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 tobe 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 ofthe 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 ofthe 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 (PM 1a), (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 standardwith a,PM1o. standard of50. Ig/ M

3

, expected annual arithmetic mean; and (4),replacing the,secondary TSP standardwith,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 ofPMo in the ambient air. The method iscontained in a new Appendix Jto Part 50.This notice also

announces a new Appendix K to Part 50, which provides rules for applying the statistical form ofthe 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 CFRPart 53), Ambient Air Quality Surveillance (40 CFR Part 58), Regulations forImplementing Revised Particulate Matter Standards (40 CFR Part 51) with associated guidelines, Approval and Promulgation of Implementation Plans (40 CFRPart 52), and Prevention ofSignificant 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 ofthe particulate
matter standards is available forpublic 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. Forthe availability ofrelated* information see SUPPLEMENTARY INFORMATION. FOR FURTHER INFORMATION CONTACT: Mr.John Haines, Strategies andAir 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 INTIS #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 ofthe National Ambient Air-Quality Standards forParticulate Matter: Assessment ofScientific 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 ofthe National Ambient Air Quality Standards forParticulate Matter: Updated Assessment ofScientific 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 ofother 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 StaffPaper E. Proposed Revisions to the Standards F. Supplemental Criteria Revisions and

Standards Review Following Proposal IIU. Summary ofPublic 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 1986Second 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 StaffPaper Addendum Ill-Executive Summary ofthe

1986 Addendum to the Staff Paper Part 50-National Primary and Secondary

Ambient Air Quality Standards Appendix J-Reference Method for the

Determination ofParticulate Matter as PM 1 o in theAtmosphere Appendix K-Interpretation of the National

Ambient Air Quality Standards for Particulate Matter

I. Background

A. LegislativeRequirementsAffecting ThisRule

1. The Standards

Two sections ofthe 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 ofall 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 ofwhich, in the judgment ofthe 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 ofair quality the attainment and maintenance of which. in thejudgment ofthe Administrator, based on the criteria, is requisite to protect the public welfare from any known or anticipated adverse effects associated with the presence ofthe 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 ofproperty, hazards to transportation, and effects on economic values and on personal comfort and well-being.

The U.S. Court ofAppeals 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. LeadIndustries Associationv.EPA, 647 F.2d 1130, 1154 

### (D.C. Cir.1980), cert.denied,101 S. Ct. 621 (1980):AmericanPetroleumInstitute

v. Castle,665 F.2d 1176, 1177 (D.C. Cir. 1981), cert.denied,102 S.Ct. 1737 (1982). Both kinds ofuncertainties are components of the risk associated with pollution at levels below those at which human health effects can be said to

occurwith reasonable scientific certainty. Thus,by selecting primary standards that provide an adequate margin of safety, the Administrator is seekingnot only toprevent pollution levels that have been demonstrated to be harmful, but also to prevent lower pollutant levels that he finds pose an unacceptable risk ofharm, even ifthat 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 ofthe health effects involved, the size ofthe sensitive population(s) at risk, and the kind and degree ofthe uncertainties that must be addressed. Given that the "margin of safety" requirement by definition only

comes intoplay where no conclusive showing ofharm exists, such factors, which involve unknown oronly partially quantified risks, have their inherent limits as guides to action. The selection ofanyparticular approach toproviding

an adequate margin of safety is a policy choice left specifically to the Administrator's judgment. Lead Industries Associationv.EPA,supra, 647 F.2d at 1161-62.

Section 109(d) ofthe Act (42U.S.C. 7409(d)) requires periodic review and, if appropriate, revision ofexisting criteria and standards. The'process by which EPAhas reviewed the original criteria and standards for particulate matter under section 109(d) is described in Sections I.C. and I.D. ofthis 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 ofthe Act (42U.S.C. 7410), States are to submit, for EPA approval, State implementation plans (SIPs) that provide for the attainment and maintenance ofsuch standards through control programs directed to sources of the pollutants involved. Other Federal programs provide for nationwide reductions in emissions ofthese and other air pollutants through the Federal Motor Vehicle Control Program under Title I1 ofthe Act (42 U.S.C. 7501 to 7534), which involves controls for automobile, truck,bus, motorcycle, and aircraft emissions, and through the development ofNew 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 andOriginal Standards forTSP

"Particulate matter" is the generic term for a broad class ofchemically and physically diverse substances that exist

as discrete particles (liquid droplets or solids) over a widerange ofsizes. 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 ofparticulate matter vary greatly with time, region, meteorology and source category, thus complicating the assessment ofhealth 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 staffpaper 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 ofthe Clean Air Act. The reference method for measuring attainment ofthese standards is the "high-volume" sampler (40 CFR Part 50, Appendix B], which collects particulate matter up to a nominal size of25 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 260j±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). 24635

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C.Developmentof RevisedAirQuality Criteria forParticulate Matter
In 1976, as a result ofinternal Agency review and therecommendations ofa committee ofEPA's Science Advisory Board, EPA decided to revise the existing criteria document for particulate matter. Because of competing priorities regarding revision ofother 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 ofthe Clean Air Scientific Advisory Committee (CASAC) ofEPA's Science Advisory Board, EPA decided to review and revise the criteria document forparticulate 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 itwas in the process ofrevising the criteria document and reviewing the existing air quality standards for possiblerevisions.

In developing the revised criteria document, EPA has provided a number ofopportunities forreview and comment by organizations and individuals outside the Agency. Three drafts ofthe 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 (45FR 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 ofresolving 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 ofthe revised criteria document were considered in the final document, issued simultaneously with theproposal ofrevisions to the standards. A summary ofEPA's responses to the comments on the three external review drafts ofthe 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 EPAoffice 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 108of the Clean AirAct, which requires that the criteria document 'shall accurately reflect the latest scientific knowledge useful in indicating thekind and extent ofall 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 inAddendum Ito this notice. Following closure, minor technical and editorial refinements were made to the criteria document forprinting (EPA, 1982b).

A number ofscientific and technical issues were raised during thepublic review process. Withrespect to the particulate matter portions of the criteria document, the majorIssues included therelationship among various

measures ofparticulate matter air quality, the implications ofparticle 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 usein revising air quality standards.A summary ofthese and other major scientific issues, as well

as CASAC's conclusions, is included in the closure memorandum on the criteria document (AddendumI).
D.Review ofthe Standards: DevelopmentofStaffPaper

In the evolving process of revising the national ambient air quality standards, EPAhas found it useful to prepare a document that helps bridge the gap between the scientific review ofhealth and welfare effects contained in the criteria document and the judgments required ofthe Administrator in setting ambient standards. This document, known as the staffpaper, has become

an important element in the standards review process, providing an opportunity forpublic comment on proposed staffrecommendations before they are presented to the Administrator.

In the spring of1981, EPA's Office of Air Quality Planning and Standards (OAQPS) prepared the first draft ofthe staffpaper, Review ofthe National Ambient Air Quality Standards for Particulate Matter: Assessment of Scientific and Technical Information. This draft staffpaper,based on the then existent draft oftherevised criteria document, evaluated and interpreted the available scientific and technical information mostrelevant to thereview ofthe air quality standards for particulate matter and presented staff recommendations on alternative approaches torevising the standards. This and a second draft ofthe paper

were reviewed at two CASAC meetings

on July 7-9, 1981 (46FR 31746, June 17, 1981), and November 16-18, 1981 (46FR 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 thepublic. A summary ofmajorrevisions made in
response to comments on the first draft iscontained in an October 31, 1981 letter to CASAC (Padgett, 1981). Following the second CASAC meeting, the staffmade further revisions in response to comments and prepared an executive summary thatwas reviewed by CASAC members before preparation ofthe closure memorandum on the staffpaper. InJanuary, 1982,EPA released the final OAQPS staffpaper (EPA, 1982a), which reflects the various suggestions made by CASAC and members ofthepublic. The January 29, 1982, CASAC closure memorandum states that the staffpaper "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 oftechnical guidance that will be needed to make appropriate revisions to the standard." This closure memorandum is reprinted in Addendum IIto this notice.

A number ofmajor issues were raised during the public review process. The

more important issues are outlined below.

1.Substantial discussion concerned the maximum size ofparticles (or particle size fraction) to be used in measuring particulate matter for regulatory purposes. Some groups favored retaining TSPas 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 15pm, 10 G6mm, 5-7 G6mm, and 2.5 G6mm. After CASAC closure on the staffpaper 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 of6 um).

2. Much attention was focused on selecting the level ofthe primary standards and on the question ofwhich 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 foruse in standard setting. In

a number ofcomments, 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 ofthe staffpaper and in later sections ofthis notice. CASAC's discussion ofthese issues and its recommendations are contained inthe closure memorandum on the staffpaper (Addendum II).

