federal register

38651

Friday

July 18, 1997

Part II

Environmental

Protection Agency

40 CFR Part 50

National Ambient Air Quality Standards

for Particulate Matter; Final Rule
38652 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

ENVIRONMENTAL PROTECTION

AGENCY

40 CFR Part 50

[AD–FRL–5725–2]

RIN 2060–AE66

National Ambient Air Quality

Standards for Particulate Matter

AGENCY: Environmental Protection

Agency (EPA).

ACTION: Final rule.

SUMMARY: This document describes

EPA’s decision to revise the national

ambient air quality standards (NAAQS)

for particulate matter (PM) based on its

review of the available scientific

evidence linking exposures to ambient

PM to adverse health and welfare effects

at levels allowed by the current PM

standards. The current primary PM

standards are revised in several

respects: Two new PM2.5 standards are

added, set at 15 μg/m3 , based on the 3-

year average of annual arithmetic mean

PM2.5 concentrations from single or

multiple community-oriented monitors,

and 65 μg/m 3 , based on the 3-year

average of the 98th percentile of 24-hour

PM2.5 concentrations at each

population-oriented monitor within an

area; and the current 24-hour PM10

standard is revised to be based on the

99th percentile of 24-hour PM10

concentrations at each monitor within

an area. The new suite of primary

standards will provide increased

protection against a wide range of PMrelated health effects, including

premature mortality and increased

hospital admissions and emergency

room visits, primarily in the elderly and

individuals with cardiopulmonary

disease; increased respiratory symptoms

and disease, in children and individuals

with cardiopulmonary disease such as

asthma; decreased lung function,

particularly in children and individuals

with asthma; and alterations in lung

tissue and structure and in respiratory

tract defense mechanisms. The current

secondary standards are revised by

making them identical in all respects to

the new suite of primary standards. The

new secondary standards, in

conjunction with a regional haze

program, will provide appropriate

protection against PM-related public

welfare effects including soiling,

material damage, and visibility

impairment. In conjunction with the

new PM2.5 standards, a new reference

method has been specified for

monitoring PM as PM2.5 .

EFFECTIVE DATE: This action is effective

September 16, 1997.

ADDRESSES: A docket containing

information relating to the EPA’s review

of the PM primary and secondary

standards (Docket No. A–95–54) is

available for public inspection in the

Central Docket Section of the U.S.

Environmental Protection Agency,

South Conference Center, Rm. 4, 401 M

St., SW., Washington, DC. This docket

incorporates the docket established for

the air quality Criteria Document

(Docket No. ECAO–CD–92–0671). The

docket may be inspected between 8 a.m.

and 3 p.m., Monday through Friday,

except legal holidays, and a reasonable

fee may be charged for copying. The

information in the docket constitutes

the complete basis for the decision

announced in this document. For the

availability of related information, see

‘‘SUPPLEMENTARY INFORMATION.’’

FOR FURTHER INFORMATION CONTACT: John

H. Haines, MD–15, Air Quality

Strategies and Standards Division,

Office of Air Quality Planning and

Standards, U.S. Environmental

Protection Agency, Research Triangle

Park, NC 27711; telephone: (919) 541–

5533; e-mail:

haines.john@epamail.epa.gov.

SUPPLEMENTARY INFORMATION:

Related Final Rules on PM Monitoring

In a separate document published

elsewhere in this issue of the Federal

Register, EPA is amending its ambient

air quality surveillance requirements (40

CFR part 58) and its ambient air

monitoring reference and equivalent

methods (40 CFR part 53) for PM.

Availability of Related Information

Certain documents are available from

the U.S. Department of Commerce,

National Technical Information Service,

5285 Port Royal Road, Springfield, VA

22161. Available documents include:

(1) Air Quality Criteria for Particulate

Matter (Criteria Document) (three

volumes, EPA/600/P–95–001aF thru

EPA/600/P–95–001cF, April 1996, NTIS

#PB–96–168224, $234.00 paper copy).

(2) Review of the National Ambient

Air Quality Standards for Particulate

Matter: Policy Assessment of Scientific

and Technical Information (Staff Paper)

(EPA–452/R–96–013, July 1996, NTIS

#PB–97–115406, $47.00 paper copy and

$19.50 microfiche). (Add a $3.00

handling charge per order.)

A limited number of copies of other

documents generated in connection

with this standard review, such as

technical support documents pertaining

to air quality, monitoring, and health

risk assessment, can be obtained from:

Environmental Protection Agency

Library (MD–35), Research Triangle

Park, NC 27711, telephone (919) 541–

2777. These and other related

documents are also available for

inspection and copying in the EPA

docket at the address under

‘‘ADDRESSES,’’ at the beginning of this

document.

Electronic Availability

The Staff Paper and human health

risk assessment support documents are

available on the Agency’s Office of Air

Quality Planning and Standards’

(OAQPS) Technology Transfer Network

(TTN) Bulletin Board System (BBS) in

the Clean Air Act Amendments area,

under Title I, Policy/Guidance

Documents. To access the bulletin

board, a modem and communications

software are necessary. To dial up, set

your communications software to 8 data

bits, no parity and one stop bit. Dial

(919) 541–5742 and follow the onscreen instructions to register for access.

After registering, proceed to choice

‘‘<T> Gateway to TTN Technical

Areas’’, then choose ‘‘<E> CAAA BBS’’.

From the main menu, choose ‘‘<1> Title

I: Attain/Maint of NAAQS’’, then ‘‘<P>

Policy Guidance Documents.’’ To access

these documents through the World

Wide Web, click on ‘‘TTN BBSWeb’’,

then proceed to the Gateway to TTN

Technical areas, as above. If assistance

is needed in accessing the system, call

the help desk at (919) 541–5384 in

Research Triangle Park, NC.

Implementation Strategy For Revised

Air Quality Standards

On Wednesday, July 16, 1997,

President Clinton signed a

memorandum to the Administrator

specifying his goals for the

implementation of the O3 and PM

standards. Attached to the President’s

memorandum is a strategy prepared by

an interagency Administration group

outlining the next steps that would be

necessary for implementing these

standards. The EPA will prepare

guidance and proposed rules consistent

with the President’s memorandum.

Copies of the Presidential document are

available in paper copy by contacting

the U.S. Environmental Protection

Agency Library at the address under

‘‘Availability of Related Information’’

and in electronic form as discussed

above in ‘‘Electronic Availability.’’

The following topics are discussed in

this preamble:

I. Background

A. Legislative Requirements

B. Related Control Requirements

C. Review of Air Quality Criteria and

Standards for PM

D. Summary of Proposed Revisions to the

PM Standards

II. Rationale for the Primary PM Standards

A. Introduction

B. Need for Revision of the Current

Primary PM Standards
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38653

C. Indicators of PM

D. Averaging Time of PM2.5 Standards

E. Form of PM2.5 Standards

F. Levels for the Annual and 24-Hour PM2.5

Standards

G. Conclusions Regarding the Current PM10

Standards

H. Final Decisions on Primary PM

Standards

III. Rationale for the Secondary Standards

A. Need for Revision of the Current

SecondaryStandards

B. Decision on the Secondary Standards

IV. Other Issues

A. Consideration of Costs

B. Margin of Safety

C. Data Availability

D. 1990 Amendments

V. Revisions to 40 CFR Part 50, Appendix

K—Interpretation of the PM NAAQS

A. PM2.5 Computations and Data Handling

Conventions

B. PM10 Computations and Data Handling

Conventions

C. Changes that Apply to Both PM2.5 and

PM10 Computations

VI. Reference Methods for the Determination

of Particulate Matter as PM10 and PM2.5

in the Atmosphere

A. Revisions to 40 CFR Part 50, Appendix

J—Reference Method for PM10

B. 40 CFR Part 50, Appendix L—New

Reference Method for PM2.5

VII. Effective Date of the Revised PM

Standards and Applicability of the

Existing PM10 Standards

VIII. Regulatory and Environmental Impact

Analyses

A. Executive Order 12866

B. Regulatory Flexibility Analysis

C. Impact on Reporting Requirements

D. Unfunded Mandates Reform Act

E. Environmental Justice

F. Submission to Congress and the

Comptroller General

IX. Response to Petition for Administrator

Browner’s Recusal

X. References

I. Background

A. Legislative Requirements

Two sections of the Clean Air Act

(Act) govern the establishment, review,

and revision of NAAQS. Section 108 of

the Act (42 U.S.C. 7408) directs the

Administrator to identify certain

pollutants which ‘‘may reasonably be

anticipated to endanger public health

and welfare’’ and to issue air quality

criteria for them. These air quality

criteria are to ‘‘accurately reflect the

latest scientific knowledge useful in

indicating the kind and extent of all

identifiable effects on public health or

welfare which may be expected from the

presence of [a] pollutant in the ambient

air * * *.’’

Section 109 of the Act (42 U.S.C.

7409) directs the Administrator to

propose and promulgate ‘‘primary’’ and

‘‘secondary’’ NAAQS for pollutants

identified under section 108 of the Act.

Section 109(b)(1) of the Act defines a

primary standard as one ‘‘the attainment

and maintenance of which in the

judgment of the Administrator, based on

[the] criteria and allowing an adequate

margin of safety, are requisite to protect

the public health.’’ The margin of safety

requirement was intended to address

uncertainties associated with

inconclusive scientific and technical

information available at the time of

standard setting, as well as to provide a

reasonable degree of protection against

hazards that research has not yet

identified. Both kinds of uncertainties

are components of the risk associated

with pollution at levels below those at

which human health effects can be said

to occur with reasonable scientific

certainty. Thus, by selecting primary

standards that provide an adequate

margin of safety, the Administrator is

seeking not only to prevent pollution

levels that have been demonstrated to be

harmful but also to prevent lower

pollutant levels that she finds may pose

an unacceptable risk of harm, even if the

risk is not precisely identified as to

nature or degree. The Act does not

require the Administrator to establish a

primary NAAQS at a zero-risk level, but

rather at a level that reduces risk

sufficiently so as to protect public

health with an adequate margin of

safety. The selection of any particular

approach to providing an adequate

margin of safety is a policy choice left

specifically to the Administrator’s

judgment. Lead Industries Ass’n v. EPA,

647 F.2d 1130, 1161–1162 (D.C.

Cir.1980).

A secondary standard, as defined in

section 109 (b)(2) of the Act, must

‘‘specify a level of air quality the

attainment and maintenance of which in

the judgment of the Administrator,

based on [the] criteria, [are] requisite to

protect the public welfare from any

known or anticipated adverse effects

associated with the presence of [the]

pollutant in the ambient air.’’ Welfare

effects as defined in section 302(h) of

the Act (42 U.S.C. 7602(h)) include, but

are not limited to, ‘‘effects on soils,

water, crops, vegetation, manmade

materials, animals, wildlife, weather,

visibility, and climate, damage to and

deterioration of property, and hazards to

transportation, as well as effects on

economic values and on personal

comfort and well-being.’’

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

periodic review and, if appropriate,

revision of existing air quality criteria

and NAAQS. Section 109(d)(2) of the

Act requires appointment of an

independent scientific review

committee to review criteria and

standards and recommend new

standards or revisions of existing

criteria and standards, as appropriate.

The committee established under

section 109(d)(2) of the Act is known as

the Clean Air Scientific Advisory

Committee (CASAC), a standing

committee of EPA’s Science Advisory

Board.

B. Related Control Requirements

States are primarily responsible for

ensuring attainment and maintenance of

ambient air quality standards once EPA

has established them. Under section 110

of the Act (42 U.S.C. 7410) and related

provisions, States are to submit, for EPA

approval, State implementation plans

(SIP’s) that provide for the attainment

and maintenance of such standards

through control programs directed to

sources of the pollutants involved. The

States, in conjunction with EPA, also

administer the prevention of significant

deterioration program (42 U.S.C. 7470–

7479) for these pollutants. In addition,

Federal programs provide for

nationwide reductions in emissions of

these and other air pollutants through

the Federal Motor Vehicle Control

Program under Title II of the Act (42

U.S.C. 7521–7574), which involves

controls for automobile, truck, bus,

motorcycle, nonroad engine, and aircraft

emissions; the new source performance

standards under section 111 of the Act

(42 U.S.C. 7411); and the national

emission standards for hazardous air

pollutants under section 112 of the Act

(42 U.S.C. 7412).

C. Review of Air Quality Criteria and

Standards for PM

Particulate matter is the generic term

for a broad class of chemically and

physically diverse substances that exist

as discrete particles (liquid droplets or

solids) over a wide range of sizes.

Particles originate from a variety of

anthropogenic stationary and mobile

sources as well as from natural sources.

Particles may be emitted directly or

formed in the atmosphere by

transformations of gaseous emissions

such as sulfur oxides (SOx), nitrogen

oxides (NOx), and volatile organic

compounds (VOC). The chemical and

physical properties of PM vary greatly

with time, region, meteorology, and

source category, thus complicating the

assessment of health and welfare effects.

The last review of PM air quality

criteria and standards was completed in

July 1987 with notice of a final decision

to revise the existing standards

published in the Federal Register (52

FR 24854, July 1, 1987). In that decision,

EPA changed the indicator for PM from

total suspended particles (TSP) to
38654 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

1 PM10 refers to particles with an aerodynamic

diameter less than or equal to a nominal 10

micrometers. Technical details further specifying

the measurement of PM10 are contained in 40 CFR

part 50, Appendices J and M.

2 A more complete history of the PM NAAQS is

presented in section II.B of the OAQPS Staff Paper,

Review of National Ambient Air Quality Standards

for Particulate Matter: Assessment of Scientific and

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

3 A court order entered in American Lung

Association v. Browner, CIV–93–643–TUC–ACM (D.

Ariz.,October 6, 1994), as subsequently modified,

requires publication of EPA’s final decision on the

review of the PM NAAQS by July 19, 1997.

4 The Staff Paper evaluates policy implications of

the key studies and scientific information in the

Criteria Document, identifies critical elements that

EPA staff believes should be considered, and

presents staff conclusions and recommendations of

suggested options for the Administrator’s

consideration.

5 PM2.5 refers to particles with an aerodynamic

diameter less than or equal to a nominal 2.5

micrometers, as further specified in 40 CFR part 50,

Appendix L in this document.

6 PM10–2.5 refers to those particles with an

aerodynamic diameter less than or equal to a

nominal 10 micrometers but greater than 2.5

micrometers. In other words, it refers to the

inhalable particles that remain if fine (PM2.5)

particles are removed from a sample of PM10

particles.

PM10.1 Identical primary and secondary

PM10 standards were set for two

averaging times: 50 μg/m3, expected

annual arithmetic mean, averaged over

3 years, and 150 μg/m3, 24-hour average,

with no more than one expected

exceedance per year.2

The EPA initiated this current review

of the air quality criteria and standards

for PM in April 1994 by announcing its

intention to develop a revised Air

Quality Criteria Document for

Particulate Matter (henceforth, the

‘‘Criteria Document’’). Thereafter, the

EPA presented its plans for review of

the criteria and standards for PM under

a highly accelerated, court-ordered

schedule3 at a public meeting of the

CASAC in December 1994. Several

workshops were held by EPA’s National

Center for Environmental Assessment

(NCEA) to discuss important new health

effects information in November 1994

and January 1995. External review drafts

of the Criteria Document were made

available for public comment and were

reviewed by CASAC at public meetings

held in August and December 1995 and

February 1996. The CASAC came to

closure in its review of the Criteria

Document, advising the Administrator

in a March 15, 1996 closure letter

(Wolff, 1996a) that ‘‘although our

understanding of the health effects of

PM is far from complete, a revised

Criteria Document which incorporates

the Panel’s latest comments will provide

an adequate review of the available

scientific data and relevant studies of

PM.’’ CASAC and public comments

from these meetings, and from

subsequent written comments and the

closure letter, were incorporated as

appropriate in the final Criteria

Document (U.S. EPA, 1996a).

External review drafts of a Staff Paper

prepared by the Office of Air Quality

Planning and Standards (OAQPS),

Review of the National Ambient Air

Quality Standards for Particulate Matter:

Assessment of Scientific and Technical

Information (henceforth, the ‘‘Staff

Paper’’), were made available for public

comment and were reviewed by CASAC

at public meetings in December 1995

and May 1996.4 The CASAC came to

closure in its review of the Staff Paper,

advising the Administrator in a June 13,

1996 closure letter (Wolff, 1996b) that

‘‘the Staff Paper, when revised, will

provide an adequate summary of our

present understanding of the scientific

basis for making regulatory decisions

concerning PM standards.’’ CASAC and

public comments from these meetings,

subsequent written comments, and the

CASAC closure letter were incorporated

as appropriate in the final Staff Paper

(U.S. EPA, 1996b).

On November 27, 1996, EPA

announced its proposed decision to

revise the NAAQS for PM (61 FR 65638,

December 13, 1996) (hereafter

‘‘proposal’’) as well as its proposed

decision to revise the NAAQS for ozone

(O3)(61 FR 65716, December 13, 1996).

In the proposal, EPA identified

proposed revisions, based on the air

quality criteria for PM, and solicited

public comments on alternative primary

standards and on the proposed forms of

the standards.

To ensure the broadest possible

public input on the PM and O3

proposals, EPA took extensive and

unprecedented steps to facilitate the

public comment process beyond the

normal process of providing an

opportunity to request a hearing and

receiving written comments submitted

to the rulemaking docket. The EPA

established a national toll-free

telephone hotline to facilitate public

comments on the proposed revisions to

the PM and O3 NAAQS, and on related

notices dealing with the implementation

of revised PM and O3 standards, as well

as a system for the public to submit

comments on the proposals

electronically via the Internet. Over

14,000 calls and over 4,000 electronic

mail messages were received through

these channels. The public could also

access key supporting documents

(including the Criteria Document, Staff

Paper, related technical documents and

fact sheets) via the Internet.

The EPA also held several public

hearings and meetings across the

country to provide direct opportunities

for public comment on the proposed

revisions to the PM and O3 NAAQS and

to disseminate information to the public

about the proposed standard revisions.

On January 14 and 15, 1997, EPA held

concurrent, 2-day public hearings in

Boston, MA, Chicago, IL, and Salt Lake

City, UT. A fourth public hearing,

which focused primarily on PM

monitoring issues, was held in Durham,

NC on January 14, 1997. Over 400

citizens and organizations testified

during these public hearings. EPA also

held two national satellite telecasts to

answer questions on the standards and

participated in meetings sponsored by

the Air and Waste Management

Association on the proposed revisions

to the standards at more than 10

locations across the country. Beyond

that, several EPA regional offices held

public meetings and workshops and

participated in hearings that States and

cities held around the country.

As a result of this intensive effort to

solicit public input, over 50,000 written

and oral comments were received on the

proposed revisions to the PM NAAQS

by the close of the public comment

period on March 12, 1997. Major issues

raised in the comments are discussed

throughout the preamble of this final

decision. A comprehensive summary of

all significant comments, along with

EPA’s response to such comments

(hereafter ‘‘Response to Comments’’),

can be found in the docket for this

rulemaking (Docket No. A–95–54).

The principal focus of this current

review of the air quality criteria and

standards for PM is on recent

epidemiological evidence reporting

associations between ambient

concentrations of PM and a range of

serious health effects. Particular

attention has been given to several sizespecific classes of particles, including

PM10 and the principal fractions of

PM10, referred to as the fine (PM2.5)5 and

coarse (PM10–2.5)6 fractions. As

discussed in the Criteria Document, fine

and coarse fraction particles can be

differentiated by their sources and

formation processes and their chemical

and physical properties, including

behavior in the atmosphere. Detailed

discussions of atmospheric formation,

ambient concentrations, and health and

welfare effects of PM, as well as

quantitative estimates of human health

risks associated with exposure to PM,

can be found in the Criteria Document

and in the Staff Paper.
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38655

D. Summary of Proposed Revisions to

the PM Standards

For reasons discussed in the proposal,

the Administrator proposed to revise the

current primary standards for PM (as

indicated by PM10), by adding two new

primary PM2.5 standards set at 15 μg/m3,

annual mean, and 50 μg/m3, 24-hour

average. The proposed annual PM2.5

standard would be based on the 3-year

average of the annual arithmetic mean

PM2.5 concentrations, spatially averaged

across an area. The proposed 24-hour

PM2.5 standard would be based on the

3-year average of the 98th percentile of

24-hour PM2.5 concentrations at each

population-oriented monitor within an

area. The proposal solicited comment

on two alternative approaches for

selecting the levels of PM2.5 standards.

The Administrator also proposed to

revise the current 24-hour primary PM10

standard of 150 μg/m3 by replacing the

1-expected-exceedance form with a 98th

percentile form, averaged over 3 years at

each monitor within an area, solicited

comment on an alternative proposal to

revoke the 24-hour PM10 standard, and

proposed to retain the current annual

primary PM10 standard of 50 μg/m3. The

proposal also solicited comment on

proposed revisions to 40 CFR part 50,

Appendix K to establish new data

handling conventions for calculating

98th percentile values and spatial

averages, revisions to 40 CFR part 50,

Appendix J to modify the reference

method for monitoring PM as PM10, and

a proposed new reference method for

monitoring PM as PM2.5 (40 CFR part 50,

Appendix L).

With regard to the secondary

standards, the Administrator proposed

to revise the current secondary

standards by making them identical to

the suite of proposed primary standards,

in conjunction with the establishment of

a regional haze program under section

169A of the Act.

II. Rationale for the Primary Standards

A. Introduction

1. Overview. This document presents

the Administrator’s final decisions

regarding the need to revise the current

primary ambient air quality standards

for PM, and, more specifically,

regarding the establishment of new

annual and 24-hour PM2.5 primary

standards and revisions to the form of

the current 24-hour PM10 primary

NAAQS. These decisions are based on

a thorough review, in the Criteria

Document, of the latest scientific

information on known and potential

human health effects associated with

exposure to PM at levels typically found

in the ambient air. These decisions also

take into account:

(1) Staff Paper assessments of the

most policy-relevant information in the

Criteria Document, upon which staff

recommendations for new and revised

primary standards are based.

(2) CASAC advice and

recommendations, as reflected in

discussions of drafts of the Criteria

Document and Staff Paper at public

meetings, in separate written comments,

and in the CASAC’s closure letters to

the Administrator.

(3) Public comments received during

the development of these documents,

either in connection with CASAC

meetings or separately.

(4) Extensive public comments

received on the proposed decisions

regarding the primary PM standards.

After taking this information and

comments into account, and for the

reasons discussed below in this unit, the

Administrator concludes that revisions

to the current primary standards to

provide increased public health

protection against a variety of health

risks are appropriate. More specifically,

the Administrator has determined that it

is appropriate to establish new annual

and 24-hour PM2.5 standards, to revise

the current 24-hour PM10 standard, and

to retain the current annual PM10

standard. As discussed more fully below

in this unit, the rationale for the final

decisions regarding the PM primary

NAAQS includes consideration of:

(1) Health effects information, and

alternative views on the appropriate

interpretation and use of the

information, as the basis for judgments

about the risks to public health

presented by population exposures to

ambient PM.

(2) Insights gained from a quantitative

risk assessment conducted to provide a

broader perspective for judgments about

protecting public health from the risks

associated with PM exposures.

(3) Specific conclusions regarding the

need for revisions to the current

standards and the elements of PM

standards (i.e., indicator, averaging

time, form, and level) that, taken

together, would be appropriate to

protect public health with an adequate

margin of safety.

As with virtually any policy-relevant

scientific research, there is uncertainty

in the characterization of health effects

attributable to exposure to ambient PM.

As discussed in the proposal, however,

there is now a greatly expanded body of

health effects information as compared

with that available during the last

review of the PM standards. Moreover,

the recent evidence on PM-related

health effects has undergone an

unusually high degree of scrutiny and

reanalysis over the past several years,

beginning with a series of workshops

held early in the review process to

discuss important new information. A

number of opportunities were provided

for public comment on successive drafts

of the Criteria Document and Staff

Paper, as well as for intensive peer

review of these documents by CASAC at

several public meetings attended by

many knowledgeable individuals and

representatives of interested

organizations. In addition, there have

been a number of important scientific

conferences, symposia, and colloquia on

PM issues, sponsored by the EPA and

others, in the U.S. and abroad, during

this period. While significant

uncertainties exist, the review of the

health effects information has been

thorough and deliberate. In the

judgment of the Administrator, this

intensive evaluation of the scientific

evidence has provided an adequate

basis for regulatory decision making at

this time, as well as for the

comprehensive research needs

document recently developed by EPA,

and reviewed by CASAC and others, for

improving our future understanding of

the relationships between ambient PM

exposures and health effects.

The health effects information and

human risk assessment were

summarized in the proposal and are

only briefly outlined below in this unit.

Subsequent units provide a more

complete discussion of the

Administrator’s rationale, in light of key

issues raised in public comments, for

concluding that it is appropriate to

revise the current primary standards

(Unit II.B. of this preamble) and to

revise the specific elements of the

standards including indicator (Unit II.C.

of this preamble); averaging time, form,

and level of new PM2.5 standards (Units

II.D., II.E., and II.F. of this preamble);

and averaging time, form, and level of

revised PM10 standards (Unit II.G. of

this preamble).

2. Summary of the health effects

evidence. In brief, since the last review

of the PM criteria and standards, the

most significant new evidence on the

health effects of PM is the greatly

expanded body of community

epidemiological studies. The Criteria

Document stated that these recent

studies provide ‘‘evidence that serious

health effects (mortality, exacerbation of

chronic disease, increased hospital

admissions, etc.) are associated with

exposures to ambient levels of PM

found in contemporary U.S. urban

airsheds even at concentrations below

current U.S. PM standard’’ (U.S. EPA,

1996a; p. 13-1). Although a variety of
38656 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

7 The risk assessment results that appear in the

Staff Paper and are summarized in the proposal

have been updated to include analyses of the

particular forms of standard alternatives contained

in the proposal and to correct estimates for one

effects category (mortality from long-term exposure)

to reflect the actual statistics used in the study upon

which they were based (Pope et al., 1995). The

corrections, which cumulatively reduce estimates of

mortality associated with long-term exposures by 20

to 35%, have no effect on risk estimates for

mortality associated with short-term exposures or

the estimates for any other effects. Because the key

sensitivity analyses that provide additional insights

regarding thresholds, copollutants, averaging time

and related issues involved the short-term exposure

studies, none of these results are affected by

changes to the long-term exposure risk estimates.

responses to constituents of ambient PM

have been hypothesized to contribute to

the reported health effects, the relevant

toxicological and controlled human

studies published to date have not

identified any accepted mechanism(s)

that would explain how such relatively

low concentrations of ambient PM

might cause the health effects reported

in the epidemiological literature.

Unit II.A. of the proposal further

outlines key information contained in

the Criteria Document, Chapters 10-13,

and the Staff Paper, Chapter V, on the

known and potential health effects

associated with airborne PM, alone and

in combination with other pollutants

that are routinely present in the ambient

air. The information highlighted there

summarizes:

(1) The nature of the effects that have

been reported to be associated with

ambient PM, which include premature

mortality, aggravation of respiratory and

cardiovascular disease (as indicated by

increased hospital admissions and

emergency room visits, school absences,

work loss days, and restricted activity

days), changes in lung function and

increased respiratory symptoms,

changes to lung tissues and structure,

and altered respiratory defense

mechanisms.

(2) Sensitive subpopulations that

appear to be at greater risk to such

effects, specifically individuals with

respiratory disease and cardiovascular

disease and the elderly (premature

mortality and hospitalization), children

(increased respiratory symptoms and

decreased lung function), and asthmatic

children and adults (aggravation of

symptoms).

(3) An integrated evaluation of the

health effects evidence, with an

emphasis on the key issues raised in

assessing community epidemiological

studies, including alternative

interpretations of the evidence, both for

individual studies and for the evidence

as a whole.

(4) The PM fractions of greatest

concern to health.

The summary in the proposal will not

be repeated here. EPA emphasizes that

the final decisions on these standards

take into account the more

comprehensive and detailed discussions

of the scientific information on these

issues contained in the Criteria

Document and Staff Paper, which were

reviewed by the CASAC and the public.

3. Key insights from the risk

assessment. The Staff Paper presents the

results of a quantitative assessment of

health risks for two example cities,

including risk estimates for several

categories of health effects associated

with: existing PM air quality levels,

projected PM air quality levels that

would occur upon attainment of the

current PM10 standards, and projected

PM air quality levels that would occur

upon attainment of alternative PM2.5

standards. The risk assessment is

intended as an aid to the Administrator

in judging which alternative PM

NAAQS would reduce risks sufficiently

to protect public health with an

adequate margin of safety, recognizing

that such standards will not be risk-free.

The risk assessment is described more

fully in the Staff Paper and summarized

in the proposal. Related technical

reports and updates7 have been placed

in the docket (Abt Associates, 1996a,b;

1997a,b).

EPA emphasizes that it places greater

weight on the overall conclusions

derived from the studies—that PM air

pollution is likely causing or

contributing to significant adverse

effects at levels below those permitted

by the current standards—than on the

specific concentration-response

functions and quantitative risk estimates

derived from them. These quantitative

risk estimates include significant

uncertainty and, therefore, should not

be viewed as demonstrated health

impacts. EPA believes, however, that

they do represent reasonable estimates

as to the possible extent of risk for these

effects given the available information.

Keeping in mind the important

uncertainties inherent in any such

analyses, the key insights from the risk

assessment that are most pertinent to

the current decision include:

(1) Fairly wide ranges of estimates of

the incidence of PM-related mortality

and morbidity effects and risk

reductions associated with attainment of

alternative standards were calculated for

the two locations analyzed when the

effects of key uncertainties and

alternative assumptions were

considered. Significantly, the combined

analysis for these two cities alone found

that the risk remaining after attaining

the current PM10 standards was on the

order of hundreds of premature deaths

each year, hundreds to thousands of

respiratory-related hospital admissions,

and tens of thousands of additional

respiratory related symptoms in

children.

(2) Based on the results from the

sensitivity analyses of key uncertainties

and the integrated uncertainty analyses,

the single most important factor

influencing the uncertainty associated

with the risk estimates is whether or not

a threshold concentration exists below

which PM-associated health risks are

not likely to occur.

(3) Over the course of a year, the few

peak 24-hour PM2.5 concentrations

appear to contribute a relatively small

amount to the total health risk posed by

the entire air quality distribution as

compared to the aggregated risks

associated with the low to mid-range

concentrations.

(4) There is greater uncertainty about

both the existence and the magnitude of

estimated excess mortality and other

effects associated with PM exposures as

one considers increasingly lower

concentrations approaching background

levels.

B. Need for Revision of the Current

Primary PM Standards

1. Introduction. The overarching issue

in the present review of the primary

NAAQS is whether, in view of the

advances in scientific knowledge

reflected in the Criteria Document and

Staff Paper, the existing PM standards

should be revised and, if so, what

revised or new standards would be

appropriate. The concluding section of

the integrative synthesis of health

effects information in the Criteria

Document, which CASAC characterized

as EPA’s ‘‘best ever example of a true

integrative summary of the state of

knowledge about the health effects of

airborne PM,’’ (Wolff, 1996b) provides

the following summary of the science

with respect to this issue:

The evidence for PM-related effects from

epidemiological studies is fairly strong, with

most studies showing increases in mortality,

hospital admissions, respiratory symptoms,

and pulmonary function decrements

associated with several PM indices. These

epidemiological findings cannot be wholly

attributed to inappropriate or incorrect

statistical methods, misspecification of

concentration-effect models, biases in study

design or implementation, measurement

errors in health endpoint, pollution

exposure, weather, or other variables, nor

confounding of PM effects with effects of

other factors. While the results of the

epidemiological studies should be

interpreted cautiously, they nonetheless

provide ample reason to be concerned that

there are detectable health effects attributable
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38657

8 As discussed more fully below in this unit,

epidemiological studies alone cannot be used to

demonstrate mechanisms of action, but they can

provide evidence useful in making inferences with

regard to causal relationships (U.S. EPA, 1996b, p.

V-9).

9 As noted in the proposal, the kinds of effects

observed in the epidemiological studies are

logically related. For example, the association of

PM with mortality is mainly linked to respiratory

and cardiovascular causes, which is coherent with

observed PM associations with respiratory and

cardiovascular hospital admissions and respiratory

symptoms. Further, similar categories of effects are

seen in long- and short-term exposure studies.

to PM at levels below the current NAAQS.

[U.S. EPA, 1996a, p. 13-92]

Given the nature of the health effects

in question, this finding, which is based

on a large number of studies that used

PM10 measurements, as well as studies

using other indicators of PM, clearly

indicates that revision of the current PM

NAAQS is appropriate. Quite apart from

the issue of whether PM10 should be the

sole indicator for the PM NAAQS, the

extensive PM epidemiological data base

provides evidence of serious health

effects (e.g., mortality, exacerbation of

chronic disease, increased hospital

admissions) in sensitive populations

(e.g., the elderly, individuals with

cardiopulmonary disease), as well as

significant adverse health effects (e.g.,

increased respiratory symptoms, school

absences, and lung function

decrements) in children. Moreover,

these effects associations are observed

in areas or at times when the levels of

the current PM10 standards are met.

Although the increase in relative risk is

small for the most serious outcomes,

EPA believes it is significant from an

overall public health perspective,

because of the large number of

individuals in sensitive populations that

are exposed to ambient PM, as well as

the significance of the health effects

involved (U.S. EPA, 1996a, p. 1-21). The

results of the two-city PM risk

assessment reinforce these conclusions

regarding the significance of the public

health risk—even under a scenario in

which the current PM10 standards are

attained.

While the lack of demonstrated

mechanisms that explain the extensive

body of epidemiological findings is an

important caution, which presents

difficulties in providing an integrated

assessment of PM health effects

research, a number of potential

mechanisms have been hypothesized in

the recent literature (U.S. EPA, 1996b; p.

V-5 to V-8; appendix D). Moreover,

qualitative information from laboratory

studies of the effects of particle

components at high concentrations and

dosimetry considerations suggest that

the kinds of effects observed in

community studies (e.g., respiratoryand cardiovascular-related responses)

are at least plausibly related to

inhalation of PM.8 Indeed, as discussed

in the Criteria Document and section

V.E of the Staff Paper, the consistency

of the results of the epidemiological

studies from a large number of different

locations and the coherent nature of the

observed effects9 are suggestive of a

likely causal role of ambient PM in

contributing to the reported effects.

2. Comments on scientific basis for

revision. A majority of the public

comments received on the proposal

agreed that, based on the available

scientific information, the current PM10

standards are not of themselves

sufficient to protect public health and it

would be appropriate to revise them.

Included in those calling for revisions to

the current standards are many public

health professionals, including

numerous medical doctors and

academic researchers. For example, a

group of 27 members of the scientific

and medical community recognized as

having substantial expertise in

conducting research on the health

effects of air pollution stated:

Health studies conducted in the U.S. and

around the world have demonstrated that

levels of particulate and ozone air pollution

below the current U.S. National Air Quality

Standards exacerbate serious respiratory

disease and contribute to early death. A large

body of scientific and medical evidence

clearly indicates that the current NAAQS are

not sufficiently protective of public health.

[Thurston, 1997]

Similar conclusions were reached in a

letter signed by more than 1,000

scientists, clinicians, researchers, and

other health care professionals (Dickey,

1997). The cosigners to this letter argued

that tens of thousands of hospital visits

and premature deaths could be

prevented with the proposed air quality

standard revisions. In fact, these

commenters argued that even stronger

standards than those proposed by EPA

are needed to protect the health of the

most vulnerable residents of our

communities.

A number of State and local

government authorities also submitted

comments in support of adopting new

air quality standards for fine particulate

matter. The commenters concurred with

conclusions reached through the EPA’s

peer review process that the PM

standards should be revised to protect

public health. A number of these

commenters suggested that the

standards proposed by EPA should be

even stronger, while several other State

agencies recommended that EPA adopt

PM2.5 standards, but at less stringent

levels. A number of the comments from

states supporting even stronger

standards acknowledged the lack of

demonstrated mechanism(s) and other

uncertainties but stressed the strength of

the other evidence in urging EPA to set

protective standards.

Many comments were also received

from representatives of environmental

or community health organizations that

supported the adoption of air quality

standards for PM2.5. These commenters

agreed with EPA’s finding that a large

body of compelling evidence

demonstrates that exposure to

particulate matter pollution, in general,

is associated with premature death,

aggravation of heart and lung diseases,

increased respiratory illness and

reduced lung function. They agreed

with EPA that these studies present a

consistent and coherent relationship

between exposure to PM and both

mortality and various measures of

morbidity. However, the majority of

these commenters argued that EPA’s

proposed standards for PM2.5 were

inadequate and recommended adoption

of more stringent levels of the 24-hour

and/or annual air quality standards for

PM2.5. Many of these commenters also

urged EPA to revise the NAAQS for

PM10 to be more protective of public

health. These commenters based their

recommendations on the findings of the

studies that were reviewed in the

preparation of the Criteria Document

and Staff Paper. One commenter used

results from five of these studies as the

basis for recommending PM2.5 standards

of 10 μg/m3 (annual) and 18 μg/m3 (24-

hour) (Dockery et al., 1993; Pope et al.,

1995; Schwartz et al., 1996; Schwartz et

al., 1994; Thurston et al., 1994). The

commenters agreed with EPA on the

significance of these studies’ results and

the need to revise the PM standards,

while differing with EPA’s

interpretation of the findings for

purposes of developing the proposed

PM standards.

Several commenters made reference

to the conclusions of a number of

international scientific panels regarding

the health effects of exposure to

airborne particulate matter—the British

Expert Panel on Air Quality Standards,

the British Committee on the Medical

Effects of Air Pollutants, the World

Health Organization, the Canadian

Ministry of Environment, Lands and

Parks, and the Health Council of the

Netherlands -- and argued that all these

panels found that PM concentrations

equivalent to the current U.S. standards

for PM10 are not protective of human

health and made recommendations for

greater protection. One commenter

noted that the findings of the British

Health Panel have resulted in a British
38658 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

proposal to adopt a 24-hour PM10

standard of 50 μg/m3, which is one-third

the level of the current U.S. NAAQS.

In these comments, some

toxicological studies were cited as

providing evidence for toxicity of

particulate pollution. These commenters

disagreed with arguments that PM

standards cannot be adopted due to a

lack of a sufficient understanding of the

biological mechanism of injury. The

commenters argued that there is

sufficient evidence that particulate

pollution is associated with adverse

health effects to make it inappropriate to

delay the establishment of standards

while further studies are undertaken.

This group of commenters was also

critical of arguments against the

establishment of additional PM

standards based on the possibility of

confounding by other pollutants, and

urged that more attention be paid

instead to the possible additive or

synergistic effects of multiple pollutant

exposures.

In general, the EPA agrees with these

commenters’ arguments regarding the

need to revise the PM standards. The

scientific studies cited by these

commenters were the same studies used

in the development of the Criteria

Document and the Staff Paper, and the

EPA agrees that there is a sufficient

body of evidence that the current

NAAQS for PM are not adequately

protective of the public health. For

reasons detailed in Unit II.F. of this

preamble and in the Response to

Comments, EPA disagrees with aspects

of these commenters’ views on the level

of protection that is appropriate and

supported by the available scientific

information.

Another body of commenters,

including almost all commenters

representing businesses and industry

associations, many local governmental

groups and private citizens, and some

States opposed revising the standards.

Many of these commenters argued that

the available scientific evidence does

not provide an adequate basis for

revising the current standards. The

central arguments made by these

commenters can be divided into two

categories: (1) General comments on the

appropriateness of relying on the

epidemiological evidence for making

regulatory decisions, and (2) more

specific comments challenging EPA’s

appraisal of the consistency and

coherence of the available information,

EPA’s conclusions regarding causality,

and the use of these studies for risk

assessment and decisions on whether to

revise the standards. While EPA has

included comprehensive responses to

these comments in the Response to

Comments, certain key points are

summarized below in this unit.

a. General comments on the use of

epidemiological studies. The first

category of comments was largely

derived from ad hoc panels of

occupational and other epidemiological

experts, consulting groups, and

individual consultants. Most of these

individuals and groups commented on

the use of epidemiology in reaching

scientific and policy conclusions

primarily from an occupational or

hazard assessment perspective, in

contrast to the perspective of the review

of ambient PM criteria and standards,

where the use of community air

pollution epidemiological studies are

central. Citing accepted criteria used in

evaluating epidemiological studies to

assess the likelihood of causality (most

notably those of Sir Austin Bradford

Hill, 1965), these commenters argued

that in the absence of a demonstrated

biological mechanism, the relative risks

of effects in the PM epidemiological

studies are too low (less than values

variously cited as 1.5 to 2.0) to reach

any conclusions regarding causality or

to form the basis for regulations. In

general, the commenters applied these

criteria to a subset of studies evaluated

in the Criteria Document, including as

few as two long-term exposure studies

(EOP Group) (API, 1997), a group of 9

selected studies (Greenland panel) (API,

1997), those studies cited in the

proposal (AIHC, 1997), or as many as 23

selected short-term exposure studies

examined in a recently published

review paper (Gamble and Lewis, 1996).

