24634 Federal Register / Vol. 52, No. 126 / Wednesday, July 1, 1987 / Rules and Regulations

ENVIRONMENTAL PROTECTION

AGENCY

40 CFR Part 50

[AD-FRL 3141-9(a)]

Revisions to the National Ambient Air

Quality Standards for Particulate

Matter

AGENCY: Environmental Protection

Agency (EPA).

ACTION: Final rule.

SUMMARY: In 1971, EPA promulgated

primary and secondary national

ambient air quality standards for

particulate matter, measured as "total

suspended particulate matter" or "TSP."

The primary standards were set at 260

jig/m s , 24-hour average not to be

exceeded more than once per year, and

75 /g/m s , annual geometric mean. The

secondary standard, also measured as

TSP, was set at 150 #Lg/m s , 24-hour

average not to be exceeded more than

once per year. In accordance with

sections 108 and 109 of the Clean Air

Act, EPA has reviewed and revised the

health and welfare criteria upon which

these primary and secondary particulate

matter standards were based.

On March 20, 1984 (49 FR 10408), EPA

proposed changes in the standards

based on its review and revision of the

criteria. Today's notice announces

EPA's final decisions regarding these

changes. The final decisions include: (1)

replacing TSP as the indicator for'

particulate matter for the ambient

standards with a new indicator that

includes only those particles with an

aerodynamic diameter less than or equal'

to a nominal 10;micrometers (PM1a), (2).

replacing the 24-hour primary. TSP

standard with. a 24-hour PMo standard

of 150 fg/m with no more than one

expected exceedance per year; (3)

replacing the annual primaryiTSP

standard with a, PM1o. standard of 50. Ig/

M3, expected annual arithmetic mean;

and (4), replacing the, secondary TSP

standard with, 24-hour' and annual PMo

standards that are identical in all

respects. to the primary, standards.

Today's notice. also, announces a new

Federal Reference Method for

measurement of PMo in the ambient air.

The method is contained in a new

Appendix J to Part 50. This notice also

announces a new Appendix K to Part 50,

which provides rules for applying the

statistical form of the revised standards.

In addition, certain clarifying changes to

Appendix B and Appendix G are set out.

Related notices published elsewhere

in today's Federal Register set out final

regulations concerning Ambient Air

Monitoring Reference and Equivalent

Methods (40 CFR Part 53), Ambient Air

Quality Surveillance (40 CFR Part 58),

Regulations for Implementing Revised

Particulate Matter Standards (40 CFR

Part 51) with associated guidelines,

Approval and Promulgation of

Implementation Plans (40 CFRPart 52),

and Prevention of Significant

Deterioration (Parts 51 and 52).

EFFECTIVE DATE: This action is effective

July 31, 1987.

ADDRESSES: A docket (No. A-82-37)

containing information related to EPA's

review and revision of the particulate

matter standards is available for public

inspection between 8:00 a.m. and 3:00

p.m. on weekdays at EPA's Central

Docket Section, South Conference

Center, Room 4, 401 M St., SW.,

Washington, DC. A reasonable fee may

be charged for copying. The information

in the docket constitutes the complete

basis for the decisions announced' in this

notice. For the availability of related*

information see SUPPLEMENTARY

INFORMATION.

FOR FURTHER INFORMATION CONTACT:

Mr. John Haines, Strategies and Air

Standards Division (MD-12), U.S.

Environmental Protection Agency,

Research Triangle Park, N.C. 27711,

telephone. (919) 541-5531 (FTS 629-5531].

SUPPLEMENTARY INFORMATION:

Availability of Related Information

The revised criteria document,, Air

Quality Criteria for Particulate Matter

and Sulfur Oxides (three volumes, EPA600/8--82-029af-cf, December, 1982;

Volume I NTIS #PB-84-120401, $24.95

paper copy and $6.50 microfiche;

Volume 11 NTIS #PB-84-120419,.$48.95

paper copy and $6.50 microfiche;

Volume III NTIS.#PB-84-120427, $48.95

paper copy and $13.50 microfiche, the

Second Addendum to Air Quality

Criteria for Particulate Matter and

Sulfur Oxides (1982]: Assessment of

Newly Available Health Effects'

Information, (EPA/600/8-86-020-F

NTIS #PB-87-176574, $24.95 paper copy,

and $6.50 microfiche), the 1982 staff

paper,. Review of the National Ambient

Air-Quality Standards for Particulate

Matter: Assessment of Scientific and

Technical Information-OAQPS Staff

Paper (EPA-450/5-82-01, January, 1982;

NTIS #PB-82-177874, $24.95 paper copy

and $6.50 microfiche), and the staff

paper addendum, Review of the

National Ambient Air Quality Standards

for Particulate Matter: Updated

Assessment of Scientific and Technical

Information (EPA-450/ 5-86-012,,

December 1986; NTIS #PB-87-176871,

$18.95 paper copy and $6.50 microfiche)

are available from: U.S. Department of

Commerce, National Technical

Information Service, 5285 Port Royal

Road, Springfield, Virginia.22161 (add

$3.00 handling charge per order). A

limited number of copies of other

documents generated in connection with

this standard review, such as the control

techniques document, can be obtained

from: U.S. Environmental Protection

Agency Library (MD-35), Research

Triangle Park, N.C. 27711, telephone

(919) 541-2777 (FTS 629-2777).

Table of Contents

I. Background

A. Legislative Requirements Affecting This

Rule

1. The Standards

2. Related Control Requirements

B. Particulate Matter and Original Standards for TSP

C. Development of Revised Air Quality

Criteria for Particulate Matter

D. Review of the Standards: Development

of Staff Paper

E. Proposed Revisions to the Standards

F. Supplemental Criteria Revisions and

Standards Review Following Proposal

IIU. Summary of Public Comments

A. Comments on 1984 Proposal

B. Comments on Subsequent Notice

1. Rationale for the Primary Standards

A. Pollutant Indicator

B. Averaging Time and Form of the Standards

1. 24-hour Standard

2. Annual Standard

C. Level of the Standards

1. 24-hour Standard

2. Annual Standard

IV., Rationale for the Secondary Standards

A. Soiling and Nuisance

B. Other Welfare Effects

V. Federal Reference Method

A. Specific Changes to Appendix J

B. Designation of Reference Methods for

PM10

C. Technical Change to Appendix G

VI. Summary of Salient Public Comments

and Agency Responses

A. Health Effects Criteria and Selection of

the Primary Standards

1. Indicator for the Primary Standards

2. Interpretation of Community Epidemiological Studies

3. Margin of Safety

B. Secondary Standards

1. Soiling and Nuisance

2. Visibility

C Averaging Time and Form of the Standards

1. Expected Exceedances for the 24-hour

Standard

2. Expected Arithmetic Mean for the

Annual Standard

VII. Regulatory and Environmental Impacts

A. Regulatory Impact Analysis

B. Impact on Small Entities

VIII. Other Reviews

References

Addendum I-CASAC Review and Closure of

the. 198ZCriteria Document for Particulate

Matter/Sulfur Oxides and the 1986 Second

Addendum to the Criteria Document

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Addendum 1l-CASAC Review and Closure

of the 1982 OAQPS Staff Paper for

Particulate Matter and the 1986 Addendum

to the Staff Paper

Addendum Ill-Executive Summary of the

1986 Addendum to the Staff Paper

Part 50-National Primary and Secondary

Ambient Air Quality Standards

Appendix J-Reference Method for the

Determination of Particulate Matter as

PM1 o in the Atmosphere

Appendix K-Interpretation of the National

Ambient Air Quality Standards for

Particulate Matter

I. Background

A. Legislative Requirements Affecting

This Rule

1. The Standards

Two sections of the Clean Air Act

govern the establishment and revision of

national ambient air quality standards

(NAAQS). Section 108 (42 U.S.C. 7408)

directs the Administrator to identify

pollutants which may reasonably be

anticipated to endanger public health or

welfare and to issue air quality criteria

for them. These air quality criteria are to

reflect the latest scientific information

useful in indicating the kind and extent

of all identifiable effects on public

health or welfare that may be expected

from the presence of a pollutant in the

ambient air.

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

Administrator to propose and

promulgate "primary" and "secondary"

NAAQS for pollutants identified under

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

primary standard as one the attainment

and maintenance of which, in the

judgment of the Administrator, based on

the criteria and allowing for an

adequate margin of safety, is requisite to

protect the public health. A secondary

standard, as defined in section 109(b)(2),

must specify a level of air quality the

attainment and maintenance of which.

in the judgment of the Administrator,

based on the criteria, is requisite to

protect the public welfare from any

known or anticipated adverse effects

associated with the presence of the

pollutant in the ambient air. Welfare

effects are defined in section 302(h) (42

U.S.C. 7602(h)) to include effects on

soils, water, crops, vegetation, manmade materials, animals, wildlife,

weather, visibility, climate, damage to

and deterioration of property, hazards to

transportation, and effects on economic

values and on personal comfort and

well-being.

The U.S. Court of Appeals for the D.C.

Circuit has held that the requirement for

an adequate margin of safety for

primary standards was intended to

address uncertainties associated with

inconclusive scientific and technical

information available at the time of

standard setting. It was also intended to

provide a reasonable degree of

protection against hazards that research

has not yet identified. Lead Industries

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

(D.C. Cir. 1980), cert. denied, 101 S. Ct.

621 (1980): American Petroleum Institute

v. Castle, 665 F.2d 1176, 1177 (D.C. Cir.

1981), cert. denied, 102 S. Ct. 1737 (1982).

Both kinds of uncertainties are

components of the risk associated with

pollution at levels below those at which

human health effects can be said to

occur with reasonable scientific

certainty. Thus, 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 he finds pose an unacceptable risk of harm, even if that

risk is not precisely identified as to

nature or degree. In selecting a margin of safety, EPA

has considered such factors as the

nature and severity of the health effects

involved, the size of the sensitive

population(s) at risk, and the kind and

degree of the uncertainties that must be

addressed. Given that the "margin of

safety" requirement by definition only

comes into play where no conclusive

showing of harm exists, such factors,

which involve unknown or only partially

quantified risks, have their inherent

limits as guides to action. The selection

of any particular approach to providing

an adequate margin of safety is a policy

choice left specifically to the

Administrator's judgment. Lead

Industries Association v. EPA, supra,

647 F.2d at 1161-62.

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

7409(d)) requires periodic review and, if

appropriate, revision of existing criteria

and standards. The'process by which

EPA has reviewed the original criteria

and standards for particulate matter

under section 109(d) is described in

Sections I.C. and I.D. of this notice.

2. 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), States are to

submit, for EPA approval, State

implementation plans (SIPs) that

provide for the attainment and

maintenance of such standards through

control programs directed to sources of

the pollutants involved. Other Federal

programs provide for nationwide

reductions in emissions of these and

other air pollutants through the Federal

Motor Vehicle Control Program under

Title I1 of the Act (42 U.S.C. 7501 to

7534), which involves controls for

automobile, truck, bus, motorcycle, and

aircraft emissions, and through the

development of New Source

Performance Standards under section

111 (42 U.S.C. 7411) and National

Emission Standards for Hazardous Air

Pollutants under section 112 (42 U.S.C.

7412).

B. Particulate Matter and Original

Standards for TSP

"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

stationary and mobile sources. They

may be emitted directly or formed in theatmosphere by transformations of

gaseous emissions such as sulfur oxides,

nitrogen oxides, and volatile organic

substances. The chemical and physical

properties of particulate matter vary

greatly with time, region, meteorology

and source category, thus complicating

the assessment of health and welfare

effects. The characteristics, origins,

concentrations, and potential effects of

particulate matter are discussed in more

detail in the staff. paper (SP) (EPA,

1982a), in the revised criteria document

(CD) (EPA, 1982b), in the criteria

document addendum (CDA) (EPA,

1986a) and in the staff paper addendum

(SPA) (EPA, 1986b). The executive

summary of the staff paper a'ddendum is

reprinted in Addendum Ill to this notice.

OnApril 30, 1971 (36 FR 8186), EPA

promulgated the original primary and

secondary NAAQS for particulate

matter under section 109 of the Clean

Air Act. The reference method for

measuring attainment of these standards

is the "high-volume" sampler (40 CFR

Part 50, Appendix B], which collects

particulate matter up to a nominal size

of 25 to 45 micrometers (/±m) (so-called

"total suspended particulate," or "TSP").

Thus, TSP is the current indicator for the

particulate matter standards. The

existing primary standards for

particulate matter (measured as TSP)

are 260 j±g/m s , 24-hour average not to be

exceeded more than once per year, and

75 g/m 3

, annual geometric mean. The

secondary standard (measured as TSP)

is 150 pg/m 3

, 24-hour average not to be

exceeded more than once per year. The

scientific and technical bases for these

standards are contained in the original

criteria document, Air Quality Criteria

for Particulate Matter (DHEW, 1969).

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C. Development of Revised Air Quality

Criteria for Particulate Matter

In 1976, as a result of internal Agency

review and the recommendations of a

committee of EPA's Science Advisory

Board, EPA decided to revise the

existing criteria document for

particulate matter. Because of competing

priorities regarding revision of other

criteria documents, and because of the

need to complete additional research on

particulate matter, the process was

scheduled to commence in 1979. With

the endorsement of the Clean Air

Scientific Advisory Committee (CASAC)

of EPA's Science Advisory Board, EPA

decided to review and revise the criteria

document for particulate matter

concurrently with that for sulfur oxides

and to produce a combined particulate

matter/sulfur oxides (PM/SO,, criteria

document. On October 2. 1979 (44 FR

56731), EPA announced that it was in the

process of revising the criteria document

and reviewing the existing air quality

standards for possible revisions.

In developing the revised criteria

document, EPA has provided a number

of opportunities for review and comment

by organizations and individuals outside

the Agency. Three drafts of the revised

particulate matter/sulfur oxides criteria

document, prepared by EPA's

Environmental Criteria and Assessment

Office (ECAO), were made available for

external review on April 11, 1980 (45 FR

24913), January 29, 1981 (46 FR 9746),

and October 28, 1981 (46 FR 53210). EPA.

received and considered numerous and

often extensive comments on each of

these drafts. CASAC held three public

meetings to review successive drafts of

the document on August 20-22, 1980 (45

FR 5164, August 4, 1980), July 7-9, 1981

(46 FR 31746, June 17, 1981), and

November 16-18, 1981 (46 FR 53210,

October 28, 1981). These reetings were

open to the public and were attended by

many individuals and representatives of

organizations who provided critical

reviews and new information for

consideration. In accordance with

CASAC recommendations made after

the first review meeting, five additional

public meetings were held at which

EPA, its consulting authors and

reviewers, and other scientifically and

technically qualified experts selected by

EPA discussed the various chapters of

the draft document and suggested ways

of resolving outstanding issues (45 FR

74047, November 7. 1980; 45 FR 78224,

November 25, 1980; 45 FR 76790,

November 20, 1980; 45 FR 80350,

December 4, 1980:46 FR 1775, January 7,

1981).

