently and strongly associated

with summertime respiratory hospital

admissions.

Since the last review, new

epidemiological studies have evaluated

the association between short-term

exposures to 03 and unscheduled

hospital admissions for respiratory causes. Large multi-city studies, as well

as many studies from individual cities,

have reported positive and often

statistically significant 03 associations

with total respiratory hospitalizations as well as asthma- and chronic obstructive

pulmonary disease (COPD)-related

hospitalizations, especially in studies

analyzing the 03 effect during the summer or warm season. Analyses using

multipollutant regression models

generally indicate that copollutants do

not confound the association between

03 and respiratory hospitalizations and

that the 03 effect estimates were robust

to PM adjustment in all-year and warmseason only data. The Criteria Document

concluded that the evidence supports a

causal relationship between acute 03

exposures and increased respiratoryrelated hospitalizations during the

warm season. In looking specifically at U.S. and

Canadian respiratory hospitalization

studies that reported positive and often

statistically significant associations (and

that either did not use GAM or were reanalyzed to address GAM-related

problems), the Staff Paper noted that

many such studies were conducted in

areas that likely would not have met the

current 03 standard, with many

providing only all-year effect estimates,

and with some reporting a statistically

significant association in the warm

season. Of the studies that provide some

indication that 0 3-related respiratory

hospitalizations may be occurring in

areas that likely would have met the

current standard, the Staff Paper noted

that some are all-year studies, whereas

others reported statistically significant

warm-season associations.

Emergency department visits for

respiratory causes have been the focus

of a number of new studies that have

examined visits related to asthma,

COPD, bronchitis, pneumonia, and

other upper and lower respiratory

infections, such as influenza, with

asthma visits typically dominating the

daily incidence counts. Among studies

with adequate controls for seasonal

patterns, many reported at least one significant positive association

involving 03. However, inconsistencies

were observed which were at least

partially attributable to differences in

model specifications and analysis

approach among various studies. In

general, 03 effect estimates from

summer-only analyses tended to be

positive and larger compared to results

from cool season or all-year analyses.

Almost all of the studies that reported

statistically significant effect estimates

were conducted in areas that likely

would not have met the current

standard. The Criteria Document

concluded that analyses stratified by

season generally supported a positive

association between 03 concentrations

and emergency department visits for

asthma in the warm season. These

studies provide evidence of effects in

areas that likely would not have met the

current standard and evidence of

associations that likely extend down to

relatively low ambient 03

concentrations.

(3) Mortality. The 1996 Criteria

Document concluded that an association

between daily mortality and 03

concentrations for areas with high 03

levels (e.g., Los Angeles) was suggested.

However, due to inconsistencies in the

results from the very limited number of

studies available at that time, there was

insufficient evidence to determine

whether the observed association was

likely causal, and thus the possibility

that 03 exposure may be associated with

mortality was not relied upon in the

1997 decision on the 03 primary

standard.

Since the last review, the body of

evidence with regard to 0 3-related

health effects has been expanded by

animal, controlled human exposure, and

epidemiological studies and now

identifies biologically plausible

mechanisms by which 03 may affect the

cardiovascular system. In addition,

there is stronger information linking 03

to serious morbidity outcomes, such as hospitalization, that are associated with

increased mortality. Thus, there is now

a coherent body of evidence that

describes a range of health outcomes

from lung function decrements to

hospitalization and premature mortality.

Newly available large multi-city

studies and related analyses (Bell et al.,

2004; Huang et al., 2005; and Schwartz,

2005) designed specifically to examine

the effect of 03 and other pollutants on

mortality have provided much more

robust and credible information.

Together these studies have reported

significant associations between 03 and

mortality that were robust to adjustment

for PM and different adjustment

methods for temperature and suggest

that the effect of 03 on mortality may be

immediate but may also persist for

several days. Further analysis of one of

these multi-city studies (Bell et al.,

2006) examined the shape of the

concentration-response function for the

0 3-mortality relationship in 98 U.S.

urban communities for the period 1987

to 2000 specifically to evaluate whether

a threshold level exists. Results from

various analytic methods all indicated

that any threshold, if it exists, would

likely occur at very low concentrations,

far below the level of the current 03

NAAQS and nearing background levels.

New data are also available from

several single-city studies conducted

worldwide, as well as from several

meta-analyses that have combined

information from multiple studies.

Three recent meta-analyses evaluated

potential sources of heterogeneity in 03-

mortality associations. All three

analyses reported common findings,

including effect estimates that were

statistically significant and larger in

warm season analyses. Reanalysis of

results using default GAM criteria did

not change the effect estimates, and

there was no strong evidence of

confounding by PM.

Overall, the Criteria Document (p. 8-

78) found that the results from U.S.

multi-city time-series studies, along

with the meta-analyses, provide

relatively strong evidence for

associations between short-term 03

exposure and all-cause mortality even

after adjustment for the influence of

season and PM. The results of these

analyses of studies considered in this

review indicate that copollutants

generally do not appear to substantially

confound the association between 03

and mortality. In addition, several

single-city studies observed positive

associations of ambient 03

concentrations with total nonaccidental

and cardiorespiratory mortality.

Finally, from those studies that

included assessment of associations

with specific causes of death, it appears

that effect estimates for associations

with cardiovascular mortality are larger

than those for total mortality; effect

estimates for respiratory mortality are less consistent in size, possibly due to

reduced statistical power in this

subcategory of mortality. For

cardiovascular mortality, the Criteria

Document (p. 7-106) suggested that

effect estimates are consistently positive

and more likely to be larger and

statistically significant in warm season

analyses. The Criteria Document (p. 8-

78) concluded that these findings are

highly suggestive that short-term 03

exposure directly or indirectly

contributes to nonaccidental and

cardiorespiratory-related mortality, but

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additional research is needed to more

fully establish underlying mechanisms

by which such effects occur.15

ii. Exposure- and Risk-Based

Considerations

In evaluating the adequacy of the

current standard, the Staff Paper also

considered estimated quantitative

exposures and health risks, and

important uncertainties and limitations

in those estimates, which are

highlighted above in section II.A.3 and

discussed in section II.B of the proposal.

These estimates are derived from an EPA assessment of exposures and health

risks associated with recent air quality

levels and with air quality simulated to

just meet the current standard to help

inform judgments about whether or not

the current standard provides adequate

protection of public health.

The Staff Paper (and the CASAC

Panel) recognized that the exposure and

risk analyses could not provide a full

picture of the 03 exposures and 03-

related health risks posed nationally.

The Staff Paper did not have sufficient

information to evaluate all relevant atrisk groups (e.g., outdoor workers,

children under age 5) or all 03-related

health outcomes (e.g., increased

medication use, school absences, and

emergency department visits that are part of a broader pyramid of effects),

and the scope of the Staff Paper analyses

was generally limited to estimating

exposures and risks in 12 urban areas

across the U.S., and to only five or just one area for some health effects

included in the risk assessment. Thus,

due to the limited geographic scope of

the exposure and risk assessments, EPA

recognizes that national-scale public

health impacts of ambient 03 exposures

would be much larger than the

quantitative exposure and risk estimates

associated with recent air quality or air

quality that just meets the current or alternative standards in the 12 urban

areas analyzed. On the other hand,

inter-individual variability in

1

5 In commenting on the Criteria Document, the CASAC Ozone Panel raised questions about the

implications of these time-series results in a policy

context, emphasizing that - * * while the timeseries study design is a powerful tool to detect very

small effects that could not be detected using other

designs, it is also a blunt tool" (Henderson, 2006b).

They note that "* * * not only is the interpretation

of these associations complicated by the fact that

the day-to-day variation in concentrations of these

pollutants is, to a varying degree, determiried by

meteorology, the pollutants are often part of a large

and highly correlated mix of pollutants, only a very

few of which are measured" (Henderson, 2006b).

Even with these uncertainties, the CASAC Ozone

Panel, in its review of the Staff Paper, found "* * *

premature total non-accidental and

cardiorespiratory mortality for inclusion in the

quantitative risk assessment to be appropriate."

(Henderson, 2006b)

responsiveness means that only a, subset

of individuals in each group estimated

to experience exposures at and above a given benchmark level while at elevated

exertion would actually be expected to

experience such adverse health effects.

The Staff Paper estimated exposures

and risks for the three most recent years

(2002-2004) for which data were available at the time of the analyses. As

discussed above in sectibn II.A.3.a,

within this 3-year period, 2002 was a year with relatively higher 03 levels in

most, but not all, areas and simulation

of just meeting the current standard

based on 2002 air quality data provides a generally higher-end estimate of

exposures and risks, while 2004 was a year with relatively lower 03 levels in

most, but not all, areas and simulation

of just meeting the current standard

using 2004 air quality data provides a generally lower-end estimate of

exposures and risks.

The Staff Paper consideration of such

exposure and risk analyses is discussed

below and in section II.C.2.b of the

proposal, focusing on both the exposure

analyses and the human health risk

assessment.

(1) Exposure analyses. EPA's exposure

analysis estimated personal exposures

to ambient 03 levels at and above

specific benchmark levels while at

elevated exertion to provide some

perspective on the potential public

health impacts of respiratory symptoms

and respiratory-related physiological

effects that cannot currently be

evaluated in quantitative risk

assessments but that may occur at

current air quality levels, and the extent

to which such impacts might be reduced

by meeting the current and alternative

standards. As noted above in section

II.A.3, theStaff Paper referred to

exposures at and above these

benchmark levels as "exposures of

concern." The Staff Paper noted that

potential public health impacts likely•

occur across a range of 03 exposure

levels, such that there is no one

exposure level that addresses all

relevant public health impacts.

Therefore, with the concurrence of the

CASAC Panel, the Staff Paper estimated

exposures of concern not only at 0.080

ppm 03, a level at which there are

demonstrated effects, but also at 0.070

and 0.060 ppm 03. The Staff Paper

recognized that there will be varying

degrees of concern about exposures at

each of these levels, based in part on the

population subgroups experiencing

them. Given that there is clear evidence

of inflammation, increased airway

responsiveness, and changes in host

defenses in healthy people exposed to

0.080 ppm 03 and reason to infer that

such effects will continue at lower

exposure levels, but with increasing

uncertainty about the extent to which

such effects occur at lower 03

concentrations, the Staff Paper focused

on exposures at or above benchmark

levels of 0.070 and 0.060 ppm 03 while

at elevated exertion for purposes of

evaluating the adequacy of the current

standard.

Exposure estimates were presented in

the Staff Paper and in section H.B (Table

1) of the proposal for the number and

percent of all school age children and

asthmatic school age children exposed,

and the number of person-days

(occurrences) of exposures, with daily 8-

hour maximum exposures at or above

several benchmark levels while at

intermittent moderate or greater

exertion. The percent of population

exposed at any given level is very

similar for all and asthmatic school age

children. Substantial year-to-year

variability in exposure estimates is

observed, ranging to over an order of

magnitude at the current standard level,

in estimates of the number of children

and the number of occurrences of

exposures at both of these benchmark

levels while at elevated exertion. The

Staff Paper stated that it is appropriate

to consider not just the average

estimates across all years, but also to

consider public -health impacts in years

with relatively higher 03 levels. The

Staff Paper also noted that there is

substantial city-to-city variability in

these estimates, and notes that it is

appropriate to consider not just the

aggregate estimates across all.cities, but

also to consider the public health

impacts in cities where these estimates

are higher than the average upon.

meeting the current standard.

About 50 percent of asthmatic of all

school age children, representing nearly

1.3 million asthmatic children and

about 8.5 million school age children in

the 12 urban areas examined, are

estimated to experience exposures at or

above the 0.070 ppm benchmark level

while at elevated exertion (i.e., these

individuals are estimated to experience

8-hour 03 exposures at or above 0.070

ppm while engaged in moderate or

greater exertion 1 or more times during

the 0 3 season) associated with 2002 03

air quality levels. In contrast, about 17

percent of asthmatic and all school age

children are estimated to experience

exposures at or above the 0.070 ppm

benchmark level while at elevated

exertion associated with 2004 03 air

quality levels. Just meeting the current

standard results in an aggregate estimate

of about 20 percent of asthmatic or 18

percent of all school age children likely

to experience exposures at or above the

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0.070 ppm benchmark level while at

elevated exertion using the 2002

simulation. The exposure estimates for

this benchmark level range up to about

40 percent of asthmatic or all school age

children in the single city with the

highest estimate among the cities

analyzed. Just meeting the current

standard based on the 2004 simulation,

results in an aggregate estimate of about

1 percent of asthmatic or all school age

children experiencing exposures

exceeding the 0.070 ppm benchmark

level while at elevated exertion.

At the benchmark level of 0.060 ppm,

about 70 percent of all or asthiatic

school age children are estimated to

experience exposures at or above this

benchmark level while at elevated

exertion for the aggregate of the 12

urban areas associated with 2002 03

levels. Just meeting the current standard

would result in an aggregate estimate of

about 45 percent of asthmatic or all

school age children likely to experience

exposures at or above the 0.060 ppm

benchmark level while at elevated

exertion using the 2002 simulation. The

exposure estimates for this benchmark

level range up to nearly 70 percent of all

or asthmatic school age children in the

single city with the highest estimate

among the cities analyzed associated

with just meeting the current standard

using the 2002 simulation. The Staff

Paper indicated an aggregate estimate of

about 10 percent of asthmatic or all

school age children would experience

exposures at or above the 0.060 ppm

benchmark level while at elevated

exertion associated with just meeting

the current standard using the 2004

simulation.

(2) Risk assessment. The health risk

assessment estimated risks for several

important health endpoints, including:

(1) Lung function decrements (i.e., _ 15

percent and _> 20 percent reductions in

FEV1) in all school age children for 12

urban areas; (2) lung function

decrements (i.e., - 10 percent and >_ 20

percent reductions in FEVI) in

asthmatic school age children for 5

urban areas (a subset of the 12 urban

areas); (3) respiratory symptoms (i.e.,

chest tightness, shortness of breath,

wheeze) in moderate to severe asthmatic

children for the Boston area; (4)

respiratory-related hospital admissions

for 3 urban areas; and (5) nonaccidental

and cardiorespiratory mortality for 12

urban areas for three recent years (2002

to 2004) and for just meeting the current

standard using a 2002 simulation and a

2004 simulation.

With regard to estimates of moderate

lung function decrements, meeting the

current standard substantially reduces

the estimated number of school age

children experiencing one or more

occurrences of FEV decrements > 15

percent for the 12 urban areas, going

from about 1.3 million children (7

percent of children) under 2002 air

quality to about 610,000 (3 percent of

children) based on the 2002 simulation,

and from about 620,000 children (3

percent of children) to about 230,000 (1

percent of children) using the 2004

simulation. In asthmatic children, the

estimated number of children

experiencing one or more occurrences of

FEV decrements > 10 percent for the 5

urlban areas goes from about 250,000

children (16 percent of asthmatic

children) under 2002 air quality to

about 130,000 (8 percent of asthmatic

children) using the 2002 simulation,

and from about 160,000 (10 percent of

asthmatic children) to about 70,000 (4

percent of asthmatic children) using the

2004 simulation. Thus, even when the

current standard is met, about 4 to 8

percent of asthmatic school age children

are estimated to experience one or more

occurrences of moderate lung function

decrements, resulting in about 1 million

occurrences (using the 2002 simulation)

and nearly 700,000 occurrences (using

the 2004 simulation) in just 5 urban

areas. Moreover, the estimated number

of occurrences of moderate or greater

lung function decrements per child is

on average approximately 6 to 7 in all

children and 8 to 10 in asthmatic

children in an 03 season, even when the

current standard is met, depending on

the year used to simulate meeting the

current standard. In the 1997 review of

the 03 standard a general consensus

view of the adversity of such moderate

respoifses emerged as the frequency.of

occurrences increases, with the

judgment that repeated occurrenpes of

moderate responses, even in otherwjise

healthy individuals, may be considered

adverse since they may well set the

stage for more serious illness.

With regard to estimates of large lung

function decrements, the Staff Paper

noted that FEV decrements > 20

percent would likely interfere with

normal activities in many healthy

individuals, therefore single

occurrences would be considered to be

adverse. In people with asthma, large

lung function responses would likely

interfere with normal activities for most

individuals and would also increase the

likelihood that these individuals would

use additional medication or seek

medical treatment. Single occurrences

would be considered to be adverse to

asthmatic individuals under the ATS

definition. They also would be cause for

medical concern in some individuals.

While the current standard reduces the

occurrences of large lung function

decrements in all children and

asthmatic children from about 60 to

70%, in a year with relatively higher 03

levels (2002), there are estimated to be

about 500,000 occurrences in all school

children across the entire 12 urban

areas, and about 40,000 occurrences in

asthmatic children across just 5 urban

areas. As noted above, it is clear that

even when the current standard is met

over a three-year period, 03 levels in

each year can vary considerably, as

evidenced by relatively large differences

between risk estimates based on 2002 to

2004 air quality. The Staff Paper

expressed the view that it was

appropriate to consider this yearly

variation in 0 3 levels allowed by the

current standard in judging the extent to

which impacts on members of at-risk

groups in a year with relatively higher

03 levels remain of concern from a

public health perspective.

With regard to other 0 3-related health

effects, the estimated risks of respiratory

symptom days in moderate to severe

asthmatic children, respiratory-related

hospital admissions, and non-accidental

and cardiorespiratory mortality,

respectively, are not reduced to as great

an extent by meeting the current

standard as are lung function

decrements. For example, just meeting

the current standard reduces the

estimated average incidence of chest

tightness in moderate to severe

asthmatic children living in the Boston

urban area by 11 to 15%, based on 2002

and 2004 simulations, respectively,

resulting in an estimated incidence of

about 23,000 to 31,000 per 100,000

children attributable to 03 exposure

(Table 6-4). Just meeting the current

standard is estimated to reduce the

incidence of respiratory-related hospital

admissions in the New York City urban

area by about 16 to 18%, based on 2002

and 2004 simulations, respectively,

resulting in an estimated incidence per

100,000 population of 4.6 to 6.4,

respectively. Across the 12 urban areas,

the estimates of non'-accidental

mortality incidence per 100,000 relevant

population range from 0.4 to 2.6 (for

2002) and 0.5 to 1.5 (for 2004). Meetifig

the current standard results in a

reduction of the estimated incidence per

100,000 population to a range of 0.3 to

2.4 based on the 2002 simulation and a

range of 0.3 to 1.2 based on the 2004

simulation. Estimates for

cardiorespiratory mortality show similar

patterns.

In considering the estimates of the

proportion'of population affected and

the number of occurrences of the health

effects that are included in the risk

assessment, the Staff Paper noted that

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these limited estimates are indicative of

a much broader array of potential 03-

related health endpoints that we

consider part of a "pyramid of effects"

that include various indicators of

morbidity that could not be included in

the risk assessment (e.g., school

absences, increased medication use,

emergency department visits) and

which primarily affect members of atrisk groups. While the Staff Paper had

sufficient information to estimate and

consider the number of symptom days

in children with moderate to severe

asthma, it recognized that there are

many other effects that may be

associated with symptom days, such as

increased medication use, school and

work absences, or visits to doct6rs'

offices, for which there was not

sufficient information to estimate risks

but which are important to consider in

assessing the adequacy of the current

standard. The same is true for more

serious, but less frequent effects. The

Staff Paper estimated hospital

admissions, but there was not sufficient

information to estimate emergency

department visits in a quantitative risk

assessment. Consideration of such

unquantified risks in the Staff Paper

reinforced the Staff Paper conclusion

that consideration should be given to

revising the standard so as to provide

increased public health protection,

especially for at-risk groups such as

people with asthma or other lung

diseases, as well as children and older

adults, particularly those active

outdoors, and outdoor workers.

iii. Summary of Staff Paper

Considerations

The Staff Paper concluded that the

overall body of evidence clearly calls

into question the adequacy of the

current standard in protecting at-risk

groups against an array of adverse

health effects that range from decreased

lung function and respiratory symptoms

to serious indicators of respiratory

morbidity including emergency

department visits and hospital

admissions for respiratory causes,

nonaccidental mortality, and possibly

cardiovascular effects. These at-risk

groups notably include asthmatic

children and other people with lung

disease, as well as all children and older

adults, especially those active outdoors,

and outdoor workers.16 The available

information provides strong support for

consideration of an 03 standard that

would provide increased health

protection for these at-risk groups. The

16 ln defining at-risk groups this way we are

including both groups with greater inherent

sensitivity and those more likely to be exposed.

Staff Paper also concluded that risks

projected to remain upon meeting- the

current standard are indicative of risks

to at-risk groups that can be judged to

be important from a public health

perspective. This information reinforced

the Staff Paper conclusion that

consideration should be given to

revising the level of the standard so as

to provide increased public health

protection.

b. CASAC Views

The CASAC Panel unanimously

concluded in a letter to the

Administrator that there is "no

-scientifi" justification for retaining" the

current primary 03 standard, and the

current standard "needs to be

substantially reduced to protect human

health, particularly in sensitive

subpopulations" (Henderson, 2006c, pp.

1-2). In its rationale for this conclusion,

the CASAC Panel concluded that "new

evidence supports and builds-upon key,

health-related conclusions drawn in the

1997 03 NAAQS xeview" (id., p. 3). The

Panel noted that several new single-city

studies and large multi-city studies have

provided more evidence for adverse

health effects at concentrations lower

than the current standard, and that these

epidemiological studies are backed-up

by evidence from controlled human

exposure studies. The Panel specifically

noted evidence from the recent Adams

(2006) study that reported statistically

significant decrements in the lung

function of healthy, moderately

exercising adults at a 0.080 ppm

exposure level, and importantly, also

reported adverse lung function effects in

some healthy individuals at 0.060 ppm.

The CASAC Panel concluded that these

results indicate that the current

standard "is'not sufficiently healthprotective with an adequate margin of

safety," noting that while similar

studies in sensitive groups such as

asthmatics have yet to be conducted, "people with asthma, and particularly

children, have been found to be more

sensitive and to experience larger

.decrements in lung function in response

to 03 exposures than would healthy

volunteers (Mortimer et al., 2002)"

(Henderson, 2006c, p. 4).

The CASAC Panel also highlighted a

number of 0 3-related adverse health

effects that are associated with exposure

to ambient 03, below the level of the

current standard based on a broad range

of epidemiological studies (Henderson,

2006c). These adverse health effects

include increases in school absenteeism,

respiratory hospital emergency

department visits among asthmatics and

patients with other respiratory diseases,

hospitalizations for respiratory illnesses,

symptoms associated with adverse

health effects (including chest tightness

and medication usage), and premature

mortality (nonaccidental,

cardiorespiratory deaths) reported at

exposure levels well below the current

standard. "The CASAC considers each

of these findings to be an important

indicator of adverse health effects"

(Henderson, 2006c).

The CASAC Panel expressed the view

that more emphasis should be placed on

the subjects in controlled human

exposure studies with FEV1 decrements

greater than 10 percent, which can be

clinically significant, rather than on the

relatively small average decrements.

The Panel also emphasized significant

0 3-related.inflammatory responses and

markers of injury to the epithelial lining

of the lung that are independent of

spirometric responses. Further, the

Panel expressed the view that the Staff

Paper did not place enough emphasis on

serious morbidity (e.g., hospital

admissions) and mortality observed in

epidemiological studies. On the basis of

the large amount of recent data

evaluating adverse health effects at

levels at and below the current 03

standard, it was the unanimous opinion

of the CASAC Panel that the current

primary 03 standard is not adequate to

protect human health, that the relevant

scientific data do not support

consideration of retaining the current

standard, and that the current standard

needs to be substantially reduced to be

protective of human health, particularly

in sensitive subpopulations (Henderson,

2006c, pp. 4-5).

Further, the CASAC letter noted that

"there is no longer significant scientific

uncertainty regarding the CASAC's

conclusion that the current 8-hour

primary NAAQS must be lowered"

(Henderson, 2006c, p. 5). The Panel

noted that a "large body of data clearly

demonstrates adverse human health

effects at the current level" of the

standard, such that "[Rietaining this

standard would continue to put large

numbers of individuals at risk for

respiratory effects and/or significant

impact on quality of life including

asthma exacerbations, emergency room

visits, hospital admissions and

mortality" (Henderson, 2006c).

c. Administrator's Proposed

Conclusions

At the time of proposal, in

considering whether the current

primary standard should be revised, the

Administrator carefully considered the

conclusions contained in the Criteria

Document, the rationale and

recommendations contained in the Staff

Paper, the advice and recommendations

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from CASAC, and public comments to

date on this issue. In so doing, the

Administrator noted the following: (1)

That evidence of a range of respiratoryrelated morbidity effects seen in the last

review has been considerably

strengthened, both through toxicological

and controlled human exposure studies

as well as through many new panel and

epidemiological studies; (2) that new

evidence from controlled human

exposure and epidemiological studies

identifies people with asthma

(including children with asthma) as an

important susceptible population for

which estimates of respiratory effects in

the general population likely

underestimate the magnitude or

importance of these effects; (3) that new

evidence about mechanisms of toxicity

further contributes to the biological

plausibility of 0 3-induced respiratory

effects and is beginning to suggest

mechanisms that may link 03 exposure

to cardiovascular effects; (4) that there is

now relatively strong evidence for

associations between 03 and total

nonaccidental and cardiopulmonary

mortality, even after adjustment for the

influence of season and PM; and (5) the

limits of the available evidence. Relative

to the information that was available to

inform the Agency's 1997 decision to set

the current standard, the newly

available evidence increased the

Administrator's confidence that

respiratory morbidity effects such as

lung function decrements and

respiratory symptoms are causally

related to 03 exposures, that indicators

of respiratory morbidity such as

emergency department visits and

hospital admissions are causally related

to 03 exposures, and that the evidence

is highly suggestive that 03 exposures

during the 03 season contribute to

premature mortality.

The Administrator judged that there is

important new evidence demonstrating

that exposures to 03 at levels below the

level of the current standard are

associated with a broad array of adverse

health effects, especially in at-risk

populations that include people with

asthma or other lung diseases who are

likely to experience more serious effects

from exposure to 03, children and older

adults with increased susceptibility, as

well as those who are likely to be

vulnerable as a result of spending a lot

of time outdoors engaged in physical

activity, especially active children and

outdoor workers. Examples of this

important new evidence include

demonstration of 0 3-induced lung

function effects and respiratory

symptoms in some healthy individuals

down to the previously observed

exposure level of 0.080 ppm, as well as

very limited new evidence at exposure

levels well below the level of the

current standard. In addition, there is

now epidemiological evidence of

statistically significant 0 3-related

associations with lung function and

respiratory symptom effects, respiratoryrelated emergency department visits and

hospital admissions, and increased

mortality, in areas that likely would

have met the current standard. There are

also many epidemiological studies done

in areas that likely would not have met

the current standard but which

nonetheless report statistically

significant associations that generally

extend down to ambient 03

concentrations that are below the level

of the current standard. Further, there

are a few studies that have examined

subsets of data that include only days

with ambient 03 concentrations below

the level of the current standard, or

below even much lower 03

concentrations, and continue to report

statistically significant associations with

respiratory morbidity outcomes and

mortality. The Administrator recognized

that the evidence from controlled

human exposure studies, together with

animal toxicological studies, provides

considerable support for the biological

plausibility of the respiratory morbidity

associations observed in the

epidemiological studies and for

concluding that the associations extend

below the level of the current standard.

However, the Administrator recognized

that in the body of epidemiological

evidence, many studies reported

positive and statistically significant

associations, while others reported

positive results that were not

statistically significant, and a few did

not report any positive 0 3-related

associations. In addition, the

Administrator judged that evidence of a

causal relationship between adverse

health outcomes and 03 exposures

became increasingly uncertain at lower

levels of exposure.

Based on the strength of the currently

available evidence of adverse health

effects, and on the extent to which the

evidence indicates that such effects

likely result from exposures to ambient

03 concentrations below the level of the

current standard, the Administrator

judged that the current standard does

not protect public health with an

adequate margin of safety and that the

standard should be revised to provide

such protection, especially for at-risk

groups, against a broad array of adverse

health effects.

In reaching this judgment, the

Administrator had also considered the

results of both the exposure and risk

assessments conducted for this review,

to provide some perspective on the

extent to which at-risk groups would

likely experience "exposures of

concern" 17 and on the potential

magnitude of the risk of experiencing

various adverse health effects when

recent air quality data (from 2002 to

2004) are used to simulate meeting the

current standard and alternative

standards in a number of urban areas in

the U.S. 18 In considering the results of

the health risk assessment, as discussed

in the proposal notice (section II.C.2),

the Administrator noted that there were

important uncertainties and

assumptions inherent in the risk

assessment and that this assessment was

most appropriately used to simulate

trends and patterns that could be

expected, as well as providing informed,

but still imprecise, estimates of the

potential magnitude of risks.

In considering the exposure

assessment results at the time of

proposal, the Administrator considered

analyses that define "exposures of

concern" by three benchmark exposure

levels: 0.080, 0.070, and 0.060 ppm.

Estimates of exposures in at-risk groups

at and above these benchmark levels

while at elevated exertion, using 03 air

quality data in 2002 and 2004, provide

some indication of the potential

magnitude.of the incidence of health

outcomes that cannot currently be

evaluated in a quantitative risk

assessment, such as increased airway

responsiveness, increased pulmonary

inflammation, increased cellular

permeability, and decreased pulmonary

defense mechanisms. These respiratoryrelated physiological effects have been

demonstrated to occur in healthy people

at 03 exposures as low as 0.080 ppm,

the lowest level tested for these effects.

These physiological effects provide

plausible mechanisms underlying

observed associations with aggravation

of asthma, increased medication use,

increased school and work absences,

" '

7 As discussed in section II.A.3 above,

"exposures of concern" are estimates of personal

exposures while at moderate or greater exertion to

8-hour average ambient 03 levels at and above

specific benchmark levels which represent

exposure levels at which 0 3-related health effects

are known or can with varying degrees of certainty

be inferred to occur in some individuals. Estimates

of exposures of concern provide some perspective

on-the public health impacts of health effects that

may occur in some individuals at recent air quality

levels but cannot be evaluated in quantitative risk

assessments, and the extent to which such impacts

might be reduced by meeting the current and

alternative standards.

18 As noted above in section Il.A.3, recent 03 air

quality distributions have been statistically adjusted

to simulate just meeting the current and selected

alternative standards. These simulations do not

represent predictions of when, whether, or how

areas might meet the specified standards.

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increased susceptibility to respiratory

infection, increased visits to doctors'

offices and emergency departments, and

increased admissions to hospitals. In

addition, these physiological effects, if

repeated over time, have the potential to

lead to chronic effects such as chronic

bronchitis or long-term damage to the

lungs that can lead to reduced quality of

life.

In considering these various

benchmark levels for exposures of

concern at the time of proposail, the

Administrator focused primarily on

estimated exposures at and above the

0.070 ppm benchmark level while at

elevated exertion as an important

surrogate measure for potentially more serious health effects in at-risk groups

such as people with asthma. This

judgment was based on the strong

evidence of effects in healthy people at

the 0.080 ppm exposure level and the new evidence that people with asthma

are likely to experience larger and more

serious effects than healthy people at

the same level of exposure. In the

Administrator's view at the time of

proposal, this evidence did not support

a focus on exposures at and above the

benchmark level of 0.080 ppm 03, as it

would not adequately account for the

increased risk of harm from exposure for

members of at-risk groups, especially

people with asthma. The Administrator

also judged-that the evidence of

demonstrated effects is too limited to

support a primary focus on-exposures

down to the lowest benchmark level

considered of 0.060 ppm. The

Administrator particularly noted that

although the analysis of "exposures of

concern" was conducted to estimate

exposures at and above three discrete

benchmark levels (0.080, 0.070, and

0.060 ppm) while at elevated exertion,

the concept is appropriately viewed as a continuum. In so doing, the

Administrator sought to balance

concern about the potential for health

effects and their severity with the

increasing uncertainty associated with

our understanding of the likelihood of

such effects at lower 03 exposure levels.

The Administrator observed that " based on the aggregate exposure

estimates for the 2002 simulation

(summarized in section II.B.1, Table 1,

of the proposal) for the 12 U.S. urban areas included in the exposure analysis,

upon just meeting the current standard

up to about 20 percent of asthmatic or

all school age children are likely to

experience one or more exposures at

and above the 0.070 ppm benchmark

level while at elevated exertion; the

2004 simulation yielded an estimate of

about 1 percent of such children. The

Administrator noted from this

comparison that there is substantial

year-to-year variability, ranging up to an

order of magnitude or more in estimates

of the number of people and the number

of occurrences of exposures at and

above this benchmark level while at

elevated exertion. Moreover, within any

given year, the exposure assessment

indicates that there is substantial cityto-city variability in the estimates of the

children exposed or the number of

occurrences of exposure at and above

this benchmark level while at elevated

exertion. For example, city-specific

estimates of the percent of asthmatic or

all school age children likely to

experience exposures at and above the

benchmark level of 0.070 ppm while at

elevated exertion ranges from about 1

percent up to about 40 percent across

the 12 urban areas upon just meeting the

current standard based on the 2002

simulation; the 2004 simulation yielded

estimates that range from about 0 up to

about 7 percent. The Administrator

judged that it was important to

recognize the substantial year-to-year

and city-to-city variability in

considering these estimates.

With regard to the results of the risk

assessment, the Administrator focused

on the risks estimated to remain upon

just meeting the current standard. Based on the aggregate risk estimates

(summarized in section II.B.2, Table 2,

of the proposal), the Administrator

obsbrved that upon just meeting the

current standard based on the 2002

simulation, approximately 8 percent of

asthmatic school age children across

urban areas (ranging up to about 11

percent in the city with the highest

estimate among the cities analyzed)

would still be estimated to experience

moderate or greater lung function

decrements one or more times within an

03 season. These estimated percentages

would be approximately 3 percent of all

school age children across 12 urban

areas (ranging up to over 5 percent in

the city with the highest estimate among

the cities analyzed). The Administrator

recognized that, as with the estimates of

exposures of concern, there is

substantial year-to-year and city-to-city

variability in these risk estimates.

In addition to the percentage of

asthmatic or all children estimated to

experience one or more occurrences of an effect, the Administrator recognized

that some individuals are estimated to

have multiple occurrences. For

example, across all the cities in the

assessment, approximately 6 to 7

occurrences of moderate or greater lung

function decrements per child are estimated to occur in all children and

approximately 8 to 10 occurrences are

estimated to occur in asthmatic children

in an 03 season, even upon just meeting

the current standard. In the last review,

a general consensus view of the

adversity of such responses emerged as

the frequency of occurrences increases,

with the judgment that repeated

occurrences of moderate responses,

even in otherwise-healthy individuals,

may be considered adverse since they

may well set the stage for more serious

illness. The Administrator continued to

support this view.

Large lung function decrements (i.e.,

> 20 percent FEV, decrement) would

likely interfere with normal activities in

many healthy individuals, therefore

single occurrences would be considered

to be adverse. In people with asthma,

large lung function responses (i.e., _ 20

percent FEV decrement), would likely

interfere with normal activities for most

individuals and would also increase the

likelihood that these individuals would

use additional medication or seek

medical treatment. Not only would

single occurrences be considered to be

adverse to asthmatic individuals under

the ATS definition, but they also would

be cause for medical concern for some

individuals. Upon just meeting the

current standard based on the 2002

simulation, close to 1 percent of

asthmatic and all school age children

are estimated to experience one or more

occurrences of large lung function

decrements in the aggregate across 5 and

12 urban areas, respectively, with close

to 2 percent of both asthmatic and all

school age children estimated to

experience such effects in the city that

receives relatively less protection from

this standard. These estimates translate

into approximately 500,000 occurrences

of large lung function decrements in all

children across 12 urban areas, and

about 40,000 occurrences in asthmatic

children across 5 urban areas upon just

meeting the current standard based on

the 2002 simulation; the 2004

simulation yielded estimates that

translate into approximately 160,000

and 10,000 such occurrences in all

children and asthmatic children,

respectively.

Upon just meeting the current

standard based on the 2002 simulation,

the estimate of the 0 3-related risk of

respiratory symptom days in moderate

to severe asthmatic children in the

Boston area is about 8,000 symptom

days; the 2004 simulation yielded an

estimate of about 6,000 such symptoms

days. These estimates translate into as

many as one symptom day in six, and

one symptom day in eight, respectively,

that are attributable to 03 exposure

during the 03 season of the total number

of symptom days associated with all

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causes of respiratory symptoms in

asthmatic children during those years.

The estimated 0 3-related risk of

respiratory-related hospital admissions

upon just meeting the current standard

based on the 2002 simulation is greater

than 500 hospital admissions in the

New York City area alone, or about 1.5

.percent of the total incidence of

respiratory-related admissions

associated with all causes; the 2004

simulation yielded an estimate of

approximately 400 such hospital

admissions. For nonaccidental

mortality, just meeting the current

standard based on the 2002 simulation

results in an estimated incidence of

from 0.3 to 2.4 per 100,000 population;

the 2004 simulation resulted in an

estimated incidence of from 0.3 to 1.2

per 100,000 population. Estimates for

cardiorespiratory mortality show similar

patterns (Abt Associates, 2007a, Table

4-26).

The Administrator recognized that in

considering the estimates of the

proportion of population affected and

the number of occurrences of those

specific health effects that are included

in the risk assessment, these limited

estimates based on 2002 and 2004

simulations are indicative of a much

broader array of 0 3-related health

endpoints that are part of a "pyramid of

effects" (discussed in section II.A.4.d of

the proposal) that include various

indicators of morbidity that could not be

included in the risk assessment (e.g.,

school absences, increased medication

use, emergency department visits) and

which primarily affect members of atrisk groups. Moreover, the

Administrator noted that the CASAC

Panel supported a qualitative

consideration of the much broader array

of 0 3-related health endpoints, and

specifically referred to respiratory

emergency department visits in

asthmatics and people with other lung

diseases, increased medication use, and

increased respiratory symptoms

reported at exposure levels well below

the current standard.

The Administrator expressed the view

in the proposal that the exposure and

risk estimates discussed in the Staff

Paper and summarized above are

important from a public health

perspective and indicative of potential

exposures and risks to at-risk groups. In

reaching this proposed judgment, the

Administrator considered the following

factors: (1) The estimates of numbers of

persons exposed at and above the 0.070

ppm benchmark level; (2) the risk

estimates of the proportion of the.

population and number of occurrences

of various health effects in areas upon

just meeting the current standard; (3)

the year-to-year and city-to-city

variability in both the exposure and risk

estimates; ,(4) the uncertainties in these

estimates; and (5) recognition that there

is a broader array of 0 3-related adverse

health outcomes for which risk

estimates could not be quantified (that

are part of a broader "pyramid of

effects") and that the scope of the

assessment was limited to just a sample

of urban areas and to some but not all

at-risk populations, leading to an

incomplete estimation of public health

impacts associated with 03 exposures

across the country. The Administrator

also noted that it was the unanimous

conclusion of the CASAC Panel that

there is no scientific justification for

retaining the current primary 03

standard, that the current standard is

not sufficiently heal~th-protective with

an adequate margin of safety, and that

the standard needs to be substantially

reduced to protect human health,

particularly in at-risk subpopulations.

Based on all of these considerations,

the Administrator proposed that the

current 03 standard is not requisite to

protect public health with an adequate

margin of safety because it does not

provide sufficient protection and that

revision would result in increased

public health protection, especially for

members of at-risk groups.

2. Comments on the Need for Revision

The above section outlines the health

effects evidence and assessments used

by the Administrator to inform his

proposed judgments about the adequacy

of the current 03 primary standard.

General comments received on the

proposal that either supported or

opposed the proposed decision to revise

the current 03 primary standard aro

addressed in this section. Comments on

the health effects evidence, which

includes evidence from controlled

human exposure and epidemiological

studies, are considered in section

II.B.2.a below. Comments on human

exposure and health risk assessments

are considered in section II.B.2.b, and

comments on other policy-related issues

are considered in section II.B.2.c, below.

Comments on specific issues, health

effects evidence, or the human exposure

and health risk assessments that relate

to consideration of the appropriate

averaging time, form, or level of the 03

standard are addressed below in

sections II.C.3 and II.C.4. General

comments based on implementationrelated factors that are not a permissible

basis for considering the need to revise

the current standard are noted in the

Response to Comments document.

a. Consideration of Health Effects

Evidence

With regard to the need to reVise the

current primary 03 standard, sharply

divergent comments were received from

two general sets of commenters. Many

public comments received on the

proposal asserted that the current 03

standard is insufficient to protect public

health, especially the health of sensitive

groups, with an adequate margin of

safety and revisions to the standard are

appropriate. Among those calling for

revisions to the current primary

standard were medical groups,

including for example, the American

Medical Association (AMA), the

American Thoracic Society (ATS), the

American Academy of Pediatrics (AAP),

and the American College of Chest

Physicians (ACCP), as well as medical

doctors and academic researchers. For

example, the ATS stated:

We believe that the Administrator has

correctly stated that, beyond any degree of

scientific uncertainty, convincing and

compelling evidence has demonstrated that

exposure to ozone at levels below the current

standard is responsible for measurable and

significant adverse health effects, both in

terms of morbidity and mortality. * * * The

known respiratory, cardiac and perinatal

effects of ozone pollution are each in their

own right major public health issues. In

combination they provide immediate,

actionable information and require a

meaningful public health policy response

from the EPA. tATS et al. pp. 1, 11]

Similar conclusions were also reached

in comments by many national, State,

and local public health organizations,

including, for example, the American

Lung Association (ALA) in a joint set of

comments with several environmental

groups, the American Heart Association

(AHA), the American Nurses

Association (ANA), the American Public

Health Association (APHA), and the

National Association of County and City

Health Officials (NACCHO), as well as

in letters to the Administrator from

EPA's advisory panel on children's

environmental health (Children's Health

Protection Advisory Committee; Marty

et al., 2007a, 2007b). Environmental

groups also commented in support of

revising the standard, including the

Sierra Club, Environmental Defense, the

Natural Resources Defense Council

(NRDC), Earthjustice, and the U.S.

Public Interest Research Group (US

PIRG). All of these medical,

environmental and public health

commenters stated that the current 03

standard needs to be revised and that an

even more protective standard than

proposed by EPA is needed to protect

the health of sensitive population

I

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groups. Many individual commenters

also expressed such views.

The majority of State and local air

pollution control authorities who

commented on the 03 standard

supported revision of the current 03

standard, as did the National Tribal Air

Association (NTAA). Environmental

agencies that supported revising the

standard include agencies from: "

Arkansas; California; Delaware; Iowa;

Illinois; Michigan; North Carolina; New

Mexico; New York; Oklahoma; Oregon;

Pennsylvania; Utah; Wisconsin; and.

Washington, DC. State organizations,

including the National Association of

Clean Air Agencies (NACAA), Northeast

States for Coordinated Air Use

Management (NESCAUM), and the

Ozone Transport Commission (OTC)

urged that EPA revise the 03 standard.

All of these commenters supported

revisions to the current standard, with

most supporting a standard consistent

with CASAC's recommendations.

In general, the commenters noted

above primarily based their views on

the body of evidence assessed in the

Criteria Document, finding it to be

stronger and more compelling than in

the last review. Some specifically agreed

with the weight of evidence approach

taken by the Criteria Document. These

commenters generally placed much

weight on CASAC's interpretation of the

body of available evidence and the

results of EPA's exposure-and risk

assessments, both of which formed the

basis for CASAC's recommendation to

revise the 03 standard to provide

increased public health protection.

In recent years, a broad scientific consensus has emerged that EPA's current air

quality standards for ozone are not sufficient

to protect public health, and that the levels

and form must be greatly tightened. This consensus is evidenced by the by the strong unanimous comments of the CASAC, which was backed by the endorsement of over 100'

leading independent air quality scientists,

EPA's Children's Health Protection Advisory

Committee, and many others. In the face of

this strong consensus, it is untenable to cite "uncertainty" as a rationale for failing to

propose tighter standards. [ALA et ql., p. 15]

Medical and public health commenters

also ekpressed the view that EPA must

not use uncertainty in the scientific

evidence as justification for retaining

the current 03 standard.

EPA generally agrees with these

commenters' conclusion regarding the'

need to revise the current primary 03

standard. The scientific evidencerelated health effects to 03 exposure

noted by these commenters was

generally the same as that assessed in

the Criteria Document and the proposal.

EPA agrees that this information

provides a basis for concluding that the

current 03 standard is not adequately

protective of public health. For reasons

discussed below in sections II.C.3 and

II.C.4, however, EPA disagrees with

aspects of these commenters' views on the level of protection that is

appropriate and supported by the

available scientific information.

Another group of commenters

representing industry aisodiations and

businesses opposed revising the current

primary 03 standard. These views were

extensively presented in comments from

the Utility Air Regulatory Group

(UARG),. representing a group of electric

generating companies and organizations

and several national trade associations,

and in comments from other industry

and business associations including, for

example: Exxon Mobil Corporation; the

Alliance of Automobile Manufacturers

(AAM); th6 National Association of

Manufacturers (NAM), the American

Petroleum Institute (API). The API

sponsored a workshop at the University

of Rochester in June 2007 to review the

scientific information and health risk

assessment considered by EPA during

the review of the 03 NAAQS. Although

the report (hereafter, "Rochester

Report") from this workshop does not

offer judgments on the specific elements

of the current or proposed standard, it

has been cited in a number of public

comments that opposed revision of the

current 8-hour standard. The Annapolis

Center for Science-Based Public Policy

issued a report (hereafter, "Annapolis.

Center") on the science and health

effects of 03, which explicitly opposed

revising the current 03 primary

standard. Several State environmental

agencies also opposed revising the

current 03 primary standard, including

agencies from: Georgia; Indiana;

Kentucky; Louisiana; Nevada; and

Texas.

As discussed more fully below in

sections dealing with specific

comments, these and other commenters

in this group generally mentioned many

of the same studies from the body of

evidence in the Criteria Document that were cited by the commenters who

supported revising the standards, but

highlighted different aspects of these

studies in reaching substantially

different conclusions about their

* strength and the extent to which

progress has been made in reducing

uncertainties in the evidence since the

last review. They then considered

whether the evidence that has become

available since the last review has

established a more certain risk or a risk

of effects that is significantly different in

character from those that provided a basis for the current standards, or

whether the evidence demonstrates that

the risk to public health upon

attainment of the current standards

would be greater than was understood

when EPA established the current 03

standard in 1997. These commenters

generally expressed the view that the

current standard provides the requisite

degree of public health protection.

In supporting their view that the

present primary 03 standard continues

to provide the requisite public health

protection and should not be revised,

UARG and others generally stated: That

the effects of concern have not changed

significantly since 1997; that the

uncertainties in the underlying health

science are as great or greater than in

1997; that the estimated number of

exposures of concern and health risks

upon attainment of the current 03

standard has not changed or decreased

since 1997; and that "new" studies not

included in the Criteria Document

continue to demonstrate uncertainties

about possible health risks associated

with exposure to 03 at levels below the

current standard. As noted above, EPA

disagrees with this general assessment,

and agrees with the general position that

the available information provides a basis for concluding that the current 03

standard is not adequately protective of

public health. The rationale for this

position is discussed more fully in the

responses to specific comments that are

presented below.

More specific comments on the

evidence and EPA's responses are discussed below. Section Il.B.2.a.i

contains comments on evidence from

controlled human exposure studies;

section II.B.2.a.ii contains comments on

evidence from epidemiological studies,

including interpretation of the evidence

and specific methodological issues.

Comments on evidence pertaining to atrisk subgroups for 0 3-related effects can

be found in section II.B.2.a.iii below.

EPA notes here that most of the issues

and concerns raised by commenters

concerning the health effects evidence,

including both the interpretation of the

evidence and specific technical or

methodological issues, were essentially

restatements of issues raised during the

review of the Criteria Document and the

Staff Paper. Most of these issues were

highlighted and thoroughly discussed

during the review of these documents

by the CASAC. More detailed responses

related to the interpretation of the

health effects evidence and its role in

the decision on the 03 NAAQS are

contained in the Response to Comments

document.