Based on a careful review of these

comments, EPA notes a number of

limitations in these commenters’

evaluations of the epidemiological

studies that they considered, as

discussed in detail in the Response to

Comments. In summary, EPA notes that

these commenters provided scientific

advice and conclusions that are in

substantial disagreement with the

conclusions of the review reflected in

the Criteria Document and Staff Paper.

EPA stands behind the scientific

conclusions reached in these documents

regarding the appropriate use of the

available community epidemiological

studies. These documents were the

product of an extended public process

that included conducting public

workshops involving the leading

researchers in the field, drafts of the

Criteria Document and Staff Paper

providing opportunities for public

scrutiny and comment on, and, not

least, receiving the advice of an

independent panel of air pollution

experts, including epidemiologists.

EPA clearly specified the key criteria

by which it evaluated the available

epidemiological studies in section

12.1.2 of the Criteria Document, with

substantial reliance on those specified

by Hill (1965). In rejecting results with

relative risks less than 1.5 to 2 as

meaningful absent demonstrated

biological mechanisms, the commenters

fail to note that Hill and other expert

groups (U.S. DHEW, 1964) have

emphasized that no one criterion is

definitive by itself, nor is it necessary

that all be met in order to support a

determination of causality (U.S. EPA,

1996a, p. 12-3).

With respect to biological plausibility,

Hill noted that ‘‘this is a feature I am

convinced we cannot demand. What is

biologically plausible depends upon the

biological knowledge of the day’’ (Hill,

1965). This statement is clearly

pertinent to the toxicological and

mechanistic understanding of the effects

of PM and associated air pollutants,

especially at lower concentrations. It is

also important to stress that while the

mechanistic evidence published as of

the time the Criteria Document closed

does not provide quantitative support

for the epidemiological results, neither

can such limited evidence refute these

findings. It is also important to stress

that our understanding of biological

mechanisms for PM pollution effects is

not sufficient to explain the effects

observed at much higher concentrations

in air pollution episodes, for which

causality is generally accepted.

Moreover, the toxicological literature

has only recently begun to examine

animal models (or controlled human

studies) that might reflect the sensitive

populations in question (the elderly,

individuals with chronic respiratory

and cardiovascular disease) or that

adequately reproduce all of the physicochemical properties of particles in the

ambient atmosphere. In short, the

absence of evidence of a particular

mechanism is hardly proof that there are

no mechanisms that could explain the

effects observed so consistently in the

epidemiological studies. The absence of

biological mechanisms did not deter

CASAC from recommending revisions

to the PM standards in 1982, 1986, and

again in 1996.

While Hill appropriately emphasized

the strength of the association as

important (e.g., size of the relative risk),

he also pointed out that ‘‘We must not

be too ready to dismiss a cause-andeffect hypothesis merely on the ground

that the observed association appears to

be slight. There are many occasions in

medicine when this in truth is so’’ (Hill,

1965). EPA believes that the effects of

air pollution containing PM is such a
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38659

case. Unlike the ‘‘textbook’’ examples of

unlikely significant associations

provided by some commenters (e.g., ice

cream consumption correlated with heat

stroke), the abundant epidemiological

literature on combustion particles

documents numerous occasions in

which single short-term episodes of

high air pollution produced

unequivocally elevated relative risks.

For the week of the well documented

1952 London air pollution episode, for

example, the relative risk of mortality

for all causes was 2.6, while the relative

risk for bronchitis mortality was as high

as 9.3 (Ministry of Health, 1954).

Hospital admissions also increased by

more than a factor of two. British

epidemiologists in the 1950s concluded

that increased mortality was likely

when PM (as mass calibrated British

Smoke <4.5 μm in aerodynamic

diameter) exceeded 500 μg/m3 (Martin

and Bradley, 1960). This is only about

a factor of 3 higher than that allowed by

the current PM standard. Unlike the

‘‘textbook’’ and other unlikely statistical

associations noted by some commenters,

where the only evidence is for low

relative risk, clear and convincing links

between high-level PM concentrations

and mortality and morbidity buttress the

findings of similar associations at much

lower PM concentrations as suggested in

the more recent epidemiological

literature.

These commenters also appear to

ignore several epidemiological studies

conducted at low PM concentrations in

U.S. and European cities, including both

short- and long-term exposures to PM

air pollution, that find statistically

significant relative risks of respiratory

symptom categories in children in the

range of 1.5 to 5 (Schwartz et al., 1994;

Pope and Dockery, 1992; BraunFahrlander et al., 1992; Dockery et al.,

1989; Dockery et al., 1996).

Concentrations in these studies extend

from moderately above to well below

those permitted by the current PM10

standards. While, as noted in the

proposal, most of the recent

epidemiological studies of mortality and

hospital admissions report

comparatively small relative risks, the

findings of relative risks well in excess

of the 1.5 to 2 criterion noted by

commenters for earlier studies of high

PM episodes, as well as the relative

risks of 1.5 to 5 reported in more recent

studies of less serious, but still

important effects categories, lend

credibility to EPA’s interpretation of the

results.

In addition to basing their

conclusions primarily on their own

assessment of a limited set of studies,

this group of commenters reached

different conclusions about the

consistency of the observed associations

because of their assumptions that all

model building strategies by all authors

are equally valid. Even the most

thorough of these treatments (Gamble

and Lewis, 1996) shared this flaw,

particularly in the discussion of the

series of Philadelphia mortality studies

and in the discussion of modeling

approaches. The authors’ treatment of

modeling and confounding issues was

further limited because they did not

include the most recent Philadelphia

results (Samet et al., 1996a,b) sponsored

by the Health Effects Institute (HEI,

1997). One of the important functions of

the Criteria Document is to evaluate the

strengths and limitations of various

studies. As discussed more fully below

in this unit, the Criteria Document

found that some of the studies cited by

commenters as suggesting a lack of

consistency had important limitations.

In general, these commenters’ analyses

suffered by ignoring the much more

thorough critical review of these studies

and issues contained in the Criteria

Document, notably that in section 12.6

on alternative modeling approaches.

EPA also rejects the notion advanced

by these commenters that

epidemiological studies must use

personal exposure monitoring to be

considered for regulatory purposes. In

particular, commenters ignore the

significant strengths of the time-series

studies and prospective cohort studies

relied on by EPA as compared to crosssectional epidemiological studies. Timeseries studies, such as the daily

mortality studies, look at changes in

response rate in relation to changes in

weather and air pollution over time

intervals of a few days. This controls for

other factors such as smoking and

socioeconomic status, which are little

changed during such short intervals.

Prospective cohort studies (e.g., Pope et

al., 1995; Raizenne et al., 1996), on the

other hand, look at changes in health

status in a selected cohort of

individuals, which allows direct

adjustment for smoking status,

socioeconomic status, and other subjectspecific factors. The commenters also

ignore the Criteria Document

conclusions on how properly conducted

monitoring can provide an adequate

index of population exposure to

ambient air pollution in such studies

that, as detailed below, is more relevant

to establishing ambient air quality

standards (U.S. EPA 1996a, chapter 7).

Although personal monitoring may be

practical for some occupational and

epidemiological studies, and has been

employed in some past studies of air

pollution, it is not realistic to require

personal monitors in air pollution

studies of daily mortality, which require

urban scale population data over a

period of years. Furthermore, the use of

community monitoring-based

epidemiological studies as a basis for

establishing standards and guidelines

has a long history in air pollution,

including the British authorities’

response to the London episodes and

the establishment of the original U.S.

NAAQS in 1971. Rejecting the use of the

vast array of such studies on this basis

alone would also go against the advice

of the independent scientific experts on

every CASAC panel that has addressed

the subject of PM pollution through the

years, each of which has recommended

general PM standards based primarily

on the results of community

epidemiological studies (Friedlander,

1982; Lippmann, 1986; Wolff, 1996b).

As noted above in this unit, EPA has

included a more detailed discussion of

its responses to these comments in the

Response to Comments.

b. Specific comments on

epidemiologic studies. The second

group of commenters noted above made

more specific challenges to EPA’s

assessment of the epidemiological

studies. These comments, although

overlapping some of those made by the

first group, were generally made by

commenters who have taken a more

active role in the review of the Criteria

Document and Staff Paper. These

commenters asserted that the

epidemiological evidence on PM is not

as consistent and coherent as EPA has

claimed, and, in particular, charged that

EPA ignored or downplayed a number

of studies that the commenters argue

contradict the evidence the Agency

cited as supporting the consistency and

coherence of PM effects. The studies, all

of which commenters contend do a

better job of addressing one or more key

issues, such as confounding pollutants,

weather, exposure misclassification, and

model specification, than earlier

studies, include several that were

available during preparation of the

Criteria Document, and a number that

appeared after the Criteria Document

and Staff Paper were completed.

Because the status of the later studies

differ from that of the earlier ones for

purposes of decisions under section 109

of the Act, the two categories are

discussed separately below in this unit.

Additional responses to comments

relating to both sets of studies have been

included in the Response to Comments.

In addition to the inclusion of specific

studies, commenters also raised other

issues regarding the limitations of the
38660 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

10 The term ‘‘negative’’ studies, as used in these

comments, should not be construed to mean those

in which there is a negative effects estimate (either

significant or non-significant) for the nominal

cause. As used by these commenters, the term also

includes statistically non-significant positive effect

estimates. In other words, the commenters define

‘‘positive’’ studies as including only those in which

the effect estimate is both positive and statistically

significant.

11 Data sets were those used in the original

studies by Dockery et al. (1992) for St. Louis and

Eastern Tennessee; Pope et al. (1992) for Utah

Valley; Schwartz and Dockery (1992a) for

Philadelphia; Schwartz (1993) for Birmingham; and

a portion of the Santa Clara data from Fairley

(1990). The data set from the Moolgavkar et al.

(1995a) Philadelphia reanalysis was also included

(Samet et al., 1995).

12 The HEI Board of Directors appointed an eight

member Oversight Committee consisting of leading

scientists in several disciplines relevant to air

pollution epidemiology to oversee key aspects of

the project and to prepare HEI’s assessment of the

results.

epidemiological information and the use

of these studies in EPA’s two-city risk

assessment. Both of these topics are also

discussed below in this unit.

(i) Studies available for inclusion in

the criteria review. With some

exceptions, most of the above

commenters cited somewhat similar

lists of ‘‘negative’’ studies that they

argue EPA ignored or downplayed in

arriving at conclusions on consistency

and coherence. Of the most commonly

cited studies, the following were

available for inclusion in the Criteria

Document: daily mortality studies by

Styer et al. (1995), Lyon et al. (1995), Li

and Roth (1995), Moolgavkar (1995a,b),

Wyzga and Lipfert (1995), Lipfert and

Wyzga (1995), and Samet et al. (1995,

1996a,b); the long-term exposure

mortality study by Abbey et al. (1991);

and the re-examination of the Six-City

mortality results (Dockery et al., 1993)

by Lipfert (1995).

The written record of EPA’s

evaluations of these studies effectively

refutes the claim that the Agency

ignored any of these studies and

supports the treatment the Agency

accorded to each of them. All of the

studies available to EPA at the time of

CASAC closure on the PM Criteria

Document (March 1996) were examined

for inclusion in the Criteria Document

and Staff Paper, which form the basis

for the PM proposal. ‘‘Negative’’10

studies were evaluated in detail along

with ‘‘positive’’ studies when they were

found to have no critical methodological

deficiencies, or to point out strengths

and limitations. Studies that had more

serious problems were generally

discussed in less detail, whether

positive or negative, than studies with

fewer or small deficiencies. The EPA

assessments were evaluated by peer

reviewers, by CASAC, and by the

public.

Most of the short-term exposure

studies cited above in this unit are

reanalyses and extensions of PM/

mortality studies that had been

published by other investigators. In

general, the Criteria Document

concluded that the most comprehensive

and thorough reanalyses were those in

the series conducted for the HEI, which

reanalyzed data sets used in studies

from six urban areas in Phase I.A (Samet

et al., 1995)11, with extended analyses

for Philadelphia in Phase I.B (Samet et

al., 1996a,b). The most important

finding in the HEI Phase I.A reanalyses

of the six areas is ‘‘the confirmation of

the numerical results of the earlier

analyses of all six data sets’’ (HEI,

1995)12. After replicating the original

investigators’ analyses, Samet et al.

(1995) also found similar results

analyzing the data using an improved

statistical model. The HEI Oversight

Committee found

[I]t is reasonable to conclude that, in these

six data sets, daily mortality from all causes

combined, and from cardiovascular and

respiratory causes in particular, increases as

levels of particulate air pollution indexes

increase. [HEI, 1995]

It is important to note that these

reanalyses by respected independent

scientists confirm the reliability and

reproducibility of the work of the

original investigators, particularly in

view of the concerns some commenters

have expressed about EPA’s reliance on

a number of PM studies published by

these authors.

The Phase I.A HEI results for

Philadelphia also found that it was

difficult to separate the effects of PM

from those of co-occurring SO2, in

agreement with the Moolgavkar et

al.(1995a) analysis. Subsequent HEI

work, and several of the other so-called

‘‘negative’’ studies cited above in this

unit, further examined this issue in

terms of confounding or effects

modification by one or more cooccurring gaseous pollutants or weather.

Contrary to commenters’ claims, this

issue and these studies received

considerable attention in the Criteria

Document and Staff Paper, and the

overall implications and conclusions

from these assessments were

summarized in the proposal. In

particular, the so-called ‘‘negative’’ and

other findings of Moolgalvkar et al.

(1995a,b) in their Philadelphia and

Steubenville studies were discussed in

great detail in section 12.6 of the PM

Critera Document and compared to

those of the original investigators

(Schwartz and Dockery, 1992a,b) and

other investigators (Li and Roth, 1995;

Wyzga and Lipfert, 1995). Further

analytical studies of the Philadelphia

data set were carried out by HEI (Samet

et al., 1996a,b) and have largely resolved

many of the uncertainties in the earlier

analyses; in EPA’s opinion, these

studies supersede the results of the

original investigators (Schwartz and

Dockery, 1992a) and the several earlier

reanalyses, including Moolgavkar

(1995a), Moolgavkar and Luebeck

(1996), Li and Roth (1995), Wyzga and

Lipfert (1995), and Samet et al. (1995).

Even though TSP is not the best PM

indicator for health effects, since it

includes a substantial fraction of nonthoracic particles, the extended Criteria

Document assessment (U.S. EPA, 1996a,

pp. 12-291 to -299; 12-327) of the Phase

I.B HEI analyses in Philadelphia (Samet

et al., 1996a,b) serves to support the

following findings:

(1) The mortality effects estimates for

TSP do not depend heavily on statistical

methods when appropriate models are

used.

(2) Estimated PM effects are not

highly sensitive to appropriate methods

for adjusting for time trends and for

weather.

(3) Air pollution has significant health

effects above and beyond those of

weather.

(4) Copollutants such as ozone, CO,

and NO2 may be important predictors of

mortality, but their effects can be

substantially separated from those of

TSP and SO2.

(5) The health effects of TSP in

Philadelphia cannot be completely

separated from SO2, which is itself a

precursor of fine particles, based solely

on the epidemiological analyses in this

single city.

The most recent HEI Oversight

Committee comments on these studies

(HEI, 1997), which were submitted to

the docket by HEI, state that:

Although individual air pollutants (TSP,

SO2, and ozone) are associated with

increased daily mortality in these data, the

limitations of the Philadelphia data make it

impossible to establish that particulate air

pollution alone is responsible for the widely

observed associations between increased

mortality and air pollution in that city. All

we can conclude is that it appears to play a

role. [HEI, 1997; p.38.]

While recognizing the limitations in the

conclusions that can be made based on

studies in a single city, the Oversight

Committee endorses the approach taken

by EPA in evaluating a broader set of

epidemiological studies:

Consistent and repeated observations in

locales with different air pollution profiles

can provide the most convincing

epidemiological evidence to support
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38661

13 Their March 20, 1996 letter to the

Administrator concludes that the HEI analysis of

Philadelphia supersedes earlier analyses,

specifically Moolgavkar et al. (1995a), Lipfert and

Wyzga (1995), and Li and Roth (1995), and points

out the limitations of Styer et al. (1995).

14 In response to comments on this rulemaking,

some papers submitted by industry commenters

Continued

generalizing the findings from these models.

This has been the approach reported by the

EPA in its recent Criteria Document and Staff

Paper. [HEI, 1997; p. 38.]

As noted in the proposal, based on

this approach, EPA’s assessment of

numerous mortality studies concludes

that when studies are evaluated on an

individual basis, the PM-effects

associations are valid and, in a number

of studies, not seriously confounded by

co-pollutants (U.S. EPA, 1996a; p. 13-

57); and when a collection of studies

from multiple areas with differing

concentrations of PM and co-pollutants

are examined together, the association

with PM10 remains reasonably

consistent across a wide range of

concentrations of these potentially

influential pollutants (U.S. EPA, 1996a;

p. 12-33; U.S. EPA, 1996b; p. V-55).

In addition to relying on the most

comprehensive and best analyses in

evaluating the reanalysis in

Philadelphia and other areas, the

Criteria Document gave less weight to

both so-called ‘‘negative’’ and

‘‘positive’’ studies with methodogical

limitations. In particular, EPA agreed

with the epidemiological experts on

CASAC (Lippmann et al., 1996; Samet,

1995) that the Li and Roth (1995) study

approach of using a ‘‘panoply’’ of

different modeling strategies to produce

seemingly conflicting findings provides

little useful insight and is superseded by

the HEI report. The attempt by Lipfert

and Wyzga (1995) to address relative

effects of different pollutants was

considered inconclusive (Lippmann et

al., 1996) and flawed by the use of a

metric (elasticity) that ignores the

absolute concentrations of the

pollutants being compared (see

Response to Comments).

Further, the Steubenville studies and

reanalyses (Schwartz and Dockery,

1992b; Moolgavkar, 1995b) were

discussed in detail to examine

methodologies, and the differences in

relative risks between the two were

regarded as small (U.S. EPA, 1996a, p.

12-280 to 283). Both studies used TSP

as the PM indicator variable, and they

are augmented by the more recent

findings of Schwartz et al. (1996) that

examine PM10 and its components. The

mixed results by Lyon et al. (1995) in

Utah Valley are compromised by loss of

information related to the methodology

(U.S. EPA, 1996a, p. 12-58). As noted

above, subsequent reanalyses of the

Utah Valley study by HEI (Samet et al.,

1995) as well as by Pope and Kalkstein

(1996) confirmed the original findings of

Pope et al. (1992) using different model

specifications. The Salt Lake City study

by Styer et al. (1995) was mentioned in

the PM Criteria Document, but received

little discussion because aspects of the

methodological approach limited its

statistical power to detect effects. The

analysis of Chicago mortality data in the

same paper shared these problems,

particularly for seasonal analyses; in

this larger city, they nonetheless found

significant associations on an annual

basis between PM10 and mortality that

are consistent with other studies. In

short, the record shows that EPA did not

ignore these short-term exposure studies

cited by commenters; moreover, EPA’s

assessment of these studies is consistent

with the views of four researchers on

the CASAC panel who have extensive

involvement in conducting population

studies of air pollution (Lippmann et al.,

1996).13

Similarly, EPA believes that

appropriate treatment and weight were

given to studies of long-term exposure

and mortality. EPA concluded that the

lack of associations in the Abbey et al.

(1991) prospective cohort study were

not inconsistent with two other such

studies because the use of days of peak

TSP levels as the PM indicator (instead

of PM10 or PM2.5) is inappropriate for

California cohorts exposed to both

urban smog and fugitive dust episodes,

and the overall sample size may have

been too small to detect significant

effects (U.S. EPA, 1996b; pp. V-17 to

-18). The inadequacy of Lipfert’s (1995)

application of state-wide average

sedentary lifestyle data to adjust

mortality for the six cities studied by

Dockery et al. (1993), in which superior

subject-specific body mass index data

had already been considered, was also

noted and addressed in the Staff Paper

(U.S. EPA, 1996b; p. V-16). Again, EPA

did not ignore these studies; the

rationale for giving them less weight

was clearly articulated in the documents

reviewed by CASAC and judged

appropriate for use in standard setting.

While the proposal presents only a

summary discussion of key Criteria

Document and Staff Paper findings, EPA

believes that discussion is fully

consistent with the state of the science.

Furthermore, the proposal highlights the

nature of alternative viewpoints on the

epidemiology in a quotation from the

Criteria Document (61 FR 65644,

December 13, 1996) and cites explicitly

the views of most of the authors noted

above in this unit (Moolgavkar et al.,

1995b; Moolgavkar and Luebeck, 1996;

Li and Roth, 1995; Samet et al., 1996;

Wyzga and Lipfert, 1995). The proposal

also summarizes EPA conclusions based

on all of the literature as assessed in the

Criteria Document and Staff Paper with

respect to issues raised in these and

other studies, including potential

confounding by independent risk factors

such as weather and other pollutants,

choice of statistical models, use of

outdoor monitors, and exposure

misclassification.

More specifically, in the proposal

EPA has not ignored the view advanced

by some that the results of individual

studies of multiple pollutants, such as

the HEI Philadelphia studies, are more

suggestive of an ‘‘air pollution’’ effect

than an effect of PM alone. Indeed, the

proposal notes that it is reasonable to

expect that other pollutants may play a

role in modifying the magnitude of the

estimated effects of PM on mortality,

either through pollutant interactions or

independent effects (61 FR 65645,

December 13, 1996). Based on the large

body of evidence at hand, however, EPA

cannot accept the suggestion that such

multi-pollutant studies are in any way

‘‘negative’’ with respect to EPA’s

conclusions that PM, alone or in

combination with other pollutants, is

associated with adverse effects at levels

below those allowed by the current

standards. This conclusion is based not

only on the consistency of PM effects

across areas with widely varying

concentrations of potentially

confounding copollutants, but also on

the extended analyses of the

Philadelphia studies in the Criteria

Document and Staff Paper.

Because commenters have tended to

ignore the latter analyses, it is

appropriate to summarize them here

briefly. As noted above in this unit, the

Criteria Document assessment of the

Philadelphia studies finds that PM can

reasonably be distinguished from

potential effects of all pollutants except

SO2. The Staff Paper builds on this

analysis through an integrated

assessment that draws on information

from atmospheric chemistry, human

exposure studies, and respiratory tract

penetration results to provide insight as

to which of these two pollutants is more

likely to be responsible for mortality in

the elderly and individuals with

cardiopulmonary disease (U.S. EPA

1996b; pp. V-46 to -50). That assessment

notes that the inhalable (PM10),

including the fine (PM2.5), components

of TSP are more likely than SO2 to

penetrate and remain indoors where the

sensitive population resides most of the

time.14 In addition, these PM
38662 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

make statements that are in substantial agreement

with these staff conclusions with respect to the

likelihood of SO2 penetrating to indoor

environments and the lesser likelihood of affecting

sensitive populations indoors (Lipfert and Wyzga,

1997; Lipfert and Urch, 1997).

15 Since the 1970 amendments, the EPA has taken

the view that NAAQS decisions are to be based on

scientific studies that have been assessed in air

quality criteria [see e.g., 36 FR 8186 (April 30, 1971)

(EPA based original NAAQS for six pollutants on

scientific studies discussed in the air quality

criteria and limited consideration of comments to

those concerning validity of scientific basis); 38 FR

25678, 25679-25680 (September 14, 1973) (EPA

revised air quality criteria for sulfur oxides to

provide basis for reevaluation of secondary

NAAQS)]. This longstanding interpretation was

strengthened by new legislative requirements

enacted in 1977 (section 109(d)(2) of the Act;

section 8(c) of the Environmental Research,

Development, and Demonstration Authorization

Act of 1978) for CASAC review of air quality

criteria and reaffirmed in EPA’s decision not to

revise the ozone standards in 1993. 58 FR 13008,

13013-13014 (March 9, 1993). Some of the

commenters now criticizing EPA for not

considering the most recent PM studies strongly

supported the Agency’s interpretation in the 1993

decision (UARG, 1992).

16 As discussed in EPA’s 1993 decision not to

revise the NAAQS for ozone, new studies may

sometimes be of such significance that it is

appropriate to delay a decision on revision of

NAAQS and to supplement the pertinent air quality

criteria so the new studies can be taken into

account. 58 FR at 13014, March 9, 1993. In the

present case, EPA’s provisional examination of

recent studies suggests that reopening the air

quality criteria review would not be warranted even

if there were time to do so under the court order

governing the schedule for this rulemaking.

Accordingly, EPA believes that the appropriate

course of action is to consider the newly published

studies during the next periodic review cycle.

17 For example, commenting on the Roth

examination of alternative model specifications, Dr.

Stolwijk noted ‘‘If you select out of his [Roth’s]

matrix the things that other people have done, he

comes to a different conclusion than when he takes

his whole matrix * * *. [Y]ou are going to get a

random effect that shows that there is no effect. He

[Roth] did this, I think, on purpose in this case.

Most epidemiologists, I think, have been trained to

limit their observations to something that they can

state or would have stated before they started and

observe that and base their conclusions on it’’ [U.S.

EPA 1996(c); May 17, 1996 Transcript, pages 45-46].

components, especially PM2.5, penetrate

far more effectively to the airways and

gas exchange regions of the lung than

does SO2. Furthermore, in Philadelphia,

it is possible that SO2 is a surrogate for

fine particulate acid sulfates. For these

reasons, even though statistical analyses

of the Philadelphia data set cannot fully

distinguish between these two highly

correlated pollutants, EPA believes that

the weight of the available evidence

from an integrated assessment more

strongly supports the notion that PM is

playing an important direct role in the

observed mortality effects associations

in Philadelphia. Moreover, as noted

above in this unit, in some other

locations with significant PM-mortality

associations, ambient SO2 levels are too

low to confound PM.

(ii) Recent studies available after

completion of criteria review. As noted

above in this unit, other studies cited by

some commenters as so-called

‘‘negative’’ evidence ignored by EPA

were published or otherwise made

available only after completion of the

PM Criteria Document. EPA agrees that

it did not rely on these studies, based on

its long-standing practice of basing

NAAQS decisions on studies and

related information included in the

pertinent air quality criteria and

available for CASAC review.15 Although

EPA has not relied on such studies in

this review and decision process, the

Agency nevertheless has conducted a

provisional examination of these and

other recent studies to assess their

general consistency with the much

larger body of literature evaluated in the

Criteria Document.16 EPA has placed its

examination of recent studies in the

rulemaking docket.

Among the most frequently cited new

studies relied on by commenters were

Davis et al. (1996), Moolgavkar et al.

(1997), and Roth and Li (1997). Davis et

al. (1996) conducted a reanalysis of the

Birmingham mortality data set

originally investigated in Schwartz

(1993). At the time of the close of the

public comment period, the paper based

on this manuscript had not been

accepted for publication in a peer

reviewed journal (Sacks, 1997).

Commenters nevertheless highlight the

authors’ claim that ‘‘when humidity is

included among the meteorological

variables (it is excluded in the analysis

by Schwartz [1993]), we find that the

PM10 effect is not statistically

significant.’’ EPA’s review found

important factual errors in this study.

Contrary to Davis et al., Schwartz did

include humidity in his 1993 study, and

his finding of a hot-and-humid-day

effect was reported there. In addition,

the PM-related variables used by Davis

et al. in their manuscript were not, as

the authors claimed, the same as those

in Schwartz (1993). Davis et al. also

used a different humidity indicator,

specific humidity. Reanalysis by one of

the co-authors (R. Smith, personal

communication, February 8, 1997)

showed that when Schwartz’s PM

metric was used, the estimated PM10

effect was of about the same magnitude,

and statistically significant at the 0.05

level, even using the characterization of

humidity effect proposed by Davis et al.

It therefore appears that the Davis et al.

PM10 result was, in fact, consistent with

that of Schwartz, and robust against a

very different weather model

specification.

Based on its examination of both the

content and the publication status of

this study, EPA believes the heavy

reliance and attention given to it are

misguided. In contrast to commenters’

assertions, this study does not

contradict EPA’s conclusions with

respect to consistency of the

epidemiological evidence and

confounding by weather variables;

indeed, the consideration of the

corrected results would actually support

EPA’s conclusions. EPA believes this

example reinforces the importance of

relying on peer reviewed studies and

also conducting the kind of critical

examination of such studies that takes

place in the criteria and standards

review process.

Several commenters note that Roth

and Li (1997) also reexamined the

Birmingham mortality data, as well as

hospital admissions data from Schwartz

(1994), and produced a number of

negative and inconsistent results that

depend on temperature effects and

choice of statistical model. Preliminary

findings from this study were presented

by Roth at the May 1996 CASAC

meeting. CASAC epidemiologists and

statisticians at the meeting pointed out

a number of shortcomings, both in the

analytical strategy and in details of the

models being evaluated.17 As discussed

in more detail in the Response to

Comments, the materials from Roth and

Li (1997) recently provided to EPA as

attachments to public comments show

that the deficiencies pointed out at the

May 1996 CASAC meeting have not

been adequately addressed. EPA

concludes that this study does not

support commenters’ claims.

The paper recently accepted for

publication by Moolgavkar et al. (1997)

examines hospital admissions and air

pollution in Minneapolis and

Birmingham and comes to different

conclusions than earlier investigators

with respect to the role of PM10. While

the paper is a useful addition to the

literature, the authors clearly do not

attempt to replicate the original studies,

making the kind of direct comparisons

suggested by commenters difficult. The

paper finds an air pollution effect in one

city that implicates ozone but is unable

to separate effects of PM from a group

of other pollutants. EPA’s provisional

examination of this study raises some

questions about the methodology, which

might usefully be supplemented to

further separate pollutants as was done

by Samet et al. (1996a,b) in

Philadelphia, and about the authors’

interpretation of the results in both

cities. In any event, EPA does not

believe this study negates the PM

associations with hospital admissions
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38663

18 CASAC panelists recommended a discussion of

this issue in the Staff Paper. The Staff Paper notes:

‘‘While greater measurement error for the coarse

fraction could depress a potential coarse particle

effect, this would not explain the results in Topeka

relative to other cities. Even considering relative

measurement error, these results provide no clear

evidence implicating coarse particles in the

reported effects.’’ (U.S. EPA, 1996b p. V-64). EPA’s

provisional examination of the Lipfert and Wyzga

(1997) paper in the Response to Comments, finds

that it is implausible that most of the effect

attributed to PM2.5 could in fact be due to PM10-2.5,

since differential measurement error cannot make a

weaker effect appear stronger than a stronger one,

except under extremely unusual circumstances.

19 The APHEA (Air Pollution and Health: a

European Approach) project was supported by the

European Union Environment 1991-1994

Programme to investigate the possible short-term

health effects of exposure to low or moderate levels

of ambient air pollutants. Eleven European research

groups carried out studies in 15 cities (Amsterdam,

Athens, Barcelona, Bratislava, Cracow, Helsinki,

Koln, Lodz, London, Lyon, Milan, Paris, Poznan,

Rotterdam and Wroclaw) in which air pollutant

concentration data had been collected for at least

5 years. Initial findings of studies on mortality and

hospital admissions were published in a series of

papers in Supplement 1 to the Journal of

Epidemiology and Community Health in 1996 and

a meta-analysis of the mortality data from 12 cities

is currently in press (Katsouyanni et al., 1997).

20 The Roth et al. (1997) study in Prague used a

measurement termed ‘‘suspended particles’’ that

appears to be close to TSP. The relation of this

indicator to PM10 or PM2.5 in this city is not

reported. Moreover, this study uses a variant of the

problematic methodology in the Roth analyses cited

above.

21 These concerns are consistent with EPA’s

treatment of a number of European and South

American studies that are included in the Criteria

Document and contributed to the evaluation of the

epidemiology in Chapter 12. Because of differences

in aerometry methods and characteristic source

classes between North America and other regions of

the world, however, the integrative assessment

chapter reported results only from studies

conducted in the U.S. and Canada (cf. Tables 13-

3 to 13-5) in reaching quantitative conclusions for

effects estimates.

22 See, for example, the United Kingdom Air

Quality Strategy, 1997; Swiss Federal Commission

of Air Hygiene, 1996; World Health Organization

Revised Air Quality Guidelines for Europe, In

Press).

reported in a number of other studies

cited in the Criteria Document.

Another recent paper by Lipfert and

Wyzga (1997) provides analyses

suggesting that differential measurement

error might account for some or all of

the observation by Schwartz et al. (1996)

that daily mortality is more strongly

associated with fine (PM2.5) than with

coarse (PM10-2.5) PM. EPA staff and

CASAC accounted for this possibility,

however, and it was factored into both

the Staff Paper and CASAC

recommendations.18

Some commenters have highlighted

selected individual papers or summaries

from the APHEA19 project conducted in

Europe, and from Roth (1996), calling

attention particularly to negative results

found in heavily polluted regions of

Eastern Europe. EPA notes that a

number of the recent APHEA and other

studies in Western Europe have shown

significant associations between

mortality and air pollution including

PM, and that a meta-analysis of 12

Western and Central-eastern European

studies ‘‘is supportive of a causal

association between PM and SO2

exposure and all-cause mortality’’

(Katsouyanni et al., 1997). The Eastern

and Western European studies used

differing measurement methods for PM,

including PM10, gravimetric ‘‘suspended

particles,’’ and the British Smoke

method.20 The differences in aerometry

and the substantial differences in

location and strength of primary PM

emissions sources in central and eastern

Europe as compared to western Europe

or the U.S. might well explain the

different results in these unique areas.

Consequently, integration of these

results would involve comprehensive

examination of the various PM

instruments used, monitor siting in

relation to sources, mass calibration

procedures and other aspects of these

studies.21 EPA notes that a number of

European authorities, who are familiar

with this recent literature, have

proceeded with recommendations to

strengthen their health guidelines, risk

assessments, or regulations for PM.22

Aside from the recent literature cited

by these commenters, there are a

number of other recent epidemiological

studies that, if considered in today’s

decision, would tend to support EPA’s

conclusions about the effects of PM at

lower concentrations, assuming their

results were accepted following a full

review in the criteria and CASAC

process. For example, in addition to the

APHEA studies, several other recent

epidemiologic studies have reported

significant positive associations

between PM and health effects (Lipsett

et al., 1997; Peters et al., 1997; BorjaAburto et al., 1997; Delfino et al., 1997;

Scarlett et al., 1996; Woodruff et al.,

1997; Wordley et al., 1977). In addition,

a number of recent toxicologic papers

have been accepted or appear in

proceedings (Costa and Dreher, 1997;

Killingsworth et al., 1997; Godleski et

al., 1997) that involve exposure to

concentrated ambient fine particles or

PM constituents and appear to provide

supportive evidence as to the

plausibility of the effects that have been

reported epidemiologically. If

considered in this decision, these

studies would also provide biological

support for the epidemiological

observation that certain susceptible

groups (notably those with

cardiopulmonary disease) are most

likely to be affected by PM, again

assuming the results were sustained in

the full criteria and CASAC review

process.

In summary, EPA has conducted a

provisional assessment of the more

recent scientific literature. Based on this

provisional assessment, EPA disagrees

with commenters’ assertion that full

consideration of selected new studies in

this decision would materially change

the Criteria Document and Staff Paper

conclusions on the consistency and

coherence of the PM data, or on the

need to revise the current standards.

(iii) Other specific comments on the

epidemiological studies. Aside from

their assertion that EPA ignored or

downplayed particular studies, this

second group of commenters raise

additional objections, based on the

statistical modeling strategies used and

the potential importance of personal

exposure misclassification, to EPA’s

conclusions regarding the consistency of

the epidemiological evidence. EPA

conclusions on these topics were

summarized in the proposal and

supported by extensive treatments in

the Criteria Document and Staff Paper.

With respect to the first issue,

commenters argued that sufficient

flexibility exists in the analyses of large

data sets that it may be possible to

obtain almost any result desired through

choice of statistical method. Analytical

choices include the specific statistical

model; methods used to adjust for

seasonal variation and the trends in the

data; treatment of other variables (e.g.,

other pollutants, weather, and day of

week); ‘‘lag’’ structure; and study

population.

A more detailed discussion of this

issue, which expands on the assessment

summarized in the Criteria Document, is

included in the Response to Comments.

In summary, EPA must reject

commenters’ contention that legitimate

alternative analyses can obtain ‘‘almost

any result.’’ As outlined above in this

unit, EPA’s detailed reviews of

individual studies have shown that not

all methods are equally valid or

legitimate. Moreover, strong arguments

can be made that the methods and

analytical strategies in the studies EPA

relied upon are more appropriate

approaches than those cited by

commenters (e.g., Li and Roth, 1995;

Lipfert and Wyzga, 1995; Davis et al.,

1996; Roth and Li, 1997). While not all

studies have addressed each of the

above issues in this unit equally well,

the most comprehensive analyses of

these issues (e.g., Samet et al., 1995,

1996a,b; Pope and Kalkstein, 1996), as

well as the EPA analyses comparing

study results for each issue (U.S. EPA,

1996a, pp. 12-261 to 12-305) found that

the authors of studies on which EPA
38664 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

23 Paradoxically, some commenters have argued

(e.g., Valdberg, 1997) that the PM results are

confounded because the weather and other factors

that cause daily variations in outdoor pollution will

cause similar daily variations in indoor generated

air pollution. For this to be true, outdoor ambient

pollution concentrations would have to be

correlated with personal exposure to indoor

generated air pollution such as that from smoking,

cleaning, and cooking. This argument is logically

inconsistent with the other comments on the lack

of any such correlation with personal exposure, and

these commenters have offered no scientific

evidence to support their claim. In response, EPA

has performed and included in the Response to

Comments a numerical analysis of the relevant

information from the PTEAM exposure study that

finds no evidence for such a correspondence in the

actual data.

24 As documented in Chapter 7 of the Criteria

Document, time-series community studies observe

the effects of varying levels of ambient air pollution;

therefore the effects of indoor-generated air

pollution would be independent of and in addition

to the effects found in these epidemiological

studies. Commenters apparently believe EPA is

claiming such studies are detecting the effects of

daily variations in total PM personal exposure from

indoor and outdoor sources. This misunderstanding

is evidenced, for example, by Wyzga and Lipfert’s

(1995) treatment of the difference between ambient

monitors and actual personal exposures as

‘‘exposure errors’’ and Brown’s comment for API

that ‘‘if (ambient) PM is causally related to

mortality/morbidity, then it is personal PM

exposure that must be reduced to have an effect.’’

On the contrary, it is personal exposure to ambient

PM that must be reduced to address the risk

identified in community air pollution studies. Any

lack of significant correlation between outdoor PM

concentrations and personal exposure to total PM

from all sources is irrelevant, except to the extent

it may decrease the power of time-series studies to

detect the effects of ambient pollution.

25 The EPA analysis finds that in order for

measurement errors in one pollutant variable to

significantly bias the estimated effect of another

pollutant, three conditions are necessary: (1) The

measurement error in the poorly measured

pollutant must be very large, roughly at least the

same size as the population variability in that

pollutant; (2) the poorly measured pollutant must

be highly correlated with the other pollutant, either

positively or negatively; and (3) the measurement

errors for the two pollutants must be highly

negatively correlated (Response to Comments,

Appendix D). This important factor was not

considered in Lipfert and Wyzga (1995) or by

commenters.

chiefly relied made appropriate

modeling choices. The Criteria

Document concludes that: ‘‘[T]he largely

consistent specific results, indicative of

significant positive associations of

ambient PM exposures and human

mortality/morbidity effects, are not

model specific, nor are they artifactualy

derived due to misspecification of any

specific model. The robustness of the

results of different modeling strategies

and approaches increases our

confidence in their validity [U.S. EPA,

1996a, p. 13-54].’’ While it is true, as

evidenced in Li and Roth (1995), that

PM-effects data can be randomly

manipulated to produce apparently

conflicting results, commenters have

provided no evidence that different

plausible model specifications could

lead to markedly different conclusions.