E.Proposed Revisionsto theStandards
OnMarch 20, 1984 (49 FR 10408) EPA proposed a number ofrevisions to the primary and secondary particulate
matter standards. Theproposed 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 ofthe 24-hour primary standard to a value to be selected from a range of150 to 250Mg/

m3 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 ofthe annual primary standard to a value to be

. selected from a range of50 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 ofthe above ranges. With respect to the secondary standards, the Administrator

was inclined to select the final standard from the upper portion ofthe range, but also called for comment on the alternative ofusing 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 ofthe particulate matter NAAQS and background information related to the proposal.

F.SupplementalCriteria Revisions and Standards ReviewFollowingProposal Following publication ofthe proposal, EPA held a public meeting in Washington, D.C. on April 30,1984 to receive comments on the proposed standards revisions. A transcript ofthe meeting has been placed in the public docket (Docket No. A-82-37). After the close ofthe 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 staffpaper in January, 1982. A transcript ofthis meeting is also available in the Docket. Based on its preliminary review ofthese new studies, the Committee recommended that the Agency prepare separate addenda to the criteria document and staffpaper for the
purpose ofevaluating 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 ofthe 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 ofthe new studies and addenda for the final standards. On September 16, 1986, EPA announced (51 FR 32878) the availability ofthe draft staffpaper addendum entitled Review of the National Ambient Air Quality Standards for Particulate Matter:

- Updated Assessment ofScientific and Technical Information. CASAC held a public meeting on October 15-16, 1986 to review both the criteria document addendum and the staffpaper addendum. At this meeting, CASAC members as well as representatives of several organizations, provided critical review ofboth EPA documents. A transcript of the CASAC meeting has been placed in thepublic 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 ofthe extensive scientific literature on these pollutants" (Lippmann, 1986b). The closure letter on the criteria document addendum is reprinted in Addendum Iof this notice. The Committee sent their closure letter on the staffpaper, addendum to the Administrator dated December 16, 1986, stating "The Committee believes that this document provides you with the kind and amount oftechnical guidance that will be needed to make appropriate revisions to the standards" (Lippmann, 1986c). The closure letter on the staffpaper addendum, which also discusses major issues addressed by the CASAC and the Committee's recommendations concerning these issues,is reprinted in Addendum Ifto this notice.The final addenda to the criteria document (EPA, 1986a) andthe staffpaper (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 staffpaper and the more recent addenda, the addenda supersede the earlier document. The executive summary of the staffpaper addendum is reprinted in Addendum III to this notice.
II.Summary ofPublic Comments

The following discussion summarizes ingeneral terms the comments received from the publicand from governmental agencies regarding theproposed revisions to the indicator, form, averaging times, and levels ofthe primary and secondary standards. Many of these comments had been made * ' previously by the-public during public," deliberations on drafts ofthe criteria document and staffpaper and were. reviewed and addressed-by EPA in. revisions to those documents. Salient comments on all aspects ofthe proposal and Agency responses to those comments are summarized by category in Section VI ofthis notice. A more.. / Rules and Regulations ; 424637 / Rules and Regulations

.... 24637

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detailed description ofindividual comments and Agency responses has been entered in thepublic docket (No. A-82-37).

A. Commentson 1984Proposal

Extensive written comments were received during the original comment period on the proposal, which closed June 5,1985. Ofsome 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 ofthe proposed standards are summarized below:

(1)Indicator forthePrimary Standard: The overwhelming majority of the comments received on this issue favored a size-selective indicator for the PM standard. Ofthe 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 PM 0 (28comments) and PM2.5 (8 comments). The principal support for PM 0 came from mining and related industries.

(2] Levels ofthePrimary 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 ofthe standards at the upperend ofthe proposed ranges or above, while most ofthe remaining commenters favored standard levels at the lowerbound ofthe ranges, and in

some cases lower. Additional comments from individual citizens, environmental groups, and government agencies urged that the level ofprotection afforded by the current particulate matter standards be maintained or strengthened.

(3)SecondaryStandards: Of the 105 written comments received on the proposed secondary standard, 44 supported retaining TSPas the indicator and 61 opposed the use ofTSP.Most of the latter commenters supported the proposed alternative ofmaking the secondary standards equal in all respects to theprimary standards.

IThis numerical distributionofcomments in each category should be compared withcaution. For example,the American Iron and Steel Institute and theAmerican Petroleum Institute submitted comments onbehalfof63 and 230 individual companies respectively, in lieu ofhaving each of their membercompanies send separate comments. Similarly, comments from interest groups suchas NRDC represent theviews of anumber of individuals. Industry commenters were virtually unanimous in opposing a TSP secondary standard, while a majority (35 of47) of government agency comments on this issued favored retaining the TSP indicator. Some ofthe 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] FormoftheStandards: A majority of the 52 comments received on this subject supported some kind of statistical 24-hour standard, but a number ofindustry and State and local
agency commenters raised concerns with aspects ofthe specific form proposed. The principal concern was that the proposed form could result in misclassification ofareas 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 ofthe 24-hour standard. Environmental groups and other government agencies opposed multiple exceedance forms. Of38 submissions from industry and government agencies, 26 favored a geometric mean for the annual standard over the proposed arithmetic mean.

(5) Federal ReferenceMethod:While
most ofthe comments generally supported the performance-based approach to the Federal Reference Method, many commenters favored

more stringent specifications for PM 1o samplers to ensure accurate and reliable performance under all ambient sampling conditions. Other comments and recommendations addressed specific requirements ofAppendix Jsuch as flow calibration and measurement, flow regulation, filter media, humidity control and sampler maintenance.

B. Commentson SubsequentNotice

As discussedearlier in this notice, EPA announced an additional public
comment period on July 3, 1986 to address the implications ofnew scientific studies on the health effects of particulate matter [51 FR 24392]. Approximately 20 additional written submissions were received by the close ofthis comment period on November 17, 1986, 17 ofwhich were provided on behalf ofindustry groups or companies, 2 from environmental groups, and 1 from

a state agency. Much ofthe material related to evaluations ofspecific 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 ofthe proposed ranges.
III. Rationale for the Primary Standards

In selecting primary standards for particulate matter, the Administrator must specify: (1)theparticle size fraction that is tobe used as an indicator ofparticulate pollution; (2) the appropriate averaging times and form(s) ofthe standards; and (3)the numerical levels ofthe 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 staffpaper and staff paper addendum (hereinafter "SP"and "SPA," respectively) outline a number of key factors to be considered in making decisions ineach ofthese areas (SP, Section VI; SPA, Section IV). Both the staffand CASAC made recommendations to focus consideration

on a discrete range ofoptions.In most respects, the Administrator has adopted the recommendations and supporting

reasons contained in the staffpaper and addendum and the CASAC closure statements (Friedlander, 1982; Lippmann, 1986c). Rather than reiterating those discussions at length, the following discussion ofthe standards revisions focuses primarily on those considerations that were most influential in the Administrator's selection ofparticular options,or that differ in somerespect from considerations that influenced the staff and/or CASAC recommendations.

A.Pollutant Indicator

Based on the staffassessment ofthe 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 publichealth policy choice, and (2) given current scientific knowledge and uncertainties, a size-specific (ratherthan, chemical-specific) indicator shouldbe used. In assessing the information in the criteria document, the staffreached several conclusions summarized here (see SP, pp.71-75):

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- 24639

(1)Health risks posedby inhaled particles are influenced both bythe penetration and deposition ofparticles in the various regions ofthe respiratory tract, and bythe 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 smallerparticles depositing in the tracheobronchial region. Still smaller particles can reach the deepest portion ofthe lung, the alveolar region. (2) Therisks ofadverse health effects associated with deposition oftypical ambient fine and coarse particles 2 in the thorax (tracheobronchial and alveolar regions ofthe 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 ormouth breathing.

(3)The size-specific indicator for primary standards shouldrepresent those particles small enough to penetrate to the thoracicregion (both the tracheobronchial and alveolar regions). Therisks ofadverse health effects from extrathoracic deposition of typical ambient particulate matter are sufficiently low that particles depositing only in thatregion 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 staffrecommended that the size-specific indicator include particles ofdiameters less than or equal
to a nominal 10 jim "cut point."P The

2Particles in ambientair usually occur intwo somewhat overlappingsize distributions, fine (diameter less than 2.5j~m) andcoarse (diameter larger than2.5 pm). Thetwo size fractions tendto havedifferent origins andcomposition (SP. AppendixD).