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i. Evidence from Controlled Human

Exposure Studies

As noted in the overview of health

effects evidence, section II.A.2 above,

two new controlled human-exposure

studies (Adams 2002, 2006) are now

available that examine respiratory

effects associated with prolonged 03

exposures at levels at and below 0.080

ppm, which was the lowest exposure

level that had been examined in the last

review. One group of commenters that

included national medical (e.g., ATS,

AMA, ACCP) and national

environmental and public health

organizations (e.g., ALA in a joint set of

comments with Environmental Defense,

Sierra Club), agreed with EPA's

reanalysis of the Adams' data while

disagreeing with EPA's characterization

of the evidence from the Adams studies

as "very limited" (72 FR 37870). These

commenters expressed the view that the

Adams studies provide evidence of

effects at lower concentrations than had

previously been reported. They noted

that Adams, while finding small group

mean changes at 0.060 ppm, reported

total subjective symptom scores reached

statistical significance (relative to preexposure) at 5.6 and 6.6 hours, with the

triangular exposure scenario, and that

pain on deep inspiration values

followed a similar pattern to total

subjective symptoms scores. In addition,

Adams (2002) reports that "some

sensitive subjects experience notable

effects at 0.060 ppm," based on a greater

than 10% reduction in FEV1 . These

commenters made the point that the

responses of individuals are more

important than group mean responses

and that when the Adams (2002, 2006)

study data are corrected for the effects

of exercise in clean air, 7 percent of

subjects experience FEV1 decrements

greater than 10% at the 0.040 and 0.060

ppm exposure levels. They expressed

the view that while 2 of 30 tested

subjects responding at the 0.060 ppm

level may seem like a small number, a

7 percent response rate is far from

trivial. Seven percent of the U.S.

population is 21.2 million people (ALAet al., p. 51). Noting that the subjects in

the Adams' studies were all healthy

adults, these groups expressed concern

that "in some vulnerable populations

the magnitude-of the response would be

greater and the exposure level at which

responses are observed to occur would

be lower" (ATS, p. 4).

These commenters generally

supported EPA's reanalysis of the

Adams' data, stating that EPA has

undertaken a careful reanalysis of the

underlying data in the Adams studies to

assess the change in FEV following

exposure to 0.060.ppm 03 and filtered

air, and concluding that "the reanalysis

employs the standard approach used by

other researchers, and supported by

CASAC" (ALA et al., p. 49), and "we

believe that the Adams study shows

significant health effects at 0.06 ppm

exposure levels" (ATS, p. 5). The

American Thoracic Society, AMA and

other medical organizations conclude:

The Adams study confirms our

understanding that in healthy populations, an important fraction of the population will

experience larger-than-average decrements in

FEVI when exposed to low levels of ozone.

It is reasonable to assume that these effects

would be even greater When extrapolated to

other populations known to have sensitivities

to ozone (children, asthmatics, COPD

patients). We feel the correct conclusion to

draw from the Adams study is that there is a significant fraction of the population that

will express significant responses to low

levels of ozone. [ATS, p. 5]

EPA generally agrees with most of the

comments summarized above, while

placing more emphasis on the limited

nature of the evidence addressing 03-

related lung function and respiratory

symptom responses at the 0.060 and

0.040 ppm exposure levels. As

characterized in the proposal notice,

EPA's reanalysis of the data from the

most recent Adams study shows small

group mean decrements in lung

function responses to be statistically

significant at the 0.060 ppm exposure

level, while acknowledging that the

author's analysis did not yield *

statistically significant lung function

responses. The Adams studies report a

small percentage of subjects

experiencing lung function decrements

(>10 percent) at the 0.060 ppm exposure

level. EPA disagrees with these

commenters that the percent of subjects

that experienced FEVI decrements

greater than 10% in this study of 30

subjects can appropriately be

generalized to the U.S. population. The

Administrator concludes that these

studies provide very limited evidence of

0 3-related lung function decrements

and respiratory symptoms at this lower

exposure level.

The second group of commenters,

who opposed revision of the standard,

raised many concerns about the role of

the Adams studies and EPA's reanalysis

of the Adams data in the decision. With

regard to the results reported by Adams,

these commenters expressed the view

that the group mean FEV decrement

measured at 0.060 ppm was small, less

than 3%, which is within the 3 to 5%

range of normal measurement variability

for an individual (UARG, p. 12).

Moreover even the reported group mean

FEVI decrements in Adams subjects

when exposed to an 03 concentration of

0.080 ppm were described as quite

minimal, likely non-detectable by the

subjects and within the range that the

EPA would consider to be normal or

mild (UARG, p. 13); With respect to the

larger decrements in FEV (>_ 10%)

experienced by some subjects in the

Adams studies, these commenters stated

the view that such decrements would

not be considered adverse in healthy

individuals, and that "reliance on the

individual responses of such a

miniscule number of subjects (2 of 30)

is woefully inadequate as any basis for

a nationwide 03 standard" (UARG,

p.14). Some of these commenters put

the results of the Adams studies (2002,

2006) in the context of the 1997

decision on the 03 standard to reach the

conclusion that there is no basis for

revising that standard. They stated that

the data from Adams (2002, 2006) on 03

levels below 0.080 ppm was too limited

-to support a revised standard, and noted

that responses reported in the Adams

studies at 0.080 ppm were similar to

responses reported previously

(Horstmann et al., 1990 and McDonnell

et al., 1991), and therefore, provided no

new information on 03 that was not

known at the tirfle of EPA's last review

(Exxon Mobil, pp. 5-6).

These commenters raised one or more

of the following concerns about EPA's

reanalysis of the Adams data: (1) EPA's

re-analysis was not published or peerreviewed, and therefore neither the

scientific community nor the public was

afforded opportunity to appropriately

review the analysis (Exxon Mobil, p. 6);

(2) EPA has misinterpreted the studies

of Dr. Adams, and over his objections

used a different analytical methodology

to reach a different conclusion; (3)

EPA's reanalysis did not employ an

appropriate statistical test; the ANOVA

statistical test employed by Adams was

preferred over the statistical test used in

EPA's reanalysis (paired t-test); and (4)

the reanalysis of the Adams data is

evidence that EPA interpreted and

presented scientific information in a

systematically biased manner, reflecting

purposeful bias because the reanalysis

supported staff policy recommendations

and Adams' own analysis did not, and

the 10% decrement in FEV1 was a posthoc threshold chosen for compatibility

with EPA staff policy recommendations

(NAM, p. 19).

First, EPA agrees that the group mean

lung fuiction decrement observed in the

Adams study at the 0.060 ppm exposure

level is relatively small. However, EPA

and the CASAC Panel observed that the

study showed some individuals

experienced lung function decrements

10 percent, which is the most

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important finding from this study in

terms of public health implications. The

magnitude of changes in the group mean

do not address whether a subset of the

population is at risk of health effects.

The clinical evidence to date makes it

clear that there is significant variability

in responses across individuals, so it is

important to look beyond group mean to

the response of subsets of the group to

evaluate the potential impact for

sensitive or susceptible parts of the

population. The Administrator also

agrees with both EPA staff and CASAC's

views that this level of response may

not represent an adverse health effect in

healthy individuals but does represent a

level that should be considered adverse

for asthmatic individuals.

Second, EPA notes that its reanalysis

of the Adams (2006) study was prepared

in response to the issues and analysis

raised by a public commenter who made

a presentation to the CASAC Panel at its

March 5, 2007 teleconference. EPA

replicated the analysis and addressed

issues raised in these public comments

concerning the statistical significance of

0.060 ppm 03 exposure on lung

function response in the Adams (2006)

publication. EPA documented its

response in a technical memorandum

(Brown, 2007), which was placed in the

rulemaking docket prior to publication"

of the proposal. EPA has clearly stated

that the additional statistical analyses

conducted by both the public

commenter and by EPA staff do not

contradict or undercut the statistical

analysis presented by Dr. Adams in his

published study, as EPA and the author

were addressing different questions.

While the author of the original study

was focused on determining whether

the changes observed on an hour-byhour basis were statistically significant

for different exposure protocols, EPA's

reanalysis was focused on the different

question of whether there was a

statistically significant difference in

lung function decrement before and

after the entire 6.6 hour exposure period

between the 0.060 ppm exposure

protocol and filtered air.

Third, with respect to the concerns

raised by Dr. Adams and other

commenters that EPA had used an

inappropriate statistical approach to

address the question regarding

statistical significance of the average

lung function response at 0.060 ppm,

members of the CASAC Panel noted on

the March 5, 2007 teleconference the

very conservative nature of the

approach used by Adams to evaluate the

research questions posed by the author.

These same CASAC Panel members also

supported the use of the statistical

approach (i.e., paired-t test) used in the

analysis prepared by the public

commenter, which was the same

approach later used in EPA's reanalysis,

as the preferred method for analyzing

the pre-minus post-exposure lung

function responses reported in this

study. EPA agrees with the

characterization of the Adams (2006)

study in the Rochester Report, which

stated, "Although these findings have

not been confirmed or replicated, the

responses to 0.06 ppm ozone in this

[Adams] study are consistent with the

presence of an exposure-response curve

with responses that do not end abruptly

below 0.08 ppm." This same report also

concluded,

The statistical test used in Adams (2006)

did not identify the response of the 0.06 ppm

exposure as statistically different from that of

the filtered air exposure. However,

alternative statistical tests suggest that the

observed small group mean response in FEVI

induced by exposure to 0.06 ppm compared

to filtered air is not the result, of chance

alone. [Rochester Report, p. 561.

Fourth, EPA rejects the contention

that the conduct and presentation of its

reanalysis of the Adams (2006) study to

address issues raised by public .

commenters represents purposeful bias

and was developed only to support a

pre-determined policy position. As

discussed above, EPA's reanalysis

addressed a different question than the

author's analysis contained in the

publication. Other controlled human

exposure studies had routinely

examined the same question EPA's

reanalysis addressed, whether or not

there was a statistically significant

group mean response for the entire "

exposure period compared to filtered

air.

ii Evidence from Epidemiological

Studies

This section contains major comments

on EPA's assessment of epidemiological

studies in the proposal and the Agency's

geneial responses to those comments.

Many of the issues discussed below are

addressed in more detail in the

Response to Comments document.

Comments on EPA's interpretation and

assessment of the body of

epidemiological evidence are discussed

first and then comments on

methodological issues and particular

study designs are discussed. EPA notes

here that most of the issues and

concerns raised by commenters on the

interpretation of the epidemiological

evidence and methodological issues are

essentially restatements of issues raised

during the review of the Criteria

Document and Staff Paper. EPA

presented and the CASAC Panel

reviewed the interpretation of the

epidemiological evidence in the Criteria

Document and the integration of the

evidence with policy considerations in

the development of the policy options

presented in the Staff Paper for

consideration by the Administrator.

CASAC reviewed both the 03 Criteria

Document and 03 Staff Paper and

approved of the scientific content and

accuracy of both documents. The

CASAC chairman sent to the

Administrator one letter (Henderson,

2006a) for the 03 Criteria Document and

another letter for the 03 Staff Paper

(Henderson, 2006cl indicating that these

documents provided an appropriate

basis for use in regulatory decision

making regarding the 03 NAAQS.

As with evidence from controlled

human exposure studies, sharply

divergent comments were received on

the evidence from epidemiological

studies, including EPA's interpretation

of the evidence. One group of

commenters from medical, public health

and environmental organizations, in

general, supported EPA's interpretation

of the epidemiological evidence (72 FR

37838, section II.a.3.a-c) with regard to

whether the evidence for associations is

consistent and coherent and whethei

there is biological plausibility for

judging whether exposure to 03 is

causally related to respiratory and

cardiovascular morbidity and mortality

effects. Comments of public health and

environmental groups, including a joint

set of comments from ALA and several

environmental groups, note that more

than 250 new epidemiological studies,

published from 1996 to 2005, were

included in the Criteria Document and

point to:a figure from the Staff Paper

and proposal (72 FR 37842, Figure 1) of

short-term 03 exposures and respiratory

health outcome showing consistency in

an array of positive effects estimates and

health endpoints observed in multiple

locations in Canada and the U.S.

Medical commenters, including ATS

and AMA, stated that these "real world"

studies support the findings of chamber

studies to show adverse respiratory

health effects at levels below the current

8-hour 03 standard. These commenters

generally expressed agreement with the

weight of evidence approach taken by

the Criteria Document and the

conclusions reached, which were

reviewed by CASAC, that the effects of

03 on respiratory symptoms, lung

function changes, emergency

department visits for respiratory and

cardiovascular effects, and hospital

admissions can be considered causal.

EPA generally agrees with this

interpretation of the epidemiological

evidence. The Criteria Document

concludesthat positive and robust

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associations were found between

ambient 03 concentrations and various

respiratory disease hospitalization

outcomes and emergency department

visits for asthma, when focusing

particularly on results of warm-season

analyses. These positive and robust

associations are supported by the

human clinical, animal toxicological,

and epidemiological evidence for lung

function decrements, increased

respiratory symptoms, airway

inflammation, and increased airway

responsiveness. Taken together, the

overall evidence supports a causal

relationship between acute ambient 03

exposures and increased respiratory

morbidity outcomes resulting in

increased emergency department visits

and hospitalizations during the warm

season (EPA, 2006a, p. 8-77).

However, in contrast with EPA, these

commenters from ALA and other

environmental, medical and public

health groups asserted that the causal

associations extend down to the lowest

ambient 03 concentrations reported in

these studies. These commenters also

expressed the view that the respiratory

and cardiovascular system effects are

well-supported by the Hill criteria'9 of

judging causality: strength of

association, consistency between

studies, coherence among studies, and

biological plausibility (ALA et al., pp.

51-52). They also noted that recent

studies provide compelling evidence

that exposure to 03 results in adverse

cardiovascular health effects (ATS,

p. 6-7).

EPA disagrees with the assertion of

these commenters that the causal

associations extend down to the lowest

ambient 03 concentrations reported in

these studies. The biological plausibility

of the epidemiological associations is

generally supported by controlled

human exposure and toxicological

evidence of respiratory morbidity effects

for levels at and below O.080ppm, but

that biological plausibility becomes

increasingly uncertain at much lower

levels. Further, at much lower levels, it

becomes increasingly uncertain as to

whether the reported associations are

related to 03 alone rather than to the

broader mix of air pollutants present in

the ambient air. With regard to

cardiovascular health outcomes, the

Criteria Document concludes that the

generally limited body of evidence from

animal toxicology, human controlled

1

9 The Hill criteria, published by Sir Bradford Hill

(1965), are commonly used criteria for reaching

judgments about causality from observed

associations, and these criteria were the basis for

the critical assessment of the epidemiological

evidence presented in the Criteria Document (pp.

7-3-7-4).

exposure, and epidemiologic studies is

suggestive that 03 can directly and/or

indirectly contribute to cardiovascular

related morbidity, and that for

cardiovascular mortality the Criteria

Document suggests that effects estimates

are more consistently positive and

statistically significant in warm season

analyses but that additional research is

needed to more fully establish the

underlying mechanisms by which such

mortality effects occur (EPA, 2006a, pp.

8-77-78).

The second group of commenters,

mostly representing industry

associations and some businesses

opposed to revising the primary 03

standard, disagreed with EPA's

interpretation of the epidemiological

evidence. These commenters expressed

the view that while many new

epidemiological studies have been

published since the current primary 03

standard was promulgated, the

inconsistencies and uncertainties

inherent in these studies as a whole

should preclude any reliance on them as

justification for a more stringent

primary 03 NAAQS. They contend that

the purported consistency is the result

of inappropriate selectivity in focusing

on specific studies and specific results

within those studies (UARG, p. 15).

With regard to daily mortality, the

proposal emphasizes the multi-city

studies, suggesting that they have the

statistical power to allow the authors to

reliably distinguish even weak

relationships from the null hypothesis

with statistical confidence. However,

these commenters note that these

studies are not consistent, with regard to

the findings concerning individual

cities analyzed in the multi-city

analyses. One commenter asserted that

each of the multi-city studies and metaanalyses cited by EPA involves cities for'

which the city-specific estimates of 03

effects have been observed to vary over

a wide range that includes negative [i.e.,

beneficial] effects (API, p. 15). To

illustrate this point, many commenters

point to EPA's use of the study by Bell

et a., 2004. They note that in focusing

on the national estimate from Bell of the

association between 24-hour average 03

levels and daily mortality, the

Administrator overlooks the very

significant and heterogeneous

information of the individual analyses

of the 95 cities used to produce the

national estimate and, based on this

inconsistency, question whether what is

being seen is actually an 03 mortality

association at all (UARG, p. 16).

EPA has accurately characterized the

inconsistencies and uncertainties in the

epidemiological evidence and strongly

denies that it has inappropriately

focused on specific positive studies or

specific positive results within those

studies. EPA's assessment of the health

effects evidence in the Criteria

Document has been reviewed by the

CASAC Panel. EPA has appropriately

characterized the heterogeneity in 03

health effects in assessing the results of

the single-city and multi-city studies

and the meta-analyses, as discussed in

section 7.6.6 of the Criteria Document.

In general, in the proposal, the

Administrator recognized that in the

body of epidemiological evidence, many

studies reported positive and

statistically significant associations,

while others reported positive results

that were not statistically significant,

and a few did not report any positive

0 3-related associations. In addition, the

Administrator judged that evidence of a

causal relationship between adverse

health outcomes and 03 exposures

became increasingly uncertain at lower

levels of exposure.

More specifically, the Bell et al.

(2004) study observed a statistically

significant, positive association between

short-term 03 concentrations (24-hour

average) and all-cause mortality using

data from 95 U.S. National Morbidity,

Mortality, and Air Pollution Study

(NMMAPS) communities. The objective

df the NMMAPS was to develop an

overall national effect estimate using

multi-city time-series analyses, by

drawing on information from all of the

individual cities. The strength of this

approach is the use of a uniform

analytic methodology, avoidance of

selection bias, and larger statistical

power. Significant intercity

heterogeneity was noted in the Bell et

al. and other multi-city studies,

probably due to many factors, including

city-specific differences in pollution

characteristics, the use of air

conditioning, time spent indoors versus

outdoors, and socioeconomic factors.

Levy et al. (2005) found suggestive

evidence that air conditioning

prevalence was a predictor of

heterogeneity in 03 risk estimates in

their meta-analysis.

Several commenters argued that EPA

overstates the probability of causal links

between health effects and exposure to

03, especially at the lower

concentrations examined, and that the

statistical associations found in the

cited epidemiological studies do not

automatically imply that a causal

relationship exists. These commenters

expressed the view that the correlation

between health effects and 03 exposure

must be rigorously evaluated according

to a standard set of criteria before

concluding that there is a causal link

and that EPA fails to articulate and

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follow the weight of the evidence or established causality criteria for

evaluating epidemiological studies in

drawing conclusion regarding causality

(Exxon Mobil, pp. 10-11).

In the proposal, EPA explicitly stated

that epidemiological studies are not

themselves direct evidence of a causal

link between exposure to 03 and the

occurrence of effects (72 FR 37879).

Throughout the 03 review, a standard

set of criteria have been used to evaluate

evidence of a causal link. The critical

assessment of epidemiological evidence

presented in the Criteria Document was

conceptually based upon consideration

of salient aspects of the evidence of

associations so as to reach fundamental

judgments as to the likely causal

significance of the observed associations

in accordance with the Hill criteria

(Criteria Document, pp. 7-3-7-4).

Moreover, consistent with the proposal

-the Administrator has specifically

considered evidence from

epidemiological studies in the context

of all the other available evidence in

evaluating the degree of certainty that

0 3-related adverse health effects occur at various levels at and below 0.080

ppm, including the strong evidence

from controlled human exposure studies

and the toxicological studies that

demonstrate biological plausibility and

mechanisms for effects. More detailed

discussion of the criteria used to

evaluate evidence with regard to

judgments about causality can be found

in the Response to Comments

document.

Several commenters made the point

that the results of the new

epidemiological studies included in this

review are not coherent. They state that

although EPA notes that estimates of

risk from cardiovascular mortality are,

higher than those for total mortality and

indicates that these findings are highly

suggestive that short-term 03 exposure

directly or indirectly contributes to

cardiovascular mortality, the Agency

fails to contrast the mortality studies to

studies of hospital admissions for

cardiovascular causes. Most studies of

cardiovascular causes have not found

statistically significant associations with

03 exposures (UARG, pp. 16-17).

EPA strongly disagrees that it has

failed to appropriately characterize the

association between 03 exposure and

potential cardiovascular morbidity and

mortality effects. As noted above, the

Criteria Document characterizes the

overall body of evidence as limited, but

highly suggestive, and concludes that

much needs to be done to more fully

integrate links between ambient 03

-exposures and adverse cardiovascular

outcomes (EPA, 2006a, p. 8-77). Some

field/panel studies that examined

associations between 03 and various

cardiac physiologic endpoints have

yielded limited epidemiological

evidence suggestive of a potential

association between acute 03 exposure

and altered HRV, ventricular

arrhythmias, and incidence of

myocardial infarction (Criteria

Document, section 7.2.7). In addition,

there were approximately 20 single-city

studies of emergency department visits

and hospital admissions for all

cardiovascular diseases or specific

diseases (i.e., myocardial infarction,

congestive heart failure, ischemic heart

disease, dysrhythmias). In the studies

using all year data, many showed

positive results but few were

statistically significant. Given the strong

seasonal variations in 03 concentrations

and the changing relationship between

03 and other copollutants by season,

inadequate adjustment for seasonal

effects might have masked or underestimated the associations. In the

limited number of studies that analyzed

data by season (6 studies), statistically

significant associations were observed

in all but one study (Criteria Document,

section 7.3.4). Newly available animal

toxicology data provide some

plausibility for the observed

associations between 03 and

cardiovascular outcomes. EPA believes

that its characterization of the evidence

for 0 3-related cardiovascular system

effects is appropriate. It is clear that

coherence is stronger in the much larger

body of evidence of 0 3-related

respiratory morbidity and mortality

effects.

Many commenters who did not

support revising the current 03 primary

standard also submitted comments on

specific methodological issues related to

the epidemiological evidence,

including: The adequacy of exposure

data; confounding by copollutants;

model selection; evidence of mortality;

and, new studies not included in the

Criteria Document. Some of the major

comments on methodological issues

raised by these commenters are

discussed below. The Response to

Comments document contains more

detailed responses to many of these

comments, as well as responses to other

comments not considered here.

(1) Adequacy of exposure data. Many

commenters expressed concern about '

the adequacy of exposure data both for

time-series and panel studies. These

commenters argued that almost all of

the epidemiological studies on which

EPA relies in recommending a more

stringent 03 standard are based on data

from ambient monitors for which there

is a poor correlation with the actual

pers.onal exposure subjects receive

during their daily activities. They

questioned the Administrator's

conclusion'that in the absence of

available data on personal 03 exposure,

the use of routinely monitored ambient

03 concentrations as a surrogate for

personal exposures is not generally

expected to change the principal

conclusions from epidemiological

studies. These commenters also note

that, in its June 2006 letter, the CASAC

Panel raised the issue of exposure error,

concluding that it called into question

whether observed associations could be

attributed to 03 alone (AP5I, p. 17). One

of these commenters cited studies (e.g.,

Sarnat et al., 2001; Sarnat et al., 2005)

that show a lack of correlation between

personal exposures and ambient

concentrations (NAM, p. 22). Another

cited studies (Sarnat et al., 2001, 2005,

and 2006; and Koutrakis et al., 2005)

that have found that the ability of

ambient gas monitors to represent

personal exposure to such gases is

similarly quite limited, including: (1)

Most personal exposures are so low as

to be not detectable at a level of 5 parts

per billion (ppb), resulting in very low

correlation between concentrations

reported from central ambient monitors

and personal monitors; (2) 03

measurements from ambient monitors

are a better surrogate for personal

exposure to PM2.5 than to 03; and (3)

populations expected to be potentially

susceptible to 03, including children,

the elderly, and those with COPD, are at

the. low end of the population exposure

distribution (Exxon Mobil, pp. 15-16).

These commenters contended that

without such a correlation there is no

legitimate way for EPA to conclude that

03 exposure has caused the reported

health effects, or to conclude that use of

routinely monitored ambient 03

concentrations as a surrogate for -

personal exposures is adequate. Some of

these commenters also contended that

EPA incorrectly concludes that the

exposure error in epidemiological

studies results in an underestimate of

risk (Exxon Mobil, p. 20).

With regard to the views on exposure

measurement error expressed by

CASAC, while the commenter is correct

that the CASAC Panel raised the

question of exposure error and whether

observed associations could be

attributed to 03 alone, the commenter

failed to note that CASAC's comment

was focused on the association between

03 and mortality, at very low 03

concentrations and in the group of

people most susceptible to premature

mortality. The CASAC Panel in its June

2006 letter stated:

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The population that would be expected to

be potentially susceptible to dying from

exposure to ozone is likely to have ozone exposures that are at the lower end of the ozone population distribution, in which case the population would be exposed to very low ozone concentrations, and especially so in

winter. Therefore it seems unlikely that the

observed associations between short-term ozone concentrations and daily mortality are

due solely to ozone itself. [Henderson 2006b,

pp. 3-41

This section of the quote, which was

not addressed in the comment

submitted by API, together with the

conclusions in the final CASAC letter

(Henderson, 2007), leads EPA to

conclude that contrary to the

commenters' assertion, the CASAC

Panel was not calling into question the

association between 03 exposure and

the full range of morbidity effects found

in panel or time-series studies that rely

on ambient monitoring data as a

surrogate for personal exposure data. It

is important to note that EPA agrees that

the evidence is only highly suggestive

that 03 directly or indirectly contributes

to mortality, as compared to the stronger

evidence of causality for respiratory

morbidity effects.

EPA agrees that exposure

measurement error may result from the

use of stationary ambient monitors as an

indicator of personal exposure in

population studies. There is a full

discussion of measurement error and its

effect on the estimates of relative risk in

section 7.1.3.1 of the Criteria Document.

However, the possibility of

measurement error does not preclude

the use of ambient monitoring data as a

surrogate for personal exposure data in

time-series or panel studies. It simply

means that in some situations where the

likelihood of measurement error is

greatest, effects estimates must be

evaluated carefully and that caution

must be used in interpreting the results

from these studies. Throughout this

review, EPA has recognized this

concern. The Criteria Document states

that there is supportive evidence that

ambient 03 concentrations from. central

monitors may serve as valid surrogate

measures for mean personal 03

exposures experienced by the

population, which is of most relevance

to time-series studies, in which

individual variations in factors affecting

exposure tend to average out across the

study population. This is especially true

for respiratory hospital admission

studies for which much of the response

is attributable to 03 effects on

asthmatics. In children, for whom

asthma is more prevalent than for

adults, ambient monitors are more likely

to correlate reasonably well with

personal exposure to 03 of ambient

origin because children tend to spend

more time outdoors than adults in the

warm season. EPA does not agree that

the correlation between personal

exposure and ambient monitoring data

is necessarily poor, especially in

children. Moreover, the CASAC Panel

supported this view as they noted that

"[plersonal exposures most likely

correlate better with central site values

for those subpopulations that spend a

good deal of time outdoors, which

coincides, for example, with children

actively engaged in outdoor activities,

and which happens to be a group that

the ozone risk assessment focuses

upon." (Henderson, 2006c. p. 10).

However, the Criteria Document notes

that there is some concern in

considering certain mortality and

hospitalization time-series studies

regarding the extent to which ambient

03 concentrations are representative of

personal 03 exposures in another

particularly susceptible group of

individuals, the debilitated elderly, as

the correlation between the two

measurements has not been examined in

this population. A better understanding

of the relationship between ambient

concentrations and personal exposures,

as well as of the factors that affect the

-relationship, will improve the

interpretation of observed associations

between ambient concentration and

population health response.

With regard to the specific comments

that reference the findings of studies by

Sarnat et a. (2001, 2005, 2006) and

Koutrakis et a]. (2005), the fact that

personal exposure monitors cannot

detect 03 levels of 5 ppb and below may

in part explain why there was a poor

correlation between personal exposure

measurements and ambient monitoring

data in the winter relative to the

correlation in the warm season, along

with differences in activity patterns and

building ventilation. In one study

conducted in Baltimore, Sarnat et a].

(2001) observed that ambient 03

concentrations showed stronger

associations with personal exposure to

PM2.

5 than to 03; however, in a later

study conducted in Boston (Sarnat et al.,

2005), ambient 03 concentrations and

personal 03 exposures were found to be

significantly associated in the summer.

Another study cited by the commenter,

but not included in the Criteria "

Document, conducted in Steubenville

(Sarnat et aL., 2006), also observed

significant associations between

ambient 03 concentrations and personal

03. The authors noted that the cityspecific discrepancy in the results may

be attributable to differences in

ventilation. Though the studies by

Sarnat et al. (2001, 2005, and 2006)

included senior citizens, the study

selection criteria required them to be

nonsmoking and physically healthy.

EPA is not relying on studies that are

not in the Criteria Document, such as

Sarnat et al. (2006), to refute the

commenters. However, EPA notes that

Sarnat et al. (2006) does not support the

conclusion drawn by the commenters

that this study shows very limited

associations between ambient 03

concentrations and personal exposures.

Existing epidemiologic models may

not fully take into consideration all the

biologically relevant exposure history or

reflect the complexities of all the

underlying biological processes. Using

ambient concentrations to determine

exposure generally overestimates true

personal 03 exposures (by

approximately 2- to 4-fold in the various

studies described in the Criteria

Document, section 3.9), which assuming

the relationship is causal, would result

in biased descriptions of underlying

concentration-response relationships

(i.e., in attenuated effect estimates).

From this perspective, the implication is

that the effects being estimated in

relationship to ambient levels occur at

fairly low personal exposures and the

potency of 03 is greater than these effect

estimates indicate. On the other hand,

as very few studies evaluating 03 health

effects with personal 03 exposure

measurements exist in the literature,

effect estimates determined from

ambient 03 concentrations must be

evaluated and used with caution to

assess the health risks of 03 (Criteria

Document, pp. 7-8 to 7-10).

Nonetheless, as noted in section II.C.3 of

the proposal, the use of routinely

monitored ambient 03 concentrations as

a surrogate for personal exposures is not

generally expected to change the

principal conclusions from 03

epidemiologic studies. Therefore,

population risk estimates derived using

ambient 03 concentrations from

currently available observational

studies, with appropriate caveats about

personal exposure considerations,

remain useful (72 FR 37839).

(2) Confounding by copollutants.

Many commenters argued that known

confounders are inadequately controlled

in the epidemiological studies of 03 and

various health outcomes and that the

health effects of 03 are often not

statistically significant when

epidemiological studies consider the

effects of confounding air pollutants

(e.g., PM2.

5 , CO, nitrogen dioxide (NO2)

in multi-pollutant models. For example,

Mortimer et al. (2002), a large multi-city.

asthma panel study, found that when

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other pollutants; i.e., sulfur dioxide

(SO 2), NO2, and particles with an

aerodynamic diameter less than or equal

to a nominal 10 micrometers (PM10),

were placed in a multi-pollutant model

with 03, the O3-related associations

with respiratory symptoms and lung

function became non-significant.

The National Cooperative Inner-City

Asthma Study (Mortimer et al., 2002)

evaluated air pollution health effects in

846 asthmatic children in 8 urban areas.

The pollutants evaluated included 03,

PM1 0 , SO 2, and NO2. Three effects were

evaluated: (1) Daily percent change in

lung function, measured as peak

expiratory flow rate (PEFR); (2)

incidence of ( 10% reduction in lung

function (PEFR); and, (3) incidence of

symptoms (i.e., cough, chest tightness,

and wheeze). EPA notes that in this

study, 03 was the only pollutant

associated with reduction in lung

function. Nitrogen dioxide had the

strongest effect on morning symptoms,

and the authors concluded it "* * *

may be a better marker for the summerpollutant mix in these cities" but had no

association with morning lung function.

In a two-pollutant model with NO2, the

03 effect on morning symptoms

remained relatively unchanged. Sulfur

dioxide had statistically significant

effects on morning symptoms but no

association with morning lung function.

Particulate matter (PM1o), which was

measured daily in 3 cities, had no

statistically significant effect on

morning lung function. In a twopollutant model with 03, the PM1 o

estimate for morning symptoms was

slightly reduced and there was a larger

reduction in the 03 estimate, which

remained positive but not statistically

significant. A more general discussion

and response to this issue concerning

confounding by copollutants is

presented in the Response to Comments

document.

(3) Model selection. Commenters who

did not support revision of the primary

03 standard raised issues.regarding the

adequacy of model specification

including control of temporal and

weather variables in the time-series

epidemiological studies that EPA has

claimed support the finding of O3-

related morbidity and mortality health

outcomes. Specifically, concerns were

expressed regarding the following

issues: (i) Commenters noted that recent

meta-analyses have confirmed the

important effects of model selection in

the results of the time-series studies,

including the choice of models to

address weather and the degree of

smoothing, in direct contradiction of the

Staff Paper's conclusion on the

robustness of the models used in the 03

time-series studies (Exxon Mobil, p. 41);

(ii) commenters contended that therewere no criteria for how confounders

such as temperature or other factors

were to be addressed, resulting in

arbitrary model selection potentially

impacting the resulting effect estimates;

and (iii) commenters expressed the view

that to appropriately address concerns

about model selection in the 03 timeseries studies, EPA should rely on an

alternative statistical approach,

Bayesian model averaging, that

incorporates a range of models

addressing confounding variables,

pollutants, and lags rather than a single

model.

In response to the first issue, EPA

agrees that the results of the metaanalyses do support the conclusion that

there are important effects of model

selection and that, for example,

alternative models to address weather.

might make a difference of a factor of

two in the effect estimates. However, as

noted in the Criteria Document, one of

the meta-analyses (Ito et a., 2005)

suggested that the stringent weather

model used in the Bell et a]. (2004)

NMMAPS study may tend to yield

smaller effect estimates than those used

in other studies (Criteria Document, p.

7-96), and, thus concerns about

appropriate choice of models could

result in either higher or lower effect

estimates than reported. In addressing

this issue, the Criteria Document

concluded,

Considering the wide variability in

possible study designs and statistical model

specification choices, the reported 03 risk

estimates for the various health outcomes are in reasonably good agreement. In the case of

0 3-mortality time-series studies,

combinations of choices in model

specifications * * * alone may explain the

extent of difference in 03 risk estimates

across studies. (Criteria Document, p. 7-174)

Second, the issues surrounding

sensitivity to model specifications were

thoroughly discussed in the Criteria

Document (see section 7.1.3.6) and

evaluated in some of the meta-analyses

reviewed in the Criteria Document and

Staff Paper. As stated in the Criteria

Document, 03 effect estimates "were

generally more sensitive to alternative

weather models than to varying degrees

of freedom for temporal trend

adjustment" (Criteria Document, p. 7-

176). The Criteria Document also

concluded that "although there is some

concern regarding the use of

multipollutant models * * * results

generally suggest that the inclusion of

copollutants into the models do not

substantially affect 03 risk estimates"

and the results of the time-series studies

are "robust and independent of the

effects of other copollutants" (Criteria

Document, p. 7-177). Overall, EPA

continues to believe that based on its

integrated assessment, the time-series

studies provide strong support for'

concluding there are 03 -related

morbidity effects, including respiratoryrelated hospital admissions and

emergency department visits during the

warm season, and that the time-series

studies provide findings that are highly

suggestive that short-term 03 exposure

directly or indirectly contributes to nonaccidental and cardiorespiratory-related

mortality.

The Administrator acknowledges that

uncertainties concerning appropriate

model selection are an important source

of uncertainty affecting the specific risk

estimates included in EPA's risk

assessment and that these quantitative

risk estimates must be used with

appropriate caution, keeping in mind

these important uncertainties, as

discussed above in section ll.A.3. As

discussed later in this notice, the

Administrator is not relying on any

specific quantitative effect estimates

from the time-series studies or any risk

estimates based on the time-series

studies in reaching his judgment about

the need to revise the current 8-hour 03,

standard.

Third, in response to commenters

who suggested that EPA adopt an

alternative statistical approach, i.e.,

Bayesian model averaging, to address

concerns about potential arbitrary

selection of models, the Criteria

Document evaluated the strengths and

weaknesses of such methods in the

context of air pollutionepidemiology.

The Criteria Document noted several

limitations, especially where there are

many interaction terms and

meteorological variables and where

variables are highly correlated, as is the

case for air pollution studies, which

makes it very difficult to interpret the

results using this alternative approach.

EPA believes further research is needed

to address concerns about model

selection and to develop appropriate

methods addressing these concerns.

(4) Evidence of mortality. Many

commenters, including those that

argued for revising the current 03

standard as well as those that argued

against revisions, focused on the new

evidence from multi-city time-series

analyses and meta-analyses linking 03

exposure with mortality. Again, the

comments were highly polarized. One

set of commenters, including medical,

public health, and environmental

organizations argued that recent

published research has provided more

robust, consistent evidence.linking 03 to

cardiovascular and respiratory

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mortality. The ATS, AMA, and others

stated that data from single-city studies,

multiple-city studies, and meta-analyses

show a consistent relationship between

03 exposure and mortality from

respiratory and cardiovascular causes.

These commenters noted that this effect

was observed after controlling for copollutants and seasonal impacts. These

commenters stated that research has

demonstrated that exposure to 03

pollution is causing premature deaths,

and has also provided clues on the

possible mechanisms that lead to

premature mortality (ATS, p. 4). These

commenters noted that people may die

from 03 exposure even when the

concentrations are well below the

current standard. They pointed to a

study (Bell et al., 2006) in which the

authors followed up on their 2004

multi-city study to estimate the

exposure-response curve for 03 and the

risk of mortality and to evaluate

whether a threshold exists below which

there is no effect. The authors applied

several statistical models to data on air

pollution, weather, and mortality for 98

U.S. urban communities for the period

1987 to 2000. The study reported that

03 and mortality results did not appear

to be confounded by temperature or PM

and showed that any threshold, if it

existed, would have to be at very low

concentrations, far below the current

standard (ALA et al., p. 74). Another

approach also indicated that the

mortality effect is unlikely to be

confounded by temperature. A casecrossover study (Schwartz 2005) of over

one million deaths in 14 U.S. cities,

designed to control for the effect of

temperature on daily deaths attributable

to 03, found that the association

between 03 and mortality risk reported

in the multi-city studies is unlikely to

be due to confounding by temperature

(ALA et al., p. 76). These commenters

argue that meta-analyses also provide

compelling evidence that the 03-

mortality findings are consistent. They

point to three independent analyses

conducted by separate research groups

at Johns Hopkins University, Harvard

University and New York University,

using their own methods and study

criteria, which reported a remarkably

consistent link between daily 03 levels

and total mortality.

In response, EPA notes that the

Criteria Document states that the results

from the U.S. multi-city time-series

studies provide the strongest evidence

to date for 03 effects on acute mortality.

Recent meta-analyses also indicate

positive risk estimates that are unlikely

to be confounded by PM; however,

future work is needed to better

understand the influence of model

specifications on the risk coefficient

(EPA; 2006a, p. 7-175). The Criteria

Document concludes that these findings

are highly suggestive that short-term 03

exposure directly or indirectly

contributes to non-accidental and

cardiorespiratory-related mortality but

that additional research is needed to

more fully establish the underlying

mechanisms by which such effects

occur (72 FR 37836). Thus while EPA

generally agrees with the direction of

the comment, EPA believes the evidence

supports a view as noted above. In

addition, it must be noted that the

Administrator did not focus on

mortality as a basis for proposing that

the current 03 standard was not

adequate..In the proposal, the

Administrator focused on the very

strong evidence of respiratory morbidity

effects in healthy people at the 0.080

ppm exposure level and new evidence

that people with asthma are likely to

experience larger and -more serious

effects than healthy people at the same

level of exposure (72 FR 37870). With

regard to the ambient concentrations at

which 0 3-related mortality-effects may

be occurring, EPA recognized in the

proposal that evidence of a causal

relationship between adverse health

effects and 03 exposures becomes

increasingly uncertain at lower levels of

exposure (72 FR 37880). This is

discussed more fully in section (b)

below.

Several industry organizations argued

against placing any reliance on the timeseries epidemiological studies,

especially those studies related to

mortality effects. The Annapolis Center

(p. 46) makes the point that although

there may be somewhat more positive

associations than negative associations,

there is so much noise or variability in

the data that identifying which positive

associations may be real health effects

and which are not is beyond the

capability of current methods. They cite

the view that the CASAC Panel

expressed in a June 2006 letter

(Henderson, 2006b), noting that

"Because results of time-series studies

implicate all of the criteria pollutants,

findings of mortality time-series studies

do not seem to allow us to confidently

attribute observed effects specifically to

individual pollutants."

Because of the importance of the 03

mortality multi-city studies in EPA's

analysis of this issue, several of these

commenters focused on them in

particular, arguing that, although these

studies have the statistical power to

distinguish weak relationships between

daily 03 and mortality, they do not

provide reliable or consistent evidence

implicating 03 exposures as a cause of

mortality. Several reasons were given,

including: (a) The multi-city studies

cited by EPA involve a wide range of

city-specific effects estimates, including

some large cities that have very slight or

negligible effects (e.g., Los Angeles)

(Bell et al., 2004), thus causing several

commenters to question the relevance of

a "national" effect of 03 on mortality

and argue that a single national 03

concentration-mortality coefficient

should be used and interpreted with

caution (Rochester Report p. 4); (b) the

multi-city mortality studies did not

sufficiently account for other pollutants,

for example, Bell et al. (2004) adjusted

for PM1o but did not have the necessary

air quality data to adequately adjust for

PM25, which EPA has concluded also

causes mortality and is correlated with

03, especially in the summer months

(Annapolis Center, p. 42); and (c) these

studies contain" several findings that are

inconsistent or implausible, such as

premature mortality reported at such

low levels as to imply that 0 3-related

m6rtality is occurring at levels well

within natural background, which is not

biologically plausible (Annapolis

Center, p. 42).

Evidence supporting ai association

between short-term 03 exposure and

premature mortality is not limited to

multi-city time-series studies. Most

single-city studies show elevated risk of

total, non-accidental mortality,

cardiorespiratory, and respiratory

mortality (> 20 studies), including one

study in an area that would have met

current standard (Vedal et al., 2003).

Three large meta-analyses, which pool

data from many single-city studies to

increase statistical power, reported

statistically significant associations and

examined sources of heterogeneity in

those associations (Bell et al., 2005; Ito

et al., 2005; Levy et al. 2005). These "studies found: (1) Larger and more

significant effects in the warm season than in the cool season or all year; (2)

no strong evidence of confounding by

PM; and (3) suggestive evidence of

publication bias, but significant

associations remain even after

adjustment for the publication bias.

Moreover, EPA asserts that the

biological plausibility of the

epidemiological mortality associations

is generally supported by controlled

human exposure and toxicological

evidence of respiratory morbidity effects

for levels at and below 0.080 ppm, but

that biological plausibility becomes

increasingly uncertain especially below

0.060 ppm, the lowest level at which

effects were observed in controlled

human exposure studies. Further, at

lower levels, it becomes increasingly

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uncertain as to whether the reported

associations are related to 03 alone

rather than to the broader mix of air

pollutants present in the ambient air.

EPA agrees that the multi-city times

series studies evaluated in this review

do not completely resolve this issue. It

also becomes increasingly uncertain as

to whether effect thresholds exist but

cannot be clearly discerned by statistical

analyses, Thus, when considering the

epidemiological evidence in light of the

other available information, it is

reasonable to judge that at some point

the epidemiological associations cannot

be interpreted with confidence as providing evidence that the observed

health effects can be attributed to 03

alone.

In the letter cited, the CASAC Panel

did raise the issue of the utility of timeseries studies in the standard setting

process with regard to time-series

mortality studies. Nevertheless, in a

subsequent letter to the Administrator,

CASAC noted these mortality studies as

evidence to support a recommendation

to revise the current primary 03

standard. "Several new single-city

studies and large multi-city studies

designed specifically to examine the

effects of ozone and other pollutants on

both morbidity and mortality have

provided more evidence for adverse

health effects at concentrations lower

than the current standard (Henderson,

2006c, p. 3)."

With regard to the specific issues

raised in the comments as to why the

times-series mortality studies do not

provide reliable or consistent evidence

implicating 03 exposure as a cause of

mortality, EPA has the following

responses:

(a) The purpose of the NMMAPS

approach is not to single out individual

city results but rather to estimate the

overall effect from the 95 communities.

It was designed to provide a general,

nationwide estimate. With regard to the

very slight or negligible effects estimates

for some large cities (e.g., Los Angeles),

an important factor to consider is that

the Bell et al. (2004) study used all

available data in their analyses. Bell et

al., reported that the effect estimate for

all available (including 55 cities with all

year data) and warm season (AprilOctober) analyses for the 95 U.S. cities

were similar in magnitude; however, in

most other studies, larger excess

mortality risks were reported in the

summer season (generally June-August

when 03 concentrations are the highest)

compared to all year or the cold season.

Though the effect estimate for Los

Angeles is small compared to some of

the other communities, it should be

noted that all year data (combined warm

and cool seasons) was used in the

analyses for this city, which likely

resulted in a smaller effect estimate.

Because all year data was used for Los

Angeles, the median 03 concentration

for Los Angeles is fairly low compared

to the other communities, ranked 23rd

out of 95 communities. The median 24-

hour average 03 concentration for Los

Angeles in this dataset was 22 ppb, with

a 10th percentile of 8 ppb to a 90th

percentile of 38 ppb. The importance of

seasonal differences in 0 3-related health

outcomes has been well documented.

(b) In section 7.4.6, 03 mortality risk

estimates adjusting for PM exposure, the

Criteria Document states that the main

confounders of interest for 03,

especially for the northeast U.S., are "summer haze-type" pollutants such as

acid aerosols and sulfates. Since very

few studies included these chemical

measurements, PM (especially PM2.

5)

data, may serve as surrogates. However,

due to the expected high correlation

among the constituents of the "summer

haze mix," multipollutant models

including these pollutants may result in

unstable coefficients; and, therefore,

interpretation of such results requires

some caution.

In this section, Figure 7-22 shows the

03 risk estimates with and without

adjustment for PM indices using all-year

data in studies that conducted twopollutant analyses. Approximately half

of the 03 risk estimates increased

slightly, whereas the other half

decreased slightly with the inclusion of

PM in the models. In general, the 03

mortality risk estimates were robust to

adjustment for PM in the models.

The U.S. 95 communities study by

Bell et al. (2004) examined the

sensitivity of acute 03-mortality effects

to potential confounding by PM1o. Restricting analysis to days when both

03 and PMo data were available, the

community-specific 0 3-mortality effect

estimates as well as the national average

results indicated that 03 was robust to

adjustment for PM10 (Bell et al., 2004).

As commenters noted, there were

insufficient data available to examine

potential confounding by PM2.

5. One

study (Lipfert et al., 2000) reported 03

risk estimates with and without

adjustment for sulfate, a component of

PM2.5. Lipfert et al. (2000) calculated 03

risk estimates based on mean (45 ppb)

less background (not stated) levels of 1-

hour max 03 in seven counties in

Pennsylvania and New Jersey. The 03

risk estimate was not substantially

affected by the addition of sulfate in the

model (3.2% versus 3.0% with sulfate)

and remained statistically significant.

Several 03 mortality studies examined

the effect of confounding by PM indices

in different seasons (Figure 7-23,

section 7.4.6, Criteria Document). In

analyses using all-year data and warm- season only data, 03 risk estimates were

once again fairly robust to adjustment

for PM indices, with values showing

both slight increases and decreases with

the inclusion of PM in the model. In the

analyses using cool season'data only,

the 03 risk estimates all increased

slightly with the adjustment of PM

indices, although none reached

statistical significance.

The three recent meta-analyses (Bell

et al., 2005; Ito et al., 2005; Levy et al.,

2005) all examined the influence of PM

on 03 risk estimates. No substantial

influence was observed in any of these

studies. In the analysis by Bell et al.

(2005), the combined estimate without

PM adjustment was 1.75% (95% PI:

1.10, 2.37) from 41 estimates, and the

combined estimate with PM adjustment

was 1.95% (95% PI: -0.06,4.00) from

11 estimates per 20 ppb increase in 24-

hour average 03. In the meta-analysis of

15 cities by Ito et al. (2005), the

combined estimate was 1.6% (95% CI:

1.1, 2.2) and 1.5% (95% CI: 0.8, 2.2) per

20 ppb in 24-hour average 03 without

and with PM adjustment, respectively.

The additional time-series analysis Of

six cities by Ito et al. found that the

influence of PM by season varied across

alternative weather models but was

never substantial. Levy et al. (2005)

examined the regression relationships

between 03 and PM indices (PM10 and

2.5) with 0 3-mortality effect estimates for

all year and by season. Positive slopes,

which might indicate potential

confounding, were observed for PM2.5

on 03 risk estimates in the summer and

all-year periods, but the relationships were weak. The effect of one causal

variable (i.., 03) is expected to be

overestimated when a second causal

variable (e.g., PM) is excluded from the

analysis, if the two variables are

positively correlated and act in the same

direction. However, EPA notes that the

results from these meta-analyses, as well

as several single- and multiple-city

studies, indicate that copollutants,

including PM, generally do not appear

to substantially confound the

association between 03 and mortality.

(c) With regard to the biological

plausibility of 0 3-related mortality

occurring at levels well within natural

background, EPA concluded in the

proposal that additional research is

needed to more fully establish

underlying mechanisms by which

mortality effects occur (72 FR 37836).

Such research would likely also help

determine whether it is plausible that

mortality would occur at such low

levels. As noted above, the multi-city

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times series studies evaluated in this

review can not resolve the issue of

whether the reported associations at

such low levels are related to 03 alone

rather than to the broader mix of air

pollutants present in the ambient air.