The comments received on the

successive drafts of the revised criteria

document were considered in the final

document, issued simultaneously with

the proposal of revisions to the

standards. A summary of EPA's

responses to the comments on the three

external review drafts of the documents

is in the public docket (Docket No. A82-37). Transcripts of the three CASAC

meetings are also in the docket. In

accordance with its established

procedures, CASAC prepared a "closure" memorandum to the

Administrator indicating its satisfaction

with the final draft (December, 1981) of

the criteria document and outlining key

issues and recommendations. The

closure memorandum, dated January 29,

1982, stated that the EPA office that

prepared this document was "responsive to Committee advice as

well as to comments provided by the

general public . . ." The closure

memorandum further stated that the

criteria document "fulfills the

requirements set forth in section 108 of

the Clean Air Act, which requires that

the criteria document 'shall accurately

reflect the latest scientific knowledge

useful in indicating the kind and extent

of all identifiable effects on public

health or welfare' from sulfur oxides

and particulates in the ambient air." The

CASAC closure memorandum on the

criteria document is reprinted in its

entirety in Addendum I to this notice.

Following closure, minor technical and

editorial refinements were made to the

criteria document for printing (EPA,

1982b).

A number of scientific and technical

issues were raised during the public

review process. With respect to the

particulate matter portions of the

criteria document, the major Issues

included the relationship among various

measures of particulate matter air

quality, the implications of particle

deposition and other studies for

selecting a particulate matter indicator,

and the development and application of

criteria for deciding which

epidemiological studies are most

appropriate for use in revising air

quality standards. A summary of these

and other major scientific issues, as well

as CASAC's conclusions, is included in

the closure memorandum on the criteria

document (Addendum I).

D. Review of the Standards:

Development of Staff Paper

In the evolving process of revising the

national ambient air quality standards,

EPA has found it useful to prepare a

document that helps bridge the gap

between the scientific review of health

and welfare effects contained in the

criteria document and the judgments

required of the Administrator in setting

ambient standards. This document,

known as the staff paper, has become

an important element in the standards

review process, providing an

opportunity for public comment on

proposed staff recommendations before

they are presented to the Administrator.

In the spring of 1981, EPA's Office of

Air Quality Planning and Standards

(OAQPS) prepared the first draft of the

staff paper, Review of the National

Ambient Air Quality Standards for

Particulate Matter: Assessment of

Scientific and Technical Information.

This draft staff paper, based on the then

existent draft of the revised criteria

document, evaluated and interpreted the

available scientific and technical

information most relevant to the review

of the air quality standards for

particulate matter and presented staff

recommendations on alternative

approaches to revising the standards.

This and a second draft of the paper

were reviewed at two CASAC meetings

on July 7-9, 1981 (46 FR 31746, June 17,

1981), and November 16-18, 1981 (46 FR

53210, October 28, 1981]. Numerous

written and oral comments were

received on the drafts from CASAC,

representatives of organizations,

individual scientists, and other

interested members of the public. A

summary of major revisions made in

response to comments on the first draft

is contained in an October 31, 1981 letter

to CASAC (Padgett, 1981). Following the

second CASAC meeting, the staff made

further revisions in response to

comments and prepared an executive

summary that was reviewed by CASAC

members before preparation of the

closure memorandum on the staff paper.

In January, 1982, EPA released the final

OAQPS staff paper (EPA, 1982a), which

reflects the various suggestions made by

CASAC and members of the public. The

January 29, 1982, CASAC closure

memorandum states that the staff paper

"has been modified in accordance with

recommendations made by CASAC," is

consistent with the criteria document,

and provides the Administrator "with

the kind and amount of technical

guidance that will be needed to make

appropriate revisions to the standard."

This closure memorandum is reprinted

in Addendum II to this notice.

A number of major issues were raised

during the public review process. The

more important issues are outlined

below.

1. Substantial discussion concerned

the maximum size of particles (or

particle size fraction) to be used in

measuring particulate matter for

regulatory purposes. Some groups

favored retaining TSP as an indicator,

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others called for alternative size-specific

standards with nominal "size cuts"

('1e"; see discussion in Section III.A.)

of 15 pm, 10 G6mm, 5-7 G6mm, and 2.5

G6mm. After CASAC closure on the

staff paper and criteria document,

comments were received from one group

favoring a so-called "Do" of 10 Atm

(approximately equivalent to a nominal

size cut [Dal of 6 um).

2. Much attention was focused on

selecting the level of the primary

standards and on the question of which

health effects studies were most

appropriate for this purpose. Significant

criticisms were received on the major

epidemiological studies of particulate

matter exposures, highlighting their

limitations for use in standard setting. In a number of comments, specific

suggestions for standards were made.

3. With respect to secondary

standards, most attention focused on the

possible need for a fine (-2.5 G6m)

particle standard designed to protect

visibility.

These and other major issues are

discussed more fully in the executive

summary of the staff paper and in later

sections of this notice. CASAC's

discussion of these issues and its

recommendations are contained in the

closure memorandum on the staff paper

(Addendum II).

E. Proposed Revisions to the Standards

On March 20, 1984 (49 FR 10408) EPA

proposed a number of revisions to the

primary and secondary particulate

matter standards. The proposed

revisions, based on the revised criteria.

included:

(1) Replacing TSP as the indicator for

particulate matter for the primary

standards with a new indicator that

includes only those particles with an aerodynamic diameter less than or equal

to a nominal 10 micrometers (PM~o);

(2) Changing the level of the 24-hour

primary standard to a value to be

selected from a range of 150 to 250 Mg/

m 3 and replacing the deterministic form

of the standard, which permitted not more than one observed exceedance of

the standard per year, with a statistical

form that would permit one expected

exceedance per year;

(3) Changing the level of the annual

primary standard to a value to be . selected from a range of 50 to 65 f~g/m3,

and changing the form from an annual

geometric mean to an expected annual

arithmetic mean: and

(4) Replacing the current 24-hour

secondary TSP standard by an annual

TSP standard selected from a range of,

70 to 90 fg/m3

, expected annual

arithmetic mean.

The Administrator expressed an

inclination to select the primary

standards from the lower portions of the

above ranges. With respect to the

secondary standards, the Administrator

was inclined to select the final standard

from the upper portion of the range, but

also called for comment on the

alternative of using PMo as the

particulate matter indicator for the

secondary standards and making the

secondary standards identical in all

respects to the primary standards. The

proposal notice sets forth the rationale

for these and other proposed revisions

of the particulate matter NAAQS and

background information related to the

proposal.

F. Supplemental Criteria Revisions and

Standards Review Following Proposal

Following publication of the proposal,

EPA held a public meeting in

Washington, D.C. on April 30, 1984 to

receive comments on the proposed

standards revisions. A transcript of the

meeting has been placed in the public

docket (Docket No. A-82-37). After the

close of the original public comment

period (June 5, 1985), the CASAC met on December 16-17, 1985 to review the

proposal and to discuss the relevance of

certain new scientific studies on the

health effects of particulate matter that

had emerged since the Committee

completed its review of the criteria

document and staff paper in January,

1982. A transcript of this meeting is also

available in the Docket. Based on its

preliminary review of these new studies,

the Committee recommended that the

Agency prepare separate addenda to the

criteria document and staff paper for the

purpose of evaluating the relevant new studies and discussing their potential

implications for standard-setting. The

Agency announced its acceptance of

these recommendations on April 1, 1986

(51 FR 11058). On July 3, 1986, EPA

announced (51 FR 24392) the availability

of the external review draft document

entitled: Second Addendum to Air

Quality Criteria for Particulate Matter

and Sulfur Oxides (1982): Assessment of

Newly Available Health Effects

Information. At the same time, the

Agency announced a supplementary

comment period on the March 20, 1984

proposal to provide the public an

opportunity to comment on the

implications of the new studies and

addenda for the final standards. On

September 16, 1986, EPA announced (51

FR 32878) the availability of the draft

staff paper addendum entitled Review of

the National Ambient Air Quality

Standards for Particulate Matter: - Upda ted Assessment of Scientific and

Technical Information. CASAC held a

public meeting on October 15-16, 1986 to

review both the criteria document

addendum and the staff paper

addendum. At this meeting, CASAC

members as well as representatives of

several organizations, provided critical

review of both EPA documents. A

transcript of the CASAC meeting has

been placed in the public docket (A-82-

37).

The CASAC sent a closure letter on

the criteria document addendum to the

Administrator dated December 15, 1986,

which concludes "that this 1986

Addendum along with the 1982 Criteria

Document, previously reviewed by

CASAC, represent a scientifically

balanced and defensible summary of the

extensive scientific literature on these

pollutants" (Lippmann, 1986b). The

closure letter on the criteria document

addendum is reprinted in Addendum I of

this notice. The Committee sent their

closure letter on the staff paper, addendum to the Administrator dated

December 16, 1986, stating "The

Committee believes that this document

provides you with the kind and amount

of technical guidance that will be

needed to make appropriate revisions to

the standards" (Lippmann, 1986c). The

closure letter on the staff paper

addendum, which also discusses major

issues addressed by the CASAC and the

Committee's recommendations

concerning these issues, is reprinted in

Addendum If to this notice. The final

addenda to the criteria document (EPA,

1986a) and the staff paper (EPA, 1986b),

which include revisions to reflect

comments from CASAC and the public,

are available from the address listed

above. Where there are differences

between the 1982 Criteria Document and

staff paper and the more recent

addenda, the addenda supersede the

earlier document. The executive

summary of the staff paper addendum is

reprinted in Addendum III to this notice.

II. Summary of Public Comments

The following discussion summarizes

in general terms the comments received

from the publicand from governmental

agencies regarding the proposed

revisions to the indicator, form,

averaging times, and levels of the

primary and secondary standards. Many of these comments had been made * ' previously by the-public during public,"

deliberations on drafts of the criteria

document and staff paper and were.

reviewed and addressed-by EPA in.

revisions to those documents. Salient

comments on all aspects of the proposal

and Agency responses to those

comments are summarized by category

in Section VI of this notice. A more..

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detailed description of individual

comments and Agency responses has

been entered in the public docket (No.

A-82-37).

A. Comments on 1984 Proposal

Extensive written comments were

received during the original comment

period on the proposal, which closed

June 5,1985. Of some 312 written

submissions, 153 were provided by individual industrial concerns or

industry groups, 93 by State, local, and

Federal government agencies and

organizations, 32 by environmental and

public interest groups, and 34 by individual private citizens.' The

comments on the key elements of the

proposed standards are summarized

below:

(1) Indicator for the Primary

Standard: The overwhelming majority of

the comments received on this issue

favored a size-selective indicator for the

PM standard. Of the 147 written

comments received on this issue, 108

supported the PMo indicator proposed

by the Agency. Most of the remaining

comments were in support of alternative

smaller particle size indicators including

PM0 (28 comments) and PM2.5 (8

comments). The principal support for

PM0 came from mining and related

industries.

(2] Levels of the Primary Standards:

Comments on the proposed levels for

the two primary standards were more

polarized than those on the indicator.

Most industry comments favored

selecting the level of the standards at

the upper end of the proposed ranges or

above, while most of the remaining

commenters favored standard levels at

the lower bound of the ranges, and in

some cases lower. Additional comments

from individual citizens, environmental

groups, and government agencies urged that the level of protection afforded by

the current particulate matter standards

be maintained or strengthened. (3) Secondary Standards: Of the 105

written comments received on the

proposed secondary standard, 44

supported retaining TSP as the indicator

and 61 opposed the use of TSP. Most of

the latter commenters supported the

proposed alternative of making the

secondary standards equal in all

respects to the primary standards.

IThis numerical distribution of comments in each

category should be compared with caution. For

example, the American Iron and Steel Institute and

the American Petroleum Institute submitted

comments on behalf of 63 and 230 individual

companies respectively, in lieu ofhaving each of

their member companies send separate comments.

Similarly, comments from interest groups such as NRDC represent the views of a number of

individuals.

Industry commenters were virtually

unanimous in opposing a TSP secondary

standard, while a majority (35 of 47) of

government agency comments on this

issued favored retaining the TSP

indicator. Some of the latter

commenters, however, recommended

testing attainment of the TSP standard

with PMo monitors. Environmental

groups commenting on this issue favored

retaining the TSP indicator.

(4] Form of the Standards: A majority

of the 52 comments received on this

subject supported some kind of

statistical 24-hour standard, but a number of industry and State and local

agency commenters raised concerns

with aspects of the specific form

proposed. The principal concern was

that the proposed form could result in

misclassification of areas as nonattainment. Some industry and

governmental commenters favored

alternative forms for the 24-hour

standards including multiple

exceedance (9 comments) and percentile

(8 comments) forms. These forms would

permit five or more exceedances per

year of the 24-hour standard.

Environmental groups and other

government agencies opposed multiple

exceedance forms. Of 38 submissions

from industry and government agencies,

26 favored a geometric mean for the

annual standard over the proposed

arithmetic mean. (5) Federal Reference Method: While

most of the comments generally

supported the performance-based

approach to the Federal Reference

Method, many commenters favored more stringent specifications for PM1o samplers to ensure accurate and reliable

performance under all ambient sampling

conditions. Other comments and

recommendations addressed specific

requirements of Appendix J such as flow

calibration and measurement, flow

regulation, filter media, humidity control

and sampler maintenance.

B. Comments on Subsequent Notice

As discussedearlier in this notice,

EPA announced an additional public

comment period on July 3, 1986 to

address the implications of new

scientific studies on the health effects of

particulate matter [51 FR 24392].

Approximately 20 additional written

submissions were received by the close

of this comment period on November 17,

1986, 17 of which were provided on

behalf of industry groups or companies,

2 from environmental groups, and 1 from

a state agency. Much of the material

related to evaluations of specific studies

and their treatment in the staff paper

addendum. The industry comments,

which included submissions from

consulting scientists and analysts,

generally found that the new studies

suffered from deficiencies that preclude

placing much weight on them in

standard setting. These commenters

concluded that their original

recommendations (summarized above)

with respect to the standards remained

valid. The two environmental groups felt

that the findings in these new studies

necessitated standards below the lower

bounds of the proposed ranges.

III. Rationale for the Primary Standards

In selecting primary standards for

particulate matter, the Administrator

must specify: (1) the particle size

fraction that is to be used as an

indicator of particulate pollution; (2) the

appropriate averaging times and form(s)

of the standards; and (3) the numerical

levels of the standards. These

specifications must be considered

collectively in evaluating the margin of

safety afforded by particulate matter

standards. Based on the assessment of

relevant scientific and technical

information in the criteria document and

addendum, the staff paper and staff

paper addendum (hereinafter "SP" and

"SPA," respectively) outline a number of

key factors to be considered in making

decisions in each of these areas (SP,

Section VI; SPA, Section IV). Both the

staff and CASAC made

recommendations to focus consideration

on a discrete range of options. In most

respects, the Administrator has adopted

the recommendations and supporting

reasons contained in the staff paper and

addendum and the CASAC closure

statements (Friedlander, 1982;

Lippmann, 1986c). Rather than

reiterating those discussions at length,

the following discussion of the

standards revisions focuses primarily on

those considerations that were most

influential in the Administrator's

selection of particular options, or that

differ in some respect from

considerations that influenced the staff

and/or CASAC recommendations.

A. Pollutant Indicator

Based on the staff assessment of the

available scientific information, EPA

concludes that (1) a separate particulate

matter standard (as opposed to a

combination standard for particulate

matter and SO) remains a reasonable

public health policy choice, and (2)

given current scientific knowledge and

uncertainties, a size-specific (rather than,

chemical-specific) indicator should be

used. In assessing the information in the

criteria document, the staff reached

several conclusions summarized here

(see SP, pp. 71-75):

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(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. Smaller

particles penetrate furthest in the

respiratory tract. The largest particles

are deposited in the extrathoracic (head)

region with somewhat smaller particles

depositing in the tracheobronchial

region. Still smaller particles can reach

the deepest portion of the lung, the

alveolar region.