Some commenters have expressed

concerns about the reliability of the

epidemiological results because some

studies showed a lack of correlation in

cross-sectional comparisons between

outdoor PM measured at central

locations and indoor or personal

exposures to PM (which includes PM

from the outdoor, indoor and personal

environments).23 EPA acknowledged

and responded to this issue in chapter

7 of the Criteria Document and the

proposal (61 FR 65645, December 13,

1996). The major premise underlying

commenters’ arguments on this issue is

incorrect.24 The question is not whether

central monitoring site measurements

contain a signal reflecting actual

exposures to total PM from both outdoor

and indoor sources at the individual

level; the relevant question is whether

central monitoring site measurements

contain a signal reflecting actual

exposures to ambient PM for the subject

population, including both ambient PM,

while individuals are outdoors, and

ambient PM that has infiltrated indoors,

while individuals are indoors. The PM

standards are intended to protect the

public from exposure to ambient PM,

not PM generated by indoor or personal

sources. There is ample evidence, as

discussed in chapter 7 of the Criteria

Document, that personal exposure to

ambient PM, while outdoors and while

in indoor micro-environments, does

correlate on a day-to-day basis with

concentrations measured at properly

sited central monitors (U.S. EPA, 1996a,

p. 1-10). EPA has, therefore, concluded

that it is reasonable to presume that a

reduction in ambient PM concentrations

will reduce personal exposure to

ambient PM, and that this will protect

the public from adverse health

outcomes associated with personal

exposure to ambient PM.

Commenters have also restated

theoretically based concerns on a

related issue, namely errors in the

measurement of the concentrations of

air pollutants, that was summarized in

the proposal. In multiple pollutant

analyses, measurement error or, more

generally, exposure misclassification,

could theoretically bias effects estimates

of PM or co-pollutants in either

direction, introducing further

uncertainties in the estimated

concentration-response relationships for

all pollutants (U.S. EPA, 1996b, pp. V39 to V-43). Relevant insights on this

issue in material appended to public

comments (Ozkaynak and Spengler,

1996) have prompted an expanded

statistical analysis of the conditions

under which such errors could inflate

the magnitude of the effects estimates or

the significance of PM relative to

gaseous pollutants, as has been

suggested by Lipfert and Wyzga (1995).

This analysis, which is summarized in

the Response to Comments, finds that

the conditions under which

measurement error could inflate the

effects estimates or significance of PM

relative to other pollutants are restricted

to a limited set of statistical

relationships. Commenters have not

provided evidence that suggest such

conditions are likely to occur with

respect to the measurement of ambient

PM in relation to those for gaseous copollutants commonly used in

epidemiological studies.25 Therefore, it

appears unlikely that measurement and

exposure errors for PM and other

pollutants have inflated the estimated

effects of PM, even in multivariate

analyses. More importantly, the

available evidence on the consistency of

the PM-effects relationships in multiple

urban locations, with widely varying

indoor/outdoor conditions and a variety

of monitoring approaches, makes it less

likely that the observed associations of

PM with serious health effects at levels

allowed under the current NAAQS are

an artifact of errors in measurement of

pollution or of exposure (U.S. EPA

1996b, pp. V-39 to V-43).

(iv) Comments on the PM risk

assessment. As noted in the proposal,

uncertainties about measurement errors,

exposure misclassification, and the

relative effects of copollutants are more

important to the quantitative estimates

of risk associated with PM than to the

existence of valid PM-effects

associations at levels found in recent

studies. A number of commenters

argued that EPA’s risk assessment is

flawed and incomplete. Chief among the

reasons they advanced is that the

assessment is based on the same

epidemiological studies these

commenters argued are inadequate for

the reasons summarized and responded

to above. Specific comments also

addressed the extent to which the risk

assessment might overstate risk

estimates because it assumes a linear

no-threshold relationship and the use of

studies that might inflate PM risk due to

inadequate consideration of copollutants and other potential

confounders. The full risk assessment

acknowledges these issues and

uncertainties, however, and it illustrates

the potential influence of such

uncertainties in sensitivity analyses

(U.S. EPA 1996b; chapter 6, appendix F;

Abt Associates, 1996a,b; 1997a,b). For

example, Figure 2c in the proposal (61

FR 65653, December 13, 1996)
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38665

illustrates the potential influence of

what appears to be the most significant

uncertainty in current information,

whether a population threshold exists

below which the effects of PM no longer

occur (61 FR 65653, December 13,

1996). EPA notes that a full

consideration of the uncertainties,

including the analysis summarized

above on measurement error, suggests

that the epidemiological studies might

well have understated the total effects of

air pollution; thus, both the direction

and the extent of any bias in the risk

estimates are less clear than commenters

suggest.

EPA believes that, even recognizing

the large uncertainties, the key

qualitative insights derived from the

risk assessment and summarized in Unit

II.A.3. of this preamble remain

appropriate. While not placing great

weight on the specific numerical

estimates, EPA believes that the risk

analysis confirms the general

conclusions drawn primarily from the

epidemiological results themselves, that

there is ample reason to be concerned

that exposure to ambient PM at levels

allowed under the current air quality

standards presents a serious public

health problem.

3. Key considerations informing the

decision. Having carefully considered

the public comments on the above

matters, EPA believes the fundamental

scientific conclusions on the effects of

PM reached in the Criteria Document

and Staff Paper, and restated in the

introduction to this unit, remain valid.

That is, the epidemiological evidence

for ambient PM, alone or in combination

with other pollutants, shows

associations with premature mortality,

hospital admissions, respiratory

symptoms, and lung function

decrements. Despite extensive critical

examination in the criteria and

standards review, these findings cannot

be otherwise explained by analytical,

data, or other problems inherent in the

conduct of such studies. Although the

evidence from toxicological studies

available during the criteria review has

not revealed demonstrated mechanisms

that explain the range of effects reported

in epidemiological studies, it does not

and cannot refute the observation of

such effects in exposed populations.

Moreover, the effects observed in the

recent epidemiological studies at lower

PM concentrations are both coherent

with each other and plausible based on

the categories of effects observed at

much higher concentrations in historic

air pollution episodes, laboratory

studies of PM effects at high doses, and

particle dosimetry studies. The

consistency of the results from a large

number of locations and the coherent

nature of the observed results suggest a

likely causal role of ambient PM in

contributing to the reported effects (U.S.

EPA, 1996a; p. 13-1). Many of the

studies showing PM effects were

conducted in areas where the current

PM10 standards are largely met, and

both the studies and EPA’s risk

assessment suggest that the collective

magnitude of the effects reflects a

significant public health problem.

For these reasons, and having

considered public comments on this

issue, the Administrator concludes that

the review of the criteria and standards

provides strong evidence that the

current PM10 standards do not

adequately protect public health, and

that revision of the standards is not only

appropriate, but necessary.

Aside from that conclusion, the

appropriateness of continuing to rely on

the use of PM10 as the sole indicator for

revised PM standards is also relevant

here. While the basis for decisions on

specific indicators is discussed more

fully in Unit II.C. of this preamble, this

issue is related to the Administrator’s

decision on the need to revise the

standards. Based on both the staff

review (U.S. EPA, 1996b, p. VII-3) and

the recommendations of some

commenters (e.g., California EPA), there

are two alternative approaches for

providing additional health protection

in revising the standards: Adopt tighter

PM10 standards and/or recognize the

fundamental differences between fine

and coarse particles and develop

separate standards for the major

components of PM10, including fine

particles. Conceptually, the first

approach would give weight to

comments that standards should be

based on pollutant indicators for which

the most data have been collected, with

less consideration of the evidence that

suggests that the current standards

provide adequate protection against the

effects of coarse particles, and that

tightening the current PM10 standards in

an attempt to control fine particles

would place unnecessary requirements

on coarse particles. Because the PM10

network is in place, a more stringent

PM10 standard would also respond to

commenters who have expressed a

desire for more immediate

implementation of revised standards.

The second approach is based on the

view that, in the long run, more

effective and efficient protection can be

provided by separately targeting

appropriate levels of controls to fine and

coarse PM.

The Staff Paper examined this issue in

detail (U.S. EPA 1996b, pp. VII-3 to VII11), and concluded that the available

information was sufficient to develop

separate indicators for fine and coarse

fractions of PM10, based on the recent

health evidence, the fundamental

differences between fine- and coarsefraction particles, and implementation

experience with PM10. Further, the staff

concluded that:

[C]onsideration of comparisons between

fine and coarse fractions suggests that fine

fraction particles are a better surrogate for

those particle components linked to mortality

and morbidity effects at levels below the

current standards. In contrast, coarse fraction

particles are more likely linked with certain

effects at levels above those allowed by the

current PM10 standards. In examining

alternative approaches to increasing the

protection afforded by PM10 standards, the

staff concludes that reducing the levels of the

current PM10 standards would not provide

the most effective and efficient protection

from these health effects. [U.S. EPA 1996b; p.

7-45]

As discussed in Unit II.C. of this

preamble, the Administrator believes

that it is more appropriate to provide

additional protection against the risk

posed by PM by adding new standards

for the fine fraction of PM10, as opposed

to tightening the current PM10

standards. Although fewer

epidemiological studies have used PM2.5

and other fine particle indicators (e.g.,

sulfates, acids), there are nonetheless

significant indications from the

scientific evidence - drawn from the

physicochemical studies of PM, air

quality and exposure information,

toxicological studies, and respiratory

tract deposition data - that this approach

will provide the most effective and

efficient protection of public health.

Several commenters have argued that

the decision on whether to revise the

PM standards should be deferred,

particularly with regard to fine particle

standards, pending establishment and

operation of a national monitoring

network to characterize fine PM and a

research program to reduce

uncertainties in the effects information.

These commenters expressed concerns

that establishing fine PM standards now

might result in needless regulation of

PM components that may be unrelated

to observed health effects. As discussed

more fully in Unit II.F. of this preamble,

such commenters recommended, at

most, that if fine PM standards were

established, they should be set at a level

‘‘equivalent’’ to the current PM

standards.

EPA strongly disagrees that the

decision on revising the standards

should be delayed to await the results

of new PM monitoring and research

programs. Under section 109(d) of the

Act, EPA’s obligation after reviewing the
38666 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

existing criteria and standards for PM is

to make such revisions in the standards

and to promulgate such new standards

as are appropriate under section 109(b)

of the Act. Based on her review of the

criteria and standards for PM, the

Administrator has concluded that the

current standards are not adequate to

protect public health and that revisions

are appropriate. In the face of the

available evidence, a delay in revising

the standards would not only be

inconsistent with the statute but -- even

under the optimistic assumption that

the same extensive monitoring and

strategy assessment as now

contemplated would occur in the

absence of a revised standard -- would

add approximately 2 years to the time

when significant health benefits can be

realized, resulting in potentially

significant numbers of additional

premature deaths and even larger

numbers of children and individuals

with air pollution-related illness and

symptoms. On the other hand,

establishing standards now will set into

motion the development of

implementation programs and

monitoring that can be conducted in

parallel with additional scientific

research, without undue delays inherent

in waiting for the research.

The question of which pollutant

components to regulate has been an

issue since the inception of the first PM

standards. Other ambient pollutants

(e.g., NO2 or CO) are uniquely defined

as individual chemicals, whether or not

they serve as proxies for a larger class

of substances (e.g., ozone as an index of

photochemical oxidants). Regulating

general PM, as opposed to multiple

chemical components of PM, raises the

spectre of a host of particulate materials

of varying composition, size, and other

physicochemical properties, not all of

which are likely to produce identical

effects.

Both EPA’s past and present

regulatory experience with PM control

programs and its successive reviews of

the standards have reaffirmed the

wisdom of retaining standards that

control particles as a group, rather than

eliminating such standards and waiting

for scientific research to develop

information needed to identify more

precise limits for the literally thousands

of particle components. Each such

decision recognized the possibility that

potentially less harmful particles might

be included in the mix that was

regulated, but concluded that the need

to provide protection against serious

health effects nonetheless required

action under section 109 of the Act. The

success of this approach is evident in

early U.S. control programs that

dramatically reduced ‘‘smoke’’ and

‘‘TSP’’ in major cities in the 1960’s and

1970’s and in the continued

improvement in air quality through the

current PM standards. The major

refinements that have been

recommended through the course of

reviews of PM standards have been to

improve the focus of control efforts by

defining scientifically based size classes

(i.e., moving from TSP to PM10 and now,

PM2.5) that will permit more effective

and efficient regulation of those

fractions most likely to present

significant risks to health and the

environment.

As discussed in Unit II.C. of this

preamble, the current review has

examined the available evidence to

determine whether it would tend to

support inclusion or exclusion of any

physical or chemical classes of PM, for

example sulfates, nitrates, or ultra-fine

particles. That examination concludes

that, while both fine and coarse

particles can produce health effects, the

fine fraction appears to contain more of

the reactive substances potentially

linked to the kinds of effects observed

in the recent epidemiological studies

(U.S. EPA 1996b, section V.F.).

However, the available scientific

information does not rule out any one

of these components as contributing to

fine particle effects. Indeed, it is

reasonable to anticipate that no single

component will prove to be responsible

for all of the effects of PM.

EPA recognizes that whether the

standards are set for PM10 only or also

for fine particles, there are uncertainties

with respect to the relative risk

presented by various components of

PM. In this regard, the Administrator

places greater weight on the concern

that by failing to act now, the PM

NAAQS would not control adequately

those components of air pollution that

are most responsible for serious effects,

than on the possibility they might also

control some component that is not.

EPA believes that moving

simultaneously to establish standards

based on the best available scientific

evidence and to conduct an aggressive

monitoring and scientific research

program designed to help resolve

current uncertainties is a prudent and

responsible approach for addressing

both the risks and the uncertainties

inherent in this important public health

issue.

In summary, given the evidence that

PM-related health effects appear likely

to occur at levels below the current

standards, the serious nature and

potential magnitude of the public health

risks involved, and the need to consider

the fine and coarse fractions as distinct

classes of particles, the Staff Paper and

the CASAC (Wolff, 1996b) concluded

that revision of the current standards is

clearly appropriate. Moreover, at their

May 1996 public meeting (U.S. EPA,

1996c), and in separate written

comments (including Lippmann et al.,

1996), a majority of CASAC panel

members recommended revisions that

would strengthen the health protection

provided by the current PM standards.

Based on the rationale and

recommendations contained in the Staff

Paper and the advice of CASAC, and

taking into account public comments,

the Administrator concludes that it is

appropriate at this time to revise the

current PM standards to increase the

public health protection provided

against the known and potential effects

of PM identified in the air quality

criteria.

C. Indicators of PM

In establishing adequately protective,

effective, and efficient PM standards, it

is necessary to specify the fraction of

particles found in the ambient air that

should be used as the indicator(s) for

the standards. In this regard, EPA

concludes that the most recent

assessment of scientific information in

the Criteria Document, summarized in

chapters IV and V of the Staff Paper,

continues to support past staff and

CASAC recommendations regarding the

selection of size-specific indicators for

PM standards. More specifically, EPA

continues to find that the following

conclusions reached in the Staff Paper

and in the 1987 review remain valid:

(1) Health risks posed by inhaled

particles are influenced both by the

penetration and deposition of particles

in the various regions of the respiratory

tract and by the biological responses to

these deposited materials.

(2) The risks of adverse health effects

associated with deposition of ambient

fine and coarse fraction particles in the

thoracic (tracheobronchial and alveolar)

regions of the respiratory tract are

markedly greater than for deposition in

the extrathoracic (head) region.

Maximum particle penetration to the

thoracic region occurs during oronasal

or mouth breathing.

(3) The risks of adverse health effects

from extrathoracic deposition of general

ambient PM are sufficiently low that

particles which deposit only in that

region can safely be excluded from the

standard indicator.

(4) The size-specific indicator(s)

should represent those particles capable

of penetrating to the thoracic region,

including both the tracheobronchial and

alveolar regions.
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38667

26 As discussed above, a number of commenters

expressed concerns that various portions of fine

particles might not be responsible for any observed

effects. One group (PG&E, 1997) recommended that

nitrates should be excluded from fine PM mass

collected on the basis of their assessment of

available effects literature on particulate and gas

phase inorganic nitrates. Based on an examination

of this information as well as the earlier staff

assessment, EPA maintains its conclusion that the

available evidence is not sufficient to exclude

nitrates or any other class of fine particles that are

collected by PM monitors comparable to those used

in the recent epidemiological studies.

These conclusions, together with

information on the dosimetry of

particles in humans, were the basis for

the promulgation in 1987 of a new sizespecific indicator for the PM NAAQS,

PM10, that includes particles with an

aerodynamic diameter smaller than or

equal to a nominal 10 μm. The recent

information on human particle

dosimetry contained in the Criteria

Document provides no basis for

changing 10 μm as the appropriate cut

point for particles capable of penetrating

to the thoracic regions.

As noted in Unit II.B. of this

preamble, however, the Staff Paper

concludes that continued use of PM10 as

the sole indicator for the PM standards

would not provide the most effective

and efficient protection from the health

effects of PM (U.S. EPA, 1996b, pp. VII4 to VII-11). Based on the recent health

effects evidence and the fundamental

physical and chemical differences

between fine and coarse fraction

particles, the Criteria Document and

Staff Paper conclude that fine and

coarse fractions of PM10 should be

considered separately (U.S. EPA, 1996a,

p. 13-93; 1996b, p. VII-18). Taking into

account such information, CASAC

found sufficient scientific and technical

bases to support establishment of

separate standards relating to these two

fractions of PM10. Specifically, CASAC

advised the Administrator that ‘‘there is

a consensus that retaining an annual

PM10 NAAQS * * * is reasonable at this

time’’ and that there is ‘‘also a

consensus that a new PM2.5 NAAQS be

established’’ (Wolff, 1996b).

Some commenters have noted that it

is often difficult to distinguish the

effects of either fine or coarse fraction

particles from those of PM10; this is to

be expected because both fractions are

themselves components of PM10, and

hence not fully independent. EPA

believes that it is more meaningful to

examine comparisons between the fine

and coarse fraction components. Such

comparisons presented in the Staff

Paper suggest that fine particles are a

better surrogate for those components of

PM that are linked to mortality and

morbidity effects at levels below the

current standards (U.S. EPA, 1996b, p.

VII-18). Moreover, a regulatory focus on

fine particles would likely also result in

controls on gaseous precursors of fine

particles (e.g., SOx, NOx, VOC), which

are all components of the complex

mixture of air pollution that has most

generally been associated with mortality

and morbidity effects. The Staff Paper

concludes that, in contrast to fine

particles, coarse fraction particles are

more clearly linked with certain

morbidity effects at levels above those

allowed by the current 24-hour

standard.

Public comments received on the

proposed indicators were

overwhelmingly in favor of EPA’s

proposal to maintain PM10 as an

indicator for PM, whether as an

indicator of coarse particles in

conjunction with a fine PM standard, or

as the sole PM indicator. This near

unanimity shows strong support for

retaining general PM standards. While a

substantial number of commenters

supported EPA’s proposal to add an

indicator for fine PM, a number of other

commenters objected to any standard

revisions, including addition of a fine

PM indicator. Beyond the general points

about the basis for any revisions

discussed in Unit II.B. of this preamble,

these commenters argued either that the

available epidemiological data did not

provide a basis for separating fine and

coarse fraction particles, or that there

were not enough fine particle studies to

support selecting standard levels. Most

of these commenters also expressed

concerns that there were insufficient

ambient fine particle data by which to

evaluate the relative protection afforded

by new standards.

EPA notes that issues relating to the

basis for separating PM10 fractions were

addressed in the Criteria Document and/

or Staff Paper assessments, and these

perspectives were also available for

CASAC consideration in developing its

recommendations. The proposal states

that the main basis for separating the

fine and coarse fractions of PM10 is that,

because they are fundamentally

different PM components with

significantly different physico-chemical

properties and origins (U.S. EPA 1996b,

section V.D), separate standards would

permit more effective and efficient

regulation of PM. While the difficulty in

separating these classes in the

epidemiological studies is noted above,

the preponderance of the available

evidence suggests that strategies to

control fine particles will more

effectively reduce population exposure

to substances associated with health

effects in the recent epidemiological

studies. Although the number of studies

using fine PM indicators is more limited

than for PM10, there are more than 20

community studies showing significant

associations for a consistent set of

mortality and morbidity effects. A

substantial subset of these studies

(Tables V-12 to V-13; U.S. EPA, 1996b)

provides a sufficient quantitative basis

for selecting standard levels, without

the need to rely on estimates based on

PM2.5/PM10 ratios.

Having considered the public

comments on this issue, the

Administrator concurs with staff and

CASAC recommendations to control

particles of health concern (i.e., PM10)

through separate standards for fine and

coarse fraction particles. The following

units outline the basis for the

Administrator’s decision on specific

indicators for fine and coarse fraction

particle standards.

1. Indicators for the fine fraction of

PM10. The Administrator continues to

conclude that it is appropriate to control

fine particles as a group, as opposed to

singling out particular components or

classes of fine particles. The more

qualitative scientific literature,

evaluated in Chapter 11 of the Criteria

Document and summarized in section

V.C of the Staff Paper, has reported

various health effects associated with

high concentrations of a number of fine

particle components (e.g., sulfates,

nitrates, organics, transition metals),

alone or in some cases in combination

with gases. Community epidemiolgical

studies have found significant

associations between fine particles or

PM10 and health effects in various areas

across the U.S. where such fine particle

components correlate significantly with

particle mass. As noted above in this

unit, it is not possible to rule out any

one of these components as contributing

to fine particle effects.26 Thus, the

Administrator finds that the present

data more readily support a standard

based on the total mass of fine particles.

EPA will conduct additional research,

in cooperation with other Federal

agencies and in partnership with State

and local agencies and the private

sector, to better identify which species

are of concern for human health, and

the sources and relative magnitude of

such species.

In specifying a precise size range for

a fine particle standard, both the staff

and CASAC recommended PM2.5 as the

indicator of fine particles (Wolff,

1996b). The particle diameter reflecting

the mass minimum between the fine

and coarse modes typically lies between

1 and 3 μm, and the scientific data

support a sampling ‘‘cut point’’ to

delineate fine particles somewhere in

this range. Because of the potential
38668 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

27 The National Mining Association (NMA) and

related companies submitted comments favoring

ultimate selection of a smaller cutpoint of 1 μm

(PM1) to further reduce coarse particle intrusion.

EPA considered this approach in developing the

Staff Paper and proposal. PM1 has not been used in

health studies, although in most cases collected

mass should be similar to those for cutpoints of 2.1

or 2.5 μm. While a PM1 indicator could reduce

intrusion of coarse particles, it might also omit

portions of hygroscopic PM components such as

acid sulfates, nitrates, and some organic compounds

in higher humidity environments picked up by

PM2.5 measurements. PM1 sampling technologies

have been developed, but have not been widely

used in the field to date; there are some concerns

about loss of certain organic materials in available

models relative to an instrument with a larger size

cut. NMA has also recommended consideration of

a methodology that could subtract coarse mass from

PM2.5 measurements where undue coarse particle

intrusion resulted in fine standard violations. EPA

will evaluate this recommendation in the context of

implementation policies.

overlap of fine and coarse particle mass

in this intermodal region, EPA

recognizes that any specific sampling

cut point would result in only an

approximation of the actual fine-mode

particle mass. Thus, the choice of a

specific diameter within this size range

is largely a policy judgment. The staff

and CASAC recommendations for a 2.5

μm sampling cut point were based on

considerations of consistency with the

community health studies, the limited

potential for intrusion of coarse fraction

particles into the fine fraction, and

availability of monitoring technology.27

PM2.5 encompasses all of the potential

agents of concern in the fine fraction,

including most sulfates, acids, fine

particle transition metals, organics, and

ultrafine particles, and includes most of

the aggregate surface area and particle

number in the entire distribution of

atmospheric particles.

The Administrator concurs with the

staff and CASAC recommendations and

concludes that PM2.5 is the appropriate

indicator for fine particle standards. As

discussed in Unit VI.B. of this preamble,

technical details of how PM2.5 is to be

measured in the ambient air are

specified in the Federal Reference

Method (40 CFR part 50, Appendix L).

2. Indicators for the coarse fraction of

PM10. The Criteria Document and Staff

Paper conclude that epidemiological

information, together with dosimetry

and toxicological information, support

the need for a particle indicator that

addresses the health effects associated

with coarse fraction particles within

PM10 (i.e., PM10-2.5). As noted above,

coarse fraction particles can deposit in

those sensitive regions of the lung of

most concern. Although the role of

coarse fraction particles in much of the

recent epidemiological results is

unclear, limited evidence from studies

where coarse fraction particles are the

dominant fraction of PM10 suggest that

significant short-term effects related to

coarse fraction particles include

aggravation of asthma and increased

upper respiratory illness. In addition,

qualitative evidence suggests that

potential chronic effects may be

associated with long-term exposure to

high concentrations of coarse fraction

particles.

In selecting an indicator for coarse

fraction particles, the Administrator

took into account the views of several

CASAC panel members who suggested

using the coarse fraction directly (i.e.,

PM10-2.5) as the indicator. However, the

Administrator notes that the existing

ambient data base for coarse fraction

particles is smaller than that for fine

particles, and that the only studies of

clear quantitative relevance to effects

most likely associated with coarse

fraction particles have used

undifferentiated PM10. In fact, it was the

consensus of CASAC that it is

reasonable to consider PM10 itself as a

surrogate for coarse fraction particles,

when used together with PM2.5

standards. The monitoring network

already in place for PM10 is large.

Therefore, in conjunction with the

decision to have separate standards for

PM2.5, the Administrator concludes,

consistent with CASAC

recommendations and public

comments, that it is appropriate to

retain PM10 as the indicator for PM

standards intended to protect against

the effects most likely associated with

coarse fraction particles.

D. Averaging Time of PM2.5 Standards

As discussed above in this unit, the

Administrator has concluded that PM2.5

is an appropriate indicator for standards

intended to provide protection from

effects associated primarily with fine

particles. The recent health effects

information includes reported

associations with both short-term (from

less than 1 day to up to 5 days) and

long-term (from a year to several years)

measures of PM.

On the basis of this information,

summarized in chapter V of the Staff

Paper and in the rationale presented in

the proposal, the Administrator has

considered both short- and long-term

PM2.5 standards.

1. Short-term PM2.5 standard. The

current 24-hour averaging time is

consistent with the majority of

community epidemiological studies,

which have reported associations of

health effects with 24-hour

concentrations of various PM indicators

such as PM10, fine particles, and TSP.

Such health effects, including

premature mortality and increased

hospital admissions, have generally

been reported with same-day, previous

day, or longer lagged single-day

concentrations, although some studies

have reported stronger associations with

multiple-day average concentrations. In

any case, the Administrator recognizes

that a 24-hour PM2.5 standard can

effectively protect against episodes

lasting several days, since attainment of

such a standard would provide

protection on each day of a multi-day

episode, while also protecting sensitive

individuals who may experience effects

after even a single day of exposure.

Although most reported effects have

been associated with daily or longer

measures of PM, evidence also suggests

that some effects may be associated with

PM exposures of shorter durations. For

example, controlled human and animal

exposures to specific components of

fine particles, such as acid aerosols,

suggest that bronchoconstriction can

occur after exposures of minutes to

hours. Some epidemiological studies of

exposures to acid aerosols have also

found changes in respiratory symptoms

in children using averaging times less

than 24 hours. However, such reported

results do not provide a satisfactory

quantitative basis for setting a fine

particle standard with an averaging time

of less than 24 hours, nor do current

gravimetric mass monitoring devices

make such shorter durations generally

practical at present. Further, the

Administrator recognizes that a 24-hour

average PM2.5 standard which leads to

reductions in 24-hour average

concentrations is likely to lead as well

to reductions in shorter-term average

concentrations in most urban

atmospheres, thus providing some

degree of protection from potential

effects associated with shorter duration

exposures.

2. Long-term PM2.5 standard.

Community epidemiological studies

have reported associations of annual

and multi-year average concentrations

of PM10, PM2.5, sulfates, and TSP with

an array of health effects, notably

premature mortality, increased

respiratory symptoms and illness (e.g.,

bronchitis and cough in children), and

reduced lung function. The relative

risks associated with such measures of

long-term exposures, although highly

uncertain, appear to be larger than those

associated with short-term exposures.

Based on the available epidemiology,

and consistent with the limited relevant

toxicological and dosimetric

information, the Administrator

concludes that significant, and

potentially independent, health

consequences are likely associated with

long-term PM exposures.
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38669

28 Of the 19 panel members who joined in the

consensus for PM2.5 standards, 17 (90 percent)

recommended a 24-hour standard and 13 (70

percent) recommended an annual standard (Wolff,

1996b).

The Administrator has considered

this evidence, which suggests that some

health endpoints reflect the cumulative

effects of PM exposures over a number

of years. In such cases, an annual

standard would provide effective

protection against persistent long-term

(several years) exposures to PM.

Requiring a much longer averaging time

would also complicate and

unnecessarily delay control strategies

and attainment decisions.

The Administrator has also

considered the seasonality of emissions

of fine particles and their precursors in

some areas (e.g., wintertime smoke from

residential wood combustion,

summertime regional acid sulfate and

ozone formation), which suggests that

some effects associated with annual

average concentrations might be the

result of repeated seasonally high

exposures. However, different seasons

are likely of concern in different parts

of the country, and the current evidence

does not provide a satisfactory

quantitative basis for setting a national

fine particle standard in terms of a

seasonal averaging time.

In addition, the Administrator

recognizes that an annual standard

would have the effect of improving air

quality broadly across the entire annual

distribution of 24-hour PM2.5

concentrations, although such a

standard would not as effectively limit

peak 24-hour concentrations as would a

24-hour standard. The risk assessment

summarized above found that because

such 24-hour peaks contribute much

less to the total health risk over a year

than the more numerous low- to midrange PM2.5 levels, an annual standard

could also provide effective protection

from health effects associated with

short-term exposures to PM2.5 as well as

those associated with long-term

exposures (see figure 2; 61 FR 65652-

65653, December 13, 1996).

3. Combined effect of annual and 24-

hour standards. For the reasons

outlined in Units II.C.1. and 2. of this

preamble, the Administrator concluded

in the proposal that a short-term PM2.5

standard with a 24-hour averaging time

can serve to control short-term ambient

PM2.5 concentrations, thus providing

protection from health effects associated

with short-term (from less than 1-day to

up to 5-day) exposures to PM2.5. Further,

a long-term PM2.5 standard with an

annual averaging time can serve to

control both long- and short-term

ambient PM2.5 concentrations, thus

providing protection from health effects

associated with long-term (seasonal to

several years) and, to some degree,

short-term exposures to PM2.5.

EPA received comparatively few

public comments on these proposed

averaging times. Those supporting PM2.5

standards also strongly supported

adopting both annual and 24-hour

averaging times. Many of those

opposing PM2.5 standards, for the

reasons discussed in Unit II.B. of this

preamble, provided contingent

comments that variously supported both

averaging times for PM2.5 standards in

the event the Administrator disagreed

with their overall recommendations.

Other opponents of PM2.5 standards

disagreed with having two standards on

administrative grounds, or because

some CASAC members did not support

both averaging times.

The relationship between standards

for the two averaging times is discussed

below in this unit. In essence, based on

its examination of the effects data and

air quality relationships, EPA believes

that a single PM2.5 standard (24-hour or

annual) either would not provide

adequate protection against effects of

concern for all averaging times, or

would be inefficient in the sense that it

was more stringent than necessary for at

least one averaging time. Contrary to

commenters who focused on minority

CASAC opinions, EPA notes that a clear

majority of CASAC supported both 24-

hour and annual standards28. After

considering public comments on

averaging time and the rationale

outlined above, the Administrator has

concluded that both 24-hour and annual

PM2.5 standards are appropriate.

The Administrator next considered

the potential combined effects of such

standards on PM concentration levels

and distributions. The existing health

effects evidence could, of course, be

used to assess the form and level of each

standard independently, with shortterm exposure health effects evidence

being used as the basis for a 24-hour

standard and the long-term exposure

health effects evidence as the entire

basis for an annual standard. Some

CASAC panel members apparently used

this approach as a basis for their views

on appropriate averaging times and

standard levels. In particular, a few

members focused only on a 24-hour

PM2.5 standard in light of the relative

strength of the short-term exposure

studies. On the other hand, two

members focused only on an annual

standard, recognizing that strategies to

meet an annual standard would provide

protection against effects of both shortand long-term exposures.

As noted above in this unit,

attempting to provide protection for all

of the effects identified in long- and

short-term PM exposure studies with a

single averaging time would result in

either inadequate protection for some

effects, or unnecessarily stringent

control for others. The Administrator

has, instead, emphasized a policy

approach that considers the consistency

and coherence, as well as the

limitations, of the body of evidence as

a whole, and recognizes that there are

various ways to combine two standards

to achieve an appropriate degree of

public health protection. Such an

approach to standard setting, which

integrates the body of health effects

evidence and air quality analyses, and

considers the combined effect of the

standards, has the potential to result in

a more effective and efficient suite of

standards than an approach that only

considers short- and long-term exposure

evidence, analyses, and standards

independently.

In considering the combined effect of

such standards, the Administrator notes

that while an annual standard would

focus control programs on annual

average PM2.5 concentrations, it would

also result in fewer and lower 24-hour

peak concentrations. Alternatively, a 24-

hour standard that focuses controls on

peak concentrations could also result in

lower annual average concentrations.

Thus, either standard could be viewed

as providing both short- and long-term

protection, with the other standard

serving to address situations where the

daily peaks and annual averages are not

consistently correlated.

The Administrator proposed that the

suite of PM2.5 standards could most

effectively and efficiently be defined by

treating the annual standard as the

generally controlling standard for

lowering both short- and long-term

PM2.5 concentrations. In conjunction

with the annual standard, the 24-hour

standard would serve to provide

protection against days with high peak

PM2.5 concentrations, localized ‘‘hot

spots,’’ and risks arising from seasonal

emissions that would not be well

controlled by a national annual

standard.

Relatively few public comments were

addressed specifically to the proposal

that the annual standard be directed

toward controlling both 24-hour and

annual levels (thereby basing the annual

standard on an evaluation of both the

short- and long-term health effects

information), with the 24-hour standard

being used to address more localized

short-term peaks. A number of

commenters, notably some among the

groups opposing any revised PM
38670 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

29 A related comment criticized the risk

assessment conclusion that peak 24-hour

concentrations contribute much less to the total risk

over a year as inconsistent with the experience in

historic air pollution episodes. EPA disagrees.

While the historic London episodes were

quantitatively different from those assumed in the

risk assessment, the record over 14 London winters

indicates a continuum of effects down to the lowest

levels. It is therefore likely that the cumulative

increase in mortality calculated for all the days in

the whole 14-year period would not be dominated

by the more limited number of episode days.

30 This point is buttressed by studies that have

taken out a limited number of higher PM

concentration days with little effect on the effects

estimates or significance of the association (e.g.,

Schwartz et al., 1996; Pope and Dockery, 1992).

standards, appeared to have ignored this

fundamental aspect of the proposal,

judging by their assertions that the sole

basis for EPA’s proposed annual

standards was two long-term exposure

studies (Dockery et al., 1993; Pope et al.

1995). This is incorrect; as the proposal

states, EPA based the proposed annual

standard level on a wider range of shortand long-term exposure studies. Other

commenters, including some

environmental groups, reserved

comment on this specific issue, but

expressed concerns that the specific

levels for both standards were not

stringent enough, regardless of which

standard is intended to be controlling.

Issues regarding specific levels are

discussed below in Unit II.F. of this

preamble.

Some commenters, however,

disagreed with the proposition that

EPA’s proposed approach would

necessarily provide the most effective

and efficient standards. In the view of

some who opposed PM2.5 standards, the

likelihood that there are thresholds

below which no effects occur means

that a 24-hour standard would be more

efficient than an annual standard. In

this view, the reductions made on days

that were below the threshold would

provide no protection.29 Some

commenters also noted that while a

majority of CASAC members favored

both annual and 24-hour standards,

more recommended 24-hour standards.

While the available epidemiological

studies provide strong evidence

suggesting that PM causes or contributes

to health effects at levels below the

current standards, EPA agrees, as stated

previously, that uncertainties increase

markedly at lower concentrations.

Nevertheless, the level or even existence

of population thresholds below which

no effects occur cannot be reliably

determined by an examination of the

results from the available studies.

Analyses have placed some limits,

however, and EPA has considered

hypothetical thresholds in its risk

assessment. As noted in Unit II.A. of

this preamble, even assuming an

example threshold of 18 μg/m3, the risk

assessment (see Figure 2c; 61 FR 65653,

December 13, 1996) finds that most of

the annual aggregate risk associated

with short-term exposures still results

from the large number of days at lower

to mid-range values above the mean.

Given that neither the Criteria

Document nor commenters have

provided quantitative evidence

regarding the likelihood of a threshold

at levels much higher than the above

example, EPA believes that the evidence

provided in the risk assessment does not

support the commenters’ position. As

noted above, EPA believes that most

CASAC opinions on averaging time

reflect panelists’ judgments on the

relative strength of the short-term

exposure epidemiological studies, a

judgment that EPA shares. Although

most CASAC panel members did not

offer an opinion on the use of short-term

exposure studies in specifying annual

standards, two panelists did support

this notion. EPA therefore believes this

approach is neither inconsistent with

the underlying science nor discordant

with the advice of CASAC.

Another concern was raised by some

air pollution control officials who

otherwise supported revised PM

standards. These commenters state that,

from an implementation perspective, it

is often easier to design control

strategies for single short-term events

than for annual averages. Aside from

whether this is a proper consideration

in establishing NAAQS, the point in fact

highlights one of the important

strengths of an annual standard in

addressing short-term risks associated

with PM2.5. As noted by the

commenters, risk management for a

short-term standard focuses on a

characteristic ‘‘design value’’ episode

responsible for peak concentrations. For

PM, such peak values can be associated

with single source contributions.

Meteorology, relative source

contributions, and resulting particle

composition for that day may or may

not be typical for the area or for the

year. Yet the short-term exposure

epidemiological results are largely

drawn from studies that associated

variations in area-wide effects with

monitor(s) that gauged the variation in

daily levels over the course of up to 8

years. The strength of the associations in

these data is demonstrably in the

numerous ‘‘typical’’ days in the upper to

middle portion of the annual

distribution, not on the peak days.30 For

these reasons, strategies that focus only

on reducing peak days are less likely to

achieve reduction of the mix and

sources of urban and regional-scale PM

pollution most strongly associated with

health effects. Although designing

control strategies to reduce annual

levels may be more difficult than for 24-

hour standards, the available short- and

long-term epidemiological data suggest

it is also likely to result in a greater

reduction in area-wide population

exposure and risk.

The Administrator concludes that the

most effective and efficient approach to

establishing PM2.5 standards is to treat

the annual standard as the generally

controlling standard for lowering both

short- and long-term PM2.5

concentrations, while the 24-hour

standard would serve to provide

protection against days with high peak

PM2.5 concentrations, localized ‘‘hot

spots,’’ and risks arising from seasonal

emissions that would not be well

controlled by a national annual

standard. In reaching this view, the

Administrator took into account the

public comments and the factors

discussed below in this unit.

(1) Based on one of the key

observations from the quantitative risk

assessment summarized above (see

Figures 2a,b,c; 61 FR 65652-65653,

December 13, 1996), the Administrator

notes that much if not most of the

aggregate annual risk associated with

short-term exposures results from the

large number of days during which the

24-hour average concentrations are in

the low- to mid-range, below the peak

24-hour concentrations. As a result,

lowering a wide range of ambient 24-

hour PM2.5 concentrations, as opposed

to focusing on control of peak 24-hour

concentrations, is the most effective and

efficient way to reduce total population

risk. Further, there is no evidence

suggesting that risks associated with

long-term exposures are likely to be

disproportionately driven by peak 24-

hour concentrations. Thus, an annual

standard that controls an area’s

attainment status is likely to reduce

aggregate risks associated with both

short- and long-term exposures with

more certainty than a 24-hour standard.

