65638 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

ENVIRONMENTAL PROTECTION

AGENCY

40 CFR Part 50

[AD-FRL–5659–5]

RIN 2060–AE66

National Ambient Air Quality

Standards for Particulate Matter:

Proposed Decision

AGENCY: Environmental Protection

Agency (EPA).

ACTION: Proposed rule.

SUMMARY: In accordance with sections

108 and 109 of the Clean Air Act (Act),

EPA has reviewed the air quality criteria

and national ambient air quality

standards (NAAQS) for particulate

matter (PM) and for ozone (O3). Based

on these reviews, EPA proposes to

change the standards for both classes of

pollutants. This document describes

EPA’s proposed changes with respect to

the NAAQS for PM. The EPA’s

proposed actions with respect to O3 are

being proposed elsewhere in today’s

Federal Register.

With respect to PM, EPA proposes to

revise the current primary PM10

standards by adding two new primary

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

mean, and 50 μg/m3, 24-hour average, to

provide increased protection against a

wide range of PM-related health effects,

including premature mortality and

increased hospital admissions and

emergency room visits (primarily in the

elderly and individuals with

cardiopulmonary disease); increased

respiratory symptoms and disease (in

children and individuals with

cardiopulmonary disease such as

asthma); decreased lung function

(particularly in children and individuals

with asthma); and alterations in lung

tissue and structure and in respiratory

tract defense mechanisms. The

proposed annual PM2.5 standard would

be based on the 3-year average of the

annual arithmetic mean PM2.5

concentrations, spatially averaged

across an area. The proposed 24-hour

PM2.5 standard would be based on the

3-year average of the 98th percentile of

24-hour PM2.5 concentrations at each

monitor within an area. The EPA also

solicits comment on two alternative

approaches for selecting the levels of

PM2.5 standards. The EPA proposes to

revise the current 24-hour primary PM10

standard of 150 μg/m3 by replacing the

1-expected-exceedance form with a 98th

percentile form, averaged over 3 years at

each monitor within an area, and

solicits comment on an alternative

proposal to revoke the 24-hour PM10

standard. The EPA also proposes to

retain the current annual primary PM10

standard of 50 μg/m3. Further, EPA

proposes new data handling

conventions for calculating 98th

percentile values and spatial averages

(Appendix K), proposes to revise the

reference method for monitoring PM as

PM10 (Appendix J), and proposes a new

reference method for monitoring PM as

PM2.5 (Appendix L).

The EPA proposes to revise the

current secondary standards by making

them identical to the suite of proposed

primary standards. In the

Administrator’s judgment, these

standards, in conjunction with the

establishment of a regional haze

program under section 169A of the Act,

would provide appropriate protection

against PM-related public welfare effects

including soiling, material damage, and

visibility impairment.

DATES: Written comments on this

proposed rule must be received by

February 18, 1997.

ADDRESSES: Submit comments in

duplicate if possible on the proposed

action to: Office of Air and Radiation

Docket and Information Center (6102),

Attention: Docket No. A–95–54, U.S.

Environmental Protection Agency, 401

M St., SW., Washington, DC 20460.

Public hearings: The EPA will

announce in a separate Federal Register

document the date, time, and address of

the public hearing on this proposed

rule.

FOR FURTHER INFORMATION CONTACT: Ms.

Patricia Koman, MD–15, Air Quality

Strategies and Standards Division,

Office of Air Quality Planning and

Standards, U.S. Environmental

Protection Agency, Research Triangle

Park, North Carolina 27711, telephone:

(919) 541–5170.

SUPPLEMENTARY INFORMATION:

Docket

Docket No. A–95–54 incorporates by

reference the docket established for the

air quality criteria document (Docket

No. ECAO–CD–92–0671). The docket

may be inspected at the above address

between 8:00 a.m. and 5:30 p.m. on

weekdays, and a reasonable fee may be

charged for copying.

Availability of Related Information

Certain documents are available from

the U.S. Department of Commerce,

National Technical Information Service,

5285 Port Royal Road, Springfield,

Virginia 22161. Available documents

include: Air Quality Criteria for

Particulate Matter (Criteria Document)

(three volumes, EPA/600/P–95–001aF

thru EPA/600/P–95–001cF, April 1996,

NTIS # PB–96–168224, $234.00 paper

copy); and Review of the National

Ambient Air Quality Standards for

Particulate Matter: Policy Assessment of

Scientific and Technical Information

(Staff Paper) (EPA–452/R–96–013, July

1996, NTIS # PB–97–115406, $47.00

paper copy and $19.50 microfiche).

(Add a $3.00 handling charge per order.)

A limited number of copies of other

documents generated in connection

with this standard review, such as

technical support documents pertaining

to air quality, monitoring, and health

risk assessment, can be obtained from:

U.S. Environmental Protection Agency

Library (MD–35), Research Triangle

Park, NC 27711, telephone (919) 541–

2777. These and other related

documents are also available for

inspection and copying in the EPA

docket identified above.

The Staff Paper and human health

risk assessment support documents are

now available on the Agency’s Office of

Air Quality Planning and Standards’

(OAQPS) Technology Transfer Network

(TTN) Bulletin Board System (BBS) in

the Clean Air Act Amendments area,

under Title I, Policy/Guidance

Documents. To access the bulletin

board, a modem and communications

software are necessary. To dial up, set

your communications software to 8 data

bits, no parity and one stop bit. Dial

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

After registering, proceed to choice

‘‘<T> Gateway to TTN Technical

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

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

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

Policy Guidance Documents.’’ To access

these documents through the World

Wide Web, click on ‘‘TTN BBSWeb’’,

then proceed to the Gateway to TTN

Technical areas, as above. If assistance

is needed in accessing the system, call

the help desk at (919) 541–5384 in

Research Triangle Park, NC.

Implementation Activities

When revisions to the primary and

secondary PM standards are

implemented by the States, the utility,

petroleum, mining, iron and steel,

automobile, and chemical industries are

likely to be affected, as well as other

manufacturing concerns that emit PM or

precursors to PM. The extent of such

effects will depend on implementation

policies and control strategies adopted

by the States to assure attainment and

maintenance of revised standards.

The EPA is developing appropriate

policies and control strategies to assist

States in the implementation of the

proposed revisions to the PM NAAQS.

The resulting implementation strategies
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65639

will be proposed for public comment in

the future.