(5) "New" studies not included in the

Criteria Docujnent. Many commenters

identified "new" studies that were not

included in the Criteria Document that

they stated support arguments both for

and against the revision of the current

03 standard. Commenters who

supported revising the current 03

standard identified new studies that

generally supported EPA's conclusions

about the associations between 03

exposure and a range of respiratory and

cardiovascular health outcomes. These

comnienters also identified new studies

that provide evidence for associations

with health outcomes that EPA has not

linked to 03 exposure, such as cancer,

and populations that EPA has not

identified as being susceptible or

vulnerable to 03 exposure, including

African-American men and women.

Commenters who did not support

revision of the current 03 standard often

submitted the same "new" studies, but

focused on different aspects of the

findings. Commenters who did not

support revision of the current 03

standard stated that these "new" studies

provide inconsistent and sometimes

conflicting findings that do little to

resolve uncertainties regarding whether

03 has a causal role in the reported

associations with adverse health

outcomes, including premature

mortality and various morbidity

outcomes. More detail about the topic

areas covered in the "new" studies can

be found in the Response to Comments

document.

To the extent that these commenters

included "new" scientific studies,

studies that were published too late to

be considered in the Criteria Document,

in support of their arguments for

revising or not revising the standards,

EPA notes, as discussed in section I

above, that as in past NAAQS reviews,

it is basing the final decisions in this

review on the studies and related

information included in the 03 air

quality criteria that have undergone

CASAC and public review and will

consider newly published studies for

purposes of decision making in the next

03 NAAQS review. In provisionally

evaluating commenters' arguments, as

discussed in the Response to Comments

document, EPA notes that its

provisional consideration of "new"

science found that such studies did not

materially change the conclusions in the

Criteria Document.

iii. Evidence Pertaining to At-Risk

Subgroups for 0 3-Related Effects

This section contains major comments

on EPA's assessment of the body of

evidence, including controlled human

exposure and epidemiological studies,

related to the effects of 03 exposure on

sensitive subpopulations. Since new

information about the increased

responsiveness of people with lung

disease, especially children and adults

with asthma, was an important

consideration in the Aoministrator's

proposed decision that the current 03

standard is not adequate, many of the

comments focused on this information

and the conclusions drawn from it.

There were also comments on other

sensitive groups identified by EPA, as

well as comments suggesting that

additional groups should be considered

at increased risk from 03 exposure.

Many of the issues discussed below, as

well as other related issues, are

addressed in more detail in the

Response to Comments document.

As with the comments on controlled

human exposure and epidemiological

studies, upon which judgments about

sensitive subpopulations were based,

the comments about EPA's delineation

of these groups were highly polarized.

In general, one group of commenters

who supported revising the current 03

primary standard, including medical

associations, public health and

environmental groups, agreed in part

with EPA's assessment of the

subpopulations that are at increased risk

from 03 exposure, but commented that

there are additional groups that need to

be considered. A comment from ATS,

AMA and other medical associations

noted:

Within this population exists a number of

individuals uniquely at much higher risk for

adverse health effects from ozone exposures,

including children, people with respiratory

illness, the elderly, outdoor workers and

healthy children and adults who exercise

outdoors. [ATS, p. 2]

These commenters agreed with-EPA

that, based on evidence from controlled

human exposure and epidemiology

studies, people with asthma, especially

children, are likely to have greater lung

function decrements and respiratory

symptoms in response-to 03 exposure

than people who do not have asthma,

and are likely to respond at lower levels.

Because of this, these commenters make

the point that controlled human

exposure studies that employ healthy

subjects will underestimate the effects

of 03 exposures in people with asthma.

These commenters agreed with EPA's

assessment that epidemiological studies

provide evidence of increased morbidity

effects, including lung function

decrements, respiratory symptoms,

emergency department visits and

hospital admissions, in people with

asthma and that controlled human

exposure studies provide biological

plausibility for these morbidity

outcomes. Further, the Rochester.

Report, funded by API, evaluated some

of the same the studies that EPA did and

found similar results with regard to the

increased inflammatory responses and

increased airway responsiveness of

people with asthma when exposed to

03. The Rochester Report reached the

same conclusion that EPA did, that this

increased responsiveness provides

biological plausibility for the respiratory

morbidity effects found in

epidemiological studies.

Several new studies have demonstrated

that exposure of individuals with atopic

asthma to sufficient levels of ozone produces an increase in specific airway responsiveness

to inhaled allergens* * * These findings, in

combination with previously observed effects

of ozone on nonspecific airway

responsiveness and airway inflammation,

supports the idea that ambient ozone exposure could result in exacerbation of

asthma several days following exposure, and

provides biological plausibility for the

epidemiologic studies in which ambient ozone concentration has been associated with

increased asthma symptoms, medication use,

emergency room visits, and hospitalizations

for asthma. [Rochester Report, pp. 57-58]

Commenters also often mentioned the

increased susceptibility of people with

COPD, and in this case cited new

studies not considered in the Criteria

Document.

They identify one potentially

susceptible subpopulation that EPA did

not focus on in the proposal is infants.

Commenters from medical associations,

and environmental and public health

groups expressed the view that 03

exposure can have important effects on infants, including reduced birth weight,

pre-term birth, and increased respDiratory

morbidity effects in infants. Exposure to

03 during pregnancy, especially during

the second and third trimesters, was

associated with reduced birth weight in

full-term infants. Although this effect

was noted at relatively low 03 exposure

levels, the ATS notes that, "* * * the

reduced birth weight in infants in the

highest ozone exposures communities

equaled the reduced birth weight

observed in pregnant women who

smoke" (ATS, p. 7).

In general, EPA agrees with comments

that there is very strong evidence from

controlled human exposure and

epidemiological studies that people

with lung disease, especially children

and adults with asthma, are susceptible

to 03 exposure and are likely to

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experience more serious effects than

those people who do not have lung

disease. This means that controlled

human exposure studies that employ

subjects who do not have lung disease

Will likely underestimate effects in

those people that do have asthma or

other lung diseases.

In summarizing the epidemiological

evidence related to birth-related health

outcomes, the Criteria Document (p. '7-

133) concludes that 03 was not an important predictor of several birthrelated outcomes including premature

births and low birth weight. Birthrelated outcomes generally appeared to

be associated with air pollutants that

tend to peak in the Winter and are

possibly traffic-related. However, given

that most of these studies did not

analyze the data by season, seasonal

confounding may have therefore

influenced the reported associations.

One study reported some results

suggestive of associations between

exposures to 03 in the second month of

pregnancy and birth defects, but further

evaluation of such potential associations

is needed. With regard to comments

about effect in infants, EPA notes that

some of the studies cited by commenters

were not considered in the Criteria

Document. More detailed responses to

studies submitted by commenters but

not considered in the Criteria Document

can be found in the Response to

Comments document.

The second group of commenters,

mostly representing industry

associations and some businesses

opposed to revising the primary 03

standard, asserted that EPA is wrong to

claim that new evidence indicates that

the current standard does not provide

adequate health public health 1rotection

for people with asthma. In support of

this position, these commenters made

the following major comments: (1) Lung

function decrements and respiratory

symptoms observed in controlled

human exposure studies of asthmatics

are not clinically important; (2) EPA

postulates that asthmatics would likely

experience more serious responses and

responses at lower levels than the

subjects of controlled human exposure

experiments, but that hypothesis is not

supported by scientific evidence; and,

(3) EPA recognized asthmatics as a

sensitive subpopulation in 1997, and new information does not suggest

greater susceptibility than was

previously believed.

With regard to the first point, these

commenters expressed the view that

asthmatics are not likely to experience

medically significant lung function

changes or respiratory symptoms at

ambient 03 concentrations at or even

above the level of the current standard.

Many of these commenters cited the

opinion of one physician who was

asked on behalf of a group of trade

associations and companies to provide

his views on the health significance for

asthmatics of the types of responses that

have been reported in controlled human

exposure studies of 03. This commenter

(McFadden) reviewed earlier controlled

human exposure studies of asthmatics

(from the last review) as well as the

recent controlled human 'exposure

studies of healthy individuals (Adams

2002, 2003a,b, and 2006) at 0.12, 0.08,.

0.06, and 0.04 ppm and expressed the

View that "* * * these studies on

asthmatics indicate that ozone

exposures at -0.12 ppm do not produce

medically significant functional changes

and are right around the inflection point

where one begins to see an increase in

symptoms; however, that increase is

small" (McFadden, p. 3). This

commenter went on to express the view

that responses to 03 exposure at levels

< 0 .08 ppm would be even less and that

the available data are not sufficiently

robust to indicate that such -exposures

would present a significant health

concern even to sensitive people like

asthmatics.

EPA notes that this commenter based

his comment on the group mean

functional and respiratory symptom

changes in the studies he reviewed. EPA

agrees that group mean changes at these

levels are relatively small and has

described them as such in both the

previous review and this one (72 FR

37828). The importance of group mean

changes is to evaluate the statistical

significance of the association between

the exposures and the observed effects,

to try to determine if the observed

effects are likely due to 03 exposure

rather than chance. In the previous

review as well as in this one, EPA has

also focused on the fact that some

individuals experience more severe

effects that may be clinically significant.

With regard to the significance of

individual responses, this commenter

(McFadden, p. 2) states "* * * transient

decreases in FEV of 10-20% are not by

themselves significant or meaningful to

asthmatics* * *. It has been my

experience from examining and

studying thousands of patients for both

clinical and research purposes that

asthmatics typically will not begin to

sense bronchoconstriction until their

FEV, falls about 50% from normal."

EPA strongly disagrees with this

assessment. As stated in the Criteria

Document (Table 8-3, p. 8-68) for

people with lung disease, even moderate functional responses re.g.,

FEV decrements _> 10% but < 20%)

would likely interfere with normal

activities for many individuals, and

would likely result in more frequent

medication use. EPA notes that in the

context of standard setting, CASAC

indicated (Henderson, 2006c) that a

focus on the lower end of the range of

moderate functional responses (e.g.,

FEVI decrements > 10%) is most

appropriate for estimating potentially

adverse lung function decrements in

people with lung disease. -

With regard to the second point,

whether asthmatics would likely

experience more serious responses and

responses at lower levels than the

subjects of controlled human exposure

experiments and EPA's discussion of

the relationship of increased airway

responsiveness and inflammation

experienced by asthmatics to

exacerbation of asthma, this commenter

stated that "there simply are no data to

support the sequence described" and

that "the assumption that these

responses would lead to clinical

manifestations in terms of exacerbations

of asthma or other adverse health effects

remains unproven theory" (McFadden,

p. 3).

In these sections of the proposal (72

FR 37826 and 37846-37847), EPA

describes the evidence indicating that

people with asthma are as sensitive as,

if not more sensitive than, normal

subjects in manifesting 0 3-induced

pulmonary function decrements.

Controlled human exposure studies

show that asthmatics present a

differential response profile for cellular,

molecular, and biochemical parameters

that are altered in response to acute 03

exposure. Asthmatics have greater 03-

induced inflammatory responses and

increased 0 3-induced airway

responsiveness (both incidence and

duration) that could have important

clinical implications.

There are two ways to interpret these

comments. One way to interpret them is

that because these controlled human

exposure studies have not produced

exacerbations of asthma in study

subjects resulting in the need for

medical attention, there are no data to

support the clinical significance of the

results. EPA rejects this interpretation

because it would be unethical to

knowingly conduct a controlled human

exposure study that would lead to

exacerbation of asthma. Controlled

human exposure studies are specifically

designed to avoid these types of

responses. The other interpretation is

that the commenter does not agree that

the differences in lung function,

inflammation and increased airway

responsiveness found in these

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controlled human exposure studies

support the inference that asthmatics

are likely to have more serious

responses than healthy subjects, and

that these responses could have

important clinical implications. EPA

rejects this interpretation as well. EPA

did not base its increased concern for

asthmatics solely on the results of the

controlled human exposure studies, but

has appropriately used a weight of

evidence approach, integrating evidence

from animal toxicological, controlled

human exposure and epidemiological

studies as a basis for this concern. The

Criteria Document concludes that the

positive and robust epidemiological

associations between 03 exposure and

emergency department visits and

hospitalizations in the warm season are

supported by the human clinical,

animal toxicological and

epidemiological evidence for lung

function decrements, increased

respiratory symptoms, airway

inflammation, and increased airway

responsiveness (72 FR 37832). The

CASAC Panel itself expressed the view

that people with asthma, especially

children, have been found to be more

sensitive to 03 exposure, and indicated

that EPA should place more weight on

inflammatory responses and serious

morbidity effects, such as increased

respiratory-related emergency

department visits and hospitalizations

(Henderson, p. 4). Moreover, the

Rochester Report, cited above, reaches

essentially the same conclusions as EPA

did, that the evidence from controlled

human exposure studies provides

biological plausibility for the

epidemiological studies in which

ambient O3 concentrations have been

associated with increased asthma

symptoms, medication use, emergency

room visits, and hospitalizations for

asthma. Therefore, EPA continues to

assert that there is strong evidence that

asthmatics likely have more serious

responses to 03 exposure than people

without asthma, and that these

responses have the potential to lead to

exacerbation of asthma as indicated by

the serious morbidity effects, such as

increased respiratory-related emergency

department visits and hospitalizations

found in epidemiological studies.

With regard to the third point,

commenters expressed the view that

there is no significant new evidence

establishing greater risk to asthmatics

than was accepted in 1997, when EPA

concluded that the existing NAAQS was

sufficiently stringent to protect public

health-including asthmatics-with an

adequate margin of safety (UARG, pp.

22-23). To support this view, these

commenters noted the points made

above and expressed the view that

epidemiological studies of asthmatics

that provide new evidence of respiratory

symptoms and medication use in

asthmatic children are subject to the

limitations of epidemiological studies

discussed above (e.g., confounding by

co-pollutants, heterogeneity of results).

In addition, these-commenters

identified a new, large multi-city panel

study, not included in the Criteria

Document, by Schildcrout et al. (2006),

which the commenters characterize as

reporting no association between 03

concentrations and exacerbation of

asthma.

At the time of the last review, EPA

concluded that people with asthma

were at greater risk because the impact

of 0 3-induced responses on alreadycompromised respiratory systems would

noticeably impair an individual's ability

to engage in normal activity or would be

more likely to result in increased selfmedication or medical treatment. At

that time there was little evidence that

people with pre-existing disease were more responsive than healthy

individuals in terms of the magnitude of

pulmonary function decrements or

symptomatic responses. The new results

from controlled exposure and

epidemiologic studies indicate that

individuals with preexisting lung

disease, especially people with asthma,

are likely to have more serious

responses than people who do not have

lung disease and therefore are at greater

risk for 03 health effects than previously

judged in the 1997 review. EPA notes

that comments on the limitations of

epidemiological studies and evidence

from "new" studies (not in the Criteria

Document) have been addressed above.

As with other "new" studies, this study

by Schildcrout et al. (2006) is

specifically discussed in the Response

to Comments document.

b. Consideration of Human Exposure

and Health Risk Assessments

Section ll.A.3 above provides a summary overview of the exposure and

risk assessment information used by the

Administrator to inform judgments

about exposure and health risk

estimates associated with attainment of

the current and alternative standards.

EPA notes here that most of the issues

and concerns raised by commenters

concerning the methods used in the

exposure and risk assessments are

essentially restatements of concerns

raised during the review of the Criteria

Document and the development and

review of these quantitative assessments

as part of the preparation and review of

the Staff Paper and the associated

analyses. EPA presented and the

CASAG Panel reviewed in detail the

approaches used to assess exposure and

health risk, the studies and health effect

categories selected for which exposureresponse and concentration-response

relationships were estimated, and the

presentation of the exposure and risk

results summarized in the Staff Paper.

As stated in the proposal notice, EPA

believes and CASAC Panel concurred,

that the model selected to estimate

exposure represent the state of the art

and that the risk assessment was "well

done, balanced and reasonably

communicated" and that the selection

of health endpoints for inclusion in the

quantitative risk assessment was

appropriate (Henderson, 2006c). EPA

does not believe that the exposure or

risk assessments are fundamentally

biased in one direction or the other as

claimed in some of the comments.

Comments received after proposal

related to the development of exposure

and health risk assessments,

interpretation of exposure and risk

results, and the role of the quantitative

human exposure and health risk

assessments in consideriig the need to

revise the current 8-hour 03 standard

generally fell into two groups. One

group of commenters that included

national environmental and p4lic

health organizations (e.g., joint set of

comments by ALA and several

environmental groups including

Environmental Defense and Sierra

Club), NESCAUM, and some State and

local health and air pollution agencies

argued that the exposure and health risk

assessments underestimated exposure

and risks for several reasons including:

(1) The geographic scope was limited to

at most only 12 urban areas and thus

underestimates national public health

impacts due to exposures to 03; (2) the

assessments did not include all relevant

at risk population groups and excluded

populations such as pre-school

children, outdoor workers, adults who

exercise outdoors; and (3) the risk

assessment did not include all of the

health effect endpoints for which there

is evidence that there are 03-related

health effects (e.g., increased medicine

use by asthmatics, lung function

decrements and respiratory symptoms

in adults, increased doctors' visits,

emergency department visits, school

absences, inflammation, and decreased

resistance to infection among children

and adults); and (4) EPA's exposure

assessment underestimates exposures

since it considers average children, not

active children who spend more time

outdoors and repeated exposures are

also underestimated. The joint set of

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comments from ALA and several

environmental groups contended that

the "exposures of concern" metric

presented in the Staff Paper and

proposal is "an inappropriate basis for

decisionmaking" and urged EPA to set

the standard based on the

concentrations shown by health studies

to cause adverse effects, not on how

much 03 Americans inhale. This same

set of commenters stated that if

exposures of concern were.to be

considered then the benchmark level of

0.060 ppm should be the focus, and not

higher benchmark levels. These same

commenters also stated that EPA should

have estimated and considered total risk

without excluding risks associated with

PRB levels because there is no rational

basis for excluding natural and

anthropogenic sources from outside

North America and that the NAAQS

must- protect against total exposure.

While disagreeing with EPA's approach

of estimating risks only above PRB,

these same commenters supported the

use of the GEOS-CHEM model as the

"best tool available to derive

background concentrations" should

'EPA continue to pursue this approach.

These comments are discussed in turn

below.

EPA agrees that the exposure and

health risk assessments are limited to

certain urban areas and do not capture

all of the populations at risk for 03-

related effects, and that the risk

assessment does not include all

potential 0 3-related health effects. The

criteria and rationale for selecting the

populations and health outcomes - included in the quantitative assessments

were presented in the draft Health

Assessment Plan, Staff Paper, and

technical support documents for the

exposure and health risk assessments

that were reviewed by the CASAC Panel

and the public. The CASAC Panel

indicated in its letter that the health

outcomes included in the quantitative

risk assessment were appropriate, while

recognizing that other health outcomes

such as emergency department visits

and increased doctors' visits should be

addressed qualitatively (Henderson,

2006c). The Staff Paper (and the CASAC

Panel) clearly recognized that the

exposure and risk analyses could not

provide a full picture of the 03-

exposures and 0 3-related health risks

posed nationally. The proposal notice

made note of this important point and

stated that "national-scale public health

impacts of ambient 03 exposures are

clearly much larger than the

quantitative estimates of 0 3-related

incidences of adverse health effects and

the numbers of children likely to

experience exposures of concern

associated with recent air quality or air

quality that just meets the current or alternative standards" (72 FR 37866).

However, as stated in the proposal

notice, EPA also recognizes that interindividual variability in responsiveness

to 03 shown in controlled human

exposure studies for a variety of effects

means that only a subset of individuals

in any population group estimated to

experience exposures exceeding a given

benchmark exposure of concern level

would actually be expected to

experience such adverse health effects.

The Administrator continues to

recognize that there is a broaddr array of

0 3-related adverse health outcomes for

which risk estimates could not be

quantified (that are part of a broader "pyramid of effects") and that the scope

of the assessment was limited to just a

sample of urban areas and to some but

not all at-risk populations, leading to an

incomplete estimation of public health

impacts associated with 03 exposures across the country. The Administrator is

fully mindful of these limitations, along

with the uncertainties in these

estimates, in reaching his conclusion

that observations from the exposure and

health risk assessments provide

additional support for his judgment that

the current 8-hour standard does not

protect public health with an adequate

margin of safety and must be revised..

For reasons discussed below in section

ll.C.4, however, the Administrator

disagrees with aspects of these

commenters' views on the level of the

standard that is appropriate and

supported by the available health effects

evidence and quantitative assessments

associated with just meeting alternative

standards.

EPA does not agree that consideration

of exposure estimates is not permitted

or is somehow inappropriate in

decisions concerning the primary

standard. EPA has considered

population exposure estimates as a

consideration in prior NAAQS review

decisions, including the 1997 revision

of the 03 primary standard and the 1994

decision on the carbon moioxide (CO)

standard. As indicated in the proposal,

estimating exposures of concern is

important because it provides some

indication of potential public. health

impacts of a range of 0 3-related health

outcomes, such as lung inflammation,

increased airway responsiveness, and

changes in host defenses. These

particular health effects have been

demonstrated to occur in some

individuals in controlled human

exposure'studies at levels as low as

0.080 ppm 03 but have not been

evaluated at lower levels. While there is

very limited evidence addressing lung

function and respiratory symptom

responses at 0.060 ppm, this evidence

does not address these other health

effects.

As noted in the proposal, EPA

emphasized that although the analysis

of "exposures of concern" was

conducted using three discrete

benchmark levels (0.080, 0.070, 0.060

ppm), the concept was more

appropriately viewed as a continuum,

with greater confidence and less

uncertainty about the existence of

health effects at the upper end and less

confidence and greater uncertainty as one considers increasingly lower 03

exposure levels. EPA recognized that

there was no sharp breikpoint within

the continuum ranging from at and

above 0.080 ppm down to 0.060 ppm. In

considering the concept of exposures of

concern, the proposal noted that it was important to balance concerns about the

potential for health effects and their

severity with the increasing uncertainty

associated with our understanding of

the likelihood of such effects at lower

levels.

As noted above, environmental and

public health group comments

expressed the view that if exposures of

concern were considered, then the

Administrator should focus only on the

0.060 ppm benchmark based on the

contention that adverse health effects

had been demonstrated down to this

level. In contrast, other commenters,

primarily industry and business groups

focused on comparisons of the

exposures of concern at the 0.080 ppm

benchmark level based on their view

that there was no convincing evidence

demonstrating adverse health effects at

levels below this benchmark. In view of

the comments received related to the

definition and use of the term "exposure

of concern" at the time of proposal, the

Administrator recognizes that that there

is a risk for confusion, as it could be

read to imply a determination that a certain benchmark level of exposure has

been shown to be causally associated

with adverse health effects. As a

consequence, the Administrator believes

that it is more appropriate to consider

such exposure estimates in the context

of a continuum rather than focusing on

any one discrete benchmark level, as

was done at the time of proposal, since

the Administrator does not believe that

the underlying scientific evidence is

certain enough to support a focus on

any single bright-line benchmark level.

Thus, the Administrator believes it is

appropriate to consider a range of

benchmark levels from 0.080 down to

0.060 ppm, recognizing that exposures

of concern must be considered in the

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context of a continuum of the potential

for health effects of concern,, and their

severity, with increasing uncertainty

associated with the likelihood of such

effects at lower 03 exposure levels.

EPA recognizes that the 0.080 ppm

benchmark level represents a level at

which several health outcomes

including lung inflammation, increased

airway responsiveness, and decreased

resistance to infection have been shown

to occur in healthy adults. The

.Administrator-places relatively great

weight on the public health significance

of exposures at and above this

benchmark level given these

physiological effects measured in

healthy adults at 03 exposures .of 0.080

ppm and the evidence from controlled

human exposure studies showing that

people with asthma have more serious

responses than people without asthma.

However, the Administrator does not

agree with those commenters who

would only consider this single

benchmark level. While the

Administrator places less weight on

exposures at and above the 0.070 pm

benchmark level, given the increased

uncertainty about the fraction of the

population and severity of the health

responses that might occur associated

with exposures at and above this level,

he believes that it is appropriate to

consider exposures at and above this

benchmark as well in judging the

adequacy of the current standard to

protect public health. Considering

exposures at and above the 0.070 ppm

benchmark level provides some

consideration for the fact that the effects

observed at 0.080 ppm were in healthy

adult subjects but sensitive population

groups such as asthmatics are likely to

respond at lower 03 levels than healthy

individuals. The Administrator

considered but placed very little weight

on exposures at and above the 0.060

ppm benchmark given the very limited

scientific evidence supporting a

conclusion that 03 is causally related to

various health outcomes at this

exposure level.

EPA does not agree that it is

inappropriate or impermissible to assess

risks that are in excess of PRB or that

EPA must focus on total risks when

using a risk assessment to inform

decisions on the primary standard.

Consistent with the approach used in

the risk assessment for the prior 03

standard review and consistent with the

approach used in risk assessments for

other prior NAAQS reviews, estimating

risks in excess of PRB is judged to be

more relevant to policy decisions

regarding the ambient air quality

standard than risk estimates that

include effects potentially attributable

to uncontrollable background 03

concentrations. EPA also notes that with

respect to the adequacy of the current

standard taking total risks into account

would not impact the Administrator's

decision, since he judges that the

current standard is not adequate even

when risks in excess of current PRB

estimates are considered. In addition,

EPA notes that consideration of the

evidence itself, as well as exposures at

and above benchmark levels in the

range-of 0.060 to 0.080 ppm, are not

impacted at all by consideration of

current PRB estimates.

EPA does agree with the ALA and

environmental groups comment that the

GEOS-CHEM model represents the best

tool currently available to estimate PRB

as recognized in the Criteria Document

evaluation of this issue and the CASAC

Panel support expressed during the

review of the Criteria Document.

The second group of commenters

mostly representing industry

associations, businesses, and some State

and local officials opposed to revising

the 8-hour standard, and most

extensively presented in comments from

UARG, API, Exxon-Mobil, AAM, and

NAM, raised one or more of the

following concerns: (1) That exposures

of concern and health risk estimates

have not changed significantly since the

prior review in 1997; (2) that

uncertainties and limitations underlying

the exposure and risk assessments make

them too speculative to be used in

supporting a decision to revise the

standard; (3) that EPA should have

defined PRB differently and that EPA

underestimated PRB levels which

results in health risk reductions

associated with more stringent

standards being overestimated; (4) that

exposures are overestimated based on

specific methodological choices made

by EPA including, for example, 03

measurements at fixed-site monitors can

be higher than other locations where

individuals are exposed, the exposure

estimates do not account for 03

avoidance behaviors, and the exposure

model overestimates elevated breathing

rates; and (5) That health risks are

overestimated based on specific

methodological choices made by EPA

including, for example, selection of

inappropriate effect estimates from

health effect studies and EPA's

approach to addressing the shape of

exposure-response relationships and

whether or not to incorporate thresholds

into its models for the various health

effects analyzed. These comments are

discussed in turn below. Additional

detailed comments related to the

development, presentation, and

interpretation of EPA's exposure and

healtbi vislk assessments, along with

EPA'stre"p, s to the specific issues

raised by these commenters can be

found in the Response to Comments

document.

(1) In asserting that the estimated

exposures and risks associated with air

quality just meeting the current

standard have not appreciably changed

since the prior review, comments from

Exxon-Mobil, the Annapolis Center and

others have compared results of EPA's

lung function risk assessment done in

the last review with those from the

Agency's risk assessment done as part of

this review and have concluded that

lung function risks upon attainment of

the current 03 standard are below those

that were predicted in 1997 and that

uncertainties about other health effects

based on epidemiological studies

remain the same. These commenters

used this conclusion as the basis for a

claim that there is no reason to depart

from the Administrator's 1997 decision

that the current 8-hour standard is

requisite to protect public health.

EPA believes that this claim is

fundamentally flawed for three reasons,

as discussed in turn below: (i) It is

factually inappropriate to compare the

quantitative risks estimated in 1997

with those estimated in the current

rulemaking; (ii) it fails to take into

account that with similar risks,

increased certainty in the risks

presented by 03 implies greater concern

than in the last review, and (iii) it fails

to recognize that the Administrator has

used these estimates in a supportive

role, in light of significant uncertainties

in the exposure and risk estimates, to

inform the conclusions drawn primarily

from integrative assessment of the

controlled human exposure and

epidemiological evidence on whether

ambient 03 levels allowed under the

current standard present a serious

public health problem warranting

revision of the 03 standard.

With respect to the first point, the

1997 risk estimates, or any comparison

of the 1997 risk estimates to the current

estimates, are irrelevant for the purpose

of judging the adequacy of the current

8-hour standard, as the 1997 estimates

reflect outdated analyses that have been

updated in this review to reflect the

current science. Just comparing the

results for lung function decrements

ignores these differences. In particular,

as discussed in section 4.6.1 of the. Staff

Paper, there have been significant

improvements to the exposure model

and the model inputs since the last

review that make comparisons

inappropriate between the prior and

current review. For example, the

geographic areas modeled are larger

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than in the previous review and when

modeling a larger area, extending well

beyond the urban core, there will be

more people exposed, but a smaller

percentage of the modeled population

will be exposed at high levels, if 03

concentrations are lower in the

extended areas. In the prior review, only

typical years, in terms of 03 air quality

were modeled, while the current review

used the most recent three-year period

(i.e., 2002-2004). Also, the prior review

estimated exposures for children who

spent more time outdoors, while the

assessment for the current review

included all school age and all

asthmatic school age children.

Therefore, the population groups

examined-in the exposure assessment

are different between those considered

in the 1997 and current review, making

comparison of the resulting estimates

inappropriate. Another important

difference making comparison between

the 1997 health risk assessment and the

current assessment inappropriate is that

a number of additional health effects

were included in the current review

(e.g., respiratory symptoms in moderate/

severe asthmatic children, nonaccidental and cardiorespiratory

mortality) based on health effects

observed in epidemiological studies that

were not included in 'the risk

assessment for the prior review. 'hese

commenters only compare the risk

estimates with respect to lung function

decrement, and fail to account for

differences in additional and more

severe health endpoints not covered in

the 1997 assessment, as well as the fact

that there are somewhat different and

more urban areas included in the

current assessment.

Second, it is important to take into

account EPA's increased level of

confidence in the associations between

short-term 03 exposures and morbidity

and mortality effects. In comparing the

scientific understanding of the risk

presented by exposure to 03 between

the last and current reviews, one must

examine not only the quantitative

estimate of risk from those exposures

(e.g. the numbers of increased hospital

admissions at various levels) but also

the degree of confidence that the

Agency has that the observed health

effects are causally linked to 03

exposure at those levels. As

documented in the Criteria Document.

and the recommendations and

conclusions of CASAC, EPA recognizes

significant advances in our

understanding of the health effects of 03

based on new epidemiological studies,

new human and animal studies

documenting effects, new laboratory

studies identifying and investigating

biological mechanisms of 03 toxicity,

and new studies addressing the utility

of using ambient monitoxs t assess

population exposures to ambient 03. As

a result of these advances, EPA is now more certain that ambient 03 presents a

significant risk to public health at levels

at or above the range of levels that the

Agency had considered for these

standards in 1997. From this more

comprehensive perspective, since the

risks presented by 03 are more certain

and the current quantitative risk

estimates include additional important

health effects, 0 3-related risks for a

wider range of health effects are now of

greater concern at the current level of

the standard than in the last review.

Third, quantitative risk estimates

were not the only basis for EPA's

decision in setting a level for the 03

standard in 1997, and they do not set

any quantified "benchmark" for the

Agency's decision to revise the 03

standard at this time. While EPA

believes that confidence in the causal

relationships between short-term

exposures to 03 and various health

effects reported in epidemiological

studies has increased markedly since

1997, the Administrator also recognizes

that the risk estimates for these effects

must be considered in the light of

uncertainties about whether or not these

0 3-related effects occur at very low 03

concentrations. The Administrator

continues to believe that the exposure

and risk estimates associated with just

meeting the c urrent standard discussed

in the Staff Paper and summarized in

the proposal notice are important from

a public health perspective and are

indicative of potential exposures and

risks to at-risk groups. In considering

the exposure and risk estimates, the

Administrator has considered the yearto-year and city-to-city variability in

both the exposure and risk estimates,

the uncertainties in these estimates, and

recognition that there is a broader array

of 0 3-related adverse health outcomes

for which risk estimates could not be

quantified (that are part of a broader "pyramid of effects") and that the scope

of the assessment was limited to just a

sample of urban areas and to some, but

not all, at-risk populations, leading to an

incomplete estimation of public health

impacts associated with 03 exposures

across the country.

(2) In asserting that uncertainties and

limitations associated with the exposure

and health risk assessments make them

too speculative to be used in supporting

a decision to revise the standard,

comments from industry associations

and others cited a number of issues

including: (i) Uncertainties about the air

quality adjustment approach used to

simulate just meeting the current and

alternative standards; (ii) uncertainties

and limitations assgciated with the

definition and estimation of PRB -

concentrations; (iii) uncertainties about

whether the respiratory symptoms,

hospital admissions, and non-accidental

and cardiorespiratory mortality effects

included in the health risk assessment

are actually causally related to ambient

03 concentrations, particularly at levels

- well below the current standard; and

(iv) uncertainties about the shape of the

exposure-response relationships for

lung function responses and

concentration-response relationships for

the health effects based on findings from

epidemiological studies and the

assumption of a linear non-threshold

relationship for these responses. In

summary, these commenters contend

that the substantial uncertainties

present in the exposure and risk

assessments preclude the Administrator

from using any of the results to support

a conclusion that the current 8-hour

standard does not adequately protect

public health.

Several of the issues raised, including

whether EPA's judgmentsabout

causality for the effects included in the

risk assessment are appropriate, the

shape of concentration-response

relationships, and use of a linear nonthreshold relationship for the health

outcomes based on the epidemiological

evidence, have been discussed in the

previous section on health effects

evidence. Concerns expressed about the

definition and estimation of PRB levels

for 03 and the role of PRB in the risk

assessment are addressed as a separate

item below. These issues also are

addressed in more detail in the

Response to Comments document.

With respect to the air quality

adjtistment approach used in the current

review to simulate air quality just

meeting the current and alternative 03

standards, as discussed- in the Staff

Paper (section 4.5.6) and in more detail

in a staff memorandum (Rizzo, 2006),

EPA concluded that the quadratic air

quality adjustment approach generally

best represented the pattern of

reductions across the 03 aix quality

distribution observed over the last

decade in areas implementing control

programs designed to attain the 03

NAAQS. While EPA recognizes that

future changes in air quality

distributions are area-specific, and will

be affected by whatever specific control

-strategies are implemented in the future

to attain a revised NAAQS, there is no

empirical evidence to suggest that future

reductions in ambient 03 will be

significantly different from past

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reductions with respect to impacting the

overall shape of the 03 distribution.

As discussed in the proposal notice,

EPA recognizes that the exposure and

health risk assessments necessarily

contain many sources of uncertainty

including those noted by these

commenters, and EPA has accounted for

such uncertainties to the extent

possible. EPA developed and presented

an uncertainty analysis addressing the

most significant uncertainties affecting

the exposure estimates. With respect to

the health risk assessment, EPA

conducted and presented sensitivity

analyses addressing the impact on risk

estimates of different assumptions about

the shape of the exposure-response

relationship for lung function

decrements and alternative assumptions

about PRB levels. EPA notes that most

of the comments summarized above

concerning limitations and uncertainties

in these assessments are essentially

restatements of concerns raised during

the development and review of these

quantitative assessments as part of the

preparation and review of the Staff

Paper and assessments. The CASAC

Panel reviewed in detail the approaches .used to assess exposure and health risks

and the presentation of the results in the

Staff Paper. EPA believes, and the

CASAC Panel concurred, that the model

used to estimate exposures represents a

state-of-the-art approach and that "there

is an explicit discussion of the

limitations of the APEX model in terms

of variability and quality of the input

data, which is appropriate and fine"

(Henderson, 2006c, p. 11). The CASAC

Panel also found the risk chapter in the

Staff Paper and the risk assessment "to

be well done, balanced, and reasonably

communicated" (Henderson, 2006c, p.

12). Although EPA agrees that important

limitations and uncertainties remain,

and that future research directed toward

addressing these uncertainties is

warranted, EPA believes that overall

uncertainties about population exposure

and possible health risks associated

with short-term 03 exposure have

dimidiished since the last review. The

Administrator has carefully considered

the limitations and uncertainties

associated with these quantitative

assessments but continues to believe

that they provide general support for

concluding that exposures and health

risks associated with meeting the

current 8-hour standard are important

from a public health perspective and

that the 8-hour standard needs to be

revised to provide additional protection

in order to protect public health with an

adequate margin of safety.

(3) Comments from several industry

organizations, businesses, and others

related to PRB included: (i) That EPA

should have defined PRB differently so

as to include anthropogenic emissions

from Canada and Mexico; (ii) that EPA

underestimated PRB levels by relying on

estimates from the GEOS-CHEM model

using 2001 meteorology and EPA should

instead rely on 03 levels observed at

remote monitoring locations or sites that

represent PRB conditions; and (iii) that

the use of underestimated PRB levels in

the risk assessment results in

overestimated health risks associated

with air quality just meeting the current

standard. Finally, some commenters

cited concerns expressed by the CASAC

Panel that "the current approach to

determining PRB is the best method to

make this estimation" (Henderson,

2007, p. 2). Each of these concerns is

addressed below and in more detail in

the Response to Comments document.

First, the U.S. government has

influence over emissions at our borders

that affect ambient 03 concentrations

entering the U.S. from Canada and

Mexico through either regulations or

international agreements, and therefore

EPA does not agree that these emissions

are uncontrollable. PRB is designed to

identify 03 levels that result from

emissions that are considered

uncontrollable because the U.S. has

little if any influence on their control,

and in that context anthropogenic

emissions from Mexico or Canada

should be excluded from PRB. EPA has

consistently defined PRB as excluding

anthropogenic emissions from Canada

and Mexico in NAAQS reviews over

more than two decades and sees no

basis in the comments to alter this

definition.

Second, the criticisms raised

concerning the use of a modeling

approach (GEOS-CHEM using 2001

meteorology) and the alternative

approach of using remote monitoring

data to estimate PRB were considered by

EPA's scientific staff and the CASAC

Panel during the course of reviewing the

Criteria Document. Both EPA's experts

and CASAC endorsed the use of the

peer-reviewed, thoroughly evaluated

modeling approach (GEOS-CHEM)

described.in the Criteria Document as

the best current approach for estimating

PRB levels. The Criteria Document

reviewed detailed evaluations of GEOSCHEM with 03 observations at U.S.

surface sites (Fiore et al., 2002, 2003)

and comparisons of GEOS-CHEM

predictions with observations at

Trinidad Head, CA (Goldstein et al.,

2004) and found no significant

differences between the model

predictions and observations for all

conditions, including those reflecting

those given in the current PRB

definition. The Criteria Document states

that the current model estimates

indicate that PRB in the U.S. is

generally 0.015 to 0.035 ppm that

declines from spring to summer and is

generally < 0.025 ppm under conditions

conducive to high 03 episodes. The

Criteria Document acknowledges that

PRB can be higher, especially at

elevated sites in the spring due to

stratospheric exchange. However,

unusually high springtime 03 episodes

tied to stratospheric intrusion arerare

and generally occur at elevated

locations and these can be readily

identified and excluded under EPA's

exceptional events rule (72 FR 13560) to

avoid any impact on attainment/nonattainment status of an area.

Third, many of the commenters who

raised the concern that EPA's estimates

of PRB were too low and had the impact

of exaggerating the risks associated with

the current standard ignored the fact

that the risk assessment included a

sensitivity analysis which showed the

potential impact of both lower and

higher estimates of PRB or only focused

on the impact of higher estimates of

PRB. The choices of lower and higher

estimates of PRB included in the risk

assessment sensitivity analyses were

based on the peer-reviewed evaluation

of the accuracy of GEOS-CHEM model.

The Criteria Document states "in

conclusion, we estimate that the PRB 03

values reported by Fiore et al. (2003) for

afternoon surface air over the United

States are likely 10 parts per billion by

volume (ppbv) too high in the southeast

in summer, and accurate within 5 ppbv

in other regions and seasons." These

error estimates are based on comparison

of model output with observations for

conditions which most nearly reflect

those given in the PRB definition, i.e.,

at the lower end of the probability

distribution. As discussed in the Criteria

Document and Staff Paper, it can be

seen that GEOS-CHEM overestimates 03

for the southeast and underestimates it

by a small amount for the northeast.

These commenters generally ignored the

scientific conclusion presented in the

Criteria Document that for some regions

of the country the evidence suggests that

the model actually overestimates PRB.

Thus, the influence of alternative

estimates of PRB on risks in excess of

PRB associated with meeting the current

standard can be to lower or increase the

risk estimates. While the choice of

estimates for PRB contributes to the

uncertainty in the risk estimates, EPA

does not agree that the approach used is

biased since peer-reviewed evaluations

of the model have shown relatively good

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agreement (i.e., generally within 5 ppb

for most regions of the country):

Finally, EPA believes that some

commenters have misread the CASAC

Panel concern "that the current

approach to determining PRB is the best

method to make this estimation"

(Henderson, 2007, p. 2) as a criticism of

the use of the GEOS-CHEM modeling

approach and/or support for primary

reliance on estimates based on remote

monitoring sites. However, the CASAC

Panel went on to state that one reason

for its concern was that the contribution

to PRB from beyond North America was

uncontrollable by EPA and that "a better

scientific understanding of

intercontinental transport of air

pollutants could serve as the basis for a

more concerted effort to control its

growth..." (Henderson, 2007, p. 3).

Hence, CASAC's concern appeared to be

more with defining what emissions to

include in defining PRB, and the role

that PRB should play, as compared to

' the technical question of the best way to

7estimate PRB levels. In reviewing the

Staff Paper, the atmospheric modeling

expert on the CASAC Panel in his

* comments on how PRB had been

estimated using the GEOS-CHEM model

concluded that the "current approach

has been peer-reviewed, and is

appropriate" (Henderson, 2006b, p.

D-48).

(4) Some commenters raised concerns

about aspects of the exposure modeling

that they felt resulted in overestimates

of modeled exposures, including: (i 03

measurements at downwind monitors

are usually higher than the overall area

and may not reflect the overall outdoor

exposures in the area; (ii) 03 exposures

near roadvays will be below that

measured at the monitor due to titration

of 03 from automobile emissions of NO;

(iii) 03 concentrations are lower at a

person's breathing height compared to

measurement height, (iv) exposure

estimates do not account for 03

avoidance behaviors; and (v) the APEX

model over predicts elevated ventilation

rate occurrences, which results in an

overestimation of the number of

exposures of concern and risk estimates

for lung function decrements.

The concern raised in the first point

is unfounded since all 03 monitors in

each area are used to take into account

the spatial variations of 03

concentrations. The geographic

variation of 03 concentration is

accounted for by using measurements

from the closest 03 monitor to represent

concentrations in a neighborhood and

the measurements at downwind

monitors are applied only to the

downwind areas.

Second, the reduction in 03

concentrations near roadways due to

titration of 03 from automobile

emissions of NO is accounted for and

explicitly modeled in APEX and thus

does not bias estimates of exposures.

This phenomenon was modeled through

the use of "proximity factors," which

adjust the monitored concentrations to

account for the titration of 03 by NO

emissions (the monitored

concentrations are multiplied by the

proximity factors). Three proximity

factor distributions were developed, one

for local roads, one for urban roads, and

one for interstates, with mean factors of

0.75, 0.75, and 0.36 respectively (section

3.10.2, Exposure Analysis TSD).

Furthermore, the uncertainty of these

proximity factor distributions was

included in the exposure uncertainty

analysis.

Third, as discussed in the exposure

uncertainty analysis, data were not

available to quantify the potential biases

of differences between 03

concentrations at a person's breathing

height compared to the heights of

nearby monitors. EPA believes that

these biases, to the extent that they

exist, are relatively small during warm

summer afternoons when 03

concentrations tend to be higher.

Fourth, behavior changes in response

to 03 pollution or in response to AQI

notification alerts ("avoidance

behavior") is not explicitly taken into

account in the exposure modeling.

There is not much information about the

extent to which people currently modify

their activities in response to 03 alerts.

However, under the scenarios modeled

for just meeting alternative standards,

03 alerts would be infrequent relative to

the number of alerts that currently occur

in the nonattainment areas modeled.

Consequently, EPA does not feel that

this is an influential factor in the

estimation of exposure for the scenarios

simulating just meeting the current or

proposed standards.

Fifth, a comparison of ventilation

rates predicted by APEX to

measurements showed APEX

overpredicting ventilation rates for ages

5 to 10, underpredicting ventilation

rates for ages 11 to 29 and greater than

39, and in close agreement for ages 30

to 39. The overall agreement was judged

favorable, and the errors of the

predicted ventilation rates were

partially incorporated into the overall

uncertainty analysis with the

uncertainties of the metabolic

equivalents (METs), which are the

primary drivers of ventilation rates.

(5) Comments from a number of

industry organizations, businesses, and

others contended that EPA's health risk

assessment was biased and that the

resulting risk assessment is "much

higher than would have been obtained

using objective methods" (NAM), and

commenters raised one or more of the

following points in support of this view:

(i) EPA inappropriately based its risk

assessment for respiratory symptoms,

hospital admissions, and non-accidental

and cardiorespiratory mortality on

positive'studies with high risk

coefficients while ignoring negative

studies and studies with lower

coefficients; (ii) EPA focused on

combined "national" effect estimates

from multi-city studies when it should

have relied on individual city effect

estimates from these studies in its risk

assessment; (iii) the risk assessment

presented single-pollutant model results

that overstate the likely impact of 03

when co-pollutant model results were

available which should have been used;

(iv) the risk assessment used linear

concentration-response relationships for

the health endpoints based on

epidemiological studies when nonlinear or threshold models should have

been used; and (v) the lung function

portion of the risk assessment should

not rely on what they characterized as "outlier" information to define

exposure-response relationships, with

reference to the data from the Adams

(2006) study, but rather should focus on

group central tendency response levels.

Each of these issues is discussed below

and in more detail in the Response to

Comments document.

First, several commenters asserted

that the results of time-series studies

should not be used at all in quantitative

risk assessments, that risk estimates

from single-city time-series studies

should not be used since they are highly

heterogeneous and influenced by

publication bias, and that -the panel

study which served as the basis for the

concentration-response relationships for

respiratory symptoms in asthmatic

children suffered from various

weaknesses and was contradicted by a

more recent study. EPA notes that the

selection of specific studies and effect

estimates was based on a careful

evaluation of the evidence evaluated in

the Criteria Document and that the

criteria and rationale for selection of

studies and effect estimates were

presented and extensively reviewed and

discussed by the CASAC Panel and in

public comments presented to the

CASAC Panel. EPA notes that the

CASAC Panel judged the selection of

the endpoints based on the

epidemiological studies for inclusion in

.the quantitative risk assessment to be

"appropriate" and that the risk

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assessment chapter of the Staff Paper

and its accompanying risk assessment

were "well done, balanced and

reasonably communicated" (Henderson,

2006c, p. 12).

While EPA notes that two of the metaanalyses, Bell et a. (2005) and Ito et of.

(2005), provided suggestive evidence of

publication bias, 0 3-mortality

associations remained after accounting

for that potential bias. The Criteria

Document (p. 7-97) concludes that the

"positive 03 effects estimates, along

with the sensitivity analyses in these

three meta-analyses, provide evidence

of a robust association between ambient

03 and mortality." Concerns about the

heterogeneity of responses observed

across different urban areas,'particularly

for 0 3-related mortality are addressed in

the section above on health effect

considerations.

Second, as discussed in more detail in

the Staff Paper (section 5.3.2.3), there

are different advantages associated with

use of single-city and multi-city effect

estimates as the basis for estimating

health risks in specific urban areas.

Therefore, the risk assessment included

estimates based on both types of effect

estimates where such information was

available.

Third, the risk assessment included

risk estimates based on both single

pollutant and multi-pollutant

concentration-response relationships

where such information was available

for the health outcomes included in the

assessment. Issues related to the

consideration of single versus multipollutant models have been addressed

in the section above on health effects

evidence.