3The more precise term is 50%cut point or50% diameter (D.). This is the aerodynamic particle diameter for which the efficiency of particle collection is 50%. Larger particles are not excluded altogether, but arecollected with substantially. decreasing efficiency and smaller particles are collected with Increasing (up to100%) efficiency. Ambieit samplers with this cut point provide a reliable estimate ofthetotal massof suspended particulate matterof aerodynamic size less thanor equal to 10 pm.See additional discussion regarding the Federal Reference Method in section V below and in the accompanyingnotice revising 40CFR Part53. factors considered in the original staff recommendations fora 10 jm cutpoint

are outlined in the staffpaper (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 oflarger particles as would be expected to reach the tracheobronchial region. It places substantially greater emphasis on controlling smaller particles than does a TSP indicator, butdoes not completely exclude larger particles from all control.

The assessment ofmore recent information on respiratory tract deposition in the criteria document and staffpaper addenda reinforces the conclusions reached in the original staff assessment. Inparticular, the staffpaper addendum found that: (1)the recent data do not provide support foran indicator that excludes all particles larger than 10 pim in diameter, 4(2) the analysis used to support an alternative indicator with anominal size cut of6 G6mm (Swiftand Proctor, 1982) significantly underestimated thoracic deposition ofparticles larger than 6 pi.m in diameter under natural breathing conditions; (3)the PM10indicator generally includes a similar orlarger fraction ofthe range ofparticles that can ' deposit in the tracheohronchial region, -although it appears to be somewhat less

conservative iiithis-regard than previously thought with respect to laige (G6<10pm) particle deposition under conditions ofnatural mouthbreathing; and (4) the studies oftracheobronchial deposition generally involved adult subjects; recent information indicating

even greater tracheobronchial deposition ofparticles in children than in adults provides an additional reason for an indicator that includes particles capable ofpenetration to the tracheobronchial region (SPA, p.36). Consideration ofthese and the earlier conclusions ledthe staffto reaffirm its recommendation for a PMo indicator (SPA, pp. 36-37). The CASAC also restated its recommendation for PMio in its review ofthe proposal and the closure letter to the.Administrator (Lippmann, 1986 a, c).

.

The Administrator accepts the recommendations ofthe staffand CASAC and their underlying rationale

'The AmericanMining Congress (AMC. 1982) had recommended such an indicator, witha"DW of 10 Am. EPA estimated that the "DIa" of this indicatorwould 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 (AppendixJto 40 CFR Part 50)being promulgated today. In defining the standards forparticulate matter, this

new indicator is termed PMo.

B.AveragingTime andFormofthe Standards

-Fewcomments on theproposed standards contested the need forboth 24-hour and annual primary standards for particulate matter. EPA's assessment ofmore recent scientific information found that the new data confirm the need for both short-and long-term standards.'The alternative ofa 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

EPAproposed that the 24-hour standard be stated in a statistical form that uses more than one year ofdata and accounts for variations in sampling frequency in order to predict the actual number ofexceedances to be expected in an average year,When used with an appropriate standardlevel, the statistical form can provide improved health protection that isless sensitive to changes-iri sampling frequency than the deterministic form, and also can offer,a--

more stable target forcontrol.programs. Recognition ofthe limitations ofthe deterministic form has ledEPA to promulgate a statistical form forthe

ozone standard(44 FR 8202).

The interpretation ofthe statistical form ofthe particulate matter standard is detailed inAppendix K ofthe proposed regulation. The standard would be attained when the expected number ofexceedances ofthe 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 ofthe expected number of exceedance will be based on three consecutive years of data. -. . .. ,. .- . .. • - ,. . As- a result ofEPA's evaluations of evidence submitted and comments received during the publicreview process, the following changes have

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been made to Appendix K ofthe proposed rule regarding:

(1) Data Capture RequirementsAppendix K to the proposed standards contained minimum data capture requirements for determining attainment ofthe standards. The amount ofdata required varies with the sampling frequency and the number ofyears 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 ofnonattainment of the standards. The proposed Appendix K to the standards, however, would have permitted states to demonstrate attainment ofthe 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 ofthe 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 ofexceedances 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 ofmeasured 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 ofthe estimated exceedances for each calendar quarter. This change will accommodate situations in which sampling frequency has been increased
to everyday according to the requirements ofPart 58.13, and situations inwhich the Regional Administrator has granted a waiver of increased sampling frequency requirements for part ofthe calendar
year under provisions ofthose monitoring regulations.

(3) Interpretation ofthe 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 ofmisjudging attainment
status. Underthe aforementioned formulas which adjust for incomplete data, a single observed exceedance could cause a site to fail the test for attainment, even ifthe true expected number ofexceedances is less than or equal to one. Such an occurrence is especially likely ifsampling is performed less frequently than everyday. In order to reduce the chances ofoccurrence 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 with40 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 ofthe standard. Ifan 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 ofPM1oair quality status.
2. Annual Standard

The Administrator has decided to change the form ofthe 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 ofthe standard. Because the arithmetic mean concentration is proportional to the sum ofthe daily

means, it reflects the total cumulative dose ofparticulate matter to which an individual is exposed. Therefore, it is an appropriate indicator to protect against
anyhealth 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 ofshort-term peak concentrations, and is heavily influenced by days ofrelatively clean air.For these reasons, the staff and CASAC recommended the change to an arithmetic mean.

The interpretation ofthe statistical form ofthe standard is detailed in Appendix Kto 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 ifemissions remain constant, due to the random nature of meteorological conditions that affect the formation and dispersion ofparticles in the atmosphere. If only one year ofdata is considered, compliance with the standard and, consequently, emission control requirements, may be determined on the basis ofa year with unusually adverse orunusually favorable weather conditions. The

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problem ofyear-to-year variability is, however, reduced by averaging three
years ofdata.

C.Level oftheStandards

The original staffpaper and CASAC recommendations set forth a framework for determining the levels forthe 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 staffused these quantitative studies to examine concentration-response relationships and to develop numerical "ranges of interest" for possible PMo standards.

A number ofuncertainties associated with use ofthese studies must be considered in selecting an appropriate margin of safety. As discussed in the staffpaper 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 ofthe 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 5or TSP as particle indicators. None ofthe published studies used the proposed PMo indicator. Thus, assumptions must be

5British Smoke(BS) is apseudo-mass indicator related tosmall particle (aerodynamic diameter less than anominal 4.5pjm) darkness. This particulate matter indicator was widely used in British and other European studies. See the criteria document for amore detailed treatment ofBS (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 ofadditional 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 staffassessed this literature to identify additional factors and uncertainties that shouldbe considered in selecting the
most appropriate margin of safety (SP,
pp. 100-101; 107-111, SPA pp. 52-53; 59).

3.Selection ofthe levels that might be considered toprovide an adequate margin ofsafety.

The intent ofthe margin ofsafety 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 ofharm decreasing, but not necessarily vanishing, as the level ofpollution is decreased.

In the absence of clearly identified thresholds forhealth effects, the selection ofa standard that provides an adequate margin ofsafety requires an exercise ofinformed judgment by the Administrator. The level selected will depend on the expected incidence and severity ofthe potential effects and on the size ofthe population atrisk, as well

as on the degree ofscientific certainty that the effects will infact occur at any given level ofpollution.For example, ifa suspected but uncertain health effect is

severe and the size ofthe population at risk is large, amore cautious approach will be appropriate than would be if the effect were less troubling or the exposed population smaller.

EPA stafforiginally recommended a range ofpotential standards for the Administrator's consideration (SP, pp. 111-114). The recommended range was below the levels at which the staff, with the concurrence ofCASAC, had concluded fromthe 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 ofstandard levels that were based on the original staffand CASAC recommendations. After consideration ofthe new scientific evidence contained in the criteria document addendum, the staffrevised its recommendations for ranges ofstandards (SPA, pp. 60-62). TheAdministrator has considered the revised assessments and the recommendations ofCASAC (Lippmann, 1986b) in making his final decision on the standard levels. The rationales for the levels ofthe 24-hour and annual standards are presented below.
1.24-Hour Standard

The revised staffassessment ofthe short-term epidemiological data is summarized in Table 1; particulate matter levels are expressed in both the original (British Smoke ["BS"] orTSP) and PMo units. The "effects likely" row in Table 1denotes concentration ranges derived from the criteria document and its addendum at orabove which a
consensus judgment suggests greatest certainty that the effects studied would
occur, at least under the conditions that occurred inthe original studies. In the "effects possible" range, the staff found credible scientific evidence suggesting the existence ofadverse 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 (asjig/mn) (24-hr. avg.) Measured TSP levels (pg/mn) (24/ Equivalent PM-o hr. avg.) Levels (jg/m) Effects/St'udy Daily Mortality in Aggravation of London Aronchitis o Combined range Small, reversible declines in lung Combine range Lnobrnhts2function inchildren 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