(2) The consistency and coherence of

the health effects data base are,

therefore, more directly related to the

more frequently occurring PM

exposures reflected in study period

mean measures of air quality (e.g., the

annual distributions of 24-hour PM

concentrations), than to the potentially

site-specific and/or otherwise infrequent

PM exposures reflected in a limited

number of peak 24-hour concentrations.

More specifically, judgments about the

quantitative consistency of the large

number of short-term exposure studies
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38671

31 The notice of proposed revisions to 40 CFR part

58 recognized that a single appropriately sited

monitor could suffice for an area in place of an

average of multiple monitors.

reporting associations with 24-hour

concentrations arise from comparing the

relative risk results per PM increment as

derived from analyzing the associations

across the entire duration of the studies.

These studies typically spanned at least

an annual time frame and the reported

associations are most strongly

influenced by the large number of days

toward the middle of the distribution.

(3) An annual average measure of air

quality is more stable over time than are

24-hour measures. Thus, a controlling

annual standard is likely to result in the

development of more consistent risk

reduction strategies over time, since an

area’s attainment status will be less

likely to change due solely to year-toyear variations in meteorological

conditions that affect the formation of

fine particles, than under a controlling

24-hour standard.

Under this policy approach, the

annual PM2.5 standard would serve in

most areas as the target for control

programs designed to be effective in

lowering the broad distribution of PM2.5

concentrations, thus protecting not only

against long-term effects but also shortterm effects as well. In combination

with such an annual standard, the 24-

hour PM2.5 standard would be set so as

to protect against the occurrence of peak

24-hour concentrations, particularly

peak concentrations that present

localized or seasonal exposures of

concern in areas where the highest 24-

hour-to-annual mean PM2.5 ratios are

appreciably above the national average.

E. Form of PM2.5 Standards

1. Annual standard. As discussed in

some detail during the last review of the

PM NAAQS (see 49 FR 10408, March

20, 1984; 52 FR 24634, July 1, 1987) and

in the December 13, 1996 proposal, the

annual arithmetic mean form of the

current annual PM10 standard (i.e., the

annual arithmetic mean averaged over 3

years) is a relatively stable measure of

air quality that reflects the total

cumulative dose of PM to which an

individual or population is exposed.

Short-term peaks have an influence on

the arithmetic mean that is proportional

to their frequency, magnitude, and

duration, and, thus, their contribution to

cumulative exposure and risk. As a

result, the annual arithmetic mean form

of an annual standard provides

protection across a wide range of the air

quality distribution contributing to

exposure and risk, in contrast to other

forms, such as the geometric mean, that

de-emphasize the effects of short-term

peak concentrations.

While almost no commenters took

specific issue with use of an annual

arithmetic mean, a number of

commenters disagreed with averaging

over 3 years for both the annual and 24-

hour standards because of their desire

for quick action in the initial

implementation of PM2.5 controls. The

Administrator recognizes the

importance of promptly implementing

appropriate control programs, but she

does not believe that implementation

start-up concerns are an adequate basis

for adopting a form (e.g., a single year

annual average) that would provide less

stable risk reduction in the long-run.

Therefore, the Administrator continues

to concur with the Staff Paper

recommendation, supported by CASAC,

to use the annual arithmetic mean,

averaged over 3 years, as the form for an

annual PM2.5 standard consistent with

the current form of the annual PM10

standard. Nevertheless, EPA intends to

address the concerns of those who

commented that the 3-year form might

prevent the public from being informed

about the air quality status of their

communities. As outlined in Unit II.H.

of this preamble, EPA plans to issue

revised Pollutant Standard Index

criteria for PM2.5, to ensure the public is

informed promptly about air quality

status.

The Staff Paper and some CASAC

panel members also recommended that

consideration be given to calculating the

PM2.5 annual arithmetic mean for an

area by averaging the annual arithmetic

means derived from multiple

monitoring sites within a monitoring

planning area. In proposing a

calculation method for annual

arithmetic averages that involves spatial

averaging of monitoring data, the

Administrator reasoned as follows:

(1) Many of the community-based

epidemiological studies examined in

this review used spatial averages, when

multiple monitoring sites were

available, to characterize area-wide PM

exposure levels and the associated

population health risk. In those studies

that used only one monitoring location,

the selected site was chosen to represent

community-wide exposures, not the

highest value likely to be experienced

within the community. Thus, spatial

averages are most directly related to the

epidemiological studies used as the

basis for the proposed revisions to the

PM NAAQS.

(2) As a part of the overall policy

approach discussed in Unit II.D. of this

preamble, the annual PM2.5 standard

would be intended to reduce aggregate

population risk from both long- and

short-term exposures by lowering the

broad distribution of PM2.5

concentrations across the community.

An annual standard based on spatially

averaged concentrations would better

reflect area-wide PM exposure levels

than would a standard based on

concentrations from a single monitor

with the highest measured values.

(3) Under this policy approach, the

24-hour PM2.5 standard would be

intended to work in conjunction with a

spatially averaged annual PM2.5

standard by providing protection against

peak 24-hour concentrations, localized

‘‘hot spots,’’ and higher PM2.5

concentrations arising from seasonal

emissions and meteorology that would

not be as well controlled by an annual

standard. Accordingly, the 24-hour

PM2.5 standard should be based on the

single population-oriented monitoring

site within the monitoring planning area

with the highest measured values.

Based on these considerations, the

Administrator proposed that the form of

an annual PM2.5 standard be expressed

as the annual arithmetic mean,

temporally averaged over 3 years and

spatially averaged over all designated

monitoring sites,31 which, in

conjunction with a 24-hour PM2.5

standard, was intended to provide the

most appropriate target for reducing

area-wide population exposure to fine

particle pollution. Recognizing the

complexities that spatial averaging

might introduce into risk management

programs, in the proposal the

Administrator also requested comment

on the alternative of basing the annual

standard for PM2.5 solely on the single

population-oriented monitor site within

the monitoring planning area with the

highest 3-year average annual mean.

The proposed approach to designating

sites that are appropriate for spatial

averaging was based on criteria and

constraints contained in the proposed

revision to the monitoring siting and

network planning requirements in 40

CFR part 58. In proposing this approach,

the Administrator noted concerns

regarding the development and

implementation of appropriate and

effective criteria for the selection of sites

and designations of areas for spatial

averaging.

A number of commenters who

otherwise favored setting PM2.5

standards objected to the concept of

population-oriented monitors and

expressed the view that any monitor

regardless of where it was sited should

be eligible for comparison to the annual

PM2.5 standard. They further maintained

that the proposed provisions for spatial

averaging would fail to provide

adequate health protection because
38672 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

32 The 40 CFR part 58 proposed rule identified

the proposed criteria for monitors to be averaged;

namely, monitors must be properly sited to reflect

population-orientation, primarily influenced by

similar sources, and within +/-20 percent of the

average levels and a specific degree of correlation

(or meet a ‘‘homogeneity’’ constraint). Additional

criteria include demonstrations that the monitors to

be averaged are influenced primarily by similar

sources (e.g., to prevent the placement of monitors

upwind in unrepresentative locations), EPA

oversight of the monitoring program which includes

regular review and approval of the State PM

monitoring network design, and other criteria to

ensure proper monitor siting. The final rule

includes the addition of provisions that the State

PM monitoring network design be available for

public inspection.

33 Daily mortality studies generally use urban or

metro-areawide effects statistics in conjunction

with single or multiple monitors that index day-today pollution changes across the area. Ito et al.

(1995) found that spatial averages from multiple PM

monitors in Chicago were better correlated with

daily mortality than were most single monitors, but

that single monitors were also associated. A number

of morbidity studies (e.g., Schwartz et al., 1994;

Neas et al., 1995; Raizenne et al.; 1996) used

community scale monitors and effects information

from a defined group of subjects from the

community, who were more closely represented by

the monitor.

34 Because the 24-hour standard is designed to

address localized peaks, it would be inappropriate

to extend spatial averaging forms to this standard.

‘‘clean areas’’ and ‘‘dirty areas’’ would

be averaged together. Some commenters

expressed concern that the proposed

constraints on spatial average would not

be sufficient to prevent use of such

averaging to avoid pollution abatement.

Others may not have fully understood

the implications of the specific

constraints and siting requirements

discussed in the proposed revisions to

40 CFR part 58, which were intended to

ensure that the population-oriented

monitors used for the annual standard

were actually reflective of communitywide exposures and that the spatial

averages did not include nonrepresentative monitored values from

either ‘‘clean areas’’ or ‘‘dirty areas.’’32

In order to clarify the intent that the

spatially averaged annual standard

protect those in smaller communities, as

well as those in larger population

centers, the final revisions to 40 CFR

part 58 adopt the term ‘‘communityoriented’’ monitors.

Other commenters, who supported

PM2.5 annual standards, endorsed the

concept of spatial averaging as being

more reflective of the air quality data

used in the underlying health studies

and because there is general uniformity

of fine particle concentrations across an

area. Opponents of the PM2.5 standards

expressed contingent support for spatial

averaging in concept, again citing the

linkage to the underlying health studies.

Indeed, they advocated the extension of

spatial averaging to the daily form of the

standard, and/or recommended less

constrained spatial averaging to allow

for averaging across entire metropolitan

areas.

The Administrator, of course, shares

commenters’ concerns that the form of

the standards, in conjunction with other

components of the standards, must

protect public health adequately against

risks associated with PM. It was for this

reason that EPA proposed a policy

approach providing for greatest overall

risk reduction for all citizens in the

community from exposures to the mix

of urban and regional scale PM

pollution most strongly associated with

health effects. In specifically

considering whether to allow for the use

of spatial averaging, the Administrator

placed great weight on consistency with

the underlying body of health effects

evidence. The Administrator is mindful

that some community studies relied

inherently on exposure and effects

estimates that reflect comparatively

broad spatial scales, as highlighted by

those commenters desiring to extend

permissible averaging; however, this

type of exposure characterization may

not be appropriate for all circumstances

and might leave some areas without

adequate protection.33

For these reasons, the 40 CFR part 58

proposal package contained criteria and

constraints on spatial averaging. These

criteria and constraints were intended to

ensure that spatial averaging would not

result in inequities in the level of

protection provided by the PM

standards. The Administrator again

recognizes that either a single properly

sited community-oriented monitor, or

an average of more than one such

monitors, are both appropriate indices

of area-wide population exposures. Both

are consistent with monitoring

approaches used in community

epidemiological studies upon which the

standards are based. On the other hand,

comparing the annual PM2.5 standard to

the maximum concentrations at a site

that is not representative of community

exposures, as some have suggested,

would be inconsistent with the

Administrator’s goal of using the annual

standard to reduce urban and regional

scale exposures and risks. Further, the

Administrator believes that the criteria

and, siting requirements contained in 40

CFR part 58, provide adequate

safeguards against inappropriate

application of spatial averaging.

Therefore, the Administrator continues

to believe that an annual PM2.5 standard

reflective of area-wide exposures, in

conjunction with a 24-hour standard

designed to provide adequate protection

against localized peak or seasonal PM2.5

levels, reflects the most appropriate

approach for public health against the

effects of PM reported in the scientific

literature.34

The majority of comments from States

stressed the need for flexibility in

specifying network designs and spatial

averaging, given that the nature and

sources of particle pollution vary from

one area to another. One State agency

specifically requested the flexibility to

choose whether to use a single

community-oriented monitor or a

spatial average of several of such

monitors, arguing that it is appropriate

to provide this flexibility as PM2.5

monitoring networks evolve and to

address the diversity of local conditions.

As a result of EPA’s evaluation of

these comments, the requirements of 40

CFR part 50, Appendix K, and 40 CFR

part 58 have been revised to clarify that

the implementing agencies have the

flexibility to compare the annual PM2.5

standard either to the measured value at

a single representative communityoriented monitoring site, or to the value

resulting from an average of communityoriented monitoring sites that meet the

revised criteria and constraints

enumerated in the 40 CFR part 58 final

rule.

In the Administrator’s view, the final

criteria and siting requirements

contained in 40 CFR part 58 and in the

new 40 CFR part 50, Appendix N,

address the concerns raised by these

commenters about the protection

afforded by the form of the annual

standard. Therefore, the Administrator

continues to believe that the form of a

PM2.5 annual standard should be

expressed as an annual arithmetic mean,

averaged over 3 years, from single or

multiple community-oriented monitors,

in accordance with 40 CFR part 50,

Appendix N and 40 CFR part 58. In her

judgment, an annual standard expressed

in this manner and set at an appropriate

level, in conjunction with a 24-hour

PM2.5 standard, will adequately protect

public health.

2. 24-hour standard. The current 24-

hour PM10 standard is expressed in a ‘‘1-

expected-exceedance’’ form. That is, the

standard is formulated on the basis of

the expected number of days per year

(averaged over 3 years) on which the

level of the standard will be exceeded.

The test for determining attainment of

the current 24-hour standard is

presented in Appendix K to 40 CFR part

50.

As discussed in the proposal, since

promulgation of the current 24-hour

PM10 standard in 1987, a number of

concerns have been raised about the 1-
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38673

35 See sections 303, 110(a)(2)(y); 40 CFR part 51.

EPA intends to establish a significant harm level for

PM2.5 and associated guidance so States can

develop appropriate emergency episode plans. The

significant harm and episode criteria will be

included in forthcoming proposed revisions to 40

CFR part 51 and 40 CFR part 58 implementation

guidance. In the interim, existing PM10 emergency

episode plans should be triggered by events of this

magnitude.

expected-exceedance form. These

include, in particular, the year-to-year

stability of the number of exceedances,

the stability of the attainment status of

an area, and the complex data handling

conventions specified in 40 CFR part 50,

Appendix K, including the procedures

for making adjustments for missing data

and less-than-every-day monitoring.

In light of these concerns, the Staff

Paper and several CASAC panel

members (Wolff, 1996b) recommended

that consideration be given to adoption

of a more stable and robust form for 24-

hour standards. In considering this

recommendation for the proposal, the

Administrator noted that the use of a

concentration-based percentile form

would have several advantages over the

current 1-expected-exceedance form:

(1) Such a concentration-based form

would be more directly related to the

ambient PM concentrations that are

associated with health effects. Given

that there is a continuum of effects

associated with exposures to varying

levels of PM, the extent to which public

health is affected by exposure to

ambient PM is related to the actual

magnitude of the concentration, not just

whether the concentration is above a

specified level. With an exceedancebased form, days on which the ambient

concentration is well above the level of

the standard are given equal weight to

those days on which the concentration

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

is counted as one exceedance), even

though the public health impact on the

2 days is significantly different. With a

concentration-based form, days on

which higher concentrations occur

would weigh proportionally more than

days with lower concentrations for the

design value, since the actual

concentrations would be used directly

in determining whether the standard is

attained.

(2) A concentration-based percentile

form would also compensate for missing

data and less-than-every-day

monitoring, thereby reducing or

eliminating the need for complex data

handling procedures in the 40 CFR part

50, Appendix K test for attainment. As

a result, an area’s attainment status

would be based directly on monitoring

data rather than on a calculated value

adjusted for missing data or less-thanevery-day monitoring.

(3) Further, a concentration-based

form, averaged over 3 years, would also

have greater stability than the expected

exceedance form and, thus, would

facilitate the development of more

stable implementation programs by the

States.

The proposal discussed various

specific percentile values for such a

form (e.g., 90th to 99th percentiles),

taking into account two factors. First,

the 24-hour PM2.5 standard is intended

to supplement the annual PM2.5

standard by providing additional

protection against extremely high peak

days, localized ‘‘hot spots,’’ and risks

arising from seasonal emissions.

Second, given an appropriate level of

health protection, the form of the 24-

hour PM2.5 standard should provide an

appropriate degree of increased stability

relative to the current form. The

Administrator noted in the proposal that

a more stable statistic would reduce the

impact of a single high exposure event

that may be due to unusual

meteorological conditions alone, and

thus would provide a more stable basis

upon which to design effective control

programs.

With these purposes in mind, the

Administrator observed in the proposal

that while a percentile value such as the

90th or 95th would provide substantially

increased stability when compared to a

more extreme air quality statistic (e.g.,

the current 1-expected-exceedance

form), it would likely not serve as an

effective supplement to the annual

standard, because it would allow a large

number of days with peak PM2.5

concentrations above the standard level.

For example, in a 365-day data base, the

90th and 95th percentiles would equal

the 37th and 19th highest 24-hour

concentrations, respectively. On the

other hand, a percentile value selected

much closer to the tail of the air quality

distribution (e.g. a 99th or greater

percentile) would not likely provide

significantly more health protection or

significantly increased stability as

compared to a 1-exceedance form. In

balancing these issues in the proposal,

the Administrator ultimately proposed a

98th percentile value form of the

standard.

Some commenters maintained that

EPA should retain the current 1-

expected-exceedance form for the 24-

hour PM2.5 standard to limit the number

of days per year that the standard is

exceeded. These commenters apparently

gave little weight to EPA’s rationale that

a concentration-based form is more

directly related to ambient PM

concentrations that are associated with

health effects because it takes into

account the magnitude of PM

concentrations, not just whether the

concentrations are above a specific

level. These commenters also

discounted the other advantages of a

concentration-based percentile form

outlined above in this unit. A number

of other commenters supported the

concentration-based percentile form for

the reasons outlined in the proposal but,

as discussed below in this unit, argued

for alternative percentile values that

were higher or lower than the proposed

98th percentile value.

EPA continues to believe that a

concentration-based percentile form is

more reflective of the health risk posed

by elevated PM concentrations, because

it gives proportionally greater weight to

days when concentrations are well

above the level of the standard than to

days when the concentrations are just

above the standard. This factor, coupled

with the other advantages outlined

above in this unit, leads EPA to

conclude that a concentration-based

percentile form will provide for more

effective health protection than a 1-

expected-exceedance form.

Some commenters supporting a single

exceedance form or a more restrictive

concentration-based percentile form

(e.g. a 99th percentile) expressed concern

that the proposed 98th percentile form

could allow too many high

concentration excursions, and thus fail

to provide adequate protection against

seasonal emissions problems or

localized peaks. In particular, some

commenters expressed concerns that in

areas with strongly seasonal emissions,

such as western areas with winter

inversions, over a three year period an

area could experience several

excursions in which levels could reach

as high as 250 μg/m3 and still comply

with both the annual and daily

standards if the remainder of the days

had low levels (e.g., 10 μg/m3).

Although this combination of events is

theoretically possible, EPA believes it is

unlikely. Moreover, if such episodic

events did occur, the Act provides for

emergency State or Federal action to

address them.35 In view of the limits on

truely episodic peak concentrations,

EPA believes that an appropriately

selected 24-hour standard with a

concentration-based 98th percentile form

can provide a stable and adequately

protective supplement to the annual

standard in areas with periodic peak

concentrations.

Other commenters who were also

concerned with monitoring

requirements associated with spatial

averaging in the annual standard,

argued that a 98th percentile form,

coupled with the proposed monitoring

requirements that would limit
38674 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

36 The 40 CFR part 58 monitoring rule proposed

to limit sites that would be eligible for comparisons

to the 24-hour standard to population-oriented

monitoring sites.

compliance monitors for the 24-hour

standard to population-oriented sites,

would not protect people residing in or

near localized ‘‘hot spots’’ in some

areas.36 The Administrator believes that

the siting requirements as proposed and

finalized in 40 CFR part 58 for

population-oriented sites will provide

adequate safeguards for such residential

areas.

Other commenters, who otherwise

opposed setting PM2.5 standards,

recommended that alternative lower

percentiles (e.g., 95th percentiles) be

used, if EPA proceeds to set such

standards. As discussed above in this

unit, however, EPA continues to hold

the view that a 90th to 95th percentile

form would not provide an adequate

limit against periodic peak values in

areas with low annual values and

periodic high seasonal or sourceoriented peaks.

After carefully assessing the

comments received, the Administrator

is persuaded that the adoption of a 98th

percentile form for the 24-hour PM2.5

standard measured at each populationoriented monitoring site in an area

would provide an effective supplement

to the annual PM2.5 standard. This form

will provide adequate protection against

24-hour peak PM2.5 levels in locations

dominated by single point sources, as

well as in areas dominated by seasonal

emissions. The Administrator also

believes that a 98th percentile form, with

more frequent sampling and averaged

over 3 years, will provide increased

stability and robustness as

recommended by several members of

the CASAC panel. For these reasons, the

Administrator has decided to adopt the

98th percentile form for the final PM2.5

24-hour standard. The 24-hour PM2.5

standard would be attained when the 3-

year average of the 98th percentile of 24-

hour concentrations at each populated

oriented monitor within an area is less

than or equal to the level of the

standard. Further details regarding the

interpretation of the form, as well as

associated calculations and other data

handling conventions are specified in

the new 40 CFR part 50, Appendix N.

F. Levels for the Annual and 24-Hour

PM2.5 Standards

As discussed in Unit II.D. of this

preamble, the Administrator believes

that an annual PM2.5 standard can

provide the requisite reduction in risk

associated with both annual and 24-

hour averaging times in most areas of

the United States. Under this approach,

the 24-hour standard would be intended

to provide supplemental protection

against extreme peak fine particle levels

that may occur in some localized

situations or in areas with distinct

variations in seasonal fine particle

levels. In reaching judgments as to

appropriate levels to propose for both

the annual and 24-hour PM2.5 standards,

the Administrator has considered the

combined protection afforded by both

the annual and 24-hour standards,

taking into account the forms discussed

in Unit II.E. of this preamble.

With this approach in mind, the

Administrator has considered the

available health effects evidence and

related air quality information presented

in the Criteria Document and

summarized in chapters IV--VII of the

Staff Paper, which provides the basis for

decisions on standard levels that would

reduce risk sufficiently to protect public

health with an adequate margin of

safety, recognizing that such standards

will not be risk-free. In so doing, the

Administrator has considered both the

strengths and the limitations of the

available evidence and information, as

well as alternative interpretations of the

scientific evidence advanced by various

CASAC panel members (Wolff, 1996b;

Lippmann et al., 1996) and public

commenters, arising primarily from the

inherent uncertainties and limitations in

the health effects studies.

Beyond those factors, but clearly

related to them, a range of views have

been expressed by CASAC panel

members and the public as to the

appropriate policy response to the

available health effects evidence and

related air quality information. Toward

one end of the spectrum, the view has

been expressed that only a very limited

policy response is appropriate in light of

the many key uncertainties and

unanswered questions that, taken

together, call into question the

fundamental issue of causality in the

reported associations between ambient

levels of PM2.5 and mortality and other

serious health effects. Toward the other

end, the view has been expressed that

the consistency and coherence of the

epidemiological evidence should be

interpreted as demonstrating causality

in the relationships between PM2.5 and

health endpoints that are clearly

adverse, and that uncertainties in the

underlying health effects information

should be treated, regardless of their

nature, as warranting a maximally

precautionary policy response. A third

view would suggest an alternative

policy response, taking into account not

only the consistency and coherence of

the health effects evidence, but also the

recognition of key uncertainties and

unanswered questions that increasingly

call into question the likelihood of PMrelated effects as PM2.5 concentrations

decrease below the mean values in areas

where effects have been observed and/

or as such concentrations approach

background levels.

Reflecting these divergent views, both

of the science itself and of how the

science should be used in making policy

decisions on proposed standards, the

Administrator considered three

alternative approaches to selecting

appropriate standard levels, as

described in the proposal, ultimately

deciding to propose standards based on

a balanced view of the strengths and

uncertainties of the scientific

information that reflects the

intermediate approach.

Judging by the public comments

received, EPA accurately reflected the

bases for divergent views. A substantial

body of public comments supported

revising the PM standards by adding

PM2.5 standards with levels at least as

stringent as those proposed by the

Administrator. In general, however,

comments on levels for PM2.5 standards

revealed a strong dichotomy between

those who recommended even stronger

standards than proposed, and those who

counseled against revising the standards

at all. As noted above in this unit, many

in this latter group made contingent

recommendations with respect to the

levels and other aspects of PM2.5

standards, if the Administrator

concluded that any revisions were

appropriate.

This latter group of ‘‘contingent’’

commenters recommended levels well

above those proposed by the

Administrator. These commenters

placed great weight on factors outlined

in Units II.B. and II.C. of this preamble

that led them to oppose any revisions to

the PM standards, including the

uncertainties and limitations in the

available health effects studies

considered individually, such as the

possible existence of effects thresholds

and unanswered questions regarding the

causal agent(s) responsible for the

reported health effects. Further, they

emphasized the limited amount of

research currently available that has

measured PM2.5 directly. A substantial

group recommended that PM2.5

standards be selected so as to be

equivalent or close in stringency to the

current PM10 standards, and cited the

opinions of some CASAC PM panel

members as support. Some of these

commenters provided supplemental

analyses of air quality data, arguing that

they demonstrate that ‘‘equivalent’’

standards would be at PM2.5 levels as
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38675

37 Nationwide PM2.5 estimates have been derived

from the current PM air quality data base, but

reflect a significant degree of uncertainty due to the

highly variable relationship between PM2.5 and

PM10 air quality values across locations and seasons

(Fitz-Simons et al., 1996). The American Iron and

Steel Institute (AISI) submitted a useful data base

(Cooper Associates, 1997) on PM2.5/PM10

relationships that examines both these predictions

and the issue of equivalence. An EPA examination

of this material, which found some problems with

the analysis and with commenters’ conclusions that

appear inconsistent with the Cooper report, is

included in the Response to Comments.

38 Some commenters suggest that CASAC and

EPA support for PM2.5 standards is based on the

need to stimulate additional monitoring and

research. While the Administrator agrees that the

additional monitoring and research that would

accompany establishment of equivalent or

marginally tighter PM2.5 standards are very

important goals, they do not form an adequate

rationale for establishing air quality standards.

39 As stated previously, section 109(d) of the Act

requires that, after reviewing the existing criteria

and standards for PM, the Administrator make such

revisions in the standards and promulgate such new

standards as are appropriate under section 109(b) of

the Act.

40 This range of levels for a 24-hour PM2.5

standard is close to the lower bound levels

recommended by four CASAC panel members (20

μg/m3); no member supported an annual PM2.5

standard as low as 10 to 12 μg/m3.

41 Some confusion is apparent in comments

regarding the basis on which the Administrator

selected levels for the proposed PM2.5 standards,

with some commenters suggesting two or at most

three studies were used, and others suggesting that

EPA relied extensively on uncertain conversion

factors to estimate levels for the standards. These

comments are in error. To clarify, as stated in the

proposal, the Administrator is basing her decision

to revise the standards on the full range of PM

health effects studies summarized in the Criteria

Document and Staff Paper, but in selecting specific

levels for PM2.5 standards, is relying chiefly on U.S.

and Canadian studies, listed in Tables V-12 and V13 of the Staff Paper, that measured fine PM levels.

To ease identification and use of these key studies,

the short-term exposure studies and key PM air

quality statistics are cited in Koman (1996) and all

long-term exposure studies are cited in this

preamble. The referenced memorandum (Koman,

1996) has been updated (Koman, 1997) to clarify

key aspects of the studies cited and relevant air

quality statistics. In accordance with EPA and

CASAC views on the relative strength of these

studies, greater weight is placed on short-term

exposure studies than on long-term exposure

studies. Where studies found statistically

significant associations with PM2.5 components

(e.g., sulfates and/or acids, in Thurston et al., 1994;

Dockery et al., 1996), the corresponding PM2.5 or

PM2.1 values from the study are cited. No

conversions were made from the original

measurements used in these studies.

high as approximately 95 μg/m3 24-hour

average and 27 μg/m3 annual average.

Having evaluated these comments, the

Administrator rejects both their

underlying rationale and the specific

recommendations for PM2.5 standard

levels that result in similar or only

marginally more protection than that

afforded by the current PM10 standards.

Aside from technical problems in the

commenters’ supporting analyses on the

issue of defining ‘‘equivalent’’

standards,37 the Administrator finds this

approach inconsistent with her

conclusions regarding the adequacy of

the current standards and the need to

provide additional protection as

articulated in Unit II.B. of this preamble.

The Administrator believes that, despite

well recognized uncertainties, the

consistency and coherence of the

epidemiological evidence and the

seriousness of the health effects require

a more protective response than

provided by ‘‘equivalence’’ or a

marginal strengthening of the standards.

Moreover, EPA believes that the

standard levels should be based on the

most recent assessment of the scientific

criteria for PM, not on applying

uncertain ratios to standard decisions

based on much more limited evidence

in 1987. The Administrator also rejects

the premise of some38 who suggest that

adopting a standard that prompts little

or no additional control would cause no

delay in risk reduction as compared to

conducting monitoring and research

now and setting a more stringent

standard after the next review. These

comments do not consider the realities

of implementing air quality standards,

which ensure that such an approach

would add several years to the risk

reduction process. Thus, aside from her

obligations under the statute,39 the

Administrator believes that the most

prudent and appropriate course is to

establish appropriately protective

standards now that put into motion

monitoring and strategy development

programs, while at the same time

pursuing an expanded research program

to improve implementation and to

inform the next periodic review of the

criteria and standards.

In sharp contrast to the commenters

discussed immediately above, a number

of other commenters strongly supported

standard levels more stringent than

those proposed by EPA. These

commenters supported EPA’s

conclusions regarding the

epidemiological studies, but would

place much less weight on uncertainties

related to the concentration-response

relationships for PM2.5 as a surrogate for

PM and the relative importance of

various PM components. Based on their

evaluation of the information, and citing

the support of some CASAC panel

members, these commenters variously

recommended 24-hour PM2.5 standards

as low as 18 to 20 μg/m3 and annual

standards of 10 to 12 μg/m3.40

EPA notes that setting such standards

would result in commensurate

reductions in health risks only if, in

fact, there is a continuum of health risks

down to the lower end of the ranges of

air quality observed in the key

epidemiological studies, and only if the

reported associations are, in fact,

causally related to PM2.5 at the lowest

concentrations measured. Setting

standards at low levels where the

possibility of effects thresholds is

greater, and where there is greater

potential that other elements in the air

pollution mix (or some subset of

particles within the fine fraction)

become more responsible for (or modify)

the effects being causally attributed to

PM2.5, might result in regulatory

programs that go beyond those that are

needed to effectively reduce risks to

public health. While placing substantial

weight on the results of the key health

studies in the higher range of

concentrations observed, EPA is

persuaded that the inherent scientific

uncertainties are too great to support

standards based on the lowest

concentrations measured in such

studies, which approach the maximum

range of PM2.5 values estimated for

short-term background conditions.

Having considered the comments

reflecting the two contrasting views

summarized above in this unit, the

Administrator concludes that the

approach she set forth in the proposal

is the most appropriate for selecting

levels for annual and 24-hour PM2.5

standards. This approach focuses

primarily on standard levels designed to

limit annual PM2.5 concentrations to

somewhat below those where the body

of epidemiological evidence is most

consistent and coherent, in recognition

of both the strengths and the limitations

of the full range of scientific and

technical information on the health

effects of PM, as well as associated

uncertainties, as interpreted by the

Criteria Document, Staff Paper, and

CASAC. The Administrator believes that

this approach appropriately reflects the

weight of the evidence as a whole.

In identifying PM2.5 standard levels

consistent with this overall approach,

the Administrator has placed greatest

weight on those epidemiological studies

reporting associations between health

effects and direct measures of fine

particles, most notably those recent

studies conducted in North America

(summarized in Tables V-12 and V-13 of

the Staff Paper).41 Key considerations

and study results upon which this

approach is based are presented as

follows.

As previously discussed, the

Administrator has concluded that it is

appropriate to select the level of the

annual standard so as to protect against

the range of effects associated with both

short- and long-term exposures to PM,
38676 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

42 As discussed in the proposal and Appendix E

of the Staff Paper (U.S. EPA, 1996b, p. E-4), there

is generally greatest statistical confidence in

observed associations for levels at and above the

mean concentration.

43 Based on a public comment, EPA found that

the mean of 18 μg/m3 in Pope et al. (1995) reported

in the Criteria Document and elsewhere was

actually the mean of median values. Based on

typical air quality relationships, the conventional

arithmetic mean would be approximately 21 to 22

μg/m3 (Freas, 1997). The lowest median

concentration measured in this study (9 μg/m3),

which was relied upon by some commenters as a

basis for annual standards of 10 μg/m3, is about 11

to 12 μg/m3 as an arithmetic mean.

44 Based on public comments and a further

evaluation of the underlying study, EPA concludes

that the comparable assessment of the

concentration-response function summarized in

Table E-3 for Pope et al. (1995) is not appropriate,

because it was based on a supplemental ‘‘ecologic’’

comparison for these cities and not on the far more

reliable prospective-cohort analysis that was the

main focus of the paper.

with the 24-hour standard level selected

to provide supplemental protection

against peak concentrations that might

occur over limited areas and/or for

limited time periods. In selecting the

level for the annual standard, therefore,

the Administrator has considered both

short- and long-term exposure studies.

In accordance with EPA staff and

CASAC views on the relative strengths

of the epidemiological studies, the

Administrator has placed greater

emphasis on the short-term exposure

studies in selecting the level of the

annual standard. The approach she took

to this issue consisted of determining a

provisional level based on the shortterm exposure studies, and then

determining whether the long-term

exposure studies are consistent with

that level or, instead, suggest the need

for a lower level. The effects estimates

from the short-term exposure studies (in

Table V-12 of the Staff Paper) are based

on analyses of daily PM2.5

concentrations that occurred over the

course of the study period. While effects

may occur over the full range of

concentrations observed in the studies,

consistent with the discussion of this

issue in Unit II.D. of this preamble, the

strongest evidence for short-term PM2.5

effects occurs at concentrations near the

long-term (e.g., annual) average. More

specifically, the strength of the evidence

of effects increases for concentrations

that are at or above the long-term (e.g.,

annual) mean levels reported for these

studies.42 Given the serious nature of

the potential effects, the Administrator

believes it is both prudent and

appropriate to select a level for an

annual standard at or below such

concentrations. An examination of the

long-term means from the combined six

city analyses of daily mortality

(Schwartz et al., 1996a) and morbidity

(Schwartz et al., 1994), together with

those from studies in individual cities

for which statistically significant PMeffects associations are reported (from

Table V-12 in the Staff Paper), finds

mean concentrations ranging from about

16 to about 21 μg/m3 (Koman, 1996;

1997). In addition, the mean

concentrations in cities where shortterm exposure associations are

characterized in the Criteria Document

as nearly statistically significant (U.S.

EPA, 1996a, p. 13-40) range from about

11 μg/m3 to 30 μg/m3. Taken together,

and placing greatest weight on those

studies that were clearly statistically

significant, this evidence suggests that

an annual standard level of 15 μg/m3 is

appropriate to reduce the risk of effects

from short-term exposure to fine

particles.

Before reaching a final conclusion, the

Administrator also examined this level

in light of the effects reported in

epidemiological studies of long-term

exposures to fine particles (Table V-13

in the Staff Paper), which may reflect

the accumulation of daily effects over

time as well as potential effects

uniquely associated with long-term

exposures. Even though subject to

additional uncertainties, the long-term

exposure studies provide important

insights with respect to the overall

protection afforded by an annual

standard. These studies were examined

for general consistency and support for

the levels derived from the short-term

exposure studies, and to determine

whether they provide evidence that a

more stringent level is needed.

The most direct comparison with the

daily fine particle mortality studies is

provided by two long-term prospective

cohort studies (Dockery et al., 1993;

Pope et al., 1995). The annual mean

PM2.5 concentration for the multiple

cities included in these studies (6 and

50 cities, respectively) was 18 μg/m3

(Dockery et al., 1993), and about 21-22

μg/m3 for the larger Pope et al. (1995)

study.43 The Staff Paper assessment of

the concentration-response results from

Dockery et al. (1993) concluded that the

evidence for increased risk was more

apparent at annual concentrations at or

above 15 μg/m3 (Table E-3; U.S. EPA;

1996b).44 EPA notes that the estimated

mean values for most of the cities in

Pope et al. (1995) are above 15 μg/m3.

As noted in the Staff Paper and the

Criteria Document, the estimated

magnitude of effects in both long-term

exposure mortality studies may be

related to higher historical

concentrations than the affected

communities experienced during the

time period of the studies; this

consideration suggests that a level of 15

μg/m3 would incorporate a margin of

safety. An examination of morbidity

effects and long-term exposures is

provided by the recent ‘‘24 city’’

studies, which found that reduced lung

function and increased respiratory

symptoms in children followed the

gradient in annual mean concentrations

of fine particles and/or acid-sulfate

components of fine particles (Raizenne

et al., 1996; Dockery et al., 1996). The

results indicate a greater likelihood of

effects at annual mean PM2.1 levels

above about 15 μg/m3 (U.S. EPA, 1996b;

Figure V-7). In the judgment of the

Administrator, these studies are

consistent with a standard level of 15

μg/m3. While they provide some

suggestion of risks extending to lower

concentrations, they do not provide a

sufficient basis for establishing a lower

annual standard level.

Taking the epidemiological studies of

both short- and long-term exposures

together, the Administrator believes the

concordance of evidence for PM effects

and associated levels provides clear

support for an annual PM2.5 standard

level of 15 μg/m3. This level is below

the range of annual data most strongly

associated with both short- and longterm exposure effects, and because even

small changes in annual means in this

concentration range can make

significant differences in overall risk

reduction and total population

exposures, the Administrator believes it

will provide an adequate margin of

safety against the effects observed in

these epidemiological studies.

Moreover, the means in areas where

PM2.5 concentrations were statistically

significantly associated with daily

mortality (about 16 to 21 μg/m3) reflect

a 7 to 9-year average; thus, the use of a

3-year mean will provide additional

protection. Although the possibility of

effects at lower annual concentrations

cannot be excluded, the evidence for

that possibility is highly uncertain and,

as previously discussed, the likelihood

of significant health risk, if any,

becomes smaller as concentrations

approach the lower end of the range of

air quality observed in the key

epidemiological studies and/or

background levels.

The final annual standard will

provide substantial protection against

short-term as well as long-term

exposures to particles. Nevertheless, for

the reasons specified above, a spatially

averaged annual standard cannot be

expected to offer an adequate margin of

safety against the effects of all potential

short-term exposures in areas with

strong local or seasonal sources. The
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38677

broad-based community studies

considered in this review generally

could not evaluate such peak exposure

conditions directly. Given the public

health purposes of the 24-hour standard,

the Administrator believes it should be

set at a level that generally supplements

the control afforded by an annual

standard and proposed an approach

based on providing a reasonable degree

of protection against the peak levels

observed or expected in communities

where health effects have been

associated with daily levels of fine

particles.

For the reasons specified in the

previous unit, the Administrator has

decided to use a 98th percentile

concentration-based form of the

standard. As noted in the proposal, the

98th percentile 24-hour PM2.5

concentrations in cities with statistically

significant or nearly significant shortterm fine particle exposure-effects

associations ranged from 34 μg/m3 to as

high as 90 μg/m3 (Koman, 1996, 1997).

Based on an examination of these

results, EPA originally proposed a level

for the 24-hour standard of 50 μg/m3,

and solicited comments on higher and

lower alternative levels.

In considering comments on

alternative levels for the purpose of

making a final decision on the 24-hour

standard, the Administrator recognizes

the significant uncertainties in

identifying the extent of the incremental

risk associated with single peak

exposures to PM2.5 in areas where the

annual standard is met. Clearly, the

risks associated with the 98th percentile

air quality data used in the selecting the

proposed level are from the same study

cities that experienced long-term levels

at varying amounts above that selected

for the annual standard. It is unclear

what risks might have been associated

with such peak levels had the long-term

averages in these areas been below that

selected for the annual standard.

Regardless of this uncertainty, it is clear

that reducing the annual concentrations

in such areas to that of the annual

standard would reduce the risk

associated with peak days, whatever the

magnitude, as well as that associated

with the far more numerous days with

concentrations near the annual average.

Given these uncertainties and the

significant degree of protection afforded

by the annual standard, the

Administrator is persuaded that it is

appropriate to adopt a different

approach for selecting the levels of the

24-hour standard than the one

proposed.