(2) The risks of adverse health effects

associated with deposition of typical

ambient fine and coarse particles 2 in

the thorax (tracheobronchial and

alveolar regions of the respiratory tract)

are markedly greater than those

associated with deposition in the

extrathoracic (head) region. Maximum

particle penetration to the thoracic

region occurs during oronasal or mouth

breathing.

(3) The size-specific indicator for

primary standards should represent

those particles small enough to

penetrate to the thoracicregion (both

the tracheobronchial and alveolar

regions). The risks of adverse health

effects from extrathoracic deposition of

typical ambient particulate matter are

sufficiently low that particles depositing

only in that region can safely be

excluded from the indicator.

* Considering these conclusions

together with other information on air

quality composition, respiratory tract -

deposition and health effects, the need

to provide protection for sensitive

individuals who may breathe by mouth

and/or oronasally, and the similar

convention on particles penetrating the

thoracic region recently adopted by the

International Standards Organization

(ISO, 1981), the staff recommended that

the size-specific indicator include

particles of diameters less than or equal

to a nominal 10 jim "cut point."P The

2 Particles in ambient air usually occur in two

somewhat overlapping size distributions, fine

(diameter less than 2.5 j~m) and coarse (diameter

larger than 2.5 pm). The two size fractions tend to

have different origins and composition (SP.

Appendix D).

3 The more precise term is 50% cut point or 50%

diameter (D.). This is the aerodynamic particle

diameter for which the efficiency of particle

collection is 50%. Larger particles are not excluded

altogether, but are collected with substantially.

decreasing efficiency and smaller particles are collected with Increasing (up to 100%) efficiency. Ambieit samplers with this cut point provide a

reliable estimate of the total mass of suspended

particulate matter of aerodynamic size less than or

equal to 10 pm. See additional discussion regarding

the Federal Reference Method in section V below

and in the accompanyingnotice revising 40 CFR

Part 53.

factors considered in the original staff

recommendations for a 10 j m cut point

are outlined in the staff paper (SP, pp.

75-79). This indicator is referred to as

"thoracic particles" (TP) in the 1982 staff

paper; it is now generally referred to as

"PMo." Such an indicator is

conservative with- respect to health

protection in that it includes all of the

particles small enough to penetrate to

the sensitive alveolar region, and

includes approximately the same

proportion of larger particles as would

be expected to reach the

tracheobronchial region. It places

substantially greater emphasis on

controlling smaller particles than does a

TSP indicator, but does not completely

exclude larger particles from all control.

The assessment of more recent

information on respiratory tract

deposition in the criteria document and

staff paper addenda reinforces the

conclusions reached in the original staff

assessment. In particular, the staff paper

addendum found that: (1) the recent

data do not provide support for an

indicator that excludes all particles

larger than 10 pim in diameter, 4 (2) the

analysis used to support an alternative

indicator with a nominal size cut of 6

G6mm (Swift and Proctor, 1982)

significantly underestimated thoracic

deposition of particles larger than 6 pi.m

in diameter under natural breathing

conditions; (3) the PM10 indicator

generally includes a similar or larger

fraction of the range of particles that can '

deposit in the tracheohronchial region,

-although it appears to be somewhat less

conservative iii this-regard than

previously thought with respect to laige

(G6<10 pm) particle deposition under

conditions of natural mouthbreathing;

and (4) the studies of tracheobronchial

deposition generally involved adult

subjects; recent information indicating

even greater tracheobronchial

deposition of particles in children than

in adults provides an additional reason

for an indicator that includes particles

capable of penetration to the

tracheobronchial region (SPA, p. 36).

Consideration of these and the earlier

conclusions led the staff to reaffirm its

recommendation for a PMo indicator

(SPA, pp. 36-37). The CASAC also

restated its recommendation for PMio in

its review of the proposal and the

closure letter to the. Administrator

(Lippmann, 1986 a, c). . The Administrator accepts the

recommendations of the staff and

CASAC and their underlying rationale

'The American Mining Congress (AMC. 1982)

had recommended such an indicator, with a "DW of

10 Am. EPA estimated that the "DIa" of this

indicator would be.6 pm.

and has decided to replace TSP as the

particle indicator for the primary

standards with a new indicator that

includes only those particles less than a

nominal 10 Om in diameter, as specified

in the Federal Reference Method

(Appendix J to 40 CFR Part 50) being

promulgated today. In defining the

standards for particulate matter, this

new indicator is termed PMo.

B. Averaging Time and Form of the

Standards

-Few comments on the proposed

standards contested the need for both

24-hour and annual primary standards

for particulate matter. EPA's assessment

of more recent scientific information

found that the new data confirm the

need for both short- and long-term

standards.' The alternative of a single

averaging time would not provide

adequate protection against potential

effects from both long- and short-term

exposures without being unduly

restrictive. The forms for the 24-hour

and annual standards are discussed

below.

1. 24-hour Standard

EPA proposed that the 24-hour

standard be stated in a statistical form

that uses more than one year of data

and accounts for variations in sampling

frequency in order to predict the actual

number of exceedances to be expected

in an average year, When used with an

appropriate standardlevel, the

statistical form can provide improved

health protection that is less sensitive to

changes-iri sampling frequency than the

deterministic form, and also can offer, a--

more stable target for control. programs.

Recognition of the limitations of the

deterministic form has led EPA to

promulgate a statistical form for the

ozone standard (44 FR 8202).

The interpretation of the statistical

form of the particulate matter standard

is detailed in Appendix K of the

proposed regulation. The standard

would be attained when the expected

number of exceedances of the 24-hour

standard level is no more than one per,

year. The expected number of.

exceedances per year is equivalent to

the long-term average number of

exceedances per year, assuming no

changes in underlying emissions.

Generally, the determination of the

expected number of exceedance will be

based on three consecutive years of

data. -. . .. , . .- . .. • - ,. .

As- a result of EPA's evaluations of

evidence submitted and comments

received during the public review

process, the following changes have

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been made to Appendix K of the

proposed rule regarding:

(1) Data Capture RequirementsAppendix K to the proposed standards

contained minimum data capture

requirements for determining attainment

of the standards. The amount of data

required varies with the sampling

frequency and the number of years of

record. The Ambient Air Quality

Surveillance regulations (40 CFR Part 58)

proposed in 1984 and being promulgated

today require that sampling be

performed every day or every other day

in areas where there is a substantial

probability of nonattainment of the

standards. The proposed Appendix K to

the standards, however, would have

permitted states to demonstrate

attainment of the standards with only 12

samples per calendar quarter, even in

those areas where everyday or every

other day sampling is required.

Commentters have argued that, for the

same reasons that everyday or every

other day sampling is required in areas

with a substantial probability of

nonattainment, 12 samples per quarter

are not sufficient to establish attainment

in those areas. These commenters also

argued that 75 percent data capture is

achievable at all sampling frequencies.

EPA agrees, and therefore the final rule

requires that 75 percent of the required

samples must be captured each calendar

quarter to establish attainment of the

NAAQS.

Additional criteria for situations in

which less than 3 years of

representative data are available are

also contained in the final rule. These

criteria are intended to permit areas to

determine their air quality status in a

reasonable time frame during the period

in which new PMo monitoring is

initiated, while minimizing the

probability of errors in classification.

Appendix K specifies that the various

data requirements do not apply when

the data available establishes

nonattainment unambiguously.

Furthermore,' data not meeting the

various criteria may also be sufficient to

show attainment; however, such

exceptions will have to be approved by

the Regional Administrator in

accordance with established guidance.

(2) Exceedance Calculations-EPA is

modifying the formulas used to account

for incomplete data in the estimation of

the expected number of exceedances per

year. In the proposal, these calculations

were based on the assumption that the

fraction of missing values that would

have exceeded the standard level is

identical to the fraction of measured

values above that level for the entire

calendar year. In the final rule, these

calculations will be required on a

quarterly basis, thereby taking into

account possible seasonal differences in

exceedance rates as well as differences

in sampling frequency or data capture.

The estimated annual number of

exceedances is defined as the sum of the

estimated exceedances for each

calendar quarter. This change will

accommodate situations in which

sampling frequency has been increased

to everyday according to the

requirements of Part 58.13, and

situations in which the Regional

Administrator has granted a waiver of

increased sampling frequency

requirements for part of the calendar

year under provisions of those

monitoring regulations.

(3) Interpretation of the First

Observed Exceedance-EPA is

additionally modifying Appendix K with

respect to the treatment of the first

observed exceedance in order to reduce

the chance of misjudging attainment

status. Under the aforementioned

formulas which adjust for incomplete

data, a single observed exceedance

could cause a site to fail the test for

attainment, even if the true expected

number of exceedances is less than or

equal to one. Such an occurrence is

especially likely if sampling is

performed less frequently than

everyday. In order to reduce the chances

of occurrence of this situation, the final

rule contains a provision that the first

observed exceedance shall not be

adjusted for incomplete sampling if (1)

everyday sampling had not been

required previously by 40 CFR 58.13, (2)

there was only one observed

exceedance in the calendar quarter, and

(3) sampling frequency has been

subsequently increased for the next 4

calendar quarters in accordance with 40

CFR 58.13. The associated reduction in

misclassification errors is discussed in

"Revising the National Ambient Air

Quality Standards for Particulate

Matter-A Selective Sampling

Monitoring Strategy" which has been

placed in the public docket.

With this change, the first observed

exceedance can be interpreted as the

only true exceedance which has

occurred in the calendar quarter. This

assumption is believed to be reasonable

since incomplete sampling is permitted

only in areas for which state

implementation plans are not initially

required and in areas in which

maximum PMo concentrations are

estimated to be less than 80 percent of

the level of the standard. If an area is

truly in nonattainment, additional

exceedances would be expected during

the subsequent year of everyday

sampling. If, however, everyday

sampling is not initiated as required by

the monitoring regulations, all observed

exceedances shall be adjusted for

incomplete sampling and accordingly

considered in the evaluation of PM1o air

quality status.

2. Annual Standard

The Administrator has decided to

change the form of the annual standard

from the current annual geometric mean

to a statistical form expressed as an

expected annual arithmetic mean. The

expected annual arithmetic mean is

equivalent to the long-term arithmetic

average concentration level, assuming

no changes in underlying emissions. The

expected arithmetic mean is more

directly related to the available health

effects information than is the annual

geometric mean, which is the. current

form of the standard. Because the

arithmetic mean concentration is

proportional to the sum of the daily

means, it reflects the total cumulative

dose of particulate matter to which an

individual is exposed. Therefore, it is an

appropriate indicator to protect against

any health effect that depends on total

dose. It is also a reasonable indicator for

protecting against health effects that

depend on repeated short-term high

concentrations; short-term peaks have

an influence on the arithmetic mean that

is proportional to their frequency,

magnitude, and duration. The geometric

mean, on the other hand, deemphasizes

the effect of short-term peak

concentrations, and is heavily

influenced by days of relatively clean

air. For these reasons, the staff and

CASAC recommended the change to an

arithmetic mean.

The interpretation of the statistical

form of the standard is detailed in

Appendix K to the proposed regulation.

Under the statistical form, the expected

annual arithmetic average is determined

by averaging the annual arithmetic

averages from three successive years of

data. The current deterministic form of

the standard does not adequately take

into account the random nature of

meteorological variations. In general,

annual mean particulate matter

concentrations will vary from one year

to the next, even if emissions remain

constant, due to the random nature of

meteorological conditions that affect the

formation and dispersion of particles in

the atmosphere. If only one year of data

is considered, compliance with the

standard and, consequently, emission

control requirements, may be

determined on the basis of a year with

unusually adverse or unusually

favorable weather conditions. The

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problem of year-to-year variability is,

however, reduced by averaging three

years of data.

C. Le vel of the Standards

The original staff paper and CASAC

recommendations set forth a framework

for determining the levels for the

proposed particulate matter standards

that would protect public health with an

adequate margin of safety. The

discussion that follows relies heavily on

that framework and on the supporting

material in the staff paper and its

addendum as well as the CASAC

closure letters. The essential steps in

this framework are summarized here.

1. Assessment of the quantitative

epidemiological studies.

The criteria document and its

addendum identify a small number of

community epidemiological studies that

are useful in determining concentrations

at which particulate matter is likely to

affect public health. The staff used these

quantitative studies to examine

concentration-response relationships

and to develop numerical "ranges of

interest" for possible PMo standards.

A number of uncertainties associated

with use of these studies must be

considered in selecting an appropriate

margin of safety. As discussed in the

staff paper and the criteria document,

and the addenda to those documents,

epidemiological studies are generally

limited in sensitivity and suhject to

inherent difficulties involving

confounding variables. Moreover, many

of the quantitative studies were

conducted in times and places where

pollutant composition may have varied

considerably from current U.S.

atmospheres. Most also have used

British Smoke 5 or TSP as particle

indicators. None of the published

studies used the proposed PMo

indicator. Thus, assumptions must be

5British Smoke (BS) is a pseudo-mass indicator

related to small particle (aerodynamic diameter less

than a nominal 4.5 pjm) darkness. This particulate

matter indicator was widely used in British and

other European studies. See the criteria document

for a more detailed treatment of BS (CD. pp. 1-88 to

I-90 and 14-8 to 14-11).

used to convert the various results to

common (PMo) units (SP, pp. 96-100;

SPA pp. 9-11).

2. Identification of additional margin

of safety considerations.

The criteria document identifies an

additional substantial body of scientific

literature that, while not providing

reliable concentration-response

relationships for ambient exposures,

does provide important qualitative

insights into the health risks associated

with human exposure to particles. This

literature includes both quantitative and

qualitative epidemiological studies,

controlled human exposure experiments,

and animal toxicological studies. The

staff assessed this literature to identify

additional factors and uncertainties that

should be considered in selecting the

most appropriate margin of safety (SP,

pp. 100-101; 107-111, SPA pp. 52-53; 59).

3. Selection of the levels that might be

considered to provide an adequate

margin of safety.

The intent of the margin of safety

requirement was to direct the

Administrator to set air quality

standards at pollution levels below

those at which adverse health effects

have been found or might be expected to

occur in sensitive groups. Experience

with the requirement has shown that the

scientific data are often so inconclusive

that it is difficult to identify with

confidence the lowest pollution level at

which an adverse effect will occur.

Moreover, in cases such as the present

one, the evidence suggests that there is a

continuum of effects, with the risk,

incidence, or severity of harm

decreasing, but not necessarily

vanishing, as the level of pollution is

decreased.

In the absence of clearly identified

thresholds for health effects, the

selection of a standard that provides an

adequate margin of safety requires an

exercise of informed judgment by the

Administrator. The level selected will

depend on the expected incidence and

severity of the potential effects and on

the size of the population at risk, as well

as on the degree of scientific certainty

that the effects will in fact occur at any

given level of pollution. For example, if a

suspected but uncertain health effect is

severe and the size of the population at

risk is large, a more cautious approach

will be appropriate than would be if the

effect were less troubling or the exposed

population smaller.

EPA staff originally recommended a

range of potential standards for the

Administrator's consideration (SP, pp.

111-114). The recommended range was

below the levels at which the staff, with

the concurrence of CASAC, had

concluded from the available data that

adverse health effects were "likely," but

in the domain where the data suggested

that such effects were "possible." The

Administrator proposed refined ranges

of standard levels that were based on

the original staff and CASAC

recommendations. After consideration

of the new scientific evidence contained

in the criteria document addendum, the

staff revised its recommendations for

ranges of standards (SPA, pp. 60-62).