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

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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 inlung
London I bronchitis = function inchildren 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, inaggregate and individually. Early winters dominated by high smoke and SO 2 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). 3Study of pollution "episodes" in Steubenville, Ohio, 1978-80; Dockery et al. (1982). 4Study of 1985 pollution episode in ljmond, The Netherlands; Dassen et al. (1986).
5.(a) Conversion of BS readings to PM 10 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 PM 0 levels, while the lower bound assumption (PMo=BS) understates PM 1 olevels. (b)Conversion ofTSP to PMio forDockeryet a1 results: Based on analysis of particle size fraction relationships InSteubenville (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 PM 1o/PM 1 0 ratio from later year (0.8), the PM 1o 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 ofDassen 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 ofexposed individuals with both the likelihood (risk) ofany effects occurring andthe
extent (incidence and severity) ofany potential effect decreasing with concentration. This is particularly true forthe,statistical analyses ofdaily mortality in London. Substantial agreement exists thatwintertime pollution episodes produced premature mortality in elderly and ill.populations, but the range and nature ofassociation 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 ofeffects
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 staffused 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 ofthis range was derived fromthe original assessment ofthe London mortality studies. As a result of its updated assessment ofreanalyses of the London mortality and more recent U.S. morbidity studies, the staff reduced the level ofthe lower bound ofthe range ofinterest to 140 pg/m a (SPA, p. 51), while noting that the difference between it and original lowerbound (150 ipg/m 3) is within the range ofuncertainty associated with converting the morbidity study results from TSP to PM1 0. 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 ofconcern both because oftheir immediate impact and because ofthe potential forinducing longer-term deterioration ofhealth 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 of250 to 350 Ag/m 3

, in PMo units.

The assessment ofthis study formed the basis for the upper bound of the
range ofPMo standards proposed by the Administrator In 1984. Considering this study alone, a PMo standard of250A*g/

m3 might appear to contain some margin ofsafety, even for the sensitive bronchitics studied, because It incorporates a conservative British Smoke/PMio conversion factor and because ofdifferences 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 ofsafety for other, less sensitive, groups. Nevertheless, this study ofbronchitics in London has inherent limitations in sensitivity that preclude derivation ofunequivocal "effects thresholds" at 250Ag/m3 as BS, and by extension PMo. The criteria document notes that associations between pollution and health status persisted at lowerBS 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 ofsafety for,

a 24-hour standard, it is also important to consider the London mortality studies. A standard at the upper portion ofthe proposed range (250jig/m 3) would he well below the levels (500 to 1000 pg/m s as BS) ofthe historical London episodes in which the scientific

consensus indicates thatpollution was responsible for excess mortality (CD, Table 14-7). The portions of the population at greatest risk ofpremature 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 oflife shortening (days, weeks, or years)
cannot be specified, the seriousness of this effect stronglyjustifies a margin of safety forit (belowthe consensus effects levels) that is larger than that warranted for the effects on bronchitics.

The staffassessment of the several reanalyses ofLondon mortality suggests, however, that the risk ofpremature mortality to sensitive individuals extends to concentrations substantially lower than those which occurred in the "episodes." The more recent analyses (Mazumdaret al., 1982; Ostro, 1984; Shumway etal., 1983) provide no objective support for a population threshold below which such a risk no longer exists. Although therisk to individuals may be small at concentrations of250 1Lg/m 3 and below, the number ofpeople 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 ofindividuals exposed increases the risk that effects will occur in the total population exposed.

Differences in the composition of particles and gases amongU.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 ofthe mortality studies, however, the stafffound that at least one of themore recent studies (Ozkaynak and Spengler, 1985) provides qualitative support foran association between daily mortality and particle concentrations in nearly contemporary U.S. atmospheres (SPA, pp.43-44).

The 1982 assessment ofthe mortality studies and related factors prompted the Administrator to consider standard levels that extended from 250Ag/mS down to the lower bound ofthe original staffrange ofinterest (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 havereinforced the Administrator's concern that a 24-hour standard at theupper end ofthe proposed range may not provide an adequate margin of safety. However, given theuncertainties in converting from BSto 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 PM1ostandard (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 ofDockery 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 ofchildren exposed
to peakPMo levels of 140-250 pg/m 3

. The decrements persisted for2-3 weeks following the exposures. The study also suggested the possibility oflarger responses in a subset ofthe 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 200to 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 ofcontemporary U.S. cities and the associated aerometry provides a more reliable estimate of PM1olevels than do the measurements used in theLondon studies. It is reasonable to-expect that the effects observed (smallreversible reductions in lung function in children] are, in most cases, more sensitive to air pollution than those observed in theLondon studies. These effects are, ofthemselves, ofuncertain significance to health, but might be associated with aggravation of respiratory syiptoms in children with preexisting illness (SPA, p.47). Longterm examination ofrespiratory health in the same community studied by Dockery et al. (1982) suggests that the children in that community have a higher incidence ofrespiratory 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 otherpollutants (e.g., S02), the consistency ofthe 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 ofPM assessed by the staff(SP, pp. 101-103; SPA, pp. 52- 53). These suggest increased risks for sensitive groups (asthmatics) and risks ofpotential effects (morbidity in adults)
not demonstrated in the more quantitative epidemiological literature. The qualitative studies do not provide clear information oneffects levels, but dojustify consideration ofeffects of particulate matter thathave 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 ofthe proposed range of150-250 jg/ms

.The present Administrator finds that the updated scientific assessment supports the original inclination and, ifanything, suggests an even wider margin ofsafety is warranted. The recent analyses of daily mortality are ofparticular concern in this regard. TheAdministrator 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 ofsafety below the levels at which there is a scientific

consensus thatparticulate matter causes premature mortality and aggravation of bronchitis. Such a margin is necessary because ofthe seriousness of these effects and because ofthe recent analyses ofdaily mortality that suggest adverse effects may occur at particulate
matter levels well below the consensus levels.The standard is in the lower portion ofthe range where sensitive, reversible physiological responses of uncertain health significance are possibly, but not definitely, observed in children. Using a conservative
assessment oflung function/particle relationship fromDockery et al., a change in concentration front background levels (-20jLg/m 3) to 150 j~g/m 3would produce lung function changes ofat most 10 to 15%in less than 5% ofexposed children (SPA, p.48). Based on theresults ofDassen 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 ofpremature mortality and allow thepossibility of

more significant functional changes. Furthermore, a standard level of 150 zg/

m

3 is fully consistent with the

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-recommendations ofCASAC 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 ofeffects at 2. Annual Standard -reducetheir sensitivity and make their lower levels-the "effects possible. interpretation more difficult than that of levels"-but the evidence is Theupdated staffassessment 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,(aspig/ PM10 levels

m3 ) Increased (,ig/m 3 ) respiratory Increased Effects/Study Increased disease, Increased respiratory Reducedlung respiratory symptoms, respiratory symptomsand function in Combined disease, small symptoms in illnesses in childreni reduced lung reduction in adults i children range C reduce lungrange 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 inSheffield, England (Lunn et al., 1967). BS levels (as pg/m3) uncertain. 2Studies 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 inlung function.were relativelysmall. 3Study conducted in 1973 intwo Connecticut towns. (Bouhuys et al., 1978). Exposure estimates reflect 1965-73 data InAnsonia. Median value (110 g/m s) used to indicate long-term concentration. No effects on lung function, but some suggestion of effects on respiratory symptoms. 4Study 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). 6Ranges reflect gradients in which no significant effects were detected for categories at top. Combined range reflects all columns.

Based on a recentassessment of PM,6/TSP ratios in areas with elevated TSP levels, the updated staffassessment revised the "effects likely" levels from theFerris et al. (1973) study to80 to 90 fg/m3 as PMo (SPA' p.58). Because of limitations in sampling duration as well

as the conversion to PMo, thisestimate is particularly uncertain. As indicated in the table, effects are possible at lower concentrations. Ofgreatest concern is thepossibility oflong-term deterioration oftherespiratory system in exposed populations, the potential for which is indicated by lung function (mechanical pulmonary) changes and increased incidence ofrespiratory disease. One set ofstudies (Ferris et al., 1973, 1976) ,providessome evidence for a "no observed effects" level forthese effects at orbelow 60to 65jig/m (130jig/n 3

as TSP)while another study (Bouhuyset al., 1978), suggests some possibility of symptomatic responses in adults at longterm median levels ator below about 50 to 55pg/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 sixU.S. cities (Ware et al., 1986). The study indicates the possibility ofincreased respiratory symptoms and illnesses in children at multi-year levels across a range of40to

over 58jig/m as PMo,but found no evidence ofreduced lung function at such concentrations. This study did not find similar gradients in symptoms and illness within some ofthe cities, which had somewhat smaller localized pollution gradients. The results ofa separate series ofstudies oflong and intermediate term (2to 6 weeks) exposures ina number ofU.S. metropolitan areas (Ostro, 1987; Hausman et al., 1984) are more supportive ofthe possibility ofeffects 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). Inparticular, the finding ofsymptomatic 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 PMo 0 levels down to 50jg/m. However, the information available to support the existence ofsignificant 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 ofthe 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 ofepidemiological, 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 ofthe 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 ofthese effects at-current annual particulate matter levels in most U.S. cities, the Administrator believes