In making a final decision on an

appropriate level for the 24-hour

standard, the Administrator considered

several key factors: the significant

protection afforded against short-term

exposures by the annual PM2.5 standard;

the role of the 24-hour standard in

providing supplemental protection

against peak exposures not addressed by

the annual standard; the air quality and

effects information in the studies cited

above; the uncertainties in the risks

associated with infrequent and isolated

peak exposures in areas that meet the

annual standard; the range of levels

recommended by EPA staff and CASAC

panel members; and the extensive

public comment on the alternative

levels proposed, which ranged between

20 and 65 μg/m3. Because of the

approach of establishing the annual

standard as the controlling standard,

and, in particular, the decision to set the

level at the lower end of the annual

range, there is no need to consider

levels in the lower portion of the 24-

hour range below the level proposed.

Therefore, the Administrator focused on

evaluating the margin of safety

associated with levels between 50 and

65 μg/m3.

As has been discussed in previous

units, the extent of total risk over the

course of a year associated solely with

a limited number of peak exposures is

uncertain, but it is considerably smaller

than that associated with the entire air

quality distribution. Further, the risk

associated with infrequent peak 24-hour

exposures in otherwise clean areas is

not well enough understood at this time

to provide a basis for selecting the more

restrictive levels in the range of 50 to 65

μg/m3. On the other hand, it is clear that

any standard level within this range

would provide some margin of safety.

Taking into account the factors outlined

above, the Administrator has concluded

that a 24-hour standard at the level of

65 μg/m3 would provide an effective

limit in the role as a supplement to the

annual standard. This level is at the

upper end of the range recommended by

staff and most CASAC panel members,

and below the levels suggested by some

CASAC panel members and by a

number of public commenters.

Although this level is not risk free, the

Administrator believes that it would

provide an appropriate degree of

additional protection over that provided

by the annual PM2.5 standard.

Accordingly, after weighing these

factors in light of the scientific

uncertainties, the Administrator

believes that a 98th percentile 24-hour

PM2.5 standard of 65 μg/m3 would

provide an adequate margin of safety

against infrequent or isolated peak

concentrations that could occur in areas

that attain the annual standard of 15 μg/

m3.

In the Administrator’s judgment, the

factors discussed above provide ample

reason to believe that both annual and

24-hour PM2.5 standards are appropriate

to protect public health from adverse

health effects associated with short- and

long-term exposures to ambient fine

particles. Further, she believes these

factors provide a clear basis for judging

that an annual PM2.5 standard set at 15

μg/m3, in combination with a 24-hour

standard set at 65 μg/m3, will protect

public health with an adequate margin

of safety.

G. Conclusions Regarding the Current

PM10 Standards

1. Averaging time and form. In

conjunction with PM2.5 standards, the

new function of PM10 standard(s) is to

protect against potential effects

associated with coarse fraction particles

in the size range of 2.5 to 10 μm. Coarse

fraction particles are plausibly

associated with certain effects from both

long- and short-term exposures (EPA

1996a,b). Based on qualitative

considerations, deposition of coarse

fraction particles in the respiratory

system could be expected to aggravate

effects in individuals with asthma. The

Criteria Document and Staff Paper

found support for this expectation in

limited epidemiological evidence on the

effects of coarse fraction particles,

suggesting that aggravation of asthma

and respiratory infections and

symptoms may be associated with daily

or episodic increases in PM10 that are

dominated by coarse fraction particles.

The potential build-up of insoluble

coarse fraction particles in the lung after

long-term exposures to high levels

should also be considered.

Based on assessments of the available

information in the Criteria Document

and Staff Paper, both the staff and

CASAC recommended retention of an

annual PM10 standard. The staff, with

CASAC concurrence, recommended

retention of the current annual

arithmetic mean form of the standard,

which is the same form being adopted

for the annual PM2.5 standard. As noted

in the staff assessment, the current

annual PM10 standard offers substantial

protection against the effects of both

long- and short-term exposure to coarse

fraction particles. Public comment was

nearly unanimous in recommending

retention of this standard. The

Administrator therefore has decided to

continue a long-term PM10 standard as

an annual arithmetic mean, averaged

over 3 years.

The staff and CASAC also

recommended that consideration be
38678 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

45 Some commenters, including some

environmental groups and the State of California

(Cal EPA, 1997), suggested that the large number of

recent studies showing effects at PM10 levels below

the current standards provides a basis for

establishing stricter annual and 24-hour PM10

standards, in conjunction with PM2.5 standards. As

discussed in Units II.B. and C. of this preamble,

while these studies could be used either to tighten

the PM10 standards or to add standards that tighten

control of the fine fraction of PM10, the weight of

evidence from all of the relevant information more

readily supports the development of additional

protection for the PM2.5 fraction.

given to retention of a 24-hour standard

to provide additional protection against

potential effects of short-term exposures

to coarse fraction particles. The staff,

with CASAC concurrence, also

recommended that if a 24-hour standard

is retained, the form of the standard

should be revised to provide a more

robust target for coarse fraction particle

controls. The Administrator originally

proposed a 98th percentile form for the

24-hour PM10 standard based primarily

on the reasons outlined above in this

unit regarding the proposed form of the

24-hour PM2.5 standard.

The EPA received few comments

supporting elimination of the 24-hour

PM10 standard. The main exceptions

were some industries, most notably the

mining industry, which as noted above

in this unit, argued that the available

data provide little evidence for coarse

particle effects at current ambient levels.

These groups, who generally opposed

PM2.5 standards, also argued that the

daily PM10 standard could be eliminated

if PM2.5 standards were set. Based on the

potential aggravation of respiratory

symptoms from short-term exposure to

coarse fraction particles discussed in the

Criteria Document and by numerous

commenters, as well as the

recommendations of a majority of

CASAC panelists who also supported

PM2.5 standards, the Administrator

concludes it is appropriate to retain a

24-hour PM10 standard.

In general, comments received on the

form of the 24-hour PM10 standard

paralleled those on the form of the PM2.5

standard. Substantial concerns were

expressed by environmental groups,

some States, and others that the 98th

percentile would not provide an

adequate limit on the number and

magnitude of 24-hour peak PM10

excursions. While a number of these

commenters suggested keeping the

current 1-expected-exceedance form,

EPA believes that a concentration- based

percentile form offers significant

advantages, as outlined above in this

unit, for both PM indicators. Some air

pollution control officials, who were

concerned about the extent to which the

24-hour PM10 standard would be

relaxed under the proposed form,

suggested consideration of a 99th

percentile form with increased

monitoring as an appropriately

protective form. Other commenters,

particularly some industry groups and

some States, strongly supported

concentration-based percentile forms,

with some recommending consideration

of the 95th percentile form.

The proposal noted that a percentile

value selected closer to the ‘‘tail’’ of the

air quality distribution (e.g., a 99th or

greater percentile) would not

significantly increase stability as

compared to the current form. However,

an association of 8 State air pollution

agencies commented that a 99th

percentile form could provide increased

stability if combined with a daily or 1-

in-3-day sampling frequency and with

greater data capture. In addition, EPA

notes that this concentration-based form

is inherently more stable than the

current exceedance-based form.

Many of these and other commenters

were concerned that the uncertainties in

the available scientific information on

the effects of coarse particles were a

reason to be concerned that, assuming

the current standard level was kept, a

98th percentile form would represent a

significant relaxation in protection

relative to the current standards. Unlike

the situation for the new PM2.5

standards, in the case of the PM10

standards, the 24-hour standard has

generally been the ‘‘controlling’’

standard, making changes to the form of

the 24-hour standard potentially more

significant to the overall national level

of protection afforded. Given the

uncertainties in the available scientific

evidence with respect to the potential

health effects of short-term exposures to

coarse fraction particles, the

Administrator is persuaded that the

somewhat more cautious approach with

respect to revising the 24-hour PM10

standard recommended by many

commenters is appropriate. The only

approaches available for increasing the

extent of protection for this standard as

compared to that of the proposed

standard involve modifying the form or

reducing the level. For reasons

discussed in the following section, the

Administrator believes it is not

appropriate to revise the level of the

standard. In order to provide adequate

protection against the potential risk

associated with multiple short-term

peak exposures to coarse fraction

particles, the Administator accepts

commenters’ recommendations to

decrease the frequency of peak values,

while still providing for a more stable

control target than afforded by the

current 1-expected-exceedance form.

Therefore, the Administrator concludes

that the 99th percentile concentrationbased form, averaged over 3 years, and

combined with more frequent sampling,

would be an appropriate form for a 24-

hour PM10 standard.

2. Levels for the annual and 24-hour

PM10 standards—a. Annual PM10

standard. As a result of the more limited

information for coarse fraction particles,

the Administrator’s approach for

selecting a level of the standard is

directly related to the approach taken in

the last review of the PM NAAQS. In

that review, evidence from limited

quantitative studies was used in

conjunction with support from the

qualitative literature in selecting the

level of the current annual PM10

standard. In the current review, the staff

assessment of the major quantitative

basis for the level of that standard (Ware

et al., 1986), together with a more recent

related study (Dockery et al., 1989),

recommended the same range of levels

of concern (40 to 50 μg/m3) as in the

1986 staff paper. The staff concludes

that it is possible, but not certain, that

coarse fraction particles, in combination

with fine particles, may have influenced

the observed effects at these levels.

Based on particle deposition

considerations, it is possible that

cumulative deposition of coarse fraction

particles could be of concern in

children, who are more prone to be

active outdoors than sensitive adult

populations.

Qualitative evidence of other longterm coarse particle effects, most

notably from long-term build-up of

silica-containing materials, supports the

need for a long-term standard, but does

not provide evidence of effects below

the range of 40 to 50 μg/m3 (U.S. EPA,

1996a, p. 13-79). The staff concludes

that the qualitative evidence with

respect to biological aerosols also

supports the need to limit coarse

materials, but should not form the major

basis for a national standard (U.S. EPA,

1996a, p. 13-79). In addition, staff notes

that the nature and distribution of such

materials, which vary from endemic

fungi (e.g., valley fever) to pollens larger

than 10 μm, are not appropriately

addressed by traditional air pollution

control programs.

Based on its review of the available

information, CASAC found ‘‘a

consensus that retaining an annual PM10

NAAQS at the current level is

reasonable at this time’’ (Wolff, 1996b).

With few exceptions, public comments

supported levels at least as stringent as

the current annual PM10 standard.45

Taking into account these comments

and the above considerations, as more

fully detailed in the Staff Paper and the
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38679

46 Congress adopted section 169A of the Act

because of concern that the NAAQS and Prevention

of Significant Deterioration programs might not

provide adequate visibility protection nationally,

particularly for ‘‘areas of great scenic importance.’’

See H.R. Rep. No. 95–294,at 203–205 (1977).

CASAC recommendations, the

Administrator has decided to retain the

current annual PM10 standard of 50 μg/

m3 to protect against the known and

potential effects of long-term exposure

to coarse fraction particles.

b. 24-hour PM10 standard. As

discussed above in this unit, EPA staff

and CASAC also recommended that

consideration be given to a 24-hour

standard for coarse fraction particles as

measured by PM10. Unlike the case for

the annual standard, however, the staff

found that the original quantitative basis

for the level of the current 24-hour PM10

standard (150 μg/m3) is no longer

appropriate. Instead, the staff found that

the main quantitative basis for a shortterm standard is provided by the two

recent community studies of exposure

to fugitive dust (Gordian et al., 1996;

Hefflin et al., 1994). Because these

studies reported multiple large

exceedances of the current 24-hour

standard, and because of limitations in

the studies themselves, the staff

concluded that they provide no basis to

lower the level of the standard below

150 μg/m3. Moreover, staff concluded

that none of the qualitative literature

regarding the potential effects of shortterm exposure to coarse particles

provides a basis for a lower standard

level. Both EPA staff and CASAC

recommended that if a 24-hour PM10

standard is retained, the level of the

standard should be maintained at 150

μg/m3, although with a revised form.

Beyond the comments summarized

above recommending elimination of the

24-hour standard, no commenters

recommended a less stringent level,

while some others, as summarized

above in this unit, recommended more

stringent levels. Most comments favored

the current level.

Having considered these factors and

the public comments, the Administrator

judges that, retention of a 24-hour PM10

standard at the level of 150 μ/m3 with

a 99th percentile form is appropriate and

will provide adequate protection against

the known and potential effects of shortterm coarse fraction particle exposures

that have been identified to date in the

scientific literature.

H. Final Decisions on Primary PM

Standards

For the reasons discussed above in

this unit, and taking into account the

information and assessments presented

in the Criteria Document and the Staff

Paper, the advice and recommendations

of CASAC, and public comments

received on the proposal, the

Administrator is revising the current PM

NAAQS by adding new PM2.5 standards

and by revising the form of the current

24-hour PM10 standard. Specifically, the

Administrator is making the following

revisions:

(1) The suite of PM standards is

revised to include an annual primary

PM2.5 standard and a 24-hour PM2.5

standard.

(2) The annual PM2.5 standard is met

when the 3-year average of the annual

arithmetic mean PM2.5 concentrations,

from single or multiple communityoriented monitors (in accordance with

EPA’s final rule on monitoring siting

guidance, 40 CFR part 58, published in

a separate document elsewhere in this

issue of the Federal Register) is less

than or equal to 15 μg/m3, with

fractional parts of 0.05 or greater

rounding up.

(3) The 24-hour PM2.5 standard is met

when the 3-year average of the 98th

percentile of 24-hour PM2.5

concentrations at each populationoriented monitor within an area is less

than or equal to 65 μg/m3, with

fractional parts of 0.5 or greater

rounding up.

(4) The form of the current 24-hour

PM10 standard is revised to be based on

the 3-year average of the 99th percentile

of 24-hour PM10 concentrations at each

monitor within an area.

In addition, the Administrator is

retaining the current annual PM10

standard at the level of 50 μg/m3, which

is met when the 3-year average of the

annual arithmetic mean PM10

concentrations at each monitor within

an area is less than or equal to 50 μg/

m3, with fractional parts of 0.5 or greater

rounding up.

As discussed below in Units V. and

VI. of this preamble, data handling

conventions and completeness criteria

for the revised standards are being

established (40 CFR part 50, Appendix

N). The reference method for monitoring

PM as PM10 for the revised standards

has been established (40 CFR part 50,

Appendix M). A new reference method

is being established for monitoring PM

as PM2.5 (40 CFR part 50, Appendix L).

In a separate document published

elsewhere in this issue of the Federal

Register, EPA is providing opportunity

for public comment on supplemental

information relating to the new

reference method for monitoring PM as

PM2.5 (40 CFR part 50, Appendix L).

As indicated previously, EPA plans to

propose related revisions to the

Pollutant Standards Index for PM (40

CFR 58.50) and the significant harm

level program (40 CFR 51.66) at a later

date.

III. Rationale for the Secondary

Standards

The Criteria Document and Staff

Paper examined the effects of PM on

such aspects of public welfare as

visibility, materials damage, and soiling.

The following discussion of the

rationale for revising the secondary

standards for PM focuses on those

considerations most influential in the

Administrator’s decision.

A. Need for Revision of the Current

Secondary Standards

1. Visibility impairment. This unit of

the document presents the

Administrator’s decision to address the

welfare effects of PM on visibility by

setting secondary standards identical to

the suite of PM2.5 primary standards, in

conjunction with the establishment of a

regional haze program under section

169A of the Act.46 In the

Administrator’s judgment, this approach

is the most effective way to address

visibility impairment given the regional

variations in concentrations of nonanthropogenic PM as well as other

regional factors that affect visibility,

such as humidity. By augmenting the

protection provided by secondary

standards set identical to the suite of

PM2.5 primary standards with a regional

haze program, the Administrator

believes that an appropriate degree of

visibility protection can be achieved in

the various regions of the country.

In coming to this decision, the

Administrator took into account several

factors, including: The pertinent

scientific and technical information in

the Criteria Document and Staff Paper,

difficulties inherent in attempting to

establish national secondary standards

to address visibility impairment, the

degree of visibility improvement

expected through attainment of

secondary standards equivalent to the

suite of PM2.5 primary standards, the

effectiveness of addressing the welfare

effects of PM on visibility through the

combination of a regional haze program

and secondary standards for PM2.5

equivalent to the suite of primary

standards, and comments received

during the public comment period. The

Administrator’s consideration of each of

these factors is discussed below in this

unit.

The Administrator first concluded,

based on information presented and

referenced in the Criteria Document and
38680 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

47 There are 156 mandatory Class I Federal areas

protected by the visibility provisions in sections

169A and 169B of the Act. These areas are defined

in section 162 of the Act as those national parks

exceeding 6,000 acres, wilderness areas and

memorial parks exceeding 5,000 acres, and all

international parks which were in existence on

August 7, 1977.

48 Visual range can be defined as the maximum

distance at which one can identify a black object

against the horizon sky. It is typically described in

miles or kilometers. Light extinction is the sum of

light scattering and absorption by particles and

gases in the atmosphere. It is typically expressed in

terms of inverse megameters (Mm-1), with larger

values representing poorer visibility. The deciview

metric describes perceived visual changes in a

linear fashion over its entire range, analogous to the

decibel scale for sound. A deciview of 0 represents

pristine conditions. Under many scenic conditions,

a change of 1 deciview is considered perceptible by

the average person.

49 Congress adopted a visibility protection

program in section 169A of the Act because it

recognized the impracticability of revising the

NAAQS to protect visibility in all areas of the

country: ‘‘It would be impracticable to require a

major city such as New York or Los Angeles to meet

the same visibility standards as the Grand Canyon

and Yellowstone Park.’’ See H.R. Rep. No. 95–294

at 205. (1977)

50 Estimates of annual average visibility

improvements assume that, on a percentage basis,

the reduction for each fine particle component is

equal to the % reduction in the mass of fine

particles, and that the overall light extinction

efficiency of the fine particle pollutant mix does not

change. Further, for the estimates presented here,

the reductions in fine mass at monitored locations

are assumed to reflect the spatial average

concentrations through the viewing distance.

(Damberg and Polkowsky, 1996.)

Staff Paper, that particulate matter can

and does produce adverse effects on

visibility in various locations,

depending on the PM concentrations

involved and other factors discussed

below. It has been demonstrated that

impairment of visibility is an important

effect of PM on public welfare, and that

it is experienced throughout the United

States, in multi-state regions, urban

areas, and remote mandatory Class I

Federal areas47 alike. Visibility is an

important welfare effect because it has

direct significance to people’s

enjoyment of daily activities in all parts

of the country. Individuals value good

visibility for the well-being it provides

them directly, both where they live and

work, and in places where they enjoy

recreational opportunities. Visibility is

highly valued in significant natural

areas, such as national parks and

wilderness areas, because of the special

emphasis given to protecting these lands

now and for future generations. The

Criteria Document cites many studies

designed to quantify the benefits

associated with improvements in

visibility.

The Administrator considered

information from the Staff Paper and

Criteria Document regarding the effect

of the composition of particulate matter

on visibility. Visibility conditions are

determined by the scattering and

absorption of light by particles and

gases, from both natural and

anthropogenic sources. Visibility can be

described in terms of visual range, light

extinction, or deciview48. The classes of

fine particles principally responsible for

visibility impairment are sulfates,

nitrates, organic matter, elemental

carbon (soot), and soil dust. Fine

particles are more efficient per unit

mass at scattering light than coarse

particles. The scattering efficiency of

certain classes of fine particles, such as

sulfates, nitrates, and some organics,

increases as relative humidity rises

because these particles can absorb water

and grow to sizes comparable to the

wavelength of visible light. In addition

to limiting the distance that one can see,

the scattering and absorption of light

caused by air pollution can also degrade

the color, clarity, and contrast of scenes.

The Administrator next considered

what would be an appropriate level for

a secondary standard to address adverse

effects of particulate matter on visibility.

The determination of a single national

level is complicated by regional

differences in visibility impairment due

to several factors, including background

and current levels of PM, composition

of particulate matter, and average

relative humidity.

The Criteria Document and Staff

Paper describe estimated background

levels of PM and natural light

extinction. In the United States,

estimated annual mean background

levels of PM2.5 are significantly lower in

the West than in the East. Based on

estimated background fine particle and

light extinction levels summarized in

Table VIII-2 of the Staff Paper, naturally

occurring visual range in the East is

approximately 105 to 195 kilometers,

whereas in the West it is approximately

190 to 270 kilometers. This significant

regional difference in estimated

background conditions results from two

main factors. First, in the western

United States, visibility is more

sensitive to an additional 1–2 μg/m3 of

PM2.5 in the atmosphere than in the

eastern United States. Secondly, light

scattering is increased for certain

particles (e.g., sulfates, nitrates, and

some organics) due to higher average

relative humidity in the East.

The combination of naturally

occurring and manmade emissions also

leads to significant differences in

current visibility conditions between

the eastern United States, 23–39

kilometers average visual range, and

western United States, 55–150

kilometers average visual range. Table

VIII-4 of the Staff Paper indicates that

the current level of annual average light

extinction in several western locations,

such as the Colorado Plateau, is about

equal to the level of background light

extinction, i.e., the level generally

regarded as representing the absence of

anthropogenic emissions in North

America, in the East. This regional

difference is due to higher background

particle concentrations in the East, a

composition of fine particles in the East

that, in association with higher eastern

humidity levels, is more efficient at

light scattering, and significantly lower

concentrations of anthropogenic PM in

remote western locations as compared

with remote eastern sites.

Because of these regional differences,

it is the Administrator’s judgment that

a national secondary standard intended

to maintain or improve visibility

conditions on the Colorado Plateau or

other parts of the West would have to

be set at or even below natural

background levels in the East, which

would effectively require elimination of

all eastern anthropogenic emissions.

Conversely, a national secondary

standard that would achieve an

appropriate degree of visibility

improvement in the East would permit

further degradation in the West. Due to

this regional variability in visibility

conditions created by differing

background fine particle levels, fine

particle composition, and humidity

effects, the Administrator finds that

addressing visibility solely through

setting more stringent national

secondary standards would not be an

appropriate means to protect the public

welfare from adverse impacts of PM on

visibility in all parts of the country.49

Aside from the problem of regional

variability, the Administrator has also

determined that the Agency currently

lacks sufficient information to establish

a level for a national secondary standard

that would represent a threshold above

which visibility conditions would

always be adverse and below which

visibility conditions would always be

acceptable. Because visibility varies not

only with PM concentration, but also

with PM composition and humidity

levels, attaining even a low

concentration of fine particles might or

might not provide adequate protection,

depending on these factors.

The Administrator next assessed

potential visibility improvements50 that

would result from attainment of the new

primary standards for PM2.5. The

spatially averaged form of the annual

standard is well suited to the protection

of visibility, which involves effects of

PM throughout an extended viewing

distance across an urban area. Indeed, as
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38681

51 IMPROVE (Interagency Monitoring of

PROtected Visual Environments) is a visibility

monitoring network managed cooperatively by EPA,

Federal land management agencies, and State

representatives. An analysis of IMPROVE data for

1992–1995 is found in Sisler et al. (1996).

the generally controlling standard

focused on reducing urban and regional

scale fine particle levels, most of the

visibility protection provided by the

PM2.5 primary standards would be

derived from the annual standard. In

many cities having annual mean PM2.5

concentrations exceeding 17 μg/m3,

improvements in annual average

visibility resulting from attainment of

the new annual PM2.5 primary standard

are expected to be perceptible (i.e., to

exceed 1 deciview). Based on annual

mean PM2.5 data reported in Table 12-

2 of the Criteria Document and Table V12 in the Staff Paper, many cities in the

Northeast, Midwest, and Southeast, as

well as Los Angeles, would be expected

to see perceptible improvement in

visibility if the annual PM2.5 primary

standard is attained.

In Washington, DC, for example,

where the IMPROVE network51 shows

annual mean PM2.5 concentrations at

about 19 μg/m3 during 1992–1995,

approximate annual average visibility

would be expected to improve from 21

km visual range (29 deciview) to 27 km

(27 deciview). Annual average visibility

in Philadelphia, where annual PM2.5

levels have been recently measured at

17 μg/m3, would be expected to change

from about 24 to 27 km, an

improvement of about 1 deciview. In

Los Angeles, where recent data shows

annual mean PM2.5 concentrations at

approximately 30 μg/m3, visibility

would be expected to improve from

about 19 to 34 km (30 to 24 deciview)

if the new annual primary PM2.5

standard is attained.

It is important to note that some urban

areas, many in the eastern United States,

would be expected to have annual mean

PM2.5 concentrations reduced below the

primary standard level of 15 μg/m3

when implementation of regional

control strategies for PM and other air

quality programs, such as those

addressing acid rain and mobile

sources, are taken into account together.

On the other hand, some urban areas

with annual PM2.5 levels at or below the

15 μg/m3 level would be expected to see

little, if any, improvement in annual

average visibility. This may be

particularly true of certain western

urban areas that are dominated by

coarse rather than fine particles.

The Administrator also considered

the potential effect on urban visibility if

the 24-hour 98th percentile PM2.5

standard of 65 m3 is attained. In areas

with violations caused by localized hot

spots, the 24-hour standard might have

little effect other than on visible source

emissions. In other areas, for example,

with seasonally high woodsmoke, a

more areawide improvement is possible.

In such urban areas, attainment of the

24-hour standard would be expected to

reduce, to some degree, the number and

intensity of ‘‘bad visibility’’ days, i.e.,

the 20% of days having the greatest

impairment over the course of a year.

For example, maximum 24-hour PM2.5

concentrations have been recorded in

recent years at over 140 μg/m3 at several

California locations. If the level and

frequency of peak PM concentrations

are reduced, improvements would be

expected in those days where visibility

is worst, even in urban areas having

annual averages below the annual PM2.5

primary standard.

Having concluded that attainment of

the annual and 24-hour PM2.5 primary

standards would lead to visibility

improvements in many eastern and

some western urban areas, the

Administrator also considered potential

improvements to visibility on a regional

scale. In the rural East, attainment of the

PM2.5 primary standards could result in

regional visibility improvement, e.g., in

certain mandatory Class I Federal areas

such as Shenandoah and Great Smoky

Mountains National Park, if regional

control strategies are adopted and

carried out in order to reduce the impact

of long-range transport of fine particles

such as sulfates. Fine particle emission

reductions achieved by other air quality

programs, such as those to reduce acid

rain or mobile source emissions, are also

expected to improve Eastern regional

visibility conditions (U.S. EPA, 1993).

In the West, strategies to attain the

primary PM2.5 standards are less likely

to significantly improve visibility on a

regional basis. However, areas

downwind from large urban areas, such

as Southern California, would likely see

some improvement in annual average

visibility.

Based on the foregoing, the

Administrator concludes that

attainment of PM2.5 secondary standards

set at the level of the primary standards

for PM2.5 would be expected to result in

visibility improvements in the eastern

United States at both urban and regional

scales, but little or no change in the

western United States except in and

near certain urban areas. Additionally,

the Administrator determined that

attainment of secondary standards

equivalent to the suite of PM2.5 primary

standards for particulate matter would

address some but not all of the effects

of particulate matter on visibility. The

extent to which these effects would be

addressed is expected to vary regionally.

The Administrator then considered

the potential effectiveness of a regional

haze program to address the remaining

effects of particulate matter on visibility

(i.e., those that would not be addressed

through attainment of secondary

standards identical to the suite of PM2.5

primary standards). A program to

address the widespread, regionally

uniform type of haze caused by a

multitude of sources is required by

sections 169A and 169B of the Act. In

1977, Congress established as a national

goal ‘‘the prevention of any future, and

the remedying of any existing,

impairment of visibility in mandatory

Class I Federal areas which impairment

results from manmade air pollution’’,

section 169A(a)(1) of the Act. The EPA

is required by section 169A(a)(4) of the

Act to promulgate regulations to ensure

that ‘‘reasonable progress’’ is achieved

toward meeting the national goal. EPA

originally deferred establishment of a

program to address regional haze in

1980 due to the need for greater

scientific and technical knowledge, but

the current Criteria Document and Staff

Paper cite information supporting the

Administrator’s conclusion that the

scientific state of understanding and

analytical tools are now adequate to

develop such a program. Because

regional emission reductions are needed

to make visibility improvements in

mandatory Class I Federal areas, the

structure and requirements of sections

169A and 169B of the Act, provide for

visibility protection programs that can

be more responsive to the factors

contributing to regional differences in

visibility than can programs addressing

a nationally applicable secondary

NAAQS. The visibility goal is more

protective than a secondary NAAQS

since the goal addresses any man-made

impairment rather than just impairment

at levels determined to be adverse.

Thus, an important factor considered

in this review is whether a regional haze

program, in conjunction with secondary

standards set identical to the suite of

PM2.5 primary standards, would provide

appropriate protection for visibility in

non-Class I areas. The Administrator

continues to believe that the two

programs and associated control

strategies should provide such

protection due to the regional

approaches needed to manage emissions

of pollutants that impair visibility in

many of these areas. Regional strategies

implemented to attain the NAAQS, meet

other air program goals, and make

reasonable progress toward the national

visibility goal in mandatory Class I

Federal areas are expected to improve
38682 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

52 EPA established the Grand Canyon Visibility

Transport Commission (GCVTC) in 1991 under

section 169B of the Act. Section 169B(d) requires

visibility transport commissions to assess the

‘‘adverse impacts on visibility from potential or

projected growth in emissions’’ and to recommend

to EPA measures to remedy such adverse impacts.

The Commission issued its final report in June

1996.

53 The Southern Appalachian Mountain Initiative

is a voluntary effort begun in 1993. Participants

include eight southeastern States, Federal land

managers, EPA, and representatives from industry

and environmental groups. A final report has not

been issued to date.

54 Indeed, Congress recognized when it adopted

section 169A that the ‘‘visibility problem is caused

primarily by emission into the atmosphere of sulfur

dioxide, oxides of nitrogen and particulate matter,

especially fine particulate matter, from

inadequately controlled sources.’’ H.R. Rep. No. 95–

294 at 204 (1977).

visibility in many urban and non-Class

I areas as well. The following

recommendation from the 1993 report of

the National Research Council,

Protecting Visibility in National Parks

and Wilderness Areas, addresses this

point:

Efforts to improve visibility in Class I areas

also would benefit visibility outside these

areas. Because most visibility impairment is

regional in scale, the same haze that degrades

visibility within or looking out from a

national park also degrades visibility outside

it. Class I areas cannot be regarded as

potential islands of clean air in a polluted

sea.

Before making a final decisions on the

secondary standards, the Administrator

also considered a number of public

comments that addressed this aspect of

the proposal. Some commenters

suggested setting secondary standards

for PM2.5 more stringent than the

proposed primary standards for the

purpose of addressing visibility

impairment and other environmental

effects. For the reasons discussed above

in this unit, however, the Administrator

has concluded that this may not be an

effective and would not be an

appropriate means of protecting against

visibility impairment in all parts of the

country. Other commenters raised the

possibility of establishing a nationally

applicable secondary standard defined

as a ‘‘floor,’’ or increment, above

regionally specific background levels of

PM2.5 or associated visibility. Although

this idea is of interest and may warrant

further study, the Administrator

determined that it was not appropriate

to pursue such an approach at this time

for two principal reasons. First, the

Agency does not currently have

adequate scientific information to

establish a specific floor or increment

level that would protect against adverse

effects nationally, nor is it clear as a

conceptual matter whether further

information would support selection of

a single, uniform increment as

providing an appropriate degree of

protection in all areas of the country.

Second, there are serious, unresolved

questions about whether such an

approach is consistent with the

statutory language and purposes of

section 109 of the Act.

Other commenters argued that

national secondary standards equivalent

to the proposed PM2.5 primary standards

are not necessary or not supported by

the Administrator’s findings. As noted

earlier, however, it is clear that coarse

and fine particles can cause adverse

effects on visibility and significant

quantitative data exist to demonstrate

that visibility impairment occurs at

small concentrations of PM2.5.

Substantial efforts have been put forth

to assess the effects of PM on visibility.

For example, the Grand Canyon

Visibility Transport Commission52 spent

several years and significant effort

studying the effects of pollution on 16

mandatory Class I Federal areas on the

Colorado plateau and has made

recommendations to the Administrator

for actions to improve visibility in these

areas (GCVTC, 1996). All of the

mandatory Class I Federal areas studied

by the GCVTC with monitoring data

have annual mean PM2.5 concentrations

below 5 μg/m3 (Sisler, 1996) while also

documenting anthropogenic visibility

impairment. The Southern Appalachian

Mountain Initiative53 is currently

assessing air pollution impacts on

visibility, terrestrial resources, and

aquatic resources in the southeastern

U.S. in order to recommend measures to

remedy existing and prevent future

adverse effects on these air quality

related values. The IMPROVE network

shows that all of the mandatory Class I

Federal areas in the SAMI region have

annual mean PM2.5 concentrations for

1992–95 between 11.0–13.5 μg/m3

(Sisler, 1996). The inclusion in section

169A of the Act of a national visibility

goal of no manmade impairment also

places significant value on reducing PM

concentrations and resulting visibility

impairment to low levels.54 The

differences between the fine particle

levels associated with visibility

impairment in eastern and western

mandatory Class I Federal areas provide

further impetus to act under the

provisions of sections 169A and 169B

enabling the Administrator to establish

a regionally-tailored visibility program

to address impairment of visibility in

mandatory Class I Federal areas. For

these reasons, the Administrator has

concluded that a national regional haze

program allowing for regional

approaches to addressing fine particle

pollution, combined with a nationally

applicable level of protection achieved

through secondary PM2.5 standards set

equal to the suite of primary standards,

would be more effective in addressing

regional variations in the adverse effects

of PM2.5 on visibility than establishing

national secondary standards for

particulate matter that are lower than

the suite of PM2.5 primary standards.

The Administrator emphasizes that in

order to appropriately address the

regional differences in adverse effects of

particulate matter on visibility, it is

essential to establish secondary

standards for PM2.5 equivalent to the

primary standards and an effective new

regional haze program. A regional haze

program will be particularly important

in those areas of the country that do not

exceed any of the primary standards for

PM2.5, yet still experience significant

visibility impairment due to particulate

matter. The EPA will propose a regional

haze regulation in the near future.

In addition to providing a more

regionally tailored approach than

establishing a more stringent national

secondary standard, an effective

regional haze program will also fulfill

the Administrator’s regulatory

responsibility under sections 169A and

169B of the Act to address both

reasonably attributable impairment and

regional haze impairment in mandatory

Class I Federal areas. Indeed, regional

haze has been shown to be the principal

cause of visibility impairment in

mandatory Class I Federal areas today.

Thus, the promulgation of a regional

haze program in conjunction with

secondary standards for PM2.5

equivalent to the suite of primary

standards will serve as an appropriate

approach for addressing adverse effects

of visibility that vary regionally, and it

will also establish a comprehensive

program for making reasonable progress

toward the national visibility goal in

mandatory Class I Federal areas by

addressing visibility impairment in the

form of both source-specific impacts

and regional haze. Further, the regional

haze rulemaking will fulfill the

Administrator’s responsibilities to

address the visibility protection

recommendations of the Grand Canyon

Visibility Transport Commission,

pursuant to section 169B(e) of the Act.

The Administrator recognizes that

people living in certain urban areas may

place a high value on unique scenic

resources in or near these areas, and as

a result might experience visibility

problems attributable to sources that

would not necessarily be addressed by

the combined effects of a regional haze

program and secondary standards

identical to the suite of primary

standards for PM2.5. Commenters from
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38683

certain western cities and States raised

this issue. In the Administrator’s

judgment, State or local regulatory

approaches, such as past action in

Colorado to establish a local visibility

standard for the City of Denver, would

be more appropriate and effective in

addressing these special situations

because of the localized and unique

characteristics of the problems involved.

Visibility in an urban area located near

a mandatory Class I Federal area can

also be improved through State

implementation of the current visibility

regulations, by which emission

limitations can be imposed on a source

or group of sources found to be

contributing to ‘‘reasonably

attributable’’ impairment in the

mandatory Class I Federal area. EPA

also intends to pursue opportunities to

obtain information on urban and nonClass I area visibility through

examination of available fine particle

monitoring data. Current or planned

monitoring networks and initiatives,

such as monitoring and chemical

analysis of PM2.5 in urban and

background sites, efforts to better

characterize real-time environmental

conditions in major populations centers,

and new automated airport visibility

monitoring networks should provide

data needed to evaluate trends in these

areas. This information should help to

better characterize the nature and

spatial extent of urban and non-Class I

visibility problems and thus serve to

inform future decisions on NAAQS

revisions or other appropriate measures.

Based on all of the considerations

discussed, the Administrator has

decided to establish secondary

standards identical to the suite of PM2.5

primary standards, in conjunction with

a regional haze program under sections

169A and 169B of the Act, as the most

appropriate and effective means of

addressing the welfare effects associated

with visibility impairment. Together,

the two programs and associated control

strategies should provide appropriate

protection against the effects of PM on

visibility and enable all regions of the

country to make reasonable progress

toward the national visibility goal.

2. Materials damage and soiling

effects. Annual and 24-hour secondary

standards for materials damage and

soiling effects of PM were established in

1987 at levels equal in all respects to the

primary standards. As discussed in the

Criteria Document and Staff Paper,

particles affect materials by promoting

and accelerating the corrosion of metals,

by degrading paints, and by

deteriorating building materials such as

concrete and limestone. Soiling is found

to reduce the aesthetic quality of

buildings and objects of historical or

social interest. Past studies have found

that residential properties in highly

polluted areas typically have lower

values than those in less polluted areas.

Thus, at high enough concentrations,

particles become a nuisance and result

in increased cost and decreased

enjoyment of the environment.

In the proposal, EPA proposed to

establish secondary standards for PM10

and PM2.5 identical to the suite of

proposed primary standards. Several

comments recommended setting

secondary standards at levels more

stringent than the proposed primary

standards in order to address various

welfare effects of PM, including soiling

and materials damage, acid deposition,

and visibility. Some commenters

specifically suggested changing the form

or level of the proposed 24-hour, 98th

percentile PM standards to better

protect against elevated PM episodes

and associated soiling, materials

damage, and visibility effects.

After reviewing the extent of relevant

studies and other information provided

since the 1987 review of the PM

standards, the Administrator concurs

with staff and CASAC conclusions that

the available data do not provide a

sufficient basis for establishing a

separate secondary standard based on

soiling or materials damage alone. In the

Administrator’s judgment, however,

setting secondary standards identical to

the suite of PM2.5 and PM10 primary

standards would provide increased

protection against the effects of fine

particles and retain an appropriate

degree of control on coarse particles.

Accordingly, the Administrator

establishes the secondary standards for

PM2.5 identical to the suite of primary

standards to protect against materials

damage and soiling effects of PM.

B. Decision on the Secondary Standards

The Administrator establishes

secondary standards identical to the

suite of primary standards. In the

Administrator’s judgment, the

establishment of these standards, in

conjunction with implementation of a

regional haze program, will provide

appropriate protection against the

welfare effects associated with particle

pollution.

IV. Other Issues

Commenters have raised a number of

legal and procedural issues that are

discussed in this unit. These include:

(1) Whether EPA must give

consideration to costs and similar

factors in setting NAAQS.

(2) Whether EPA erred in its selection

of a methodology for determining the

level of a NAAQS that protects public

health with an adequate margin of

safety.

(3) Whether EPA committed a

procedural error by not entering into the

rulemaking docket underlying data from

certain epidemiological studies.

(4) Whether the 1990 amendments to

the Act preclude EPA from revising the

PM NAAQS to establish a new PM2.5

indicator.

Responses to other legal and procedural

issues are included in the Response-toComments Document.

A. Consideration of Costs

For more than a quarter of a century,

EPA has interpreted section 109 of the

Act as precluding consideration of the

economic costs or technical feasibility

of implementing NAAQS in setting

them. As indicated in the proposal, a

number of judicial decisions have

confirmed this interpretation. Natural

Resources Defense Council v.

Administrator, 902 F.2d 962, 972–973

(D.C. Cir. 1990)(PM NAAQS)(‘‘PM10’’),

vacated, in part, dismissed, 921 F.2d

326 (D.C. Cir.), certs. dismissed, 498

U.S. 1075, and cert. denied, 498 U.S.

1082 (1991); Natural Resources Defense

Council v. EPA, 824 F.2d 1146, 1157–

1159 (D.C. Cir. 1987)(en banc)(CAA

section 112 standards for vinyl

chloride)(‘‘Vinyl Chloride’’); American

Petroleum Institute v. Costle, 665 F.2d

1176, 1185–1186 (D.C. Cir. 1981)(ozone

NAAQS)(‘‘Ozone’’), cert. denied, 455

U.S. 1034 (1982); Lead Industries Ass’n

v. EPA, 647 F.2d 1130, 1148–1151 (D.C.