Table of Contents

The following topics are discussed in

today’s preamble:

I. Background

A. Legislative Requirements

B. Related Control Requirements

C. Review of Air Quality Criteria and

Standards for PM

II. Rationale for Proposed Decisions on

Primary Standards

A. Health Effects Information

1. Nature of the Effects

2. Sensitive Subpopulations

3. Evaluation of Health Effects Evidence

4. Particulate Matter Fractions of

Concern

B. Quantitative Risk Assessment

1. Overview

2. Key Observations

C. Need for Revision of the Current

Primary PM Standards

D. Indicators of PM

1. Indicators for the Fine Fraction of

PM10

2. Indicators for the Coarse Fraction of

PM10

E. Averaging Time of PM2.5 Standards

1. Short-term PM2.5 Standard

2. Long-term PM2.5 Standard

3. Combined Effect of Annual and 24–

Hour Standards

F. Form of PM2.5 Standards

1. Annual Standard

2. 24–Hour Standard

G. Levels for the Annual and 24–Hour

PM2.5 Standards

H. Conclusions Regarding the Current PM10

Standards

1. Averaging Time and Form

2. Levels for Alternative Averaging

Times

I. Proposed Decisions on Primary

Standards

III. Rationale for Proposed Decision on the

Secondary Standards

A. Visibility Impairment

B. Materials Damage and Soiling Effects

C. Proposed Decision on Secondary

Standards

IV. Revisions to Appendix K—Interpretation

of the PM NAAQS

A. PM2.5 Computations and Data Handling

Conventions

B. PM10 Computations and Data Handling

Conventions

V. Reference Methods for the Determination

of Particulate Matter as PM10 and PM2.5

in the Atmosphere

A. Revisions to Appendix J—Reference

Method for PM10

B. Appendix L—New Reference Method for

PM2.5

VI. Implementation Program

VII. Regulatory and Environmental Impact

Analyses References

I. Background

A. Legislative Requirements

Two sections of the Act govern the

establishment, review, and revision of

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

directs the Administrator to identify

pollutants which ‘‘may reasonably be

anticipated to endanger public health

and welfare’’ and to issue air quality

criteria for them. These air quality

criteria are to ‘‘accurately reflect the

latest scientific knowledge useful in

indicating the kind and extent of all

identifiable effects on public health or

welfare which may be expected from the

presence of [a] pollutant in the ambient

air * * * .’’

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

the Administrator to propose and

promulgate ‘‘primary’’ and ‘‘secondary’’

NAAQS for pollutants identified under

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

primary standard as one ‘‘the attainment

and maintenance of which, in the

judgment of the Administrator, based on

the criteria and allowing an adequate

margin of safety, [are] requisite to

protect the public health.’’ The margin

of safety requirement was intended to

address uncertainties associated with

inconclusive scientific and technical

information available at the time of

standard setting, as well as to provide a

reasonable degree of protection against

hazards that research has not yet

identified. Both kinds of uncertainties

are components of the risk associated

with pollution at levels below those at

which human health effects can be said

to occur with reasonable scientific

certainty. Thus, by selecting primary

standards that provide an adequate

margin of safety, the Administrator is

seeking not only to prevent pollution

levels that have been demonstrated to be

harmful but also to prevent lower

pollutant levels that she finds may pose

an unacceptable risk of harm, even if the

risk is not precisely identified as to

nature or degree. The Act does not

require the Administrator to establish a

primary NAAQS at a zero-risk level, but

rather at a level that reduces risk

sufficiently so as to protect public

health with an adequate margin of

safety.

A secondary standard, as defined in

section 109(b)(2), must ‘‘specify a level

of air quality the attainment and

maintenance of which, in the judgment

of the Administrator, based on [the]

criteria, are requisite to protect the

public welfare from any known or

anticipated adverse effects associated

with the presence of [the] pollutant in

the ambient air.’’ Welfare effects as

defined in section 302(h) [42 U.S.C.

7602(h)] include, but are not limited to,

‘‘effects on soils, water, crops,

vegetation, manmade materials,

animals, wildlife, weather, visibility and

climate, damage to and deterioration of

property, and hazards to transportation,

as well as effects on economic values

and on personal comfort and wellbeing.’’

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

periodic review and, if appropriate,

revision of existing air quality criteria

and NAAQS. Section 109(d)(2) requires

appointment of an independent

scientific review committee to review

criteria and standards and recommend

new standards or revisions of existing

criteria and standards, as appropriate.

The committee established under

section 109(d)(2) is known as the Clean

Air Scientific Advisory Committee

(CASAC), a standing committee of

EPA’s Science Advisory Board.

B. Related Control Requirements

States are primarily responsible for

ensuring attainment and maintenance of

ambient air quality standards once EPA

has established them. Under section 110

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

provisions, States are to submit, for EPA

approval, State implementation plans

(SIP’s) that provide for the attainment

and maintenance of such standards

through control programs directed to

sources of the pollutants involved. The

States, in conjunction with EPA, also

administer the prevention of significant

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

7479) for these pollutants. In addition,

Federal programs provide for

nationwide reductions in emissions of

these and other air pollutants through

the Federal Motor Vehicle Control

Program under Title II of the Act (42

U.S.C. 7521–7574), which involves

controls for automobile, truck, bus,

motorcycle, and aircraft emissions; the

new source performance standards

under section 111 (42 U.S.C. 7411); and

the national emission standards for

hazardous air pollutants under section

112 (42 U.S.C. 7412).

C. Review of Air Quality Criteria and

Standards for PM

Particulate matter is the generic term

for a broad class of chemically and

physically diverse substances that exist

as discrete particles (liquid droplets or

solids) over a wide range of sizes.

Particles originate from a variety of

anthropogenic stationary and mobile

sources as well as from natural sources.

Particles may be emitted directly or

formed in the atmosphere by

transformations of gaseous emissions

such as sulfur oxides (SOX), nitrogen

oxides (NOX), and volatile organic

compounds (VOC). The chemical and

physical properties of PM vary greatly

with time, region, meteorology, and

source category, thus complicating the

assessment of health and welfare effects.

The last review of PM air quality

criteria and standards was completed in
65640 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

1PM10 refers to particles with an aerodynamic

diameter less than or equal to a nominal 10

micrometers.

2A more complete history of the PM NAAQS is

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

Review of National Ambient Air Quality Standards

for Particulate Matter: Assessment of Scientific and

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

3A court order entered in American Lung

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

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

requires publication of proposed and final decisions

on the review of the PM NAAQS by November 29,

1996 and June 28, 1997, respectively.

4The Staff Paper evaluates policy implications of

the key studies and scientific information in the

Criteria Document, identifies critical elements that

EPA staff believes should be considered, and

presents staff conclusions and recommendations of

suggested options for the Administrator’s

consideration.

5PM2.5 refers to particles with an aerodynamic

diameter less than or equal to a nominal 2.5

micrometers.

6PM10–2.5 refers to those particles with an

aerodynamic diameter less than or equal to a

nominal 10 micrometers but greater than 2.5

micrometers.