- that the seriousness ofthe potential. effects and the large population atrisk
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 of50to 65 Ag/m 3

.In the proposal, the Administrator favored

a standard in the lower portion ofthe range. Themore recent evidence, although subject to substantial uncertainty, serves to reinforce this inclination. In lightof theupdated
assessment and in accordance with the recommendation ofCASAC, the Administrator has decided to set the level ofthe annual standard at the lower bound of the original range, 50 pgg/m s

, expected annual arithmetic mean. This standard provides a reasonable margin ofsafety against the serious effect of long-term degradation in lung function, which has beenjudged 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 alsoprovides reasonable protection against the less serious symptomatic effects forwhich

some studies provide evidence at PMo levels down to 50 g/mS*Although some smallrisk of increased respiratory symptoms may exist at this concentration, the available data are currently inconclusive on this point. Moreover, the staffand 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 ofair quality data show thatimplementation of the 24-hour standard will substantially reduce annual levels in a number ofareas to below 50Ag/m3, adding to the protection afforded bythe annual standard in areas with higher 24-hour peakto mean ratios (SPA, p.61; Freas, 1986). Based on thepresent 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 AirAct 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 ofan airpollutant in the ambient air.Thecriteria document and staffpaper 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. Thefollowing discussion ofthe rationale forthe secondary standards focuses primarily

.on considerations that were most influential in the Administrator's decision orthat differ in some respect from, or expand upon,-considerations that influenced the staffand/orCASAC recommendations.
A. SoilingandNuisance

At high enough concentrations, both large and small particles may soil household and other surfaces, or otherwise become a nuisance. Both effects can resultin increased cleaning
costs and decreased enjoyment ofthe 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 ofreduced soiling and nuisance (CD, p. 1-51). The staffpaper 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 thepollutant indicator (PMio), averaging times and form, and range oflevels ofthe 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 ofthe extent of effects associated with specificparticle sizes and concentrations or deposition, and bythe fact that theprotection afforded by primary standards depends upon theparticular combination of levels chosen within the ranges that

were proposed for the primary standards. TheAdministrator 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 theproposed primary standards forPMo. In so doing, the Administrator noted that "depending

on the exact levels ofprimary standards chosen, the combined requirements for meeting both 24-hour and annual primary standards forPM1omightbe considered adequate to protect against possible adverse effects relating to soiling and nuisance from all relevant particle sizes." (49FR 10418].

The decision to adopt the specific revised primary standards discussed in section IV above permits a more definitive assessment of theprotection afforded by those standards against potential adverse welfare effects. In addition, information submitted in the public comments, thereview ofthe March 20, 1984 proposal by the CASAC, and further analysis of the welfare effects information by Agency staffhave amended the basis for the final decision

on the secondarystandards. The basis for the original p'i6osal and the' implications ofthe 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 70-90pg/ in s
,expected annual arithmetic meap. Given the nature ofthe evidence available, the Administrator expressed

an inclination to select the level forthe 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. PM1ois useful because ina 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 ofparticles in the atmosphere (SP, pp. 14-19), control ofparticles less than 10 gAm in diameter would also limit the concentration oflarger particles. The TSPindicator was proposed, however, because ofthe lack ofdata'permitting clear distinctions among size ranges with respect to soiling and nuisance, the

more inclusive nature ofTSP, and the fact that most ofthe available information relating soiling and nuisance to airpollution used TSPas an indicator.

Information submitted in the public
comments expanded on some ofthe limitations ofTSP as an indicator that

were noted in thepreamble, namely: (1) The collection efficiency ofthe high volume sampler, which measures TSP, decreases rapidly for particles with diameters in excess of25-40 A.m; thus, the TSP measurement itselfcan omit a substantial fraction ofthe very large particles that can make a substantial contribution to soiling of horizontal surfaces; and (2) because the collection efficiency ofthe high volume sampler varies more with windspeed than do PMlo samplers, TSPmay be a less reliable indicator ofelevated " concentrations oflarger particles than PM1o.

In light ofthese considerations, the CASAC in reviewing the March 20 proposal package concluded that it could findno convincing scientific support for maintaining TSPas an indicator for the secondary stahdards (Transcript ofDecember 16, 1985 CASAC meeting,.pp. 56-71; Docket No. A-82-37). 24645

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. In developing a range oflevels for the

secondary 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 ofparticulate 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 ifan accumulation is large enough to be noticed, itis not • necessarily considered to be a problem. Thus, the critical judgment for selecting

a standard level is todetermine 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 ismerely noticeable and higher levels at which it is considered a nuisance. A study ofthe response ofa panel of-human subjects to dust on surfaces concluded that the level ofdustiness 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 ofstudy. A more direct study ofperception 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 ofthe current annual primary TSP standard (75jug/ms, annual geometric mean). The upper bound of:

. the proposed range ofinterest (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 ofthe proposed range (70 ig/m 3)was supported by a rough analysis ofeconomic benefits of. reduced outdoor soiling that. might be associated with decreased TSPlevels in U.S. cities (CD, p. 10-73). During the 1ublic comment period, one ofthe authors ofthe analysis thatformed 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 ofbenefits from reduced TSPconcentrations 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 foreconomic soiling effects at an annual TSP level ofabout 150 ;g/

M 3

.

EPA staffexamined the underlying experimental data used in the original analysis. This staffexamination (Haines, 1987) has been placed in the rulemaking docket. The stafffound 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 inTSP, 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 of90pg/

m3was used as a benchmark in an analysis to determine whether the primary particulate matterNAAQS would protect against soiling and nuisance (SP, Table 2-1). An earlier version ofthese results was presented at the December 16, 1985 CASAC meeting. The analytical approach, assumptions, and limitations ofthe methodology used in the analysis are discussed in a separate report,which has been'placed in the rulemaking docket (Pace etal. *1986). The results indicated that the

combined implementation ofthe 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 meanTSP levels inexcess of90 pg/m s and none would exceed 1001g/

in 3

.

In short,EPAhas determined that there is.no convincing evidence of significant adverse soiling and nuisance at TSP levels below 90-100 pug/m3, and that theprimary standards promulgated today would permit few, ifany, 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 isno scientific support for a TSP-based secondary ' standard. (Transcript ofDecember 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. OtherWelfareEffects

The other welfare effects of particulate matter ofprincipal interest

are impairment of 'visibility,potential modification ofclimate, and contribution to acidic deposition. All three ofthese effects are believed to be related to regional-scale levels offine' 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 ofthe likely overlap between control measures designed to protect visibility and control measures designed
to address acidic deposition, EPA, in its March 20,1984, notice ofproposed. rulemaking on the particulate matter. standards, didnot 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 ofthe notice of proposed rulemaking, EPA has continued to gather information on acidic deposition and on visibility, and to analyze thepotential 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 ofthe TaskForces recommendations as well as other information gathered by the Agency, EPA is now reassessing its position with. regard t0consideration ofa 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 wouldnow'be appropriate to: proceed with consideration ofa 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 ofproposed rulemaking soliciting public comment on the appropriateness ofa separate secondary fine particle standard designed to protect visibility, and on a number ofissues that wouldhave to be resolved inproposing 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 ofatmospheric particulate
matter asPM1o,promulgated today as Appendix Jto 40 CFR Part 50,is based

on selection ofPM1oparticles 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 (orsampler inlets) areprescribed as performance specifications in amendments to 40 CFR Part 53, promulgated elsewhere in today's Federal Register.

The requirements in Appendix Jare generally prescribed as functional or performance specifications in orderto allow sampler manufacturers flexibility In designing or configuring theirPMo samplers.Sampler shape, inlet geometry, operational flow rate, degree ofautomation, and other sampler characteristics orfeatures are specified onlyin terms ofrequired function or performance.

While most ofthe comments received

on Appendix 

### Igenerally supported the performance-based approach to specifying PMo reference methods, many commentors felt that the sampler performance specifications in the proposed Appendix Jand 40 CFR Part 53

were not adequate to ensure accurate collection ofPM10under all conditions ofambient sampling. Inresponse to such comments, the sampler performance specifications in Part 53 and the corresponding references to such requirements inAppendix Ihave been revised. Other comments were received

on various requirements ofAppendix J such as flow calibration and measurement, flowregulation, filter media, filter equilibration, and sampler maintenance. Specific changes to Appendix

### Jresulting from these
comments and from review ofother pertinent information are discussed below. A. Specific ChangestoAppendixI
Section 3.0 has been revised to specify that all samplers should be capable of measuring 24-hour PMjo mass concentrations ofat least 300 pgg/m3 while maintaining the operating flow
rate within specified limits.