Cir.)(lead NAAQS)(Lead Industries),

cert. denied, 449 U.S. 1042 (1980).

Some commenters have argued that

costs and similar factors should,

nonetheless, be considered, both in this

rulemaking and in the rulemaking on

proposed revisions to the NAAQS for

ozone. Although most of the

commenters’ arguments are inconsistent

with the judicial decisions cited in this

unit, several commenters have argued

that those decisions are not dispositive.

For reasons discussed in this unit and

in the Response-to-Comments

Document, EPA disagrees with these

comments and maintains its

longstanding interpretation of the Act as

precluding consideration of costs and

similar factors in setting NAAQS.

1. Background. Given the nature of

the points raised, a brief review of the

issue seems useful before addressing the

comments. The requirement that EPA

establish national ambient air quality

standards for certain pollutants, to be

implemented by the States, was enacted

in 1970 as part of a set of

comprehensive amendments that

established the basic framework for
38684 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

55 36 FR 8186, April 30, 1971. EPA has

maintained this interpretation consistently since

then.

56 That consideration of such factors was not

intended in NAAQS decisions is also supported by

section 109(a)(1) of the Act. For pollutants for

which air quality criteria had been issued prior to

the 1970 amendments, that provision required EPA

to propose NAAQS within 30 days after enactment

and to take final action 90 days later. The criteria

issued previously did not include information on

costs and similar factors, and it would have been

difficult if not impossible for EPA to supplement

them in time to include meaningful consideration

of such factors in NAAQS proposed 30 days after

enactment.

57 See, e.g., sections 110(e)(1), 111(a)(1), 231(b) of

the 1970 Act; see also, e.g., sections 113(d)(4)(C)(ii),

125(a)(3), 202(a)(3)(C), 317 of the 1977 Act.

58 Union Electric Co. v. EPA, 427 U.S. 246, 257–

58 (1976).

59 The Senate report on the 1970 amendments

stated: ‘‘In the Committee discussions, considerable

concern was expressed regarding the use of the

concept of technical feasibility as the basis of

ambient air standards. The Committee determined

that (1) the health of people is more important than

the question of whether the early achievement of

ambient air quality standards protective of health is

technically feasible; and, (2) the growth of pollution

load in many areas, even with application of

available technology, would still be deleterious to

public health.’’

‘‘Therefore, the Committee determined that

existing sources of pollutants either should meet

the standard of the law or be closed down * * *

.’’

S. Rep. No. 91–1196, at 2–3 (1970).

60 These limitations would, of course, make little

sense if such factors could be considered in setting

the NAAQS themselves.

61 Such requirements ‘‘are expressly designed to

force regulated sources to develop pollution control

devices that might at the time appear to be

economically or technologically infeasible.’’’ Id.

(quoting Union Electric Co. v. EPA, 427 U.S. at 257).

62 In the PM10 case, for example, the Court

considered an argument that EPA should have

considered potential health consequences of

unemployment that might result from revision of

the primary NAAQS for PM:

‘‘This claim is entirely without merit. In three

previous cases, this court has emphatically stated

that § 109 does not permit EPA to consider such

costs in promulgating national ambient air quality

standards * * * . It is only health effects relating

to pollutants in the air that EPA may consider * *

* . Consideration of costs associated with alleged

health risks from unemployment would be flatly

inconsistent with the statute, legislative history and

case law on this point.’’

902 F.2d at 973 (emphasis in original; citations

omitted).

Federal, State, and local air pollution

control. When EPA promulgated the

original NAAQS in 1971, its first

Administrator, William D. Ruckelshaus,

concluded that costs and similar factors

could not be considered in that

decision.55 This conclusion was not

challenged in litigation on the original

NAAQS. It has been confirmed since

then, however, by every judicial

decision that has considered the issue.

As discussed in this unit, EPA’s

interpretation rests primarily on the

language, structure, and legislative

history of the statutory scheme adopted

in 1970. It is also supported by the

judicial decisions cited in this unit, as

well as by legislative developments

since 1970 that reaffirm Congress’

original approach to the issue.

Without cataloguing all relevant

aspects of the 1970 amendments and

their legislative history, several basic

points should be noted. Under section

109(b) of the Act, NAAQS are to be

‘‘based on’’ the air quality criteria issued

under section 108 of the Act. Under

section 108(a)(2) of the Act, the kind of

information EPA is required to include

in criteria documents is limited to

information about health and welfare

effects ‘‘which may be expected from

the presence of [a] pollutant in the

ambient air * * * .’’ There is no mention

of the costs or difficulty of

implementing the NAAQS, nor of

‘‘effects’’ that might result from

implementing the NAAQS (as opposed

to effects of pollution in the air).56 By

contrast, Congress explicitly provided

for consideration of costs and similar

factors in decisions under other sections

of the Act.57 Moreover, States were

permitted to consider economic and

technological feasibility in developing

plans to implement the NAAQS to the

extent such consideration did not

interfere with meeting statutory

deadlines for attainment of the

standards.58 Finally, the legislative

history indicated that Congress had

considered the issue and had

deliberately chosen to mandate NAAQS

that would protect health regardless of

concerns about feasibility.59

The first judicial decision on the issue

came in the Lead Industries case. An

industry petitioner argued that EPA

should have considered economic and

technological feasibility in allowing a

‘‘margin of safety’’ in setting primary

standards for lead. Based on a detailed

review of the language, structure, and

legislative history of the statutory

scheme, the U.S. Court of Appeals for

the District of Columbia Circuit

concluded that:

This argument is totally without merit.

[The petitioner] is unable to point to

anything in either the language of the Act or

its legislative history that offers any support

for its claim * * * . To the contrary, the

statute and its legislative history make clear

that economic considerations play no part in

the promulgation of ambient air quality

standards under section 109.

647 F.2d at 1148.

The Court cited a number of reasons

for this conclusion. Id. at 1148–1150.

Among other things, it noted the

contrast between section 109(b) of the

Act and other provisions in which

Congress had explicitly provided for

consideration of economic and

technological feasibility, as well as the

requirement that NAAQS be based on

air quality criteria defined without

reference to such factors. Id. at 1148–

1149 and n.37. The Court also noted

that, in developing plans to implement

NAAQS, States may consider economic

and technological feasibility only to the

extent that this does not interfere with

meeting the statutory deadlines for

attainment of the standards; and that

EPA may not consider such factors at all

in deciding whether to approve State

implementation plans. Id. at 1149 n.37

(citing Union Electric Co. v. EPA, 427

U.S. 246, 257–258, 266 (1976)).60

As to the legislative history of the

1970 amendments, the Court observed

that:

[T]he absence of any provision requiring

consideration of these factors was no

accident; it was the result of a deliberate

decision by Congress to subordinate such

concerns to the achievement of health goals.

Id. at 1149. Citing several leading

Supreme Court decisions, as well as the

Senate report quoted in this unit, the

Court noted that Congress had intended

a drastic change in approach toward the

control of air pollution in the 1970

amendments and was well aware that

sections 108–110 of the Act imposed

requirements of a ‘‘technology-forcing’’

character. Id.61

The Court also noted that Congress

had already acted, in further

amendments adopted in 1977, to relieve

some of the burdens imposed by the

1970 amendments. Id. at 1150 n.38.

Observing that Congress had, however,

declined to amend section 109(b) of the

Act to provide for consideration of costs

and similar factors as requested by

industrial interests, Id. n.39, the Court

concluded:

A policy choice such as this is one which

only Congress, not the courts and not EPA,

can make. Indeed, the debates on the [1970

amendments] indicate that Congress was

quite conscious of this fact * * * .

* * * [I]f there is a problem with the

economic or technological feasibility of the

lead standards, [the petitioner], or any other

party affected by the standards, must take its

case to Congress, the only institution with

the authority to remedy the problem.

Id. at 1150.

After the decision in Lead Industries,

Supreme Court review was sought on

the question whether costs and similar

factors could be considered in setting

NAAQS, among other issues. The

Supreme Court declined to review the

decision. Lead Industries Ass’n v. EPA,

449 U.S. 1042 (1980). The subsequent

decisions in Ozone, Vinyl Chloride, and

PM10, cited in this unit, strongly

reaffirmed the interpretation adopted in

Lead Industries.62 Supreme Court
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38685

63 See, e.g., H.R. Rep. No. 95-294, at 207–217

(l977).

64 See, e.g., Id. at 110–112; Id. at 43-51.

65 Section 109(d)(2)(C)(iv) of the Act. Some

commenters have argued that this provision

requires EPA to consider such effects in setting

NAAQS. From the language and structure of section

109(d) of the Act, however, it is clear that CASAC’s

responsibility to advise on these factors is separate

from its responsibility to review and recommend

revision of air quality criteria and NAAQS, and that

the advice pertains to the implementation of

NAAQS rather than to setting them. The legislative

history confirms this view, indicating that the

advice was intended for the benefit of the States

and Congress. See H.R. Rep. No. 95-294, at 183

(1977).

66 The 1977 amendments also required EPA to

prepare economic impact assessments for specified

actions but limited the requirement to non-healthbased standards, excluding decisions under

sections 109 and 112 of the Act. Section 317; H.R.

Rep. No. 95-294, at 51–52 (1977). In this and other

respects, Congress continued the approach it took

in the l970 amendments, making careful choices as

to when consideration of costs and similar factors

would be required and giving paramount priority to

protection of health. See 123 Cong. Rec. H8993

(daily ed. Aug. 4, 1977) (Clean Air Conference

Report (1977); Statement of Intent; Clarification of

Select Provisions), reprinted in 3 Senate Committee

on Environment and Public Works, 95th Cong., A

Legislative History of the Clean Air Act

Amendments of 1977, at 319 (1978).

67 In the interim, the National Commission on Air

Quality had also submitted its report to Congress as

required by a provision of the 1977 amendments.

Among other things, the Commission recommended

that the statutory approach of requiring NAAQS to

be set at levels necessary to protect public health,

without consideration of economic factors, be

continued without change. National Commission on

Air Quality, To Breathe Clean Air 55 (1981).

68 As the Administrator indicated in EPA’s

proposal to revise the PM standards:

‘‘[T]hat review has revealed a highly limited data

base—particularly where quantitative studies are

concerned—and a wide range of views among

qualified professionals about the exact pollution

levels at which health effects are likely to occur.

The setting of an ‘adequate margin of safety’ below

these levels calls for a further judgment—in an area

for which the scientific data base is even more

sparse and uncertain * * * .’’

‘‘* * * [L]ong and expert review of public health

issues has to date revealed no scientific method of

assessing exactly what level of standards public

health requires. The scientific review indicates

substantial uncertainties concerning the health risks

associated with lower levels of particulate matter.’’

(49 FR 10408, 10409, March 20, l984)

69 Congress was clearly aware of the 1987

decision to revise the PM NAAQS, which among

other things involved changing the indicator for

particulate matter from ‘‘total suspended

particulate’’ to PM10, because it enacted special

nonattainment provisions, as well as provisions for

PSD increments, applicable to PM10. Sections 188–

190 of the Act; section 166(f) of the Act. It was

clearly aware of the Vinyl Chloride decision

because it amended section 112 of the Act in

response to that decision, essentially creating a new

scheme for setting emission standards for hazardous

pollutants.

70 H.R. Rep. No. 101–490, pt. 1, at 145 (1990). See

also S. Rep. No. 101–228, at 5 (1989).

71 Additional responses to points raised by this

commenter and others are included, as appropriate,

in the Response-to-Comments Document.

72 Several other commenters argue that the cited

decisions are not dispositive because they held only

that EPA is not required to consider costs and

similar factors in setting NAAQS. As discussed in

this unit in connection with Chevron, however, the

decisions clearly concluded that Congress intended

to preclude consideration of such factors, and that

EPA is not free to alter that congressional choice.

Although these conclusions are technically dicta,

nothing in the Court’s opinions suggests that it

would have interpreted section 109 of the Act

differently had EPA claimed authority to consider

costs and similar factors in NAAQS decisions.

Indeed, the tone of the opinions argues to the

contrary. See, e.g., PM10, 902 F.2d at 973. Cf. Ethyl

Corp. v. EPA, 51 F.3d 1053 (D.C. Cir. 1995).

review of the Ozone and PM10 decisions

was sought but denied. American

Petroleum Institute v. Gorsuch, 455 U.S.

1034 (1984); American Iron and Steel

Institute v. EPA, 498 U.S. 1082 (1991).

The Lead Industries opinion focused

largely, though not exclusively, on the

1970 amendments and their legislative

history. Perhaps as a result, it did not

canvass all the factors that, in fact,

supported its conclusions at the time.

For example, when Congress enacted

major amendments to the Act in 1977,

it was clearly aware that some areas of

the country had experienced difficulty

in attempting to attain some of the

NAAQS.63 It was also aware that there

might be no health-effects thresholds for

the pollutants involved, and that

significant uncertainties are inherent in

setting health-based standards under the

Act.64 In response, Congress made

significant changes in the provisions for

implementation of the NAAQS,

including changes intended to ease the

burdens of attainment. It also amended

sections 108 and 109 of the Act in

several ways; for example, by requiring

periodic review and, if appropriate,

revision of air quality criteria and

NAAQS and by establishing a special

scientific advisory committee (CASAC)

to advise EPA on such reviews. Notably,

Congress recognized that

implementation of NAAQS could cause

‘‘adverse public health, welfare, social,

economic, or energy effects’’ and

charged CASAC with advising EPA on

such matters.65 Yet it made no changes

in section 109(b) or section 108(a)(2) of

the Act; that is, in the substantive

criteria for setting or revising NAAQS.

In other words, Congress chose to

address economic and other difficulties

associated with attainment of the

NAAQS by adjusting the scheme for

their implementation, rather than by

changing the instructions for setting

them.66

Congress enacted major amendments

to the Act again in 1990, well after the

Lead Industries and Ozone decisions

that interpreted section 109 of the Act

as precluding consideration of costs in

NAAQS decisions.67 In doing so,

Congress was clearly aware of

intervening developments such as EPA’s

decision to revise the PM NAAQS in

1987—the result of an elaborate review

in which the Administrator strongly

underscored the scientific uncertainties

involved68—and the Vinyl Chloride case

drawing a sharp distinction between

sections 109 and 112 of the Act with

regard to consideration of costs and

similar factors.69 Indeed, the legislative

history of the 1990 amendments reflects

Congress’ understanding that primary

NAAQS were to be based on protection

of health ‘‘without regard to the

economic or technical feasibility of

attainment.’’70 Again, however,

Congress chose to respond to severe,

widespread, and persistent problems

with attaining the NAAQS by adjusting

the scheme for their implementation

rather than by changing the basis for

setting them. See, e.g., sections 181–192

of the Act.

2. Public comments. As noted

previously, a number of commenters

have argued that costs and similar

factors should be considered in EPA’s

final decisions on revision of both the

particulate and ozone NAAQS. Aside

from arguments that are simply

inconsistent with the judicial decisions

cited in this unit, some of the

commenters argue that those decisions

are not dispositive for a variety of

reasons. One commenter submitted a

particularly comprehensive version of

this argument; the following discussion

focuses primarily on points raised by

that commenter, among others.71

As a general matter, the commenter

acknowledges that Congress intended to

preclude consideration of economic

costs and similar factors in setting

NAAQS. The commenter argues,

however, that this is so only when the

scientific basis for NAAQS is ‘‘clear and

compelling’’ or ‘‘unambiguous.’’ From

that premise, the commenter advances

three key assertions:

a. Where non-threshold pollutants are

involved and the health evidence is

ambiguous, section 109 of the Act must

be interpreted to allow consideration of

all relevant factors, including the

practical consequences of EPA’s

decisions.

b. To the extent the judicial decisions

cited in this unit are read as precluding

this, they rest on a faulty analysis that

pre-dates and cannot survive scrutiny

under Chevron, U.S.A. v. Natural

Resources Defense Council, 467 U.S.

837 (1984).72

c. Because EPA has discretion to

consider costs and similar factors where

the health evidence is ambiguous, it

must do so in light of Executive Order

12866 (58 FR 51735, October 4, 1993),

and two recent statutes, the Unfunded
38686 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

73 See, e.g., Lead Industries, 647 F.2d at 1146–

1147, 1153–1156, 1160–1161, 1167 n.106. In

enacting the 1970 amendments, Congress was aware

that there were gaps in the scientific information

available then as a basis for establishing the original

NAAQS. See, e.g., S. Rep. No. 91-1196, at 9–11

(1970). If anything, Congress had an even greater

understanding of the point when it enacted the

1977 amendments without changing the substantive

criteria for setting NAAQS. See H.R. Rep. No. 95-

294, at 43–51, 181–182 (1977).

74 Lead Industries, 647 F.2d at 1147 (quoting

Ethyl Corp. v. EPA, 541 F.2d 1, 24–27 (D.C. Cir.)

(en banc), cert. denied, 426 U.S. 941 (1976)).

75 They may have methodological flaws, for

example, but nonetheless report effects that are of

serious medical significance; or they may be of

impeccable quality but involve effects of uncertain

significance. Others may involve results that are

striking but hard to explain in terms of previous

knowledge, or results that seem plausible and

important but are not yet replicated by other

studies.

76 See, e.g., Lead Industries, 647 F.2d at 1155–

1156; H.R. Rep. No. 94-295, at 43–51 (1977).

77 As previously discussed, the Administrator

strongly emphasized the uncertainties involved in

that review. As a result of the uncertainties, he

proposed ‘‘relatively broad’’ ranges for comment,

though he focused on lower levels within the ranges

as providing greater margins of safety against the

health risks involved. See 49 FR 10408, 10409,

March 20, l984.

78 See, e.g., Lead Industries, 647 F.2d at 1152–53

and n. 43, 1159–60; Ozone, 665 F.2d at 1185, 1187;

PM10, 902 F.2d at 969–71, 972.

79 Indeed, the present decisions on the NAAQS

for PM and ozone are based on some of the best

scientific information the Agency has ever been

able to rely on in NAAQS decision-making. In

particular, the science underlying these decisions is

much more extensive and of much better quality

than the science underlying the existing NAAQS for

PM and ozone.

80 In practice, analysis of this question is

sometimes referred to as a ‘‘Chevron step one’’

analysis.

81 See, e.g., 647 F.2d at 1148–51, 1152–53 and

n.43, 1160–61.

Mandate Reform Act of 1995, 2 U.S.C.

1501–1571 (UMRA), and the Small

Business Regulatory Enforcement

Fairness Act of 1996, Pub. L. 104–121,

110 Stat. 857 (SBREFA), which in part

amended the Regulatory Flexibility Act,

5 U.S.C. 601–808.

EPA believes all three assertions are

clearly incorrect. Regarding the first

point, it should be evident, both from

previous NAAQS decisions and from

the court opinions upholding them, that

the scientific basis for NAAQS decisions

has never pointed clearly and

unambiguously to a single ‘‘right

answer.’’73 This is inherent in the

statutory scheme for the establishment

and revision of NAAQS, which in effect

requires them to be based on the ‘‘latest

scientific knowledge’’ on potential

health and welfare effects of the

pollutant in question. See sections

109(b) and 108(a)(2) of the Act.

Although advances in science increase

our understanding of such effects, they

also raise new questions. For this

reason, the key studies for any given

decision on revision of a NAAQS are,

almost by definition, ‘‘at the very

‘frontiers of scientific knowledge.’’’73

That is, studies that call into question

the adequacy of a standard are always

those that go beyond previous studies—

by reporting new kinds of effects, for

example, or effects at lower

concentrations than those at which

effects have been reported previously.

As with pioneering work in other

fields, such studies may have a variety

of strengths and limitations.875 As a

result, the validity and implications of

such studies may be both uncertain and

highly controversial. Given the

precautionary nature of section 109 of

the Act,76 however, it is precisely these

kinds of studies that the Administrator

must grapple with when advances in

science suggest that revision of a

NAAQS is appropriate.

As a result, the EPA staff typically

recommends for consideration, and the

Administrator may propose for

comment, a range of alternatives based

on what the commenter would call

‘‘ambiguous’’ science. In this respect,

the current reviews of the NAAQS for

ozone and particulate matter are not

unusual and do not differ, for example,

from the review that led to adoption of

the PM10 NAAQS in 1987.77 Indeed, the

NAAQS that were upheld in the Lead

Industries, Ozone, and PM10 decisions

were all based on highly controversial

health evidence; the Lead Industries

decision took note of congressional

statements recognizing that there may

be no thresholds for criteria pollutants;

and the Ozone and PM10 decisions

noted the Administrator’s findings that

clear thresholds could not be identified

for ozone and particulate matter,

respectively.78 Thus, the present

decisions on revision of the NAAQS for

ozone and particulate matter cannot be

distinguished from those past decisions

in terms of the nature of the health

evidence or pollutants involved.78

Regarding the second of the

commenter’s key assertions, EPA

determines it is clear that the judicial

decisions cited in this unit were

correctly decided and continue to be

good law under Chevron. In Chevron,

the Supreme Court essentially

reaffirmed the principle that courts

must defer to reasonable agency

interpretations of the statutes they

administer where Congress has

delegated authority to them to elucidate

particular statutory provisions. Where

the intent of Congress on an issue is

clear, however, it must be given effect

by the agency and the courts. See 467

U.S. at 842–45. Thus, the first question

on review of an agency’s interpretation

under Chevron is ‘‘whether Congress

has directly spoken to the precise

question at issue.’’ If the court

determines that it has not, the remaining

question for the court is ‘‘whether the

agency’s answer is based on a

permissible construction of the statute.’’

467 U.S. at 842–843 (footnote omitted).

In determining whether Congress ‘‘had

an intention on the precise question at

issue,’’ a court employs ‘‘traditional

tools of statutory construction.’’ Id. at

843 n.9.80

In essence, the commenter’s argument

here is that the Lead Industries decision

did not address whether Congress had

‘‘spoken directly’’ to the precise issue

posed by the commenter; that is,

whether section 109 of the Act must be

interpreted differently for NAAQS

decisions involving non-threshold

pollutants and ‘‘ambiguous’’ health

evidence. The Lead Industries opinion,

which pre-dated Chevron, did not pose

the question in those terms. Its focus,

however, was clearly on what Congress

intended to be the basis for NAAQS

decisions, in a context the Court

understood to involve considerable

uncertainty and debate about the health

evidence, as well as the possibility that

there was no threshold for health effects

of the pollutant.81 In short, the health

evidence was hardly ‘‘unambiguous,’’

yet the Court interpreted section 109 of

this Act as precluding consideration of

costs and similar factors even in

allowing a margin of safety. Nothing in

the Lead Industries decision or in the

subsequent cases suggests in any way

that section 109 of the Act should be

interpreted differently based on the

nature of the pollutants or health

evidence involved, and the Court’s

findings on congressional intent admit

of no exceptions:

* * * [T]he statute and its legislative

history make clear that economic

considerations play no part in the

promulgation of ambient air quality

standards under Section 109.

647 F.2d at 1148.

Alternatively, the commenter argues

that the Lead Industries case decided

the issue incorrectly in light of the

principles announced subsequently in

Chevron. In this context, the commenter

essentially argues that the Lead

Industries decision rested on two factors

that are no longer probative:

(1) That there was no indication that

Congress meant to allow consideration

of costs in NAAQS decisions, and

(2) That Congress specifically

provided for such consideration in other

sections of the Act but not in section

109.
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38687

82 See 647 F.2d at 1148–51. By contrast, the

commenter’s argument that Congress actually

intended EPA to consider such factors relies heavily

on statements made in subsequent legislative

history, most of which were made in floor debate,

that sought to justify controversial amendments to

establish a different program than the NAAQS and

did not involve any proposed changes in section

109 of the Act or related provisions; and statements

in early judicial decisions involving programs

under other statutory provisions. In context, EPA

determines these and other statements cited by the

commenter are consistent with and do not alter the

conclusion that Congress intended to preclude

consideration of costs and similar factors under

section 109 of the Act.

83 The commenter argues that the post-Chevron

cases accepted the Lead Industries analysis

uncritically rather than re-examining it under

Chevron. Clearly, this elevates form over substance.

It is true that neither case referred to Chevron in

discussing the point at issue. In Vinyl Chloride,

however, the Court retraced the steps in the Lead

Industries analysis in some detail, characterized

some of the key evidence reviewed in that analysis

in terms going beyond mere rote repetition (e.g., ‘‘a

far clearer statement than anything in the present

case that Congress considered the alternatives’’),

and used Chevron-like language in discussing the

significance of that evidence; that is, that it

demonstrated congressional intention on the point

at issue. E.g., 824 F.2d at 1159. Given that the Vinyl

Chloride case was decided three years after

Chevron, that it was an en banc decision of the D.C.

Circuit involving interpretation of statutory

language very similar to that in Lead Industries, and

that the Court cited Chevron twice in analyzing the

language and history of section 112 of the Act, it

seems highly unlikely that the Court was unmindful

of Chevron principles in concluding that Congress

intended to preclude consideration of costs under

section 109 of the Act but not under section 112 of

the Act.

In the PM10 decision, the Court confirmed the

sharp distinction it had drawn, based on such

evidence of congressional intent, between sections

109 and 112 of the Act in Vinyl Chloride. 902 F.2d

at 972–973. Although discussion of the point was

brief and did not mention Chevron, the industry

petitioner raising the point had cited Chevron in

arguing that the Lead Industries interpretation was

not binding, and that EPA’s decision on the PM10

standards should be reversed on the ground that it

rested on a legal position that EPA unjustifiably

believed was mandated by Congress. Reply Brief of

the American Iron and Steel Institute at 11 and

n.10, Natural Resources Defense Council v.

Administrator, 902 F.2d 962 (D.C. Cir. 1990) (Nos.

87-1438 et al.). Thus, Chevron issues were properly

before the Court and were brought squarely to its

attention.

84 See also 52 FR 24854, July 1, 1987.

On the first point, the commenter

argues that EPA is free under Chevron

to consider costs and similar factors (by

reinterpreting section 109 of the Act)

unless there is evidence that Congress

intended to restrict its discretion. As to

the second point, the commenter argues

that similar reasoning was rejected in

Vinyl Chloride.

In Vinyl Chloride, however, an en

banc decision that post-dated Chevron,

the Court essentially underscored the

point that such issues cannot be decided

mechanically but must turn, instead, on

more analytical attention to relevant

indicia of congressional intent. See, e.g.,

824 F.2d at 1157 n.4; Id. at 1157–1163.

With reference to NAAQS decisions in

particular, the Court concluded that

there were concrete indications of

congressional intent to preclude

consideration of costs and similar

factors; for example, the fact that section

108 of the Act ‘‘enumerate[s] specific

factors to consider and pointedly

exclude[s] feasibility.’’ 824 F.2d at 1159.

In a later case, moreover, the same Court

held that EPA could not consider

certain factors, in decisions under

section 211(f)(4) of the Act, for reasons

exactly parallel to those that the

commenter criticizes in Lead Industries.

See Ethyl Corp. v. EPA, 51 F.3d 1053,

1057–1063 (D.C. Cir. 1995).

Beyond this, the commenter’s

characterization of the Lead Industries

decision ignores or discounts much of

the key evidence cited by the Court,

including the language, structure, and

legislative history of the statutory

scheme established in 1970, for its

conclusion that Congress intended to

preclude consideration of costs and

similar factors in NAAQS decisions.82

As indicated in this unit, the Vinyl

Chloride and PM10 cases, both of which

post-dated Chevron, reached the same

conclusion.

Moreover, this series of decisions

went far beyond mere deference to an

agency interpretation. As indicated in

the Vinyl Chloride case, the Lead

Industries court found ‘‘clear evidence’’

of Congressional intent, which was to

limit the factors EPA may consider

under section 109 of the Act. 824 F.2d

1159. Consistent with Chevron, these

findings were based on traditional tools

of statutory construction. See Id. at

1157–1159; Lead Industries, 647 F.2d at

1148–1151. In terms of the analytical

framework later established by Chevron,

these were Chevron step one findings,

meaning that the statute spoke directly

to the issue and that the courts, as well

as the agency, must give effect to

Congress’ intent as so ascertained. See

467 U.S. at 842–843.83 Thus, absent a

more recent legislative enactment

overriding that intent, EPA has no

discretion to alter its longstanding

interpretation that consideration of costs

and similar factors is precluded in

NAAQS decisions under section 109 of

the Act.84

As to the commenter’s third key

assertion, Executive Order 12866,

UMRA sections 202 and 205, and the

Regulatory Flexibility Act (RFA), as

amended by SBREFA, do not conflict

with this interpretation or require a

different result. Basically, the

commenter argues that the Executive

Order, UMRA, and the RFA (as

amended by SBREFA) require agencies

to use cost (or similar factors) as a

decisional criterion in making

regulatory decisions, and that this

modifies the Clean Air Act’s directive

that EPA is precluded from considering

costs when setting a NAAQS. The

commenter’s argument is flawed on a

number of grounds. First, UMRA and

the RFA (as amended by SBREFA) do

not conflict with section 109 of the Act

because they do not apply to this

decision, as discussed in Unit VIII. of

this preamble. Second, the Executive

Order and both statutes are quite clear

that they do not override the substantive

provisions in an authorizing statute.

Third, the commenter’s premise that

UMRA and the RFA (as amended by

SBREFA) establish substantive

decisional criteria that agencies are

required to follow is wrong.

As a matter of law, the Executive

Order cannot (and does not purport to)

override the Clean Air Act. The

Executive Order does not conflict with

section 109 of the Act because the

requirement that agencies ‘‘select

approaches that maximize net benefits’’

does not apply if a ‘‘statute requires

another regulatory approach.’’ Executive

Order 12866, section (1)(a), (58 FR

51735, October 4, 1993). More generally,

the Executive Order provides that

agencies are to adhere to its regulatory

principles only ‘‘to the extent permitted

by law.’’ Id., section (1)(b).

UMRA sections 202 and 205 do not

apply to this decision, as discussed in

Unit VIII. of this preamble. Even when

they do apply to a regulatory action,

they do not establish decisional criteria

that an agency must follow, much less

override decisional criteria established

in the statute authorizing the regulatory

action. UMRA does not require an

agency to select any particular

alternative. Rather, an agency can select

an alternative that is not the least costly,

most cost-effective or least burdensome

if the agency explains why. Section

205(b)(1) of UMRA. Such an

explanation is not required if the least

costly, most cost-effective or least

burdensome alternative would have

been ‘‘inconsistent with law,’’ section

205(b)(2) of UMRA, and the only

alternatives that an agency should

consider are ones that ‘‘achieve[] the

objectives of the rule,’’ section 205(a) of

UMRA. The UMRA Conference Report

confirms that UMRA does not override

the authorizing statute. ‘‘This section

[202] does not require the preparation of

any estimate or analysis if the agency is

prohibited by law from considering the

estimate or analysis in adopting the

rule.’’ 141 Cong. Rec. H3063 (daily ed.

March 13, 1995).

The RFA (as amended by SBREFA)

also does not apply to this decision, as
38688 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

85 126 Cong. Rec. 21452, 21455 (1980)

(Description of Major Issues and Section-By-Section

Analysis of Substitute for S. 299).

86 Contrary to one of the comments received,

EPA’s use of risk assessment in this rulemaking is

by no means a departure from past practice. The

EPA first considered and began applying risk

assessment methods in the late 1970’s (44 FR 8210,

8211, February 8, 1979).

discussed in Unit VIII. of this preamble.

As is the case with UMRA, even when

the RFA (as amended by SBREFA) does

apply to a regulatory action, it does not

establish decisional criteria that an

agency must follow, much less override

the underlying substantive statute.

When the RFA was adopted in 1980,

Congress made clear that it did not alter

the substantive standards contained in

authorizing statutes: ‘‘The requirements

of section 603 and 604 of this title [to

prepare initial and final regulatory

flexibility analyses] do not alter in any

manner standards otherwise applicable

by law to agency action.’’ Section 606 of

the RFA. The legislative history further

explains that section 606 ‘‘succinctly

states that this bill does not alter the

substantive standard contained in

underlying statutes which defines the

agency’s mandate.’’85 When Congress

passed SBREFA in 1996 and amended

parts of the RFA, it did not amend

section 606.

Even when a regulatory decision is

subject to sections 603 and 604 of the

RFA and an agency is therefore required

to analyze alternatives that minimize

significant economic impacts on small

entities, the RFA (as amended by

SBREFA) does not establish decisional

criteria that an agency is required to

follow. Both section 603 and 604 of the

RFA provide that the alternatives an

agency should consider are to be

‘‘consistent with the stated objectives of

applicable statutes.’’ Section 603(c) and

604(a)(5) of the RFA. Furthermore,

although the RFA (as amended by

SBREFA) requires agencies to consider

alternatives that minimize impacts on

small entities subject to the rules’

requirements and to explain their choice

of regulatory alternatives, it does not

require agencies to select such

alternatives. For these reasons, the RFA

(as amended by SBREFA) does not

conflict with or override the Clean Air

Act’s preclusion of considering costs

and similar factors in setting NAAQS.

3. Conclusion. In summary, EPA

determines that the judicial decisions

cited in this unit are both correct and

dispositive on the question of

considering costs in setting NAAQS,

and that the Agency is not free to

reinterpret the Act on that question.

B. Margin of Safety

Several commenters questioned the

approach used by the Administrator in

specifying PM standards that protect

public health with an adequate margin

of safety. Rather than the integrative

approach applied by the Administrator,

these commenters maintained that EPA

must employ a two-step process. One

line of argument was that the

Administrator must first determine a

‘‘safe level’’ and then apply a margin of

safety taking into account costs and

societal impacts. It was argued that this

was the only approach that would

enable the Administrator to reach a

reasoned decision on a standard level

that protects public health against

unacceptable risk of harm, such that any

remaining risk was ‘‘acceptable.’’ In

effect, these commenters adopted the

two-step methodology endorsed by

Vinyl Chloride, 824 F.2d 1146, for

setting hazardous air pollutant

standards under section 112 of the Act.

Another commenter also maintained

that the Administrator must apply a

two-step process but from a different

perspective. It was argued that EPA

should first identify the lowest observed

effect level and then apply a margin of

safety to address uncertainties and to

protect the most sensitive individuals

within the at-risk population(s). This

commenter also maintained that the use

of risk assessment in establishing a

NAAQS was a departure from past

practice, and that this departure was not

adequately explained.

In recognition of the complexities

facing the Administrator in determining

a standard that protects public health

with an adequate margin of safety, the

courts have declined to impose any

specific requirements on the

Administrator’s methodological

approach. Thus, in Lead Industries the

court held that the selection of any

particular approach to providing an

adequate margin of safety ‘‘is a policy

choice of the type Congress specifically

left to the Administrator’s judgment.

This court must allow him the

discretion to determine which approach

will best fulfill the goals of the Act.’’

647 F.2d at 1161–1162. As a result, the

Administrator is not limited to any

single approach to determining an

adequate margin of safety and, in the

exercise of her judgment, may choose an

integrative approach, a two-step

approach, or perhaps some other

approach, depending on the particular

circumstances confronting her in a

given NAAQS review.

With respect to the approaches

advanced in comment, the PM10 case

made clear that the two-step process

endorsed in Vinyl Chloride was

necessary because of the need under

section 112 of the Act to ‘‘sever

determinations that must be based

solely on health considerations from

those that may include economic and

technical considerations.’’ 902 F.2d at

973. Because the Administrator may not

consider cost and technological

feasibility under section 109 of the Act,

however, the Court concluded that ‘‘the

rationale for parsing the Administrator’s

determination into two steps is

inapposite.’’ Id.

The claim that EPA must follow a

two-step process of first identifying the

lowest observed effects level and then

applying a margin of safety has also

been rejected by the courts. In Lead

Industries, the Court specifically held

that the Administrator need not apply a

margin of safety at the end of the

analytical process but may take into

account margin of safety considerations

throughout the process as long as such

considerations are fully explained and

supported by the record. 647 F.2d 1161–

1162. Accord, PM10, 902 F.2d at 973–

974.

Because such factors as the nature and

severity of the health effects involved,

the size of the sensitive population(s) at

risk, the types of health information

available, and the kind and degree of

uncertainties that must be addressed

will vary from one pollutant to another,

the most appropriate approach to

establishing a NAAQS with an adequate

margin of safety may be different for

each standard under review. Thus, no

generalized paradigm such as that

imbedded in EPA’s cancer risk policy

can substitute for the Administrator’s

careful and reasoned assessment of all

relevant health factors in reaching such

a judgment. As noted in this unit, both

Congress and the courts have left to the

Administrator’s discretion the choice of

analytical approaches and tools,

including risk assessments, rather than

prescribing a particular formula for

reaching such determinations.86 Because

of the inherent uncertainties that the

Administrator must address in margin

of safety determinations, they are largely

judgmental in nature, particularly with

respect to non-threshold pollutants, and

may not be amenable to quantification

in terms of what risk is ‘‘acceptable’’ or

any other metric. In view of these

considerations, the task of the

Administrator is to select an approach

that best takes into account the nature

of the health effects and other

information assessed in the air quality

criteria for the pollutant in question and

to apply appropriate and reasoned

analysis to ensure that scientific
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38689

87 Contrary to this commenter’s assertion, both

the health and air quality data used in the 1996

Schwartz study are available to interested parties.

EPA’s Office of Research and Development

maintains a copy of the air pollution database used

in the Schwartz study and it has previously been

made available in response to Freedom of

Information Act requests from interested parties,

such as the American Iron and Steel Institute (AISI).

The Harvard School of Public Health has also made

this data available to several collaborators and to

the Health Effects Institute. With regard to the

health data underlying the Schwartz study, that

mortality data was compiled by the National Center

for Health Statistics (NCHS) and can be purchased

from the NCHS by interested parties. Thus, there is

no real data availability concern with regard to the

1996 Schwartz study. However, even were this not

the case, for the reasons discussed more fully in this

unit and elsewhere in the preamble, EPA believes

it would be entitled to rely upon this study and

other studies, including the Dockery and Pope

studies, regardless of the availability of the

underlying health data.

88 API’s letter stated that ‘‘API petitions EPA to

identify all studies that rely, in any way, on data

not available for public review as part of the

rulemaking process and remove those studies from

the record.’’ To the extent this letter constitutes a

‘‘petition’’ for EPA action, EPA hereby denies the

‘‘petition’’ for the reasons stated in this unit and

elsewhere in this preamble.

89 One commenter argued that the failure to

obtain and disclose the underlying data was a

violation of the Administrative Procedure Act

(APA). The NAAQS rulemaking is promulgated

under section 307(d) of the Act; the APA generally

does not apply to such rulemakings. See section

307(d)(1) of the Act.

90 It is important to note that while EPA did use

the Dockery and Pope studies to confirm its

conclusions regarding the health effects of fine

particulate air pollution and thus as support for its

decision to revise the PM standard, these studies do

not provide the sole (or even primary) basis for

EPA’s decision regarding PM2.5, despite the

assertions of numerous commenters. The proposed

standards are based on a consideration of a large

body of epidemiological studies, a clear majority of

which suggest PM is strongly linked to mortality

and other serious health effects at concentrations

permitted under the current standards. Although

the specific levels of the PM2.5 standards are based

on a more limited number of studies that actually

measured fine particles and/or components of fine

particles, the Dockery and Pope studies were not

used in initially selecting the annual fine particle

standard level, which was principally based on

examination of other daily mortality and respiratory

effects studies (Koman, 1996, 1997) that found

significant associations between fine PM and effects

in cities with annual average PM2.5 concentrations

of about 16 to 21 μg/m3. Only then were the longterm Dockery and Pope studies examined and used

to help corroborate this result; in the opinion of the

Administrator, neither study alone (or together)

provided sufficient evidence to support more

stringent levels below those identified from the

daily studies. Thus, removal of the Dockery and

Pope studies would not affect the conclusions about

the significance of the risks and therefore, while

these long-term studies tend to strengthen the need

for fine particle control and provide important

insights into the nature of PM effects, removal of

these two studies from consideration would not

have changed the selected standard level.

91 Some commenters noted that with regard to the

health data underlying the 1993 Dockery and 1995

Pope studies, since EPA provided partial funding

for these studies, EPA has access to this data and

cannot shield itself from the duty to obtain this data

by claiming that it is not in its possession. Although

a legal argument potentially exists that EPA may

obtain access to such data, this legal argument has

not been tested in the courts. More importantly,

EPA’s ability to rely on studies without reviewing

the raw data should not depend on whether some

Agency of the Federal government funded the

science.

uncertainties are taken into account in

an appropriate manner.