The Administrator has considered the

revised assessments and the

recommendations of CASAC (Lippmann,

1986b) in making his final decision on

the standard levels. The rationales for

the levels of the 24-hour and annual

standards are presented below.

1. 24-Hour Standard

The revised staff assessment of the

short-term epidemiological data is

summarized in Table 1; particulate

matter levels are expressed in both the

original (British Smoke ["BS"] or TSP)

and PMo units. The "effects likely" row

in Table 1 denotes concentration ranges

derived from the criteria document and

its addendum at or above which a

consensus judgment suggests greatest

certainty that the effects studied would

occur, at least under the conditions that

occurred in the original studies. In the "effects possible" range, the staff found

credible scientific evidence suggesting

the existence of adverse health effects

in sensitive populations, but substantial

uncertainty exists regarding the

conclusions to be drawn from such

evidence.

TABLE 1.-UPDATED STAFF ASSESSMENT OF SHORT-TERM EPIDEMIOLOGICAL STUDIES

(After Table 4-1, SPA)

Measured British smoke levels (as jig/mn) (24-hr. avg.) Measured TSP levels (pg/mn) (24/ Equivalent PM-o

Effects/St'udy hr. avg.) Levels (jg/m) Daily Mortality in Aggravation of London Aronchitis o Combined range Small, reversible declines in lung Combine range Lnobrnhts2function in children 3.4 Cmin'ag

1000 250-*500"

?1 1 <250*

250-500 ......................................................

< 250 220-420 3-200-250 4

350-600

140-350

Effects Likely ..............................

Effects Possible .........................

24641,

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TABLE 1..--UPDATED STAFF ASSESSMENT OF SHORT-TERM EPIDEMIOLOGICAL STUDIES-Continued

(After Table 4-1, SPA)

Measured British smoke levels (as fig/m 3) (24-hr. avg.) Measured TSP levels (,Ug/m 3

) (24/ Equivalent PM-,o

hr. avg.) Levels (Ag/m 3

)

Effects/Study Daily Mortality in Aggravation of Combined range Small, reversible declines in lung

London I bronchitis = function in children 6 Combine range

No Significant Effects Noted ......................................................................................................... 125* -160 < 125

*Indicates levels used for upper and lower bound of range.

Various analyses of daily mortality encompassing the London winter of 1958-59, 14 winters from 1958-72, in aggregate and individually. Early winters dominated by high smoke and SO2 from coal combustion with frequent fogs. From 1982 CD: Martin and Bradley (1960); Ware et al., (1981); Mazumdar et al. (1981). From 1986 CD Addendum: Mazumdar et al. (1982); Ostro (1984); Schwartz and Marcus (1986). Later studies

show association, across entire range of smoke, with no clear delineation of "likely" effects or threshold of response possible. 2 Study of symptoms reported by bronchitis patients in London, mid-50's to early 70's; Lawther et al. (1970).

3 Study of pollution "episodes" in Steubenville, Ohio, 1978-80; Dockery et al. (1982). 4 Study of 1985 pollution episode in ljmond, The Netherlands; Dassen et al. (1986). 5.(a) Conversion of BS readings to PM10 levels: Assumes for London conditions and BS readings in the range 100-500 t.g/m3, BS<PM1o<TSP.. Precise conversions are not possible. Uncertainty in measurements of BS and conversion relationships preclude quantitative estimates of range for lower BS levels. The upper bound assumption (PMo=TSP=BS+ 100 pg/m3) overestimates PM0 levels, while the lower

bound assumption (PMo=BS) understates PM1o levels.

(b) Conversion of TSP to PMio for Dockery et a1 results: Based on analysis of particle size fraction relationships In Steubenville (Spengler et

al. 1986). The lower bound TSP of 220 pgg/m was the peak reported for the Spring 1980 study. A PM, 1/TSP ratio of about 0.8 occurred at a

nearby site on days surrounding this peak. Using, lower bound of PM1o/PM10 ratio from later year (0.8), the PM1o to TSP ratio estimate used In

0.64. The 160 pgi/m3 reflects peak level in Fall 1980 from episode with no significant functional decline noted.

(c) Conversion of Dassen et al. results to PMo: Both PM indices (Respirable Suspended Particles [RSP] and TSP) reached, similar levels.

Results suggest TSP levels, too low, but PMto levels unlikely to be much higher than RSP. Thus RSP=PMo assumed for conditions of, higher concentrations in this study. The 125 gIg/m 3 entry reflects an excursion occurring 2 days prior to date on which no decrements noted.

The data do not provide evidence of

clear thresholds in expnsed populations.

Instead, they suggest a continuum of

response for a given number of exposed

individuals with both the likelihood

(risk) of any effects occurring and the

extent (incidence and severity) of any

potential effect decreasing with

concentration. This is particularly true

for the, statistical analyses of daily

mortality in London. Substantial

agreement exists that wintertime

pollution episodes produced premature

mortality in elderly and ill. populations,

but the range and nature of association

provide no clear basis for distinguishing

any particular lowest "effects likely"

levels or for defining a concentration

below which no association remains.

The recent lung function studies in

children also provide evidence of effects

at concentrations in the range listed in

Table 1, but the relationships are not

certain enough to derive "effects likely"

levels for PM~o. The lung function

studies do, however, suggest levels

below which detectable functional

changes are unlikely to occur in exposed

populations. Following CASAC

recommendations, the staff used the

combined range listed in the "effects

possible" row as a starting point for

developing alternative standards.

The original range proposed by the

Administrator, drawn from the 1982 staff

analysis, was 150 to 250 Ag/m3 PMo, 24-

hour average with no more than one

expected exceedance per year. The

lower bound of this range was derived

from the original assessment of the

London mortality studies. As a result of

its updated assessment of reanalyses of

the London mortality and more recent

U.S. morbidity studies, the staff reduced

the level of the lower bound of the range

of interest to 140 pg/m a (SPA, p. 51),

while noting that the difference between

it and original lower bound (150 ipg/m 3 )

is within the range of uncertainty

associated with converting the

morbidity study results from TSP to

PM10.

As indicated in Table 1, the study of

Lawther et al. (1970) judged to provide

evidence that health effects are likely at

particulate matter concentrations above

250 Ag/m 3 (as BS). The effects observed

in this study (related to aggravation of

bronchitis) are of concern both because

of their immediate impact and because

of the potential for inducing longer-term

deterioration of health status in a

significant sensitive group. There were

approximately 6.5 million bronchitics in,

the U.S. in 1970 (DHEW, 1973). Based on

the uncertain conversion between

smoke and PMo outlined in Table 1, the

lowest "effects likely" level derived

from the Lawther study (250 ,g/m s as

BS) should be in the range of 250 to 350

Ag/m 3, in PMo units.

The assessment of this study formed

the basis for the upper bound of the

range of PMo standards proposed by the

Administrator In 1984. Considering this

study alone, a PMo standard of 250 A*g/ m3 might appear to contain some margin

of safety, even for the sensitive

bronchitics studied, because It

incorporates a conservative British

Smoke/PMio conversion factor and

because of differences between

exposure conditions in the British study

and current U.S. air quality (SP, pp. 100-

101). Because bronchitics are identified

as a group particularly sensitive to

particulate pollution, a standard of 250:

pg/m3 (as PMzo) also might provide

some margin of safety for other, less

sensitive, groups. Nevertheless, this

study of bronchitics in London has

inherent limitations in sensitivity that

preclude derivation of unequivocal "effects thresholds" at 250 Ag/m3 as BS,

and by extension PMo. The criteria

document notes that associations

between pollution and health status

persisted at lower BS concentrations in

selected, more sensitive individuals.

Although the lead author of the study

objects to attaching any importance to

these latter findings (Lawther, 1986),

EPA, with CASAC concurrence, finds no

basis for asserting that this study

demonstrates a population threshold at

250 p.g/m3.

In evaluating the margin of safety for,

a 24-hour standard, it is also important

to consider the London mortality

studies. A standard at the upper portion

of the proposed range (250 jig/m 3)

would he well below the levels (500 to

1000 pg/m s as BS) of the historical

London episodes in which the scientific

consensus indicates that pollution was

responsible for excess mortality (CD,

Table 14-7). The portions of the

population at greatest risk of premature

mortality associated with particulate

matter exposures in such episodes

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include the elderly and persons with

pre-existing respiratory or cardiac

disease. Although the extent of life

shortening (days, weeks, or years)

cannot be specified, the seriousness of

this effect strongly justifies a margin of

safety for it (below the consensus

effects levels) that is larger than that

warranted for the effects on bronchitics.

The staff assessment of the several

reanalyses of London mortality suggests,

however, that the risk of premature

mortality to sensitive individuals

extends to concentrations substantially

lower than those which occurred in the "episodes." The more recent analyses

(Mazumdar et al., 1982; Ostro, 1984;

Shumway et al., 1983) provide no

objective support for a population

threshold below which such a risk no

longer exists. Although the risk to

individuals may be small at

concentrations of 250 1Lg/m 3 and below,

the number of people exposed to lower

concentrations given current U.S. levels

is substantially larger than the number

exposed to higher levels (SPA, Table 2-

1). The increased number of individuals

exposed increases the risk that effects

will occur in the total population

exposed.

Differences in the composition of

particles and gases among U.S. cities

and between current conditions in the

U.S. and those in London at the time the

mortality and morbidity data were

gathered add to the complexity of

assessing the risk associated with

particulate matter in the U.S. In the case

of the mortality studies, however, the

staff found that at least one of the more

recent studies (Ozkaynak and Spengler,

1985) provides qualitative support for an

association between daily mortality and

particle concentrations in nearly

contemporary U.S. atmospheres (SPA,

pp. 43-44).

The 1982 assessment of the mortality

studies and related factors prompted the

Administrator to consider standard

levels that extended from 250 Ag/mS

down to the lower bound of the original

staff range of interest (150 gg/m 3) and

even lower. The more recent analyses of

the London mortality data provide

additional evidence that serious adverse

health effects may occur at particulate

concentrations below 250 1g/m 3 . These

analyses have addressed a number of

the uncertainties associated with the

earlier studies, and have reinforced the

Administrator's concern that a 24-hour

standard at the upper end of the

proposed range may not provide an

adequate margin of safety. However,

given the uncertainties in converting

from BS to PMo measurements,

particularly at lower concentrations,

and the possible differences in

particulate composition between

London at the time the data were

gathered and the contemporary U.S., it

is difficult to use these studies to set a

precise level for a PM1o standard (SPA,

pp. 49-51).

Given these difficulties, it is important

to examine contemporary studies that

utilize gravimetric measurements of

particulate concentrations. The staff

found the studies of Dockery et al. (1982)

and Dassen et al. (1986) to be

particularly useful. The Dockery study

observed physiologically small but

statistically significant decreases in lung

function in a group of children exposed

to peak PMo levels of 140-250 pg/m 3 . The decrements persisted for 2-3 weeks

following the exposures. The study also

suggested the possibility of larger

responses in a subset of the children,

including those with existing respiratory

symptoms. The Dassen study recorded

similar decrements in children in the

Netherlands following exposure to PMo

levels estimated at 200 to 250 gg/m 3, but

no observable effects two days after

exposure to PMo levels estimated at 125

tg/m3. The particle composition, at

least in the Dockery study, is more

representative of contemporary U.S.

cities and the associated aerometry

provides a more reliable estimate of

PM1o levels than do the measurements

used in the London studies. It is

reasonable to-expect that the effects

observed (small reversible reductions in

lung function in children] are, in most

cases, more sensitive to air pollution

than those observed in the London

studies. These effects are, of themselves,

of uncertain significance to health, but

might be associated with aggravation of

respiratory syiptoms in children with

preexisting illness (SPA, p. 47). Longterm examination of respiratory health

in the same community studied by

Dockery et al. (1982) suggests that the

children in that community have a

higher incidence of respiratory illness

and symptoms than children in

communities with lower particle levels,

but the data show no evidence for any

persistent reduction in lung function

(Ware et al., 1986). Uncertainties with

respect to the effects of other pollutants

(e.g., S02), the consistency of the

changes, and exposures preclude

specifying unequivocal "effects likely"

levels based on this study. The staff

assessment therefore suggests that

short-term lung function effects in

children are possible across a range of

140-250 l±g/m3 or more as PM 0 (SPA, p.

50).

In making a decision on a final

standard level, the Administrator also

considered information from the more

qualitative studies of PM assessed by

the staff (SP, pp. 101-103; SPA, pp. 52-

53). These suggest increased risks for

sensitive groups (asthmatics) and risks

of potential effects (morbidity in adults)

not demonstrated in the more

quantitative epidemiological literature.

The qualitative studies do not provide

clear information on effects levels, but

do justify consideration of effects of

particulate matter that have not been

sufficiently investigated.

Based on the scientific assessment at

the time, the Administrator in 1984

expressed an inclination to select a 24-

hour level from the lower portion of the

proposed range of 150-250 jg/ms. The

present Administrator finds that the

updated scientific assessment supports

the original inclination and, if anything,

suggests an even wider margin of safety

is warranted. The recent analyses of

daily mortality are of particular concern

in this regard. The Administrator has,

therefore, decided to set the final

standard at the extreme lower bound of

the range originally proposed; that is, at

150 p.g/M 3 . This standard provides a

substantial margin of safety below the

levels at which there is a scientific

consensus that particulate matter causes

premature mortality and aggravation of

bronchitis. Such a margin is necessary

because of the seriousness of these

effects and because of the recent

analyses of daily mortality that suggest

adverse effects may occur at particulate

matter levels well below the consensus

levels. The standard is in the lower

portion of the range where sensitive,

reversible physiological responses of

uncertain health significance are

possibly, but not definitely, observed in

children. Using a conservative

assessment of lung function/particle

relationship from Dockery et al., a

change in concentration front

background levels (-20 jLg/m 3) to 150

j~g/m 3 would produce lung function

changes of at most 10 to 15% in less than

5% of exposed children (SPA, p. 48).

Based on the results of Dassen et al.

(1986), it appears unlikely that any

functional changes would be detected

one or two days following such

exposures (SPA, p. 50). Thus, the

maximum likely changes in lung

function appear to present little risk of

significant adverse responses.

.Standards set at a somewhat higher

level would, however, present an

unacceptable risk of premature

mortality and allow the possibility of

more significant functional changes.

Furthermore, a standard level of 150 zg/

m3 is fully consistent with the

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-recommendations of CASAC on the 24- term epidemiological studies are'subject can be identified for all effects

hour standard (Lippmann, 1986c). to additional confounding variables that categories. Evidence exists of effects at

2. Annual Standard -reduce their sensitivity and make their lower levels-the "effects possible.

interpretation more difficult than that of levels"-but the evidence is

The updated staff assessment of short-term studies. The "effects likely" inconclusive and effects are difficult to

important long-termepidemiological levels are derived from the criteria detect In the available epidemiological

data is summarized in Table 2. Long- document, but again, no clear thresholds studies.

TABLE 2.-UPDATED STAFF ASSESSMENT OF LONG-TERM EPIDEMIOLOGICAL STUDIES (AFTER TABLE 4-2, SPA)

Measured BS Measured TSP levels (pg/m3) Equivalent levels,(as pig/ PM10 levels m 3

) Increased (,ig/m 3

) respiratory Increased

Effects/Study Increased disease, Increased respiratory Reducedlung respiratory symptoms, respiratory symptoms and function in Combined

disease, small symptoms in illnesses in childreni

reduced lung reduction reduce in adults i lungrange children range C 5

function in lung function children 4 children I in adults 2

Effects likely ...................... 230-300 "180 ................................. .......... >180 >80-90

Effects possible ................. <230 "130-180 60-150(110) 60-114 ............................. 60-180 40-90

No significant 6 effects

noted ....... .. ....................... 80-130 .......................................................... 40-114 <60 <40

*Indicates levels Used for upper and lower bound of range.