In Section4.0 the term "reproducibility" has been changed to "precision" and the specification for PMo samplers has been changed from 15 percent or better to 7percent or 5 g.g/ M, whichever is higher. Theparticle size for 50 percent sampling effectiveness inSection 5.0 has been changed from 10± 1micrometers to 10±0.5micrometers. These changes are

a result ofcorresponding changes in the PM1osampler performance specifications in 40 CFR Part 53, promulgated elsewhere in today's Federal Register. Refer to the Part 53 action forfurther discussion ofthese changes.

In Section 6.0the subsection on nonsampled particulate matter has been removed. The design ofparticle size discriminating inlet systems for PMo samplers essentially precludes the transport ofwindborne 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 duringidle periods, they wouldhave to take a tortuous path with several changes in direction to reach the collection filter.

References to "automatic flow controller" throughout Appendix

### Jhave been changed to "flow control device". The latterterm is less restrictive and

more clearly allows the use ofany type offlow regulation device, provided that the other flow-related requirements of Appendix Jare met. In particular, Section 7.1 has been changed to require that a PM osampler have a flow control device capable ofmaintaining the sampler's operating flow rate within the limits specified for the sampler inlet. Therequirement that the flow control device have aflow rate adjustment capability has been removed to allow. forthe use ofcertain types offlow controllers (e.g., Venturi-type critical flow devices) that regulate flowat a constant but unadjustable rate.Flow controllers ofthis type generally employ

afixed-geometry orifice and control the sampler's flowrate 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 ofdevices (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 ofthe sampler. Since much emphasis is placed on the role ofthe sampler manufacturer's instruction manual in Appendix J, it is important that it contain detailed information on all aspects ofsampler operation. The instruction manual for each designated reference method would be reviewed and approved as part ofthe Part 53 reference method designation process.

The filter alkalinity specification in Subsection 7.2.4 has heen changed from <0.005 milliequivalents/gram offilter to <25 microequivalents/gram offilter.In addition, the method used for the alkalinity determination has been changed to anewly developed, more sensitive, and more reliable method.The change in the magnitude ofthe specification results fromthe change in procedures (alkalinitymeasurements

are approximately 5 times higher with the new method), and from the change in the measurement units.

:Section 7.3 includes specifications and otherrequirements forthe flow rate transfer standard used during sampler calibration. The specifications for the reproducibility and resolution ofthe 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 ofmeasuring the sampler's operating flow rate with an accuracy of ±2percent. An accuracy specification, stated in this context, is

more meaningful and useful than specifications forreproducibility 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 ofa 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 of45±5 percent relative humidity (RH) toseparate specifications: for humidity range (20percent to45 percent RH] and humidity control (±5 percent RH). Under the revised requirements, filters may be equilibrated
at any.preselected humidity betWeen20 Z4647

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and45 percent RH, provided that the humidity is controlled to within 5 percent RH. Language has alsobeen added to Section 9.0 to require that the

same temperature and humidity conditions be used forboth pre- and post-sampling filter equilibration.

The calibration and operational procedures forPM 0 samplers vary considerably depending on the type of sampler (e.g., high-volume, mediumvolume, low-volume)and the type of flow control and flowmeasurement devices employed in the sampler. Accordingly, the calibration and procedure sections ofAppendix 

### 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 ofa 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 onsampler • maintenance hasbeen incorporated'into Appendix Jto explicitly,require that PM1osamplers be maintained in strict accordance with theprocedures provided in thesampler manufacturer's instruction manual. Theperformance of

somePM 1osamplers may be adversely affected by the buildup ofsubstantial quantities ofnon-PMo particulate
matter within the sampler inlet. Such samplers may require periodic cleaning and other maintenance to ensure accurate collection ofPMo particulate
matter. Thisnew section has been added as Section 10.0. and the calculations and references sections havebeen renumbered accordingly.

When temperature and pressure corrections to samplerflow indicator readings are required, corrections based

on existing temperature and pressure at the time thereadings are taken (ordaily
average values during the sampling period in some cases) are preferable. However, incorporation ofsite 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 (ordaily average values during the samplingperiod in

somecases) must be used. Likewise, the calculations section has been changed. to require that the average barometric pressure and average ambient temperature duringthesampling period be used to calculate Qtd. Site or . seasonal average values fortemperature and barometric pressure may be required in the adjustment of the setpoint ofcertain types offlow 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 Jto clarify the requirements.
B. Designationof ReferenceMethods for PMo

Before a method forPM1ois approved

as a PM1oreference method, it must meet the requirements ofAppendix J andbe tested and designated as a reference method Inaccordance with the provisions of40,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 PM 1oreference method determination is received by EPA. Likewise, a notice ofdesignation and other information pertinent to the designation willbe published in the Federal Register each time a PMo reference method is approved for use. PMo sampler manufacturers are required toprovide sampler purchasers with an operation or instruction manual containing detailed procedures forthe calibration, operation, and maintenance ofthe sampler. Additional guidance and recommendations regarding filter media, type ofanalytical balance required for

mass determinations, and other requirements ofthe method should also be provided In the manual. Part53 requires submission ofthe manual as part ofa manufacturer's application for

a reference method determination. The instruction manual will be reviewed for technical accuracy and consistency with the requirements ofAppendix Jand
mustbe approved as part ofthe requirements for designation ofthe method as a reference method.
C. TechnicalChangetoAppendix G

Because the high-volume method described inAppendix Bwill continue to be usedin conjunction with Appendix G("Reference Method forthe Determination ofLead 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 rulethe reference 10 in* Appendix G has been deleted and section 5.1.1 ofthe Appendix has been revised to read as follows:

"High Volume Sampler. Use and calibrate the'sampler as described in Appendix Bto this Part." The Appendix has also been revised to specify more directly that thehigh-volume method described in Appendix Bis to be used in conjunction with thereference method for lead.

VI. Summary ofSalient Public Comments and Agency Responses

An overview ofpublic comments on the major aspects of theMarch 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 andAgency responses is contained in a separate Response to Comments Document that has been placedin the Docket,(No. A-82-37).

A. HealthEffects CriteriaandSelection ofthe Primary Standards

1.Indicator for the Primary Standards

Comments:PMe rather than PMo shouldbe 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 thatare relatively inert than does PMo.

AgencyResponse:EPAconsidered 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 judgmentpending additional analysis and review,the decision to propose PM 1oand not PM.

was based, in part, on reservations concerning the PMs indicator. The likelihoodthat the available data from mouthpiece studies overstated thoracic deposition during "natural" breathing

wasrecognized in aqualitative sense by CASAC (cf. July 1981 transcript, p. 581; Docket No. A-82-37) and presented as
one reasonfor recommending PMo rather than PM1
. orTSP as an indicator. The 1982 staffpaper reflected this argument in recommending 10prm 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 wouldreduce any margin ofsafety associated with an

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indicator derived from these data. Extension of the Swift and Proctor analysis itselfsuggests that approximately 10 to 20%of10 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 ofparticle deposition are reviewed in the criteria document and staffpaper addendum. The more recent assessments tend to support the original proposal ofPMIo. The criteria document addendum compares the work ofMiller et al. (1986), using the more recent deposition data, with the Swift and Proctor analysis and confirms that the latter understates deposition ofparticles larger than6 pm in individuals who habitually breathe through the mouth.

The more recent data also show some fraction ofparticles of10 pm and larger

can penetrate as far as the alveolar region (CDA, Figure 2-1). Therisk associated with deposition ofinsoluble

coarse particles in thisregion is of particular concern because ofslow 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 staffpapertook these factors into account in the original recommendation fora 10pm indicator that included all ofthe fine and a portion of the coarse fraction.

After considering these updated assessments, the EPA staffreaffirmed its original recommendation ofPMo as
an indicator for the standards (SP,p. 32). Inreviews oftheMarch 20,1984 proposal and ofthe criteria document and staffpaper addenda, the CASAC also reaffirmed its recommendation for PMo as an indicator (Lippmann 1986 a,c). Themajority ofpublic comments on this issue also favored PMo.

In summary, EPA finds that the presently available record clearly favors the PMo indicator overthe alternative PMK indicator.

Comments:Some commenters suggested thatwhile PM, 0 represents an improvement over TSP,the fine fraction (<2.5 pm) is ofrelatively greater

concern to health than the coarse fraction (2.5 to 10pm). Such commenters suggest that a PM 2
.

5 standard is needed-in addition to or,in some comments, instead ofa PM,0 standard.