Fourth, EPA's approach of using

linear concentration-response

relationships for the health outcomes

based on epidemiological studies and

whether or not to include any nonlinear models or assumed threshold

were reviewed and discussed by the

CASAC Panel during the development

of the Staff Paper and risk assessment,

and the Panel concurred with the

approach used. As discussed in the

proposal notice, Staff Paper (section

3.4.5), and above in the prior section on

health effects evidence, EPA recognizes

that the available epidemiological

evidence neither supports or refutes the

existence of thresholds at the

population level for effects such as

increased hospital admissions and

premature mortality. Noting the

limitations of epidemiological evidence

to address such questions, EPA

concluded that if a population threshold

does exist, it would likely be well below

the level of the current 03 standard. The

Administrator is very mindful of the

uncertainties related to whether the

observed associations between 03

concentrations at levels well below

0.080 ppm and the health outcomes

reported in the epidemiological studies

reflect actual causal relationships, and

has taken this into account in

considering the risk assessment

estimates in his decision. - Fifth, consistent with the prior

review, the lung function component of

the risk assessment has focused on the

number and percentage of children that

are estimated to experience a degree of

lung function decrement that represents

an adverse health effect. EPA does not

agree that the focus of the quantitative

risk assessment should be on the

average lung function response in the

population, since such an assessment

would not address the public health

policy question concerning to extent to

which a portion of the population

would likely experience health effects of

concern. Looking at just-the average for

the population would ignore the

evidence of health effects for sensitive

subpopulations, an important aspect of

public health impact in this and other

03 reviews. EPA believes that it is

appropriate to include all of the

individual data from the series of

controlled human exposure studies that

address lung function responses

associated with 6.6-hour exposures to

03 and which were reviewed and

included in the final Criteria Document,

and this includes the Adams (2006)

study. EPA notes that the CASAC Panel

clearly did not judge the responses

observed in this study to be an "outlier." Rather, CASAC stated in its

comments on the Staff Paper's

discussion of this study, "there were

clearly a few individuals who

experienced declines in lung function at

these lower concentrations. These were

healthy subjects so the percentage of

asthmatic subjects, if they had been

studied, would most likely be

considerably greater" (Henderson,

2006c, p. 10).

Having considered comments on the

quantitative exposure and health risk

assessments from both groups of

commenters, the Administrator finds no

basis to change his position on these

quantitative assessments that was taken

at the time of proposal. That is, as

discussed above, while the

Administrator recognizes that the

assessments rest on a more extensive

body of data and is more comprehensive

in scope than the assessment conducted

in the last review, he is mindful that

significant uncertainties continue to

underlie the resulting quantitative

exposure and risk estimates.

Nevertheless, the Administrator

concludes that the exposure and risk

estimates are sufficiently reliable to

inform his judgment about the -

significance of the exposures and risk of

health effects in susceptible and

vulnerable populations at 03 levels

associated with just meeting the current

8-hour standard. However, the

Administrator disagrees with aspects of

these commenters' views on the level of

the standard that is appropriate and

supported by the available health effects

evidence and quantitative assessments

associated with just meeting alternative

standards.

3. Conclusions Regarding the Need for

Revision

Having carefully considered the

public comments, as discussed above,

the Administrator believes the

fundamental scientific conclusions on

the effects of 03 reached in the Criteria

Document and Staff Paper, briefly

summarized above in section II.A.2 and

discussed more fully in section II.A of

the proposal, remain valid. In

considering whether the primary 03

standard should be revised, the

Administrator places primary

consideration on the body of scientific

evidence available in this review on the

health effects associated with 03

exposure, as summarized above in

section II.B.1. The Administrator notes

that there is much new evidence that

has become available since the last

review, including an especially large

number of new epidemiological studies.

The Administrator believes that this

body of scientific evidence is very

robust, recognizing that it includes large

numbers of various types of studies,

"including toxicological studies,

,controlled human exposure studies,

field panel studies, and community

epidemiological studies, that provide

consistent and coherent evidence of an

array of 0 3-related respiratory morbidity

effects and possibly cardiovascularrelated morbidity as well as total

nonaccidental and cardiorespiratory

mortality. The Administrator observes

that (1) the evidence of a range of '

respiratory-related morbidity effects

seen in the last review has been

considerably strengthened, both through

toxicological and controlled human

exposure studies as well as through

many new panel and epidemiological

studies; (2) newly available evidence

from controlled human exposure and

epidemiological studies identifies

people with asthma as an important

susceptible population for which

estimates of respiratory effects in the

general population likely underestimate

the magnitude or importance of these

effects; (3) newly available evidence

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about mechanisms of toxicity mole

completely explains the biological

plausibility of 0 3-induced respiratory

effects and is beginning to suggest

mechanisms that may link 03 exposure

to cardiovascular effects; and (4) there is

now relatively strong evidence for

associations between 03 and total

nonaccidental and cardiopulmonary

mortality, even after adjustment for the

influence of season and PM. The

Administrator believes that this very

robust body of evidence, taken together,

enhances our understanding of 03-

related effects relative to what was

known at the time of the last review.

Further, he believes that the available

evidence provides increased confidence

that respiratory morbidity effects such

as lung function decrements and

respiratory symptoms are causally

related to 03 exposures, that indicators

of respiratory morbidity such as

emergency department visits and

hospital admissions are causally related

to 03 exposures, and that the evidence

is highly suggestive that 03 exposures

during the warm 03 season contribute to

premature mortality.

Further, the Administrator judges that

there is important new evidence

demonstrating that exposures to 03 at

'levels below the level of the current

standard are associated with a broad

array of adverse health effects. This is

especially true in at-risk populations

that include people with asthma or

other lung diseases, who are likely to

experience more serious effects from

exposure to 03, children, and older

adults with increased susceptibility, as well as those who are likely to be

vulnerable as a result of spending a lot

of time outdoors engaged in physical

activity, especially active children and

outdoor workers. The Administrator

notes that this important new evidence

demonstrates 0 3-induced lung function

effects and respiratory symptoms in

some healthy individuals down to the

previously observed exposure level of

0.080 ppm, as well as very limited new

evidence at exposure levels well below

the level of the current standard. In

addition, the Administrator notes that

(1) there is now epidemiological

evidence of statistically significant 03-

related associations with lung function

and respiratory symptom effects,

respiratory-related emergency

department visits and hospital

admissions, and increased mortality, in areas that likely would have met the

current standard; (2) there are also many

epidemiological studies done in areas

that likely would not have met the

current standard but which nonetheless

report statistically significant

associations that generally extend down

to ambient 03 concentrations that are below the level of the current standard;

(3) there are a few studies that have

examined subsets of data that include

only days with ambient 03

concentrations below the level of the

current standard, or below even much

lower 03 concentrations, and continue

to report statistically significant

associations with respiratory morbidity

outcomes and mortality; and (4) the

evidence from controlled human

exposure studies, together with animal

toxicological studies, provides

considerable support for the biological

plausibility of the respiratory morbidity

associations observed in the

epidemiological studies and for

concluding that the associations extend

below the level of the current standard.

Based on the available evidence, the

Administrator agrees with the CASAC

Panel and the majority of public,

commenters that the current standard is

not requisite to protect public health

with an adequate margin of safety

because it is does not provide sufficient

protection and that revision of the

current 03"standard is needed to

provide increased public health

protection. The Administrator notes that

extensive critical- review of this body of

evidence and related uncertainties

during the criteria and standard review"

process, including review by the

CASAC Panel and the public of the

basis for EPA's proposed decisfion to

revise the primary 03 standard, has

identified a number of issues about

which different reviewers disagree and

for which additional research is

Warranted. Nonetheless, on balance, the

Administrator believes that the

remaining uncertainties in the available

evidence do not diminish confidence in

the causal relationships between 03

exposures and indicators of serious

respiratory morbidity effects, or the

highly suggestive evidence of

associations between 03 exposures and

premature mortality, nor do they

diminish confidence in the conclusion

that the associations extend below the

level of the current standard. .Beyond a primary consideration of the

available evidence, the Administrator

has also taken into consideration the

Agency's exposure and risk assessments

to help inform his evaluation of the

adequacy of the current standard. As at

the time of proposal, the Administrator'

believes the results of those assessments

inform his judgment on the adequacy of

the current standard to protect against

health effects of concern. In considering

the exposure analysis results at this

time, the Administrator recognizes that

that there is a risk for confusion in the

term "exposure of concern" that was

used at the time of proposal, as it could

be read to imply a determination that a

certain benchmark level of exposure has

been shown to be causally associated

with adverse health effects. As a consequence, the Administrator believes

that it is more appropriate to consider

such exposure estimates in the context

of a continuum rather than focusing on

any one discrete benichmark level, as

was done at the time of proposal, since

the Administrator does not believe that

the underlying scientific evidence is

certain enough to support a focus on

any bright-line benchmark level. In so

doing, the Administrator recognizes that

associations between 03 exposures and

health effects of concern become

increasingly uncertain at lower 03

exposure levels. Thus, the

Administrator has taken into

consideration the pattern of such

exposure estimates across the range of

discrete benchmark levels considered in

EPA's exposure assessment to provide

some indication of the potential

magnitude of the incidence of health

outcomes that could not be evaluated in

the Agency's quantitative risk

assessment but which have been

demonstrated to occur in healthy people

at 03 exposures as low as 0.080 ppm,

the lowest level at which such health

outcomes have been tested.20

More specifically, the Administrator

has considered the pattern of reductions

in such exposures across the benchmark

levels of 0.080, 0.070, and 0.060 ppm,

which span the level at which there is

strong evidence of effects in healthy

people down to a level at which the

Administrator judges the-evidence of

effects to be very limited. The

Administrator observes that based on

the aggregated exposure estimates for

the 2002 simulation for the 12 urban

areas included in the exposure analysis,

upon just meeting the current standard,

the percentages of asthmatic or all

school age children likely to experience

one of more exposures at and above

these benchmark levels of 0.080, 0.070,

and 0.060 ppm (while at moderate or

greater exertion) are approximately 4%,

20 As noted above, such health outcomes include

increased airway responsiveness, increased

pulmonary inflammation, increased cellular

permeability, and decreased pulmonary defense

mechanisms. These physiological effects provide

plausible mechanisms underlying observed

associations with aggravation of asthma, increased

medication use, increased school and workabsences, increased susceptibility to respiratory

infection, increased visits to doctors' offices and

emergency departments, and increased admissions

to hospitals. In addition, these physiological effects,

if repeated over time, have the potential to lead to

chronic effects such as chronic bronchitis or longterm damage to the lungs that can lead to reduced

quality of life.

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20%, and 45%, respectively. As noted at

the time of proposal, the Administrator

recognizes that there is substantial yearto-year and city-to-city variability in

these estimates and that it is important

to recognize this variability in

considering these estimates. For

example, for the 0.080, 0.070, and 0.060

ppm benchmark levels, these

percentages are estimated to range from

approximately 1 to 10%, 1 to 40%, and

7 to 65%, respectively, across each of

the 12 urban areas based on the 2002

simulation, and from approximately 0 to

1%, 0 to 7%, and 1 to 25%,

respectively, based on the 2004

simulation.

With regard to the results of the risk

assessment, the Administrator again

considered the risks estimated to remain

upon just meeting the current standard.

The Administrator takes note of the

estimated magnitudes of such risks,

which are presented above in section

ll.B.1.c for a range of health effects

including moderate and large lung

function decrements (including

percentages of children and number of

occurrences), respiratory symptom days,

respiratory-related hospital admissions,

and nonaccidental and cardiorespiratory

mortality, as well as year-to-year and

city-to-city variability, and the

uncertainties in these estimates.

Further, the Administrator recognizes

that these estimated risks for the

specific health effects that could be -

analyzed in the Agency's risk

assessment are indicative of a much

broader array of 0 3 -related health

endpoints that are part of a "pyramid of

effects" that include various indicators

of morbidity that could not be included

in the risk assessment (e.g., school

absences, increased medication use,

emergency department visits) and

which primarily affect members of atrisk groups.

In considering these quantitative

exposure and risk estimates, as well as

the broader array of 0 3-related health

endpoints that could not be quantified,

the Administrator believes that they are

important from a public health

perspective and indicative of potential

exposures and risks to at-risk groups.

The Administrator thus finds that the

exposure and risk estimates provide

additional support to the evidencebased conclusion, reached above, that

the current standard needs to be revised.

Based on these considerations, and

consistent with CASAC Panel's

unanimous conclusion that there is no

scientific justification for retaining the

current standard, the Administrator

concludes that the current primary 03

standard is not sufficient and thus not

requisite to protect public health with

an adequate margin of safety, and that

revision is needed to provide increased

public health protection. It is important

to note that this conclusion, and the

reasoning on which it is based, does not

address the question of what specific

revisions are appropriate. That requires

looking specifically at the current

indicator, averaging time, form, and

level of the 03 standard, and evaluating

the evidence relevant to determining

whether and to what extent any of these

elements should be revised, as is

discussed in the following section.

C. Conclusions on the Elements of the

Primary 03 Standard

1. Indicator

In the last review of the air quality

criteria for 03 and other photochemical

oxidants and the 03 standard, as in

other prior reviews, EPA focused on a

standard for 03 as the most appropriate

surrogate for ambient photochemical

oxidants. In this review, while the

complex atmospheric chemistry in

which 03 plays a key role has been

highlighted, no alternatives to 03 have

been advanced as being a more

appropriate surrogate for ambient

photochemical oxidants.

The Staff Paper (section 2.2.2) noted

that it is generally recognized that

control of ambient 03 levels provides

the best means of controlling

photochemical oxidants. Among the

photochemical oxidants, the acute

exposure chamber, panel, and field

epidemiological human health database

provides specific evidence for 03 at

levels commonly reported in the

ambient air, in part because few other

photochemical oxidants are routinely

measured. However, recent

investigations on copollutant

interactions have used simulated urban

photochemical oxidant mixes. These

investigations suggest the need for

similar studies to help in understanding

the biological basis for effects observed

in epidemiological studies that are

associated with air pollutant mixtures,

where 03 is used as the surrogate for the

mix of photochemical oxidants. Meeting

the 03 standard can be expected to

provide some degree of protection

against potential health effects that may

be independently associated with other

photochemical oxidants but which are

not discemable from currently available

studies indexed by 03 alone. Since the

precursor emissions that lead to the

formation of 03 generally also lead to

the formation of other photochemical

oxidants, measures leading to

reductions in population exposures to

03 can generally be expected to lead to

reductions in population exposures to

other $ntkhihehmical oxidants.

The Staff Paper noted that while the

new body of time-series epidemiological

evidence cannot resolve questions about

the relative contribution of other

photochemical oxidant species to the

range of morbidity and mortality effects

associated with 03 in these types of

studies, control of ambient 03 levels is

generally understood to provide the best

means of controlling photochemical

oxidants in general, and thus of

protecting against effects that may be

associated with individual species and/

or the broader mix of photochemical

oxidants, independent of effects

specifically related to 03. No public

comments specifically suggested

changing the indicator for the 03

NAAQS.

In its letter to the Administrator, the

CASAC Panel noted that 03 is "the key

indicator of the extent of oxidative

chemistry and serves to integrate

multiple pollutants." The CASAC also

stated that "although 03 itself has direct

effects on human health and

ecosystems, it can also be considered as

indicator of the mixture of

photochemical oxidants and of the

oxidizing potency of the atmosphere"

(Henderson, 2006c, p. 9).

Based on the available information,

and consistent with the views of EPA

staff and the CASAC, the Administrator

concludes that it is appropriate to

continue to use 03 as the indicator for

a standard that is intended to address

effects associated with exposure to 03,

alone or in combination with related

photochemical oxidants. In so doing,

the Administrator recognizes that

measures leading to reductions in

population exposures to 03 will also

reduce exposures to other

photochemical oxidants.

2. Averaging Time

a. Short-Term and Prolonged (1 to 8

Hours)

The current 8-hour averaging time for

-the primary 03 NAAQS was set in 1997.

At that time, the decision to revise the

averaging time of the primary standard

from 1 hour to 8 hours was supported

by the following key observations and

conclusions:

(1) The 1-hour averaging time of the

previous NAAQS was originally

selected primarily on the basis of health

effects associated with short-term (i.e.,

1- to 3-hour) exposures.

(2) Substantial health effects

information was available for the 1997

review that demonstrated associations

between a wide range of health effects

(e.g., moderate to large lung function

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decrements, moderate to seve:e

respiratory symptoms and pulmonary

infiammation) and prolonged (i.e., 6- to

8-hour) exposures below the level of the

then current 1-hour NAAQS.

(3) Results of the quantitative risk

analyses showed that reductions in risks

from both short-term and prolonged

exposures could be achieved through a

primary standard with an averaging

period of either 1 hour or 8 hours. Thus

establishing both a 1-hour and an 8-hour

standard would not be necessary to

reduce risks associated with the full

range of observed health effects.

(4) The 8-hour averaging time was

more directly associated with health

effects of concern at lower 03

concentrations than the 1-hour

averaging time. It was thus the

consensus of the CASAC "that an 8-

hour standard was more appropriate for

a human health-based standard than a 1-

hour standard." (Wolff, 1995)

(5) An 8-hour averaging resulted in a

significantly more uniformly protective

national standard than the then current

1-hour standard.

(6) An 8-hour averaging time

effectively limits both 1- and 8-hour

exposures of concern. In looking at the new information that

is discussed in section 7.6.2 of the

current Criteria Document, the Staff

Paper noted that epidemiological

studies have used various averaging

periods for 03 concentrations, most

commonly 1-hour, 8-hour and 24-hour

averages. As described more specifically

in sections 3.3 and 3.4 of the Staff

Paper, in general the results presented

from U.S. and Canadian studies showed

no consistent difference for various

averaging times in different studies.

Because the 8-hour averaging time

continues to be more directly associated

with health effects of concern from

controlled human exposure studies at

lower concentrations than do shorter

averaging periods, the Staff Paper did

not evaluate alternative averaging times

in this review dnd did not conduct

exposure or risk assessments for

standards with averaging times other

than 8 hours.

The Staff Paper discussed an analysis

of a recent three-year period of air

quality data (2002 to 2004) which was

conducted to determine whether the

comparative 1- and 8-hour air quality

patterns that were observed in the last

review continue to be observed based on

more recent air quality data. This

updated air quality analysis (McCluney,

- 2007) was very consistent with the

analysis done in the last review in that

it indicated that only two urban areas of

the U.S. have such "peaky" air quality

patterns such that the ratio of 1-hour to

8-hour design values is greater than 1.5.

This suggested that based on recent air

quality data, it was again reasonable to

conclude that an 8-hour average

standard at or below the current level

would generally be expected to provide

protection equal to or greater than the

previous 1-hour standard of 0.12 ppm in

almost all urban areas. Thus, the Staff

Paper again concluded that setting a

standard with an 8-hour averaging time

can effectively limit both 1- and 8-hour

exposures of concern and is appropriate

to provide adequate and more uniform

protection of public health from both

short-term and prolonged exposures to

03 in the ambient air. In its letter to the

Administrator, the CASAC Panel

unanimously supported the continued

use of an 8-hour averaging time for the

primary 03 standard (Henderson 2007,

p. 2).

With respect to comments received on

the proposal, most public commenters

did not address the issue of whether

EPA should consider additional or

alternative averaging time standards. A

few commenters, most notably the CA

EPA and joint comments by ALA and

several environmental groups,

expressed the view that consideration

should be given to setting or reinstating

a 1-hour standard, in addition to

maintaining the use of an 8-hour

averaging time, to protect people in

those parts of the country with

relatively more "peaky" exposure

profiles (e.g., Los Angeles). These

commenters pointed out that when

controlled exposure studies using

triangular exposure patterns (with

relatively higher 1-hour peaks) have

been compared to constant exposure

patterns with the same aggregate 03

dose (in terms of concentration

multiplied by time), "peaky" exposure

patterns are seen to lead to higher risks.

The CA EPA made particular note of

this point, expressing the view that a 1-

hour standard would more closely

represent actual exposures, in that many

people spend only 1 to 2 hours a day

outdoors, and that it would be better

matched to 03 concentration profiles

along the coasts where 03 levels are

typically high for shorter averaging

periods than 8 hours.

For the reasons discussed in the Staff

Paper and summarized above and

considering the unanimous views of the

CASAC Panel supporting the continued

use of an 8-hour averaging time for the

primary 03 standard, the Administrator

finds that, in combination with the

decisions on form and level described

below, the 8-hour standard provides

adequate protection from both shortterm (1 to 3 hours) and prolonged (6 to

8 hours) exposures to 03 in the ambient

air and that it is appropriate to continue

use of the 8-hour averaging time for the

03 NAAQS.

b. Long-term

During the last review, there was a

large animal toxicological database for

consideration that provided clear

evidence of associations between longterm (e.g., from several months to years)

exposures and lung tissue damage, with

additional evidence of reduced lung.

elasticity and accelerated loss of lung

function. However, there was no

corresponding evidence for humans,

and the state of the science had not

progressed sufficiently to allow

quantitative extrapolation of the animal

study findings to humans. For these

reasons, consideration of a separate

long-term primary 03 standard was not

judged to be appropriate at that time,

recognizing that the 8-hour standard

would act to limit long-term exposures

as well as short-term and prolonged

exposures.

Taking into consideration the

currently available evidence on longterm 03 exposures, discussed above in

section II.A.2.a.ii, the Staff Paper

concluded that a health-based standard

with a longer-term averaging time than

8 hours is not warranted at this time.

The Staff Paper noted that while

potentially more serious health effects

have been identified as being associated

with longer-term exposure studies of

laboratory animals and in epidemiology

studies, there remains substantial

uncertainty regarding how these data

could be used quantitatively to develop

a basis for setting a long-term health

standard. Because long-term air quality

patterns would be improved in areas

coming into attainment with an 8-hour

standard, the potential risk of health

effects associated with long-term

exposures would be reduced in any area

meeting an 8-hofr standard. Thus, the

Staff Paper did not recommend

consideration of a long-term, healthbased standard at this time.

In its final letter to the Administrator,

the CASAC Panel offered no views on

the long-term exposure evidence, nor

did it suggest that consideration of a

primary 03 standard with a long-term

averaging time was appropriate, and

instead the CASAC Panel agreed with

the choice of an 8-hour averaging time

for the primary 03 NAAQS suggested by

Agency staff (Henderson, 2007).

Similarly, no public commenters

expressed support for considering such

a long-term standard. Taking into

account the evidence, the CASAC

Panel's views, and the public

comments, the Administrator finds that

there is not a sufficient basis for setting

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a long-term primary 03 NAAQS at this

time.

c. Administrator's Conclusions on

Averaging Time

In considering the information

discussed above, the CASAC Panel's

views and public comments, the

Administrator concludes that a standard

with an 8-hour ayeraging time can

effectively limit both 1- and 8-hour

exposures of concern and that an 8-hour

averaging time is appropriate to provide

adequate and more uniform protection

of public health from both short-term (1-

to 3-hour) and prolonged (6- to 8-hour)

exposures to 03 in the ambient air. This

conclusion is based on the observations

summarized above, particularly: (1) The

fact that the 8-hour averaging time is

more directly associated with health

effects of concern at lower 03

concentrations than are averaging times

of shorter duration and (2) results from

quantitative risk analyses showing that

attaining an 8-hour standard reduces the

risk of experiencing health effects

associated with both 8-hour and shorter

duration exposures. Furthermore, the

Administrator observes that the CASAC

Panel agreed with the choice of

averaging time (Henderson, 2007).

Therefore, the Administrator finds it

appropriate to retain the 8-hour

averaging time and to not set a separate

1-hour standard. The Administrator also

concludes that a standard with a longterm averaging time is not warranted at

this time.

3. Form

In 1997, the primary 03 NAAQS was

changed from a "l-expectedexceedance" form per year over three

years 21 to a concentration-based

statistic, specifically the 3-year average

of the annual fourth-highest daily

maximum 8-hour concentrations. The

principal advantage of the

concentration-based form is that it is

more directly related to the ambient 03

concentrations that are associated with

health effects of concern. With a

concentration-based form, days on

which higher 03 concentrations occur

would weigh proportionally more than

days with lower cortcentrations, since

the actual concentrations are used in

determining whether the standard is

attained. That is, given that there is a

continuum of effects associated with

exposures to varying levels of 03, the

extent to which public health is affected

21 The 1-expected-exceedance form essentially

requires that the fourth-highest air quality value in

3 years, based on adjustments for missing data, be

less than or equal to the level of the standard for

'the standard to be met at an air quality monitoring

site.

by exposure to ambient 03 is related to

the actual mnagnitde of the 03

concentration,. not *ist whether the

concentration is above a specified level.

During the 1997 review, consideration

was given to a range of alternative

forms, including the second-, third-,

fourth- and fifth-highest daily maximum

8-hour concentrations in an 03 season,

recognizing-that the public health risks

associated with exposure to a pollutant

without a clear, discernable threshold

can be appropriately addressed through

a standard that allows for multiple

exceedances'to provide increased

stability, but that also significantly

limits the number of days on which the

level may be exceeded and the

magnitude of such exceedances.

Consideration was given to setting a

standard with a form that would

provide a margin of safety against

possible, but uncertain, chronic effects

and would also provide greater stability

to ongoing control programs. The

fourth-highest daily maximum was

selected because it was decided that the

differences in the degree of protection

against potential chronic effects

afforded by the alternatives within the

range were not well enough understood

to use any such differences as a basis for

choosing the most restrictive forms. On

the other hand, the relatively large

percentage of sites that would

experience 03 peaks well above 0.08

ppm and the number of days on which

the level of the standard may be

exceeded even when attaining a fifthhighest 0.08 ppm concentration-based

standard, argued against choosing that

form.

As an initial matter, the Staff Paper

considered whether it is appropriate to

continue to specify the level of the 03

standard to the nearest hundredth (two

decimal places) ppm, or whether the

precision with which ambient 03

concentrations are measured supports

specifying the standard level to the

thousandth (three decimal places) ppm

(i.e., to the part per billion (ppb)). The

Staff Paper discussed an analysis

conducted by EPA staff to determine the

impact of ambient 03 measurement

error on calculated 8-hour average 03

design value concentrations, which are

compared to the level of the standard to

determine whether the standard is

attained (Cox and Camalier, 2006). The

results of this analysis suggested that

instrument measurement error, or

possible instrument bias, contribute

very little to the uncertainty in design

values. More specifically, measurement

imprecision was determined to

contribute less than 1 ppb to design

value uncertainty, and a simulation

study indicated that randomly occurring

instruiaent bias could contribute

apprqxciuately, , ppb. EPA staff

interpreted this analysis as being

supportive of specifying the level of the

standard to the thousandth ppm. If the

current standard were to be specified to

this degree of precision, the current

standard would effectively be at a level

of 0.084 ppm, reflecting the data

rounding conventions that are part of

the definition of the current 0.08 ppm

8-hour standard. This information was

provided to the CASAC Panel and made

available to the public.

In evaluating alternative forms for the

primary standard in conjunction with

specific standard levels, the Staff Paper

considered the adequacy of the public

health protection provided by the

combination of the level and form to be

the foremost consideration. In addition,

the Staff Paper recognized that it is

important to have a form of the standard

that is stable and insulated from the

impacts of extreme meteorological

events that are conducive to 03

formation. Such instability can have the

effect of reducing public health

protection, because frequent shifting in

and out of attainment due of

meteorological conditions can disrupt

an area's ongoing implementation plans

and associated control programs.

Providing more stability is one of the

reasons that EPA moved to a

concentration-based form in 1997.'

The Staff Paper considered two

concentration-based forms of the

standard: the nth-highest maximum

concentration and a percentile-based

form. A percentile-based statistic is

useful for comparing datasets of varying

length because it samples approximately

the same place in the distribution of air

quality values, whether the dataset is

several months or several years long.

However, a percentile-based form would

allow more days with higher air quality

values in locations with longer 03

seasons relative to places with shorter

03 seasons. An nth-highest maximum

concentration form would more

effectively ensure that people who live

in areas with different length 03 seasons

receive the same degree of public health

protection. For this reason, the exposure

and risk analyses were based on a form

specified in terms of an nth-highest

concentration, with n ranging from 3 to

5.

The results of some of these analyses

are shown in the Staff Paper (Figures 6-

1 through 6-4) and specifically

discussed in chapter 6. These figures

illustrate the estimated percent change

in risk estimates for the incidence of

moderate or greater decrements in lung

function (__ 15 percent FEV,) in all

school age children and moderate or

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greater lung function decrements ( - 10

percent FEV) in asthmatic school age

children, associated with going from

meeting the current standard to meeting

alternative standards with alternative

forms based on the 2002 and 2004

simulations. Figures 6-5 and 6-6

illustrate the estimated percent change

in the estimated incidence of nonaccidental mortality, associated with

going from meeting the current standard

to meeting alternative standards, based

on the 2002 and 2004 simulations.

These results are generally

representative of the patterns found in

all of the analyses. The estimated

reductions in risk associated with

different forms of the standard, ranging

from third- to fourth-highest daily

maximum concentrations at 0.084 ppm,

and from third- to fifth-highest daily

maximum concentrations at 0.074 ppm,

are generally less than the estimated

reductions associated with the different

levels that were analyzed. As seen in

these figures, there is much city-to-city

variability, particularly in the percent

changes associated with going from a

fourth-highest to third-highest form at

the current level of 0.084 ppm, and with

estimated reductions associated with

the fifth-highest form at a 0.074"pprm

level. In most cities, there are generally

only small differences in the estimated

reductions in risks associated with the

third- to fifth-highest forms at a level of

0.074 ppm simulated using 2002 and

2004 03 monitoring data.

The Staff Paper noted that there is not

a clear health-based rationale for

selecting a particular nth-highest daily

maximun form of the standard from

among the ones analyzed. It also noted

that the changes in the form considered

in the analyses result in only small

differences in the estimated reductions

in risks in most cities, although in sonde

cities larger differences are estimated.

The Staff Paper concluded that a range

of concentration-based forms from the

third-to the fifth-highest daily maximum

8-hour average cbncentration is

appropriate for 'consideration in setting

the standard. Given that there is a

continuum of effects associated with

exposures to varying levels of 03, the

extent to which public health is affected

by exposure to ambient 03 is related to

the actual magnitude of the 03

concentration, not just whether the

concentration is above a specified level.

The principal advantage of a

concentration-based form is that it is

more directly related to the ambient 03

concentrations that are associated with

health effects. Robust, concentrationbased forms, in the range of the thirdto fifth-highest daily maximum 8-hour

average concentration, including the

current 4th-highest daily maximum

form, minimize the inherent lack of

year-to-year stability of exceedancebased forms and provide insulation

from the impacts of extreme

meteorological events. Such instability

can have the effect of reducing public

health protection by disrupting ongoing.

implementation plans and associated

control programs.

With regard to the precision of the

standard, in its letter to the

Administrator, the CASAC concluded

that current monitoring technology "allows accurate measurement of 03

concentrations with a precision of parts

per billion" (Henderson, 2006c). The

CASAC recommended that the

specification of the level of the 03

standard should reflect this degree of

precision (Henderson, 2006c). While the

CASAC Panel unanimously supported

specifying the level of the standard to

this degree of precision, public

comments were mixed. Environmental

organizations (e.g., ALA et al.) and some

State/regional agencies (e.g.,

NESCAUM, PA Department of

Environmental Protection) supported

the proposed increased precision and

but did not support truncating to the

third decimal. However, several

industry associations (e.g., API, EMA,

AAAM) suggested that there is not

sufficient evidence to modify the 1997

decision to round to two decimal places.

These comments are addressed in the

Response to Comments document.

The Administrator concludes that the

level of the standard should be specified

to the thousandth ppm (three decimal

places), based on the staff's analysis and

conclusions discussed in the Staff Paper

that current monitoring technology

allows accurate measurement of 03 to

- support specifying the 8-hour standard

to this degree of precision, and on the

CASAC Panel's reasoning and

recommendation with respect to this

aspect of the standard.

With regard to the form of the

standard, in its letter to the

Administrator prior to proposal, the

CASAC recommended that "a range of

concentration-based forms from the

third-to the fifth-highest daily maximum

8-hour average concentration" be

considered (Henderson, 2006c, p, 5).

Several commenters supported

maintaining the current form of the

standard because it strikes an

appropriate balance between stability

and protection, as well as because EPA

used this form in their analyses (e.g.,

EMA, NESCAUM, and Pennsylvania

Department of Environmental

Protection). Some public commenters

that expressed the view that the current

primary 03 standard is not adequate

also submitted comments that

supported a more health-protective form

of the standard than the current form

(e.g., a second-or third-highest daily

maximum form) (e.g., ALA et al.). Most

commenters who expressed the view

that the current standard should not be

revised did not provide any views on

alternative forms that would be

appropriate for consideration should the

Administrator consider revisions to the

standard. A few industry association

and business commenters supported

changing to a 5th highest form (e.g.,

Dow Chemical, AAM). One commenter

(Oklahoma Department of

Transportation) suggested the use of a

6th or 7th highest daily maximum form.

The Administrator recognizes that

there is not a clear health-based

threshold for selecting a particular nthhighest daily maximum form of the

standard from among the ones analyzed

in the Staff Paper and that the current

form of the standard provides a stable

target for implementing programs to

improve air quality. The Administrator

also agrees that the adequacy of the

public health protection provided by the

combination of the level and form is a

foremost consideration. Based on this,

the Administrator finds that the form of

the current standard, 4th-highest daily

maximum 8-hour average concentration,

should be retained, recognizing that the

public health protection that would be

provided by this standard is based on

combining this form with the increased

health protection provided by the lower

level of the standard discussed in the

section below.

4. Level

a. Proposed Range

For the reasons discussed below, and

taking into account information and

assessments presented in the Criteria

Document and Staff Paper, the advice

and recommendations of the CASAC,

and the public comments received prior

to proposal, the Administrator proposed

to revise the existing 8-hour primary 03

standard. Specifically, the

Administrator proposed to revise the

level of the primary 03 standard to

within'a range from 0.070 to 0.075 ppm.

The Administrator's consideration of

alternative levels of the primary 03

standard builds on his proposal,

discussed above, that the overall body of

evidence indicates that the current 8-

hour 03 standard is not requisite to

protect public health with an adequate

margin of safety because it does not

provide sufficient protection, and that

revision would result in increased

public health protection, especially for

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members of at-risk groups, notably

including asthmatic children and other

people with lung disease, as well as all

children and older adults, especially

those active outdoors, and outdoor

workers, against an array of adverse

health effects. These effects range from

health outcomes that could be

quantified in the risk assessment,

including decreased lung function,

respiratory symptoms, serious

indicators of respiratory morbidity such

as hospital admissions for respiratory

causes, and nonaccidental mortality, to

health outcomes that could not be

directly estimated, including pulmonary

inflammation, increased medication

use, emergency department visits, and

possibly cardiovascular-related

morbidity effects. In reaching a

proposed decision about the level of the

03 primary standard, the Administrator

considered: the evidence-based

considerations from the Criteria

Document and the Staff Paper; the

results of the exposure and risk

assessments discussed above and in the

Staff Paper, giving weight to the

exposure and risk assessments as judged

appropriate; CASAC advice and

recommendations, as reflected in

discussions of drafts of the Criteria

Document and Staff Paper at public

meetings, in separate written comments,

and in CASAC's letters to the

Administrator; EPA staff

recommendations; and public

comments received during the

development of these documents, either

in connection with CASAC meetings or

separately. In considering what 8-hour

standard is requisite to protect public

health with an adequate margin -of

safety, the Administrator noted at the

time of proposal that he was mindful

that this choice requires judgment based

on an interpretation of the evidence and

other information that neither overstates

nor understates the strength and

limitations of the evidence and

information nor the appropriate

inferences to be drawn.

The Administrator noted that the

most certain evidence of adverse health

effects from exposure to 03 comes from

the clinical studies and that the large

bulk of this evidence derives from

studies of exposures at levels of 0.080

and above. At those levels, there is

consistent evidence of lung function

decrements and respiratory symptoms

in healthy young adults, as well as

evidence of inflammation and other

medically significant airway responses.

Moreover, there is no evidence that the

0.080 ppm level is a threshold for these

effects. Although the Administrator took

note of the very limited new evidence

of lung function decrements and

respiratory symptoms in some healthy

individuals at the 0.060 ppm exposure

level, he judged this evidence too

limited to support a primary focus at

this level. The Administrator also noted

that clinical studies, supported by

epidemiological studies, provide

important new evidence that people

with asthma were likely to experience

larger and more serious effects than

healthy people from exposure to 03.

There were also epidemiological studies

that provide evidence of statistically

significant associations between shortterm 03 exposures and more serious

health effects, such as emergency

department visits, hospital admissions,

and premature mortality, in areas that

likely would have met the current

standard. The Administrator also took

note of the many epidemiological

studies done in areas that likely would

not have met the current standard but

which nonetheless report statistically

significant associations that generally

extend down to ambient 03

concentrations that were below the level

of the current standard. Further, there were a few studies that have examined

subsets of data that include only days

with ambient 03 concentrations below

the level of the current standard, or

below even much lower 03

concentrations, and continued to report

statistically significant associations with

respiratory morbidity outcomes and

mortality. In considering this evidence,

the Administrator noted that the extent

to which these studies provide evidence

of causal relationships with exposures

to Oi alone, down to the lowest levels

observed, remains uncertain. EPA

sought comment on the degree to which

associations observed in

epidemiological studies reflect causal

relationships between important health

endpoints and exposure to 03 alone at

ambient 03 levels below the current

standard.

Therefore, the Administrator judged

at the time of pr6posal, and continues

to judge as discussed in section II.B.3,

that revising the current standard to

protect public health with an adequate

margin of safety is warranted and would

reduce risk to public health, based on:

(1) The strong body of clinical evidence

in healthy people at exposure levels of

0.080 and above of lung function

decrements, respiratory symptoms,

pulmonary inflammation, and other

medically significant airway responses,

as well as some indication of lung

function decrements and respiratory

symptoms at lower levels; (2) the

substantial body of clinical and

epidemiological evidence indicating

that people with asthma are likely to

experience larger and more serious

effects than healthy people; and (3) the

body of epidemiological evidence

indicating associations are observed for

a wide range of serious health effects,

including respiratory emergency

department visits, hospital admissions,

and premature mortality, at and below

0.080 ppm. The Administrator also

judged at the time of proposal and

continues to conclude that the estimates

of exposures of concern and risks

remaining upon just meeting the current

standard or a standard at the 0.080 ppm

level provide additional support for this

view. For the same reasons stated in the

proposal notice and discussed above in

section II.B on the adequacy of the

current standard, the Administrator

judges that the standard should be set

below 0.080 ppm, a level at which the

evidence provides a high degree of

certainty about the adverse effects of 03

exposure even in healthy people.

The Administrator next considered

what standard level below 0.080 ppm

would be requisite to protect public

health with an adequate margin of safety

that is sufficient, but not more than

necessary, to achieve that result,

recognizing that such a standard would

result-in increased public health

protection. The assessment of a standard

level calls for consideration of both the

degree of additional protection that

alternative levels of the standard might

be expected to provide as well as the

certainty that any specific level will in

fact provide such protection. In the

circumstances present in this review,

there is no evidence-based bright line

that indicates a single appropriate level.

Instead there is a combination of

scientific evidence and other

information that needs to be considered

holistically in making this public health

policy judgment and selecting a standard level from a range of

reasonable values.

The Administrator noted that at

exposure levels below 0.080 ppm there

is only a very limited amount of

evidence from clinical studies,

indicating effects in some healthy

individuals at levels as low as 0.060

ppm. The great majority of the evidence

concerning effects below 0.080 ppm is

from epidemiological studies. The

epidemiological studies do not identify

any bright-line threshold level for

effects. At the same time, the

epidemiological studies are not in and

of themselves direct evidence of a

causal link between exposure to 03 and

the occurrence of the effects. The

Administrator considers these studies in

the context of all the other available

evidence in evaluating the degree of

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certainty that 0 3-related adverse health

effects would occur at various ambient

levels below 0.080 ppm, including the

strong human clinical studies and the

toxicological studies that demonstrate

the biological plausibility and

mechanismis for the effects of 03 on

airway inflammation and increased

airway responsiveness at exposure

levels of 0.080 ppm and above.

Based on consideration of the entire

body of evidence and information

available at this time, as well as the

recommendations of the CASAC, the

Administrator proposed that a standard

within the range of 0.070 to 0.07"5 ppm

would be requisite to protect public

health with an adequate margin of

safety. As noted at the time of proposal,

a standard level within this range is

estimated to reduce the risk of a variety

of health effects associated with

exposure to 03, including the

respiratory symptoms and lung function

effects demonstrated in clinical studies,

and in emergency department visits,

hospital admissions, and mortality

effects indicated in the epidemiological

studies. All of these effects are

indicative of a much broader array of

03-related health endpoints, as

represented by the pyramid of effects,

such as school absences and increased

medication use that are plausibly linked

to these observed effects.

The Administrator also considered

the degree of improvements in public

health that potentially could be

achieved by a standard of 0.070 to 0.075

ppm, giving weight to the exposure and

risk assessments as he judged

appropriate. As discussed in the

proposal notice (section II.D.4) in

considering the results of the exposure

assessment, the Administrator primarily

focused on exposures at and above the

0.070 ppm benchmark level as an

important surrogate measure for

potentially more serious health effects

for at-risk groups, including people with

asthma. In so doing, the Administrator

noted that although the analysis of

"exposures of concern" was conducted

to estimate exposures at and above three

discrete benchmark levels, the concept

is appropriately viewed as a continuum.

As discussed above, the Administrator

strives to balance concern about the

potential for health effects and their

severity with the increasing uncertainty

associated with our understanding of

the likelihood of such effects at lower

03 exposure levels. In focusing on this

benchmark, the Administrator noted

that upon just meeting a standard

within the range of 0.070 to 0.075 ppm

based on the 2002 simulation, the

number of school age children likely to

experience exposures at and above this

benchmark level in aggregate (for the 12

cities in the assessment) was estimated

to be approximately 2 to 4 percent of all

and asthmatic children and generally

less than 10 percent of children even in

cities that receive the least degree of

protection from such a standard in a

recent year with relatively high 03

levels. A standard within the 0.070 to

0.075 ppm range would thus

substantially reduce exposures of

concern by about 90 to 80 percent,

respectively, from those estimated to

occur upon just meeting the current

standard. While placing less weight on

the results of the risk assessment, in

light of the important uncertainties

inherent in the assessment, the

Administrator noted that the results

indicated that a standard set within this

range would likely reduce risks to atrisk groups from the 0 3-related health

effects considered in the risk

assessment, and by inference across the

much broader array of 0 3-related health

effects that could only be considered

qualitatively, relative to the level of

protection afforded by the current

standard. This lent support to the

proposed range.

The Administrator judged that a

standard set within the range of 0.070 to

0.075 ppm would provide a degree of

reduction in risk that is important from

a public health perspective and that a

standard within this range would be

requisite to protect public health,

including the health of at-risk groups,

with an adequate margin of safety.

EPA's evaluation of the body of

scientific evidence and quantitative

estimates of exposures and risks

indicated that substantial reductions in

public health risks would occur

* throughout this range. As noted in the

proposal notice, because there is no

bright line clearly directing the choice

of level within this reasonable range, the

choice of what is appropriate,

considering the strengths and

limitations of the evidence, and the

appropriate inference to be drawn from

the evidence and the exposure and risk

assessments is a public health policy

judgment. To further inform this

judgment, EPA sought public comment

on the extent to which the

epidemiological and clinical evidence

provide guidance as to the level of a

standard that would be requisite to

protect public health with an adequate

margin of safety, especially for at-risk

groups.

In considering the available

information, the Administrator also

judged that a standard level below 0.070

ppm would not be appropriate. In

reaching this judgment, the

Administrator noted that there was only

quite limited evidence from clinical

studies at exposure levels below 0.080

ppm 03. Moreoyer, the Administrator

recognized that in the body of

epidemiological evidence, many studies

reported positive and statistically '

significant associations, while others

reported positive results that were not

statistically significant, and a few did

not report any positive 03-related

associations. In addition, the

Administrator judged that evidence of a

causal relationship between adverse

health outcomes and 03 exposures

became increasingly uncertain at lower

levels of exposure.

The Administrator also considered

the results of the exposure assessments

in reaching his judgment that a standard

level below 0.070 ppm would not be

appropriate. The Administrator noted

that in considering the rdsults from the

exposure assessment, a standard set at

the 0.070 ppm level, with the same form

as the current standard, was estimated

to provide substantial reductions in.

exposures of concern (i.e.,

approximately 90 to 92 percent

reductions in the numbers of school age

children and 94 percent reduction in the

total number of occurrences) for both all

and asthmatic school age children

relative to just meeting the current -

standard based on a simulation of a

recent year with relatively high 03

levels (2002). Thus, a 0.070 ppm

standard would be expected to provide

protection from the exposures of

concern that the Administrator had

primarily focused on for over 98 percent

of all and asthmatic school age children

even in a year with relatively high 03

levels, increasing to over 99.9 percent of

children in a year with relatively low 03

levels (2004).

In considering the results of thehealth risk assessment, as discussed in

the proposal notice (section II.C.2), the

Administrator noted that there were

important uncertainties and

assumptions inherent in the risk

assessment and that this assessment was

most appropriately used to simulate

trends and patterns that could be

expected, as well as providing informed,

but still imprecise, estimates of the

potential magnitude of risks. The

Administrator particularly noted that as

lower standard levels were modeled,

including a standard set at a level below

0.070 ppm, the risk assessment

continued to assume a causal link

between 03 exposures and the

occurrence of the health effects

examined, such that the assessment

continued to indicate reductions in 03-

related risks upon meeting a lower

standard level. As discussed above,

however, the Administrator recognized

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that evidence of a causal relationship

between adverse health effects and 03

exposures becomes increasingly

uncertain at lower levels of exposure.

Given all of the information available to

him at the time of the proposal, the

Administrator judged that the increasing

uncertainty of the existence and

magnitude of additional public health

protection that standards below 0.070

ppm might provide suggested that such

lower standard levels would likely be

below what is necessary to protect

public health with an adequate margin

of safety.

In addition, the Administrator judged

that a standard level higher than 0.075

ppm would also not be appropriate.

This judgment took into consideration

the information discussed in the

proposal notice (sections IL.A and B)

and was based on the strong body of

clinical evidence in healthy people at

exposure levels of 0.080 ppm and above,

the substantial body of clinical and

epidemiological evidence indicating

that people with asthma are likely to

experience larger and more serious'

effects than healthy people, the body of

epidemiological evidence indicating

that associations are observed for a wide

range of more serious health effects at

levels below 0.080 ppm, and the

estimates of exposure and risk

remaining upon just meeting a standard

set at 0.080 ppm. The much greater

certainty of the existence and magnitude

of additional public health protection

that such levels would forego provides

the basis for judging that levels above

0.075 ppm would be higher than what

is requisite to protect public health,

including the health of at-risk groups,

with an adequate margin of safety.

For the reasons discussed in more

detail in the proposal notice and

summarized above, the Administrator

proposed to revise the level of the

primary 03 standard to within the range

of 0.070 to 0.075 ppm.

At the time of proposal, the

Administrator recognized that sharply

divergent views on the appropriate level

of this standard had been presented to

EPA as part of the NAAQS review

process, and he solicited comment on a

wide range of standard levels and

alternative approaches to characterizing

and addressing scientific uncertainties.

One such alternative view focused very

strongly on the uncertainties inherent in

the controlled human exposure and

epidemiological studies and

quantitative exposure and health risk

assessments as the basis for concluding

that no change to the current 8-hour 03

standard of 0.084 ppm was warranted.

In sharp contrast, other viewed the

controlled human exposure and

epidem iological studies as strong and

robust, and generally placed more

weight on the results of the quantitative

exposure and risk assessments and the

unanimous CASAC recommendations as

a basis for concluding that an 8-hour

standard at or below*0.070 ppm was.

warranted. As discussed below, the

-same sharply divergent views were

generally repeated in comments on the

proposal by the two distinct groups of

commenters identified in II.B:2 above.

b. Comments on Level

i. Health Evidence Considerations

With regard to the evaluation and

consideration of the health effects

evidence and how such information

should be considered in the decision on

the standard level, EPA notes that the

commenters fell into the same two

groups discussed above in section II.B.2.

The two groups often cited the same

studies and evidence, but they reached

sharply divergent conclusions as to

what standard level is supported by the

health effects evidence. The general

views of both groups on the

interpretation and use of the health

effects evidence are presented above in

section II.B.2.a, with most comments

from one group arguing that this

evidence supports a decision to revise

the 8-hour standard to 0.060 ppm or

be14w, and the other group arguing that

it supports a decision not to revise the

current 8-hour standard.

With regard to the evidence from

controlled human exposure studies,

commenters that included public health

and environmental groups who

supported revising the current standard

expressed the view that the large body

of evidence available at the time of the

last review, demonstrating an array of

adverse health effects (i.e., reduced lung

function, respiratory symptoms,

increased airway responsiveness,

inflammation, and increased

susceptibility to respiratory infection),

at concentrations of 0.080 ppm 03,

indicated that the standard should have

been set at a lower level. These

commenters noted that standards must

be set below the level shown to cause

effects in healthy subjects in order to

protect sensitive populations with an

adequate margin of safety. As discussed

in section II.B.2.a above, these

commenters focused on the results of -

the Adams studies (2002, 2006) as

evidence that exposure to 0.060 ppm 03

will result in a significant proportion

(i.e., 7%) of the adult population who

do not have asthma or other lung

diseases experiencing notable lung

function decrements (FEV decrement

(>10%), and furthermore that larger

decrements in FEVI would be expected

in more susceptible populatiohs. This

evidence caused these commenters to

reject EPA's proposed range:

Clearly, EPA's proposed standard of 0.070

to 0.075 ppm cannot be considered protective

of public health in light of experimental

evidence demonstrating adverse respiratory

effects in healthy individuals exposed to

0.060 ppm, and the legal requirements to

protect sensitive populations with an adequate margin of safety. [ALA et al., p. 511

The second group of commenters,

who opposed revision of the standard,

expressed the view that the group. mean

changes reported in the Adams studies

(2002, 2006) were small, that such

decrements should not be considered to

be adverse, and that the individuals

who experienced larger responses were -

too few to serve as a basis for a revised

03 standard. This group included

virtually all commenters representing

industry associations and businesses.