':Study conducted in 1963-65 in Sheffield, England (Lunn et al., 1967). BS levels (as pg/m3

) uncertain.

2 Studies conducted in 1961-73 in Berlin. NH (Ferris et al., 1973, 1976). Effects likely level (180 fg/m3

) based on uncertain 2-month average. Effects in lung function. were relatively small.

3 Study conducted in 1973 in two Connecticut towns. (Bouhuys et al., 1978). Exposure estimates reflect 1965-73 data In Ansonia. Median

value (110 g/ms

) used to indicate long-term concentration. No effects on lung function, but some suggestion of effects on respiratory symptoms. 4 Study conducted in 1976-1980 in 6 U.S. cities (Ware et al., 1986). Exposure estimates reflect 4-year averages across cities. Comparable pollution/effects gradients not noted within cities. . Conversion of TSP to PMo equivalents for Berlin, Ansonia studies based on estimated ratio of PM,o/TSP for current U.S. atmospheres (Pace, 1983). The estimated ratio ranged between 0.45 and 0.5. Conversion for six-city study based on site-specific analysis of particle size data

(Spengler et' al., 1986). 6 Ranges reflect gradients in which no significant effects were detected for categories at top. Combined range reflects all columns.

Based on a recent assessment of

PM,6/TSP ratios in areas with elevated

TSP levels, the updated staff assessment

revised the "effects likely" levels from

the Ferris et al. (1973) study to 80 to 90

fg/m 3 as PMo (SPA' p. 58). Because of

limitations in sampling duration as well

as the conversion to PMo, this estimate

is particularly uncertain. As indicated in

the table, effects are possible at lower

concentrations. Of greatest concern is

the possibility of long-term deterioration

of the respiratory system in exposed

populations, the potential for which is

indicated by lung function (mechanical

pulmonary) changes and increased

incidence of respiratory disease. One set

of studies (Ferris et al., 1973, 1976)

,provides some evidence for a "no

observed effects" level for these effects

at or below 60 to 65 jig/m (130 jig/n 3

as TSP) while another study (Bouhuys et

al., 1978), suggests some possibility of

symptomatic responses in adults at longterm median levels at or below about 50

to 55 pg/m3 as PMo. The importance of

these symptomatic responses, which

were unaccompanied by lung function

changes, to long-term respiratory health

is unclear.

- The most important recent study of

long-term effects is an ongoing

* examination of six U.S. cities (Ware et

al., 1986). The study indicates the

possibility of increased respiratory

symptoms and illnesses in children at

multi-year levels across a range of 40 to

over 58 jig/m as PMo, but found no

evidence of reduced lung function at

such concentrations. This study did not

find similar gradients in symptoms and

illness within some of the cities, which

had somewhat smaller localized

pollution gradients. The results of a

separate series of studies of long and

intermediate term (2 to 6 weeks)

exposures in a number of U.S.

metropolitan areas (Ostro, 1987;

Hausman et al., 1984) are more

supportive of the possibility of effects

within cities (respiratory related activity

restrictions in adults) at comparable

U.S. exposure levels. The results of

these more recent studies are generally

consistent with the earlier U.S. studies

listed in Table 2 (SPA, 57). In particular,

the finding of symptomatic responses in

children with no change in lung function

(Ware et al., 1986) is consistent with

similar findings in adults (Bouhuys et al.,

1973) at estimated long-term PMo0 levels

down to 50 jg/m. However, the

information available to support the

existence of significant adverse effects

at annual PMo levels below 50 g/m3 -

especially when 24-hour levels are

maintained below 150 p.g/m-is quite

limited and uncertain.

Because of the uncertainties in (SP,

pp. 104-110; SPA, 54-59), as well as the

limited scope and number of, these longterm quantitative studies, it is

particularly important to examine the

results of qualitative data from a

number of epidemiological, animal, and

ambient particle composition studies

when evaluating what constitutes an

adequate margin of safety for an annual

standard. These studies justify concern

for serious effects not directly evaluated

in the studies listed in Table 2. Such

effects include damage to lung tissues

contributing to chronic respiratory

disease, cancer, and premature

mortality (SP, pp. 109-111). Substantial

segments of the population may be

susceptible to one or more of these

effects (SP, p. 46). Although the

qualitative data do not provide evidence

for major risks of these effects at-current

annual particulate matter levels in most

U.S. cities, the Administrator believes -

that the seriousness of the potential.

effects and the large population at risk

warrant caution in setting the standard;

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Based on the then current scientific

assessment, the Administrator proposed

in 1984 to select the annual standard

level from a range of 50 to 65 Ag/m 3 .In

the proposal, the Administrator favored

a standard in the lower portion of the

range. The more recent evidence,

although subject to substantial

uncertainty, serves to reinforce this

inclination. In light of the updated

assessment and in accordance with the

recommendation of CASAC, the

Administrator has decided to set the

level of the annual standard at the lower

bound of the original range, 50 pgg/m s,

expected annual arithmetic mean. This

standard provides a reasonable margin

of safety against the serious effect of

long-term degradation in lung function,

which has been judged likely at

estimated PMo levels above 80-90 #Lg/.

ms and for which there is some evidence

at PMo levels above 60 to 65 Ag/m 3 .

Such a standard also provides

reasonable protection against the less

serious symptomatic effects for which

some studies provide evidence at PMo

levels down to 50 g/mS* Although some

small risk of increased respiratory

symptoms may exist at this

concentration, the available data are

currently inconclusive on this point.

Moreover, the staff and CASAC have

recommended that the combined

protection afforded by both 24-hour and

annual standards be considered in

selecting the final standard level. In this

regard, analyses of air quality data

show that implementation of the 24-hour

standard will substantially reduce

annual levels in a number of areas to

below 50 Ag/m3, adding to the

protection afforded by the annual

standard in areas with higher 24-hour

peak to mean ratios (SPA, p. 61; Freas,

1986). Based on the present evidence

with respect to risks associated with

annual exposures, the Administrator

finds that the annual and 24-hour

standards announced today provide an

adequate margin of safety.

IV. Rationale for the Secondary

Standards

Section 109(b)(2) of-the Clean Air Act

states that secondary NAAQS should be

set at a level requisite to protect the

public welfare from any known or

anticipated adverse effects associated

with the presence of an air pollutant in

the ambient air. The criteria document

and staff paper examined the effects of

particulate matter on such aspects of

public welfare as visibility and climate,

man-made materials, vegetation, and

personal comfort and well being. Each

aspect is discussed in some detail in

those documents. The following

discussion of the rationale for the

secondary standards focuses primarily

.on considerations that were most

influential in the Administrator's

decision or that differ in some respect

from, or expand upon, -considerations

that influenced the staff and/or CASAC

recommendations.

A. Soiling and Nuisance

At high enough concentrations, both

large and small particles may soil

household and other surfaces, or

otherwise become a nuisance. Both

effects can result in increased cleaning

costs and decreased enjoyment of the

environment (SP, p. 140). Efforts to

control particulate matter in U.S. cities

from 1970 to 1978 were estimated to

have produced substantial economic

.benefits because of reduced soiling and

nuisance (CD, p. 1-51). The staff paper

therefore recommended consideration of

soiling and nuisance generated by dust

and other particles in setting a

secondary standard (SP, p. 141).

In proposing secondary standard(s)

for particulate matter, the Administrator

first examined whether the pollutant

indicator (PMio), averaging times and

form, and range of levels of the

proposed primary standards would

provide adequate protection against

soiling and nuisance. This examination

was complicated by uncertainties in the

scientific data base that largely preclude

accurate quantification of the extent of

effects associated with specific particle

sizes and concentrations or deposition,

and by the fact that the protection

afforded by primary standards depends

upon the particular combination of

levels chosen within the ranges that

were proposed for the primary

standards. The Administrator proposed

a separate indicator and range of

secondary standards, while also

soliciting comment on the alternative of

making the secondary standards

identical in all respects to the proposed

primary standards for PMo. In so doing,

the Administrator noted that "depending

on the exact levels of primary standards

chosen, the combined requirements for

meeting both 24-hour and annual

primary standards for PM1o might be

considered adequate to protect against

possible adverse effects relating to

soiling and nuisance from all relevant

particle sizes." (49 FR 10418].

The decision to adopt the specific

revised primary standards discussed in

section IV above permits a more

definitive assessment of the protection

afforded by those standards against

potential adverse welfare effects. In

addition, information submitted in the

public comments, the review of the

March 20, 1984 proposal by the CASAC,

and further analysis of the welfare

effects information by Agency staff have

amended the basis for the final decision

on the secondarystandards. The basis

for the original p'i6osal and the'

implications of the more recent findings

are summarized below.

The Administrator originally proposed

(1) to retain TSP as the indicator for the

secondary standard and (2) to select the

standard level from a range of 70-90 pg/

in s, expected annual arithmetic meap.

Given the nature of the evidence

available, the Administrator expressed

an inclination to select the level for the

standard from the upper portion of the

range.

The proposal noted that both PMo

and TSP could be useful indicators for a

secondary standard for soiling and

nuisance. PM1o is useful because in a

qualitative sense: (1) Particles smaller

than 10 Am in diameter are more likely

than larger particles to penetrate

indoors; they are also more likely than

larger particles to soil vertical surfaces

(SP, pp. 136-137) and (2) due to the

.characteristic size distributions and

origins of particles in the atmosphere

(SP, pp. 14-19), control of particles less

than 10 gAm in diameter would also limit

the concentration of larger particles. The

TSP indicator was proposed, however,

because of the lack of data'permitting

clear distinctions among size ranges

with respect to soiling and nuisance, the

more inclusive nature of TSP, and the

fact that most of the available

information relating soiling and

nuisance to air pollution used TSP as an

indicator.

Information submitted in the public

comments expanded on some of the

limitations of TSP as an indicator that

were noted in the preamble, namely: (1)

The collection efficiency of the high

volume sampler, which measures TSP,

decreases rapidly for particles with

diameters in excess of 25-40 A.m; thus,

the TSP measurement itself can omit a

substantial fraction of the very large

particles that can make a substantial

contribution to soiling of horizontal

surfaces; and (2) because the collection

efficiency of the high volume sampler

varies more with windspeed than do

PMlo samplers, TSP may be a less

reliable indicator of elevated "

concentrations of larger particles than

PM1o.

In light of these considerations, the

CASAC in reviewing the March 20

proposal package concluded that it

could find no convincing scientific

support for maintaining TSP as an

indicator for the secondary stahdards

(Transcript of December 16, 1985

CASAC meeting,. pp. 56-71; Docket No.

A-82-37).

24645

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.In developing a range of levels for the secon dary standard, EPA found that the.

available data base provides compelling

evidence that elevated levels of

particulate matter can produce adverse

welfare effects, but provides little

quantitative information on, -.

concentration-effects relationships.

Physical damage and economic studies

tend to show no obvious welfare effects

"thresholds" for soiling. With time,

particulate matter may accumulate on

surfaces even at low concentrations. At

very low concentrations, however, the

amounts of particulate matter may be

virtually invisible to the human eye or be so slight as to be ignored by most

people (Carey, 1959; Hancock et al.,

1976). Up to a point, the buildup of

particles on surfaces may notbe

generally regarded as a social problem

because it is removed'by rain-or routine

cleaning and maintenance before

substantial accumulation can oqcur.

Moreover, even if an accumulation is

large enough to be noticed, it is not • necessarily considered to be a problem.

Thus, the critical judgment for selecting

a standard level is to determine a

particulate matter concentration at or. above which the soiling effect becomes

important enough that it should be

regarded as an "adverse" effect under

section 109(b)(2) of the Act.

-The available information suggests

that the public does make a distinction

between concentrations at which

particulate pollution is merely

noticeable and higher levels at which it

is considered a nuisance. A study of the

response of a panel of-human subjects to

dust on surfaces concluded that the

level of dustiness that is found to be

objectionableis higher than the level

that can be perceived or discriminated

(Hancock et al., 1976). It is not, however,

possible to derive unique. ambient

concentration thresholds for adverse

effects from this kind of study. A more direct study of perception of air

pollution as a nuisance (CD, p. 9-67)

suggested that people considered air

pollution a nuisance in areas where

annual levels were at or somewhat

above the level of the current annual

primary TSP standard (75 jug/ms, annual

geometric mean). The upper bound of: . the proposed range of interest (90 #g/m3

TSP), expected annual arithmetic mean,

was derived by taking that-level and

making appropriate conversions to

account for the expected arithmetic

mean form.

The lower bound of the proposed

range (70 ig/m 3

) was supported by a

rough analysis of economic benefits of.

reduced outdoor soiling that. might be

associated with decreased TSP levels in

U.S. cities (CD, p. 10-73). During the

1ublic comment period, one of the

authors of the analysis that formed the

basis for these estimates submitted a'

more recent analysis which called the

earlier analysis into question (Watson

and Jaksch, 1984). The author claimed

that estimates of benefits from reduced

TSP concentrations were significantly

overstated because they did not take

into account the extent to which the

public could perceive improvements

associated with reduced concentrations.

Other commenters indicated that the

underlying experimental data suggested

a threshold for economic soiling effects

at an annual TSP level of about 150 ;g/ M 3 .

EPA staff examined the underlying

experimental data used in the original

analysis. This staff examination

(Haines, 1987) has been placed in the

rulemaking docket. The staff found that

of 27 household cleaning activity

categories examined in the underlying

experiment (Booz, Allen, Hamilton,

1970), 6 (5 outdoor) were statistically

significantly associated with particulate

matter across some concentration

gradient. In further comparing areas

with differing concentrations of in TSP,

it was found that the number of

significant associations decreased with

decreasing TSP levels. The staff

concluded that these data provide no

convincing evidence to support

estimates of significant economic

benefits from reducing PM levels below

90 to 100 ltg/m3. . Following the original inclination of

the Administrator and the more recent

findings, an annual TSP level of 90 pg/

m3was used as a benchmark in an

analysis to determine whether the

primary particulate matter NAAQS

would protect against soiling and

nuisance (SP, Table 2-1). An earlier

version of these results was presented at

the December 16, 1985 CASAC meeting.

The analytical approach, assumptions, and limitations of the methodology used

in the analysis are discussed in a

separate report, which has been 'placed in the rulemaking docket (Pace et al.

* 1986). The results indicated that the

combined implementation of the primary

24-hour and annual PMo standards

announced above would substantially

reduce TSP levels to the extent that only

6 counties nationwide would experience

annual mean TSP levels in excess of 90

pg/m s and none would exceed 100 1g/ in 3

.

In short, EPA has determined that

there is.no convincing evidence of

significant adverse soiling and nuisance

at TSP levels below 90-100 pug/m3, and

that the primary standards promulgated

today would permit few, if any, areas to'

sustain'TSP levels above 90-100 Pg/mn.

On the basis of these determinations,

the Administrator concludes that a

secondary standard different from the

primary standards is not-requisite to

protect the public welfare against soiling

and nuisance. This conclusion is

supported by the CASAC's

determination that there is no scientific

support for a TSP-based secondary '

standard. (Transcript of December 16

1985, CASAC meeting, p. 71; Docket No.