AgencyResponse:Thepossibility ofa fine particle indicator forthe 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 ofdifficulties in using fine particles (less than a nominal 2.5 pm) alone instead ofPMo

as the indicator forthe 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 ofthe modes, each is chemically heteorgeneous. Therespiratory tract,in effect, alters the ambient distribution, with a mixture offine and coarse modes being deposited in both the tracheobronchial and alveolar regions. Indeed, the 2.5pm !'cut"is withinthe size range ofmaximum efficiency for alveolar deposition (2 to4 pm). The mixing ofthese size fractions in the respiratory tract and theheterogeneity within each fraction therefore blurs the distinction between the fractions in
terms ofhealth 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 ofthe effects in the British, U.S., and other epidemiological studies to the fine fraction, orto 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 of40 to 70%ofPM,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 offine 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 ofchemical-specific (e.g., acid aerosols) standards rather than a fine particle standard in future primary standard revisions. 2. Interpretation ofCommunity Epidemiological Studies

Comments:A number ofcommenters took issue with EPA's interpretation of the various analyses ofLondon mortality data. These commenters suggest that (a) the London data can be used to show only an association of

excess mortality with high concentrations ofpollution during unique episodes inwhich BS and SO levels exceeded 500 to 1000 pjg/m3, (b) a number ofthe 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 withno identifiable threshold is not supportable, (d) the results ofMazumdar 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 ofthe various London mortality analysis Is discussed at length in the criteria document, the staffpaper, and the addenda to these documents. The 1982 criteria document found that in the
context ofhistorical 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 oflikely increases in daily mortality at levels of both pollutants in the range of500 pg/
M

3 ormore (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 ofthese data by Ware et al. (1981) and the analysis ofsubsequent London winters by Mazumdar et al. (1981), the criteria document also concluded small increases indaily 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

.Anumber ofcommenters, however, including some ofthe original British investigators (Holland et al., 1985), object to this latter suggestion. 24649

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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 ofthe 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 itsexternal science advisors, that these data at least suggest the possibility ofeffects of particulate matter at BS levels as low as 150pg/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 ofassociation 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 inwhich BS levels did not exceed 250pg/m s

. The relative consistency of the results from year-toyear despite these changes suggests that the observed effect isnot 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 ofLawther 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 ofhigher 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 10jum may not have declined as much as did the black carbon content detected in the smoke measurement (Lodge, 1986), coefficients related onlyto smokemight be expected to increase. An additional possibility suggested by Schwartz and Marcus is that the effect ofhigher 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 ofa multi-day pollution episode.

Theuse ofthe 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 yearperiod. 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 notby rigorous analysis, butby visual examination ofstrip 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 analysisjointly incorporating pollution and weather factors mighthave 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 that250 pg/m s (in this case as PMo) is not a reliable effects threshold.

Comments:The derivation of the proposed range oflevels for the annual primary standard is without scientific basis. In particular, limitations in the
two major series ofstudies used preclude finding effects ofparticulate
matter at the lower TSPlevels shown. In addition, the conversion of theresults of these studies to PMzo uses an inappropriately low PM1 o/TSP ratio. AgencyResponse:EPA's assessment ofstudies used to derive therange of levels for theprimary 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) wasreviewed 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.

TheFerris et al. work (See Table 2 above) involved a "longitudinal" tracking oflung function and respiratory illness in adultsvs. pollution overa 12 year period in Berlin, NH, a small town in which a pulpmill was a major pollution source. As commenters note, the "effects likely" level drawn from the first year ofthis study is particularly uncertain, as it is based on very limited aerometry. This level, however, wasnot important indeveloping the range for theproposed standard. Because of the seriousness ofthe effect (a prolonged decrement in lung function), theby then decreased concentration observed in the first followup study(130 p.g/m sas TSP).

was usedin developing the upperbound ofthe range ofproposed annual standards. Thisconcentration was based on a full year ofmonitoring. Based on the historical record, there can be little doubt that pollution declined in thiscommunity from 1981 to 1967, the year of the first follow-up. The nature of theparticular pollution source (a pulp mill) in this study, together with a finding ofvery low British smoke level. indicates that a variety ofparticles, not justproducts ofcombustion, may be. associated with adverse effects. Although commenters have suggested that other pulpmill emissions mayhave beenresponsible 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 thathigh PMo/TSP ratios (e.g., 0.8) shouldbe used because sites in the eastern U.S.tend tohave higher ratios. The data on PMo/TSP ratios,however, also show ageneral tendency forlower ratios to occur in industrialized areas with high TSPconcentrations (Pollack,
et al., 1985). Moreover, air quality measurements taken in the 1960's document the presence of substantial quantities oflarger size particles, as evidenced byhigh dust fall levels and low soiling indexes (Kenline, 1962). The latter author concludes that this would be expected "ifthe majority ofparticles present had diameters of10 microns or

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greater

. . . ...EPA therefore believes that the use ofratios characteristic of industrialized areas with high particle concentrations isjustified and does not contribute to any excess margin of safety inthe estimated effects levels.

TheBouhuys et al. (1978) study (see Table 2above) was used to set the lower bound forthe proposed standard range, which is the level at which the final standard isbeing promulgated. The study found a difference in three offive respiratory symptoms but no differences in lung functions between two Connecticut towns (Ansonia and Lebanon) thathad a historically large (butcurrently small) difference in levels ofparticulate matter.Although the authors believed that airpollution 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 notunique. Similar findings were also obtained in theFerris (1973) follow up study and the more recent six citystudy results (Ware etal., 1986).

Some commenters argued that the estimated TSP levels derived for the Bouhuys studywere too low. EPA disagrees. The stafftook 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 smallto resultin such effects, and (2)it is unreasonable to attribute all ofthe 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 ofFerris
et al. (1973, 1976), which show an apparent measurable reduction in symptoms and improved lung function after only a five to sixyear 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. Themedian value used byEPA forthe Bouhuys study is, Infact, also relatively close to the weighted average ofall TSP observations reported for Ansonia for the seven years preceding the Bouhuys
et al., (1978) measurements, which were taken in1973 (Lounsbury, 1986),

The approach used to convert the TSP
measurements in this study to PMo equivalents was also questioned. The staffrejected use ofthelimited (15 days) particle size data forAnsonia as unrepresentative because of questions concerning their quality and because they were taken in 1973, after particulate matter concentrations had been reduced to lowerlevels (SP,p. 62). Absent reliable site-specific particle size data, the staffused the median PMo/ TSPratio 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 ofhistorical 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) oftrends inparticle 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 tobe 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 etal., 1986). This work also suggests an increased risk ofrespiratory illness and symptoms, butno differences in lung function, in children across a gradient ofpollution that extends to concentrations below those observed in the previous studies.Theresults are therefore qualitatively consistent with bothofthe 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 of50

### jg/

M 3

. 3.Margin of Safety

Comments:TheAgency has incorporated an unrecognized three-fold margin ofsafety in the 24-hour standards through the means used to convert British Smoke measurements into PMo.

AgencyResponse:British Smoke
measurements collect particles smaller than about4.5 microns indiameter (PM 4
.

0)on a substrate and then measure their absorption oflight. Because the measurement depends on light absorption, it is sensitive only to the dark, "sooty" component ofthe 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.

Thecommenters note that the dark, sooty component ofthe particulate matter in London today constitutes only 40% as large a fraction ofthe total particulate mass as it did during the period ofthe studies on which EPAhas relied. They argue that the use of those studies to set standards for contemporary particulate pollution therefore Introduces an error ofa factor of2.5 (1/0.4). Multiplying this by a typical ratio ofPMo to PMs of 1.2 (Lodge, 1986), the commenters arrive at

an alleged error ofa factor ofthree arising from the Agency's use ofthe British Smoke measurements.

Thecommenters rely on the unstated assumption that it is only the dark fraction ofparticulate pollution that affects human health, and that, since the dark fraction has declined since the time ofthe studies, the particulate matter in the atmosphere today isless dangerous than that present at thetime ofthe 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 ofparticles and not on their color.