In this instance, the Administrator has

clearly articulated the factors she has

considered, the judgments she has had

to make in the face of uncertain and

incomplete information, and alternative

views as to how such information

should be interpreted, in reaching her

decision on standard specifications that

will protect public health with an

adequate margin of safety. See Unit II.

of this preamble. Her conclusions on

these matters are fully supported by the

record.

C. Data Availability

Several commenters questioned EPA’s

ability to rely on studies demonstrating

an association between PM and excess

mortality without obtaining and

disclosing the raw ‘‘data’’ underlying

these studies for public review and

comment. In particular, a number of

commenters cited Dockery, D.W., et al.

1993 and Pope, C.A. III, et al., 1995, as

studies upon which EPA relied without

obtaining and disclosing the underlying

raw data. One commenter also cited J.

Schwartz et al., 1996 in the same

context.87 According to the commenters,

without the underlying data used in

these studies, the reliability of these

studies cannot be assessed accurately.

These commenters requested that EPA

obtain the relevant data and make it

available for public review. In light of

the court-ordered requirement that EPA

publish its rule by July 19, 1997, the

commenters argued that EPA must

retain the current PM10 NAAQS pending

additional review of the raw data and

the studies at issue. One commenter, the

American Petroleum Institute (API)

requested that EPA remove the studies

from the docket, unless the underlying

data was also included in the docket.88

A few commenters argued that section

307(d) of the Act requires that EPA

obtain the raw data underlying these

studies and that a failure to do so

contradicts the plain language of section

307(d)(3) of the Act, which requires EPA

to place in the docket any ‘‘factual data

on which the proposed rule is based.’’

Other commenters argued that under

section 307(d)(8) of the Act, a failure to

obtain and disclose the underlying raw

data used in the studies would

constitute an error ‘‘so serious and

related to matters of such central

relevance to the rule that there is a

substantial likelihood that the rule

would have been significantly changed

if such errors had not been made.’’ Id.

According to one commenter, without

the raw data and an opportunity for an

analysis of it, ‘‘EPA has no legal

alternative other than to conclude that

no new air quality standard would be

appropriate within the meaning of CAA

section 109(a)(1)(B).’’ Finally, a number

of commenters have argued that recent

caselaw under the Clean Air Act and

other statutes makes clear that EPA has

a legal obligation to obtain and disclose

the data used in these studies.89

In developing the proposed revisions

to the PM NAAQS, the Administrator

relied on the scientific studies cited in

the rulemaking record, rather than on

the raw data underlying them.90 In this

case, the raw data consists of responses

to health questionnaires based on

information supplied by individual

citizens, or computer tabulations of this

information, which remains

confidential, and air quality and

monitoring data, most of which is now

publicly available. EPA does not

generally undertake evaluations of raw,

unanalyzed scientific data as part of its

public health standard setting process.

Only in extreme cases—for example

where there are credible allegations of

fraud, abuse or misconduct—would a

review of raw data be warranted. It

would be impractical and unnecessary

for EPA to review underlying data for

every study upon which it relies as

support for every proposed rule or

standard. If EPA and other

governmental agencies could not rely on

published studies without conducting

an independent analysis of the

enormous volume of raw data

underlying them, then much plainly

relevant scientific information would

become unavailable to EPA for use in

setting standards to protect public

health and the environment. In

addition, such data are often the

property of scientific investigators and

are often not readily available because

of the proprietary interests of the

investigators or because of arrangements

made to maintain confidentiality

regarding personal health status and

lifestyle information of individuals

included in such data. Without

provisions of confidentiality, the

possibility of conducting such studies

could be severely compromised.91

In this case, the merits of the studies

considered and used in developing the

PM2.5 standard have been discussed and

debated extensively over the past

several years, both as part of the EPA

review of the pertinent science and in

a number of other public forums. The

studies at issue were critically evaluated
38690 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

by the Agency’s Office of Research and

Development (ORD) and by the EPA’s

independent Clean Air Scientific

Advisory Committee (CASAC), in a

multi-year process for assessment of the

science at issue. As with other studies

on which EPA relied, particular

attention was given to the strengths and

limitations of the Dockery, Schwartz

and Pope studies during this process,

which involved numerous opportunities

for public participation and extensive

input from interested parties. The

results of these studies are not only

consistent with each other, but they are

also consistent with the results of other

studies demonstrating significant

associations between long-term

exposure to fine particle indicators and

mortality. See U.S. EPA, 1996b, p. V–62.

The CASAC concluded that EPA’s

assessments of the pertinent science

properly characterized both the current

state of knowledge and the range of

policy options for revising the

standards.

In fact, many peer reviewed studies

have reported associations between PM

and premature death; the Dockery,

Schwartz and Pope studies are among

the most recent studies to corroborate

this association. In the early 1990s,

several studies were published showing

associations at levels below the current

PM standards. Some critics began

raising questions about the extent to

which the results could be reproduced

and the unavailability of underlying

data. In response, an independent group

of investigators under the auspices of

the Health Effects Institute (HEI), a

highly respected research organization

jointly funded by EPA and several

motor vehicle manufacturers, undertook

a reanalysis of several such studies. The

original investigators of several studies,

including studies conducted at Harvard

University, Brigham Young University,

and the San Francisco Bay Area Air

Quality Management District provided

their raw air quality data sets to the HEI

investigation team for reanalysis. HEI’s

reanalysis produced numerical results

from the data sets for all six cities that

closely agree with and, in general,

confirm the results of the original

investigators. Thus, as noted in Unit II.

of this preamble, these reanalyses by

respected independent scientists

confirmed the reliability and

reproduceability of prior work of the

original investigators, including work by

Dockery et al. (1992), Pope et al. (1992),

Schwartz and Dockery (1992a), and

Schwartz (1993).

Thus, the 1993 Dockery and 1995

Pope studies build upon previous

studies done by a number of different

researchers and have been subject to an

extensive peer review process by EPA’s

ORD, CASAC and HEI. They also

underwent a peer review process at the

time of their publication in reputable

scientific journals. Given the

consistency and coherence of the

scientific evidence and the scrutiny the

studies have received in peer review

and in the extensive scientific review

process described in this unit, EPA does

not agree that review of the underlying

data for these studies is also necessary.

Considering the various reviews

described in this unit and the fact that

EPA has received no specific and

substantiated reason, such as plausible

allegations of fraud or scientific abuse,

to doubt the overall validity of their

conclusions, EPA agrees with CASAC

that revision of the standard is

appropriate, based on these and other

studies.

In spite of EPA and CASAC’s

conclusion that it is appropriate to rely

on the Pope, Dockery and other studies

to establish a PM2.5 NAAQS, EPA also

believes in public disclosure and

supports efforts to seek appropriate

release of data underlying the studies in

question. On January 31, 1997, EPA

wrote to the principal scientific

investigators at the Harvard School of

Public Health and at Brigham Young

University and urged them to make the

data associated with their studies

available to interested parties. Studies

conducted by these investigators relied

on data compiled as part of the Harvard

Six-Cities Study and data compiled by

the American Cancer Society (ACS) as

part of the Cancer Prevention Study II.

The studies in question combined

health data on individuals with air

pollution data. The air pollution data

are publicly available. The health data

consist of personal and confidential

information, e.g. age, sex, weight,

eduction level, smoking history,

occupational exposures, medical

history. These data are not publicly

available. In compiling these data,

researchers have promised study

participants that private, personal

information would be kept confidential

under signed assurances of

confidentiality. Data-sharing

arrangements with outside parties must,

therefore, accommodate interests both

in making data accessible and in

protecting the confidentiality of the

information contained within them.

Both the Harvard School of Public

Health and the American Cancer Society

have made such arrangements. Both

have processes which allow ouside

scientists, in collaboration with Harvard

and ACS researchers, to access their

databases for the conduct of legitimate

scientific research. Scientists from all

over the world have applied for and

have been granted such access and

numerous studies have been conducted

and published using the databases.

Because of increased interest resulting

from EPA’s rulemaking on PM standards

and at the request of the Harvard School

of Public Health, HEI is taking

additional steps to provide a forum for

outside researchers to access health data

associated with the Harvard-Six Cities

Study and perhaps others. HEI has

convened an expert panel of esteemed

scientists to access underlying data and

to conduct additional reanalyses. This

arrangement appears to provide a

constructive venue for testing legitimate

scientific hypotheses while protecting

the confidentiality of the underlying

data.

Nevertheless, as noted previously,

EPA has full confidence in the scientific

integrity of the Dockery, Schwartz, and

Pope studies and their suitability for use

in the Agency’s rulemaking on PM,

without undertaking a separate or

additional review and analysis of the

underlying raw data. The decision to

propose revisions of the current PM

standards was based on careful

assessment of the scientific and

technical information presented in the

PM Criteria Document and Staff Paper.

The decision was also consistent with

the consensus of CASAC that ‘‘although

an understanding of health effects of PM

is far from complete, the Staff Paper,

when revised, will provide an adequate

summary of our present understanding

of the scientific basis for making

regulatory decisions concerning PM

standards.’’ The extensive PM

epidemiological data base provides

evidence that serious adverse health

effects, e.g., mortality, exacerbation of

chronic disease, increased hospital

admissions, respiratory symptoms, and

pulmonary function decrements, in

sensitive subpopulations, e.g., the

elderly, individuals with

cardiopulmonary disease and children,

are attributable to PM at levels below

the current standards. The increase in

risk is significant from an overall public

health perspective because of the large

number of individuals in sensitive

subpopulations that are exposed to

ambient PM and the significance of the

health effects. These considerations, as

well as others discussed in the proposal

and Staff Paper, such as the need to

consider fine and coarse particles as

distinct classes, led both the

Administrator and CASAC to conclude

that revision of the current standards is

clearly appropriate. This conclusion

remains unchanged despite the fact that

EPA is without the actual raw and
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38691

92 EPA also does not agree that because the

language of section 307(d) of the Act mentions

‘‘factual data’’ as well as ‘‘the methodology used in

obtaining and analyzing the data,’’ EPA cannot rely

on a study alone. In this case, the study is the

‘‘factual data’’ and EPA’s methodology used in

obtaining and analyzing the ‘‘factual data’’ is the

method that EPA used to review and rely upon the

studies. This methodology is discussed extensively

in the staff paper and summarized in some detail

elsewhere in this preamble. In fact, as is clear from

the overall structure of section 307(d) of the Act, as

well as the legislative history cited in this unit,

section 307(d) of the Act merely requires that EPA

summarize and disclose the information and

methodology that it relied upon in developing its

rule. It leaves unchanged the ‘‘level’’ of support that

an agency must bring to bear in drafting a proposed

rule.

unanalyzed health data underlying the

studies.

A number of commenters cited

section 307(d) of the Act in support of

their position that EPA is required to

obtain and disclose the underlying raw

data. Under section 307(d)(3) of the Act,

EPA is required to issue a notice of

proposed rulemaking in the Federal

Register that is accompanied by a

‘‘statement of basis and purpose’’ that

includes ‘‘a summary’’ of:

(A) The factual data on which the

proposed rule is based.

(B) The methodology used in

obtaining the data and in analyzing the

data.

Thus, it is clear from the language of

section 307(d) of the Act that where

EPA relies on any ‘‘data’’ as support in

its rulemakings under the Clean Air Act,

it has an obligation to include such data

or information in the rulemaking docket

that is open to the public. Where EPA

fails to do so and the error is ‘‘so serious

and related to matters of such central

relevance to the rule that there is a

substantial likelihood that the rule

would have been significantly changed

if such errors had not been made,’’ a

reviewing court may overturn the rule.

In this case, as noted previously, EPA

did not rely upon the raw health data

supporting the Dockery and Pope

studies; it relied instead upon the

studies themselves. These studies may

properly be considered ‘‘data.’’ The EPA

has never had the raw health data in its

possession; thus EPA has neither

reviewed it nor had an opportunity to

place it in the docket. The EPA did rely

on the studies and these studies are

included in the docket and are available

for public review. Because EPA neither

reviewed nor relied upon the raw data,

there is no obligation to obtain it or to

make it available.

Some commenters argued that the

language of section 307(d) of the Act,

which refers to the ‘‘factual data’’ and

which also discusses the ‘‘methodology

used in obtaining and analyzing the

data’’ distinguishes between raw data

and studies. In the view of these and

other commenters, the plain language of

section 307(d) of the Act requires that

EPA obtain and disclose the raw data

used in the Dockery and Pope studies.

According to these commenters, without

such raw ‘‘data,’’ EPA cannot legally

promulgate its rule.

The EPA disagrees with this narrow

interpretation of the word ‘‘data’’ and of

section 307(d) of the Act. Data can take

many forms, including studies, reports,

tabulations, graphs and summaries, as

well as more raw forms, such as

questionnaire responses, test results and

even actual physical specimens. The

‘‘factual data’’ called for by section

307(d) of the Act may clearly include

peer-reviewed scientific studies. Nor

does section 307(d) of the Act prohibit

EPA from relying on a study for

standard setting without obtaining the

raw, underlying data supporting a

study. Indeed, as noted in the legislative

history to section 307(d) of the Act,

* * * [t]he [House Commerce] Committee

recognizes that the factual support needed for

a rule may vary greatly according to the

subject being addressed and that rules on

some subjects, such as procedures, may not

require any factual basis at all. There is no

intention to increase the amount of ‘factual’

support now required to support ‘policy

judgments where no factual certainties exist

or where facts alone do not provide the

answer,’ Industrial Union Department, AFLCIO v. Hodgson, 499 F.2d 467, 476 (D.C. Cir.

1974). Nor is there any intent to diminish the

Administrator’s authority to adopt

precautionary regulations based on a

showing of risk * * * .

H.R. Rep. No. 95-294, at 323 (1977)

(footnote omitted). As this legislative

history makes clear, the language in

section 307(d) of the Act is not intended

to require EPA to change the amount of

‘‘factual support’’ that EPA must

assemble in order to promulgate a rule

and EPA may adopt ‘‘precautionary’’

regulations ‘‘where no factual certainties

exist.’’ Given this clarification in the

legislative history, it is evident that EPA

is entitled under section 307(d) of the

Act to rely on studies rather than raw

data in developing its Clean Air Act

rules, despite the arguably ambiguous

use of the term ‘‘data.’’92

Moreover, EPA has relied on studies

in the past (including studies using the

undisclosed Six Cities data) without

obtaining or disclosing the underlying

raw data, and EPA’s reliance on such

studies to set Clean Air Act standards

has been upheld in court. In NRDC v.

EPA, 902 F. 2d 962 (D.C. Cir. 1990), the

D.C. Circuit declined to delay its review

of the PM10 NAAQS rulemaking due to

concerns raised by the American Iron

and Steel Institute about the integrity of

the Six Cities data base. 902 F.2d at 974.

In that case, EPA had relied upon an

earlier Dockery study based on the Six

Cities data base. Although the National

Institutes of Health (NIH) undertook a

review of the allegations regarding the

Six Cities database, the court

nevertheless upheld EPA’s reliance on

that Dockery study without waiting for

the results of the NIH review. NIH

eventually concluded that the

allegations were without merit.

According to the court in the NRDC

case:

AISI claims that the EPA relied too much

on the Six Cities Study, which is comprised

of the Dockery study and the Ware study *

* * . We do not agree that the Administrator’s

selection of the twenty-four hour standard

lacks the necessary reasoned analysis and

supportive evidence * * * . After carefully

reviewing the record, we find EPA’s selection

of the twenty four hour standard reasonable

in light of the divergent results in the studies

and the agency’s mandate to provide an

adequate margin of safety. Studies contained

in the record provided evidence of adverse

health effects at levels below 250 μg/m3.

902 F.2d at 969 (footnotes omitted;

emphasis in original). The court also

stated that:

In setting a standard under section 109 of

the Act, the Administrator must ‘‘take into

account all the relevant studies revealed in

the record‘‘ and ‘‘make an informed judgment

based on available evidence.’’ American

Petroleum Institute v. Costle, 665 F.2d at

1187. The record shows that the

Administrator did so. The Administrator

relied on studies which showed adverse

effects at and below the 250 μg/m3 level.

AISI essentially asks this court to give

different weight to the studies than did the

Administrator. We must decline. It is simply

not the court’s role to ‘‘second-guess the

scientific judgments of the EPA. * * * [T]he

Administrator did not act arbitrarily in

drawing conclusions from the uncertain and

conflicting data. The Administrator may

reasonably apply his expertise to draw

conclusions from ‘‘imperfect data,’’ Ethyl

Corp., 541 F.2d at 28, as he did here.

Id. at 971.

As this language makes plain, the

term ‘‘data’’ may include a study relied

upon by EPA. It should be equally plain

that EPA may properly rely on such a

study in setting a standard despite the

fact that such ‘‘data’’ may be

‘‘imperfect,’’ ‘‘conflicting,’’ and

‘‘uncertain.’’ There are numerous other

cases in which EPA has relied on

studies in setting standards under the

Clean Air Act. See, e.g., Engine

Manufacturers Association v. EPA, 88 F.

3d 1075, 1099 (D.C. Cir.

1996)(upholding EPA’s use of the 1993

Dockery study for setting mobile source

standards); API v. Costle, 665 F.2d 1176,

1185 (D.C. Cir. 1981)(Administrator’s

conclusion that normal body functions
38692 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

are disrupted by ozone is ‘‘supported by

the studies’’).

A number of commenters cited

Endangered Species Committee v.

Babbitt, 852 F. Supp. 32 (D.D.C. 1994)

(hereafter ‘‘Gnatcatcher’’) in support of

the proposition that EPA must obtain

and disclose the raw data underlying

the Dockery and Pope studies. Relying

on cases such as Connecticut Light and

Power Co. v. NRC, 673 F.2d 525 (D.C.

Cir. 1982), Portland Cement v.

Ruckelshaus, 486 F.2d 375 (D.C. Cir.

1973), and United States v. Nova Scotia

Food Processing Corp, 568 F.2d 240

(2nd Cir. 1977), these commenters

suggest that ‘‘a body of legal decisions

is emerging whereby federal courts are

increasingly dubious of final regulatory

decisions that are being made absent

public scrutiny of the data underlying

and purportedly supporting such

decisions.’’ According to these

commenters, based on Gnatcatcher and

other cases, failure by EPA to obtain and

place in the docket the raw unanalyzed

data used in the Dockery and Pope

studies constitutes serious procedural

error under the Clean Air Act.

Under Connecticut Light and Power,

agencies must make available technical

studies and data that have been relied

upon during the rulemaking process in

order for the public to have an adequate

opportunity for notice and comment.

There is no question that EPA has done

this with regard to the Dockery and

Pope studies, which are included in the

rulemaking docket. The Portland

Cement case makes clear that where an

agency actually relies on factual data it

cannot ‘‘promulgate rules on the basis of

inadequate data, or on data that, [to a]

critical degree, is known only to the

agency.’’ 486 F.2d at 393. See also, Nova

Scotia, 568 F.2d 240, at 251 (where all

of the research was collected by the

agency, and none of it was disclosed ‘‘as

the material upon which the proposed

rule would be fashioned,’’ error

resulted); CMA v. EPA, 870 F.2d 177,

200 (5th Cir. 1989) (‘‘fairness requires

that the agency afford interested parties

an opportunity to challenge the

underlying factual data relied on by the

agency’’).

However, in this case, EPA did not

rely on, nor did it ever have or review,

the underlying data used in the Dockery

and Pope studies. Instead, it relied upon

the studies themselves. Thus, the cases

cited in this unit are inapposite. They

stand only for the proposition that

where an agency actually reviews and

relies on ‘‘data,’’ which may be raw

data, a study or a variety of other forms

of information, it must make these data

available. They do not and cannot stand

for the proposition that an agency may

not rely on a study alone and must

always obtain the raw and unanalyzed

data underlying a study. Indeed, as one

D.C. Circuit case noted: ‘‘Portland

Cement and Nova Scotia simply cannot

be twisted so as to require notices of

proposed or interim rules to contain

elaborate reproductions of underlying

studies.’’ Petry v. Block, 737 F.2d 1193,

1198 (D.C. Cir. 1984). Requiring EPA to

obtain, analyze and disclose the data

underlying the Pope and Dockery

studies, which EPA neither reviewed

nor relied upon, would be to require

EPA to attempt such an ‘‘elaborate

reproduction.’’ Such a step is not

required under the law and would make

it extremely difficult, if not impossible,

for EPA to regulate in complex,

technical areas ‘‘at the frontiers of

science.’’ Baltimore Gas and Electric Co.

v. NRC, 462 U.S. 87 (1983).

The district court’s decision in the

Gnatcatcher case is similarly inapposite.

That case concerned a scientific study

regarding the range of the California

Gnatcatcher, a small insectivorous

songbird. As the Gnatcatcher opinion

itself notes, ‘‘courts have generally

allowed agencies to rely on scientific

reports.’’ Gnatcatcher, 852 F.Supp. at

37. Thus, the question at issue in

Gnatcatcher was whether specific

circumstances exist in which an agency

may not be entitled to rely on studies

alone. In the Gnatcatcher case, a single

author had published two directly

contradictory studies on the same issue,

while relying on the same data. In light

of this clear contradiction, commenters

in that rulemaking argued that without

the underlying data it was impossible to

determine whether the conclusions in

either study were correct. The district

court noted that:

The Secretary had before him a report by

an author who, two years before had

analyzed the same data and come to an

opposite conclusion. It is the disputed nature

of this report that distinguishes this from

other cases where a scientific report alone

has been considered sufficient for ESA

purposes.

Id. Thus, according to the court: ‘‘While

courts have generally allowed agencies

to rely on scientific reports * * * this is

not sufficient in this case because the

report itself is under serious question.’’

Id.

The EPA’s current reliance on the

Dockery and Pope studies bears no

resemblance to the circumstances

present in the Gnatcatcher decision. As

noted previously, these studies have

been subject to extensive peer review

and scrutiny, and neither researcher has

published a contradictory study on the

same issue, much less using the same

data base. The EPA is not aware of, nor

have any of the commenters raised any

particular issues relating to either gross

error, fraud or scientific abuse arising

from the data. Indeed, as noted

previously, the prior work of these

particular researchers has been subject

to extensive independent scrutiny and

reanalysis, which has confirmed, rather

than called into question, the

underlying validity of their conclusions

and the integrity of their research

methods. Reading Gnatcatcher to

suggest that EPA cannot rely on such a

study, where the study and its methods

have been subject to extensive peer

review, would place the district court’s

rationale in Gnatcatcher in conflict with

applicable D.C. Circuit precedent that

makes evident the right of agencies to

rely on studies alone. See, e.g., Engine

Manufacturers Association v. EPA, 88

F.3d 1075, 1099 (D.C. Cir 1996); API v.

Costle, 665 F.2d 1176, 1185 (D.C. Cir.

1981), ‘‘studies discussed in the Criteria

Document constitute a rational basis for

the finding that adverse health effects

occur at ozone levels of 0.15-0.25 ppm

for sensitive individuals’’; see also,

NRDC v. Thomas, 805 F.2d 410, 418

(D.C. Cir. 1986)(EPA use of a summary

of confidential data that was not

disclosed provides ‘‘a reasoned

explanation for moving from a 4.0 to 5.0

long term NOx standard’’).

In addition, to require EPA to obtain

and analyze the data prior to revising

the standard would also contradict the

‘‘common sense notion that Congress, in

providing for notice and comment

under the APA, could not have intended

to subject the agencies—and the public

on whose behalf they regulate—to [a]

sort of interminable back and forth.’’

International Fabricare Institute v. EPA,

972 F.2d 384, 399 (D.C. Cir. 1992). In

the view of some commenters, EPA has

no choice but to either postpone its

decision for a year or more awaiting a

review of data or choose to retain the

current standard. Yet were EPA to adopt

such an approach, these commenters

would undoubtedly insist that EPA be

required to include an analysis of the

data in the docket; further questions

would likely be raised regarding the reanalysis and once again EPA might find

itself unable to promulgate its rule

pending review of further hypothetical

questions. This type of unending

inquiry is not required under the law.

As the D.C. Circuit has noted:

* * * [D]isagreement among the experts is

inevitable when the issues involved are at the

‘‘very frontiers of scientific knowledge,’’ and

such disagreement does not prevent us from

finding that the Administrator’s decisions are

adequately supported by the evidence in the

record * * * . It is not our function to resolve

disagreement among the experts or to judge
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38693

93 One commenter argued that EPA’s failure to

place the ‘‘data’’ in the docket was not an ‘‘error’’

but a ‘‘refusal to comply with the clear language of

the law that should be reviewed by the courts under

section 307(d)(9)(C), rather than 307(d)(9)(D).’’ As

noted previously, EPA does not agree with this

interpretation of section 307(d)(3) of the Act. Under

applicable caselaw, the term ‘‘data’’ may include

information in many forms, including studies that

EPA has placed in the docket. See Endangered

Species Committee v. Babbitt, 852 F. Supp. 32, 37

(D.D.C., 1994) (‘‘data can come in many forms: it

can be a scientific report, it can be graphs and

tabulations * * * it can be raw numbers’’).

94 A number of commenters did argue these

studies do not form a sufficient basis for EPA’s

decision to revise the NAAQS and that attempts to

replicate these studies have not been universally

successful. These same commenters also listed a

number of hypothetical questions and issues that

might be resolved through a review of the

underlying data and suggested that before EPA may

properly rely on these studies to revise the NAAQS,

a variety of confounders (such as smoking) should

also be ruled out by reviewing the data. As set forth

more fully in Unit II. of this preamble, neither EPA

nor CASAC agrees that any of these factors

precludes reliance on the studies in question.

the merits of competing expert views * * *

. Cf. Hercules, Inc. v. EPA, 598 F.2d 91,115

(D.C. Cir. 1978) (‘‘[c]hoice among scientific

test data is precisely the type of judgment

that must be made by EPA, not this court’’).

Lead Industries Association v. EPA, 647

F.2d 1130, 1160 (D.C. Cir. 1980).

Neither Gnatcatcher, nor any other

case can fairly be read to suggest that

EPA has an obligation to respond to all

possible questions that might be raised

regarding its scientific conclusions or

that where EPA relies on a study, it

must engage in a multi-phased and

possibly unending re-examination of the

data supporting such a study until all

commenters are satisfied in full with the

details of the underlying science. Even

assuming that EPA could obtain the

confidential Six Cities data through

litigation, a substantial delay of many

months, if not years, would likely result,

in order for both EPA and industry to

reanalyze the data. In the meantime,

some tens of thousands of premature

deaths could result. Neither the Clean

Air Act nor relevant case law requires

or permits such a result.

Indeed, the suggestion that EPA

cannot and should not rely upon the

Pope, Dockery, and Schwartz studies,

unless and until interested parties have

had an opportunity to examine and

reanalyze the underlying raw data, is

extraordinary. Given the precautionary

nature of section 109 of the Act and the

need to allow an adequate margin of

safety, see Lead Industries, 647 F.2d at

1154, 1155, there are limits on EPA’s

discretion to disregard even studies that

are clearly flawed, if they are

nonetheless ‘‘useful’’ in indicating the

kind and extent of health effects that

may result from the presence of a

pollutant in the ambient air. See

sections 109(b)(1) and 108(a)(2) of the

Act.

A few commenters cited Kennecott v.

EPA, 684 F.2d 1007 (D.C. Cir. 1982) and

argued that under sections 307(d)(8) and

307(d)(9)(D) of the Act, a failure by EPA

to obtain and include in the docket the

data underlying the Pope and Dockery

studies would constitute an ‘‘error’’ that

is ‘‘so serious and related to matters of

such central relevance to the rule that

there is a substantial likelihood that the

rule would have been significantly

changed if such error[] had not been

made.’’93 EPA disagrees. Peer reviewed

studies conducted by outside parties

were not at issue in Kennecott.

Kennecott involved a dispute over

financial analyses that EPA itself had

previously conducted and used in

earlier rulemakings. The court

determined that the financial analyses at

issue must have provided at least part

of the factual basis for EPA’s rule, and

EPA referenced these analyses in the

preamble to the final rule without

placing them in the docket until one

week before promulgation. The factual

circumstances in Kennecott are

substantially different than the current

situation and thus, Kennecott cannot

fairly be read to establish the applicable

legal standard with regard to EPA’s

reliance on peer reviewed studies for

use in setting the NAAQS.

In this case, EPA—well before

proposal—has placed the information

that it relied upon in the docket. This

information is in the form of studies.

These studies have been subject to

extensive scrutiny and peer review. To

date no specific allegation has been

made that the studies are clearly in error

or that the data underlying them are the

subject of fraud, scientific misconduct,

or gross error going to the basic validity

of the studies.94 Instead, various

commenters have merely stated their

view that were the raw data behind

these studies available, they would be

able to better verify and assess the

results reached in the studies.

As one commenter noted, ‘‘In the

absence of data on which EPA’s

proposal is based, [key scientific] issues

remain shrouded in uncertainty and

skepticism. The disclosure of the data

would allow for robust scientific

analysis and discussion of these issues.’’

A similarly hypothetical concern is

raised by another commenter who stated

that ‘‘seeing the data would clarify

substantial questions of methodology’’

and ‘‘had the Harvard data been

available, a far broader evaluation of the

defects of the Harvard Studies would

have been possible with the same

expenditure of time and money.’’ Yet,

despite having spent ‘‘in the

neighborhood of a million dollars to

duplicate and reanalyze the Harvard

data set’’ this commenter was unable to

allege any particular defect in the

methodology or results of these studies

and noted instead that ‘‘the track record

to date suggests that the claimed

associations to PM2.5 and health effects

would not have held up under such a

broader evaluation.’’

EPA is not required to await the

results of such an inquiry before

proceeding to regulate to protect human

health and the environment. The

concerns raised by the commenters

regarding these studies remain

hypothetical; the comments themselves

raise no allegations of fraud, scientific

misconduct or gross error that calls into

question the fundamental validity of the

studies. Given this fact, EPA does not

agree with the commenters that reliance

on these studies and/or a failure to place

the underlying data in the docket

constitutes an error, much less an error

that is ‘‘so serious and related to matters

of such central relevance that there is a

substantial likelihood that the rule

would have been significantly

changed.’’ EPA is entitled to rely upon

these studies and it has satisfied its

obligation to provide the ‘‘factual data’’

upon which the proposed rule is based

by placing these studies in the docket.

In fact, the concerns raised by the

commenters ultimately boil down to a

disagreement with EPA over the level of

scientific certainty necessary to adopt

the NAAQS revisions. In setting

standards under the Clean Air Act, EPA

is not required to resolve all scientific

issues to the complete satisfaction of

every interested party. As noted by the

D.C. Circuit in Lead Industries

Association v. EPA, 647 F.2d 1130, 1160

(D.C. Cir. 1980):

To be sure, the Administrator’s

conclusions were not unchallenged; both LIA

and the Administrator are able to point to an

impressive array of experts supporting each

of their respective positions. However,

disagreement among the experts is inevitable

when the issues involved are at the ‘‘very

frontiers of scientific knowledge,’’ and such

disagreement does not preclude us from

finding that the Administrator’s decisions are

adequately supported by the evidence in the

record. It may be that LIA expects this court

to conclude that LIA’s experts are right, and

the experts whose testimony supports EPA

are wrong. If so, LIA has seriously

misconceived our role * * * . It is not our

function to resolve disagreement among the

experts or to judge the merits of competing

expert views * * * . Cf. Hercules, Inc., v. EPA,

598 F.2d 91, 115 (D.C. Cir. 1978) (‘‘[c]hoice

among scientific test data is precisely the

type of judgment that must be made by EPA,

not this court’’).
38694 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

647 F.2d at 1160 (footnotes omitted).

The EPA’s rationale for proposing to

add a fine particle standard was detailed

in the preamble to the proposed rule,

most notably at 61 FR 65654–65662,

December 13, 1996. This decision is

based on the extensive review of the

science and policy issues contained in

the PM Criteria Document and Staff

Paper; the CASAC concluded, after

extensive review, that both of these

documents were appropriate for use in

decision making on standards. These

documents contain a full discussion of

both what is known about PM and the

information gaps and uncertainties.

Considering the full weight of the

scientific evidence, including the

uncertainties, the CASAC recommended

that the Administrator adopt fine

particle standards and a number of

panel members based their support for

a PM2.5 standard on the following

reasoning:

[T]here is strong consistency and

coherence of information indicating that high

concentrations of urban air pollution

adversely affect human health, there are

already NAAQS that deal with all of the

major components of that pollution except

PM2.5, and there are strong reasons to believe

that PM2.5 is at least as important as PM10-2.5

in producing adverse health effects.

Wolff, 1996.

Given the consistency and coherence

of the evidence that premature mortality

and sickness occur in large numbers of

Americans at concentrations permitted

by the current standards, it would be

irresponsible to delay action that would

put more appropriate air quality goals

into place based on the most recent

scientific information. After a review of

the comments submitted, the Agency’s

conclusion that it is appropriate to rely

on the existing studies remains

unchanged.

D. 1990 Amendments

Contrary to the view expressed in

some public comments, the provisions

of subpart 4 of Part D of Title I of the

Act, enacted in 1990, do not preclude

EPA from adopting PM2.5 as an

additional indicator for PM and

establishing standards for PM2.5. The

provisions of subpart 4 of Part D of Title

I of the Act simply do not limit EPA’s

clear authority under section 109 of the

Act to revise the PM standards.

The basic contention is that because

the provisions of subpart 4 of Part D of

Title I of the Act refer to PM10, they

prohibit EPA from regulating any other

type of PM, for example, by revising the

existing NAAQS for PM by adopting an

ambient air quality standard for PM2.5.

These provisions, however, do not lead

to such a conclusion. Moreover, this

view ignores provisions indicating that

Congress believed that EPA could revise

any existing NAAQS or adopt a new

NAAQS.

At the outset, it should be noted that

Congress expressly authorized EPA to

revise any ambient air quality standard

and to adopt a new NAAQS in section

109 of the Act. That section, which

requires EPA to review and revise, as

appropriate, each NAAQS every five

years, contains no language expressly or

implicitly prohibiting EPA from revising

a NAAQS or adopting a new NAAQS. If

Congress had intended to preclude EPA

from reviewing and revising a NAAQS

or adopting a new NAAQS, which are

part of EPA’s fundamental functions,

Congress would have specifically done

so. Clearly, Congress knew how to

preclude EPA from exercising otherwise

existing regulatory authority and did so

in other instances. See section

202(b)(1)(C) of the Act (expressly

precluding EPA from modifying certain

motor vehicle standards prior to model

year 2004); section 112(b)(2) of the Act

(preventing EPA from adding to the list

of hazardous air pollutants any air

pollutants that are listed under section

108(a) of the Act unless they meet the

specific exceptions of section 112(b)(2)

of the Act); section 249(e)(3), (f) and

section 250(b) (limiting EPA’s authority

regarding certain clean-fuel vehicle

programs). No such language was

included either in section 109 of the Act

or elsewhere in the Act and no such

implication may properly be based on

the provisions of subpart 4 of Part D of

Title I of the Act.

Second, other provisions of the Act

expressly contemplate EPA’s ability to

promulgate a new or revised NAAQS,

and provide no indication that such

ability is limited to standards other than

those whose implementation is the

subject of subparts 2, 3 and 4 of Part D

of Title I of the Act. For example,

section 110(a)(2)(H)(i) of the Act

provides that SIPs are to provide for

revisions ‘‘from time to time as may be

necessary to take account of revisions of

such national primary or secondary

ambient air quality standard * * * .’’

Section 107(d)(1)(A) of the Act provides

a process for designating areas as

attainment, nonattainment, or

unclassifiable ‘‘after promulgation of a

new or revised standard for any

pollutant under section 109 * * * .’’

Section 172(e) of the Act addresses

modifications of national primary

ambient air quality standards. Finally,

section 172(a)(1) of the Act expressly

contemplates that EPA may revise a

standard in effect at the time of

enactment of the 1990 Clean Air Act

Amendments. Section 172(a)(1)(A) of

the Act provides EPA with authority to

classify nonattainment areas on or after

the designation of an area as

nonattainment with respect to ‘‘any

revised standard, including a revision of

any standard in effect on the date of the

enactment of the Clean Air Act

Amendments of 1990.’’ Plainly,

Congress had no intention of prohibiting

EPA from revising any of the ambient

standards in effect at the time of the

enactment of the 1990 amendments.

Third, the provisions of subpart 4 of

Part D of Title I of the Act do not

support the contention that they

somehow preclude EPA from exercising

its authority to adopt a revised PM

NAAQS based on a metric other than

PM10. The fact that Congress laid out an

implementation program for the PM

standard existing at the time of the 1990

amendments in no way suggests that

Congress intended to preclude EPA

from exercising the authority it

provided EPA to revise the NAAQS

when the health data on which EPA

bases such decisions warranted a

change in the standard.

The fact that Congress drafted subpart

4 of Part D of Title I of the Act in 1990

to specify the implementation regime

for the PM standard then in effect, a

PM10 standard, in terms that explicitly

refer to PM10 in no way suggests that

Congress meant to preclude EPA from

adopting a PM standard based on

another metric if scientific information

supported such a change. Obviously,

PM10 was the standard in existence in

1990 and Congress drafted subpart 4 of

Part D of Title I of the Act, the purpose

of which was to delineate an

implementation regime for that

standard, in terms of that standard.

There is simply no language in subpart

4 of Part D of Title I of the Act that

limits EPA’s ability to establish a

different PM standard if such a standard

were warranted under section 109 of the

Act or indicates any implicit intent on

the part of Congress to limit EPA’s

authority under section 109 of the Act

in such a way. Subpart 4 of Part D of

Title I of the Act simply does not speak

to the question of whether EPA may

establish a PM standard based on a

different metric. In addition, section

107(d)(4) of the Act, the only provision

outside of subpart 4 of Part D of Title

I of the Act invoked as a basis for the

view that the Act prohibits EPA from

adopting a PM2.5 standard, does not

support that view. That provision

simply preserved pre-existing

designations for ‘‘total suspended

particulates,’’ the PM metric utilized

prior to PM10, for certain purposes. It

provides no suggestion that Congress

intended to prohibit EPA from adopting
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38695

a metric other than PM10. Indeed, if

anything, it indicates that Congress was

fully aware that EPA had previously

changed the PM metric used in the PM

NAAQS and confirms the view that

Congress would have explicitly barred

EPA from changing the metric had it

intended to do so.

Finally, for the reasons stated in this

unit, EPA’s analysis of its ability to

implement a PM2.5 standard under the

provisions of subpart 1 of Part D of Title

I does not support the view that

Congress prohibited EPA from

promulgating such a standard. Congress

clearly specified an approach to the

implementation of the PM10 standard in

the provisions of subpart 4 of Part D of

Title I of the Act. The EPA believes that

the clear and express linkage of that

approach to the PM10 standard indicates

that a different PM standard should be

implemented under the general

principles of subpart 1 of Part D of Title

I of the Act. That Congress directed

specifically how EPA and the States

should implement the PM10 standard

does not carry with it the implication

that Congress intended to prohibit EPA

from exercising its otherwise clear and

express authority to adopt a PM

standard based on a different metric in

order to carry out one of its fundamental

missions, the establishment of ambient

air quality standards to protect public

health with an adequate margin of

safety. It is entirely reasonable and

logical for Congress to, on the one hand,

specify an implementation regime for

the PM standard in effect at the time of

enactment of the 1990 amendments, but,

on the other hand, leave EPA free to

exercise the authority provided it by

Congress in section 109 of the Act to

adopt a new or revised standard when

EPA determined that such a standard

was needed to protect public health

with an adequate margin of safety.

Congress explicitly required EPA to

review and revise as appropriate the

NAAQS every five years. If Congress did

not intend for EPA to revise the NAAQS

when warranted, it would not have

required EPA to review and revise them.

If Congress had intended to prohibit

EPA from exercising such a

fundamental authority it would have

clearly specified, as it did in other

instances, that EPA could not do so.