These general comments are addressed

above in section ll.B.2.a and in more

detail in the Response to Comments

document.

In considering comments received on

controlled human exposure studies, and

how these studies support a focus on

particular standard levels, the

Administrator observes that in general

the comments support his original view

that these studies provide the mpst

certain evidence of adverse health

effects, and that the large bulk of

evidence derives from studies of

exposures at levels of 0.080 ppm and

above. The Administrator notes that

since the last review important new

evidence includes demonstration of 03-

induced lung function effects and

respiratory symptoms in some healthy

adults down to the previously observed

exposure level of 0.080 ppm, as well as

very limited new evidence of the same

effects at exposure levels well below the

level of the current standard (Adams,

2'002, 2006). EPA disagrees with these

comrnmenters that the percent of subjects

that experienced FEV decrements

greater than 10% in this study of 30

subjects can appropriately be

generalized'to the U.S. population.

Based on careful consideration of the

comments, the Administrator again

concludes that while the Adams studies

provide evidence that some healthy

individuals will experience lung

function decrements and respiratory

symptoms at the 0.060 ppm exposure

level, this evidence is too limited to

support a primary focus at this level.

Moreover, the Administrator notes that

while the CASAC Panel supported a

level of 0.060 ppm, they also supported

a level above 0.060, indicating that they

disagree with the commenters' view that

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the resi;lt ofAdams studies mean that.,,

the level, qthe standard has to be set- ,

at 0.060 ppm.

With regard to the information from

epidemiological studies, commenters

representing public health,

environmental, and medical

organizations generally asserted that the

large body of new epidemiological

studies provides evidence of causal

associations between 03 exposures and

a wide array of respiratory and

cardiovascular morbidity effects,

including emergency department visits

and hospital admissions. They

expressed the view that a significant

body of strong, consistent evidence

links short-term exposures to premature

mortality and noted that this evidence is

supported by new research that

provides biological plausibility for such

effects. These conmenters noted that

various approaches, including air .

quality' assessments which show that

statistically significant associations

occurred in areas that likely would have

met the current standard, or statistical

approaches that examined subsets of the

data which indicate that statistically

significant associations remain down to

very low ambient 03 levels, show effects

well below the level of the current

standard. Moreover they identified

particular studies, including some "new" studies not considered in the

Criteria Document, that-indicated there

are additional sub-populations that are

likely to be sensitive to 03, including

infants, women, and African-Americans,

that should be considered in deciding

the requisite level of protection. They

asserted that this information supports a

standard set at a level no higher than

0.060 ppm 03.

With regard to the information from

epidemiological studies, the second

group of commenters focused strongly

on EPA's interpretation of the

epidemiological evidence and the

uncertainties they saw in this evidence

as a basis for concluding that no change

to the currentlevel of the 8-hour 03

standard is warranted. In commenting

on the proposed range of levels, these

commenters generally relied on the

same arguments presented above in

section II.B.2.a as to why they believed

it would be inappropriate for EPA to

make any revisions to the primary 03

standard. That is, they asserted that the

health effects of concern associated with

short-term or prolonged exposures to 03

have not changed significantly since

1997; that the inconsistencies and

uncertainties inherent in these studies

as a whole should preclude any reliance

on them as justification for a more

stringent standard; and that "new"

science not included in the Criteria

Doqvment continues to increase

uncertainty about possible health risks

associated with exposure to 03. Specific

methodological issues cited as

additional support for their conclusions

included: adequacy of exposure data;

potential confounding by copollutants;

model selection; inconsistent evidence

relating 03 exposure to mortality, and "new" studies that provide additional

evidence of inconsistencies. These.

general comments are addressed above

in section IIB.2.a, and in greater detail

in the Response to Comments

document.

In considering these comments on the

epidemiological evidence with regard to

the interpretation of the epidemiological

evidence and methodological issues, the

Administrator notes that in general,

most of the issues and concerns raised

by those who do not support any

revisions to the primary 03 standard

with regard to the interpretation of the

epidemiological evidence fid . I .

methodological issues" 'e§i i Wtii":

restatements if issues rii '& ing th&

review of the Criteria Documen and

Staff Paper. The same is true of the

views of commenters who supported a

level of the standard no higher than

0.060 ppm 03. EPA presented and the

CASAC Panel reviewed the

interpretation of the epidemiological

evidence in the Criteria Document and

the integration of the evidence with

policy considerations in the

development of the policy options

presented in the Staff Paper for

consideration by the Administrator.

CASAC reviewed the scientific content

of both the Criteria Document and'Staff

Paper and advised the Administrator

that these documents provided an

appropriate basis for use in regulatory

decision making. Therefore, these

comments do not provide a basis for the

Administrator to reach fundamentally

different conclusions than he reached at

the time of proposal.

Moreover, the Administrator notes

that epidemiological evidence is most

appropriately evaluated.in the context

of all available evidence, including

evidence from controlled human

exposure and toxicological studies. In

general, the Administrator agrees with

the weight of evidence approach used in

the Criteria Document and believes that

this body of scientific evidence across

all types of studies is very robust,

recognizing that it includes a large

number of various types of studies that

provide consistent and coherent

evidence of an array of 0 3-related

respiratory morbidity effects and

possibly cardiovascular-related

morbidity as well as total nonaccidental

and cardiorespiratory mortality. More

specifically, the Administrator judges

that the body of epidemiological

evidence indicating associations with a

wide range of serious health effects,

including respiratory emergency

department visits and hospital

admissions and premature mortality, at

and below 0.080 ppm suppprts revising

the current standard to -protect public

health. While the great majority of

evidence concerning effects below 0.080

ppm was from epidemiological studies,

the epidemiological studies do not

identify any bright-line threshold level

for effects. At the same time, the

epidemiological studies are nbt

themselves direct evidence of a causal

link between exposure to 03 and the

occurrence of the effects. Therefore,

Administrator has considered these

studies in the context of all the other

available evidence in evaluating the

degree of certainty that 0 3-related

adverse health effects would occur at

various ambient levels below 0.080

ppm. In that context, there is only quite

limited evidence from controlled human

exposure studies at exposure levels

below 0.080 ppm 03. The Administrator

recognizes that in the body of

epidemiological evidence, many studies

reported positive and statistically

significant associations, while others

reported positive results that were not

statistically significant, and a few did

not report any positive 0 3-related

associations. In addition, the

Administrator judged that evidence of a

causal relationship between adverse

health outcomes and 03 exposures'

became increasingly uncertain at lower

levels of exposure. Based on this the

Administrator continues to believe that

the body of epidemiological evidence

does not support setting a standard as

low as 0.060 as suggested by some

commenters.

The Administrator also notes the

many epidemiological studies done in

areas that likely would not have met the

current standard but which nonetheless

report statistically significant

associations that generally extend down

to ambient 03 concentrations that were

below the level of the current standard.

Further, there were a few studies that

have examined subsets of data that

include only days with ambient 03

concentrations below the level of the

current standard, or below even much

lower 03 concentrations, and continued

to report statistically significant

associations with respiratory morbidity

outcomes and mortality. In the context

of the strong clinical evidence of

adverse effect in healthy adults at 0.080,

the Administrator finds that the body of

epidemiological evidence does not

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support retaining a standard of 0.080, as

suggested by commenters.

Both groups of commenters also

considered evidence from controlled

human exposure and epidemiological

studies of increased susceptibility in

people with lung disease, especially

people with asthma, but they reached

sharply divergent conclusions about

what standard level is supported by this

evidence. As discussed above in section

II.B.2.a, medical organizations and

public health and environmental groups

agreed with EPA that, based on

evidence from controlled human

exposure and epidemiological studies,

people with asthma, especially children,

are likely to have greater lung function

decrements and respiratory symptoms

in response to 03 exposure than people

who do not have asthma, and are likely

to respond at lower levels. Furthermore,

these commenters noted that

epidemiological studies have identified

other potentially sensitive

subpopulations, including for example,

infants, women and African-Americans,

and that effects in these groups should

be part of the consideration in providing

an adequate margin of safety. These

commenters concluded that the

appropriate level for the primary 03

standard is 0.060 ppm, to provide

protection for members of sensitive

groups, especially people with asthma,

who are likely to have more serious

responses and to respond at lower levels

that healthy people. They also

contended that a standard set at this

level also would provide protection

against anticipated, but as yet unproven

effects in the additional groups cited.

The Administrator agrees with these

commenters that important new

evidence shows that asthmatics have

more serious responses, and are more

likely to respond at lower O3 leVels,

than healthy individuals. Moreover, he

agrees that this evidence supports a

standard set at a level below 0.080 ppm

03, based on the strong evidence from

human clinical studies in healthy adults

at this level. However, for the reasons

described above, he does not agree that

the controlled human exposure and

epidemiological evidence provide

support for a standard set at 0.060 ppm,

for the reasons discussed above.

In contrast, industry association and

business commenters asserted that EPA

is wrong to claim that new evidence

indicates that the current standard does

not provide adequate health public

health protection for people with

asthma. In support of this position,

these commenters made the following

major comments: (1) The lung function

decrements and respiratory symptoms

observed in clinical studies of

asthmatics are not clinically important;

(2) EPA postulates that asthmatics . -1

would likely experience more serious

responses and responses at lower levels

than the subjects of controlled human

exposure experiments, but that

hypothesis is not supported by scientific

evidence; and, (3) EPA recognized

asthmatics as a sensitive subpopulation

in 1997, and new information does not

suggest greater susceptibility than was

previously believed. EPA has generally

responded to these comments and those

summarized in the paragraph above in

section II.B.2.a above, and in greater

detail in the Response to Comments

document.

After careful consideration of these

comments, the Administrator continues

to judge that there is important new

evidence demonstrating that exposures

to 03 at levels below the level of the

current standard are associated with a

broad array of adverse health effects,

especially in at-risk populations that

include people with asthina or other

lung diseases who are likely to

experience more serious effects from

exposure to 03, as well as children and

older adults with increased

susceptibility, and those who are likely

to be vulnerable as a result of spending

a lot of time outdoors engaged in

physical activity, especially active

children and outdoor workers. The

Administrator notes that this important

new evidence demonstrates 0 3-induced

lung function effects and respiratory

symptoms in some healthy individuals

down to the previously observed

exposure level of 0.080 ppm, as well as very limited new evidence at exposure

levels well below the level of the

current standard. In addition, there are

many epidemiological studies done in

areas that likely would not have met the

current standard but which nonetheless

report statistically significant

associations that generally extend down

to ambient 03 concentrations that were

below the level of the current standard.

Further, there were a few studies that

have examined subsets of data that

include only days with ambient 03

concentrations below the level of the

current standard, or below even much

lower 03 concentrations, and continued

to report statistically significant

associations with respiratory morbidity

outcomes and mortality. The

Administrator recognizes that in the

body of epidemiological evidence, many

studies reported positive and

statistically significant-associations,

while others reported positive results

that were not statistically significant,

and a few did not report any positive

0 3-related associations. In addition, the

Administrator judged that evidence of a

causal relationship between adverse

health outcomes and 03 exposures

became increasingly uncertain at lower

levels of exposure. This body of

evidence provides a strong basis for the

Administrator's judgment that the

standard needs to be revised to provide

more protection, and that a revised

standard must be set at a level

appreciably below 0.080 ppm, the level

at which there is considerable evidence

of effects in healthy people. At the same

time, for the reasons discussed above

the Administrator judges that this body

of evidence does not support setting a standard as low as 0.060, as suggestedby other commenters.

ii. Exposure and Risk Considerations

With regard to considering how the

quantitative exposure and health risk

assessments should factor into.a

decision on the standard level, EPA

notes that both groups of commenters

generally consider these assessments in

their comments on the standard level,

but they reach sharply divergent

conclusions as to what standard level is

supported by these assessments. The

general views of both groups on the

implications of the exposure and risk

assessment are presented above in

section II.B.2.b, with one group arguing

that it supports a decision to revise the

8-hour standard to 0.060 ppm or below,

and the other group arguing that it

supports a decision not to revise the

current 8-hour standard.

A joint set of comments from ALA

and several environmental groups

expressed the view that EPA cannot use

exposures of concern to justify a

standard in the range of 0.070 to 0.075

ppm. These commenters contended that

standards in the proposed range would

continue to expose too many asthmatic

children, as well as other at risk groups

such as outdoor workers and preschool

children, to "demonstrably unhealthy

levels of ozone pollution" in only 12

cities which does not represent a

national estimate (ALA et al., p, 106).

'These same commenters asserted that if

EPA were to consider exposures of

concern, then the benchmark level must

be defined as 0.060 ppm based on the

considerable evidence of adverse health

effects occurring at this level. As

disoussed in section II.B.2.b above, they

also cited various reasons why the

exposure estimates were

underestimated, including: only 12

cities were included in the assessment,

various at risk groups including outdoor

workers and preschool children were

not included in the assessment, and

EPA's exposure assessment

underestimated exposures since it

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children -Who spend more time outdoors'

and repeated exposures also were

underestimated.

In contrast, industry association and

business group commenters expressed

the view that the concept of exposures

of concern should not be considered as

a basis for revising the level of the

standard because it provided no

indication of the probability that

individuals would actually experience

an adverse health effect. These same

commenters also provided various

reasons why the exposure estimates

were overestimated based on specific

methodological choices made by EPA

including, for example, 03

measurements at fixed-site monitors can

be higher than other locations where

individuals are exposed, the exposure

estimates do not account for 03

avoidance behaviors, and the exposure

model overestimates elevated breathing

rates. Finally, these commenters also

contended that the estimates of

exposures of concern associated with

just meeting the current standard, using

the 0.080 ppni benchmark levels, have

not appreciably changed since the prior

review and, thus provide no support for

revising the current standard.

EPA has responded to the criticisms

from both groups of commenters related

to concerns that the exposute estimates

are either underestimated or

overestimated in section II.B.2.b above

and in more detail in the Response to

Comments document. EPA also has

addressed the issues raised by both

groups of commenters concerning the

appropriateness of considering

exposures at and above various

benchmark levels as an element in the

decision on the adequacy of the current

standard in section ll.B.2.b.

As discussed in section H.B.2b, the

Administrator believes that it is

appropriate to consider such exposure

estimate-in the context of a continuum

rather than focusing on any one discrete

benchmark level, as was done at the

time of proposal, since the

Administrator does not believe that the

underlying evidence is certain enough

to support a focus on any single brightline benchmark level. Thus, the

Administrator believes it is appropriate

to consider a range of benchmark levels

from 0.080 down to 0.060 ppm,

recognizing that exposures at and above

these benchmark levels must be

considered in the context of a

continuum of the potential for health

effects of concern, and their severity,

with increasing uncertainty associated

With the likelihood of such effects at

lower 03 exposure levels.

The Administrator recognizes that the

0.080 ppm benchmark level represents a

level at which several health outcomes,

including lung inflammation, increased

airway responsiveness, and decreased

resistance to infection have been shown

to occur in healthy adults. The

Administrator places great weight on

the public health significance of

exposures at and above this benchmark

level given the greater certainty that

these adverse health responses are likely

to be observed in a significant fraction

of the at-risk population. With respect to

his decision on the level of the 8-hour

standard, the Administrator notes that

upon just meeting a standard within the

range of 0.070 to 0.075 ppm based on

the 2002 simulation, the number of

school age asthmatic children likely to

experience exposuresat and above the

0.080 ppm benchmark level in aggregate

(for the 12 cities in the assessment) is

estimated to range from 0,1. to 0.4

percent of asthmatic scbqc,age.

children. Based on the,2P0jiljqWrA- ethe estimates are even lower, with no

asthmatic children estimated to

experience exposures at and above the

0.080 ppm benchmark level. Similar

patterns are observed for all school age

children. Recognizing the uncertainties

inherent in the exposure assessment, the

Administrator concludes that the

exposure assessment suggests that

exposures at and above the 0.080 ppm

level, where several health effects have

been shown to occur in healthy

individuals, are eliminated or nearly

eliminated depending on the modeling

year upon just meeting a standard

within the range of 0.070 to 0.075 ppm.

The Administrator does not agree

with those commenters who would only

consider the single benchmark level of

0.080 ppm. While the Administrator

places less weight on exposures at and

above the 0.070 pm benchmark level,

given the increased uncertainty about

the fraction of the population and

severity of the health responses that

might occur associated with exposures

above this level, he believes that it is

appropriate to consider exposures at

this benchmark as well in judging the

adequacy of the current standard to

protect public health. Consideration of

the 0.070 ppm benchmark level

recognizes that the effects observed at

0.080 ppm were in healthy adult

subjects and sensitive population

groups, such as asthmatics, are expected

to respond at lower 03 levels than

healthy individuals. The Administrator

notes that upon just meeting a standard

within the range of 0.070 to 0.075 ppm

based on the 2002 simulation, the

number of asthmatic school age children

likely to experience exposures at and

above the 0.070 ppm benchmark level in

aggregate (for the 12 cities in the

assessment) is estimated to range from

about 2 to 5 percent of asthmatic school

age children. Based on the 2004

simulation, the estimates are

substantially lower, with 0 to 0.6

percent of asthmatic children estimated

to experience exposures at and above

the 0.070 ppm benchmark level upon

just meeting a standard within the range

of 0.070 to 0.075 ppm.

Finally, the Administrator has

considered but places very little weight

on the benchmark level of 0.060 ppm

given the very limited scientific

evidence supporting a conclusion that

03 is causally related to various health

outcomes at this exposure level.

Nevertheless, the Administrator

observes that there is a similar pattern

of reductions in exposures of concern

for all and asthmatic school age children

at this benchmark level as well when

comparing the 0.070 ppm and 0.075

ppm 8-hour standards.

Given the degree of uncertainty

associated with the exposure assessment

discussed in the Staff Paper and

uncertainty assessment (Langstaff,

2007), the Administrator judges that for

each specific benchmark level examined

there is not an appreciable difference

from a public health perspective, in the

estimates of exposures associated with

air quality just meeting an 8-hour

standard at 0.075 ppm versus an 8-hour

standard set at 0.070 ppm. For example,

given the uncertainty in the exposure

estimates, the difference between an

estimate of 2 percent and 5 percent of

asthmatic children for the exposure

benchmark of 0.070 is not'an

appreciable difference from a public

health perspective. While directionally

there are likely to be fewer exposures at

and above this benchmark for a standard

of 0.070 than a standard of 0.075 ppm,

given the uncertainty in the exposure

assessment it is not at all clear that the

actual difference is large enough to

present a public health concern. With regard to considering how the

quantitative risk assessment should

factor into a decision on the standard

level, as noted above both groups of

commenters generally considered the

risk assessment in their comments on

the standard level, but they reached

sharply divergent conclusions as to

what standard level is supported by the

risk assessment. More specifically, the

environmental, public health, and most

medical organizations, and some State

and regional air pollution agencies (e.g.,

California, NESCAUM) contended that

EPA's proposed range of 0.070 to 0.075

ppm would result in significant residual

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public health risks. As articulated most

fully in the joint set of comments from

ALA and several environmental

organizations, these commenters

expressed the view that EPA's risk

assessment clearly demonstrates that a

more stringent 8-hour 03 standard of

0.065 ppm, the most stringent standard

analyzed by EPA, would significantly

decrease 0 3-related lung function

decrements, respiratory symptoms,

hospital admissions, and mortality and

that "EPA must adopt a more stringent

ozone standard of 0.060 ppm or belowa level that incorporates a more

adequate margin of safety" (ALA et aL.,

p. 108). These same commenters also

cited various reasons for asserting that

the risk assessment likely

underestimates health risks to a

substantial degree, including the limited

nature of the assessment with respect to

number of cities, populations covered,

and health endpoints analyzed. EPA has

responded to the comments concerning

the scope of the risk assessment and

assertion that health risks are likely

underestimated both in section ll.B.2.b

above and in more detail in the

Response to Comments document. The

Administrator's reasoning and

conclusions regarding the weight he

places on the health risk assessment in

reaching a judgment about the

appropriate level for the primary

standard are discussed below in section

II.C.4.c.

In contrast, industry association and

business group commenters who

supported not revising the level of the

current 8-hour standard generally

asserted the following points: (1) That

risk estimates have not changed

significantly since the prior review in

1997; (2) that uncertainties and

limitations underlying the risk

assessment make it too speculative to.be

used in supporting a decision to revise

the standard; (3) that EPA should have

defined PRB differently and that EPA

underestimated PRB levels, which

results in health risk reductions

associated with more stringent

standards being overestimated; and (4)

that health risks are overestimated based

on specific methodological choices

made by EPA including, for example,

selection of inappropriate effect

estimates fi-Rm health effect studies,

EPA's appro ch to addressing the shape

of exposure-response relationships, and

whether or not to incorporate thresholds

into its models for the various health

effects analyzed. EPA has responded to

these comments both in section II.B.2.b

above and in more detail in the

Response to Comments document.

In summary, the Administrator

concludes that the exposure assessment

suggests that exposures at and above the

0.080 ppm benchmark level, where 1 - ,-

several health effects have been shown

to occur in healthy individuals, are

essentially eliminated for standards in

the range of 0.070 to 0.075 ppm. He also

concludes that at the 0.070 ppm

benchmark level, the exposures are

substantially reduced and eliminated for

the vast majority of people in at-risk

groups, and that the very low estimates

of such exposures are not appreciably

different, from a public health

perspective, between those exposures

associated with just meeting a standard

set at 0.070 ppm or 0.075 ppm. Further,

the Administrator places relatively little

weight on the exposures using the 0.060

ppm benchmark level given the very

limited scientific evidence supporting a

conclusion that 03 is causally related to

health outcomes at this exposure level.

Considering the uncertainties associated

with the exposure assessment, the

Ad.pinstrat roncludes that the

exposure esa es associated with each

of the b6UBiML levels are not

appret bly different, between a 0.070

or 0.075 ppm standard, and therefore,

the exposure assessment does not

provide a basis for choosing a level

within the proposed range.

While the Administrator places less

weight on the results of the risk

assessment, he notes that the results

indicate that a standard set within the

proposed range would likely reduce

risks to at-risk groups from the 03-

related health effects considered in the

assessment, and by inference across the

much broader array of 0 3-related health

effects that can only be considered

qualitatively, relative to the level of

protection afforded by the current

standard. Moreover, he notes that the

results of the assessment suggest a

gradual reduction in risks with no clear

breakpoint as increasingly lower

standard levels are considered. In light

of this continuum and the important

uncertainties inherent in the assessment

discussed above and in the proposal, the

Administrator concludes that the risk

assessment does not provide a basis for

choosing a level *within the proposed

range.

c. Conclusions on Level

Having carefully considered the

public comments on the appropriate

level of the 03 standard, as discussed

above, the Administrator believes the

fundamental scientific conclusions on

the effects of 03 reached in the Criteria

Document and Staff Paper, briefly

summarized above in section II.A.2 and

discussed more fully in section ll.A of

the proposal, remain valid. In

considering the level at which the

primary 03 standard should be'set, the

Administrator continues to pla~e

primary consideration on the body of

scientific evidence available in this

review on the health effects associated

with 03 exposure, as summarized above

in section II.C.4.a, while viewing the

results of exposure and risk assessment,

discussed above in section II.C.4.b, as

providing information in support of his

decision. In considering the available

scientific evidence he judges that, as at

the proposal, a focus on the proposed

range of 0.070 to 0.075 ppm is

appropriate in light of the large body of

controlled human exposure and

epidemiological and other scientific

evidence! As discussed above, this body

of evidence does not support retaining

the current standard, as suggested by

some commqnters. Nor does it support

setting a level just below 0.080 ppm

because, based on the entire body of

evidence, such a level would not

provide a significant increase in

protection compared to the current

standard. Further, such a level would

not be appreciably below the level in

controlled human exposure studies at

which adverse effects have been

demonstrated (i.e., 0.080 ppm). This

body of evidence also does not support

setting a level of 0.060 ppm or below,

as suggested by other commenters. The

Administrator has also evaluated the

information from the exposure

assessment and the risk assessment, and

judges that this evidence does not

provide a clear enough basis for

choosing a specific level within the

range of 0.075 to 0.070 ppm. In making

a final judgment about the level of the

03 standard, the Administrator notes

that the level of 0.075 ppm is above the

range recommended by the CASAC (i.e.,

0.070 to 0.060 ppm). Placing great

weight on the views of CASAC, the

Administrator has carefully considered

its stated views and the scientific basis

and policy views for the range it

recommended. In so doing, the

Administrator notes that he fully agrees

that the scientific evidence supports the

conclusion that the current standard is

not adequate and must be revised.

With respect to CASAC's

recommended range of standard levels,

the Administrator observes that the

basis for its recommendation appears to

be a mixture of scientific and policy

considerations. The Administrator notes

that he is in general agreement with

CASAC's views concerning the

interpretation of the scientific evidence.

The Administrator also notes that there

is no bright line clearly directing the

choice of level, and the choice of what

is appropriate is clearly a public health

| I ll I I I hll " T I I I I I

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policy judgment entrusted to the

Administrator. This judgment must

include consideration of the strengths

and limitations of the evidence and the

appropriate inferences to be drawn from

the evidence and the exposure and risk

assessments. In reviewing the basis for

the CASAC Panel's recommendations

for the range of the 03 standard, the

Administrator observes that he reaches

a different policy judgment than the

CASAC Panel based on apparently

placing different weight in two areas:

the role of the evidence from the Adams

studies and the relative weight placed

on the results from the exposure and

risk assessments. While he found the

evidence reporting effects at the 0.060

ppm level from the Adams'studies to be

too limited to support a primary focus

at this level, the Administrator observes

that the CASAC Panel- appears to place

greater weight on this evidence, as

indiqated by its recommendation of a

range down to 0.060 ppm. The

Administrator also observes that while

the CASAC Panel supported a level of

0.060 ppm, they also supported a level

above 0.060, indicating that they do not

believe that the results of Adams studies

mean that the level of the standard has

to be set at 0.060 ppm. The.

Administrator also observes that the

CASAC Panel appeared to place greater

weight on the results of the risk

assessment as a basis for its

recommended range. In referring to the

results of the risk assessment results for

lung function, respiratory. symptoms,

hospital admissions and mortality, the

CASAC Panel concluded that:

"beneficial effects in terms of reduction

of adverse health effects were calculated

to occur at the lowest concentration

considered (i.e., 0.064 ppm)"

(Henderson, 2006c, p. 4). However, the

Administrator more heavily weighs the

implications of the uncertainties

associated with the Agency's

quantitative human exposure and health

risk assessments, as discussed above in

section H.A.3. Given these uncertainties,

the Administrator does not agree that

these assessment results appropriately

serve as a primary basis for concluding

that levels at or below 0.070 ppm are

required for the 8-hour 03 standard.

After carefully taking the above

comments and considerations into

account, and fully considering the

scientific and policy views of the

CASAC, the Administrator has decided

to revise the level of the primary 8-hour

03 standard to 0.075 ppm. In the

Administrator's judgment, based on the

currently available evidence, a standard

set at this level would be requisite to

protect public health with an adequate

margin of safety, including the health of

sensitive subpopulations, from serious

health effects including respiratory

morbidity, that is judged to be causally

associated with short-term and

prolonged exposures to 03, and

premature mortality. A standard set at

this level provides a significant increase

in protection compared to the current

standard, and is appreciably below

0.080 ppm, the level in controlled

human exposure studies at which

adverse effects have been demonstrated.

At a level of 0.075, exposures at and

above the benchmark of 0.080 ppm are

essentially eliminated, and exposures at

and above the benchmark of 0.070 are

substantially reduced or eliminated for

the vast-majority of people in at-risk

groups. A standard set at a level lower

than 0.075 would only result in

significant further public health

protection if, in fact, there is a

continuum of health risks in areas with

8-hour average 03 concentrations that

are well below the concentrations

observed in the key controlled human

exposure studies and if the reported

associations observed in

epidemiological studies are, in fact,

causally related to 03 at those lower

levels. Based on the available evidence,

the Administrator is not prepared to

make these assumptions. Taking into

account the uncertainties that remain in

interpreting the evidence from available

controlled human exposure and

epidemiological studies at very low

levels, the Adminisitrator notes that the

likelihood of obtaining benefits to

public health with a standard set below

0.075 ppm 03 decreases, while the

likelihood of requiring reductions in

ambient concentrations that go beyond

those that are needed to protect public

health increases. The Administrator

judges that the appropriate balance to be

drawn, based on the entire body of

evidence and information available in

this review, is a standard set at 0.075.

The Administrator believes that a

standard set at 0.075 ppm would be

sufficient to protect public health with

an adequate margin of safety, and does

not believe that a lower standard is

needed to provide this degree of

protection. This judgment by the

Administrator appropriately considers

the requirement for a standard that is

neither more nor less stringent than

necessary for this purpose and

recognizes that the CAA does not

require that primary standards be set at

a zero-risk level, but rather at a level

that reduces risk sufficiently so as to

protect public health with an adequate

margin of safety.

D. Final Decision on the Primary 03

Standard

For the reasons discussed above, and

taking into account information and

assessments presented in the Criteria

Document and Staff Paper, the advice

and recommendations of the CASAC

Panel, and the public comments to date,

the Administrator has decided to revise

the existing 8-hour primary 03 standard.

Specifically, the Administrator is

revising (1) the level of the primary 03

standard to 0.075 ppm and (2) the

degree of precision to which the level of

the standard is specified to the

thousandth ppT. The revised 8-hour

primary standard, with a level of 0.075

ppm, would be met at an ambient air

monitoring site when the 3-year average

of the annual fourth-highest daily

maximum 8-hour average 03

concentration is less than or equal to

0.075 ppm. Data handling conventions

are specified in the new Appendix P

that is adopted, as discussed in section

V below.

At this time, EPA is also promulgating

revisions to the Air Quality Index for 03

to be consistent with the revisions to the

primary 03 standard. These revisions

are discussed below in section III. Issues

related to the monitoring requirements

for the revised 03 primary standard are

discussed below in section VI.

mI. Communication of Public Health

Information

Information on the public health

implications of ambient concentrations

of criteria pollutants is currently made

available primarily through EPA's Air

Quality Index (AQI) program (40 CFR

58.50). The current Air Quality Index

has been in use since its inception in

1999 (64 FR 42530). It provides

accurate, timely, and easily

understandable information about daily

levels of pollution. The AQI establishes

a nationally uniform system of indexing

pollution levels for 03, CO, NO2, PM

and SO 2. The AQI converts pollutant

concentrations in a community's air to

a number on a scale from 0 to 500.

Reported AQI values enable the public

to know whether air pollution levels in

a particular location are characterized as

good (0-50), moderate (51-100),

unhealthy for sensitive groups (101-

150), unhealthy (151-200), very

unhealthy (201-300), or hazardous

(301-500). The AQI index value of 100

typically corresponds to the level of the

short-term NAAQS for each pollutant.

For the 1997 03 NAAQS, an 8-hour

average concentration of 0.084 ppm

corresponds to an AQI value of 100. An

AQI value greater than 100 means that

a pollutant is in one of the unhealthy

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categories (i.e., unhealthy for sensitive

groups, unhealthy, very unhealthy, or

hazardous) on a given day; an AQI value

at or below 100 means -that a pollutant

concentration is in one of the

satisfactory categories (i.e., good or

moderate). Decisions about the pollutant

concentrations at which to set the

various AQI breakpoints, that delineate

the various AQI categories, draw

directly from the underlying health

information that supports the NAAQS

review.

The Agency recognized the

importance of revising the AQI in a

timely manner to be consistent with any

revisions to the NAAQS. Therefore, EPA

proposed to finalize conforming changes

to the AQI, in connection with the

Agency's final decision on the 03

NAAQS if revisions to the primary

standard were promulgated. These

conforming changes would include

setting the 100 level of the AQI at the

same level as the revised primary 03

NAAQS, and also making proportional

adjustments to AQI breakpoints at the

* lower end of the range (i.e., AQI values

of 50, 150 and 200). EPA did not

propose to change breakpoints at the

higher end of the range (from 301 to

500), which would apply to State

contingency plans or the Significant

Harm Level (40 CFR 51.16), because the

information from this review does not

inform decisions about breakpoints at

those higher levels.

EPA received relatively few

comments on the proposed changes to

the AQI. Three major issues came up in

the comments, including: (1) Whether

the AQI should be revised at all, even

if the primary standard is revised; (2)

whether the AQI should be revised in

conjunction with this rulemaking, or in

a separate rulemaking; and, (3) whether

an AQI value of 100 should be set equal

to or lower than the level of the shortterm primary 03 standard, and the other

breakpoints adjusted accordingly.

UARG asserted that EPA should not

revise the AQI at all, even if EPA does

revise the primary 03 standard. In

support of this view, UARG noted that

there is no requirement for EPA to set

an AQI value of 100 equal to the level

of the short-term standard, and cited the

1999 decision to set an AQI value of 100

for PM2 .

5 equal to 40 gig/m 3 , when the

level of the short-term standard was

then 65 gg/m 3

. UARG also expressed the

view that lowering the ambient

concentrations associated with different

AQI values would confuse and mislead

the public about actual trends in air

quality, which UARG asserted are

improving. ALA and other

environmental groups in a joint set of

comments did not support revising the

AQI in conjunction with this

rulemaking. ALA et a1. expressed the

view that since EPA did not propose

specific breakpoints in its proposed

revisions to the AQI, EPA should

conduct a separate rulemaking,

specifying the'proposed breakpoints to

allow the public an opportunity to

comment on them. Several State

agencies, including agencies from

Pennsylvania, Wisconsin and

Oklahoma, and State organizations,

including NACAA and NESCAUM,

supported revising the AQI at the same

time that the standard is revised.

NACAA expressed the view that: "The

effectiveness of the AQI as a public

health tool will be undermined if EPA

undertakes regulatory changes to the

ozone NAAQS without simultaneously

revising the AQI." (NACAA, p. 5) The

Wisconsin Department of Natural

Resources (WI DNR) further noted that:

"* * * when the 24-hour PM2 .

5 standard

was revised, EPA missed an opportunity to

adopt- conforming changes to the AQI. The

Administrator signed the Federal Register

notice promulgating a revised fine-particle

standard in September 2006, but EPA still

hqs not changed the AQI to reflect the revised

standard. We recommend that the AQI be

amended to be consistent with the revised ozone and PM 2.

5 standards." [WI DNR, p. 3]

Finally, ALA et al. and NESCAUM

expressed the view that an AQI value of

100 should be set at an ambient

concentration below the range for the

proposed primary standard. These

commenters cited the health evidence

showing adverse health effects below

the proposed range of the standard, the

recommended range of.CASAC, and also

cited the 1999 decision to set an AQI

value of 100 for PM2.

5 equal to 40 gg/ m3 when the level of the short-term

standard was 65 ig/m3, as support for

this view. Most other State commenters

supported setting an AQI value of 100

equal -to the level of the primary 03

standard.

Recognizing the importance of the

AQI as a communication tool that

allows the public to take exposure

reduction measures when air quality

may pose health risks, EPA agrees with

State agencies and organizations that

favored revising the AQI at the same

time as the primary standard. EPA

agrees with State agency commenters

that its historical approach of setting an

AQI value of 100 equal to the level of

the revised primary standard is

appropriate, both from a public health

and a communication perspective.

Both UARG and ALA et al. cite the

1999 AQI rulemaking, which set an AQI

value of 100 for PM2.

5 equal to 40 jig/

m3 , a lower level than the level of the

short-term PM2.

5 standard, as support

for their view that an AQI value of 100

does not need to be set at the level of

the revised 03 standard. However, the

sub-index for PM2.5 was developed

using an approach that was

conceptually consistent with past

practice for selecting the air quality

concentrations associated with the AQI

breakpoints. The Agency's historical

approach to selecting index breakpoints

had been to simply set the AQI value of

100 at the level of the short-term

standard (e.g., 24 hours) for a pollutant.

This method of structuring the index is

appropriate in the case where a shortterm standard is set to protect against

the health effects associated with shortterm exposures and/or an annual

standard is set to protect against health

effects associated with long-term

exposures. In such cases, the short-term

standard in effect defines a level of

health protection provided against

short-term risks and thus can be a useful

benchmark against which to compare

daily air quality concentrations.

In the case of the 1997 PM2 .

5

standards, EPA took a different

approach to protecting against the

health risks associated with short-term

exposures. The intended level of

protection against short-term risk was

not defined by the 24-hour 9tandard (set

at a level of 65 gg/m 3 ) but by the

combination of the 24-hour and the

annual standards working in concert. In

fact, the annual standard (set 't a level

of 15 gg/m 3 ) was intended to serve as

the principal vehicle for protecting

against both long-term and short-term

PM2 .

5 exposures by lowering the entire

day-by-day distribution of PM2 .

5

concentrations in an area throughout the

year. See generally 62 FR at 38668-70

(July 18, 1997). Because the 24-hour

standard served to provide additional

protection against very high short-term

concentrations, localized "hotspots," or

risks arising from seasonal emissions

that would not be well-controlled by a

national annual standard, EPA

consequently concluded that it would

be appropriate to caution members of

sensitive groups exposed to

concentrations below the level of the 24-

hour standard. EPA also concluded that

it would be inappropriate to compare

daily air quality concentrations directly

with the level of the annual standard by

setting an AQI value of 100 at that level.

EPA wanted to set the AQI value of 100

to reflect the general level of health

protection against short-term risks

offered by the annual and 24-hour

standards combined, consistent with the

underlying logic of the historical

approach to establishing AQI 100 levels.

Therefore EPA set the AQI value of 100

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at the midpoint of the range between the

annual and the 24-hour PM 2.

5 standards

(i.e., 40 gg/m3) in order to reflect the

.combined role of the 24-hour and the

annual PM2.5 standards in protecting

against short-terjn risks. Therefore, this

approach for defining an AQI value of

100 is conceptually consistent with the

proposed decision to set an AQI value

of 100 equal to the level of the primary

03 standard.

Therefore, EPA is revising the AQI for

03 by setting an AQI value of 100 equal

to 0.075 ppm, 8-hour average, the level

of the revised primary 03 standard. EPA

is also revising the following

breakpoints: An AQI valde of 50 is set

at 0.059 ppm, an AQI value of 150 is set

at 0.095 ppm, and an AQI value of 200

is set at 0.115 ppm. All these levels are

averaged over 8 hours. As indicated in

the proposal, these levels were

developed by making proportional

adjustments to the other AQI

breakpoints (i.e., AQI values of 50, 150

and 200). The proportional adjustments

were modified slightly to allow for each

category to span at least a 0.015 ppm

range to allow for more accurate

forecasting. So, for example, simply

making a proportional adjustment to the

level of an AQI value of 150 (0.104 ppm)

would result in a level of about 0.092

ppm. Since most of these ranges are

rounded to the nearest 5 thousandths of

a ppm, that rounding would have -

resulted in a 0.014 ppm range (i.e.,

0.076 to 0.090 ppm). So, the number

was rounded upward to the nearest 5

thousandths of a ppm, to allow for at

least a 0.015 ppm range for forecasting.

The same principle applies to the

calculation of an AQI value for 200

(0.115 ppm). EPA believes that the

finalized breakpoints provide a balance

between proportional adjustments to

reflect the revised 03 standard and

providing category ranges that are large

enough to be forecasted accurately, so

that the new AQI for 03 can be

implemented more easily in the public

forum for which the AQI ultimately

exists.

IV. Rationale for Final Decision on

Secondary 03 Standard

A. Introduction

1. Overview

This section presents the rationale for

the Administrator's final decisions

regarding the need to revise the current

secondary 03 NAAQS, and the

appropriate revisions to the standard.

As discussed more fully below, the

rationale for the final decisions on

appropriate revisions to the secondary

03 NAAQS is based on a thorough

review of the latest scientific

information on vegetation effects

associated with exposure to ambient

levels of 03, as assessed in the Criteria

Document. This rationale also takes into

account: (1) Staff assessments of the

most policy-relevant information in the

Criteria Document regarding the

evidence of adverse effects of 03 to

vegetation and ecosystems, information

oh biologically-relevant exposure

metrics, and staff analyses of air quality,

vegetation exposure and risks, presented

in the Staff Paper and described in

greater detail in the associated

Technical Report on Ozone Exposure,

Risk, and Impact Assessments for

Vegetation (Abt, 2007), upon which staff

recommendations for revisions to the

secondary 03 standard were based; (2)

CASAC Panel advice and

recommendations as reflected in

discussion of drafts of the Criteria

Document and Staff Paper at public

meetings, in separate written comments,

and in CASAC's letters to the

Administrator (Henderson, 2006a, b, c;

2007); (3) public comments received

during development of these documents

either in conjunction with CASAC

meetings or separately and on the

proposal notice; (4) consideration of the

degree of protection to vegetation

potentially afforded by the revised 8-

hour primary standard; and (5) the

limits of the available evidence.

In developing this rationale, EPA has

again focused on direct 03 effects on

vegetation, specifically drawing upon an

integrative synthesis of the entire body

of evidence, published through early

2006, on the broad array of vegetation

effects associated with exposure to

ambient levels of 03 (EPA, 2006a,

chapter 9). In addition, because 03 can

also indirectly affect other ecosystem

components such as soils, water, and

wildlife, and their associated ecosystem

goods and services, through its effects

on vegetation, a qualitative discussion

of these other indirect impacts is also

included, though these effects are not

quantifiable at this time. As was

concluded in the 1997 review, and

based on the body of scientific-literature

assessed in the current Criteria

Document, the Administrator believes

that it is reasonable to conclude that a

secondary standard protecting the

public welfare from known or

anticipated adverse effects to trees,

native vegetation and crops would also

afford increased protection from adverse

effects to other environmental

components relevant to the public -

welfare, including ecosystem services

and function. The peer-reviewed

literature includes studies conducted in

the U.S., Canada, Europe, and many

*other countries around the world. In its

assessment of the evidence judged to be

most relevant to making decisions on

the level of the 03 secondary standard,

however, EPA has placed greater weight

on U.S. studies, due to the often

species-, site- and climate-specific

nature of 0 3-related vegetation response.

As with virtually any policy-relevant

vegetation effects research, there is

uncertainty in the characterization of

vegetation effects attributable to

exposure to ambient 03. As discussed

below, however, research conducted

since the last review provides important

information coming from field-based

exposure studies, including free air,

gradient and biomonitoring surveys, in

addition to the more traditional

controlled open top chamber (OTC)

studies. Moreover, the newly available

studies evaluated in the Criteria

Document have undergone intensive

scrutiny through multiple layers of peer

review and many opportunities for

public review and comment. While

important uncertainties remain, the

review of the vegetation effects

information has been extensive and

deliberate. In the judgment of the.

Administrator, the intensive evaluation

of the scientific evidence that has

occurred in this review has provided an

adequate basis for regulatory decisionmaking at this time. This review also

provides important input to EPA's

research plan for improving our future

understanding of the effects of ambient

03 at lower levels.

Information related to vegetation and

ecosystem effects, biologically relevant

exposure indices, and quantitative

vegetation exposure and risk

assessments were summarized in

sections IV.A through IV.C of the

proposal (72 FR at 37883-37895),

respectively, and are only briefly

outlined below in sections IV.A.2

through IV.A.4. Subsequent sections of

this preamble provide a more complete

discussion of the Administrator's

rationale, in light of key issues raised in

public comments, for concluding that

the current standard is not requisite to

protect public welfare from known or

anticipated adverse effects, and it is

appropriate to revise the current

secondary 03 standard to provide

additional public welfare protection

(section IV.B) by making the secondary

standard identical to the revised

primary standard (section IV.C). A

summary of the final decisions on

revisions to the secondary 03 standard

is presented in section IV.D.

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2. Overview of Vegetation Effects

Evidence

This section outlines the information

presented in section IV.A of the

proposal on known or potential effects

on public welfare which may be

expected from the presence of 03 in

ambient air. Exposures to 03 have been

associated quantitatively and

qualitatively with a wide range of

vegetation effects. The decision in the

last review to set a more protective

secondary standard primarily reflected

consideration of the quantitative

information on vegetation effects

available at that time, particularly

growth impairment (e.g., biomass loss)

in sensitive forest tree species during

the seedling growth stage and yield loss

in important commercial crops. This

information, derived mainly using the

OTC exposure method, found

cumulative, seasonal 03 exposures were

most strongly associated with observed

vegetation response. The Criteria

Document prepared for this review

discussed a number of additional

studies that support and strengthen key

conclusions regarding 03 effects on

vegetation and ecosystems found in the

previous Criteria Document (EPA,

1996a, 2006a), including further

clarification of the underlying

mechanistic and physiological processes

at the subcellular, cellular, and whole

system levels within the plant. More

importantly, however, in the context of

this review, new quantitative

information is now available across a

broader array of vegetation effects (e.g.,

growth impairment during seedlings,

saplings and mature tree growth stages,

visible foliar injury, and yield loss in

annual crops) and across a more diverse

set of exposure methods, including

chamber, free air, gradient, model, and

field-based observation. These nonchambered, field-based study results

begin to address one of the key data

gaps cited by the Administrator in the

last review.

Section IV.A of the proposal provides

a detailed summary of key information

contained in the Criteria Document

(EPA, 2006, chapter 9) and in the Staff

Paper (EPA, 2007, chapter 7) on known

or potential effects on public welfare

which may be expected from the

presence of 03 in ambient air (72 FR

37883-37890). The information in that

section summarized:

(1) New information available on

potential mechanisms for vegetation

effects associated with exposure to 03,

including information on plant uptake

of 03, cellular to systemic responses,

compensation and detoxification

responses, changes to plant metabolism,

and plant responses to chronic 03

exposures;

(2) The nature of effects on vegetation

that have been associated with exposure

to 03 including effects related to

carbohydrate production and allocation,

growth effects on trees and yield

reductions in crops, visible foliar injury,

and reduced plant vigor, as well as

consequent potential impacts on

ecosystems including potential

alteration of ecosystem structure and

function and effects on ecosystem

services and carbon sequestration; and

(3) Considerations in characterizing

what constitutes an adverse welfare

impact of 03, including an approach

that expands the consideration of

adversity beyond the species level by

making explicit the linkages between

stress-related effects such as 03

ex~osure at the species level and at

higher levels within an ecosystem

hierarchy.

3. Overview of Biologically Relevant

Exposure Indices

This section outlines the information

presented in section IV.B of the

proposal on biologically relevant

exposure indices that relate known or

potential effects on vegetation to

exposure to 03 in ambient air. The

Criteria Document concluded that 03

exposure indices that cumulate

differentially weighted hourly

concentrations are the best candidates

for relating exposure to plant growth

responses (EPA, 2006a). This conclusion

followed from the extensive evaluation

of the relevant studies in the 1996

Criteria Document (EPA, 1996a) and the

recent evaluation of studies that have

been published since that time (EPA,

2006a). The depth and strength of these

conclusions are illustrated by the

following observations that are drawn

from the 1996 Criteria Document (EPA,

1996a, section 5.5):

(1) Specifically, with respect to the

importance of taking into account

exposure duration, "when 03 effects are

the primary cause of variation in plant

response, plants from replicate studies

of varying duration showed greater

reductions in yield or growth when

exposed for the longer duration" and

"the mean exposure index of

unspecified duration could not account

for the year-to-year variation in

respoAse" (EPA, 1996a, pg. 5-96).

(2) "[Blecause the mean exposure

index treats all concentrations equally

and does not specifically include an

exposure duration component, the use

of a mean exposure index for

characterizing plant exposures appears

inappropriate for relating exposure with

vegetation effects" (EPA, 1996a, pg. 5- 88).,

(3) Regarding the relative importance

of higher concentrations than lower in

determining plant response, "the

ultimate impact of long-term exposures

to 03 on crops and seedling biomass

response depends on the integration of

repeated peak concentrations during the

growth of the plant" (EPA, 1996a, pg. 5-

104).

(4) "[Alt this time, exposure indices

that weight the hourly 03

concentrations differentially appear to

be the best candidates for relating

exposure with predicted plant

response" (EPA, 1996a, pgs. 5-136).

At the conclusion of the last review,

the biological basis for a cumulative,

seasonal form was not in dispute. There

was general agreement between the EPA

staff, CASAC, and the Administrator,

based on their review of the air quality

criteria, that a cumulative, seasonal

form was more biologically relevant

than the previous 1-hour and new 8-

hour average forms (61 FR 65716).