July 1987 with notice of a final decision

to revise the existing standards (52 FR

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

EPA changed the indicator for particles

from total suspended particles (TSP) to

PM10.1 Identical primary and secondary

PM10 standards were set for two

averaging times: (1) 50 μg/m3, expected

annual arithmetic mean, averaged over

3 years, and (2) 150 μg/m3, 24-hour

average, with no more than one

expected exceedance per year.2

The EPA formally initiated the

current review of the air quality criteria

for PM in April 1994 by announcing its

intention to develop a revised Air

Quality Criteria Document for

Particulate Matter (henceforth, the

‘‘Criteria Document’’). Thereafter, the

EPA presented its plans for review of

the criteria and standards for PM under

a highly accelerated, court-ordered

schedule 3 at a public meeting of the

CASAC in December 1994. Several

workshops were held by EPA’s National

Center for Environmental Assessment

(NCEA) to discuss important new health

effects information in November 1994

and January 1995. External review drafts

of the Criteria Document were made

available for public comment and were

reviewed by CASAC at public meetings

held in August and December 1995 and

February 1996. The CASAC came to

closure in its review of the Criteria

Document, advising the Administrator

in a March 15, 1996 closure letter

(Wolff, 1996a) that ‘‘although our

understanding of the health effects of

PM is far from complete, a revised

Criteria Document which incorporates

the Panel’s latest comments will provide

an adequate review of the available

scientific data and relevant studies of

PM.’’ CASAC and public comments

from these meetings and from

subsequent written comments and the

closure letter were incorporated as

appropriate in the final Criteria

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

External review drafts of a staff paper

prepared by the Office of Air Quality

Planning and Standards (OAQPS),

Review of the National Ambient Air

Quality Standards for Particulate Matter:

Assessment of Scientific and Technical

Information (henceforth, the ‘‘Staff

Paper’’) were made available for public

comment and were reviewed by CASAC

at public meetings in December 1995

and May 1996.4 The CASAC came to

closure in its review of the Staff Paper,

advising the Administrator in a June 13,

1996 closure letter (Wolff, 1996b) that

‘‘the Staff Paper, when revised, will

provide an adequate summary of our

present understanding of the scientific

basis for making regulatory decisions

concerning PM standards.’’ CASAC and

public comments from these meetings,

subsequent written comments, and the

CASAC closure letter were incorporated

as appropriate in the final Staff Paper

(U.S. EPA, 1996b).

The principal focus of this current

review of the air quality criteria and

standards for PM is on recent

epidemiological evidence reporting

associations between ambient

concentrations of PM and a range of

serious health effects. Particular

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

PM10 and the principal fractions of

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

coarse (PM10–2.5) 6 fractions. As

discussed in the Criteria Document, fine

and coarse fraction particles can be

differentiated by their sources and

formation processes and their chemical

and physical properties, including

behavior in the atmosphere. Detailed

discussions of atmospheric formation,

ambient concentrations, and health and

welfare effects of PM, as well as

quantitative estimates of human health

risks associated with exposure to PM,

can be found in the Criteria Document

and Staff Paper.

This review of the scientific criteria

for PM has occurred simultaneously

with the review of the criteria for ozone

(O3). These criteria reviews as well as

related implementation strategy

activities to date have brought out

important linkages between O3 and PM.

A number of community

epidemiological studies have found

similar health effects to be associated

with exposure to O3 and PM, including,

for example, aggravation of respiratory

disease (e.g., asthma), increased

respiratory symptoms, and increased

hospital admissions and emergency

room visits for respiratory causes.

Laboratory studies have found potential

interactions between O3 and various

constituents of PM. Other key

similarities relating to exposure patterns

and implementation strategies exist

between O3 and PM, specifically fine

particles. These similarities include: (1)

Atmospheric residence times of several

days, leading to large urban and

regional-scale transport of the

pollutants; (2) similar gaseous

precursors, including NOX and VOC,

which contribute to the formation of

both O3 and fine particles in the

atmosphere; (3) similar combustionrelated source categories, such as coal

and oil-fired power generation and

industrial boilers and mobile sources,

which emit particles directly as well as

gaseous precursors of particles (e.g.,

SOX, NOX, VOC) and O3 (e.g., NOX,

VOC); and (4) similar atmospheric

chemistry driven by the same chemical

reactions and intermediate chemical

species that form both high O3 and fine

particle levels. High fine particle levels

are also associated with significant

impairment of visibility on a regional

scale.

These similarities provide

opportunities for optimizing technical

analysis tools (i.e., monitoring networks,

emission inventories, air quality

models) and integrated emission

reduction strategies to yield important

co-benefits across various air quality

management programs. These cobenefits could result in a net reduction

of the regulatory burden on some source

category sectors that would otherwise be

impacted by separate O3, PM, and

visibility protection control strategies.

In recognition of the multiple linkages

and similarities in effects and the

potential benefits of integrating the

Agency’s approaches to providing for

appropriate protection of public health

and welfare from exposure to O3 and

PM, EPA plans to complete the review

of the NAAQS for both pollutants on the

same schedule. Accordingly, today’s

Federal Register contains a separate

notice announcing proposed revisions

to the O3 NAAQS. Linking the O3 and

PM review schedules provides an

important opportunity to materially

improve the nation’s air quality

management programs—both in terms of

communicating a more complete

description of the health and welfare

effects associated with the major

components of urban and regional air

pollution, and by helping the States and

local areas to plan jointly to address

both PM and O3 air pollution at the

same time with one process, and to
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65641

work together with industry to address

common sources of air pollution. The

EPA believes this integrated approach

will lead to more effective and efficient

protection of public health and the

environment.

II. Rationale for Proposed Decisions on

Primary Standards

This notice presents the

Administrator’s proposed decisions to

establish new annual and 24-hour PM2.5

primary standards and to revise the

form of the current 24-hour PM10

primary NAAQS, based on a thorough

review, in the Criteria Document, of the

latest scientific information on known

and potential human health effects

associated with exposure to PM at levels

typically found in the ambient air.

These decisions also take into account

and are consistent with: (1) Staff Paper

assessments of the most policy-relevant

information in the Criteria Document,

upon which staff recommendations for

new and revised primary standards are

based; (2) CASAC advice and

recommendations, as reflected in

discussions of drafts of the Criteria

Document and Staff Paper at public

meetings, in separate written comments,

and in the CASAC’s closure letters to

the Administrator; and (3) public

comments received during the

development of these documents, either

in connection with CASAC meetings or

separately.

As discussed more fully below, the

rationale for the proposed revisions of

the PM primary NAAQS includes

consideration of: (1) Health effects

information, and alternative views on

the appropriate interpretation and use of

the information, as the basis for

judgments about the risks to public

health presented by population

exposures to ambient PM; (2) insights

gained from a quantitative risk

assessment conducted to provide a

broader perspective for judgments about

protecting public health from the risks

associated with PM exposures; and (3)

specific conclusions regarding the need

for revisions to the current standards

and the elements of PM standards (i.e.,

indicator, averaging time, form, and

level) that, taken together, would be

appropriate to protect public health

with an adequate margin of safety.

As with virtually any policy-relevant

scientific research, there is uncertainty

in the characterization of health effects

attributable to exposure to ambient PM.

As discussed below, however, there is

now a greatly expanded body of health

effects information as compared with

that available during the last review of

the PM standards. Moreover, the recent

evidence on PM-related health effects

has undergone an unusually high degree

of scrutiny and reanalysis over the past

several years, beginning with a series of

workshops held early in the review

process to discuss important new

information. A number of opportunities

were provided for public comment on

successive drafts of the Criteria

Document and Staff Paper, as well as for

intensive peer review of these

documents by CASAC at several public

meetings attended by many

knowledgeable individuals and

representatives of interested

organizations. In addition, there have

been a number of important scientific

conferences, symposia, and colloquia on

PM issues, sponsored by the EPA and

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

this period. While significant

uncertainties exist, the review of the

health effects information has been

thorough and deliberate. In the

judgment of the Administrator, this

intensive evaluation of the scientific

evidence has provided an adequate

basis for regulatory decision making at

this time, as well as for the

comprehensive research plan recently

developed by EPA, and reviewed by

CASAC and others, for improving our

future understanding of the

relationships between ambient PM

exposures and health effects.