A-82-37). Therefore, the Administrator

has decided to set 24-hour and annual

secondary PMo standards that are equal

in all respects to the primary standards.

B. Other Welfare Effects

The other welfare effects of

particulate matter of principal interest

are impairment of 'visibility, potential

modification of climate, and

contribution to acidic deposition. All

three of these effects are believed to be

related to regional-scale levels of fine'

particles, and control programs deaigned

to ameliorate them would likely involve

region-wide reductions in emissions of

sulfur oxide (SP, p. 147; Friedlander,

1982).

Because of the likely overlap between

control measures designed to protect

visibility and control measures designed

to address acidic deposition, EPA, in its

March 20,1984, notice of proposed.

rulemaking on the particulate matter.

standards, did not propose a secondary

standard designed to protect visibility.

Instead, the Agency decided to defer

action pending development of

.compatible strategies to address both of;

these related regional air quality

problems.

Since publication of the notice of

proposed rulemaking, EPA has

continued to gather information on

acidic deposition and on visibility, and

to analyze the potential impact on

visibility of strategies designed to

control acidic deposition. In particular,

EPA has received the report of an

Interagency Task Force on Visibility. In

light of the Task Forces

recommendations as well as other

information gathered by the Agency,

EPA is now reassessing its position with.

regard t0consideration of a secondary

fine particle standard for.visibility. In

particular, the Agency is considering

whether, given the time that would be

required to develp, propose,'

promulgate, and implement a visibility

based standard, it would now'be

appropriate to: proceed with

consideration of a visibility based -

standard in parallel with work on acid

deposition, so that compatible strategies

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for dealing with the two problems can

be developed at the implementation

stage., :

Accordingly, EPA is publishing

elsewhere in today's Federal Register

an advance notice of proposed

rulemaking soliciting public comment on

the appropriateness of a separate

secondary fine particle standard

designed to protect visibility, and on a

number of issues that would have to be

resolved in proposing such a standard.

The Administrator also concurs with

the staff suggestions that a separate

secondary particle standard is not

needed to protect vegetation or to

prevent adverse effects on personal

comfort and well-being (SP, pp. 143-144).

V. Federal Reference Method

The reference method for the

measurement of atmospheric particulate

matter as PM1o, promulgated today as

Appendix J to 40 CFR Part 50, is based

on selection of PM1o particles by inertial

separation, followed by filtration and

gravimetric determination of the PMo

mass on the filter substrate. The particle

size discrimination characteristics of

reference method samplers (or sampler

inlets) are prescribed as performance

specifications in amendments to 40 CFR

Part 53, promulgated elsewhere in

today's Federal Register.

The requirements in Appendix J are

generally prescribed as functional or

performance specifications in order to

allow sampler manufacturers flexibility

In designing or configuring their PMo

samplers. Sampler shape, inlet

geometry, operational flow rate, degree

of automation, and other sampler

characteristics or features are specified

only in terms of required function or

performance.

While most of the comments received

on Appendix I generally supported the

performance-based approach to

specifying PMo reference methods,

many commentors felt that the sampler

performance specifications in the

proposed Appendix J and 40 CFR Part 53

were not adequate to ensure accurate

collection of PM10 under all conditions

of ambient sampling. In response to such

comments, the sampler performance

specifications in Part 53 and the

corresponding references to such

requirements in Appendix I have been

revised. Other comments were received

on various requirements of Appendix J

such as flow calibration and

measurement, flow regulation, filter

media, filter equilibration, and sampler

maintenance. Specific changes to

Appendix J resulting from these

comments and from review of other

pertinent information are discussed

below.

A. Specific Changes to Appendix I

Section 3.0 has been revised to specify

that all samplers should be capable of

measuring 24-hour PMjo mass

concentrations of at least 300 pgg/m3

while maintaining the operating flow

rate within specified limits.

In Section 4.0 the term "reproducibility" has been changed to

"precision" and the specification for

PMo samplers has been changed from

15 percent or better to 7 percent or 5 g.g/

M, whichever is higher. The particle

size for 50 percent sampling

effectiveness in Section 5.0 has been

changed from 10± 1 micrometers to

10±0.5 micrometers. These changes are

a result of corresponding changes in the

PM1o sampler performance

specifications in 40 CFR Part 53,

promulgated elsewhere in today's

Federal Register. Refer to the Part 53

action for further discussion of these

changes.

In Section 6.0 the subsection on

nonsampled particulate matter has been

removed. The design of particle size

discriminating inlet systems for PM o

samplers essentially precludes the

transport of windborne particulate

matter to the particle collection filterduring periods when the sampler is idle..'

Although windborne particles could

potentially enter a PMo sampler's air

inlet opening during idle periods, they

would have to take a tortuous path with

several changes in direction to reach the

collection filter.

References to "automatic flow

controller" throughout Appendix J have

been changed to "flow control device".

The latter term is less restrictive and

more clearly allows the use of any type

of flow regulation device, provided that

the other flow-related requirements of

Appendix J are met. In particular,

Section 7.1 has been changed to require

that a PM o sampler have a flow control

device capable of maintaining the

sampler's operating flow rate within the

limits specified for the sampler inlet.

The requirement that the flow control

device have aflow rate adjustment

capability has been removed to allow.

for the use of certain types of flow

controllers (e.g., Venturi-type critical

flow devices) that regulate flow at a

constant but unadjustable rate. Flow

controllers of this type generally employ

a fixed-geometry orifice and control the

sampler's flow rate without any moving

parts or electronic components. The

requirement that the flow control device

be disabled during calibration has also:

been removed because it is, only

applicable to certain types of devices

(e.g., electronic flow controllers).

Sampler-specific operational

requirements such as this are better

addressed in the sampler manufacturer's

instruction manual.

Subsection 7.1.6 has also been

changed to explicitly require that the

instruction manual associated with the

sampler include detailed procedures for

calibration, operation, and maintenance

of the sampler. Since much emphasis is

placed on the role of the sampler

manufacturer's instruction manual in

Appendix J, it is important that it

contain detailed information on all

aspects of sampler operation. The

instruction manual for each designated

reference method would be reviewed

and approved as part of the Part 53

reference method designation process.

The filter alkalinity specification in

Subsection 7.2.4 has heen changed from

<0.005 milliequivalents/gram of filter to

<25 microequivalents/gram of filter. In

addition, the method used for the

alkalinity determination has been

changed to a newly developed, more

sensitive, and more reliable method. The

change in the magnitude of the

specification results from the change in

procedures (alkalinity measurements

are approximately 5 times higher with

the new method), and from the change

in the measurement units.

:Section 7.3 includes specifications and

other requirements for the flow rate

transfer standard used during sampler

calibration. The specifications for the

reproducibility and resolution of the

flow rate transfer standard have heen

removed and replaced with an accuracy

specification. The revised Section 7.3

requires that the flow rate transfer

standard be capable of measuring the

sampler's operating flow rate with an

accuracy of ±2 percent. An accuracy

specification, stated in this context, is

more meaningful and useful than

specifications for reproducibility and

resolution. In addition, the requirement

that the flow rate transfer standard

include a means to vary the sampler's

flow rate during calibration is not

appropriate for all types of samplers

and/or flow rate transfer standards and

has been removed, This is another

example of a sampler-specific

requirement that is better addressed in

the sampler manufacturer's instruction

manual.

The humidity requirement for the filter

conditioning environment in Section 7.4

has been changed from a single

specification of 45±5 percent relative

humidity (RH) toseparate specifications:

for humidity range (20 percent to 45

percent RH] and humidity control (±5

percent RH). Under the revised

requirements, filters may be equilibrated

at any.preselected humidity betWeen20

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and 45 percent RH, provided that the

humidity is controlled to within 5

percent RH. Language has also been

added to Section 9.0 to require that the

same temperature and humidity

conditions be used for both pre- and

post-sampling filter equilibration.

The calibration and operational

procedures for PM 0 samplers vary

considerably depending on the type of

sampler (e.g., high-volume, mediumvolume, low-volume)and the type of

flow control and flow measurement

devices employed in the sampler.

Accordingly, the calibration and

procedure sections of Appendix J

(Sections 8.0 and 9.0) have been revised

substantially to be more general in

nature. The revised procedures serve to

illustrate the steps involved in the

calibration and operation of a PM~o

sampler, and place more emphasis on

the sampler manufacturer's instruction

manual and the Quality Assurance

Handbook for specific guidance.* A new section on sampler •

maintenance has been incorporated'into

Appendix J to explicitly, require that

PM1o samplers be maintained in strict

accordance with the procedures

provided in the sampler manufacturer's

instruction manual. The performance of

some PM1o samplers may be adversely

affected by the buildup of substantial

quantities of non-PMo particulate

matter within the sampler inlet. Such

samplers may require periodic cleaning

and other maintenance to ensure

accurate collection of PMo particulate

matter. This new section has been

added as Section 10.0. and the

calculations and references sections

have been renumbered accordingly.

When temperature and pressure corrections to sampler flow indicator

readings are required, corrections based

on existing temperature and pressure at

the time the readings are taken (or daily

average values during the sampling

period in some cases) are preferable.

However, incorporation of site or

seasonal average temperatures and

barometric pressures into the sampler

calibration to avoid daily temperature

and pressure corrections is also

allowed. When temperature and

pressure corrections to flow indicator

readings are required, existing

temperature and pressure at the time the

readings are taken (or daily average

values during the sampling period in

some cases) must be used. Likewise, the

calculations section has been changed.

to require that the average barometric

pressure and average ambient

temperature during the sampling period

be used to calculate Qtd. Site or .

seasonal average values for temperature

and barometric pressure may be

required in the adjustment of the setpoint of certain types of flow control

devices (e.g., mass flow controllers). Site

or seasonal average values for

temperature and pressure are used in

these cases to ensure that the deviations

in actual volumetric flow rates, resulting

from daily changes in temperature and

pressure at the monitoring site, are

centered about the sampler inlet's

design flow rate.

Other minor wording changes have

been made throughout Appendix J to

clarify the requirements.

B. Designation of Reference Methods for PMo

Before a method for PM1o is approved

as a PM1o reference method, it must

meet the requirements of Appendix J

and be tested and designated as a

reference method In accordance with

the provisions of 40,CFR Part 53. Testing

of candidate reference methods will

generally be conducted by the sampler

manufacturers. A notice will be

published in the Federal Register in,

accordance with Part 53 whenever an

application for a PM1o reference method

determination is received by EPA.

Likewise, a notice of designation and

other information pertinent to the

designation will be published in the

Federal Register each time a PMo

reference method is approved for use.

PMo sampler manufacturers are

required to provide sampler purchasers

with an operation or instruction manual

containing detailed procedures for the

calibration, operation, and maintenance

of the sampler. Additional guidance and

recommendations regarding filter media,

type of analytical balance required for

mass determinations, and other

requirements of the method should also

be provided In the manual. Part 53

requires submission of the manual as

part of a manufacturer's application for

a reference method determination. The

instruction manual will be reviewed for

technical accuracy and consistency with

the requirements of Appendix J and

must be approved as part of the

requirements for designation of the

method as a reference method.

C. Technical Change to Appendix G

Because the high-volume method

described in Appendix B will continue

to be used in conjunction with Appendix

G ("Reference Method for the

Determination of Lead in Suspended

Particulate Matter Collected from

Ambient Air") and for other purposes

that may be specified, EPA is

promulgating the technical changes to

Appendix G as proposed. Under the

final rule the reference 10 in* Appendix G

has been deleted and section 5.1.1 of the

Appendix has been revised to read as

follows:

"High Volume Sampler. Use and

calibrate the'sampler as described in

Appendix B to this Part." The Appendix

has also been revised to specify more

directly that the high-volume method

described in Appendix B is to be used in

conjunction with the reference method

for lead.

VI. Summary of Salient Public

Comments and Agency Responses

An overview of public comments on

the major aspects of the March 20, 1984

proposal are presented in Section II. The

most important comments on specific

issues are categorized and summarized

below together with Agency responses.

A more comprehensive compilation of

comments and Agency responses is

contained in a separate Response to

Comments Document that has been

placed in the Docket,(No. A-82-37).

A. Health Effects Criteria and Selection

of the Primary Standards

1. Indicator for the Primary Standards

Comments: PMe rather than PMo

should be used as the indicator for the

primary standards because PM. more

accurately reflects particle deposition in

the thoracic regions, provides an ample

margin of safety in protecting health,

and puts less emphasis on coarse

particles that are relatively inert than

does PMo.

Agency Response: EPA considered the

major analysis (Swift and Proctor, 1982)

and preliminary arguments (AMC, 1982)

in support of a PMs indicator in

developing the 1984 proposal. Although

EPA deferred judgment pending

additional analysis and review, the

decision to propose PM1 o and not PM.

was based, in part, on reservations

concerning the PMs indicator. The

likelihood that the available data from

mouthpiece studies overstated thoracic

deposition during "natural" breathing

was recognized in a qualitative sense by

CASAC (cf. July 1981 transcript, p. 581;

Docket No. A-82-37) and presented as

one reason for recommending PMo

rather than PM1. or TSP as an indicator.

The 1982 staff paper reflected this

argument in recommending 10 prm rather

than 15 ftm as the cutpoint for the

indicator (SP, pp. 76-77). The criteria

document addendum points out that

assumptions used in the quantitative

analyses used to support PM. (Swift and

Proctor, 1982) appear to underestimate

thoracic particle deposition; this

underestimation would reduce any

margin of safety associated with an

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indicator derived from these data.

Extension of the Swift and Proctor

analysis itself suggests that

approximately 10 to 20% of 10 pm

particles could penetrate to the thoracic

region, rather than the 0% penetration

implied by some commenters who

argued for a "Do" at 10 pm.

The Swift and Proctor analysis as well

as several more recent analyses and

experimental studies of particle

deposition are reviewed in the criteria

document and staff paper addendum.

The more recent assessments tend to

support the original proposal of PMIo.

The criteria document addendum

compares the work of Miller et al. (1986),

using the more recent deposition data,

with the Swift and Proctor analysis and

confirms that the latter understates

deposition of particles larger than 6 pm

in individuals who habitually breathe

through the mouth.

The more recent data also show some

fraction of particles of 10 pm and larger

can penetrate as far as the alveolar

region (CDA, Figure 2-1). The risk

associated with deposition of insoluble

coarse particles in this region is of

particular concern because of slow

clearance time (CDA, p. 2-6). Although

removal in the tracheobronchial region

is more rapid, deposition of coarse

particles in the tracheobronchial region

may be associated with

bronchoconstriction and alteration of

clearance mechanisms (SP, Table 5-2).

The 1982 staff paper took these factors

into account in the original

recommendation for a 10 pm indicator

that included all of the fine and a

portion of the coarse fraction.

After considering these updated

assessments, the EPA staff reaffirmed

its original recommendation of PMo as

an indicator for the standards (SP, p. 32).

In reviews of the March 20,1984

proposal and of the criteria document

and staff paper addenda, the CASAC

also reaffirmed its recommendation for

PMo as an indicator (Lippmann 1986

a,c). The majority of public comments on

this issue also favored PMo.

In summary, EPA finds that the

presently available record clearly favors

the PMo indicator over the alternative

PMK indicator.

Comments: Some commenters

suggested that while PM,0 represents an

improvement over TSP, the fine fraction

(<2.5 pm) is of relatively greater

concern to health than the coarse

fraction (2.5 to 10 pm). Such commenters

suggest that a PM2 .

5 standard is

needed-in addition to or, in some

comments, instead of a PM,0 standard.