The Staff Paper prepared for this

review evaluated the most appropriate

choice of a cumulative, seasonal form

for a secondary standard to protect the

public welfare from known and

anticipated adverse vegetation effects in

light of the new information available in

this review. Specifically, the Staff Paper

considered: (1) The continued lack of

evidence within the vegetation effects

literature of a biological threshold for

vegetation exposures of concern and (2)

new estimates of PRB that are lower

than in the last review. The form

commonly called W126 was evaluated

in the last review and was compared

with the form called SUM06, which

incorporates a threshold level above

which exposures are summed, that was

proposed in the last review. The

concentration-weighted form commonly

called W126 is defined as the sum of

sigmoidally weighted hourly 03

concentrations over a specified period,

where the daily sigmoidal weighting

function is defined in the Staff Paper

(EPA, 2007a, p. 7-16.) as:

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W126

i=8 AM•

Ci ,.,'wfre Ci = hourly 03 at hour i, and wc,

1 + 4403e - 2

1

C.

Regarding the first consideration, the

Staff Paper noted that the W126 form,

by its incorporation of a continuous

sigmoidal weighting scheme, does not

create an artificially imposed

concentration threshold, yet also gives

proportionally more weight to the

higher and typically more biologically

potent concentrations, as supported by

the scientific evidence. Second, the

index value is not significantly

influenced by 03 concentrations within

the range of estimated PRB, as the

weights assigned to concentrations in

this range are very small. Thus, the Staff

Paper concluded that it would provide

a more appropriate target for air quality

management programs designed to

reduce emissions from anthropogenic

sources contributing to 03 formation.

On the basis of these considerations, the

Staff Paper and the CASAC Panel

concluded that the W126 form is the

most biologically-relevant cumulative,

seasonal form appropriate to consider in

the context of the secondary standard

review.

4. Overview of Vegetation Exposure and

Risk Assessments

This section outlines the information

presented in section IV.C of the

proposal on the vegetation exposure and

risk assessments conducted for this

review, which improved and built upon

similar analyses performed in 'the last

review. The vegetation exposure

assessment was performed using

interpolation and included information

from ambient monitoring networks and

results from air quality modeling. The

vegetation risk assessment included

both tree and crop analyses. The tree

risk analysis included three distinct

lines of evidence: (1) Observations of

visible foliar injury in the field linked

to recent monitored 03 air quality for

the years 2001-2004; (2) estimates of

seedling growth loss under current and

alternative 03 exposure conditions; and

(3) simulated mature tree growth

reductions using the TREGRO model to

simulate the effect of meeting

alternative air quality standards on the

predicted annual growth of a single

western species (ponderosa pine) and

two eastern species (red maple and tulip

poplar). The crop analysis includes

estimates of the risks to crop yields from

current and alternative 03 exposure

conditions and the associated change in

economic benefits expected to accrue in

the agriculture sector upon meeting the

levels of various alternative standards.

Each element of the assessment is

outlined below, together with key

observations from this assessment.

a. Exposure Characterization

The exposure analyses examined 03

air quality patterns in the U.S. relative

to the location of 03 sensitive species

that have a known concentrationresponse in order to predict whether

adverse effects are occurring at current

levels of air quality, and whether they

are likely to occur under alternative

standard forms and levels. The most

important information about exposure

to vegetation comes from the 03

monitoring data that are available from

two national networks: (1) Air Quiality

System (AQSI http://www.epa.gov/ttnairs/airsaqs) and (2) Cletq Statt4jfii and Trends Network- (,', t I -Irl, .:-¢($ 

htt :/www.epa.gov/cstnqt) ~~

to characterize exposures to vegtation

at the national scale, however, the Staff

Paper concluded that it could not rely

solely on limited site-specific

monitoring data, and that it was -

necessary to use an interpolation

method to characterize 03 air qualityover broad geographic areas. The

analyses used the 03 outputs from the

EPA/NOAA Community Multi-scale Air

Quality (CMAQ) 2 2 model system

(http://www.epa.gov/asmdnerl/CMAQ,

Byun and Ching, 1999; Arnold et al.

2003, Eder and Yu, 2005) to improve

spatial interpolations. based solely on existing monitoring networks.

Based on the significant difference in

monitor network density between the

eastern and western U.S., the Staff Paper

concluded that it was appropriate to use

separate interpolation techniques in

these two regions: AQS and CASTNET

monitoring data were solely used for the

eastern interpolation, and in the western

U.S., where rural monitoring is more

sparse, 03 values generated by the

CMAQ model Were used to develop

scaling factors to augment the

interpolation. In order to characterize

22 The CMAQ model is a multi-pollutant,

multiscale air quality model that contains state-ofthe-science techniques for simulating all

atmospheric and land processes that affect the

transport, transformation, and deposition of

atmospheric pollutants and/or their precursors on

both regional and urban scales. It is designed as a

science-based modeling tool for handling many

major pollutants (including photochemical

oxidants/0 3 , particulate matter, and nutrient

deposition) holistically. The CMAQ model can

generate estimates of hourly 03 concentrations for

the contiguous U.S., making it possible to express

model outputs in terms of a variety of exposure

indices (e.g., W126, 8-hour average).

uncertainty in the interpolation method,

monitored 03 concentrations were

systematically compared to interpolated

03 concentrations in areas where

monitors were located. In general, the

interpolation method used in the

current review performed well in many

areas in the U.S., although it underpredicted higher 12-hour W126

exposures in rural areas. Due to the

important influence of higher exposures

in determining risks to plants, this

feature of the interpolated surface could

result in an under-estimation of risks to

vegetation in some areas. Taking these

uncertainties into account, and given

the absence of more complete rural

monitoring data, this approach was used

in developing national vegetation

exposure and risk assessments that

estimate relative changes in risk for the

various alternative standards analyzed.

To evaluate changing vegetation

exposures and risks under selected air

quality scenarios, the Staff Paper

utilized adjusted 2001 base year 03 air

quality distributions with a rollback

method (Horst and Duff, 1995; Rizzo,

2005, 2006) to reflect meeting the

current and alternative secondary

standard options. The following key

observations were drawn from

comparing predicted changes in

interpolated air quality under each

alternative standard form and level

scenario analyzed:

(1) The results of the exposure

assessment indicate that current air

quality levels could result in significant

impacts to vegetation in some areas. For

example, for the base year (2001), a large

portion of California had 12-hr W126 03

levels above 31 ppm-hour, which has

been associated with approximately up

to 14 percent biomass loss in 50 percent

of tree seedling cases studies. Broader

multi-state regions in the east (NC, TN,

KY, IN, OH, PA, NJ, NY, DE, MD, VA)

and west (CA, NV, AZ, OK, TX) are

predicted to have levels of air quality

above the W126 level of 21 ppm-hour,

which is approximately equal to the

secondary standard proposed in 1996

and is associated with approximately up

to 10 percent biomass loss in 50 percent

of tree seedling cases studied. Much of

the east and Arizona and California

have 12-hour W126 03 levels above 13

ppm-hour which has been associated

with approximately up to 10 percent

biomass loss in 75 percent of tree

seedling cases studied.

(2) When 2001 air quality is rolled

back to meet the current 8-hour

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12-hour W126 03 levels were somewhat

improved, but not substantially. Under

this scenario, there were still many

areas in California with 12-hour W126

03 levels above 31 ppm-hour. A broad

multi-state region in the east.(NC, TN,

KY, IN, OH, PA, MD) and west (CA, NV,

- AZ, OK, TX) were still predicted to have

03 levels above the W126 level of 21

ppm-hour.

(3) Exposures generated for just

meeting a 0.070 ppm, 4th-highest

maximum 8-hour average alternative

standard (the lower end of the proposed

range for the primary 03 standard)

showed substantially improved 03 air

quality when compared to just meeting

the current 0.08 ppm, 8-hour standard.

Most areas were predicted to have 03

levels below the W126 level of 21 ppmhr, although some areas in the east (KY,

TN, MI, AR, MO, IL) and west (CA, NV,

AZ, UT, NM, CO, OK, TX) were still

predicted to have 03 levels above the

W126 level of 13 ppm-hour.

(4) While these results suggest that

meeting a proposed 0.070 ppm, 8-hour

secondary standard would provide

substantially improved protection in some areas, the Staff Paper recognized

that other areas could continue to have

elevated seasonal exposures, including

forested park lands and other natural

areas, and Class I areas which are

federally mandated to preserve certain

air quality related values. The proposal

notes that this is especially important in

the high elevation forests in the Western

U.S. where there are few 03 monitors

and where air quality patterns can result

in relatively low 8-hour averages while

still experiencing relatively high

cumulative exposures (72 FR 37892).

To further characterize 03 air quality

in terms of current and alternative

secondary standard forms, an analysis

was performed in the Staff Paper to

evaluate the e-ktent to which countylevel 03 air quality measured in terms

of various levels of the current 8-hour

average form overlapped with that

measured in terms of various levels of

the 12-hour W126 cumulative, seasonal

form. 23 This analysis was limited by the

lack of monitoring in rural areas where

important vegetation and ecosystems are lbcated, especially at higher elevation

sites. This is because 03 air quality

distributions at high elevation sites

often do not reflect the typical urban

and near-urban pattern of low morning

and evening 03 concentrations with a

23 The Staff Paper presented this analysis using

recent-(2002-2004) county-level 03 air quality data

(using 3-year average data as well as data from each

individual year) from AQS sites and the subset of

CASTNET sites having the highest 03 levels for the

counties in which they are located.

high mid-day peak, but instead maiatain

relatively flat patterns with many , i

concentrations in the mid-range (e.g.,

0.05-0.09 ppm) for extended periods.

These conditions can lead to relatively

low daily maximum 8-hour averages

concurrently with high cumulative

values so that there is potentially less

overlap between an 8-hour average and

a cumulative, seasonal form at these

sites. The Staff Paper concluded that it

is reasonable to anticipate that

additional unmonitored rural high

elevation areas important for vegetation

may not be adequately protected even

with a lower level of the 8-hour form.

The Staff Paper indicated that it

further remains uncertain as to the

extent to which air quality

improvements designed to reduce 8-

hour 03 average concentrations would

reduce 03 exposures measured by a

seasonal, cumulative W126 index. The

Staff Paper indicated this to be an

important consideration because: (1)

The biological database stresses the

importance of cumulative, seasonal

exposures in determining plant

response; (2) plants have not been

specifically tested for the importance of

daily maximum 8-hour 03

concentrations in relation to plant

response; and (3) the effects of

attainment of a 8-hour standard in

upwind urban areas on rural air quality

distributions cannot be characterized

with confidence due to the lack of

monitoring data in rural and remote

areas. These factors are important

considerations in determining whether

the current 8-hour form can

appropriately provide requisite

protection for vegetation.

b. Assessment of Risk to Vegetation

The Staff Paper presented results from

quantitative and qualitative risk

assessments of 03 risks to vegetation. In

the last review, crop yield and seedling

biomass loss OTC data provided the

basis for staff analyses, conclusions, and

recommendations (EPA, 1996b). Since

then, several additional lines of

evidence have progressed sufficiently to

provide a basis for a more complete and

coherent picture of the scope of Q3-

related vegetation risks, especially those

currently faced by seedling, sapling and

mature tree species growing in field

settings, and indirectly, forested

ecosystems. Specifically, new research

reflects an increased emphasis on fieldbased exposure methods (e.g., free air

exposure and ambient gradient),

improved field survey biomonitoring

techniques, and mechanistic tree

process models. Key observations and

insights from the vegetation risk

assessment, together with important

caveats and limitations, were dscussed

in section IV.C of the proposal. ,

Highlights from the analyses that

addressed visible foliar injury, seedling

and mature tree biomass loss, and

effects on crops are summarized below:

(1) Visible foliar injury. Recent

systematic injury surveys continue to

document visible foliar injury

symptoms diagnostic of phytotoxic 03

exposures on sensitive bioindicator

plants. These surveys produced more

expansive evidence than that available

at the time of the last review that visible

foliar injury is occurring in many areas

of the U.S. under current ambient

conditions. The Staff Paper presented an

assessment combining recent U.S.

Forest Service Forest Inventory and

Analysis (FIA) biomonitoring site data

with the county level air quality data for

those counties containing the FIA

biomonitoring sites. This assessment

showed that incidence of visible foliar

injury ranged from 21 to 39 percent of

the counties during the four-year period

(2001-2004) across all counties with air

quality levels at or below that of the

current 0.08 ppm 8-hour standard. Of

the counties that met an 8-hour level of

0.07 ppm in those years, 11 to 30

percent of the counties still had

incidence of visible foliar injury. The

magnitude of these percentages suggests

that phytotoxic exposures sufficient to

induce visible foliar injury would still

occur in many areas after meeting the

level of the current secondary standard

or alternative 0.07 ppm 8-hour standard.

While the data show that visible foliar

injury occurrence is geographically

widespread and is occurring on a

variety of plant species in forested and

other natural systems, linking visible

foliar injury to other plant effects is still

problematic. However, its presence

indicates that other 0 3-related

vegetation effects might also be present.

(2) Seedling and mature tree biomass

loss. In the last review, analyses of the

effects of 03 on trees were limited to 11

tree species for which C-R functions for

the seedling growth stage had been

developed from OTC studies. Important

tree species such as quaking apen,

ponderosa pine, black cherry, and tulip

poplar were found to be sensitive to

cumulative seasonal 03 exposures.

Work done since the last review at the

AspenFACE site in Wisconsin on

quaking aspen (Karnosky et al., 2005)

and a gradient study performed in the

New York City area (Gregg et al., 2003)

have confirmed the detrimental effects

of 03 exposure on tree growth in field

studies without chambers and beyond

the seedling stage (King et al., 2005). To

update the seedling biomass loss

analysis, C-R functions for biomass loss

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for availgble seedling tree species taken

from the Csiteria Document and

informatioiY on tree growing regions

derived from the U.S. Department of

Agriculture's Atlas of United States

Trees were combined with projections

of air quality based on 2001 interpolated

exposures, to produce estimated

biomass loss for each of the seedling

tree species individually.24 In summary,

these analyses showed that biomass loss

still occurred in many tree species when

03 air quality was adjusted to meet the

current 8-hour standard. For instance,

black cherry, ponderosa pine, eastern

white pine, and aspen had estimated

median seedling biomass losses over

portions of their growing range as high

as 24, 11, 6, and 6 percent, respectively,

when 03 air quality was rolled back to

just meet the current 8-hour standard.

The Staff Paper noted that these results

are for treo seedlings and that mature

trees of the same species may have more

or less of a response to 03 exposure. Due

to the potential for compounding effects

over multiple years, a consensus

workshop on 03 effects reported that a

biomass loss greater than 2 percent

annually can be significant (Heck and

Cowling, 1997). Decreased seedling root

growth and survivability could affect

overall stand health and composition in

the long term.

Recent work has also enhanced our

understanding of risks beyond the

seedling stage. In order to better

characterize the potential 03 effects on

mature tree growth, a tree growth model

(TREGRO) was used to evaluate the

effect of changing 03 air quality

scenarios from just meeting alternative

03 standards on the growth of mature

trees. 25 The model integrates

interactions between 03 exposure,

precipitation and temperature as they

affect vegetation, thus providing an

internal consistency for comparing

effects in trees under different exposure

scenarios and climatic conditions. The

TREGRO model was used to assess 03-

related impacts on the growth of

Ponderosa pine in the San Bernardino

Mountains of California (Crestline) and

the growth of yellow poplar and red

maple in the Appalachian mountains of

Virginia and North Carolina,

Shenandoah National Park (Big

2 4 Maps of these biomass loss projections were

presented in the Staff Paper (chapter 7).

Z TREGRO is a process-based, individual. tree

growth simulation model (Weinstein et a). 1991)

and has been used to evaluate the effects of a

variety of 03 scenarios and linked with concurrent

climate data to account for 03 and climate/

meteorology interactions on several species of trees

in different regions of the U.S. (Tingey et al., 20.01;

Weinstein et al., 1991; Retzlaff et al., 2000;

Laurence et al., 1993; Laurence et al., 2001;

Weinstein at al., 2005).

Madows) and Linville Gorge

Wilderness Area (Cranberry),

respectively. Ponderosa pine is one of

the most widely distributed pines in

western North America, a major source

of timber, important as wildlife habitat,

and valued for aesthetics (Burns and

Honkala, 1990). Red maple is one of the

most abundant species in the eastern

U.S. and is important for its brilliant fall

foliage and highly desirable wildlife

browse food (Burns and Honkala, 1990).

Yellow poplar is an abundant species in

the southern Appalachian forest. It is 10

percent of the cove hardwood stands in

southern Appalachians which are

widely viewed as some of the country's

most treasured forests because the

protected, rich, moist set of conditions

permit trees to grow the largest in the

eastern U.S. The wood has high

commercial value because of its

versatility and as a substitute for

increasingly scarce softwoods in

furniture and framing construction. 41-

Yellow poplar is also val~ad, ai[l hb 1r

tree, a source of wildlife fod, tid Jh;'"

shade tree for large areas (Burns and

Honkala, 1990).

The Staff Paper analyses found that

just meeting the current standard would

likely continue to allow 0 3-related

reductions in annual net biomass gain

in these species. This is based on model

outputs that estimate that as 03 levels

are reduced below those of the current

standard, significant improvements in

growth would occur. Though there is

uncertainty associated with the above

analyses, it is important to note that

new evidence from experimental studies

that go beyond the seedling growth stage

continues to show decreased growth

under elevated 03 (King et al., 2005);

some mature trees such as red oak have

shown an even greater sensitivity of

photosynthesis to 03 than seedlings of

the same species (Hanson et al., 1994);

and the potential for cumulative "carry

over" effects as well as compounding

must be considered since the

accumulation of such "carry-over"

effects over time may affect long-term

survival and reproduction of

individuals and ultimately the

abundance of sensitive tree species in

forest stands.

(3) Crops: Similar to the tree seedling

analysis, an analysis that combined C-R

information on crops, crop growing

regions, and interpolated exposures

during each crop growing season was

conducted for commodity crops, fruits

and vegetables. NCLAN crop functions

developed in the 1980s were used for

commodity crops, including 9

commodity crop species (i.e., cotton,

field corn, grain sorghum, peanut,

soybean, winter wheat, lettuce, kidney

bean, potato) that accounted for 69

percent of 2004 principal crop acreage

planted in the U.S. in 2004. The C-R

functions for six fruit and vegetable

species (tomatoes-processing, grapes,

onions, rice, cantaloupes, Valencia

oranges) were identified from the -

California fruit and vegetable analysis

from the last review (Abt, 1995). The

risk assessment estimated that just

meeting the current 8-hour standard

would still allow 0 3-related yield loss to

occur in some commodity crop species

and fruit and vegetable species currently

grown in the U.S. For example, based on

median C-R function response, in

counties with the highest 03 levels,

potatoes and cotton had estimated yield

losses of 9-15 percent and 5-10 percent,

respectively, when 03 air quality just

met the level of the current standard.

Estimated yield improved in these

counties when the alternative W126

standard levels were met. The very

important soybean crop had generally

small yield losses throughout the

country under just meeting the current

standard (0-4 percent).

The Staff Paper also presented

estimates of monetized benefits for

crops associated with the current and

alternative standards. The Agriculture

Simulation Model (AGSIM) (Taylor,

1994; Taylor, 1993) was used to

calculate annual average changes in

total undiscounted economic surplus for

commodity crops and fruits and

vegetables when current and alternative

standard levels were met. Meeting the

various alternative standards did show

some significant benefits beyond the

current 8-hour standard. However, the

Staff Paper recognized that the modeled

economic benefits from AGSIM had

-many associated uncertainties which

limited the usefulness of these

estimates.

B. Need for Revision of the Current

Secondary 03 Standard

1. Introduction

The initial issue to be addressed in

this review of the 03 standard is

whether, in view of the advances in

scientific knowledge reflected in the

Criteria Document and Staff Paper, the

current standard should be revised. As

discussed in section IV.D of the

proposal, in evaluating whether it was

appropriate to piropose to retain or

revise the current standard, the

Administrator built upon the last review

and reflected the broader body of

evidence and information now

available. In the proposal, EPA

presented information, judgments, and

conclusions from the last review, which

revised the secondary 03 standard by

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setting it identical to the revised

primary 03 standard, and from the

current review's evaluation of the

adequacy of the current secondary

standard, including both evidence- and

exposure/risk-based considerations in

the Staff Paper, as well as from the

CASAC Panel's advice and

recommendations. The Staff Paper

evaluation, the CASAC Panel's views,

and the Administrator's proposed

conclusions on the adequacy of the

current secondary standard are

presented below. -

a. Staff Paper Evaluation

The Staff Paper considered the

evidence presented in the Criteria

Document as a basis for evaluating the

adequacy of the current 03 standard,

recognizing that important uncertainties

remain. The Staff Paper concluded that

the new evidence available in this

review as described in the Criteria

Document continues to support and

strengthen key policy-relevant

conclusions drawn in the previous

review. Based on this new evidence, the

current Criteria Document once more

concluded that: (1) A plant's response to

03 depends upon the cumulative nature

of ambient exposure as well as the

temporal dynamics of those

concentrations; (2) current ambient

concentrations in many areas of the

country are sufficient to impair growth

of numerous common and economically

valuable plant and tree species; (3) the

entrance of 03 into the leaf through the

stomata is the critical step in 03 effects;

(4) effects can occur with only a few

hourly concentrations above 0.08 ppm;

(5) other environmental biotic and

abiotic factors are also influential to the

overall impact of 03 on plants and trees;

and (6) a high degree of uncertainty

remains in our ability to assess the

impact of 03 on ecosystem services.

In light of the new evidence, as

described in the Criteria Document, the

Staff Paper evaluated the adequacy of

the current standard based on

assessments of both the most policyrelevant vegetation effects evidence and

exposure and risk-based information,

highlighted above in section IV.A and

discussed in sections 1V.A-C of the

proposal. In evaluating the strength of

this information, the Staff Paper took

into account the uncertainties and

limitations in the scientific evidence

and analyses as well as the views of

CASAC. The Staff Paper concluded that

progress has been made since the last

review and generally found support in

the available effects- and exposure/riskbased information for consideration of

an 03 standard that is more protective

than the current standard. The Staff

Paper further concluded that tiere is no

support for consideration of an 03 ' :" '

standard that is less protective than the

current standard. This general

conclusion is consistent with the advice

and recommendations of CASAC.

i. Evidence-Based Considerations

In the last review, crop yield and tree

seedling biomass loss data obtained in

OTC studies provided the basis for the

Administrator's judgment that the then

current 1-hour, 0.12 ppm secondary

standard was inadequate (EPA, 1996b).

Since then, several additional lines of

evidence have progressed sufficiently to

provide a more complete and coherent

picture of the scope of 0 3-related

vegetation risks, especially those

currently faced by sensitive seedling,

sapling and mature growth stage tree

species growing in field settings, and

their associated forested ecosystems.

Specifically, new research reflects an

increased, emphasis on field-based

ekpEsumrxndsto& (e.g., free air, ambient

gradieiiamiihbiomonitoring surveys). In

reaching conclusions regarding the

adequacy of the current standard, the

Staff Paper considered the combined

information from all these areas

together, along with associated

uncertainties, in an integrated, weightof-evidence approach.

Regarding the 0 3-induced effect of

visible foliar injury, observations for the

years 2001 to 2004 at USDA FIA

biomonitoring sites showed widespread

0 3-induced leaf injury occurring in the

field, including in forested ecosystems,

under current ambient 03 conditions.

For a few studied species, it has been

shown that the presenc4 of visible foliar

injury is further linked to the presence

of other vegetation effects (e.g., reduced

plant growth and impaired below

ground root developrhent) (EPA, 2006),

though for most species, this linkage has

not been specifically studied or where

studied, has not been found..

Nevertheless, when visible foliar injury

is present, the possibility that other 03-

induced vegetation effects could also be

present for some species should be

considered. Likewise, the absence of

visible foliar injury should not be

construed to demonstrate the absence of

other 0 3-induced vegetation effects. The

Staff Paper concluded that it is not

possible at this time to quantitatively

assess the degree of visible foliar injury

that should be judged adverse in all

settings and across all species, and that

other environmental factors can mitigate

or exacerbate the degree of O3-induced

visible foliar injury expressed at any

given concentration of 03. However, the

Staff Paper also concluded that the

presence of visible foliar injury alone

can be adverse to the public welfare,

especially when it occurs incpirttected

areas such as national parks and

wilderness areas. Thus, on the basis of

the available information on the

widespread distribution of O3-sensitive

species within the U.S. including in

areas, such as national parks, which are

afforded a higher degree of protection,

the Staff Paper concluded that the

current standard continues to allow

levels of visible foliar injury in some

locations that could reasonably be

considered to be adverse from a public

welfare perspective. Additional

monitoring of both 03 air quality and

foliar injury levels are needed in these

areas of national significance to more

fully characterize the spatial extent of

this public welfare impact.

With respect to 03-induced biomass

loss in trees, the Staff Paper concluded

that the new body of field-based

research on trees strengthens the

conclusions drawn on tree seedling

biomass loss from earlier OTC work by

documenting similar seedling responses

in the field. For example, recent

empirical studies conducted on quaking

aspen at the AspenFACE site in

Wisconsin have confirmed the

detrimental effects of 03 exposure on

tree growth in a field setting without

chambers (Isebrands et al., 2000, 2001).

In addition, results from an ambient

gradient study (Gregg et al., 2003),

which evaluated biomass loss in

cottonwood along an urban-to-rural

gradient at several locations, found that

conditions in the field were sufficient to

produce substantial biomass loss in

cottonwood, with larger impacts

observed in downwind rural areas due

to the presence of higher 03

concentrations. These gradients from

low urban to higher rural 03

concentrations occur when 03

precursors generated in urban areas are

transported to downwind sites and are

transformed into 03. In addition, 03

concentrations typically fall to near 0

ppm at night in urban areas due to

scavenging of 03 by NOx and other

compounds. In contrast, rural areas, due

to a lack of nighttime scavenging, tend

to maintain elevated 03 concentrations

for longer periods. On the basis of such

key studies, the Staff Paper concluded

that the expanded body of field-based

evidence, in combination with the

substantial corroborating evidence from

OTC data, provides stronger evidence

than that available in the last review

that ambient levels of 03 are sufficient

to produce visible foliar injury

symptoms and biomass loss in sensitive

vegetative species growing in natural

environments. Further, the Staff Paper

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judged that the consistency in response

in studied species/genotypes to 03

under a variety of exposure conditions

and methodologies demonstrates that

these sensitive genotypes and

populations of plants are susceptible to

adverse impacts from 03 exposures at

levels known to occur in the ambient

air. Due to the potential for

compounded risks from repeated insults

over multiple years in perennial species,

the Staff Paper concluded that these

sensitive subpopulations are not

afforded adequate protection under the

current secondary 03 standard. Despite

the fact that only a relatively small

portion of U.S. plant species have been

studied with respect to 03 sensitivity,

those species/genotypes shown to have

03 sensitivity span a broad range of

vegetation types and public use

categories, including direct-use

categories like food production for

human and domestic animal

consumption; fiber, materials, and

medicinal production; urban/private

landscaping. Many of these species also

contribute to the structure and

functioning of natural ecosystems (e.g.,

the EEAs) and thus, to the goods and

services those ecosystems provide

(Young and Sanzone, 2002), including

non-use categories such as relevance to

public welfare based on their aesthetic,

existence or wildlife habitat value.

The Staff Paper therefore concluded

that the current secondary standard is

inadequate to protect the public welfare

against the occurrence of adverse levels

of visible foliar injury arfd tree seedling

biomass loss occurring in tree species

(e.g., ponderosa pine, aspen, black

cherry, cottonwood) that are sensitive.

and clearly important to the public

welfare.

ii. Exposure- and Risk-Based

Considerations

In evaluating the adequacy of the

current standard, the Staff Paper also

presented the results of exposure and

risk assessments, which are highlighted

above in section IV.A.3 and discussed in

section IV.C of the proposal. Due to

multiple sources of uncertainty, both

known and unknown, that continue to

be associated with these analyses, the

Staff Paper put less weight on this

information in drawing conclusions on

the adequacy of the current standard.

However, the Staff Paper also

recognized that some progress has been

made since the last review in better

characterizing some of these associated

uncertainties and, therefore concluded

that the results of the exposure and risk

assessments continue to provide

information useful to informing

judgments as to the relative changes in

risks predicted to occur under exposure

scenarios associated with the different

standard alternatives considered.

Importantly, with respect to two key

uncertainties, the uncertainty associated

with continued reliance on C-R

functions developed from OTC exposure

systems to predict plant response in the

field and the potential for changes in

tree seedling and crop sensitivities in

the intervening period since the C-R

functions were developed, the Staff

Paper concluded that recent research

has provided information useful in

judging how much weight to put on

these concerns. Specifically, new fieldbased studies, conducted on a limited

number of tree seedling and crop

species to date, demonstrate plant

growth and visible foliar injury

responses in the field that are similar in

nature and magnitude to those observed

previously under OTC exposure

conditions, lending qualitative support

to the conclusion that OTC conditions

do not fundamentally alter the nature of

the 03-plant response. Second, nothing

in the recent literature suggests that the

03 sensitivity of crop or tree species

studied in the last review and for which

C-R functions were developed has

changed significantly in the intervening

period. Indeed, in the few recent studies

where this is examined, 03 sensitivities

were found to be as great as or greater

than those observed in the last review.

The Staff Paper consideration of such

exposure and risk analyses is discussed

below and in section IV.D.2.b of the

proposal, focusing on seedling and

mature tree biomass loss, qualitative

ecosystem risks, and crop yield loss.

(1) Seedling and mature tree biomass

loss. Biomass loss in sensitive tree

seedlings is predicted to occur under 03

exposures that meet the level of the

current secondary standard. For

instance, black cherry, ponderosa pine,

eastern white pine, and aspen had

estimated median seedling biomass

losses as high as 24, 11, 6, and 6

percent, respectively, over some

portions of their growing ranges when

air quality was rolled back to meet the

current 8-hr standard with the 10

percent downward adjustment for the

potential 03 gradient between monitor

height and short plant canopies applied.

The Staff Paper noted that these results

are for tree seedlings and that mature

trees of the same species may have more

or less of a response to 03 exposure.

Decreased root growth associated with

biomass loss has the potential to

indirectly affect th6 vigor and

survivability of tree seedlings. If such

effects occur on a sufficient number of

seedlings within a stand, overall stand

health and composition can be affected

in the long term. Thus, the Staff Paper

concluded that these levels of estimated

tree seedling growth reduction should

be considered significant and

potentially adverse, given that they are

well above the 2 percent level of

concern identified by the 1997

consensus workshop (Heck and

Cowling, 1997).

Though there is significant

uncertainty associated with this

analysis, the Staff Paper recommended

that this information should be given

careful consideration in light of several

other pieces of evidence. Specifically,

limited evidence from experimental

studies that go beyond the seedling

growth stage continues to show

decreased growth under elevated 03

levels (King et a1., 2005). Some mature

trees such as red oak have shown an

even greater sensitivity of

photosynthesis to 03 than seedlings of

the same species (Hanson et a., 1994).

The potential for effects to "carry over"

to the following year or cumulate over

multiple years, including the potential

for compounding, must be considered

(see 72 FR 37885; Andersen et al., 1997;

Hogsett et el., 1989; Sasek et al., 1991;

Temple et al., 1993; EPA, 1996). The

accumulation of such "carry-over"

effects over time may affect long-term

survival and reproduction of individual

trees and ultimately the abundance of

sensitive tree species in forest stands.

(2) Qualitative Ecosystem Risks. In

addition to the quantifiable risk

categories discussed above, the Staff

Paper presented qualitative discussions

on a number of other public welfare

effects categories. In so doing, the Staff

Paper concluded that the quantified

risks to vegetation estimated to be

occurring under current air quality or

upon meeting the current secondary

standard likely represent only a portion

of actual risks that may be occurring for

a number of reasons. First, as mentioned above, out of the

over 43,000 plant species catalogued as

growing within the U.S. (USDA

PLANTS database, USDA, NRCS, 2006),

only a small percentage have been

studied with respect to 03 sensitivity.

Most of the studied species were

selected because of their commercial

importance or observed 0 3-induced

visible foliar injury in the field. Given

that 03 impacts to vegetation also

include less obvious but often more

significant impacts, such as reduced

"annual growth rates and below ground

root loss, the paucity of information on

other species means the number of 03-

sensitive species that exists within the

U.S. is likely greater than what is now

known. Since no state in the lower 48

states hag less than seven known 03-

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sensitive plant species, with the

majority of states having between 11

and 30 (see Appendix 7J-2 in Staff

Paper), protecting 0 3-sensitive

vegetation is clearly important to the

public welfare at the national scale.

Second, the Staff Paper also took into

consideration the possibility that more

subtle and hidden risks to ecosystems

are potentially occurring in areas where

vegetation is being significantly

impacted. Given the importance of these

qualitative and anticipated risks to

important public welfare effects

categories such as ecosystem impacts

leading to potential losses or shifts in

ecosystem goods and services (e.g.,

carbon sequestration, hydrology, and

fire disturbance regimes), the Staff Paper

concluded that any secondary standard

set to protect against the known and

quantifiable adverse effects to vegetation

should also consider the anticipated,

but currently unquantifiable, potential

effects on natural ecosystems. (3) Crop Yield Loss. Exposure and risk

assessments in the Staff Paper estimated

that meeting the current 8-hour standard

would still allow 0 3-related yield loss to occur in several fruit and vegetable and

commodity crop species currently

grown in the U.S. These estimates of

crop yield loss are substantially lower

than those estimated in the last review

as a result of several factors, including

adjusted exposure levels to reflect the

presence of a variable 03 gradient

between monitor height and crop

canopies, and use of a different

econometric agricultural benefits model

updated to reflect more recent

agricultural policies (EPA, 2006b).

Though these sources .of uncertainty

associated with the crop risk and

benefits assessments were better

documented in this review, the Staff

Paper concluded that the presence of

these uncertainties make the risk

estimates suitable only as a basis for

understanding potential trends in

relative yield loss and economic

benefits. The Staff Paper further

recognized that actual conditions in the

field and management practices vary

from farm to farm, that agricultural

systems are heavily managed, and that

adverse impacts from a variety of other

factors (e.g., weather, insects, disease)

can be orders of magnitude greater than

that of yield impacts predicted for a

given 03 expbsure. Thus, the relevance

of such estimated impacts on crop

yields to the public welfare are

considered highly uncertain and less

useful as a basis for assessing the

adequacy of the current standard. The

Staff Paper noted, however, that in some

experimental cases, exposure to 03 has

made plants more sensitive or

vulnerable to some of these other

important stressors, including disease,

insect pests, and harsh weather (EPA,

2006a). The Staff Paper therefore

concluded that this remains an

important area of uncertainty and that

additional research to better

characterize the nature and significance

of these interactions between 03 and

other plant stressors would be useful.

iii. Summary of Staff Paper

Considerations

In summary, the Staff Paper

concluded that the current secondary 03

standard is inadequate. This conclusion

was based on the extensive vegetation

effects evidence, fn particular the recent

empirical field-based evidence on

biomass loss in seedlings, saplings and

mature trees, and foliar injury incidence

that has become available in this review,

which demonstrates the occurrence of

adverse vegetation effects at ambient

levels of recent 03 air quality, as well as

evidence and exposure- and risk-based

analyses indicating that adverse effects

would be predicted to occur under air

quality scenarios that meet the current

standard.

b. CASAC Views

In a letter to the Administrator

(Henderson, 2006c), the CASACO 3

Panel,"with full endorsement of the

chartered CASAC, unanimously

concluded that "despite limited recent

research, it has become clear since the

last review that adverse effects on a

wide range of vegetation including

visible foliar injury are to be expected

and have been observed in areas that are below the level of the current 8-hour

primary and secondary ozone

standards." Therefore, "based on the

Ozone Panel's review of Chapters 7 and

8 [of the Staff Paper], the CASAC

unanimously agrees that it is not

appropriate to try to protect vegetation

from the substantial, known or

anticipated, direct and/or indirect,

adverse effects of ambient 03 by

continuing to promulgate identical

primary and secondary standards for 03.

Moreover, the members of the

Committee and a substantial majority of

the Ozone Panel agree with EPA staff

conclusions and encourage the

Administrator to establish an alternative

cumulative secondary standard for 03

and related photochemical oxidants that

is distinctly different in averaging time,

form and level from the currently

existing or potentially revised 8-hour

primary standard" (Henderson,

2006c).26

26 One CASAC Panel member reached different

conclusions from those of the broader Panel

c. Administrator's Proposed

Conclusions

At the time of proposal, in

considering whether the current

secondary standard should be revised,

the Administrator carefully considered

the conclusions contained in the

Criteria Document, the rationale and

recommendations contained in the Staff

Paper, the advice and recommendations

from CASAC, and public comments to

date on this issue. In so doing, the

Administrator recognized that the

secondary standard is to protect against "adverse" 03 effects, as discussed in

section IV.A.3 of the proposal. In

considering what constitutes a

vegetation effect that is also adverse to

the public welfare, the Administrator

took into account the Staff Paper

conclusions regarding the nature and

strength of the vegetation effects

evidence, the exposure and risk

assessment results, the degree to which

the associated uncertainties should be

considered in interpreting the results,

and the views of CASAC and members

of the public. On these bases, the

Administrator proposed that the current

secondary standard is inadequate to

protect the public welfare from known

and anticipated adverse 0 3-related

effects on vegetation and ecosystems.

Ozone levels that would be expected to

remain after meeting the current

secondary standard were judged to be

sufficient to cause visible foliar injury,

seedling and mature tree biomass loss,

and crop yield reductions to degrees

that could be considered adverse

depending on the intended use of the

plant and its significance to the public

welfare, and the current secondary

standard does not provide adequate

protection from such effects. Other 03-

induced effects described in the

literature, including an impaired ability

of many sensitive species and genotypes

within species to adapt to or withstand

other environmental stresses, such as

freezing temperatuves, pest infestations

and/or disease, and to compete for

available resources, would also be

anticipated to occur. In the long run, the

result of these impairments (e.g., loss in

vigor) could lead to premature plant

death in 03 sensitive species. Though

effects on other ecosystem components

regarding certain aspects of the vegetation effects

information and the appropriate degree of emphasis

that should be placed on the associated

uncertainties. These concerns related to how the

results of 0 3/vegetation exposure experiments

carried out in OTC can be extrapolated to the

ambient environment and how C--R functions

developed in the 1980s can be used today given that

he did not expect that current crop species/cultivars

in use in 2002 would have the same 03 sensitivity

as those studied in NCLAN (Henderson, 2007, pg.

C-18).

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have only been examined in isolated

cases, effects such as those described

above could have significant

implications for plant community and.

associated species biodiversity and the

structure and function of whole

ecosystems. These considerations also

support the proposed conclusion that

the current secondary standard is not

adequate and that revision is needed to

provide additional public welfare

protection.

2. Comments on the Need for Revision

The above section outlines the

vegetation and ecosystem effects

evidence and assessments used by the

Administrator to inform his proposed

judgments about the adequacy of the

current 03 secondary standard. General

comments received on the proposal that

either supported or opposed the

proposed decision to revise the current

03 secondary standard are addressed in

this section. Comments related to the

vegetation and ecosystem effects

evidence and information related to

exposure indices are considered in

section IV.B.2.a below, and comments

on vegetation exposure and risk

assessments are considered in section

IV.B.2.b. Comments on specific issues,

vegetation and ecosystem effects

evidence, information on exposure

indices, or the vegetation exposure and

risk assessments that relate to

consideration of the appropriate form,

averaging time, or level of the 03

standard are addressed below in section

IV.C. General comments based on

implementation-related factors that are

not a permissible basis for considering

the need to revise the current standard

are noted in the Response to Comments

document.

a. Evidence of Effects and Exposure

Indices

Sections IV.A.2 and IV.A.3 above

provide a summary overview of the

information on vegetation and

ecosystem effects and exposure indices

used by the Administrator to inform his

proposed judgments about the adequacy

of the current 03 secondary standard. As

discussed more fully below, comments

received on the proposal regarding the

nature and strength of the vegetation

and ecosystem effects information,

information on exposure indices, and

the conclusions that could appropriately

be drawn from such information fell

generally into two groups.

One group of commenters.that

included national and local

environmental organizations (e.g.,

Environmental Defense, Appalachian

Mountain Club, Rocky Mountain Clean

Air Action), NESCAUM, NACAA,

individual States, Tribal Associations,

and the National Park Service (NPS)

argued that the available science clearly

.showed that 0 3-induced vegetation and

ecosystem effects are occurring at and

below levels that meet the current 8-

hour standard, and therefore provides a

strong basis and support for the

conclusion that the current secondary

standard is inadequate. In support of

their view, these commenters relied on

the entire body of evidence available for

consideration in this review, including

evidence assessed previously in the last

review. These commenters pointed to

the information and analyses in the Staff

Paper and the conclusions and

recommendations of CASAC as

providing a clear basis for concluding

that the current standard does not

adequately protect vegetation from an

array of 0 3-related effects. For example,

the NPS noted that "wlidespread foliar

injury has been documented in areas

meeting the current standard; field and

chamber studies indicate that 03-

induced significant growth reductions

are also occurring at levels below the

current standard" (NPS, p. 3).

In addition to the body of information

already considered by EPA in this

review, these same commenters also

presented new information for the

Administrator's consideration,

including a number of "new" studies

published after completion of the

Criteria Document, as well as additional

information on air quality and

vegetation exposures and effects

pertaining to local conditions within

their State, Tribal or federal lands, as

additional support for their views that

the Current standard is inadequate. For

example, NESCAUM, NY, PA, and NPS

all provided air quality information

describing typical 03 concentrations in

areas that rarely, if ever, exceeded the

level of the current 8-hour standard in

areas that still showed 0 3-related

vegetation effects, particularly visible

foliar injury.

Building on EPA's qualitative

discussions of the potential linkage

between 03 vegetation effects and

effects on ecosystems, a number of these

commenters expressed concern that the

possible impact of 03-related reductions

in plant productivity could result in a

reduced capacity of vegetation to serve

as a carbon sink to mitigate the impacts

of rising CO 2 in a changing climate,

citing to a "new" study on that topic

(Sitch et al., 2007). Many of these same

commenters also cited to "new" fieldbased studies, in the Great Smoky

Mountain National Park that find a

relationship between 03 exposure, tree

stem growth loss, tree water use and

stream flow as evidence that current

ambient 03 levels can impact

ecosystems and that ecosystems should

be afforded protection from such

potential effects. For example, some of

these commenters note that "new"

studies in the Great Smoky Mountain

National Park (McLaughlin, et a].,

2007a, b) have found that (1) ambient 03

caused substantial growth reductions in

mature trees in a-mixed deciduous

forest, which was due in part to

increased 0 3-induced water loss and led

to seasonal losses in stem growth of 30-

50 percent for most species in a highozone year; (2) increasing ambient 03

levels also resulted in depletion of soil

moisture in the rooting zone and

reduced late-season stieamflow in the

watershed; and (3) 03 may amplify the

adverse effects of increasing

temperature on forest growth and forest

hydrology and may exacerbate the

effects of drought on forest growth and

stream health. Other "new" research

noted by these commenters as

supporting EPA's findings that current

03 exposures cause significant biomass

losses in sensitive seedlings of various

tree species include a study that

predicted up to 31 percent growth loss

in aspen in certain areas of its North

American range in 2001-2003 (Percy, et

a., 2007). These commenters

encouraged the Administrator to

consider these "new" studies in making

his final decisionThis group of commenters strongly

supported revising the current standard,

not only because in their view the

available evidence conclusively

demonstrates that the current standard

is inadequate to protect sensiti~e

vegetation, but also because the Staff

Paper provides abundant evidence that

it is appropriate to establish an

alternative cumulative, seasonal

secondary standard that is distinctly

different in form from the current or

revised primary standard. For example,

NESCAUM states that "[in light of the

EPA Staff and CASAC

recommendations, and the extensive

body of historical and recent monitoring

and research data upon which these

recommendations were based, the

option of equating the ozone secondary

NAAQS with the 8-hour primary is

inappropriate and clearly not supported

by the weight of scientific evidence."

EPA agrees with these commenters

that when evaluated as a whole, the

entire body of vegetation and ecosystem

effects information available in this

review supports the need to revise th

current standard to provide increased

protection from an array of 03:related

effects on sensitive vegetation and

ecosystems. EPA also agrees that the

available evidence indicates that a

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cumulative, seasonal form better reflects

the scientific information on

biologically relevant exposures for

vegetation. For reasons discussed below

in sections IV.C, however, EPA

disagrees with aspects of these

coimenters' views as to whether a

standard defined in terms of a

cumulative, seasonal form is requisite to

protect public welfare based on the

available scientific information.

To the extent that these and other

commenters whose comments arediscussed below included "new"

scientific studies, studies that were

published too late to be considered, in

the Criteria Document, in support of

their arguments for revising or not

revising the standards, EPA notes, as

discussed in section I above, that as in

past NAAQS reviews, it is basing the

final decisions in this review on the

studies and related information

included in the 03 air quality criteria

that have undergone CASAC and public

review and will consider newly

published studies for purposes of

decision making in the next 03 NAAQS

review. In provisionally evaluating

commenters' arguments, as discussed in

the Response to Comments document,

EPA notes that its provisional

consideration of "new" science found

that such studies did not materially

change the conclusions in the Criteria

Document.

The other main group of commenters,

which included Exxon-Mobil, UARG,

API, other industry groups, The

Annapolis Center for Science Based

Public Policy, individual States and

other organizations representing local

energy, agriculture or business interests,

expressed the contrasting view that the

limited number of studies published

since the last review and addressed in

the Criteria Document provided

insufficient evidence to support a

conclusion different than what was

reached in the last review. In particular,

they asserted that the types of vegetation

effects evaluated in the last review have

not changed, and that the Criteria

Document, Staff Paper, and CASAC

have acknowledged that the information

that has become available since the last

review does not fundamentally change

the conclusions reached in the last

review. As a result, they argued that the

currently available evidence fails to

show that revision to the standard is

requisite to provide additional

protection from these effects. In

particular, Exxon-Mobil stated that

"EPA is incorrect in concluding

vegetation impacts [occur] at or below

the level of the current standard" * * *

and that the "newer field-based

evidence EPA cites for ozone impacts on

seedlings, saplings and mature trees

indicates ozone impacts but at

exposures that are likely in exceedence

of the current secondary standard." Thiscommenter concluded that while these

studies provide additional support for

0 3-related impacts on vegetation,

including observing effects in field

settings without chambers, they do not

provide support for the conclusion that

ambient levels in compliance with the

current standard would result in

significant 03 impact. In addition, these

commenters also generally asserted that

the evidence that has become available

since the last review does not materially

reduce the uncertainties that were

present and cited by the Administrator

in the last review as important factors in

her decision to set the secondary

identical to the revised primary. Those

aspects of these comments that include

uncertainties associated with the

exposure, risk and benefits assessments

are addressed below in section IV.2.b

and in the Response to Comments

document.

EPA disagrees with the commenters'

assertion that the currently available

evidence has not materially reduced key

uncertainties present in the last review

that factored into the Administrator's

decision. For example, there is an

expansion of field-based evidence

across a broad array of vegetation effects

categories, as -discussed in the Criteria

Document, Staff Paper, and highlighted

above in section IV.A.2. Though in some

such studies (e.g., the FACE studies) the

03 exposures are indeed at or above

ambient levels, the observed vegetation

response is similar to that observed -In

OTC studies at similar levels of

exposure. Though these studies are still

limited in scope, it is nevertheless

EPA's view that such field-based

evidence reduces the uncertainties

associated with the C-R functions

generated in OTC studies that were

noted by the Administrator in the last

review. Thus, the current body of

evidence increases EPA's confidence in

the results from the OTC studies which

demonstrate 0 3-related effects below the

level of the current standard. EPA has

also considered this evidence in

conjunction with USDA FIA foliar

injury survey data and the Gregg et al.

(2003) tree seedling biomass loss

gradient study showing effects on a

sensitive tree species occurring in the

field across a range of exposure levels

including levels of air quality at to well

below the level of the current secondary

standard. Taken together, EPA

concludes that these studies fprm a

coherent body of evidence that

significantly strengthens EPA's

confidence that such effects are

currently occurring in the field and

would cofitinue to be anticipated at and

below the level of the current secondary

standard. A more detailed discussion of

these issues can be found in the

Response to Comments document.

b. Vegetation Exposure and Risk

Assessments

Section IV.A.4 above provides a

summary overview of the vegetation

exposure and risk assessment

information used by the Administrator

to help inform judgments about

vegetation exposure and risk estimates

associated with attainment of the

current and alternative standards. As an

initial matter, EPA notes that at the time

of proposal, the Administrator primarily

based his conclusion on whether

revision of the secondary standard was

needed primarily on evidence-based

considerations, while using the more

uncertain exposure and risk assessments

in a supportive role. As discussed more fully below, comments received on the

proposal regarding these assessments

and the conclusions that could

appropriately be drawn from them fell

generally into two groups. One group of

commenters generally included those

noted above who supported revising the

current secondary standard, while the

other group of commenters were those

noted above who expressed the view

that no revision was appropriate.