A. Health Effects Information

This section outlines key information

contained in the Criteria Document

(Chapters 10–13) and the Staff Paper

(Chapter V) on known and potential

health effects associated with airborne

PM, alone and in combination with

other pollutants that are routinely

present in the ambient air. The

information highlighted here

summarizes: (1) The nature of the effects

that have been reported to be associated

with ambient PM; (2) sensitive

subpopulations that appear to be at

greater risk to such effects; (3) an

integrated evaluation of the health

effects evidence; and (4) the PM

fractions of greatest concern to health.

Since the last review of the PM

criteria and standards, the most

significant new evidence on the health

effects of PM is the greatly expanded

body of community epidemiological

studies. The Criteria Document stated

that these recent studies provide

‘‘evidence that serious health effects

(mortality, exacerbation of chronic

disease, increased hospital admissions,

etc.) are associated with exposures to

ambient levels of PM found in

contemporary U.S. urban airsheds even

at concentrations below current U.S. PM

standards’’ (U.S. EPA, 1996a, p. 13–1).

Although a variety of responses to

constituents of ambient PM have been

hypothesized to contribute to the

reported health effects, the relevant

toxicological and controlled human

studies published to date have not

identified an accepted mechanism(s)

that would explain how such relatively

low concentrations of ambient PM

might cause the health effects reported

in the epidemiological literature. The

discussion below notes the key issues

raised in assessing community

epidemiological studies, including

alternative interpretations of the

evidence, both for individual studies

and for the evidence as a whole.

1. Nature of the Effects

As discussed in the Criteria Document

and Staff Paper, the key health effects

categories associated with PM include:

(1) Premature mortality; (2) aggravation

of respiratory and cardiovascular

disease (as indicated by increased

hospital admissions and emergency

room visits, school absences, work loss

days, and restricted activity days); (3)

changes in lung function and increased

respiratory symptoms; (4) changes to

lung tissues and structure; and (5)

altered respiratory defense mechanisms.

Most of these effects have been

consistently associated with ambient

PM concentrations, which have been

used as a measure of population

exposure, in a number of community

epidemiological studies. Additional

information and insights on these effects

are provided by studies of animal

toxicology and controlled human

exposures to various constituents of PM

conducted at higher-than-ambient

concentrations. Although, as noted

above, mechanisms by which particles

cause effects have not been elucidated,

there is general agreement that the

cardio-respiratory system is the major

target of PM effects.

a. Mortality

i. Short-Term Exposure Studies

As discussed in the Staff Paper, the

most notable evidence on the health

effects of community air pollution

containing high concentrations of PM

has come from the dramatic pollution

episodes of Belgium’s industrial Meuse

Valley, Donora, Pennsylvania, and

London, England. Based on analyses of

a series of episodes in London, there

was general acceptance in the last

Criteria Document (U.S. EPA, 1982a)

and in critical reviews of PM-associated

health effects that London air pollution

at high concentrations (at or above 500–
65642 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

7Measured as British Smoke (BS), which gauges

the darkness of PM collected on a filter and is most

sensitive to combustion generated carbon particles.

When calibrated to a mass measurement, as in the

historical London studies, BS is an indicator of fine

mode particles.

8Statistically significant results are reported at a

95% confidence level.

9Many of the recent epidemiological studies

report effects estimates in terms of a percentage

increase in the risk of mortality in the study

population (as compared to the baseline rate in the

population as a whole) associated with a specific

increase in ambient PM concentrations measured by

one or more outdoor monitors. These effects

estimates generally are based on a statistical model

of the entire study period, which typically spanned

multiple years or seasons.

1000 μg/m 3 of PM 7 and sulfur dioxide

(SO 2)) was causally related to increased

mortality. Further analyses of daily

mortality over 14 London winters

suggested that particles were more

likely to be responsible for the

associations of health effects with air

pollution than SO2, and that the

association continued to the lower

concentrations of PM measured in

London (150 μg/m3, measured as BS).

From 1987 to present, numerous

epidemiological studies using improved

statistical techniques and expanded

particle monitoring data have reported

statistically significant 8 positive

associations between increased daily or

several-day average concentrations of

PM [as measured by a variety of indices,

including TSP, PM10, PM2.5, sulfate, and

BS] and premature mortality in

communities across the U.S. as well as

in Europe and South America. Of 38

analyses and reanalyses of these studies

(referred to as daily mortality studies)

published between 1988 and 1996, most

found statistically significant

associations between increases in shortterm ambient PM concentrations and

total non-accidental mortality (U.S.

EPA, 1996a, Table 12–2).

More specifically, the effects

estimates for PM10 reported in these

studies fall within a range of

approximately 2 to 8 percent increase in

the relative risk 9 of mortality for a 50

μg/m3 increase in 24-hour average PM10

concentrations. The consistency in these

results is notable, particularly since

these studies examined PM-mortality

relationships in 18 different locations

varying significantly in climate, human

activity patterns, aerosol composition,

and amounts of co-occurring gaseous

pollutants [e.g., SO2 and ozone(O3)],

using a variety of statistical techniques.

A rough estimate of the incremental

relative risk attributed to PM

concentrations seen in the worst

London episode also falls within this

range (U.S. EPA, 1996b, p. V–13). It is

also important to note that the

magnitude of the relative risks, while

significant from a public health

perspective because the potentially

exposed population is large, are small

compared to those usually found in

epidemiological studies of occupational

and other risk factors.

Some of these daily mortality studies

examined PM-mortality associations for

both total non-accidental mortality and

cause-specific mortality. In general,

such studies have reported higher

relative risks for respiratory and

cardiovascular causes of death than for

total mortality, as well as higher risks

for mortality in the elderly (>65 years of

age) than for mortality in the general

population.

ii. Long-Term Exposure Studies

By the time of the previous review of

the PM criteria in 1987, numerous

epidemiological studies of a crosssectional design had reported

statistically significant associations

linking higher long-term (single or

multi-year) concentrations of various

indices of PM with higher mortality

rates across numerous U.S.

communities. However, the usefulness

of such studies for quantitative purposes

was at that time limited by the lack of

supporting evidence available from

daily mortality studies or the

toxicological literature, and by

unaddressed confounders and

methodological problems inherent in

these cross-sectional studies.

More recently, epidemiological

studies of a prospective-cohort design

have been conducted, including in

particular the Six City study (Dockery et

al., 1993) and the American Cancer

Society (ACS) study (Pope et al., 1995),

that lend support to the earlier crosssectional studies of mortality. These two

recent studies reflect significant

methodological advances over the

earlier studies, including the use of

subject-specific information, and

provide evidence for an association

between long-term PM concentrations

and mortality. At least some fraction of

mortality was reported to reflect

cumulative PM impacts in addition to

those associated with short-term

concentrations (U.S. EPA, 1996a, p. 13–

34).