Although it is possible that dark, carbonaceous particles wereprimarily responsible forthe 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 staffhas 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 forimputing 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, sootyfraction of particulate matter in London has been accompanied by the elimination of pollution-related health effects, and that
current excursions offine particle mass in excess of250pg/m3 have not been associated with health effects in London

or elsewhere. EPA finds these assertions to be unsupported. The studies of mortality inLondon over a 14-year period ofdeclining pollution from 1958 through 1971 found that therelationship 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 I

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continuing studies In the contemporary revised form, inparticular, makes direct U.S. and Europe have suggested health comparison oftherelative stringency of effects at PMo levels below 250Pg/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 InLondonjustify 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 oflung function fromhistorical 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 theone chosen, As

are equal in toxicity to those found in discussed in Section III.C.1 above, London at the time ofthose uncertainties in estimating PMlo measurements. Any margin ofsafety equivalents oflow British Smoke inherent in the British Smoke/PMo concentrations in the lateryears ofthe conversion for the earlier years when London studies makeit difficult to use gravimetric calibrations were available the studies to set aprecise level fora is more likely to be on the order ofa PMo standard.Therefore, itis important factor of 1.2 (the ratio ofPM. toPMo to examine the more contemporary estimatedby Lodge, 1986) rather than studies oflung function that permit a thefactor ofthree suggested by the more direct estimation ofPM1oeffects commenters. For particulate levels lower levels. In considering these studies in than those observed in the e'arlieryears, conjunction with theLondon mortality EPAhas supplemented the London and otherrelevant health studies,EPA studies with the more contemporary finds that a 24-hour standard of150pg/ American and European studies using m 3 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 oflevels proposed changes in lung function.As discussed forthe 24-hour standard is insufficient. in Section III.C.1, a standard of150 1kg/ Commenters based these concerns on: ms will clearly prevent lung function (a) Calculations suggesting that even the decrements that mightbe considered to lower bound may be less stringent than be indicative ofadverse effects in well the current standards, (b) evidence from over 95%ofchildren exposed; in fact the the more recent studies oflung function evidence suggests that even reversible decrements in children and the analyses lung function changes (FEVo.75) in excess ofLondon mortality data, and (c) of10%areunlikely 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 ofsafety. commenters felt that, in view ofthe Some commenters favoring standards available evidence, the standard should below thelower bounds oftheproposed be set at levels at orbelow the lower ranges relied on studies or analyses bound oftheproposed ranges. found by EPA and CASAC to be oflittle

AgencyResponse: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 ofsuch studies in selecting a its relative stringency as compared to margin ofsafety (e.g., SPA 52-53; SP the previous standard. EPA believes that 109-111), but in EPA'sjudgment they do standards chosen provide an adequate notprovide a sufficient basis for margin ofsafety irrespective ofthe establishing standards at levelsbelow relationship to the former TSP those derived from the more standards. Nevertheless, EPA has quantitative studies summarized in compared the stringency ofthe revised Tables 1and 2above. standards with thatof 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 theresults of attain each set ofstandards. By this Ware et al. (1986), which suggest a measure, the new PMo standards are possible gradient ofeffects 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 (25jg/m 3).

or asserted otherwise often did not take AgencyResponse:EPA disagrees. all ofthe aspects of the standards into EPA stafffound that thepollution and account. Themargin ofsafety is a effects gradient in the three cleanest function not only oflevel, but also ofthe cities to be too small to provide any indicator and form of the staiidards. The

- -strong suggestiQn ofeffects at such levels. Moreover, the lack of consistency for "within city" effects in this study argue against placing undue reliance on the suggestion ofeffects at levels outside oftherange suggested bythe other long-term studies ofinterest (Ferris etal., 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. SecondaryStandards

1.Soiling and Nuisance

Comments:The Agency should maintain a secondary TSP standard. Some commenters feltthat the proposed secondary annual TSPstandard is inadequate, and that the current 24-hour TSP standard should be retained.

AgencyResponse: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 ofthe relative protection afforded bythe 24-hour PMo standard indicate that it is relatively more stringent than the upper portion ofthe 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 wasinitially inclined. As detailed above, the data do notprovide convincing evidence ofsignificant soiling and nuisance effects at concentrations below thatpermitted by the primary standards.

2. Visibility

Comment:A secondary fine particle standard is needed to protect against visibility impairment and related effects.

AgencyResponse:TheAdministrator deferredjudgment with respect to a secondary fine particle standard in orderto examine therelationship between control programs forregional visibility and the related problems of acid deposition. Theinitial phase ofthat 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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## / Rules and Regulations

C.Averaging TimeandFormofthe 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 orpreferred a multiple exceedance or percentile form ofthe 24-hour standard. Others. supported the proposal to adopt a single expected exceedance statistical form. Many ofthe 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.

.AgencyResponse: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 forthe primary standards and the proposed adjustments for incomplete sampling appropriately reflect thehealth basis forthe standard. When sampling, isperformed less frequently than every day, the number ofobserved exceedances ofthe standard level will obviously be, ingeneral, fewer than the actual number ofexceedances. 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 ofthe 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

areprovided in the "Guideline on the Identification and (Use ofAir Quality Data'Affected by Exceptional Events", EPA-450/4-86--007. Moreover, single high concentrations will not necessarily

cause a location tofail the test for attainment. Appendix Khas been modified so that the first observed exceedance is not adjusted for incomplete sampling, ifthe 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 inorder to fail the test for attainment.'Sites sampling every. otherday orevery day must record three or four exceedarices over a threeyear period in order tofail the test. This change reduces the chances for misclassifying a site as,nonattainment.

Although a multiple exceedande form ofthe 24-hour'standard could reduce sampling requirements, such a form would reduce the level ofhealth protection by allowing particulate levels
to exceed, on multiple days, the levels that the Administrator has determined to pose an unacceptable healthrisk. An analysis ofalternative 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 ofthis 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 forthe Annual Standard

Comment:Many commenters favored retaining thegeometric mean to describe annual average particulate matter concentrations but several supported theproposed use ofthe arithmetic mean. Those opposed to theproposed 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 ofthe annual standard and that the arithmetic mean does notproperly 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 fora long-term primary air quality standard than is the geometric

mean. Itprovides 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 therationale, the effect of averaging multiple years of datain order to estimate the expected annual value

as well as theuse of the arithmetic

mean were both considered in setting the concentration level ofthe standard. The use of the arithmetic mean does not necessarily increase the stringency of the,standard level; the stringency depends atthe combination ofthe 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. RegulatoryImpactAnalysis

Under Executive Order 12291, EPA

must judge whether a regulation is a "major" regulation forwhich a Regulatory Impact Analysis (RIA] is required. At the time ofthe 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 ofthe National Ambient Air Quality Standards forParticulate 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 ofthe draft RIA, the Agency stated that neither the RIA nor the contractors' reports were considered in developing the proposed revisions. Subsequent to the release ofthe draft RIA, the public and othergovernmental agencies raised

a number ofquestions 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 ofthe 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 

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Order 12291. Comments from OMB and EPA'sresponses to those comments have been placed inthe docket.
Reporting Requirements

This final rule does not contain any information collection requirements subjectto OMB review under the Paperwork Reduction Act of1980 U.S.C. 3501 etseq. B.ImpactonSmallEntities

Under the Regulatory Flexibility Act, 5 U.S.C. 600-612; EPAmust prepare initial and final regulatory flexibility analyses that assess the impact aproposed or finalrule will have on small entities, which include small businesses, small not-for-profit enterprises, and governmental entities with jurisdiction

over populations ofless than 50,000. The requirement ofpreparing such an analysis is waived, however,if the Administrator certifies that the rule will
not have a significant economic Impact

on a substantial number ofsmall 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 ofcontrols 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%ofthe entities in those industries would be affected by the proposed standards.

During thepublic comment period, EPA received no comments on the regulatory flexibility analysis. Onthe 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 ofManagement and Budget (OMB) forreview. Comments from'OMB and.EPA's responses to these comments :have been placed Inthe docket. , , List ofSubjects 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.

References AMC [American Mining Congress] (1982).

American Mining Congress Position Paper

onParticle Size Issue. American Mining Congress, Washington, DC. June 17,1982. Docket *A-79-29, II-D-81a. Argonne (1983). Costs andAir Quality

Impacts ofAlternative National Ambient AirQuality Standards for Particulate Matter,Technical Support Document, prepared for U.S. EPA,Ambient Standards Branch. Research Triangle Park, NC, January 1983. Docket #A-79-29, II-A-35. Biller, W.F. (1984). Investigation ofPM1o

National AmbientAir Quality Standards Based onMultiple Exceedances. Prepared for Strategies and AirStandards Division. Office ofAir Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park,NC:
contract no. 68-02-3875. Docket #A-82-37, IV-A-2. Biller,W.F. (1986). Letter toHenry C.

Thomas, U.S. EPA, Office ofAir Quality Planning and Standards. Re: Multiple Exceedance PM Standards. December 18, 1986. Docket #A-82-37, IV-D-344. Booz, Allen and Hamilton, Inc. (1970). Study

to Determine Residential Soiling Costsof Particulate AirPollution. APTD-0715, U.S. Department ofHealth. Education and Welfare,National AirPollution Control Administration, Raleigh, NC. Bouhuys, A., G.J. Beck. and J.B. Schoenberg

(1978). Do present levels ofairpollution outdoors affect respiratory health? Nature 276: 466-471. Carey,W.F. (1959). Atmospheric deposits in

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