The first group of commenters

primarily focused on evidence-based

considerations in their support of a

revised standard, while some also

referenced EPA's findings from the

exposure and risk assessments in

supporting their view that the standard

needed to be revised to provide

increased protection for sensitive

vegetation. A few of these commenters

also provided additional exposure, risk

and benefits information from localized

assessments conducted by themselves or

others in their behalf in support of their

view that the standard needed to be

revised. In so doing, these commenters

have generally shown support for using

such assessments to help inform a final

decision on the need to revise..

The other group of commenters

expressed a number of concerns with

these assessments and generally

asserted that these assessments do not

support revision of the current standard.

These commenters' concerns generally

focused on (1) the method used by EPA

to estimate PRB, (2) the lack of new

information since the last review that

would, in their judgment, materially

reduce the uncertainties present in the

assessments conducted for the last

review, and (3) EPA's interpretation and

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use of the results in making a judgment

about the adequacy of the current

standard. These comments are

addressed below.

(1) Regarding concerns related to the

method used by EPA to estimate PRB,

EPA notes that this issue has been

raised repeatedly throughout the review

in the context of both the primary and

secondary standards. Most generally,

these commenters asserted that EPA

used unrealistically low levels of PRB

that resulted in an overestimate of risks

and benefits associated with just

meeting alternative standards. EPA

disagrees with this view, for the reasons

discussed above in section II.B.2.b,

which addresses this and other

comments related to EPA's approach to

estimating PRB and its role in exposure

and risk assessments related to the

primary standard.

(2) Another concern posed by these

commenters was the lack of any new

information that, in their judgment,

would materially reduce the

uncertainties present in the exposure,

risk and benefits assessments conducted

for the last review. For example, the

Annapolis Center asserted that "[s]ome

of the most important caveats and

uncertainties concerning the exposure

and risk assessments for crop yield that

were listed in the [19961 proposal

included (1) extrapolating from

exposure-response functions generated

in open-top chambers to ambient

conditions; (2) the lack of a performance

evaluation of the national air quality

extrapolation; (3) the methodology to

adjust modeled air quality to reflect

attainment of various alternative

standard options; and (4) inherent

uncertainties in models to estimate

economic values associated with

attainment of alternative standard.

* * * Because of the lack of new data

or substantive improvements in the risk

assessment, these same issues remain

today, contributing a similar degree of

uncertainty, as was the case in the prior

review." EPA recognizes that important

uncertainties remain in estimates of

vegetation exposure and 0 3-related risk

to vegetation, especially with regard to

0 3-related effects on crop yields.

However, EPA disagrees with comments

that assert that uncertainties have not

been reduced since the last review, as

discussed below.

With regard to the uncertainties

associated with using the OTC C-R

functions, the Annapolis Centerfurther

stated that "ten years have now elapsed,

and the same concentration-response

functions from the OTC studies of the

1980's are still the only viable data to

use to estimate crop loss. * * * The

1996 CASAC Panel agreed that the

estimates of crop loss at that time were

highly uncertain." While EPA agrees

that important uncertainties continue to

be associated with the use of the C-R

functions geneiated many years ago

using OTC studies for crop yield loss,

EPA does not agree that the new

information available in this review

does nothing to reduce such

uncertainties identified in the last

review. As described above and in the

Staff Paper and proposal, results from

the new SoyFACE and AspenFACE

studies provide qualitative support that

the levels of vegetation response that

have been observed in the field are of

similar magnitude as those predicted at

similar exposure levels using the OTC

generated C-R functions. Therefore,

EPA believes that the uncertainties cited

in the last review regarding the

appropriateness of using OTC generated

C-R functions to predict vegetation

response in the field have been reduced.

Providing some further support in this

regard is the limited information

available in this review on some

sensitive crop species (e.g., soybean)

suggesting that 03 sensitivity has not

changed significantly in the intervening

years. Taking all the above into account,

EPA's level of confidence in the

applicability of the OTC generated C-R

functions to represent ambient

conditions in the field has increased.

With regard to the lack of a

performance evaluation of the national

air quality extrapolation, EPA notes that

there have been advancements in the

tools and methods used for such

extrapolations since the last review.

With respect to the generation of

interpolated 03 exposure surfaces, EPA

employed a different approach than that

used in the last review and undertook

a quantitative assessment of the

uncertainties associated with the use of

this method. This uncertainty

assessment was accomplished by

sequentially dropping out of the

interpolation each monitoring site, and

then recalculating the exposure surface

using the remaining monitoring sites. As

discussed in the Staff Paper, this

method of evaluation may result in a

slight overestimation of error and bias

for the exposure surface, since dropping

out monitors loses information that the

interpolation uses in that local area. As

another point of comparison, EPA also

examined the subset of rural CASTNET

sites to illustrate how the interpolation

technique predicted air quality in that

rural monitoring network. For this

subset, the-evaluation indicated that in

general, the interpolation technique

slightly overestimated W126 exposures

at relatively low levels and

underestimated W126 exposure at

relatively high levels. This aspect of the

estimation method potentially resulted

in an underestimation of the more

important risks associated with higher

cumulative exposures in some areas.

Based on this evaluation, EPA reiterates

the conclusion in the Staff Paper that

"the calculation of error and bias

metrics for the interpolation represents

a notable improvement over the 1996

assessment which did not have such an evaluation." EPA further concludes that

in general, the sources and likely

direction of uncertainties associated

with ihe exposure and risk assessments

have been better accounted for and

characterized than in the last review.

With Tegard to criticisms of the

methodology used to adjust modeled air

quality to reflect attainment of various

alternative standard options, EPA notes

that this issue has been raised in the

context of both the primary and

secondary standards. As noted above in

section ll.B.2.b, based on information in

the Staff Paper (section 4.5.6) and in

more detail in a staff memorandum

(Rizzo, 2006), EPA concluded that the

quadratic air quality adjustment

approach used in this assessment

generally best represented the pattern of

reductions across the 03 air quality

distribution observed over the last

decade in areas implementing control

programs designed to attain the 03

NAAQS. While EPA recognizes that

future changes in air quality

distributions are area-specific, and will

be affected by whatever specific control

strategies are implemented in the future

to attain a revised NAAQS, there is no

empirical evidence to suggest that future

reductions in ambient 03 will be

significantly different from past

reductions with respect to impacting the

overall shape of the 03 distribution.

With regard to comments that asserted

that inherent uncertainties in models to

estimate ecdnomic values of crop loss

have not been reduced since the last

review, EPA acknowledges that while

an updated state of the art model, the

AGSIM benefits model, was used in this

review, substantial uncertainties remain

in these estimates of economic crop

loss. Further, EPA notes that these

estimates were not relied on as a basis

for reaching a decision on the need to

revise the current standard.

(3) Some commenters also asserted

that the estimated exposures and risks

associated with air quality just meeting

the current standard have not -

appreciably changed since the last

review. These commenters used this

conclusion as the basis for a claim that

there is no reason to depart from the

Administrator's 1997 decision that the

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current secondary standard is requisite

to protect public welfare. EPA believes

that this claim is fundamentally flawed

for three reasons. First, it is

inappropriate to compare quantitative

vegetation risks estimated in the last

review with those estimated in the

current review. The 1997 risk estimates,

or any comparison of the 1997 risks

estimates to the current estimates, are

irrelevant for the purpose of judging the

adequacy of the current standard, as the

1997 estimates reflect outdated analyses

that have been updated in this review to

reflect the current science and as there

have. been significant improvements to

the modeling approaches and model

inputs. Second, it is important to take

into account EPA's increased

confidence in some of the model inputs,

as discussed above, since in judging the

weight to place on quantitative risk

-estimates it is important to examine not

only the magnitude of the estimated

risks but also the degree of confidence

in those estimates. Third, quantitative

vegetation risk estimates were not the

main basis for EPA's decision in setting

a level for the secondary standard in

1997, and they do not set any quantified

"benchmark" for the Agency's decision

to revise the current standard at this

time. The proposal notice made clear

that decisions about the need to revise

the-current standard are mainly based

on an integrated evaluation of evidence

available across a broad array of

vegetation effects, while the more

uncertain exposure, risk and benefits

-estimates were used in a supportive

role. Both the Staff Paper and proposal

clearly distinguished the roles that these

different types of information played in

informing the Administrator's proposed

decision. The proposal states that "due

*to multiple sources of uncertainty, both

known and unknown, that continue to

be associated with these analyses, the

Staff Paper put less weight on this

information in drawing conclusions on

the adequacy of the current standard.

However, the Staff Paper also recognizes

that some progress has been made since

the last review in better characterizing

some of these associated uncertainties

and, therefore, concluded that the

results of the exposure and risk

assessments continue to provide

information useful to informing

judgments as to the relative changes in

risks predicted to occur under exposure

scenarios associated with the different

standard alternatives considered." In

determining the requisite level of

protection, the Staff Paper recognized

that it is appropriate to weigh the

importance of the predicted risks of

these effects in the overall context of

public welfare protection, along with a

determination as to the appropriate

weight to place on the associated

uncertainties and limitations of this

information. Thus, while the

Administrator is fully mindful of the

uncertainties associated with the

estimates of exposure, risk and benefits,

as discussed above, he judges that these

estimates are still useful in providing

additional support for his judgment that

the current 8-hour secondary standard

does not adequately protect sensitive

vegetation.

3. Conclusions Regarding the Need for

Revision

Having carefully considered the

public comments, discussed above, the

Administrator believes the fundamental

scientific conclusions on the effects of

03 on vegetation and sensitive

ecosystems reached in the Criteria

Document and Staff Paper, as discussed

above in section IV.A, remain valid. In

considering whether the secondary 03

standard should be revised, the

Administrator finds that evidence that

has become available in this review

demonstrates the occurrence of adverse

vegetation effects at ambient levels of

recent 03 air quality, and that evidence

and exposure- and risk-based analyses

indicate that adverse effects would be

predicted to occur under air quality

scenarios that meet the current

standard, taking into consideration both

the level and form of the current

standard. Ozone exposures that would

be expected to remain after meeting the

current secondary standard are

sufficient to cause visible foliar injury

and seedling and mature tree biomass

loss in 0 3 -sensitive vegetation. The

Administrator believes that-the degree

to which such effects should be

considered to be adverse depends on the

intended use of the vegetation and its

significance to the public welfare. Other

0 3-induced effects described in the

literature, including an impaired ability

of many sensitive species and genotypes

within species to adapt to or withstand

other environmental stresses, such as

freezing temperatures, pest infestations

and/or disease, and to compete for

available resources, would also be

anticipated to occur. In the long run, the

result of these impairments (e.g., loss in

vigor) could lead to premature plant

death in 03 sensitive species. Though

effects on other ecosystem components

have only been examined in isolated

cases, effects such as those described

above could have significant

implications for plant community and

associated species biodiversity and the

structure and function of whole

ecosystems.

The Administrator recognizes that the

secondary standard is not meant to

protect against all known observed or

anticipated 0 3-related effects, but only

those that can reasonably be judged to

be adverse to the public welfare. In

considering what constitutes a

vegetation effect that is adverse from a

public welfare perspective, the

Administrator believes it is appropriate

to continue to rely on the definition of "adverse," discussed in section IV.A.3

of the proposal, that imbeds the concept

of "intended use" of the ecological

receptors and resources that are

affected, and applies that concept

beyond the species level to the

ecosystem level.27 In so doing, the

Administrator has taken note of a

number of actions taken by Congress to

establish public lands that are set aside

for specific uses that are intended to

provide benefits to the public welfare,

including lands that are to be protected

so as to conserve the scenic value and

the natural vegetation and wildlife

within such areas, and to leave them

unimpaired for the enjoyment of future

generations. Such public lands that are

protected areas of national interest

include national parks and forests,

wildlife refuges, and-wilderness areas.

Because 0 3-sensitive species are

generally found in such areas, and

because levels of 03 allowed by the

current secondary standard are

sufficient to cause known or anticipated

impairment that the Administrator

judges to be adverse to sensitive

vegetation and ecosystems in such

areas, the Administrator concludes that

it is appropriate to revise the secondary

standard, in part, to provide increased

protection against 0 3-caused

impairment to such protected vegetation

and ecosystems.

The Administrator further recognizes

that States, Tribes and public interest

groups also set aside areas that are

intended to provide similar benefits to

the public welfare, for residents on State

and Tribal lands, as well as for visitors

to those areas. Given the clear public

interest in and value of maintaining

these areas in a condition that does not

impair their intended use, and the fact

that many of these areas contain 03-

sensitive vegetation, the Administrator

further concludes that it is appropriate

to revise the secondary standard in part

to provide increased protection against

0 3-caused impairment to vegetation and

ecosystems in such specially designated

areas.

2 7 The Administrator also recognizes that other

aspects of public welfare, as welfare is defined in

the CAA, may rely on concepts other than

"intended use."

I t I1 il i lill IiillffTT i n

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The Administrator also recognizes

that 0 3-related effects on sensitive

vegetation occur in areas that have not

been afforded such special protections,

ranging from vegetation used for

residential or commercial drnamental

purposes, such as urban/suburban

landscaping, to land use categories that

are heavily managed for commercial

production of commodities such as

agricultural crops, timber, and

ornamental vegetation. For vegetation

used for residential or commercial

ornamental purposes, such as urban/

suburban landscaping, there are

indications that impairment to the

intended use of such vegetation can

occur from 03 exposures allowed by the

current standard. While the

Administrator believes that there is not

adequate information at this time to

establish a secondary standard based

specifically on impairment of urban/

suburban landscaping and other uses of

ornamental vegetation, he notes that a

secondary standard revised to provide

protection for sensitive natural

vegetationand ecosystems may also

provide some degree of protection for

such ornamental vegetation.

With respect to commercial

production of commodities, however,

the Administrator notes that judgments

about the extent to which 0 3-related

effects on commercially managed

vegetation are adverse from a public

welfare perspective are particularly

difficultto reach, given that what is

known about the relationship between

03 exposures .and agricultural crop yield

response derives largely from data

generated almost 20 years ago. The

Administrator recognizes that there is

substantial uncertainty at this time as to

whether these data remain relevant to

the majority of species and cultivars of

crops being grown in the field today. In

addition, the extensive management of

such vegetation may to some degree

mitigate potential 0 3-related effects. The

management practices used on these

lands are highly variable and are

designed to achieve optimal yields,

taking into consideration various

environmental conditions. Thus, while

the Administrator believes that a

secondary standard revised to provide

protection for sensitive natural

vegetation and ecosystems may also

provide some degree of additional

protection for heavily managed

commercial vegetation, the need for

such additional protection is uncertain.

Based on these considerations, and

taking into consideration the advice and

recommendations of CASAC, the

Administrator concludes that the

protection afforded by the current

secondary 03 standard is not sufficient

and that the standard needs to be

revised to provide additional protection

from known and anticipated adverse

effects on sensitive natural vegetation

and sensitive ecosystems, and that such

a revised standard could also be

expected to provide additional

protection to sensitive ornamental

vegetation. The Administrator also

concludes that there is not adequate

information to establish a separate

secondary standard based on other

effects of 03 on public welfare. It is

important to note that these

conclusions, and the reasoning on

which they are based, do not address

the question of what specific revisions

to the current secondary standard are

appropriate. Addressing that question

requires looking specifically at the two

proposed options: establishing a new

standard defined in terms of a

cumulative, seasonal form, or revising

the current secondary standard by

making it identical to the revised

primary standard. These alternative

secondary standards are discussed in

the following section.

As highlighted below, the discussion

of public comments above indicates that

deciding the appropriate secondary

standard inVolves making a difficult

choice between two possible

alternatives, each with their strengths

and weaknesses. EPA's decision, and

the reasons for it, are described in detail

above. In reaching this decision, there

has been a robust discussion within the

Administration of these same strengths

and weaknesses. As part of that process

EPA received a Memorandum on March

6, 2008 from Susan Dudley,

Administrator, Office of Information

and Regulatory Affairs, Office of

Management and Budget, indicating

various concerns over adopting a

cumulative, seasonal secondary

standard. Deputy Administrator Marcus

Peacock responded with a

Memorandum dated March 7, 2008

stating EPA's views supporting adoption

of a cumulative, seasonal secondary

standard. On March 11, 2008, the

President "concluded that, consistent

with Administration policy, added

protection should be afforded to public

welfare by strengthening the secondary

ozone standard and setting it to be

identical to the new primary standard,

the approach adopted when ozone

standards were last promulgated. This

policy thus recognizes the

Administrator's judgment that the

secondary standard needs to be adjusted

to provide increased protection to

public welfare and avoids setting a

standard lower or higher than is

necessary." EPA's decision therefore

also reflects the view of the

Administration as to the most

appropriate secondary standard. While

the Administrator fully considered the

President's views, the Administrator's

decision, and the reasons for it, are

based on and supported by the record in

this rulemaking.

C. Conclusions on the Secondary 03

Standard

As an initial matter, EPA has

considered the indicator for a secondary

03 standard. As discussed above in

section ll.C.1 on the primary standard,

in the last review, EPA focused on a

standard for 03 as the most appropriate

surrogate for ambient photochemical

oxidants. In this review, while the

complex atmospheric chemistry in

which 03 plays a key role has been

highlighted, no alternatives to 03 have

been advanced as being a more

appropriate surrogate for ambient

photochemical oxidants and their

effects on vegetation. Thus, as is the

case for the primary standard, the

Administrator concludes that it is

appropriate to continue to use 03 as the

indicator for a standard that is intended

to address effects associated with

exposure to 03, alone and in

combination with related

photochemical oxidants. In so doing,

the Administrator recognizes that

measures leading to reductions in

vegetation exposures to 03 will also

redude exposures to other

photochemical oxidants.

1. Staff Paper Evaluation

The current Criteria Document and

Staff Paper concluded that the recent

vegetation effects literature evaluated in

this review strengthens and reaffirms

conclusions made in the last review that

the use of a cumulative exposure index

that differentially weights ambient

concentrations is best able to relate

ambient exposures to vegetation

response at this time (EPA, 2006a, b).

The last review focused in particular on

two of these cumulative forms, the

SUM06 and W126 (EPA, 1996). Given

that the data available at that time were

unable to distinguish between these

forms, the Administrator, based on the

policy consideration of not including 03

concentrations considered to be within

the PRB, estimated to be between 0.03

and 0.05 ppm, concluded that the

SUM06 form would be the more

appropriate choice for a cumulative,

exposure index for a secondary

standard, though a cumulative form was

not adopted at that time.

In this review, the Staff Paper

evaluated the continued

appropriateness of the SUM06 form in

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light of two key pieces of information:

new estimates of PRB that are lower

than in the last review, and continued

lack of evidence within the vegetation

effects literature of a biological

threshold for vegetation exposures of

concern. On the basis of those policy

and science-related considerations, the

Staff Paper concluded that the W126

form was more appropriate in the

context of this review. Specifically, the

W126, by its incorporation of a

sigmoidal weighting function, does not

create an artificially imposed

concentration threshold, gives

proportionally more weight to the

higher and typically more biologically

potent concentrations, and is not

significantly influenced by 03

concentrations within the range of

estimated PRB.

The Staff Paper also considered that

in the 1997 final rule, the decision was

made, on the basis of both science and

policy considerations, to make the

secondary standard identical to the

primary standard (62 FR 38876). On the

basis of that history, the current Staff

Paper analyzed the degree of overlap

expected between alternative 8-hour

and cumulative seasonal secondary

standards using recent air quality

monitoring data. Based on the results,

the Staff Paper concluded that the

degree to which the current 8-hour

standard form and level would overlap

with areas of concern for vegetation

expressed in terms of the 12-hour W126

standard is inconsistent from year to

year and would depend greatly on the

level of the 12-hour W126 and 8-hour

standards selected and the distribution

of hourly 03 concentrations within the

annual and/or 3-year average period.

Thus, though the Staff Paper -

recognized again that meeting the

current or alternative levels of the 8-

hour average standard could result in air

quality improvements that would

potentially benefit vegetation in some

areas, it urged caution be used in

evaluating the likely vegetation impacts

associated with a given level of air

quality expressed in terms of the 8-hour

average form in the absence of parallel

W126 information. This caution is due

to the concern that the analysis in the

Staff Paper may not be an accurate

reflection of the true situation in nonmonitored, rural counties due to the

lack of more complete monitor coverage

in many rural areas. Further, of the

counties that did not show overlap

between the two standard forms, most

were located in rural/remote high

elevation areas which have 03 air

quality patterns that are typically

different from those associated with

urban and near urban sites at lower

elevations. Because the majority of such

areas are currently not monitored, it is

believed there are likely to be additional

areas that have similar air quality

distributions that would lead to the

same disconnect between forms. Thus,

the Staff Paper concluded that it

remains problematic to determine the

appropriate level of protection for

vegetation using an 8-hour average form.

2. CASAC Views

The CASAC, based on its assessment

of the same vegetation effects science,

agreed with the Criteria Document and

Staff Paper and unanimously concluded

that protection of vegetation from the

known or anticipated adverse effects of

ambient 03 "requires a secondary

standard that is substantially different

from the primary standard in averaging

time, level, and form," i.e. not identical

to the primary standard for 03

(Henderson, 2007). Moreover, the

members of CASAC and a substantial

majority of the CASAC Panel agreed

with Staff Paper conclusions and

encouraged the Administrator to

establish an alternative cumulative

secondary standard for 03 and related

photochemical oxidants that is

distinctly different in averaging time,

form" and level from the current or

potentially revised 8-hour primary

standard (Henderson, 2006c). The

CASAC Panel also stated that "the

recommended metric for the secondary

ozone standard is the (sigmoidally

weighted) W126 index" (Henderson,

2007).

3. Administrator's Proposed

Conclusions

In EPA's proposal, the Administrator

agreed with the conclusions drawn in

the Criteria Document, Staff Paper and

by CASAC that the scientific evidence

available in the current review

continues to demonstrate the

cumulative nature of 0 3-induced plant

effects and the need to give greater

weight to higher concentrations. Thus,

the Administrator proposed that a

cumulative exposure index that

differentially weights 03 concentrations

could represent a reasonable policy

choice for a seasonal secondary

standard to protect against the effects of

03 on vegetation. The Administrator

further agreed with both the Staff Paper

and CASAC that the most appropriate

cumulative, concentration-weighted

form to consider in this review is the

sigmoidally weighted W126 form, due

to his recognition that there is no

evidence in the literature for an

exposure threshold that would be

appropriate across all 03-sensitive

vegetation and that this form is unlikely

to be significantly influenced by 03 air

quality within the range of PRB levels

identified in this review. Thus, the

Administrator proposed as one option to

replace the current 8-hour average

secondary standard form with the

cumulative, seasonal W126 form.

The Administrator also proposed to

revise the current secondary standard by

making it identical to the proposed 8-

hour primary standard, which was

proposed to be within the range of 0.070

to 0.075 ppm. For this option, EPA also

solicited comment on a wider range of

8-hour standard levels, including levels

down to 0.060 ppm and up to the

current standard (i.e., effectively 0.084

ppm with the current rounding

convention). In putting forward such a

proposal, the Administrator focused on

the decision made in the last review,

and the rationale for that decision that

made the revised secondary standard

identical to the revised primary

standard.

4. Comments on the Secondary

Standard Options

Comments received following

proposal regarding revising the

secondary standard either to reflect a

new, cumulative form or by remaining

equal to a revised primary standard

generally fell into two groups. These

comments were similar to those raised

prior to the proposal during earlier

phases of the NAAQS review, as

summarized in the proposal notice and

highlighted below.

One group of commenters, including

the National Park Service,

Environmental Defense,-NESCAUM,

NACAA, individual States, Tribal

Associations, and local environmental

organizations, asserted that the weight

of scientific evidence was unambiguous

with regard to the need for a cumulative

form, and specifically supported the

proposed W126 exposure index. For

example, New York State DEC

explained that "scientific research

recognizes that exposure-based indices

considering seasonal time period,

exposure duration, diurnal dynamics,

peak hourly ozone concentrations, and

cumulative effects are important when

assessing vegetation effects of ozone

exposure (Musselman et al., 2006). The

W126 exposure index has long been

recognized as a biologically meaningful

and useful way to summarize hourly

ozone data as a measure of ozone

exposure to vegetation (Lefohn et aL.,

1989)". Similarly, Environmental

Defense stated "[for reasons amply

explained by CASAC and the Staff,

neither the existing secondary standard

for ozone nor the proposed primary

standards are requisite to protect against

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adverse welfare effects on vegetation

and forested ecosystems. CASAC and

Staff further amply justified the need for

a separate cumulative seasonal welfare

standard to protect against these effects,

rather than relying solely on the primary

standards to provide such protection."

The National Park Service (NPS)

comment provided additional support

to this view and more sptecifically stated

that "the NPS supports both the

conclusion that a seasonal, cumulative

metric is needed to protect vegetation,

and that the W126 is a more appropriate

metric than the SUM06." EPA agrees

with these comments for the reasons

discussed above in sections IV.A.3 and

IV.B.2.a).

In addition to expressing strong

support for the W126 cumulative

seasonal form, commenters in this group

also expressed serious concerns with

EPA's other proposed option of setting

the secondary standard equal to a

revised primary standard. For example,

NPS agreed with CASAC that "retaining

the current form of the 8-hour standard

for the secondary NAAQS is

inappropriate and inadequate for

characterizing ozone exposures to

vegetation." NESCAUM stated "we also

strongly encourage EPA to avoid the

flawed rationale employed in the

previous 1997 ozone NAAQS review,

i.e., that many of the benefits of a

secondary NAAQS would be achieved if

the primary NAAQS were attained. This

rationale is flawed in at least two ways:

first, ozone damage to vegetation

persists in areas that attain the primary

NAAQS; and second, the relationship

between short-term 8-hour peak

concentrations and longer-term seasonal

aggregations is not constant, but varies

over space and time * * * as EPA notes

at 72 FR 37904. * * * EPA should set

a secondary NAAQS on its own

independent merits based on adverse

welfare effects. Real or perceived

relationships between primary and

secondary nonattainment areas are

irrelevant to setting the appropriate

form and level of the secondary

NAAQS." Environmental Defense made

the argument that "[b]ecause there is no

rational connection between the

proposed primary standards and the

level of protection needed to protect

vegetation against adverse ozoneinduced welfare effects, any EPA

finding that the primary standards

would be sufficient for secondary

standards purposes would be

arbitrary.* * * The mere fact that the

primary might provide ancillary welfare

benefits does not satisfy the statute and

does not provide a rational basis for

concluding that the primary standards

are also requisite to protect to [sic) any

adverse welfare effects."

The other set of commenters,

including UARG, API, Exxon-Mobil,

The Annapolis Center, ASL and

Associates, and AAM, did not support

adopting an alternative, cumulative

form for the secondary standard. Some

of these cornmenters, while agreeing

that "directionally a cumulative form of

the standard may better match the

underlying data," believe that further

work is needed to determine whether a

cumulative exposure index for the form

of the secondary standard is requisite to

protect public welfare. These

commenters also restated concerns that

have been described above in section

IV.B.2 regarding the remaining

uncertainties associated with the

vegetation effects evidence and/or the

exposure, risk and benefits assessments.

They point to the uncertainties cited by

the Administrator in the 1997 review as

part of her rationale for deciding it was

not appropriate to move forward with a

seasonal secondary, and state that these

same uncertainties have not been

materially reduced in the current

review. These commenters also asserted

that EPA's analysis of the impact of the

nation's 03 control program for the 8-

hour standard on W126 exposures is not

scientifically sound due to the use of

low estimates of PRB and an arbitrary

rollback method that is uninformed by

atmospheric chemistry from

photochemical models. They argue that

EPA must first realistically evaluate the

total 03 reductions that would occur byusing a state-of-the-art photochemical

model and perform an analysis of the

exposure-response data to determine if

effects are observed for exposures which

do not exceed the 8-hour standard.

These commenters also stated that

without producing C-R functions for the

8-hour form of the standard, EPA has

failed to show that the current 8-hour

standard would provide less than

requisite protection. These commenters

asserted that substantial uncertainties

remain in this review, and that the

benefits of changing to a W126 form are

too uncertain to warrant revising the

form of the standard at this time.

This group of commenters also

addressed limitations associated with

selection of the W126 cumulative form.

Commenters asserted that: (1) The W126

form lacks a biological basis, since it is

merely a mathematical expression of

exposure that has been fit to specific

responses in OTC studies, such that its

relevance for real world biological

responses is unclear; (2) aflux-based

model would be a better choice than a

cumulative metric because it is an

improvement over the many limitations

and simplifications associated with the

cumulative form; however, there is

insufficient data to apply such a model

at present; (3) the European experience

with cumulative 03 metrics has been

disappointing and now Europeans are

working on their second level approach,

which will be flux-based; and (4) the

W126 form 6annot provide nationally

uniform protection, as the same value of

an exposure index may relate to

different vegetation responses; some

commenters support adding a second

index that reflects the accumulation of

peaks at or above 0.10 ppm (called

N100).

5. Administrator's Final Conclusions

In considering the appropriateness of

establishing a new standard defined in

terms of a cumulative, seasonal form, or

revising the current secondary standard

by making it identical to the revised

primary standard, the Administrator

took into account the approach used by

the Agency in the last review, the

conclusions of the Staff Paper, CASAC

advice, and the views of public

commenters. In giving careful

consideration to the approach taken in

the last review, the Administrator first

considered the Staff Paper analysis of

the projected degree-of overlap between

counties with air quality expected to

meet the revised 8-hour primary

standard, set at a level of 0.075 ppm,

and alternative levels of a W126

standard based on currently monitored

air quality data. This analysis showed

significant overlap between the revised

8-hour primary standard and selected

levels of the W126 standard form being

considered, with the degree of overlap

between these alternative standards

depending greatly on the W126 level

selected and the distribution of hourly

03 concentrations within the annual

and/or 3-year average period. 28 On this

basis, as an initial matter, the

Administrator recognizes that a

secondary standard set identical to the

proposed primary standard would

provide a significant degree of

additional protection for vegetation as

compared to that provided by the

current secondary standard. In further

considering the significant uncertainties

that remain in the available body'of

evidence of 0 3-related vegetation effects

and in the exposure and risk analyses

conducted for this review, and the

difficulty in determining at what point

various types of vegetation effects

become adverse for sensitive vegetation

and ecosystems, the Administrator

focused his consideration on a level for

28 EPA has done further analysis of the degree of

overlap, and that analysis is in the docket.

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an alternative W126 standard at the

upper end of the proposed range (i.e., 21

ppm-hours). The Staff Paper analysis

shows that at that W126 standard level,

there would be essentially no counties

with air quality that would be expected

both to exceed such an alternative W126

standard and to meet the revised 9-hour

primary standard-that is, based on this

analysis of currently monitored

counties, a W126 standard would be

unlikely to provide additional

protection in any areas beyond that

likely to be provided by the revised

primary standard.

The Administrator also recognizes

that the general lack of rural monitoring

data makes uncertain the degree to

which the revised 8-hour standard or an

alternativi W126 standard would be

protective, and that there would be the

potential for not providing the

appropriate degree of protection for

vegetation in areas with air quality

distributions that result in a high

cumulative, seasonal exposure but do

not result in high 8-hour average

exposures. While this potential for

under-protection is clear, the number

and size of areas at issue and the degree

of risk is hard to determine. However,

such a standard would also tend to

avoid the potential for providing more

protection than is necessary, a risk that

would arise from moving to a new form

for the secondary standard despite

significant uncertainty in determining

the degree of risk for any exposure level

and the appropriate level of protection,

as well as uncertainty in predicting

exposure and risk patterns.

The Administrator also considered

the views and recommendations of

CASAC, and agrees that a cumulative,

seasonal standard is the most

biologically relevant way to relate

exposure to plant growth response.

However, as reflected in the public

comments, the Administrator also

recognizes that there remain significant

uncertainties in determining or

quantifying the degree of risk

attributable to varying levels of 03

exposure, the degree of protection that

any specific cumulative, seasonal

standard would produce, and the

associated potential for error in

determining the standard thak'will

provide a requisite degree of

protection-i.e., sufficient but not more

than what is necessary. Given these

significant uncertainties, the

Administrator concludes that

establishing a new secondary standard

with a cumulative, seasonal form at this

time would result in uncertain benefits

beyond those afforded by the revised

primary standard and therefore may be

more than necessary to provide the

requisite degree of protection.

Based on his consideration of the full

range of views as described above, the

Administrator judges that the

appropriate balance to be drawn is to

revise the secondary standard to be

identical in every way to the revised

primary standard. The Administrator

believes that such a standard would be

sufficient to protect public welfare from

known or anticipated adverse effects,

and doesnot believe that an alternative

cumulative, seasonal standard is needed

to provide this degree of protection.

This judgment by the Administrator

appropriately considers the requirement

for a standard that is neither more nor

less stringent than necessary for this

purpose.

D. Final Decision on the Secondary 03

Standard

For the reasons discussed above, and

taking into account information and

assessments presented in the Criteria

Document and Staff Paper, the advice

and recommendations of the CASAC

Panel, and the public comments to date,

the Administrator has decided to revise

the existing 8-hour secondary standard.

Specifically, the Administrator is

revising the current standard by making

it identical to the revised primary

standard. Data handling conventions for

the secondary standard are the same as

for the primary standard, and are

specified in the new Appendix P that is

adopted, as discussed in section V

below. Issues related to the monitoring

requirements for the revised 03

secondary standard are discussed below

in section VI.

V. Creation of Appendix PInterpretation of the NAAQS for 03

This section presents EPA's final

decisions regarding the addition of

Appendix P to 40 CFR part 50 on

interpreting the primary and secondary

NAAQS for 03. EPA did not propose to

address revocation of the existing 8-

hour standard in this rulemaking.

Therefore, EPA is retaining Appendix I

to 40 CFR part 50 in its current form. A

new Appendix P explains the

computations necessary for determining

when the new 8-hour primary and

secondary standards are met. More

specifically, Appendix P addresses data

completeness requirements, data

reporting and handling conventions,

and rounding conventions, and provides

example calculations.

In the proposal, two alternative

secondary standards were proposed: a 3-

month secondary standard expressed as

a cumulative peak-weighted index form;

or a standard set to be identical to the

primary standard. For reasons stated

above, the Administrator has decided to

set the secondary standard to be

identical in all respects to the primary

standard. Therefore, the portions of the

proposed Appendix P providing data

handling procedures for a non-identical

secondary standard are not included in

the final rule.

Key elements of Appendix P are

outlined below.

A. General

As proposed, EPA is adding several

new definitions to section 1.0 and using

these definitions throughout Appendix

P.

B. Data Completeness

EPA proposed data completeness

requirements for the new Appendix P

for the revised 8-hour primary standard

that would be the same as those in

Appendix I applicable to the preexisting standard. To satisfy the data

completeness requirement, Appendix P

as proposed would require 90% data

completeness, on average, for the 3-year

period at a monitoring site, with no

single year within the period having less

than 75% data completeness. This data

completeness requirement applies only

during the required 03 monitoring

season and must be satisfied in order to

determine that the standard has been

met at a monitoring site. A site could be

found to violate the standard with less

than complete data. EPA concluded in

adopting these same data completeness

requirements in Appendix I in 1997 that

these proposed requirements are

reasonable based on its earlier analysis

of available air quality data that showed

that 90% of all monitoring sites that are

operated on a continuous basis

routinely meet this objective. EPA

received no comments on these

requirements, and the final Appendix P

includes them as proposed.

Appendix I and the proposed

Appendix P allow missing days to be

counted for the purpose of meeting the

data completeness requirements if

meteorological conditions on these

missing days were not conducive to

concentrations above the level of the

standard. Such determinations under

Appendix I and the proposed Appendix

P would be made on a case-by-case basis

using available evidence. In the

proposal, EPA specifically requested

comment on whether meteorological

data could provide an objective basis for

determining, for a day for which there

is missing data, that the meteorological

conditions were not conducive to high

03 concentrations, and therefore, that

the day could be assumed to have an 03

concentration less than the level of the

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NAAQS. Further, the proposal

requested comments on whether days

assumed less than the level of the

standard should be counted as nonmissing when computing whether the

data completeness requirements have

been met at the site. The proposal

pointed out that this could allow a determination of attainment which

would otherwise be precluded by the

75% and/or 90% completeness tests.

Most commenters supported the use of

meteorological data to establish that

missing days could be assumed to have

low 03 levels. However, no commenter

suggested any particular objective

criteria or formula for making such

determinations. Based on these

comments, EPA will continue to use the

current case-by-case approach as proposed in Appendix P, as is the

current approach in Appendix I, to

count missing days when computing whether the data completeness

requirement has been met for the

primary standard.

As noted above, because the

Administrator has decided to set the

secondary standard identical in all

respects to the primary standard, the

final Appendix P provides that its data

completeness requirements apply to

both standards.

C. Data Reporting and Handling and

Rounding Conventions

For reasons discussed above, the

Administrator has set the level of the

revised 8-hour primary and secondary

standards at 0.075 ppm. As explained in

the proposal, the level of the 8-hour

standard is expressed to the third

decimal place. Almost all State agencies

now report hourly 03 concentrations to

three decimal places, in ppm, or in a

format easily convertible to ppm, since

the typical incremental sensitivity of

currently used 03 monitors is 0.001

ppm. Consistent with the current

approach for computing 8-hour

averages, in calculating 8-hour average

03 concentrations from hourly data, any

calculated digits beyond the third

decimal place would be truncated,

preserving the number of digits in the

reported data. In calculating 3-year

averages of the fourth highest maximum

8-hour average concentrations, digits to

the right of the third decimal place

would also be truncated, prdserving the

number of digits in the reported data.

Analyses discussed in the Staff Paper

demonstrated that taking into account

the precision and bias in 1-hour 03

measurements, the 8-hour design value

has an uncertainty of approximately

0.001 ppm. Truncating both the

individual 8-hour averages used to

determine the annual fourth maximum

as well as the 3-year average of the

fourth maxima to the third decimal

place is consistent with the approach

used in Appendix I for the previous 8-

hour 03 standard. In the proposal, EPA

sought comment on the appropriateness

of rounding rather than truncating to the

third decimal place as well as the

scientific validity of truncating the 3-

year average and the policy reasons

behind either truncating or roundifig the

3-year average to the third decimal

place. Many of the comments EPA

received on the rounding/truncation

issue in effect were comments that

supported expressing the level of the

NAAQS to either the second or third

decimal place. These comments are addressed in the Response to Comment

document. EPA continues to believe the

conclusions from the Staff paper

regarding monitor precision and error

propagation when calculating 8-hour 03

averages are appropriate. EPA has

decided to continue to truncate, as done

in Appendix I, and this approach is

included in the final Appendix P.

As discussed above in section II.C.3,

EPA is setting an 8-hour standard

extending to three decimal places.

Given that both the standard and the

calculated value of the 3-year average of

the fourth highest maximum 8-hour 03

concentration are expressed to three

decimal places, the two values can be

compared directly.

As noted above, because the

Administrator has decided to set th&

secondary standard identical in all

respects to the primary standard, the

same data reporting and handling and

rounding conventions will apply to

both.

VI. Ambient Monitoring Related to

Revised 03 Standards

As noted in the 03 NAAQS proposal

(see 72 FR 37906), EPA did not propose

any specific changes to existing

requirements for monitoring of 03 in the

ambient air. However, comment was

invited on a number of specific issues

which were expected.to be of

significance in the event that one or

more of the 03 NAAQS was revised.

Comments were received from Federal

agencies, State monitoring agencies,

State organizations, environmental

organizations, and industrial trade

associations. As noted elsewhere in this

rulemaking, EPA is finalizing changes to

both the primary and secondary 03

NAAQS. In light of these revisions, EPA

intends to issue a monitoring rule to

address the issues identified in the

proposal, as well as other issues raised

in the comments. EPA intends to issue

a proposed monitoring rule in June 2008

and a final rule by March 2009. In

recognition of the comments received

on the proposed 03 standards and to

provide EPA's initial thinking on 03

specific monitoring rule amendments,

we offer the following observations. The

following paragraphs also point out one way in which some State/local

monitoring agencies might need to make

changes to their 03 monitoring network

as a result of the revision to the primary

and secondary 03 NAAQS, based on the

existing minimum monitoring

requirements including a factor based

on the comparison of design value to the

03 NAAQS (see 71 FR 61318). The

following text explains why an

amendment to the monitoring

regulations is not required to trigger

these increased 03 monitoring

requirements.

Presently, States (including the

District of Columbia, Puerto Rico, and

the Virgin Islands, and including local

agencies when so delegated by the State)

are required to operate minimum

numbers of EPA-approved 03 monitors

based on the population of each of their

Metropolitan Statistical Areas (MSA)

and the most recently measured 03

levels in each area. These requirements

are contained in 40 CFR part 58

Appendix D, Network Design Criteria

for Ambient Air Quality Monitoring,

Table D-2. These requirements were last

revised on October 17, 2006 as part of

a comprehensive review of ambient

monitoring requirements for all criteria

pollutants. (See 71 FR 61236).

The minimum number of monitors

required in an MSA ranges from zero

(for an area with population under

350,000 and no recent history of an 03

design value greater than 85 percent of

the NAAQS) to four (for an area with

population greater than 10 million and

an 03 design value greater than 85

percent of the NAAQS). Because these

requirements apply at the MSA level,

large urban areas consisting of multiple

MSAs can require more than four

monitors. In total, about 400 monitors

are required in MSAs, but about 1100

are actually operating in MSAs because

most States operate more than the

minimum required number of monitors.

As noted above, the requirements

listed in Table D-2 of 40 CFR part 58

Appendix D are based on the percentage

of the 03 NAAQS, with a design value

breakpoint at 85 percent of the NAAQS.

For an MSA of a given population size,

there are a greater number of required

monitors when the design value is

greater than or equal to 85 percent of the

03 NAAQS compared with MSAs that

have a design value of less than 85

percent of the 03 NAAQS. At the preexisting level of 0.084 ppm for the 8-

hour primary and secondary standards,

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an 8-hour 03 design value of 0.068 ppm

would trigger such increased minimum

monitoring requirements for in MSA. 29

With the decision to revise the 8-hour

primary and secondary standards to a

level of 0.075 ppm, the 8-hour 03 design

value that will trigger increased

minimum monitoring requirements for

an MSA has decreased from 0.068 ppm

to 0.064 ppm. Therefore, MSAs with 8-

hour design values between 0.064 ppm

and 0.067 ppm are now required to

increase the number of monitors

operating to meet minimum

requirements based on existing

monitoring requirements. 30 In practice,

however, virtually all of these areas

already are operating at least as many

monitors as required based on the

revised primary standard, so the number

of new monitors that are needed (or

needed to be moved from a location of

excess monitors) is negligible to meet

the existing minimum requirements.

About 100 MSAs with populations

less than 350,000 presently are without

any 03 monitors, and hence they do not

have an 03 design value for use with

Table D-2. These unmonitored MSAs

are not required to add monitors.

Commenters from State monitoring

agencies and State organizations

expressed concern that these current

requirements ignore the needs that

States and localities will have for

additional monitors to measure 03

levels in currently under-monitored

areas and, in particular, in unmonitored

areas with populations under 350,000.

They stated that unless this deficiency

is corrected, the health benefits of EPA's

03 NAAQS revision would likely be

limited to those living in Metropolitan

Statistical Areas (MSAs) having

populations of more than 350,000. Other

commenters noted the difficulty in

defining the boundaries of new

attainment/non-attainment areas

without additional monitoring in the

MSAs below 350,000.

EPA recognizes that the issues raised

by the commenters are important. EPA

intends to address these issues as part

of its proposed monitoring rule.

In relation to the proposed secondary

standard options, EPA invited comment

on whether, where, and how monitoring

in rural areas specifically focused on the

secondary NAAQS should be required.

As noted in the 03 NAAQS proposal

and described earlier in this section,

existing 03 monitoring requirements

29 Calculated as 85 percent of 0.08 ppm, per the

stated level of the pre-existing 8-hour primary and

secondary standards. 30 Approximately 16 MSAs that are subject to

minimum monitoring requirements have 8-hour

design values between 0.064 ppm and 0.067 ppm

based on an analysis of 2004-2006 ambient 03 data.

and current State monitoring practices

are primarily oriented towards

protecting against health effects in

people and therefore the primary

NAAQS. This accounts for the current

focus of the monitoring requirements on

urban areas, where large populations

reside, in which significant emissions of

03 -forming precursors are found, and

where 03 concentrations of concern are

likely to occur.

There are no EPA requirements for 03

monitoring in less populated areas

outside of MSA boundaries or in rural

areas. However, at present there are

about 250 03 monitors in counties that

are not part of MSAs. These monitors

are operated by State, local, and tribal

monitoring agencies for a variety of

objectives including the assessment of

03 transport and the support of research

programs including studies of

atmospheric chemistry and ecosystem

impacts. Additionally, EPA operates a

network of about 56 03 monitors as part

of its Clean Air Status and Trends

Network (CASTNET). The National Park

Service (NPS) operates about 27

monitors at other CASTNET sites. On an

overall basis, the spatial density of nonurban 03 monitors is relatively high in

the eastern one-third of the U.S. and in

California, with significant gaps in

coverage elsewhere across the country.

Some commenters expressed concern

about the quality assurance practices at

CASTNET sites with regard to certain

aspects of 03 monitoring. They

recommended that EPA upgrade such

practices to meet the 40 CFR part 58

Appendix A quality assurance

requirements already followed by the

States so that the resulting data could be

used in assessing compliance with the

revised secondary standard. EPA notes

that such upgrades have been completed

at some of the CASTNET sites, and that

such upgrades will be completed at all

CASTNET sites by 2009. EPA notes that

the resulting 03 ambient data from the

upgraded sites will meet Appendix A

requirements as is presently the case for

03 data from State operated monitors

and NPS monitors. These data will be

deemed acceptable for NAAQS- .

comparison objectives and available in

the AQS database beginning in 2008.

Most commenters noted the relative

lack of rural 03 monitors, stating that

EPA should consider adding monitoring

requirements that support a revised

secondary 03 standard by requiring 03

monitors in locations that contain 03-

sensitive plants or ecosystems. These

commenters also noted that the

placement of current 03 monitors may

not be appropriate for evaluating

vegetation exposure since many of these

monitors were likely located to meet

other objectives.

In light of the Administrator's

decision to revise the 8-hour secondary

standard, EPA believes that it is

appropriate to consider whether the

existing urban-based monitoring

requirements described elsewhere in

this section are adequate and

appropriate to characterize the exposure

in more rural areas where 0 3-sensitive

plant species and more sensitive

ecosystems exist and where resulting

vegetation d amage would adversely

affect land usage. Such areas would

likely include public lands that are

protected areas of national interest (e.g.,

national parks, wilderness areas).

In consideration of the spatial gaps

that currently exist in the rural ozone

monitoring network, and to the extent

that the existence of such gaps has

contributed to the overall uncertainty

that exists in the level of protection that

would be provided by the revised

secondary standard, EPA believes that

there is merit in considering whether

additional monitoring requirements in

certain rural areas would help support

ongoing ecosystem research studies as

well as future reviews of the 03 NAAQS

by providing a more robust data set with

which to assess the relationship of

vegetation damage to 03 concentrations.

Accordingly, as part of its separate

monitoring rulemaking, EPA intends to

,consider specific requirements for a

minimum number of rural monitors per

State, with detailed rule language to

ensure that States locate such monitors

in appropriate areas. For example, these

areas could include Federal, State, or

Tribal lands characterized by areas of

sensitive vegetation species subject to

visible foliar injury, seedling and

mature tree biomass loss, and other

adverse impacts to a degree that could

be considered adverse depending on the

intended use of the plant and its

significance to the public welfare. EPA

is also considering recommending that

States and Tribes employ other

quantitative tools, such as

photochemical modeling and/or the

spatial interpolation of ambient data

from existing 03 monitors, to determine

the adequacy of existing locations of

rural monitors and to inform the

locations of new or relocated monitors

that might be required to meet revised

rural minimum monitoring

requirements.

Finally, EPA solicited comment on

the issue of 03 monitoring seasons.

Unlike the year-round monitoring

required for other criteria pollutants, the

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required 03 monitoring seasons 31 vary

in length due to the inter-relationship of

0 3-forming photochemical activity with

ambient temperature, strength of solar

insolation, and length of day. For

example, in States with colder climates

such as Montana and South Dakota, the

03 season has q length of 4 months. In

States with warmer climates such as

California; Nevada, and Arizona, the 03

season has a length of 12 months.

With the decision to revise the 8-hour

primary standard to a level of 0.075

ppm, and to set the secondary standard

identical in all respects to the primary

standard, the issue arises of whether in

some areas the required 03 monitoring

season should be made longer. EPA

notes that under the existing

regulations, the Regional Administrator

may approve State-requested deviations

from the established 03 monitoring

season, but EPA may not increase the

length of the season for an area at EPA's

own initiative other than by notice and

comment rulemaking.