The Six City study, which followed

more than 8,000 adults for 14 years,

found that long-term PM concentrations

(PM15/10, PM2.5, and sulfate) in six U.S.

cities were statistically significantly

associated with increased rates of total

mortality and cardiopulmonary

mortality, even after adjustment for

smoking, education level, and

occupation. Specifically, this study

reported increases in relative risk of

26% and 37% for total and

cardiopulmonary-related mortality,

respectively, between the cities with the

highest and lowest PM concentrations.

The ACS study was designed to follow

up on the findings from the Six City

study, using a much larger number of

individuals (more than half a million

adults followed for seven years) and

cities. The ACS investigators reported

that, after adjustment for other risk

factors, multi-year concentrations of

PM2.5 (for 47 U.S. cities) and sulfate (for

151 cities) were found to be statistically

significantly associated with both total

and cardiopulmonary mortality. The

ACS study reported increases in relative

risk of 17% and 31% for total and

cardiopulmonary mortality,

respectively.

Some reviewers have raised concerns

regarding the adequacy of the

adjustment for confounders in these

prospective-cohort studies, maintaining

that other uncontrolled factors may be

responsible for the observed mortality

rates (Lipfert and Wyzga, 1995;

Moolgavkar and Luebeck, 1996;

Moolgavkar, 1994). The Criteria

Document indicates, however, that it is

unlikely that these studies overlooked

plausible confounders, although the

addition of factors not taken into

account might well alter the magnitude

of the association (U.S. EPA, 1996a, p.

12–180). In particular, the Criteria

Document cautions that the magnitude

of relative risks associated with PM

concentrations reported in these studies

may be overestimated because some of

the effects may be due to historical PM

concentrations that were significantly

higher than the ones used to estimate

population exposures in these studies.

The Criteria Document concludes that

the Six City and ACS studies, taken

together with the earlier cross-sectional

studies, suggest that: 1) there may be

increases in mortality in disease

categories that are consistent with longterm exposure to PM, and 2) at least

some fraction of these deaths reflects

cumulative PM impacts greater than

those reported in the daily mortality

studies (U.S. EPA, 1996a, p. 13–34).

iii. Degree of Lifespan Shortening

The degree of lifespan shortening

associated with PM exposure in these

studies is viewed by many as an

important consideration in evaluating

mortality effects in a public health

context. The epidemiological findings of

associations between short- and longterm ambient PM concentrations and

premature mortality provide some

insight into this issue. The mortality

effects estimates associated with longterm PM concentrations in the

prospective-cohort studies are
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10 Ischemic heart disease is a general term for

heart diseases in which there is an insufficient

blood supply to the heart muscle.

considerably larger (Six City study) to

somewhat larger (ACS study) than those

from the daily mortality studies,

suggesting that a substantial portion of

the deaths associated with long-term PM

exposure may be independent of the

deaths associated with short-term

exposure (U.S. EPA, 1996a, p. 13–44).

The Criteria Document suggests that the

extent of lifespan shortening implied by

the long-term exposure studies could be

on the order of years (U.S. EPA, 1996a,

p. 13–45).

As discussed in the Staff Paper,

attempts to quantitatively evaluate the

extent of lifespan shortening in the daily

mortality studies to date provide no

more than suggestive results, with the

investigators recognizing that more

research is needed in this area (U.S.

EPA, 1996b, p. V–19–20). The limited

analyses available suggest that at least

some portion of the daily mortality

associated with PM may occur in

individuals who would have died

within days in the absence of PM

exposure (U.S. EPA, 1996b, p. V–19–

20). Researchers in this area also note

that it is possible that the reported

deaths might be substantially premature

if a person becomes seriously ill but

would have otherwise recovered

without the extra stress of PM exposure

(U.S. EPA, 1996b, p. V–19–20).

Quantification of the degree of

lifespan shortening inherent in the longand short-term exposure mortality

studies is difficult and requires

assumptions about life expectancies

given other risk factors besides PM

exposure, including the ages at which

PM-attributable deaths occur and the

general levels of medical care available

to sensitive subpopulations in an area.

Because of these uncertainties, it is not

possible to develop with confidence

quantitative estimates of the extent of

life-shortening accompanying the

increased mortality rates that have been

associated with exposures to PM (U.S.

EPA, 1996a, p. 13–45).

b. Aggravation of Respiratory and

Cardiovascular Disease

Given the statistically significant

positive associations between ambient

PM concentrations and mortality

outlined above, it is reasonable to

expect that community epidemiological

studies should also find increased PMmorbidity associations. As noted in the

Criteria Document, this is indeed the

case. Twelve of the 13 epidemiological

studies of hospital admissions in North

America (U.S. EPA, 1996a, Table 13–3)

report statistically significant positive

associations between short-term

concentrations of PM and hospital

admissions for respiratory-related and

cardiac diseases. More specifically,

these studies report increases from 6 to

25 percent in the relative risk of hospital

admissions for respiratory disease,

pneumonia, and chronic obstructive

pulmonary disease (COPD), for a 50 μg/

m3 increase in 24-hour average PM10

concentrations. A smaller, but

statistically significant, increase in

relative risk of 2 percent was reported

in one study of hospital admissions for

ischemic heart disease.10

Indirect measures of morbidity,

including school absences, restricted

activity days, and work loss days have

also been used as indicators of acute

respiratory conditions in community

studies of PM. For example, the

statistically significant association

reported between short-term PM

concentrations and school absences is

consistent with an effect from PM

exposure, because respiratory

conditions are the most frequent cause

of school absences (U.S. EPA, 1996a,

Chapter 12). Recent studies have also

reported statistically significant

associations between short-term PM

concentrations and both (1) respiratoryrelated restricted activity days and (2)

work loss days (U.S. EPA, 1996b, p. V–

22).

c. Altered Lung Function and Increased

Respiratory Symptoms

Community epidemiological studies

of ambient PM concentrations and

laboratory studies of human and animal

exposures to high concentrations of PM

components show that PM exposure can

be associated with altered lung function

and increased respiratory symptoms. A

number of epidemiological studies in

the U.S. (U.S. EPA, 1996a, Tables 13–3

and 13–4) show associations between

short-term PM concentrations and

increased upper and lower respiratory

symptoms and cough, as well as

decreases in pulmonary function [e.g.,

forced expiratory capacity for one

second (FEV1) and peak expiratory flow

rate (PEFR)]. Taken together, these

studies suggest that sensitive

individuals, such as children (especially

those with asthma or pre-existing

respiratory symptoms), may have

increased or aggravated symptoms

associated with PM exposure, with or

without reduced lung function.

Results from respiratory symptom

studies of long-term PM concentrations

(U.S. EPA, 1996a, Table 13–5) are

consistent with and supportive of the

associations reported for short-term PM

concentrations. Studies conducted in

multiple U.S. communities in recent

years have reported that increased

symptoms of respiratory ailments in

children, including bronchitis, are

associated with increasing annual PM

concentrations across the communities

(U.S. EPA, 1996a, p. 12–372). Recent

evidence for an association between

long-term exposure to PM and

decreased lung function in children and

adults is suggestive, but more limited

(U.S. EPA, 1996a, p. 12–202).