Agency Response: The possibility of a

fine particle indicator for the primary

standard was examined in the staff

paper (pp. 68-70). This suggestion is

based in part on the recognition that

ambient particle mass and volume are

distributed such that a rough division ..minimum" at about I to 3 pm separates

the "fine" (smaller) and "coarse"

fractions. Each fraction has somewhat

distinct chemical and physical

properties and sources. The staff,

however, noted a number of difficulties

in using fine particles (less than a

nominal 2.5 pm) alone instead of PMo

as the indicator for the primary

standards. These include:

(1) Substantial overlap can occur

between the two modes and in some

cases the division minimum can

disappear. Moreover, despite the

differing origins and chemistries of the

modes, each is chemically

heteorgeneous. The respiratory tract, in

effect, alters the ambient distribution,

with a mixture of fine and coarse modes

being deposited in both the

tracheobronchial and alveolar regions.

Indeed, the 2.5 pm !'cut" is within the

size range of maximum efficiency for

alveolar deposition (2 to 4 pm). The

mixing of these size fractions in the

respiratory tract and the heterogeneity

within each fraction therefore blurs the

distinction between the fractions in

terms of health effects.

(2) Coarse dusts have been associated

with responses such as

bronchoconstriction, altered clearance

and alveolar tissue damage (SP, Table

5-2). Given current Information, it would

be premature to ascribe all of the effects

in the British, U.S., and other

epidemiological studies to the fine

fraction, or to any single chemical entity

within that fraction.

EPA believes that a separate fine

particle standard in addition to the PMo

standard is not warranted for the

following reasons:

(1) Fine mass typically comprises on

the order of 40 to 70% of PM,0 .

Therefore, the PM,0 standards provide

substantial limits on fine mass, and

(2) The limited epidemiological data

presently available must provide the

principal basis for any particulate

matter standard. Because these data do

not separate the effects of fine and

coarse fractions, it is most reasonable to

use these data to support a single set of

standards.

(3) To the extent that emerging

information suggests additional

protection may be necessary, it may be

more appropriate to consider the

addition of chemical-specific (e.g., acid

aerosols) standards rather than a fine

particle standard in future primary

standard revisions.

2. Interpretation of Community

Epidemiological Studies

Comments: A number of commenters

took issue with EPA's interpretation of

the various analyses of London

mortality data. These commenters

suggest that (a) the London data can be

used to show only an association of

excess mortality with high

concentrations of pollution during

unique episodes in which BS and SO

levels exceeded 500 to 1000 pjg/m3, (b) a

number of the analyses suffer from

methodological flaws precluding valid

conclusions, (c) the conclusion that

effects may be possible at low pollution

levels (e.g., <250 pg/m s) or that there is

a continuum of association with no

identifiable threshold is not supportable,

(d) the results of Mazumdar et al. (1982)

and Ostro (1984) are more consistent:

with the hypothesis that particulate

matter is acting as a surrogate for some

other causal agent rather than as a

causal agent itself, and (e) it is

biologically implausible that mortality

could be affected by particulate matter

at levels below those shown by Lawther

et al. (1970) to produce morbid effects in

,sensitive populations.

Agency Response: EPA's'assessment

of the various London mortality analysis

Is discussed at length in the criteria

document, the staff paper, and the

addenda to these documents. The 1982

criteria document found that in the

context of historical London exposures,

these data indicate clear increases in

daily mortality occurred with BS and

SO2 concentrations in excess of 1000

pg/m with some indications of likely

increases in daily mortality at levels of

both pollutants in the range of 500 pg/

M3 or more (CD, Table 14-7). These

original conclusions on likely effects

levels, based largely on the Martin and

Bradley (1960) and Ware et al. (1981)

analyses, appear reasonably consistent

with the original assessment of these

data by the original British investigators

and the 1969 criteria document. From the

re-examination of these data by Ware et

al. (1981) and the analysis of subsequent

London winters by Mazumdar et al.

(1981), the criteria document also

concluded small increases in daily

mortality might occur at levels below

500 pg/m s

. The more recent analyses of

these data by Mazumdar et al. (1982),

Ostro (1984), and Shumway et al. (1983)

all serve to reinforce the possibility that

effects were associated with particulate

matter at concentrations below 500 jLg/

in s . A number of commenters, however,

including some of the original British

investigators (Holland et al., 1985),

object to this latter suggestion.

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EPA has carefully examined these

studies and the various criticisms of

them submitted as comments on the

proposal. In order to respond fully to

these criticisms, EPA conducted more

sophisticated reanalyses of the original

London data to further determine the

degree of reliance that can be placed on

the published results (Schwartz and

Marcus, 1986, CDA, Appendix A). Each

of these studies does suffer from

limitations and uncertainties delineated

in EPA's updated assessment (SPA pp.

17-23; 39-44); these limitations preclude

definitive conclusions with- respect to

causality as well as identification of

clear "no observed effects" levels.

Nevertheless, EPA maintains its original

interpretation, supported by its external

science advisors, that these data at least

suggest the possibility of effects of

particulate matter at BS levels as low as

150 pg/m 3 and possibly even lower.

None of the difficulties in statistical

methodology or alternative mechanisms

cited by commenters provide an

adequate explanation for the consistent.

finding of association between

particulate pollution and mortality at

levels below 500 g/m33 (as BS). The

association was found for the majority

of 14 winters (analyzed individually)

spanning a period when pollution in

London and indoor heating practices

showed marked changes, and including

winters in which BS levels did not

exceed 250 pg/m s . The relative

consistency of the results from year-toyear despite these changes suggests that

the observed effect is not explained by

indoor air pollution or by long-term

demographic shifts in the population.

The findings were consistent among

different investigators, and persisted

after taking SO2,.temperature, and other

weather variables into account, and

after correcting for autocorrelation

structure.,

The principal arguments for the

suggestion by some (including

Mazumdar et al., 1982) that smoke may

be acting as a surrogate for some more

toxic pollutant or related non-pollution

variable are: (1) The coefficients in the

regression equations appear to increase

with decreasing pollution across the 14

winters, (2) surrogate behavior is

commonly observed in statistical

analyses, (3) the work of Lawther

suggests a threshold for morbidity at

around 250 jg/m as BS; hence

mortality would not be expected at

lower levels. While the possibility of

surrogate behavior remains, the above

arguments do not demonstrate that

smoke acts as a surrogate for nonpollution variables. The trend toward

higher coefficients with lower pollution

is not clearly consistent in the

Mazumdar and Ostro regressions. The

existence of higher coefficients in later

years, however, prompted these authors

to suggest some plausible alternative to

non-pollution surrogates, including: (a)

The possibility that the composition of

pollution changed with time, with an

increase in more toxic components, and

(b) because the gravimetric mass of

particles in the range under 10 jum may

not have declined as much as did the

black carbon content detected in the

smoke measurement (Lodge, 1986),

coefficients related only to smoke might

be expected to increase. An additional

possibility suggested by Schwartz and

Marcus is that the effect of higher

pollution episodes in earlier winters was

blunted by public awareness (and hence

reduced exposure) or by a tendency for

the most susceptible individuals to

succumb on an early day of a multi-day

pollution episode.

The use of the Lawther morbidity data

as a threshold for mortality is

questionable. The London mortality data

involve an unequivocal endpoint in a

relatively large population (several

hundred per day) over a 14 year period.

As pointed out by Roth et al. (1986),

although the bronchitic population

studied was clearly susceptible, the

effects indicator used by Lawther was a

relatively insensitive one. Moreover, the

threshold was determined not by

rigorous analysis, but by visual

examination of strip chart data.

Although the principal author strongly

objects (Lawther, 1982), the criteria

document points out that the data do not

clearly indicate an effects threshold at

250 ;g/mg. Furthermore, the simple

correlation results provided by Lawther

et al. (1970) suggest the possibility that a

more sophisticated analysis jointly

incorporating pollution and weather

factors might have found increased

morbidity occurring at lower levels. The

recent findings of small changes in

pulmonary function at lower particulate

matter levels in the U.S. and the

Netherlands (See Table 1) support the

notion that 250 pg/m s (in this case as

PMo) is not a reliable effects threshold.

Comments: The derivation of the

proposed range of levels for the annual

primary standard is without scientific

basis. In particular, limitations in the

two major series of studies used

preclude finding effects of particulate

matter at the lower TSP levels shown. In

addition, the conversion of the results of

these studies to PMzo uses an

inappropriately low PM1o/TSP ratio.

Agency Response: EPA's assessment

of studies used to derive the range of

levels for the primary standard (Ferris et

al., 1973,1976;) and Bouhuys et al., 1978)

(CD, pp. 14-44 to 46 and SP, pages 61-62

and 104 -107) was reviewed by CASAC

and found to be an appropriate basis for

developing revised standard levels

(Friedlander. 1982). The assessment

clearly points out the limitations and

strengths associated with the uses of

these studies.

The Ferris et al. work (See Table 2

above) involved a "longitudinal"

tracking of lung function and respiratory

illness in adults vs. pollution over a 12

year period in Berlin, NH, a small town

in which a pulp mill was a major

pollution source. As commenters note,

the "effects likely" level drawn from the

first year of this study is particularly

uncertain, as it is based on very limited

aerometry. This level, however, was not

important in developing the range for

the proposed standard. Because of the

seriousness of the effect (a prolonged

decrement in lung function), the by then

decreased concentration observed in the

first followup study (130 p.g/m s as TSP).

was used in developing the upper bound

of the range of proposed annual

standards. This concentration was

based on a full year of monitoring.

Based on the historical record, there can

be little doubt that pollution declined in

this community from 1981 to 1967, the

year of the first follow-up. The nature of

the particular pollution source (a pulp

mill) in this study, together with a

finding of very low British smoke level.

indicates that a variety of particles, not

just products of combustion, may be.

associated with adverse effects.

Although commenters have suggested

that other pulp mill emissions may have

been responsible for the effects, ambient

levels of the gaseous effluents from such

sources (reduced sulfur compounds and

SO2 ) have not been shown to cause

reduced lung function.

Estimating PMo levels from this study

by using typical national average PMo7

TSP ratios does not-as some

commenters argued--clearly understate

PMo levels. These commenters argued

that high PMo/TSP ratios (e.g., 0.8)

should be used because sites in the

eastern U.S. tend to have higher ratios.

The data on PMo/TSP ratios, however,

also show a general tendency for lower

ratios to occur in industrialized areas

with high TSP concentrations (Pollack,

et al., 1985). Moreover, air quality

measurements taken in the 1960's

document the presence of substantial

quantities of larger size particles, as

evidenced by high dust fall levels and

low soiling indexes (Kenline, 1962). The

latter author concludes that this would

be expected "if the majority of particles

present had diameters of 10 microns or

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greater . . . ... EPA therefore believes

that the use of ratios characteristic of

industrialized areas with high particle

concentrations is justified and does not

contribute to any excess margin of

safety in the estimated effects levels.

The Bouhuys et al. (1978) study (see

Table 2 above) was used to set the

lower bound for the proposed standard

range, which is the level at which the

final standard is being promulgated. The

study found a difference in three of five

respiratory symptoms but no differences

in lung functions between two

Connecticut towns (Ansonia and

Lebanon) that had a historically large

(but currently small) difference in levels

of particulate matter. Although the

authors believed that air pollution did

not play a role in the observed

differences in symptoms, the data

presented do not demonstrate that the

differences were due solely to other

factors associated with the conduct of

the study. Moreover, the finding of

excess respiratory symptoms

unaccompanied by a persistent change

in lung function is not unique. Similar

findings were also obtained in the Ferris

(1973) follow up study and the more

recent six city study results (Ware et al.,

1986).

Some commenters argued that the

estimated TSP levels derived for the

Bouhuys study were too low. EPA

disagrees. The staff took the median

TSP values reported by Bouhuys et al.

over the previous several years as the

relevant exposure level for this study

because (1) the current gradient in

pollution appeared to be too small to

result in such effects, and (2) it is

unreasonable to attribute all of the

observed gradient in effects among

urban and rural residents, as measured

in 1973, to the maximum historical

concentrations reported 8 to 10 years

prior to that time. EPA's position is

supported by the observations of Ferris

et al. (1973, 1976), which show an

apparent measurable reduction in

symptoms and improved lung function

after only a five to six year decline in

pollution. This decline suggests that any

gradient in effects due to pollution eight

to ten years ago would be diminished

relative to effects that may be

associated with the more recent past.

The median value used by EPA for the

Bouhuys study is, In fact, also relatively

close to the weighted average of all TSP

observations reported for Ansonia for

the seven years preceding the Bouhuys

et al., (1978) measurements, which were

taken in 1973 (Lounsbury, 1986),

The approach used to convert the TSP

measurements in this study to PMo

equivalents was also questioned. The

staff rejected use of the limited (15 days)

particle size data for Ansonia as

unrepresentative because of questions

concerning their quality and because

they were taken in 1973, after

particulate matter concentrations had

been reduced to lower levels (SP, p. 62).

Absent reliable site-specific particle size

data, the staff used the median PMo/

TSP ratio seen at other sites in the

eastern U.S. with higher than average

PMo levels. Because the long-term ratio

can vary between 0.3 and 0.65 among

such sites, such estimates are

admittedly uncertain. Nevertheless, the

staff examination of historical air

quality and source data associated with

the Bouhuys et al. study found no

factors that would make the ratio

unusually high or low relative to other

high concentration sites In the eastern

U.S. The analysis by Spengler et al.

(1986) of trends in particle size ratios

from the 1970's to the present in six

eastern cities suggests that the ratio of

PMo to TSP in early years with higher

TSP levels tends to be comparable to or

somewhat lower than the current ratios.

The basis for the final ambient

standard is considerably strengthened

by the recent results from the six-cities

study (Ware et al., 1986). This work also

suggests an increased risk of respiratory

illness and symptoms, but no differences

in lung function, in children across a

gradient of pollution that extends to

concentrations below those observed in

the previous studies. The results are

therefore qualitatively consistent with

both of the earlier studies. In addition,

the associated aerometry permits

substantially better estimates of

historical PMo data. Taken together,

these studies provide substantial

support for an annual standard of 50 jg/ M 3 .

3. Margin of Safety

Comments: The Agency has

incorporated an unrecognized three-fold

margin of safety in the 24-hour

standards through the means used to

convert British Smoke measurements

into PMo.

Agency Response: British Smoke

measurements collect particles smaller

than about 4.5 microns in diameter

(PM4 .

0 ) on a substrate and then measure

their absorption of light. Because the

measurement depends on light

absorption, it is sensitive only to the

dark, "sooty" component of the

particulate matter. EPA has relied on

gravimetric calibrations, performed

during the earlier years of the mortality and morbidity studies, that related the

British Smoke measurements to

partidulate mass concentrations that

included light-colored as well as dark

particles.

The commenters note that the dark,

sooty component of the particulate

matter in London today constitutes only

40% as large a fraction of the total

particulate mass as it did during the

period of the studies on which EPA has

relied. They argue that the use of those

studies to set standards for

contemporary particulate pollution

therefore Introduces an error of a factor

of 2.5 (1/0.4). Multiplying this by a

typical ratio of PMo to PMs of 1.2

(Lodge, 1986), the commenters arrive at

an alleged error of a factor of three

arising from the Agency's use of the

British Smoke measurements.

The commenters rely on the unstated

assumption that it is only the dark

fraction of particulate pollution that

affects human health, and that, since the

dark fraction has declined since the time

of the studies, the particulate matter in

the atmosphere today is less dangerous

than that present at the time of the

studies. EPA disagrees with this

assumption and believes that a more

plausible and prudent assumption is that

effects on health depend on the mass

concentration of particles and not on

their color.