EPA has done a preliminary analysis

of 2004-2006 ambient data to address

the issue of whether extensions of

currently required 03 monitoring.

seasons are appropriate in light of the

revised level for the primary and

secondary 03 standards and the revised

breakpoints for the AQI. The results of

the analysis demonstrated that out-ofseason exceedances of the revised level

occurred in eight States during the

study period. Additionally, the

frequency of days with 03

concentrations that reached the revised

Moderate AQI category (based on a

breakpoint of 0.060 ppm) was much

greater compared with the frequency of

days with concentrations that reached

the pre-existing Moderate AQI category

(based on a breakpoint of 0.065 ppm).

This increased frequency of days with

Moderate AQI levels was noted to occur

during periods before and after the

currently required 03 seasons. Based on these preliminary analyses,

EPA intends to consider changes to the

length of the required 03 season for the

coming monitoring rulemaking. Such

changes could be based solely on the

frequency of exceedances of the revised

primary and secondary standards, or

could also consider the frequency of

concentrations in the Moderate category

of the AQI.

VII. Implementation and Related

Control Requirements

A. Future Implementation Steps

In today's rule, EPA is replacing the

existing (1997) standards with revised

31 See 40 CFR Part 58 Appendix D, section 2.5 for

a table of required 03 seasons.

primary and secondary 03 standards.

However, the 1997 standards-and the

implementation rules for those

standards-will remain in place for

'implementation purposes as EPA

undertakes rulemaking to address the

transition from the 1997 03 standards to

the 2008 03 standards. States are

required to continue to develop and

implement their State Implementation

Plans (SIPs) for the 1997 standards as

they begin the process of recommending

designations for the 2008 standards.

1. Designations

After EPA establishes or revises a

NAAQS, the CAA requires EPA and

States to begin taking steps to ensure

that the new or revised standards are

met. The first step is to identify areas of

the country that do not attain the new

or revised standards, or that contribute

to violations of the new or revised

standards. Section 107(d)(1) provides

"By such date as the Administrator may

reasonably require, but not later than 1

year'after promulgation of a new or

revised national ambient air quality

standard for any pollutant under section

109, the Governor of each State shall

* * * submit to the Administrator.a list

of all areas (or portions thereof) in the

State". that designates those areas as

non-attainment, attainment, or

unclassifiable. Section 107(d)(f)(B)(i)

further provides, "Upon promulgation

or revision of a national ambient air

quality standard, the Administrator

shall promulgate the designations of all

areas (or portions thereof) * * * as

expeditiousl as practicable, but in no

case later than 2 years from the date of

promulgation. Such period may be

extended for up to one year in the event

the Administrator has insufficient

information to promulgate the

designations."

The term "promulgation" has been

interpreted by the courts to be signature

and dissemination of a rule.3 2 As noted

above, the CAA requires EPA to

establish a deadline for the States'

submission of the designation

recommendations, but under the CAA,

it can be no later than March 12, 2009,

one year after the promulgation of this

rule. Therefore, Governors of States

should submit their designation

recommendations to EPA no later than

March 12, 2009. EPA's promulgation of

designations must occur no later than

March 12, 2010, although that date may

be extended by up to one year Linder the

CAA (no later than-March 12, 2011) if

EPA has insufficient information to

promulgate the designations.

32 American Petroleum Institute v. Costle, 609

F.2d 20 (D.C. Cir. 1979).

EPA intends to provide additional

guidance to the States concerning the

technical considerations for establishing

boundaries for designated areas. For the

revised primary and secondary

standards, we anticipate relying on past

03 designation guidance issued by EPA

prior to the designations for the 1997 03

standards.3 3 We anticipate working

closely with State air agencies and

Tribes on establishing new guidance on

designations, if needed.

2. State Implementation Plans

CAA sectioi 110 provides the general

requirements for SIPs. Within 3 years

after the promulgation of new or revised

NAAQS (or such shorter period as the

Administrator may prescribe) each State

must adopt and submit "infrastructure"

SIPs to EPA to address the requirements

of section 110(a)(1). Thus, States should

submit these SIPs no later than March

12, 2011. These "infrastructure SIPs"

provide assurances of State resources

and authorities, and establish the basic

State programs, to implement, maintain,

and enforce new or revised standards.

In addition to the infrastructure SIPs,

which apply to all States, CAA title I,

part D outlines the State requirements

for achieving clean air in designated

nonattainment areas. These

requirements include timelines for

when designated nonattainment areas

must attain the standards, deadlines for

developing SIPs that demonstrate how

the State will ensure attainment of the

standards, and specific emissions

control requirements. EPA plans to

address how these requirements, such

as attainment demonstrations and

attainment dates, reasonable further

progress, new source review,

conformity, and other implementation

requirements, apply to the revised 03

NAAQS in a proposed rulemaking in

Fall 2008. Also in that rulemaking EPA

will establish deadlines for submission

of nonattainment area SIPs but

anticipates that the deadlines will be no later than 3 years after final designation.

Depending on the classification of an

area, the SIP must provide for

attainment within 3 years (for areas

6lassified marginal) to 20 years (for

areas classified extreme) after final

designations.

3. Trans-boundary Emissions

Cross border 03 contributions from

within North America (Canada and

Mexico) entering the U.S. are generally

thought to be small. Section 179B of the

33 Memorandum of March 28, 2000 frwom John

Seitz, "Boundary Guidance on Air Quality

Designations for the 8-Hour Ozone National

Ambient Air Quality Standards (NAAQS or

Standard).-

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Clean Air Act allows designated

nonattainment areas to petition EPA to

consider whether such a locality might

have met a clean air standard "but for"

cross border contributions. To date, few

areas have petitioned EPA under this

authority. The impact of foreign

emissions on domestic air quality in the

United States is a challenging and

complex problem to assess. EPA is

engaged in a number of activities to

improve our understanding of

international transport. As work

progresses on these activities, EPA will

be able to better address the

uncertainties associated with transboundary flows of air pollution and

their impacts.

4. Monitoring Requirements

As discussed more fully in section VI,

EPA intends, in light of the revisions of

the 03 standards, to issue a monitoring

rule to address a variety of monitoringrelated issues identified in the preamble

to the proposed rule or in comments

received by the Agency on the proposal.

EPA intends to issue a proposed

monitoring rule in June 2008 and a final

rule by March 2009.

B. Related Control Requirements

The man-made oxides of nitrogen

(NOx) and volatile organic carbon (VOC)

emissions that contribute to 03

formation in the United States come

from a variety of source categories,

including mobile sources, industrial

processes, area-wide sources (which

include consumer and commercial

products), and the electric power

industry.34 Emissions from natural

sources, such as trees and wildfires can also constitute a significant portion of

total VOC emissions in certain regions

of the country, especially during the 03

season. Natural sources such as wildfires, lightning, and soils also emit

NOx. Emissions of VOCs and NOx from

these sources are considered natural

background emissions. 35

34 National Emission Inventory posted at the

following Web site: http://www.epa.gov/ttn/chieftrends/index.html. 35 In some cases natural emissions may cause or

significantly contribute to violations of the ozone

standard. EPA has issued rules that address how

these "exceptional events" can be discounted in

regulatory determinations. The Exceptional Events

Rule (72 FR 13560 (March 22, 2007) implements

CAA section 319(b)(3)(B) and section 107(d)(3)

authority to exclude air quality monitoring data

from regulatory determinations related to

exceedances or violations of the National Ambient

Air Quality Standards (NAAQS). If an event is

determined by EPA to be a qualifying exceptional

event, the affected area may avoid being designated

as nonattainment, being redesignated as.

nonattainment, or being reclassifed to a higher

classification, The requirements for demonstrating

that elevated ozone levels are the result of a

EPA has developed new emissions

standards for many types of stationary

sources and for nearly every class of

mobile sources in the last decade to

reduce 03 by decreasing emissions of

NOx and VOC. These programs

complement State and local efforts to

improve air quality and to meet the

national 03 standards. Under the

Federal Motor Vehicle Control Program

(FMVCP, see title H of the CAA, 42

U.S.C. 7521-7574), EPA has established

new emissions standards for nearly

every type of automobile, truck, bus,

motorcycle, earth mover, and aircraft

engine, and for the fuels used to power

these engines. Also, EPA established

new standards for the smaller engines

used in small watercraft, lawn and

garden equipment. Recently, EPA

proposed new standards for locomotive

and marine diesel engines. Vehicles and

engines are replaced over time with

newer, cleaner models. In time, these

programs will yield substantial

emissions reductions. Emissionsreductions associated with fuel

programs generally begin as soon as a

new fuel is available.

The reduction of VOC emissions from

industrial processes and consumer and

commercial product categories has been

achieved either directly or indirectly

through implementation of control

technology standards, including

reasonably available control technology,

best available control technology, and

maximum achievable control

technology standards; or is anticipated

due to proposed or upcoming proposals

based on generally available control

technology or best available controls

under provisions related to consumer

and commercial products. These

standards have resulted in VOC

emissions reductions of almost a million

tons per year accumulated starting in

1997 from a variety of sources including

combustion sources, coating categories,

and chemical manufacturing. In 2006

and 2007, EPA issued national rules and

control techniques guidelines for

control of VOC emissions from 10

categories of consumer and commercial

products. EPA is currently working to

finalize new Federal rules, or

amendments to existing rules, intended

to establish new nationwide VOC

content limits for several categories of

consumer and commercial products,

including aerosol coatings, architectural

and industrial maintenance coatings,

and household and institutional

commercial products. EPA anticipates

that final rules addressing emissions

qualifying exceptional event are provided in the

Exceptional Events Rule.

from these sources will take effect in

2009.

Fuel combustion is one of the largest

anthropogenic sources of emissions of

NOx in the United States. Power

industry emission sources include large

electric generating units and some large

industrial boilers and turbines. The

EPA's landmark Clean Air Interstate

Rule (CAIR), issued on March 10, 2005,

permanently caps power industry

emissions of NOx in the eastern United

States. The first phase of the cap begins

in 2009, and a lower second phase cap

begins in 2015. By 2015, EPA projects

that the CAIR and other programs in the

Eastern U.S. will reduce power industry

annual NOx emissions in that region by

about 60 percent from 2003 levels.

With respect to agricultural sources,

the U.S. Department of Agriculture

(USDA) has recommended conservation

systems and activities that can reduce

agricultural emissions of NOx and VOC.

Current practices that may reduce

emissions of NOx and VOC include

engine replacement programs,

management of pesticide applications,

and manure management techniques.

The EPA recognizes that USDA has been

working with the agricultural

community to plan conservation

systems and activities to manage

emissions of 03 precursors.

These conservation systems and

activities can be voluntarily adopted in

areas where mitigation of 03 precursors

have been identified as an air quality

concern through the use of incentives

provided to the agricultural producer. In

cases where the States need these measures to attain the 03 standards,

agricultural producers could choose to

adopt these measures. The EPA will

continue to work with USDA on

planning the implementation of these

conservation systems and activities in

order to identify and/or improve

mitigation efficiencies, prioritize their

adoption, and ensure that appropriate

criteria are used for identifying the most

effective application of conservation

systems and activities.

The EPA will work together with

USDA and with States to identify

appropriate measures to meet the

primary and secondary standards,

including site-specific conservation

systems and activities. Based on prior

experience identifying conservation

measures and practices to meet the PM

NAAQS requirements, the EPA will use

a similar process to identify measures

that could meet the 03 requirements.

The EPA anticipates that certain USDAapproved conservation systems and

activities that reduce agricultural

emissions of NOx and VOC may be able

to satisfy the requirements for

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applicable sources to implement '

reasonably available control measures

for purposes of attaining the primary

and secondary 03 NAAQS.

VIII. Statutory and Executive Order

Reviews

A. Executive Order 12866: Regulatory

Planning and Review

Under section 3(f)(1) of Executive

Order (EO) 12866 (58 FR 51735, October

4, 1993), this action is an "economically

significant regulatory action" because it

is likely to have an annual effect on the

economy of $100 million or more.

Accordingly, EPA submitted this action

to the Office of Management and Budget

(OMB) for review under EO 12866 and

any changes made in response to OMB

recommendations have been

documented in the docket for this

action. In addition, EPA prepared an

analysis of the potential costs and

benefits associated with this action.

This analysis is contained in the Final

Ozone NAAQS Regulatory Impact

Analysis, March 2008 (henceforth,

"RIA"). A copy of the analysis is

available in the RIA docket (EPA-HQOAR-2007-0225) and the analysis is

briefly summarized here. The RIA

estimates the costs and monetized

human health and welfare b~nefits of

attaining three alternative 03 NAAQS

nationwide. Specifically, the RIA

examines the alternatives of 0.079 ppm,

0.075 ppm, 0.070 ppm, and 0.065 ppm.

The RIA contains illustrative analyses

that consider a limited number of

emissions control scenarios that States

and Regional Planning Organizations

might implement to achieve these

alternative 03 NAAQS. However, the

CAA and judicial decisions make clear

that the economic and technical

feasibility of attaining ambient

standards are not to be considered in

setting or revising NAAQS, although

such factors may be considered in the

development of State plans to

implement the standards. Accordingly,

although a RIA has been prepared, the

results of the RIA have not been

considered in issuing this final rule.

B. Paperwork Reduction Act

This action does not impose an

information collection burden under the

provisions of the Paperwork Reduction

Act, 44 U.S.C. 3501 et seq. There are no

information collection requirements

directly associated with the

establishment of a NAAQS under

section 109 of the CAA.

Burden means the total time, effort, or

financial resources expended by persons

to generate, maintain, retain, or disclose

or provide information to or for a

Federal agency. This includes the time

needed to review instructions; develop,

acquire, install, and utilize technology

and systems for the purposes of

collecting, validating, and verifying

information, processing and

maintaining information, and disclosing

and providing information; adjust the

existing ways to comply with any

previously applicable instructions and

requirements; train personnel to be able

to respond to a coll~ctionof

information; search data sources;

complete and review the collection of

information; and transmit or otherwise

disclose the information.

An agency may not conduct or

sponsor, and a person is not required to

respond to a collection of information

unless it displays a currently valid OMB

control number. The OMB control

numbers for EPA's regulations in 40

CFR are listed in 40 CFR part 9.

C. Regulatory Flexibility Act

The Regulatory Flexibility Act (RFA)

generally requires an agency to prepare

a regulatory flexibility analysis of any

rule subject to notice and comment

rulemaking requirements under the

Administrative Procedure Act or any

other statute unless the agency certifies

that the rule will not have a significant

economic impact on a substantial

number of small entities. Small entities

include small businesses, small

organizations, and small governmental

jurisdictions.

For purposes of assessing the impacts

of this rule on small entities, small

entity is defined as: (1) A small business

that is a small industrial entity as

defined by the Small Business

Administration's (SBA) regulations at 13

CFR 121.201; (2) a small governmental

jurisdiction that is a government of a

city, county, town, school district or

special district with a population of less

than 50,000; and (3) a small

organization that is any not-for-profit

enterprise which is independently

owned and operated and is not

dominant in its field.

After considering the economic

impacts of this final rule on small

entities, I certify that this action will not

have a significant economic impact on

a substantial number of small entities.

This final rule will not impose any

requirements on small entities.-Rather,

this rule establishes national standards

for allowable concentrations of 03 in

ambient air as required by section'109

of the CAA. American Trucking Ass'ns

v. EPA, 175 F. 3d 1027, 1044-45 (D.C.

cir. 1999) (NAAQS do not have

significant impacts upon small entities

because NAAQS themselves impose no

regulations upon small entities).

D. Unfunded Mandates Reform Act

Title H of the Unfunded Mandates

Reform Act of 1995 (UMvRA), Publir.

Law 104-4, establishes requirements for

Federal agencies to assess the effects of

their regulatory actions on State, local,

and Tribal governments and the private

sector. Under section 202 of the UMRA,

EPA generally must prepare a written

statement, including a cost-benefit

analysis, for proposed and final rules

with "Federal mandates" that may

result in expenditures to State, local,

and Tribal governments, in the

aggregate, or to the private sector, of

$100 million or more in any one year.

Before promulgating an EPA rule for

which a written statement is needed,

section 205 of the UMRA generally

requires EPA to identify and consider a

reasonable number of regulatory

alternatives and to adopt the least

costly, most cost-effective or least

burdensome alternative that.achieves

the objectives of the rule. The

provisions of section 205 do not apply

when they are inconsistent with

applicable law. Moreover, section 205

allows EPA to adopt an alternative other

than the least costly, most cost-effective

or least burdensome alternative if the

Administrator publishes with the final

rule an explanation why that alternative

was not adopted. Before EPA establishes

any regulatory requirements that may

significantly or uniquely affect small

governments, including Tribal

governments, it must have developed

under section 203 of the UMRA a small

government agency plan. The plan must

provide for notifying potentially

affected small governments, enabling.

officials of affected small governments

to have meaningful and timely input in

the development of EPA regulatory

proposals with significant Federal

intergovernmental mandates, and

informing, educating, and advising

small governments on compliance with

the regulatory requirements.

This final rule contains no Federal

mandates (under the regulatory

provisions of Title II of the UMRA) for

State, local, or Tribal governments or

the private sector. The rule imposes no

new expenditure or enforceable duty on

any State, local or Tribal governments or

the private sector, and EPA has

determined that this rule contains no

regulatory requirements that might

significantly or uniquely affect small

governments. Furthermore, as indicated

previously, in setting a NAAQS EPA

cannot consider the economic or

technological feasibility of attaining

ambient air quality standards, although

such factors may be considered to a

degree in the development of State

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plans to implement the standards. See

also American Trucking Ass'ns v. EPA,

175 F. 3d at 1043 (noting that because

EPA is precluded from considering costs

of implementation in establishing

NAAQS, preparation of a Regulatory

Impact Analysis pursuant to the

Unfunded Mandates Reform Act would

not furnish any information which the

court could consider in reviewing the

NAAQS). Thus, this rule is not subject

to the requirements of sections 202 and

205 of the UMRA. EPA has determined

that this rule contains no regulatory

requirements that might significantly or

uniquely affect small governments.

E. Executive Order 13132: Federalisnr

Executive Order 13132, entitled

"Federalism" (64 FR 43255, August 10,

1999), requires EPA to develop an

accountable process to ensure "meaningful and timely input by State

and local officials in the development of

regulatory policies that have federalism

implications." "Policies that haye

federalism implications" is defined in

the Executive Order to include

regulations that have "substantial direct

effects on the States, on the relationship

between the national government and

the States, or on the distribution of

power and responsibilities among the

various levels of government."

This final rule does not have

federalism implications. It will not have

substantial direct effects on the States,

on the relationship between the national

government and the States, or on the

distribution of power and

responsibilities among the various

levels of government, as specified in

Executive Order 13132. The rule does

not alter the relationship between the

Federal government and the States

regarding the establishment and

implementation of air quality

improvement programs as codified in

the CAA. Under section 109 of the CAA,

EPA is mandated to establish NAAQS;

however, CAA section 116 preserves the

rights of States to establish more

stringent requirements if deemed

necessary by a State. Furthermore, this

rule does not impact CAA section.107

which establishes that the States have

primary responsibility for

implementation of the NAAQS. Finally,

as noted in section E (above) on UMRA,

this rule does not impose significant

costs on State, local, or Tribal

governments or the private sector. Thus,

Executive Order 13132 does not apply

to this rule.

F. Executive Order 13175: Consultation

and Coordination With Indian Tribal

Governments

Executive Order 13175, entitled

"Consultation and Coordination with

Indian Tribal Governments" (65 FR

67249, November 9, 2000), requires EPA

to develop an accountable process to

ensure "meaningful and timely input by

tribal officials in the development of

regulatory policies that have tribal

implications." This final rule does not

have Tribal implications, as specified in

Executive Order 13175. It does not have

a substantial direct effect on one or

more Indian Tribes, since Tribes are not

obligated to adopt or implement any

NAAQS. Thus, Executive Order 13175

does not apply to this rule.

Although Executive Order 13175 does

not apply to this rule, EPA contacted

Tribal environmental professionals

during the development of this rule.

EPA staff participated in the regularly

scheduled Tribal Air call sponsored by

the National Tribal Air Association

during the spring of 2007 as the

proposal was under development. EPA

specifically solicited additional

comment on the proposed rule from

Tribal officials. Comments from Tribal

officials on the proposed rule are

summarized in the Response to

Comments document.

G. Executive Order 13045: Protection of

Children From Environmental Health &

Safety Risks

Executive Order 13045, "Protection of

Children from Environmental Health

Risks and Safety Risks" (62 FR 19885,"

April 23, 1997) applies to any rule that:

(1) Is determined to be "economically

significant" as defined under Executive

Order 12866, and (2) concerns an

environmental health or safety risk that

EPA has reason to believe may have a

disproportionate effect on children. If

the regulatory action meets both criteria,

the Agency must evaluate the

environmental health or safety effects of

the planned rule on children, and

explain why the planned regulation is

preferable to other potentially effective

and reasonably feasible alternatives

considered by the Agency.

This final rule is subject to Executive

Order 13045 because it is an

economically significant regulatory

action as defined by Executive Order

12866, and we believe that the

environmental health risk addressed by

this action may have a disproportionate

effect on children. Accordingly, we have

evaluated the environmental health or

safety effects of exposure to 03 pollution

among children. These effects and the

size of the population affected are

summarized in section 8.7 of the

Criteria Document and section 3.6 of the

Staff Paper, and the results of our

evaluation of the effects of 03 pollution

on children qre discussed in sections

II.A-C of this preamble.

H. Executive Order 13211: Actions That

Significantly Affect Energy Supply,

Distribution or Use

Executive Order 13211, "Actions

Concerning Regulations That

Significantly Affect Energy Supply,

Distribution, or Use" (66 FR 28355 (May

22, 2001)), requires EPA to prepare and

submit a Statement of Energy Effects to

the Administrator of the Office of

Information and Regulatory Affairs,

Office of Management and Budget, for

certain actions identified as "significant

energy actions." Section 4(b) of

Executive Order 13211 defines "significant energy actions" as "any

action by an agency (normally

published in the Federal Register) that

promulgates or is expected to lead to the

promulgation of a final rule or

regulation, including notices of inquiry,

advance notices of proposed

rulemaking, and notices of proposed

rulemaking: (1)(i) That is a significant

regulatory action under Executive Order

12866 or any successor order, and (ii) is

likely to have a significant adverse effect

on the supply, distribution, or use of

energy; or (2) that is designated by the

Administrator of the Office of

Information and Regulatory Affairs as a

significant energy action." The U.S.

Office of Management and Budget has

designated this rulemaking as a

significant energy action. Accordingly,

EPA has prepared a Statement of Energy

Effects for this action which appears in

Chapter 9 of the RIA conducted for this

rulemaking. A copy of the RIA is

available in the RIA docket (EPA-HQOAR-2007-0225) and the energy

analysis is briefly summarized here. The

analysis estimates potential impacts of

an illustrative control strategy, for the

0.070 ppm primary standard alternative

on the production of coal, crude oil,

natural gas, and electricity; on energy

prices; on control technologies adopted

by the electricity generating sector; and

on the mix of electricity generation. EPA

believes that the energy impacts

estimated for this illustrative control

strategy for the 0.070 ppm primary

standard alternative are higher than

those that would be estimated for an

illustrative control strategy for the

primary standard level of 0.075 ppm

which was selected by the

Administrator. However, due to

modeling limitations, EPA did not

generate separate estimates of the energy

impacts associated specifically with an

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illustrative control strategy designed for

a primary standard of 0.075 ppm. It is

important to note that the CAA make

clear that the economic impacts

associated with attaining ambient

standards are not to be considered in

setting or revising the NAAQS.

Accordingly, although the Statement of

Energy Effects has been prepared, the

results of EPA's energy analysis have

not been considered in issuing this final

rule.

L National Technology Transfer and

Advancement Act

As noted in the proposed rule, section

12(d) of the National Technology

Transfer and Advancement Act of 1995

(NTTAA), Public Law 104-113, section

12(d) (15 U.S.C. 272 note) directs EPA

to use voluntary consensus standards in

its regulatory activities unless to do so

would be inconsistent with applicable

law or otherwise impractical. Voluntary

consensus standards are technical

standards (e.g., materials specifications,

test methods, sampling procedures, and

business practices) that are developed or

adopted-by voluntary consensus

standards bodies. The NTTAA directs

EPA to provide Congress, through OMB,

explanations when the Agency decides

not to use available and applicable

voluntary consensus standards.

This action does not involve technical

standards. Therefore, EPA did not

consider the use of any voluntary

consensus standards.

1. Executive Order 12898: Federal

Actions To Address Environmental

Justice in Minority Populations and

Low-Income Populations

Executive Order 12898 (59 FR 7629;

Feb. 16, 1994) establishes Federal

executive policy on environmental

justice. Its main provision directs

Federal agencies, to the greatest extent

practicable and permitted by law, to

make environmental justice part of their

mission by-identifying and addressing,

as appropriate, disproportionately high

and adverse human health or

environmental effects of their programs,

policies, and activities on minority

populations and low-income

populations in the United States.

EPA has determined that this final

rule will not have disproportionately

high and adverse human health or

environmental effects on minority or

low-income populations because it

increases the level of environmental

protection for all affected populations

without having any disproportionately

high and adverse human health or

environmental effects on any

population, including any minority or

low-income population. This final rule

will establish uniform national

standards for 03 air pollution.

K. Congressional Review Act

The Congressional Review Act, 5

U.S.C. 801 et seq., as added by the Small

Business Regulatory Enforcement

Fairness Act of 1996, generally provides

that before a rule may take effect, the

agency promulgating the rule must

submit a rule report, which includes a

copy of the rule, to each House of the

Congress and to the Comptroller General

of the United States. EPA submitted a

report containing this rule and other

required information to the U.S. Senate,

the U.S. House of Representatives, and

the Comptroller General of the United

States prior to.publication of the rule in

the Federal Register. A major rule

cannot take effect until 60 days after it

is published in the Federal Register.

This action is a "major rule" as defined

by 5 U.S.C. 804(2). This rule will be

effective May 27, 2008.

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Risk Assessment for Selected Urban Areas.

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and Standards, U.S. Environmental

Protection Agency, Research Triangle Park,

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Abt Associates Inc. (2007b) Technical Report

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4191. October 9, 2007.

American Academy of Pediatrics (2007)

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American Association of State Highway and

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Letter and Comments Sent to Docket No.

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4325. October 9, 2007.

American Chemistry Council (ACC) (2007)

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OAR-2005-0172 re: Proposed Rule--

National Ambient Air Quality Standards

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American Enterprise Institute (2007) Letter

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October 9, 2007.

American Electric Power (2007) Letter and

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American Heart Association (2007) Letter

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October 5* 2007.

American Lung Association/Environmental

Defense/Sierra Club (ALA et ol.) (2007)

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American Nurses Association (2007) Letter

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American Petroleum Institute (2007) Letter

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American Thoracic Society/American

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for Ozone. Docket No. OAR-2005-0172-

4409. October 9, 2007.

Tingey, D. T.; Laurence, J. A.; Weber, J. A.;

Greene, J.; Hogsett, W. E.; Brown, S.; Lee,

E. H. (2001) Elevated CO2 and temperature

alter the response of Pinus ponderosa to

ozone: A simulation analysis. Ecol.

Appl.11: 1412-1424.

U.S. Department of Agriculture, 2006. The

PLANTS Database (http://plants.usda.gov,

I

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December 2006). National Plant Data

Center, Baton Rouge, LA.

Utah Department of Environmental Quality,

Division of Air Quality (2007) Letter and

Comments Sent to Docket No. OAR-2005-

0172 re: Proposed Rule-National Ambient

Air Quality Standards for Ozone. Docket

No. OAR-2005-0172-4138. October 9,

2007.

Utility Air Regulatory Group (2007) Letter

and Comments Sent to Docket No. OAR2005-0172 re: Proposed Rule-National

Ambient Air Quality Standards for Ozone.

Docket No. OAR-2005-0172-4183.

October 9, 2007.

Union of Concerned Scientists (UCS) (2007)

Letter and Comments Sent to Docket No.

OAR-2005-0172 re: Proposed RuleNational Ambient Air Quality Standards

for Ozone. Docket No. OAR-2005-0172-

4768. October 9, 2007.

Vedal, S.; Brauer, M.; White, R.; Petkau, J.

(2003) Air pollution and daily mortality in

a city with low levels of pollution.

Environ. Health Perspect. 111: 45-51.

Washington State Department of

Transportation (2007) Letter and

Comments Sent to Docket No. OAR-2005-

0172 re: Proposed Rule-National Ambient

Air Quality Standards for Ozone. Docket

No. OAR-2005-0172-4157. October 8,

2007.

Washington State Department of Ecology

(2007) Letter and Comments Sent to Docket

No. OAR-2005-0172 re: Proposed RuleNational Ambient Air Quality Standards

for Ozone. Docket No. OAR-2005-0172-

4267. October 9, 2007.

Weinstein, D.A., Beloin, R.M., R.D. Yanai

(1991) "Modeling changes in red spruce

carbon balance and allocation in response

to interacting ozone and nutrient stress."

Tree Physiology 9: 12 7-146.

Weinstein, D.A., J.A. Laurence, W.A. Retzlaff,

J.S. Kern, E.H. Lee, W.E. Hogsett, J. Weber

(2005) Predicting the effects of

tropospheric ozone on regional

productivity of ponderosa pine and white

fir. Forest Ecology and Management 205:

73-89.

Wisconsin Department of Natural Resources

(2007) Letter and Comments Sent to Docket

No. OAR-2005-0172 re: Proposed RuleNational Ambient Air Quality Standards

for Ozone. Docket No. OAR-2005-0172-

4358. October 9, 2007.

Whitfield, R.; Biller, W.; Jusko, M.; and

Keisler, J. (1996) A Probabilistic

Assessment of Health Risks Associated

with Short- and Long-Term Exposure to

Tropospheric Ozone. Argonne National

Laboratory, Argonne, IL.

Whitfield, R. (1997) A Probabilistic

Assessment of Health Risks Associated

with Short-term Exposure to Tropospheric

Ozone: A Supplement. Argonne National

Laboratory, Argonne, IL.

Whitfield, R.G.; Richmond, H.M.; and

Johnson, T.R. (1998) "Overview of Ozone

Human Exposure and Health Risk Analyses

Used in the U.S. EPA's Review of the

Ozone Air Quality Standard," pp.483-516

in: T. Schneider, ed. Air Pollution in the

21st Century: Priority Issues and Policy

Elsevier; Amsterdam.

Wolff, G.T. (1995) Letter from Chairman of

Clean Air Scientific Advisory Committee to

the EPA Administrator, dated November

30, 1995. EPA-SA.B-CASAC-LTR-96-002.

Wolff, G.T. (1996) Letter from Chairman of

Clean Air Scientific Advisory Committee to

the EPA Administrator, dated April 4,

1996. EPA-SAB-CASAC-LTR-96-006.

Young, T. F.; Sanzone, S., eds. (2002) A

framework for assessing and reporting on

ecological condition: an SAB report.

Washington, DC: U.S. Environmental

Protection Agency, Science Advisory

Board; report no. EPA-SAB-EPEC-02-009.

Available online at: http://

yosemite.epa.govlsab/sabproduct.nsfl

C3F89E598D843B58852570CA007571 7E/

$File/epecO2009a.pdf.

List of Subjects

40 CFR Part 50

Environmental protection, Air

pollution control, Carbon monoxide,

Lead, Nitrogen dioxide, Ozone,

Particulate matter, Sulfur oxides.

40 CFR Part 58

Environmental protection, Air

pollution control, Reporting and

recordkeeping requirements.

Dated: March 12, 2008.

Stephen L. Johnson,

Administrator.

m For the reasoni stated in the preamble,

title 40, chapter I of the code of Federal

regulations is to be amended as follows:

PART 50-NATIONAL PRIMARY AND

SECONDARY AMBIENT AIR QUALITY

STANDARDS

a 1. The authority citation for part 50

continues to read as follows:

Authority: 42 U.S.C. 7401, et seq.

* 2. Section 50.15 is added to read as

follows:

§50.15 National primary-and secondary

ambient air quality standards for ozone.

(a) The level of the national 8-hour

primary and secondary ambient air

quality standards for ozone (03) is 0.075

parts per million (ppm), daily maximum

8-hour average, measured by a reference

method based on Appendix D to this

part and designated in accordance with

part 53 of this chapter or an equivalent

method designated in accordance with

part 53 of this chapter.

(b) The 8-hour primary and secondary

03 ambient air quality standards are met

at an ambient air quality monitoring site

when the 3-year average of the annual

fourth-highest daily maximum 8-hour

average 03 concentration is less than or

equal to 0.075 ppm, as determined in

accordance with Appendix P to this

part.

m 3. Appendix P is added to read as

follows:

Appendix P to Part 50-Interpretation

of the Primary and Secondary National

Ambient Air Quality Standards for

Ozone

1. General

(a) 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 (03)

specified in § 50.15 are met at an ambient 03

air quality monitoring site. Ozone is

measured in the ambient air by a reference

method based on Appendix D of this part, as

applicable, and designated in accordance

with part 53 of this chapter, or by an

equivalent method designated in accordance

with part 53 of this chapter. Data reporting,

data handling, and computation procedures

to be used in making comparisons between

reported 03 concentrations and the levels of

the 03 standards are specified in the

following sections. Whether to exclude,

retain, or make adjustments to the data

affected by exceptional events, including

stratospheric 03 intrusion and other natural

events, is determined by the requirements

under §§50.1, 50.14 and 51.930.

(b) The terms used in this appendix are

defined as follows:

8-hour average is the rolling average of

eight hourly 03 concentrations as explained

in section 2 of this appendix.

Annual fourth-highest daily maximum

refers to the fourth highest value measured at

a monitoring site during a particular year.

Daily maximum 8-hour average

concentration refers to the maximum

calculated 8-hour average for a particular day

as explained in section 2 of this appendix.

Design values are the metrics (i.e.,

statistics) that are compared to the NAAQS

levels to determine compliance, calculated as

shown in section 3 of this appendix.

03 monitoring season refers to the span of

time within a calendar year when individual

States are required to measure ambient 03

concentrations as listed in part 58 Appendix

D to this chapter.

Year refers to calendar year.

2. Primary and Secondary Ambient Air

Quality Standards for Ozone

2.1 Data Reporting and Handling

Conventions

Computing 8-hour averages. Hourly

average concentrations shall be reported in

parts per million (ppm) to the third decimal

place, with additional digits to the right of

the third decimal place truncated. Running 8-

hour averages shall be computed from the

hourly 03 concentration data for each hour

of the year and shall be stored in the first,

or start, hour of the 8-hour period. An 8-hour

average shall be considered valid if at least

75% of the hourly 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 of the

hours available using 6 or 7 as the divisor.

8-hour periods with three or more missing

hours shall be considered valid also, if, after

substituting one-half the minimum detectable

limit for the missing hourly concentrations,

the 8-hour average concentration is greater

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than the level of the standard. The computed

8-hour average 03 concentrations shall be

reported to three decimal places (the digits to

the right of the third decimal place are

truncated, consistent with the data handling

procedures for the reported data).

Daily maximum 8-hour average

concentrations. (a) There are 24 possible

running 8-hour average 03 concentrations for

each calendar day during the 03 monitoring

season. The daily maximum 8-hour

concentration for a given calendar day is the

highest of the 24 possible 8-hour average

concentrations computed for that day. This

process is repeated, yielding a daily .

maximum 8-hour average 03 concentration

for each calendar day with ambient 03

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 03 monitoring day shall be counted

as a valid day if valid 8-hour averages are

available for at least 75% of possible hours

in the day (i.e., at least 18 of the 24 averages).

In the event that less than 75% of the 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 of the standard.

2.2 Primary and Secondary Standardrelated Summary Statistic

The standard-related summary statistic is

the annual fourth-highest daily maximum 8-

hour 03 concentration, expressed in parts per

million, averaged over three years. The 3-year

average shall be computed using the three

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 03 concentrations shall be

reported to three decimal places (the digits to

the right of the third decimal place are

truncated, consistent with the data handling

procedures for the reported data).

2.3 Comparisons with the Primary and

Secondary Ozone Standards

(a) The primary and secondary 03 ambient

air quality standards are met at an ambient

air quality monitoring site when the 3-year

average of the annual fourth-highest daily

maximum 8-hour average 03 concentration is

less than or equal to 0.075 ppm.

(b) This comparison shall be based on three

consecutive, complete calendar years of air

quality monitoring data. This requirement is

met for the 3-year period at a monitoring site

if daily maximum 8-hour average

concentrations are available for at least 90%

of the days within the 03 monitoring season,

on average, for the 3-year period, with a

minimum data completeness requirement in

any one year of at least 75% of the days

within the 03 monitoring season. When

computing whether the minimum data

completeness requirements have been met,

meteorological or ambient data may be

sufficient to demonstrate that meteorological

conditions on missing days were not

conducive to concentrations above the level

of the standard. Missing days assumed less

then.the level of the standard are counted for

the purpose of meeting the data completeness

requirement, subject to the approval of the

appropriate Regional Administrator.

(c) Years with concentrations greater than

the level of the standard shall be included

even if 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 if the 3-year

average fourth-highest 8-hour concentration

is greater than the level of the standard.

(d) Comparisons with the primary and

secondary 03 standards are demonstrated by

examples 1 and 2 in paragraphs (d)(1) and

(d)(2) respectively as follows:

EXAMPLE 1.-AMBIENT MONITORING SITE ATTAINING THE PRIMARY AND SECONDARY 03,STANDARDS

Percent valid days (within 1st Highest 2nd Highest 3rd Highest 4th Highest 5th Highest

Year the required daily max 8- daily max 8- daily max 8- daily max 8- daily max 8-

monitoring hour Conc. hour Conc. hour Conc. hour Conc. hour Conc.

season) (ppm) (ppm) (ppm) (ppm) (ppm)

2004 ......................................................... 100 0.092 0.090 0.085 0.079 0.078

2005 ......................................................... 96 0.084 0.083 0.075 0.072 0.070

2006 ......................................................... 98 0.080 0.079 0.077 0.076 0.060

Average . .............................. 98............................................0075............

(1) As shown in Example 1, this ppm) is less than or equal to 0.075 ppm. The I completeness. In Example 1, the individual

monitoring site meets the primary and data completeness reguirement-is also met 8-hour averages used to determine the annual

secondary 03 standards because the 3-year because the average percent of days within fourth maximum have also been truncated to

average of the annual fourth-highest daily the required monitoring season with valid the third decimal place.

maximum 8-hour average 03 concentrations ambient monitoring data is greater than 90%,

(i.e., 0.075666 * * * ppm, truncated to 0.075 and no single year has less than 75% data

EXAMPLE 2.-AMBIENT MONITORING SITE FAILING TO MEET THE PRIMARY AND SECONDARY 03 STANDARDS

Percent valid 1st Highest 2nd Highest 3rd Highest 4th Highest 5th Highest days (within 1tHget 2i ihs r ihs t ihs t ihs

Year the required daily max 8- daily max 8- daily max 8- daily max 8- daily max 8-

monitoring hour Conc. hour Conc. hour Conc. hour Conc. hour Conc. season) (ppm) (ppm) (ppm) (ppm) (ppm)

2004 ......................................................... 96 0.105 0.103 0.103 0.103 0.102

2005 ......................................................... 74 0.104 0.103 0.092 0.091 0.088

2006 ......................................................... 98 0.103 0.101 0.101 0.095 0.094

Average .............................. ..................... 0.096 ............

As shown in Example 2, the primary and

secondary 03 standards are not met for this

monitoring site because the 3-year average of

the fourth-highest daily maximum 8-hour

average 03 concentrations (i.e., 0.096333

* . * ppm, truncated to 0.096 ppm) is

greater than 0.075 ppm, even though the data

capture is less than 75% and the average data

capture for the 3 years is less than 90%

within the required monitoring season. In

Example 2, the individual 8-hour averages

used to determine the annual fourth

maximum have also been truncated to the

third decimal place.

I =2111ITT

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3. Design Values for Primary and Secondary

Ambient Air Quality Standards for Ozone

The air quality design value at a

monitoring site is defined as that

concentration that when reduced to the level

of the 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 standards, the 3-year

average annual fourth-highest daily

maximum 8-hour average 03 concentration is

also the air quality design value for the site.

PART 58-AMBIENT AIR QUALITY

SURVEILLANCE

* 4. The authority citation of part 58

continues to read as follows:

Authority: 42 U.S.C. 7403, 7410, 7601(a),

7611, and 7619.

a S. Appendix G to Part 58 is amended

as follows:

" a. By revising section 9.

" b. By revising section 10.

m c. By revising section 12.

" d. By revising section 13.

Appendix G to Part 58-Uniform Air

Quality Index (AQI) and Daily

Reporting

9. How Does the AQI Relate to Air Pollution

Levels?

For each pollutant, the AQI transforms

ambient concentrations to a scale from 0 to

500. The AQI is keyed as appropriate to the

national ambient air quality standards

(NAAQS) for each pollutant. In most cases,

the index value of 100 is associated with the

.numerical level of the short-term standard

(i.e., averaging time of 24-hours or less) for

each pollutant. A different approach is taken

for NO 2, for which no short-term standard

has been established. The index value of 50

is associated with the numerical level of the

annual standard for a pollutant, if there is

one, at one-half the level of the short-term

standard for the pollutant, or at the level at

which it is appropriate to begin to provide

guidance on cautionary language. Higher

categories of the index are based on

increasingly serious health effects and

increasing proportions of the population that

are likely to be affected. The index is related

to other air pollution concentrations through

linear interpolation based on these levels.

The AQI is equal to the highest of the

numbers corresponding to each pollutant.

For the purposes of reporting the AQI, the

sub-indexes for PM10 and PM 2 _5 are to be

considered separately. The .pollutant

responsible for the highest index value (the

reported AQI) is called the "critical"

pollutant.

10. What Monitors Should I Use To Get the

Pollutant Concentrations for Calculating the

AQI?

You must use concentration data from

population-oriented State/Local Air

Monitoring Station (SLAMS) or parts of the

SLAMS required by 40 CFR 58.10 for each

pollutant except PM. For PM, calculate and

report the AQI on days for which you have

measured air quality data (e.g., from

continuous PM2.

5 monitors required in

Appendix D to this part). You may use PM

measurements from monitors that are not

reference or equivalent methods (for

example, continuous PM,o or PM2.5 monitors). Detailed guidance for relating nonapproved measurements to approved

methods by statistical linear regression is

referenced in section 13 below.

12. How Do I Calculate the AQI?

i. The AQI is the highest value calculated

for each pollutant as follows:

a. Identify the highest concentration among

all of the monitors within each reporting area

and truncate the pollutant concentration to

one more than the significant digits used to

express the level of the NAAQS for that

pollutant. This is equivalent to the rounding

conventions used in the NAAQS.

b. Using Table 2, find the two breakpoints

that contain the concentration.

c. Using Equation 1, calculate the index.

d. Round the index to the nearest integer.

TABLE 2.-BREAKPOINTS FOR THE AQI

These breakpoints Equal these AQI's

03 (ppm) 03 (ppm) PM 2.

5 PM10 Sp

8-hour 1-hour1 (uIg/m3

) (jig/m3 ) CO (ppm) S 2 (PPM) N 2 (PPM) AQl Category

0.000-0.059 ............................ 0.0-15.4 0-54 0.0-4.4 0.000-0.034 (3) 0-50 Good.

0.060-0.075 ............................ 15.5-40.4 55-154 4.5-9.4 0.035-0.144 (3) 51-100 Moderate.

0.076-0.095 0.125-0.164 40.5-65.4 155-254 9.5-12.4 0.145-0.224 (3) 101-150 Unhealthy for

Sensitive

Groups. 0.096-0.115 .... 0.165-0.204 465.5-150.4 255-354 12.5-15.4 0.225-0.304 (3) 151-200 Unhealthy. 0.116-0.374 .... 0.205-0.404 4150.5-250.4 355-424 15&5-.30.4 0.305-0.604 0.65-1.24 201-300 Very

Unhealthy. (2) .................... 0.405-0.504 4250.5-350.4 425-504 30.5-40.4 0.605-0.804 1.25-1.64 301-400 (2) .................... 0.505-0.604 4350.5-500.4 505-604- 40.5-50.4 0.805-1.004 1.65-2.04 401-500 Hazardous..

Areas are generally required to report the A0l based on 8-hour ozone values. However, there are a small number of areas where an AQl

based on 1-hour ozone values would be more precautionary. In these.cases, in addition to calculating the 8-hour ozone index value, the 1-hour ozone index value may be calculated, and the maximum of the two values reported. 2

8-hour 03 values do not define higher AQI values (2- 301). AQI values of 301 or greater are calculated with 1 -hour 03 concentrations. 3N02 has no short-term NAAQS, and can generate an AQl only above the value of 200..

4 If a different SHL for PM 2.5 is promulgated, these numbers will change accordingly.

ii. If the concentration is equal to a breakpoint, then the index is equal to the

corresponding index value in Table 2.

However, Equation 1 can still be used. The

results will be equal. If the concentration is

between two breakpoints, then calculate the

index of that pollutant with Equation 1. You

must also note that in some areas, the AQI

based on 1-hour 03 will be more

precautionary than using 8-hour values (see

footnote 1 to Table 2). In these cases, you

may use 1-hour values as well as 8-hour

values to calculate-index values and then use

the maximum index value as the AQI for 03.

lp=IIE- ILO (C, - BP, ) + 1, °

BP, - 8P,

Where: Ip = the index value for pollutantp

(Equation 1)

Cp = the truncated concentration of

pollutantp

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BPHi = the breakpoint that is greater

than or equal to C,

BP = the breakpoint that is less than

or equal to C,

=Hi the AQI value corresponding to

BPi

I,, = the AQI value corresponding to

BPL.

iii. If the concentration is larger than the

highest breakpoint in Table 2 then you may

use the last two breakpoints in Table 2 when

you apply Equation 1.

Example

iv. Using Table 2 and Equation 1, calculate

the index value for each of the pollutants

measured and select the one that produces

the highest index value for the AQI. For

example, if you observe a PM1o value of 210

jtg/m 3 , a 1-hour 03 value of 0.156 ppm, and

an 8-hour 03 value of 0.130 ppm, then do

this:

a. Find the breakpoints for PM10 at 210 jgg/

m3 as 155 gg/m 3 and 254 gg/m 3 ,

corresponding to index values 101 and 150;

b. Find the breakpoints for 1-hour 03 at

0.156 ppm as 0.125 ppm and 0.164 ppm,

corresponding to index values 101 and 150;

c. Find the breakpoints for 8-hour 03 at

0.130 ppm as 0.116 ppm and 0.374 ppm,

corresponding to index values 201 and 300;

d. Apply Equation 1 for 210 gg/m 3

, PMo:

150 - 101 254 - 155 (210 - 155) + 101 = 128

e. Apply Equation 1 for 0.156 ppm, 1-hour

03:

150-101 06 - 10125 (0.156 - 0.125) + 101 = 140 0.164 - 0.125 '

f. Apply Equation 1 for 0.130 ppm, 8-hour

300- 201 (0.130 - 0.116) +201 = 206

0.374 - 0.116

g. Find the maximum, 206. This is the AQI.

The minimal AQ report would read:

v. Today, the AQI for my city is 206 which

is Very Unhealthy, due to ozone. Children

and people with asthma are the groups most

at risk.

13. What-Additional Information Should I

Know?

The EPA has developed a computer

program to calculate the AQI for you. The

program prompts for inputs, and it displays

all the pertinent information for the AQI (the

index value, color, category, sensitive group,

health effects, and cautionary language). The

EPA has also prepared a brochure on the AQI

that explains the index in detail (The Air

Quality Index), Reporting Guidance

(Guideline for Public Reporting of Daily Air

Quality) that provides associated health

effects and cautionary statements, and

Forecasting Guidance (Guideline for

Developing an Ozone Forecasting Program)

that explains the steps necessary to start an

air pollution forecasting program. You can

download the program and the guidance

documents at www.airnow.gov. Reference for

relating non-approved PM measurements to

approved methods (Eberly, S., T. Fitz-

.Simons, T. Hanley, L. Weinstock., T.

Tamanini, G. Denniston, B. Lambeth, E.

Michel, S. Bortnick. Data Quality Objectives

(DQOs) For Relating Federal Reference

Method (FRM) and Continuous PM 2.5

Measurements to Report an Air Quality Index

(AQI). U.S. Environmental Protection

Agency, research Triangle Park, NC. EPA454/B-02-002, November 2002) can be found

on the Ambient Monitoring Technology

Information Center (AMTIC) Web site, http://

www.epa.gov/ttnamtil/.

[FR Doc. E8-5645 Filed 3-26-08; 8:45 am]

BILUNG CODE 6560-50-P

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