The increased risk for respiratory

symptoms and related respiratory

morbidity reported in the

epidemiological studies is important not

only because of the immediate and nearterm symptoms produced, but also

because of the longer-term potential for

increases in the development of chronic

lung disease. Specifically, recurrent

childhood respiratory illness has been

suggested to be a risk factor for later

susceptibility to lung damage (U.S. EPA,

1996b, p. V–27).

d. Alteration of Lung Tissue and

Structure

Community epidemiological studies

have generally not been used to evaluate

the extent to which exposure to PM

directly alters lung tissues and cellular

components, although some autopsy

studies have found limited qualitative

evidence of such effects from

community air pollution (U.S. EPA,

1996b, p. V–27). Evidence of

morphological (i.e., structural) damage

from PM exposure has come primarily

from animal and occupational studies of

high concentrations of acid aerosols and

other PM components, including coarse

particle dusts. While morphological

alterations have been extensively

studied for exposures to acid aerosols,

such studies have been conducted at

concentrations well above current

ambient levels. Long-term exposure of

animals to somewhat lower

concentrations of acid mixtures have

been shown to induce morphological

changes, which may be relevant to

clinical small airway disease. Recent

work in animals using lower

concentrations, approaching ambient

levels, of ammonium sulfate and nitrate

suggest morphometric changes that

could lead to a decrease in compliance

or a ‘‘stiffening’’ of the lung (U.S. EPA,

1996b, p. V–27–29).

Occupational exposure to crystalline

silica, which is a component of coarse

dust, has been associated with a specific

form of pulmonary inflammation and

fibrosis (silicosis) (U.S. EPA, 1996a, p.

11–127). Based on analyses of the silica

content of resuspended crustal material

collected from several U.S. cities as part

of the last review, staff concluded that
65644 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

11 In subsequent discussions, the term ‘‘exposure

misclassification’’ is used to refer to combined

uncertainties introduced by the related issues of

the risk of silicosis at levels permitted

by the current annual PM10 NAAQS was

low. The 1982 Staff Paper (U.S. EPA,

1982b) summarized qualitative evidence

for morphometric changes associated

with long-term exposure to crustal

dusts, as suggested by autopsy studies of

humans and animals exposed to various

crustal dusts near or slightly above

current ambient levels in the Southwest;

however, no inferences regarding

quantitative exposures of concern can

be drawn from these studies.

e. Changes in Respiratory Defense

Mechanisms

Responses to air pollutants often

depend upon their interaction with

respiratory tract defense mechanisms

that can detoxify or physically remove

inhaled material (e.g., antigenic

stimulation of the immune system and

mucocilliary clearance). Either

depression or over-activation of such

defense systems may be involved in the

development of lung diseases (U.S. EPA,

1996a, p. 11–55). Acid aerosols (H2SO4)

have been shown to alter mucocilliary

clearance in healthy human subjects at

levels as low as 100 μg/m3; such effects

are also reported in animals (U.S. EPA,

1996a, pp. 11–60–61). Persistent

impairment of clearance may lead to the

inception or progression of acute or

chronic respiratory disease, and may be

a plausible link between acid aerosol

exposure and respiratory disease.

Alveolar macrophages play a role in

resistance to bacterial infection, the

induction and expression of immune

reactions, and the production of a

number of biologically active chemicals

that are involved in respiratory defense

mechanisms (U.S. EPA, 1996a, pp. 11–

56–66). Various exposures to PM

constituents (e.g., acid aerosols, sulfates,

and road dust) at concentrations that

range from near to well above ambient

levels have been shown to affect such

macrophage functions in experimental

animals (U.S. EPA, 1996b, pp. V–29–

31).

2. Sensitive Subpopulations

The recent epidemiological

information summarized in the Criteria

Document provides evidence that

several subpopulations are apparently

more sensitive (i.e., more susceptible

than the general population) to the

effects of community air pollution

containing PM. As discussed above, the

observed effects in these subpopulations

range from the decreases in pulmonary

function reported in children to

increased mortality reported in the

elderly and in individuals with

cardiopulmonary disease. Such

subpopulations may experience effects

at lower levels of PM than the general

population, and the severity of effects

may be greater.

Based on a qualitative assessment of

the epidemiological evidence of effects

associated with PM for subpopulations

that appear to be at greatest risk with

respect to particular health endpoints

(U.S. EPA, 1996a, Tables 13–6, 13–7),

the Staff Paper draws the following

conclusions with respect to sensitive

subpopulations (U.S. EPA, 1996b, pp.

V–31–36):

(1) Individuals with respiratory disease

(e.g., COPD, acute bronchitis) and

cardiovascular disease (e.g., ischemic heart

disease) are at greater risk of premature

mortality and hospitalization due to exposure

to ambient PM.

(2) Individuals with infectious respiratory

disease (e.g., pneumonia) are at greater risk

of premature mortality and morbidity (e.g.,

hospitalization, aggravation of respiratory

symptoms) due to exposure to ambient PM.

Also, exposure to PM may increase

individuals— susceptibility to respiratory

infections.

(3) Elderly individuals are also at greater

risk of premature mortality and

hospitalization for cardiopulmonary causes

due to exposure to ambient PM.

(4) Children are at greater risk of increased

respiratory symptoms and decreased lung

function due to exposure to ambient PM.

(5) Asthmatic children and adults are at

risk of exacerbation of symptoms associated

with asthma, and increased need for medical

attention, due to exposure to PM.

3. Evaluation of Health Effects Evidence

As discussed above, a range of serious

health effects in sensitive

subpopulations has been associated

with ambient PM concentrations in a

large number of community

epidemiological studies. Questions as to

whether the reported associations

represent causal relationships can be

addressed by consideration of the

adequacy and strength of the individual

studies; the consistency of the

associations, as evidenced by repeated

observations by different investigators,

in different places, circumstances, and

time; the coherence of the associations

(i.e., the logical or systematic

interrelationships between different

types of health effects); and the

biological plausibility of the reported

associations. Because of limitations in

the available evidence from controlled

laboratory studies of PM components, it

is generally recognized that an

understanding of biological mechanisms

that could explain the reported

associations has not yet emerged. Thus,

the following discussion focuses on the

epidemiological evidence as a basis for

assessing the weight of evidence for

inferences about the causality of the

relationships between health effects and

exposures to ambient PM

concentrations. In particular, issues

associated with interpreting individual

study results are presented, followed by

a discussion of the consistency and

coherence of the health effects evidence

as a whole.

a. Interpretation of Individual Study

Results

While it is widely accepted that

serious effects are causally related to the

high concentrations of air pollution

observed in the historical episodes,

there is less consensus as to the most

appropriate interpretation of the more

recent studies finding associations of

such effects with ambient PM

concentrations below the levels of the

current NAAQS (e.g., Schwartz, 1994b;

Dockery et al., 1995; Moolgolvkar et al.,

1995b; Moolgolvkar and Luebeck, 1996;

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

Wyzga and Lipfert, 1995b):

In this regard, several viewpoints currently

exist on how best to interpret the

epidemiology data: one sees PM exposure

indicators as surrogate measures of complex

ambient air pollution mixtures and reported

PM-related effects represent those of the

overall mixture; another holds that reported

PM-related effects are attributable to PM

components (per se) of the air pollution

mixture and reflect independent PM effects;

or PM can be viewed both as a surrogate

indicator as well as a specific cause of health

effects. In any case, reduction of PM

exposure would lead to reductions in the

frequency and severity of the PM-associated

health effects. (U.S. EPA, 1996a, p. 13–31)

Such alternative interpretations as to the

causality underlying the reported PMeffects associations result from a

number of specific issues that have been

raised regarding the adequacy and

strength of individual studies.