Although it is possible that dark,

carbonaceous particles were primarily

responsible for the observed effects on

human health in the London studies, this

has not been documented, and there is

no evidence to support the assumption

that light-colored particles have no

significant effect on human health. EPA

staff has compared the composition of

particulate matter in historical London

and in the current U.S, and has

concluded that, given the variety of

particle types present in the U.S., there

is no clear basis for imputing higher

acute toxicity to the historical London

particles (SP pp. 21-22, 100).

The commenters support their

argument with the assertions that the

decrease in the dark, sooty fraction of

particulate matter in London has been

accompanied by the elimination of

pollution-related health effects, and that

current excursions of fine particle mass

in excess of 250 pg/m3 have not been

associated with health effects in London

or elsewhere. EPA finds these assertions

to be unsupported. The studies of

mortality in London over a 14-year

period of declining pollution from 1958

through 1971 found that the relationship

between pollution and mortality

persisted throughoutthe period and that,

in fact, the regression coefficients

assigned to mortality appeared to

increase over the period. (Mazumdar et

al., 1982; Ostro, 1984). Moreover,

24651 I 

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continuing studies In the contemporary revised form, in particular, makes direct

U.S. and Europe have suggested health comparison of the relative stringency of

effects at PMo levels below 250 Pg/m3 proposed range with the current TSP

(Dockery et al., 1982; Ozkaynak and standard inappropriate. Spengler, 1985; Dassen at al., 1986). EPA agrees that the analyses of

For these reasons, EPA concludes that mortality In London justify caution In

it is reasonable and prudent to use the selecting a 24-hour standard level, and

mass concentration estimates derived that the recent studies of lung function

from historical British Smoke provide a useful basis for selecting the

measurements to set ambient standards level. EPA does not, however, believe

for current U.S. atmospheres under the that these studies compel a standard

assumption that current U.S. particles more stringent than the one chosen, As

are equal in toxicity to those found in discussed in Section III.C.1 above, London at the time of those uncertainties in estimating PMlo

measurements. Any margin of safety equivalents of low British Smoke

inherent in the British Smoke/PMo concentrations in the later years of the

conversion for the earlier years when London studies make it difficult to use

gravimetric calibrations were available the studies to set a precise level for a

is more likely to be on the order of a PMo standard. Therefore, it is important factor of 1.2 (the ratio of PM. to PMo to examine the more contemporary

estimated by Lodge, 1986) rather than studies of lung function that permit a

the factor of three suggested by the more direct estimation of PM1o effects

commenters. For particulate levels lower levels. In considering these studies in

than those observed in the e'arlier years, conjunction with the London mortality EPA has supplemented the London and other relevant health studies, EPA

studies with the more contemporary finds that a 24-hour standard of 150 pg/ American and European studies using m3 provides an adequate margin of

direct gravimetric measurements. safety. EPA does not agree with Comments: Several commenters bommenters suggestions that it is

expressed concerns that the margin of necessary to prevent any detectable

safety for the range of levels proposed changes in lung function. As discussed

for the 24-hour standard is insufficient. in Section III.C.1, a standard of 150 1kg/ Commenters based these concerns on: ms will clearly prevent lung function

(a) Calculations suggesting that even the decrements that might be considered to

lower bound may be less stringent than be indicative of adverse effects in well

the current standards, (b) evidence from over 95% of children exposed; in fact the

the more recent studies of lung function evidence suggests that even reversible

decrements in children and the analyses lung function changes (FEVo.75) in excess

of London mortality data, and (c) of 10% are unlikely at this level. EPA

various studies found to be mainly of therefore believes that the standard

qualitative value. In general, such provides an adequate margin of safety.

commenters felt that, in view of the Some commenters favoring standards

available evidence, the standard should below the lower bounds of the proposed

be set at levels at or below the lower ranges relied on studies or analyses bound of the proposed ranges. found by EPA and CASAC to be of little

Agency Response: The overriding quantitative value for establishing

consideration in selecting a standard is ranges of concern. EPA considered a

how well it protects public health, not number of such studies in selecting a

its relative stringency as compared to margin of safety (e.g., SPA 52-53; SP

the previous standard. EPA believes that 109-111), but in EPA's judgment they do

standards chosen provide an adequate not provide a sufficient basis for

margin of safety irrespective of the establishing standards at levels below

relationship to the former TSP those derived from the more

standards. Nevertheless, EPA has quantitative studies summarized in

compared the stringency of the revised Tables 1 and 2 above.

standards with that of the existing Comments: Some commenters argued standards by estimating the number of that in selecting annual standards much

areas that would be expected not to greater weight be given to the results of

attain each set of standards. By this Ware et al. (1986), which suggest a

measure, the new PMo standards are possible gradient of effects at

equivalent to or somewhat more concentrations extending to the lowest

stringent than the TSP standards (SP, levels observed in the six cities studied

Table 2-1). Commenters who calculated (25 jg/m3).

or asserted otherwise often did not take Agency Response: EPA disagrees. all of the aspects of the standards into EPA staff found that the pollution and

account. The margin of safety is a effects gradient in the three cleanest

function not only of level, but also of the cities to be too small to provide any indicator and form of the staiidards. The - -strong suggestiQn of effects at such

levels. Moreover, the lack of consistency

for "within city" effects in this study

argue against placing undue reliance on

the suggestion of effects at levels

outside of the range suggested by the

other long-term studies of interest

(Ferris et al., 1973,1976, Bouhuys et al.,

1978). In addition, the 24-hour standard

provides an increased margin of safety

against annual exposures at levels

below 50 jg/m3, in areas where longterm exposures are dominated by

repeated short-term Peaks (Freas, 1986).

B. Secondary Standards

1. Soiling and Nuisance

Comments: The Agency should

maintain a secondary TSP standard.

Some commenters felt that the proposed

secondary annual TSP standard is

inadequate, and that the current 24-hour

TSP standard should be retained.

Agency Response: As discussed in

Section IV.A. above, the CASAC found

little scientific support for maintaining a

secondary TSP standard. It follows that

little data exist to support maintaining

the present level or an alternative level for a 24-hour standard designed to

protect against soiling and nuisance.

Nevertheless, the changes made in the

final standard result in both a 24-hour

and annual secondary PMo standard.

Analysis of the relative protection

afforded by the 24-hour PMo standard

indicate that it is relatively more

stringent than the upper portion of the

proposed range for an annual TSP

standard. Thus, the final standards

should provide more protection than

that afforded by the proposed TSP

alternative toward which the

Administrator was initially inclined. As

detailed above, the data do not provide

convincing evidence of significant

soiling and nuisance effects at

concentrations below that permitted by

the primary standards.

2. Visibility

Comment: A secondary fine particle

standard is needed to protect against

visibility impairment and related effects.

Agency Response: The Administrator

deferred judgment with respect to a

secondary fine particle standard in

order to examine the relationship

between control programs for regional

visibility and the related problems of

acid deposition. The initial phase of that

examination has now been completed

(EPA, 1985). Based on the available

information, the Administrator has

decided to issue an Advance Notice of

Proposed Rulemaking on a secondary

fine particle standard in a separate

notice in today's Federal Register.

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C. Averaging Time and Form of the

Standards

1. Expected Exceedances for the 24-hour

Standard

Comment: Several commenters were

opposed to the proposed statistical form

and either favored the current simpler

deterministic form or preferred a

multiple exceedance or percentile form

of the 24-hour standard. Others.

supported the proposal to adopt a single

expected exceedance statistical form.

Many of the opposing commenters were

concerned that the adjustment for

incomplete sampling could cause areas

with less than one actual exceedance

per year to be misclassified as

nonattainment and that the method is

sensitive to spurious high

concentrations. Those in favor of

adopting a single exceedance statistical

form recognized the need to account for

missing data and argued that this form

provides proper health protection. .Agency Response: EPA has carefully

reviewed these comments and has

decided to maintain the basic proposed

statistical form for-the 24-hour standard

but has made some technical changes

and clarifications in response to

reviewers comments. The Agency

believes that a single exceedance form

for the primary standards and the

proposed adjustments for incomplete

sampling appropriately reflect the health

basis for the standard. When sampling,

is performed less frequently than every

day, the number of observed

exceedances of the standard level will

obviously be, in general, fewer than the

actual number of exceedances. If, for

example, sampling is performed only

every sixth day, as is permitted by the

Air Quality Surveillance regulations (40

CFR Part 58) being promulgated today,

then, on average, the number of

observed exceedances will only be onesixth of the actual number of

exceedances. To fail to correct for this

effect would be irrational and would

seriously degrade the health protection

afforded by the standards. The Agency

believes that adequate procedures for

handling spurious high concentrations

are provided in the "Guideline on the

Identification and (Use of Air Quality

Data'Affected by Exceptional Events",

EPA-450/4-86--007. Moreover, single

high concentrations will not necessarily

cause a location to fail the test for

attainment. Appendix K has been

modified so that the first observed

exceedance is not adjusted for

incomplete sampling, if the sampling

frequency is promptly increased to

eve'y day in accordance with 40 CFR

Part 58.13. Accordingly, sites sampling

once in six days must observe at least

two exceedances in order to fail the test

for attainment.' Sites sampling every.

other day or every day must record

three or four exceedarices over a threeyear period in order to fail the test. This

change reduces the chances for

misclassifying a site as, nonattainment.

Although a multiple exceedande form

of the 24-hour'standard could reduce

sampling requirements, such a form

would reduce the level of health

protection by allowing particulate levels

to exceed, on multiple days, the levels

that the Administrator has determined

to pose an unacceptable health risk. An

analysis of alternative numbers of

exceedances found that, in the long run,

the single exceedance form provided

much more consistent health protection

than did the percentile form

recommended by some commenters

(Biller, 1984; 1986).

In response to comments regarding'

the potential for seasonal variation in

particulate matter concentrations, as

well as possible intrayear changes in

sampling frequency as described in Part

58 of this Chapter, the Agency has

decided to require that adjustments for

incomplete sampling be performed on a

quarterly basis instead of a yearly basis.

2. Expected Arithmetic Mean for the

Annual Standard

Comment: Many commenters favored

retaining the geometric mean to describe

annual average particulate matter

concentrations but several supported

the proposed use of the arithmetic mean.

Those opposed to the proposed method

noted that the geometric mean is a more

stable statistic and is less sensitive to

occasional high readings. In addition,

opposing commenters were concerned

that a change to an arithmetic mean

increases the stringency of the annual

standard and that the arithmetic mean

does not properly relate to health

effects.

Response: As discussed above, EPA

has decided to adopt annual primary

and secondary standards in terms of

expected annual arithmetic mean PMo.

The Agency believes that the annual

arithmetic mean is a more appropriate

indicator for a long-term primary air

quality standard than is the geometric

mean. It provides a better estimate of

total exposure and, with its multipleyear averaging, more appropriately

takes into account year-to-year

fluctuations in meteorology. As

discussed in the rationale, the effect of

averaging multiple years of data in order

to estimate the expected annual value

as well as the use of the arithmetic

mean were both considered in setting

the concentration level of the standard.

The use of the arithmetic mean does not

necessarily increase the stringency of

the, standard level; the stringency

depends at the combination of the form,

indicator, and level. Holding all. else

equal. however, the arithmetic form is

relatively more protective in areas

subject to multiple elevations in 24-hour

concentrations. EPA views this as a

desirable characteristic:

VII. Regulatory and Environmental

Impacts

A. Regulatory Impact Analysis

Under Executive Order 12291, EPA

must judge whether a regulation is a "major" regulation for which a

Regulatory Impact Analysis (RIA] is

required. At the time of the proposal, the

Agency judged the proposed revisions to

the particulate matter NAAQS to be a

major 'action, and made available to the

public a draft analysis entitled:

Regulatory Impact Analysis of the

National Ambient Air Quality Standards

for Particulate Matter-Draft (EPA,

1983). The draft RIA was based on

information developed by several EPA

contractors (inter alia., Argonne, 1983;

Mathtech, 1983) and provided estimates

of costs, benefits, and net benefits

associated with alternative standards.

In announcing the availability of the

draft RIA, the Agency stated that

neither the RIA nor the contractors'

reports were considered in developing

the proposed revisions. Subsequent to

the release of the draft RIA, the public

and other governmental agencies raised

a number of questions regarding the

underlying data bases and analyses

discussed in the draft RIA. In response

to these questions, the Agency modified

the costmodel used and made other,

more limited, changes to the benefits

analyses. The number and extent of the

changes were constrained, however, by

the underlying model structure and the

available data. The Agency has

carefully evaluated the revised analysis

and has concluded that despite the

significant improvement made,

fundamental questions remain with

regard to certain aspects of the

methodology used, particularly with

respect to the emission reduction/air

quality improvement relationship which

affects the subsequent cost and benefit

calculations. Consistent with its past

practice, the Agency has not considered

the final Regulatory Impact Analysis of

National Ambient Air Quality Standards

for Particulate Matter (EPA, 1986c) in

reacfhing decisions on the final

standards.

The final RIA has been submitted to

the Office of Management and Budge et

(OMB) for review under Executiv'e

24653

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24654 Federal Register / Vol. 52, No. 126 / Wednesday, July 1, 1987 / Rules and Regulations

Order 12291. Comments from OMB and

EPA's responses to those comments

have been placed in the docket.

Reporting Requirements

This final rule does not contain any

information collection requirements

subjectto OMB review under the

Paperwork Reduction Act of 1980 U.S.C.

3501 et seq.

B. Impact on Small Entities

Under the Regulatory Flexibility Act, 5

U.S.C. 600-612; EPA must prepare initial

and final regulatory flexibility analyses

that assess the impact a proposed or

finalrule will have on small entities,

which include small businesses, small

not-for-profit enterprises, and

governmental entities with jurisdiction

over populations of less than 50,000. The

requirement of preparing such an

analysis is waived, however, if the

Administrator certifies that the rule will

not have a significant economic Impact

on a substantial number of small

entities.

The national ambient air quality

standards do not have a direct impact

on small businesses or enterprises

because the standards themselves do

not contain emission limits or Other

pollution controls. Rather, 'such controls are contained in State implementation'

plans promulgated under section 110 of

the Act, 42 U.S.C. § 7410. The States are

given considerable discretion in

selecting a mix of controls to attain and

maintain the ambient standards, and the

impact on small entities depends on

how the States choose to exercise their

discretion.

Nonetheless, EPA conducted an

analysis of the impact of a hypothetical

control strategy, designed to minimize

costs, on entities in the industries that

would be most affected under that

hypothetical control strategy. That

analysis, discussed in the notice of

proposed rulemaking, 49 FR at 10422,

indicated that less than 20% of the

entities in those industries would be

affected by the proposed standards.

During the public comment period,

EPA received no comments on the

regulatory flexibility analysis. On the

basis of that analysis, the Administrator

certifies that the revisions being

promulgated today will not have a

significant impact on a substantial

number of small entities..

VIII. Other Reviews

* This final rule was submitted to the

Office of Management and Budget

(OMB) for review. Comments from'OMB

and.EPA's responses to these comments

:have been placed In the docket. , ,

List of Subjects in 40 CFR Part 50

Air pollution control, Carbon

monoxide, Ozone, Sulfur oxides,

Particulate matter, Nitrogen dioxide,

Lead.

Dated: June 2, 1987.:

Lee M. Thomas,

Administrator.

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