V. Revisions to 40 CFR Part 50,

Appendix K—Intrepretation of the PM

NAAQS

Because the revocation of the existing

PM10 standards will become effective at

a later date (as discussed in Unit VII. of

this preamble), EPA is retaining 40 CFR

part 50, Appendix K, although it is

being published today in revised format

to conform with the format of the other

appendices in this part. A new

Appendix N to 40 CFR part 50 explains

the computations necessary for

determining when the primary and

secondary PM2.5 and PM10 standards

being adopted today are met. The

discussion in this unit sometimes refers

to the contents of the new Appendix N

as revisions to Appendix K, so as to

highlight how the new Appendix N

differs from the current Appendix K.

Key elements of the new 40 CFR part

50, Appendix N, particularly as they

differ from those of Appendix K, are

outlined in this unit.

A. PM2.5 Computations and Data

Handling Conventions

As discussed in Unit II.E. of this

preamble, the form of the annual PM2.5

standard is a spatially averaged annual

mean averaged over 3 years, and the

form of the 24-hour PM2.5 standard is a

98th percentile concentration averaged

over 3 years.

With regard to the annual PM2.5

standard, the EPA proposed a form

expressed as the annual arithmetic

mean, averaged over 3 years and

spatially averaged over all designated

monitoring sites to represent population

exposures. As discussed in Unit II.E.1.

of this preamble, the form of the annual

PM2.5 standard has been clarified to

make explicit that implementing

agencies have the flexibility to base

comparison of the standard level with

measured values from either a single

community-oriented site or an average

of measured values from such monitors

within the constraints enumerated in 40

CFR part 58. The new Appendix N of 40

CFR part 50 reflects this clarification.

The spatial average, if used, is to be

carried out using data from monitoring

sites designated in a State PM

Monitoring Network Description in

accordance with the provisions of 40

CFR part 58.

Also, the EPA proposed that, for

spatial averaging, the requirements for 3

years of data for comparison with the

standard be fulfilled by the spatial

averaging network as a whole, not by

individual monitors within the network.

The EPA received comments regarding

the application of the 75 percent data

completeness requirement to spatial

averaging. The commenters stated that

the inclusion or exclusion of a site not

meeting the data completeness

requirements from a spatial average,

based on the level of the single site

average, would bias the spatial average

for that year. The EPA has responded to

the comment by demonstrating in

Example 1 in 40 CFR part 50, Appendix

N the application of the data

completeness criterion that is consistent

with a spatially averaged network.

Specifically, the application of the data

completeness requirement has been

altered in the example if a particular site

has quarters in a year that do not meet

the minimum data completeness

requirement. Instead of comparing a

site’s annual average to the level of the

standard to decide whether or not to

keep the site in the calculations, the

annual average for all the sites (the

spatial average) is compared to the level

of the standard. If the spatial average is

above the level of the standard, the site

is kept in the calculations. If it is below,

the site is omitted from the calculations.

The EPA also proposed that averaging

over calendar quarters be retained for

the annual average form of the standard.

Although several commenters stated

that the step of calculating quarterly

averages to obtain the annual average

was unnecessary, the EPA maintains

that quarterly averages are important to

ensure representative sampling in areas

with extreme seasonal variation.

Regarding the 75 percent data

completeness requirement, the proposal

stated that a given year meets data

completeness requirements when at

least 75 percent of the scheduled

sampling days for each quarter have

valid data, and high values measured in

incomplete quarters shall not be ignored

but shall be included if their value

causes the annual calculation to be

above the level of the standard. Some

commenters felt that this treatment was

unfair in that measured data below the

standard in incomplete quarters are not

retained. In addition, the commenters

felt that this could create a bias where

a single sample could inflate an annual

average to a level above the standard.

The EPA agrees and has incorporated in

40 CFR part 50, Appendix N the

following provisions.

(1) A statement has been added that

less than complete data may be used in

certain cases subject to the approval of

the appropriate Regional Administrator

in accordance with EPA guidance for

dealing with less than complete data.

This statement was considered

necessary for those situations where

measured data and air quality analyses

would indicate that the area met or did

not meet the standard although it did

not exactly meet the data completeness

requirements.

(2) A provision has been added that

a minimal amount of data is needed

before the requirement to retain high

values in an incomplete quarter comes

into effect for the annual standards.

Sites with at least 11 samples but less

than 75 percent data completeness in a

quarter will have to include high values
38696 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

if they result in calculated values which

are above the level of the standard. This

provision is based upon the change in

sampling frequency set forth in the

revisions to 40 CFR part 58 which

effectively doubles the minimum

sampling frequency from 1-in-6 day

sampling to 1-in-3 day sampling. The

data completeness requirement for the

annual form of the standard under the

original 1-in-6 day sampling schedule is

equivalent to a minimum of 37.5

percent under the new sampling

schedule of 1-in-3 days. This is

equivalent to a minimum of 11 samples

in each quarter. Therefore, a minimum

of 11 samples in a quarter should be

sufficient for an annual average above

the level of the standard to be used

under the new sampling schedule.

(3) In sharp contrast, this minimum

requirement was considered

unnecessary for the 24-hour form of the

standard when the 98th percentile is

above the level of the standard. That is,

for a site with a 98th percentile above the

level of the standard that does not meet

the 75 percent data completeness

requirement, the 98th percentile would

be equivalent to the maximum or

second maximum daily concentration in

that year. While adding more data

samples up to the minimum data

completeness requirement of 75 percent

could help to ensure that the second

maximum value (rather than the

maximum value) corresponds to the 98th

percentile, this difference is not

considered significant enough to require

some minimal number of data samples

when dealing with the form of the 24-

hour standard.

With regard to the 24-hour PM2.5

standard, the proposed revision to 40

CFR part 50, Appendix K defined the

98th percentile as the daily value out of

a year of monitoring data below which

98 percent of all values in the group fall.

The calculation of the percentile form

has been revised to reflect general

comments that the form of the standard

and its calculation should be simplified.

The EPA maintains that the revised

calculation is consistent with the

definition of the percentile being that

number below which a certain percent

of the data fall.

Regarding the expression of the

annual standard to the nearest 0.1 μg/m3

and the 24-hour standard to the nearest

1 μg/m3, virtually no commenters

disagreed with the EPA’s proposed

approach. The few that did, however,

took issue with the overall stringency of

the standards, not the rationale

discussed in the proposal. The EPA

maintains its position that instrument

sensitivity and the number of measured

values used in calculating the values to

be compared to the standard, as

discussed at length in the proposal,

point to keeping the expressions of the

standards stated in this unit.

B. PM10 Computations and Data

Handling Conventions

As discussed in Unit II.G. of this

preamble, the EPA proposed retaining

the current annual arithmetic mean,

averaged over 3 years, as the form of the

annual PM10 standard, and changing the

form of the 24-hour PM10 standard to a

98th percentile value form, averaged

over 3 years. As discussed in Unit II.G.

of this preamble, the form of the daily

PM10 standard has been revised to a 99th

percentile instead of the 98th percentile,

and the related calculations have been

revised accordingly. The same revision

described above in Unit V.A. of this

preamble to simplify the formula used

to calculate the percentile form of the

24-hour PM2.5 standard also applies to

the PM10 99th percentile calculation.

The revisions made to the annual and

24-hour PM2.5 standards regarding the

75 percent data completeness

requirement also apply to the annual

and 24-hour PM10 standards. Appendix

N of 40 CFR part 50 reflects this change.

As with the PM2.5 standards, the EPA

maintains its position that instrument

sensitivity and the number of measured

values used in calculating the values to

be compared to the standard, as

discussed in detail in the proposal,

point to keeping the expressions of the

standards to the nearest 1 μg/m3 for the

annual standard and to the nearest 10

μg/m3 for the 24-hour standard.

C. Changes That Apply to Both PM2.5

and PM10 Computations

In the proposal, the EPA stated that

revisions to 40 CFR part 50, Appendix

K would not address the treatment of

exceptional events data, which are

considered part of the standards

implementation process. Since several

commenters mentioned the handling of

these events in conjunction with the

proposed revisions to Appendix K, the

EPA has addressed this concern in

Appendix N of 40 CFR part 50, which

states that whether to exclude, retain, or

make adjustments to data affected by

uncontrollable or natural events is

subject to the approval of the

appropriate Regional Administrator.

Comments were also received

expressing the desire of some areas to

conduct seasonal sampling, reducing

the frequency of monitoring during a

period of expected low concentrations

to save resources. The proposed revision

to 40 CFR part 50, Appendix K did not

prohibit this course of action, and

referred matters of sampling frequency

to 40 CFR 58.13. For clarification, 40

CFR part 50, Appendix N adds that

exceptions to specified sampling

frequencies, such as a reduced

frequency during a season of expected

low concentrations, shall be subject to

the approval of the appropriate Regional

Administrator.

VI. Reference Methods for the

Determination of Particulate Matter as

PM10 and PM2.5 in the Atmosphere

A. Revisions to 40 CFR Part 50,

Appendix J—Reference Method for PM10

Because the revocation of the existing

PM10 standards will become effective at

a later date (as discussed in Unit VII. of

this preamble), EPA is retaining

Appendix J in its current form. A new

Appendix M to 40 CFR part 50

establishes the reference method for

measuring PM10 in the ambient air for

the revised PM10 standards. The

discussion in this unit sometimes refers

to the contents of the new Appendix M

as revisions to Appendix J, so as to

highlight how the new Appendix M

differs from the current Appendix J. As

discussed below, the only revision to

the Reference Method for PM10 relates to

the calculation of the volume of air

sampled.

During the course of this standards

review, EPA has received a number of

comments regarding the appropriateness

of the current practice of adjusting

measured PM10 concentrations to reflect

standard conditions of temperature and

pressure (25° C and 760 mm Hg,

respectively), as required by 40 CFR part

50, Appendix J. The practice was

originally adopted to provide a standard

basis for comparing all pollutants

measured in terms of mass per unit

volume (e.g., μg/m3). As EPA has

reviewed the ambient standards for

gaseous pollutants, however, technical

changes have been made to express

them on a pollutant volume/air volume

basis (i.e., ppm) that is insensitive to

differences in altitude and temperature.

Such an approach is not applicable to

particulate pollutants. The question

arises whether continuing the past

practice of making temperature and

pressure adjustments for PM is

appropriate or necessary.

Information in the Criteria Document

on the health and welfare effects of PM

provides no clear basis for making such

adjustments. Recent health effects

studies have been conducted in cool

and warm climates, and in cities at high

altitude, e.g., Denver, as well as near sea

level, e.g., Philadelphia (U.S. EPA,

1996a). These studies provide no

evidence that risk associated with PM

exposures is affected by variations in
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38697

altitude. Accordingly, any effect that

would be accounted for by temperature

and pressure adjustments would be

below the detection limits of

epidemiological studies. While extremes

of altitude might be expected to increase

the delivered dose of PM in those not

acclimatized to such locations, the

dosimetric studies summarized in the

Criteria Document provide no clear

support for any quantitative adjustment

to standard conditions. With respect to

welfare effects, visibility is directly

related to the actual mass of fine

particles in the atmosphere. Adjustment

of PM concentrations collected at higher

altitudes to standard conditions would

therefore lead to an overstatement of the

effect of PM on visibility in such

locations. Similarly, there is no

evidence in the Criteria Document

suggesting that effects on materials

damage and soiling are dependent on

altitude.

Based on this assessment, EPA

proposed to delete the requirement to

adjust PM10 concentrations to standard

conditions of temperature and pressure

from 40 CFR part 50, Appendix J for the

revised standards and to make

corresponding revisions in 40 CFR 50.3.

Comments received on this issue were

divided. A number of commentors

supported EPA’s proposal for the

reasons set forth above. A few States

opposed the change because the lack of

adjustment for very cold temperature in

areas near sea level could make the

standard more stringent. Some

commentors were concerned that the

proposed change would relax protection

afforded for areas at high altitude. A few

commentors expressed concern that

‘‘sojourners’’ who visit high altitude

area would have higher ventilation rates

and receive reduced protection as

compared to local residents whose

ventilation patterns were more adapted

to these conditions.

The EPA does not believe that the

localized comparisons regarding

increased or decreased stringency of

standards relative to the proposed

change are an appropriate rationale for

keeping the current adjustment for

temperature and pressure. The issue is

whether the available scientific

evidence on the health and welfare

effects of PM provides a basis for

continuing with the traditional

adjustments. The comments with

respect to sojourners at altitude are

relevant, but this issue was considered

in reaching the proposed decision.

Furthermore, commentors provided

neither laboratory nor epidemiologic

evidence that would support their

theoretical concerns regarding increased

annual or 24-hour PM effects at

altitudes typical of mountainous urban

areas in the United States.

Based on its assessment of the

available evidence and public

comments, EPA concludes that a

continuation of the practice of adjusting

PM10 concentrations to standard

conditions of temperature and pressure

is not warranted or appropriate.

Accordingly, this requirement is not

included in 40 CFR part 50, Appendix

M and corresponding revisions are

made in 40 CFR 50.3. In addition, EPA

is also incorporating the proposed

minor modifications to 40 CFR part 50,

Appendix J in Appendix M.

B. 40 CFR Part 50, Appendix L - New

Reference Method for PM2.5

1. Introduction. A new reference

method for the measurement of fine

particles (as PM2.5) in the ambient air

has been developed for the primary

purpose of determining attainment of

the new PM2.5 standards. The method is

described in the new 40 CFR part 50,

Appendix L, and joins the other

reference methods (or measurement

principles) specified for other criteria

pollutants in other appendices to 40

CFR part 50.

In developing the proposed new

reference method for PM2.5, EPA staff

consulted with a number of individuals

and groups in the monitoring

community, including instrument

manufacturers, academics, consultants,

and experts in State and local agencies.

The approach and key specifications

were submitted to the CASAC Technical

Subcommittee for Fine Particle

Monitoring, which held a public

meeting to discuss the proposed new

reference method for PM2.5 and related

monitoring issues on March 1, 1996.

Comments on the proposed method

were provided orally and in writing by

interested parties. The Technical

Subcommittee indicated their overall

satisfaction with the method in a letter

(Price, 1996) forwarded by CASAC to

the Administrator.

On December 13, 1996, EPA proposed

the new 40 CFR part 50, Appendix L at

61 FR 65676 for public comment. The

proposal described in detail the

approach taken and the design

specifications and performance

requirements for the new PM2.5 sampler.

On January 14, 1997, EPA held a public

hearing on the proposed new 40 CFR

part 50, Appendix L and associated 40

CFR parts 53 and 58 requirements.

2. Basic reference method approach.

In addition to the primary purpose of

the new PM2.5 reference method

(determining attainment of the

standards), EPA considered a variety of

possible secondary goals and objectives

that the PM2.5 reference method might

also fulfill. Subsequently, various

alternative PM2.5 measurement

techniques were evaluated. From this

analysis, EPA proposed to base its PM2.5

reference method on a conventional

type sampler that collects 24-hour

integrated PM2.5 samples on a 47 mm

Teflon filter that is subsequently

moisture and temperature conditioned

and analyzed gravimetrically. The

sampler is a low volume sampler that

operates at a flow rate of 1 cubic meter

per hour, for a total sample volume of

24 m3 for the specified 24-hour sample

collection period. The sampler is easy to

operate, operates over a wide range of

ambient conditions, produces a

measurement that is comparable to large

sets of previously collected PM data in

existing databases, and provides a

physical sample that can be further

analyzed for chemical composition.

3. Public comments and responses—

a. Sampler design. The EPA received

many general comments concerning the

proposed sampler design. Commenters

suggested the use of a different

indicator, use of a different size cut,

inclusion of additional constituents

(e.g., acid aerosols, carbon, metals, and

semi-volatiles), and/or use of a multifilter method. Early in the development

process, design decisions were based on

public input and the advice of CASAC

on these and other basic design issues.

Other factors affecting the basic design

of the method were the need for

historical continuity, high measurement

precision, and simplicity of operation,

all in response to current national

monitoring objectives and available

resources. In selecting the basic

measurement approach, substantial

weight was given to maintaining

comparability to PM2.5 samplers, such as

the ‘‘dichotomous sampler,’’ that were

widely used to obtain the data upon

which the new standards are based.

Given this objective, EPA concludes that

the conventional PM measurement

approach is appropriate and will

provide PM2.5 measurements that are

comparable to the air quality data used

in the health studies that provide the

basis for the PM2.5 standards.

Although the sampler is conventional

in configuration, its design is much

more sophisticated than that of previous

PM samplers. This more sophisticated

sampler, together with improved

manufacturing and operational quality

assurance, is necessary to achieve the

more stringent data quality objectives

established for PM2.5 monitoring data.

To meet precision requirements, the

critical mechanical components of the

inlet, particle size separator, downtube,

and upper portion of the filter holder
38698 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

are specified by design. All other

aspects of the sampler are specified by

performance-based specifications.

Several commenters felt that the

portions of the sampler that were

specified by design would stifle further

improvements and innovations.

Although the EPA specifies methods by

performance whenever possible, for the

PM2.5 reference method, development of

adequate performance specifications for

inlet aspiration and particle size

discrimination would have been a very

difficult, costly, lengthy, and

problematic process. Moreover,

manufacturer testing of proposed inlet

and particle size discrimination devices

against such performance specifications

would require elaborate specialized

facilities and would be extremely costly.

For these reasons, the EPA believes that

specification of these critical

components by design is a prudent and

very cost-effective way to ensure good

inter-manufacturer and intramanufacturer precision of the PM2.5

measurements. Therefore, these

components are specified by design, and

other aspects of the sampler are

specified by performance, as proposed.

Innovations and improved samplers or

measurement methods are encouraged

and provided for as Class II and III

equivalent methods (see 40 CFR part

53).

b. Inlet and impactor design. Several

commenters addressed the inlet design,

noting that the inlet could allow

entrance of precipitation and possibly

insects. In fact, the inlet selected for the

sampler has been used effectively for

many years to obtain many of the PM2.5

measurements that formed the basis of

the epidemiological studies. While EPA

acknowledges that there have been some

reports of intrusion of precipitation, the

Agency believes the problem is

relatively minor. Nevertheless, a

modification of the inlet has been

developed to further reduce the

possibility of precipitation (and possibly

small insects) reaching the sample filter

to damage the PM2.5 sample. Extensive

wind tunnel tests have shown no

significant compromise in the PM2.5

aspiration performance of the modified

inlet.

In addition, a new provision has been

added, in 40 CFR part 50, Appendix L,

section 7.3.8, to require that the

sampling air entrance of the inlet be at

a height of 2 ± 0.2 meters above the

supporting surface to help ensure

homogeneous air samples when

collocated samplers of different types

are operated simultaneously.

Other commenters addressed the

sharpness of the size cut and how it is

obtained, e.g., whether more than two

stages should be used and what size cut

should be used for each stage. These

aspects were carefully considered in

selecting the sampler configuration. The

selection by EPA of the previously used

PM10 inlet established the size cut for

the first stage, and the second stage was

designed to be simple, reliable, and low

in cost for user agencies. In EPA’s

estimation, the advantages of this

configuration outweigh any modest

advantage that might have been gained

by designing a new inlet/separation

configuration that would further refine

the cut points at each of two (or more)

stages.

A few commenters questioned

whether the inlet was wind speed

dependent at high wind speeds. The

selected inlet has been shown to

perform well up to 24 km/hr with 10 μm

aerosols and is expected to perform well

at higher speeds with 2.5 μm aerosols.

The EPA again determined that the

advantages of using the selected inlet

outweighed the possible minor

improvement in wind-speed

characteristics that might have been

obtained by a newly-designed inlet.

Some commenters felt that other types

of particle discrimination techniques

such as cyclones and virtual impactors,

should be allowed. Again, these

alternatives were evaluated previously

and the specified inlet and impactor

were determined to best meet the

various objectives of the sampler.

However, EPA has provided for

considerations of other particle size

selection techniques or devices for

approval if incorporated into candidate

equivalent methods for PM2.5.

Several commenters addressed the

impactor design, noting that the

impactor should be changed to sharpen

the size-cut characteristic, to address

concerns regarding possible

contamination and/or performance loss

due to impactor oil, and to improve ease

of access to service. To address the first

concern, the initial prototype impactor

has been modified slightly to sharpen its

size-cut. The current impactor is

designed to lower cost and to optimize

cut sharpness, loading capacity,

manufacturing simplicity,

manufacturing quality control,

serviceability, and reliability. A report

containing the penetration efficiency of

the impactor is available in Docket No.

A-95-54. With regard to impactor oil

concerns, the impactor oil selected has

a very low vapor pressure, and testing

has indicated no contamination of the

sample filters with impactor oil. The

EPA believes that the impactor design is

as accessible as possible, given the

design objectives. Some flexibility may

be allowed for manufacturers to develop

improved closure devices or other

external modifications. Proper

maintenance will, of course, be very

important and will be stressed in the

associated operator instruction manuals

and in other training and guidance

materials. The EPA has been performing

field and laboratory tests that will

provide detailed guidance for all

necessary preventive maintenance.

Proper installation procedures for the

oil and the impactor filter, as well as all

other maintenance requirements, will be

available in the quality assurance

procedures and guidance contained in

the new section 2.12 of Appendix L to

be added to EPA’s Quality Assurance

Handbook for Air Pollution

Measurement Systems (EPA/600/R-94/

038b).

c. Anodized aluminum surface. All

internal surfaces exposed to sample air

prior to the filter are required to be

anodized aluminum as stated in 40 CFR

part 50, Appendix L, section 7.3.7. A

few commenters expressed concern that

the anodized aluminum surfaces in high

volume PM10 samplers have shown

substantial pitting, particularly in the

venturi flow control device. The

anodized aluminum surfaces are

required in the PM2.5 sampler to

maintain comparability to previously

used samplers. The EPA believes that

the much lower flow rate in the PM2.5

sampler will greatly reduce the pitting

tendency, and the active flow control in

the PM2.5 sampler is not dependent on

the physical dimensions of a critical

orifice as it is in a venturi flow control

device.

d. Filter for PM2.5 sample collection.

The proposed reference method called

for the sample to be collected on a 47

mm Teflon filter. Many of the comments

received on the measurement method

concerned the proposed filter medium

and its performance. Commenters

expressed concerns with the use of

Teflon filters and with the selection of

a single-filter method. Several

commenters recommended that

alternative filter media be allowed, in

most cases to support speciation and/or

to allow the capture of all PM

components. Other comments noted

potential advantages of other media in

operating characteristics or chemistry

requirements. Operational concerns

expressed about Teflon filters included

tearing, possible loss of integrity, and

high cost. Other concerns were that

Teflon is generally not conducive to

carbon analysis, and that Teflon filters

may not hold deposited PM. Many

commenters recommended use of a

multi-filter sampler to support chemical

speciation in addition to compliance

determination.
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38699

To address some of these general

concerns about the performance of the

specified filter material, some minor

refinements to the filter specifications

concerning the filter diameter and the

filter support ring have been made to

ensure proper performance of the filter

in the specified filter holder. Additional

clarifications have been made to the

maximum moisture pickup and the

filter weight stability requirements.

Although Teflon may preclude certain

chemical analyses (e.g., elemental and

organic carbon), the EPA believes that

Teflon filter material is the best overall

choice to meet the objectives of

compliance monitoring and to provide

good measurement precision. Other

filter media are likely to provide

reduced gravimetric precision and

preclude more types of subsequent

chemical analysis. Additional or

alternative samplers or filter types can

be considered as candidate equivalent

methods under 40 CFR part 53 and can

be used for non-compliance monitoring,

where necessary.

Compliance monitoring based on

mass concentration of PM2.5 is the

primary objective of the reference

method. Multi-filter capability would

have substantially increased the cost

and complexity of the sampler.

However, multi-filter samplers can be

considered as candidate equivalent

methods. In addition, multi-filter

samplers can be used as special purpose

monitors (SPMs) to perform

characterization studies, develop

control strategies, and conduct other

special studies as has been done

previously for PM10.

In response to numerous comments

received on 40 CFR part 50, Appendix

L and on the provisions of 40 CFR part

58 regarding the need for chemical

speciation, the EPA is assigning a high

priority to a chemical speciation trends

network through section 105 of the Act

grant allocation program and will issue

guidance describing the monitoring

methods and scenarios under which

speciation should be performed. The

program will incorporate additional

PM2.5 samplers that allow for the

simultaneous collection of aerosols on

multiple filter media.

The associated requirement for

archiving filters has been removed from

40 CFR part 50, Appendix L, section

10.17 and relocated to 40 CFR part 58,

Appendix A. This change has been

made because this is a supplemental

monitoring requirement and not an

integral part of the reference method for

determining compliance with the PM2.5

NAAQS.

Provisions of 40 CFR part 50,

Appendix L have been clarified to apply

not only to a single-sample sampler, but

also to a sequential-sample sampler,

provided that all specifications are met

and no deviations, modifications, or

exceptions are made to the inlet,

downtube, impactor, or the upper

portion of the filter holder. Samplers

that have minor changes or

modifications in these components,

have changes that alter the aerosol’s

flow path, or contain other significant

deviations will be required to meet the

requirements of Class I equivalent

methods, in the amendments to 40 CFR

part 53. Further, a provision has been

added to require that sequential sample

filters stored in a sequential sampler be

adequately covered and protected from

contamination during storage periods in

the sampler.

A few commenters expressed concern

about who must carry out filter tests to

determine if they meet the filter

specifications. In response, the filter

specifications have been clarified to

indicate that filter manufacturers should

generally carry out most or all of the

filter performance tests in order to

certify that their filters meet the filter

specifications for the PM2.5 reference

method. In addition, EPA conducts

acceptance tests on filters procured for

NAMS/SLAMS networks prior to

distribution to State and local agencies.

Some commenters requested

additional information on the

requirement that an ID number be

attached to each filter. Preliminary

information indicates that it is not

practical at this time for either filter

manufacturers or users to print an ID

number directly on the filter. However,

EPA is continuing to pursue this goal.

In the meantime, alternative means,

such as attaching an appropriate ID

number to the filter’s storage container,

will be necessary. Additional details

and possible alternative filter

identification methods will be provided

in new section 2.12 of the Quality

Assurance Handbook for Air Pollution

Measurement Systems.

e. Filter handling/weighing/

conditioning requirements. Many

commenters felt that the filter handling

requirements for collected PM2.5

samples were too burdensome.

However, handling of the exposed filter

between retrieval from the sampler and

commencement of the conditioning

period is expected to be one of the most

significant sources of PM2.5

measurement variability. Thus, EPA

concludes that specific requirements for

this activity are necessary, and this

position was supported by several

commenters.

Some commenters felt that the

samples should be kept cold until

analysis to prevent volatile losses. In

response to this concern, the restriction

on the maximum temperature exposure

for collected samples has been reduced

from 32 to 25° C, and a recommendation

has been added for sampler operators to

keep the samples as cool as practical

between retrieval from the sampler and

delivery to the conditioning

environment. Further, the length of time

permitted between retrieval of the filter

and post-collection weighing is

increased from 10 to 30 days, provided

that the sample is maintained at 4° C or

less between retrieval and the start of

the conditioning period. The new

section 2.12 of the Quality Assurance

Handbook for Air Pollution

Measurement Systems will provide

guidance and techniques for keeping

samples cool during this period and

may suggest devices to document

maximum temperature exposure of the

sample.

Commenters also requested additional

specifications and guidance for field

blanks. The EPA will provide additional

clarification and detailed procedures

and guidance regarding field blanks in

the new section 2.12 of the Quality

Assurance Handbook for Air Pollution

Measurement Systems.

Other commenters felt that the filter

weighing requirements were too

restrictive. Because filter weighing is

one of the most significant sources of

PM2.5 measurement variability, specific

requirements and restrictions are

deemed necessary. However, in

response to some of the concerns

expressed, the proposed requirement

that both pre- and post-weighings be

carried out by the same analyst has been

reduced to a non-mandatory

recommendation. Detailed

recommendations and guidance on filter

weighing, based on information

obtained in current field tests, will be

provided in the new section 2.12 of the

Quality Assurance Handbook for Air

Pollution Measurement Systems.

Several commenters questioned the

filter conditioning requirements, with

some requesting a lower humidity

range. Since humidity can profoundly

affect the weight of the PM2.5 on the

filter, EPA maintains that filter

conditioning requirements need to be

tight to control measurement variability

and to ensure satisfactory precision. But

in response to at least one of the

concerns, the filter conditioning

humidity requirement has been changed

to allow conditioning at a relative

humidity within ±5 RH percent of the

mean ambient humidity during

sampling (down to a minimum of 20 RH

percent) for samples collected at average

ambient humidities lower than 30
38700 Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations

percent. The EPA will provide further

details on filter conditioning controls in

the new section 2.12 of the Quality

Assurance Handbook for Air Pollution

Measurement Systems.

f. Sampler performance requirements.

Several commenters addressed sampler

performance requirements, including

sampler flow control specifications,

filter temperature control, sampler

performance under extreme conditions,

and data reporting. In response to

concerns that various sampler flow

control specifications are too tight, EPA

contends that good flow control is

necessary to maintain uniform

sampling, to ensure correct particle size

discrimination, and to control

measurement variability. Sampler

manufacturers have been able to meet

the specified flow control requirements,

and field studies to date confirm that

prototype samplers are able to meet

these flow control requirements.

In response to comments about the

ambient temperature plus 3° C filter

temperature control requirement, EPA

believes that fairly tight control of the

sample filter temperature is necessary to

minimize losses of semi-volatile

components over a wide temperature

range, and tight temperature control has

been strongly recommended by the

CASAC. Monitoring of the filter

temperature difference from ambient

temperature is necessary to verify that

the sampler filter temperature control is

functioning properly. Testing to date

indicates that the proposed 3° C (above

ambient temperature) limit is somewhat

difficult to meet; however, a 5° C limit

can be reasonably met. Therefore, the

filter temperature control requirement

has been relaxed slightly from 3° C to

not more than 5° C above the concurrent

ambient temperature. Ambient and filter

temperature sensors will require

periodic calibration or verification of

accuracy. In response to a frequent

comment, the method has been clarified

to indicate that exceedance of the filter

temperature difference limit would not

necessarily invalidate the sample.

In response to concerns about the

performance of the sampler under

extreme weather conditions (e.g., high

or low temperatures, low pressures,

high winds, high or low humidity, fog,

dust storms), the EPA has established

sampler specifications that are intended

to cover reasonably normal

environmental conditions at about 95

percent of expected monitoring sites.

Qualification test requirements in 40

CFR part 53 address most, if not all, of

these operational requirements.

Specification of the sampler

performance for sites with extreme

environmental conditions would

substantially raise the cost of the

sampler for other users, most of whom

do not require the extra capability.

Users requiring operation of samplers

under extreme conditions are

encouraged to develop supplemental

specifications for modified samplers to

cover those specific conditions. Sampler

manufacturers have indicated a

commitment to respond to the need for

modified samplers for such extreme

conditions.

Although concerns were expressed

that the amount of data required to be

reported from each sampler is excessive,

EPA stresses that only a portion of the

data collected by the sampler needs to

be reported to AIRS. These limited data

reporting requirements (i.e., ambient

and filter temperature, barometric

pressure, sample volume, variation in

sample run flow rate) are important to

establish or verify the reliability and

confidence of the PM2.5 measurements

and to aid in utilization of those data.

The substantial amount of additional

data generated by the sampler are of use

to the site operator to provide

confirmation of a given sample’s

validity, and to aid in troubleshooting

should outlier measurements appear in

the monitoring data. A variety of current

electronic devices and systems may be

used to acquire and handle the data, and

these devices can easily accommodate

the amount of data required to be

reported, as well as the additional,

optional data. Printers, modem

connections, and alternative data output

connections or devices are not

precluded.

4. Additional changes. Additional

clarifying changes have also been made

throughout 40 CFR part 50, Appendix L,

based on comments received or recently

obtained field test information. In 40

CFR part 50, Appendix L, section 3.1,

the lower concentration of the method

has been revised from 1 to 2 μg/m3,

based on the results of field blanks

associated with available field test data.

In 40 CFR part 50, Appendix L, section

3.3, the sample period specification has

been augmented to clarify that a

measured PM2.5 concentration for a

sample period less than 23 hours that is

greater than the NAAQS level(s) is to be

considered a valid measurement for

comparison to the NAAQS, even though

not valid for other purposes. Sections 4

(Accuracy) and 5 (Precision) have been

revised to properly reflect associated

changes to the data quality and method

performance assessment requirements

set forth in 40 CFR part 58, Appendix

A.

A provision has been added in 40 CFR

part 50, Appendix L, section 7.4.17 to

require sampler manufacturers to make

available computer software to input

sampler output data and translate the

data into a standard spreadsheet format

(since no specific format is specified for

output of the sample data acquired by

the sampler).

The requirements for the sampler to

display current flow rate, temperature,

filter temperature, and barometric

pressure readings have been changed to

require updating of these readings at

least every 30 seconds. This change is

based on operational experience of

prototype samplers in 40 CFR part 50,

Appendix L, section 7.4.5.1, and will

make it easier for the operators to

perform status checks and calibrations.

In 40 CFR part 50, Appendix L, section

7.4.8.1, the requirements for the ambient

temperature sensor have been changed

to specify an external sensor with a

passive sun shield, to provide better

uniformity in the ambient temperature

measurements among different types of

reference method samplers. The

reference method has also been clarified

to indicate that PM2.5 samples for which

the sampler reported an out-ofspecification (FLAG) occurrence during

or after the sample period are not

necessarily invalid, and that such

samples should be reviewed by a quality

assurance officer (40 CFR part 50,

Appendix L, section 10.12). Finally, a

new reference has been added in section

13 of the Act to provide applicable

standards for meteorological

measurements and measurement

systems.

5. Decision on 40 CFR part 50,

Appendix L. After fully considering the

public comments on the proposed new

reference method for PM2.5, EPA has

concluded that the proposed design and

performance specifications for the

reference sampler, with the

modifications discussed in this unit,

will achieve the design objectives set

forth in the proposal and outlined

above. Therefore, EPA is adopting the

sampler and other method requirements

specified in 40 CFR part 50, Appendix

L as the reference method for measuring

PM2.5 in the ambient air.

Since proposal, a series of field tests

have been performed using prototype

samplers manufactured in accordance

with the proposed design and

performance specifications. The results

of these field tests confirm that the

prototype samplers perform in

accordance with design expectations.

Operational experience gained through

these field tests did, however, identify

the need for minor modifications as

discussed above in this unit. In

addition, EPA made other modifications

to the proposed design and performance

specification in response to public
Federal Register / Vol. 62, No. 138 / Friday, July 18, 1997 / Rules and Regulations 38701

comment as discussed above. As part of

this process, EPA performed laboratory

tests to ensure that the modifications

achieved the intended objective.

While the results of these field tests

and laboratory tests were largely

confirmatory in nature and did not

indicate a need to alter the basic design

and performance specifications, they

did identify areas that needed further

refinement. Given that these tests were

performed, by necessity, during and

after the close of the public comment

period and because the results were not

available for placement in the docket

until late in the rulemaking process,

EPA is announcing, in a separate

Federal Register notice being signed

today, a supplemental comment period

for the limited purpose of taking

comments on these field and laboratory

test results.

VII. Effective Date of the Revised PM

Standards and Applicability of the

Current PM10 Standards

In summary, the primary and

secondary NAAQS for PM have been

revised by establishing annual and 24-

hour PM2.5 standards; and by changing

the form of the existing 24-hour PM10

standards. The existing PM10 annual

standards have been retained. Section

50.3 (reference conditions) of 40 CFR

part 50 has been revised to remove the

adjustment of measured PM10

concentrations to standard conditions of

temperature and pressure with respect

to the revised PM standards. (Although

EPA is retaining the current annual

PM10 standards, the revision of 40 CFR

50.3 potentially may affect the effective

stringency of the annual standards.) A

new Appendix M has been added to 40

CFR part 50 that reflects the revision of

40 CFR 50.3. A new Appendix N to 40

CFR part 50 has been added to reflect

the forms of the PM2.5 and revised PM10

standards. Finally, a new Appendix L to

40 CFR part 50 has been added that

specifies the reference method for

measuring PM2.5 in the ambient air.

The revised PM NAAQS, the revisions

to 40 CFR 50.3, and the new

Appendices M, N, and L to 40 CFR part

50 will become effective September 16,

1997. Inherent in the establishment of

this revised set of PM standards and

related provisions is the revocation of

the current set of PM10 standards and

associated provisions. To provide for an

effective transition from the existing PM

standards to the revised PM standards

—in light of the need to establish PM2.5

monitoring networks, designate areas,

and develop control strategies for

PM2.5—the Administrator has

determined that the effective date of the

revocation of the current set of PM10

standards and associated provisions

should be delayed so that the existing

standards and associated provisions will

continue to apply for an interim period.

The duration of the interim period

would depend on whether the area in

question has attained the current PM10

standards, as described below in this

unit.

First, section 172(e) of the Act

provides that, if the Administrator

relaxes a national primary ambient air

quality standard, she shall, within 12

months after the relaxation, promulgate

requirements applicable to all areas that

have not attained that standard as of the

date of the relaxation. Those

requirements shall provide for controls

that are not less stringent than the

controls applicable to areas designated

nonattainment before such relaxation.

Although the set of revised PM

standards, viewed as a whole, is more

stringent than the set of current PM

standards, it appears that the shift from

the current PM10 standards to the

revised PM10 standards, viewed in and

of itself, represents a relaxation of the

current PM10 standards. As a result,

section 172(e) of the Act requires EPA

to issue a rule within 12 months to

apply implementation requirements no

less stringent than the currently

applicable requirements for those areas

that have not yet attained the current

PM10 standard(s) by today’s

promulgation. However, the Act does

not specifically provide how to ensure

that States with current PM10 problems

should maintain the necessary public

health protection in the interim between

promulgation of a relaxed standard and

issuance of a rule under section l72(e)

of the Act. For that reason, EPA believes

that it is both necessary and appropriate

to defer the effective date of the

revocation of the current PM10

standards, for areas that have not

attained those standards, until EPA

issues the rule called for by section

172(e) of the Act.

Second, since it will take many years

for States to identify PM problems

under the revised standards and to

develop effective means for addressing

those problems, EPA believes it is

necessary for even those areas that have

already attained the current PM10

standards (and hence are not subject to

the terms of section 172(e) of the Act)

to continue their current PM10

implementation efforts for the purpose

of protecting public health in the

transition to implementation of the

revised standards.

In order to deal with both of these

categories of areas—those that are not

attaining the current PM10 standards

and those that are in attainment of the

current PM10 standards—EPA is taking

a two-pronged approach towards

deferral of the effective date of the

revocation of the current PM10

standards. For those areas that are not

attaining the current PM10 standards at

the time of the promulgation of the

revised PM10 standards, the current

standards will continue to apply until

EPA has completed its rulemaking

under section 172(e) of the Act to

prevent backsliding in those areas. This

will assure that no backsliding can

occur in the interim period between the

promulgation of the revised standards

and the completion of the rulemaking

under section 172(e) of the Act. For

those areas that are attaining the current

PM10 standards at the time of

promulgation of the revised PM10

standards, the existing PM10 standards

will continue to apply until the areas

have an approved SIP that includes any

control measures that had been adopted

and implemented at the State level to

meet the current PM10 NAAQS and have

an approved section 110 SIP for

purposes of implementing the revised

PM standards. If an area has already

received approval of a PM10 SIP

embodying all of the measures that had

been adopted and implemented at the

State level, no further Part D submission

or approval would be necessary. If an

area has already submitted such

measures, EPA would need to take

action to approve them. Finally, if an

area has not yet submitted such

measures to EPA for inclusion in the

SIP, the area would need to submit them

and EPA would need to approve them.

This submission and approval would

serve to satisfy both the area’s remaining

subpart D obligations and, in part, its

new obligations under section 110(a)(1)

of the Act regarding the implementation

of the revised PM NAAQS. EPA

emphasizes that it is not requiring an

approval of a modeled attainment

demonstration for the current PM10

NAAQS, only an approval of the control

measures that had in fact been adopted

and implemented and that, therefore,

were responsible for the area’s

attainment of the current PM10

standards.

The existing definition of reference

conditions and 40 CFR part 50,

Appendices J and K will remain in force

as long as the current PM10 standards

apply to an area. Additional policies

and guidance for assuring an effective

transition will be set forth in future EPA

guidance, policies, and/or rules.

VIII. Regulatory and Environmental

Impact Analyses

As discussed in Unit IV of this

preamble, the Clean Air Act and judicial