Of particular concern is the

possibility that independent risk factors,

related to both ambient PM

concentrations and the reported effects,

could potentially confound or modify

the apparent PM-effects associations.

Possible independent risk factors

include weather-related variables and

other pollutants present in the ambient

air (e.g., SO2, CO, O3, NO2), which have

been addressed to varying degrees in

most of the epidemiological studies.

Other concerns are related to the

influence of the choice of statistical

models used by investigators and to the

uncertainties introduced by the

imprecision in measurements of

ambient air pollutants, as well as the

use of such measurements as surrogates

for population exposures.11 The Criteria
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errors in measurement of pollution and in the use

of outdoor measurements to index population

exposures.

Document and Staff Paper evaluated the

studies with respect to each of these

issues, as summarized below:

(1) Many recent studies, including a

reanalysis by the Health Effects Institute

(HEI) (Samet et al., 1996), have

considered the influence of weather on

the results reported in studies of shortterm exposures, because fluctuations in

weather are associated with both

changes in PM and other pollutant

levels and the reported health effects.

The Criteria Document concludes that

the PM effects estimates are relatively

insensitive to the different methods of

weather adjustment used in these

studies, that the role of weather-related

variables has been addressed

adequately, and that it is highly unlikely

that weather can explain a substantially

greater portion of the health effects

attributed to PM than has already been

accounted for in the models (U.S. EPA,

1996a, p. 13–54).

(2) A number of recent reanalyses of

daily mortality studies have examined

the influence of other pollutants that

commonly occur in the ambient air

together with PM. Most attention has

been focused on Philadelphia, where

extensive data are available on TSP,

NO2, O3, CO, and SO2. In fact,

reanalyses of the Philadelphia data have

led HEI investigators to conclude that a

single pollutant cannot be readily

identified as the best predictor of air

pollution-related mortality in

Philadelphia based on analyses of

Philadelphia data alone (Samet et al.,

1996). Based on such single-city

analyses, some have argued that

estimated PM effects may be overstated

or potentially non-existent due to

confounding by other pollutants that

might actually be responsible for the

effects. While it is reasonable to expect

that other pollutants may play a role in

modifying the magnitude of the

estimated effects of PM on mortality,

either through pollutant interactions or

independent effects, the extent of any

such co-pollutant modification is less

clear. The Criteria Document notes that

some mortality and morbidity studies

have found little change in the PM

relative risk estimates after inclusion of

other co-pollutants in the model, and, in

analyses where the PM relative risk

estimates were reduced, the PM effects

estimates typically remained

statistically significant. Accordingly, the

Criteria Document concludes that the

PM-effects associations are valid and, in

a number of studies, not seriously

confounded by co-pollutants (U.S. EPA,

1996a, p. 13–57).

(3) Many investigators have examined

how the choice of statistical models or

the ways in which they were specified

may have influenced reported PMeffects associations. In reviewing this

issue, the Criteria Document finds that,

while model specification is important

and can influence PM-effects estimates,

appropriate modeling strategies have

been adopted by most investigators

(U.S. EPA, 1996a, section 13.4.2.2). The

Criteria Document concludes that, ‘‘the

largely consistent specific results,

indicative of significant positive

associations of ambient PM exposures

and human mortality/morbidity effects,

are not model specific, nor are they

artifactually derived due to

misspecification of any specific model.

The robustness of the results of different

modeling strategies and approaches

increases our confidence in their

validity’’ (U.S. EPA, 1996a, p. 13–54).

(4) A difficulty noted by many

reviewers in interpreting the

epidemiological studies, particularly for

quantitative purposes, is the uncertainty

and possible bias introduced by the use

of outdoor monitors to estimate a

population-level index of exposure.

Even in studies where outdoor PM

levels near population centers are well

represented by monitors, the extent to

which fluctuations in outdoor

concentrations are found to affect

indoor concentrations and personal

exposure to PM of outdoor origin

remains an issue of importance. This

issue is particularly salient since some

of the sensitive subpopulations in the

daily mortality and hospital admissions

studies can be expected to spend more

time indoors than the general

population. Some commentors have

expressed concerns regarding the lack of

correlation shown in some studies that

made cross-sectional comparisons of

outdoor PM with indoor or personal

exposures to PM (which includes PM

from the indoor and personal

environment). The Criteria Document

found, however, that on a longitudinal

basis (e.g., day-to-day), personal

exposure to PM10 can be well correlated

with outdoor measurements, and that

the effects reported in the short-term

epidemiological studies are not due to

indoor-generated particles (U.S. EPA,

1996a, p. 1–10). Specifically, the

Criteria Document concluded that ‘‘the

measurements of daily variations of

ambient PM concentrations, as used in

the time-series epidemiological studies

of Chapter 12, have a plausible linkage

to the daily variations of human

exposures to PM from ambient sources,

for the populations represented by the

ambient monitoring stations’’ (U.S. EPA,

1996a, p. 1–10).

The strength of the correspondence

between outdoor concentrations and

personal exposure levels on a day-today basis serves to reduce, but not

eliminate, the potential error introduced

by using outside monitors as a surrogate

for personal exposure. Some

commentors have suggested the net

effect of misclassifying total exposure to

PM might bias reported relationships

between outdoor PM and mortality (or

morbidity) effects towards a linear, nonthreshold relationship, when in fact a

threshold model of response may be

more appropriate. While such a

threshold has not been demonstrated in

studies to date, the potential influence

of exposure misclassification serves to

increase the uncertainty in the reported

concentration-response relationships,

particularly for the lower range of

concentrations.

(5) A closely related issue, namely

errors in the measurement of the

concentrations of air pollutants, can also

introduce uncertainty and bias in effects

estimates reported in epidemiological

studies of PM and co-pollutants. While

questions about the magnitude of

measurement error and its effect on the

PM-health effects associations have not

been resolved, some aspects of this issue

have been examined in two recent

studies (Schwartz and Morris, 1995;

Schwartz et al., 1996). These results

suggest that the influence of

measurement error for individual

variables is to bias the PM-effects

estimates downward (i.e., to

underestimate effects). These analyses,

however, do not assess the potential

effect of exposure misclassification on

effects estimates for different

components of PM, or for other copollutants. In such multiple pollutant

analyses, measurement error or, more

generally, exposure misclassification

can theoretically bias effects estimates

of PM or co-pollutants in either

direction, introducing further

uncertainties in the estimated

concentration-response relationships for

all pollutants (U.S. EPA, 1996b, pp. V–

39–43). A comprehensive, formal

treatment of the potential influences of

exposure misclassification is, therefore,

an important research need. As noted

below, however, the available evidence

on the consistency of the PM effects

relationships in multiple urban

locations with widely varying indoor/

outdoor conditions and a variety of

monitoring approaches makes it less

likely that the observed findings are an

artifact of errors in measurement of

pollution or of exposure.
65646 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

b. Consistency and Coherence of the

Health Effects Evidence

As discussed above, the individual

epidemiological studies indicate that

health effects are likely associated with

PM, even after taking into account

issues regarding the adequacy and

strength of these studies. However,

because individual studies are

inherently limited as a basis for

addressing questions of causality, the

consistency and coherence of the

evidence across the studies have also

been considered in the Criteria

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

13.4.2.5) and Staff Paper (U.S. EPA,

1996b, pp. V–54–58), as summarized

below.

Of the more than 80 community

epidemiological studies that evaluated

associations between short-term

concentrations of various PM indicators

and mortality and morbidity endpoints

(U.S. EPA, 1996a, Tables 12–2, 12–8 to

13), more than 60 such studies reported

positive, statistically significant

associations. These studies have been

conducted by a number of different

investigators, in a number of geographic

locations throughout the world (with

different climates and co-pollutants),

using a variety of statistical techniques,

and with varying temporal

relationships. Despite these differences,

the finding of statistically significant

associations is relatively consistent

across the studies (U.S. EPA, 1996a,

Table 12–2).

More specifically, in looking across

those studies that evaluated associations

between short-term PM10 concentrations

and mortality and morbidity endpoints,

various aspects of consistency and

coherence can be observed. These

observations are discussed below in

reference to Figure 1 (adapted from

Figure V–2 in the Staff Paper). Figure 1

displays the estimated relative risk for a

50 μg/m3 increase in measured 24-hour

PM10 levels, derived from studies that

the Criteria Document concluded permit

quantitative comparisons across various

cause-specific mortality and morbidity

endpoints (i.e., respiratory hospital

admissions, COPD or ischemic heart

disease hospital admissions, and cough

and lower and upper respiratory

symptoms) (U.S. EPA, 1996b, Tables

V–4, V–6; U.S. EPA, 1996a, Section

12.3.2.2).

Figure 1 illustrates that the effects

estimates for each health endpoint are

relatively consistent across the studies.

Some variation would be expected,

however, due to the differences among

the study areas in the concentrations

and relative composition of PM and

other air pollutants, and in the

demographic and socioeconomic

characteristics of the study populations,

including the distributions of sensitive

subpopulations, as well as a result of

random error. Thus, the Criteria

Document concludes that the relatively

small ranges of variability in the effects

estimates observed in these studies are

consistent with expectations based on

assuming causal relationships between

mortality and morbidity effects and PM

exposure (U.S. EPA, 1996a, Section

13.4.1.1).

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Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65647

BILLING CODE 6560–50–C
65648 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

As noted above, it is reasonable to

expect that co-pollutants present in the

study areas might modify the apparent

effects of PM by atmospheric

interactions (e.g., through dissolution/

adsorption or aerosol formation

reactions) or by independent and/or

interactive effects on sensitive

subpopulations (e.g., respiratory

function changes from exposures to O3

or SO2). Moreover, the possibility of

exposure misclassification for primary

gaseous pollutants (e.g., CO, SO2) could

diminish their apparent significance

relative to PM. If such PM effects

modification was occurring to an

appreciable degree, the associations

with PM would be expected to be

consistently high in areas with high copollutant concentrations, and

consistently low in areas with low copollutant concentrations. On the

contrary, in an examination of reported

PM10-mortality associations as a

function of the varying levels of copollutants in study areas, consistent

effects estimates were observed across

wide ranges of co-pollutant

concentrations (U.S. EPA, 1996b,

Figures V–3a, V–3b). While it is possible

that different pollutants may serve to

confound or otherwise influence

particles in different areas, it seems

unlikely that this would lead to such

similar associations and consistent

relative risk estimates as have been

reported for PM in a large number of

studies.

In addition to the consistency

observed in the PM associations for each

health endpoint, these studies also

exhibit coherence in the kinds of health

effects that have been associated with

PM exposure. For example, the

association of PM with mortality is

mainly linked to respiratory and

cardiovascular causes, which is

coherent with the observed PM

associations with respiratory- and

cardiovascular-related hospital

admissions.

Coherence is also observed across

studies of both short- and long-term

exposures to PM. For example, the

existence of statistically significant PMmortality associations from long-term as

well as short-term exposures reinforces

the likelihood that PM is a causal factor

for premature mortality relative to that

which might be reasonably inferred

from either type of study alone.

Furthermore, the fact that mortality has

been associated with both short- and

long-term exposures is important with

respect to the credibility of ambient PM

as a cause of mortality involving

significant life-years lost. If there was no

evidence of excess mortality from

studies of long-term exposures, it might

be inferred based on the short-term

studies that reported daily mortality was

due solely to lifespan shortening of only

days or weeks in individuals already

near death.

This qualitative coherence is further

supported by the quantitative coherence

across several health endpoints. For

example, if the relationships were

causal, PM-related hospitalization

would be expected to occur

substantially more frequently than PMrelated mortality (even though many

deaths attributed to air pollution

probably do not occur in hospitals). The

Criteria Document notes that is indeed

the case (U.S. EPA, 1996a, p. 13–64 and

Table 13–8). Based on the relative risk

estimates from the short-term exposure

studies, expected increases in

respiratory- and cardiovascular-related

hospital admission rates associated with

PM are substantially larger than the

expected increases in mortality rates for

the same causes.

The coherence in the epidemiological

evidence is strengthened by those

studies in which different health effects

are associated with ambient PM

concentrations in the same study

population. Specifically, studies of

Detroit, Birmingham, Philadelphia, and

Utah Valley all find that ambient PM

concentrations in each of these cities are

associated with increases in a variety of

respiratory- and cardiovascular-related

health effects in the elderly and adult

subpopulations in these cities (U.S.

EPA, 1996a, p. 13–66).

As summarized above, there is

evidence that PM exposure is associated

with increased risk for health effects

ranging in severity from asymptomatic

pulmonary function decrements, to

respiratory and cardiopulmonary illness

requiring hospitalization, to excess

mortality from respiratory and

cardiovascular causes (U.S. EPA, 1996a,

p. 13–67). The consistency and

coherence of the epidemiological

evidence greatly adds to the strength

and plausibility of the reported

associations. The Criteria Document

concludes that the overall coherence of

the health effects evidence suggests (a

likely causal role of ambient PM in

contributing to the reported effects)

(U.S. EPA, 1996a, p. 13–1).

4. Particulate Matter Fractions of

Concern

The previous criteria and standards

review included an integrated

examination of available literature on

the potential mechanisms,

consequences, and observed responses

to particle deposition in the major

regions of the respiratory tract (U.S.

EPA, 1982b). The review concluded

with general agreement that particles

that deposit in the thoracic region

(tracheobronchial and alveolar regions)

(i.e., particles smaller than 10 μm

diameter), were of greatest concern for

public health. Thus, the PM NAAQS

were revised as a result of the last

review from TSP to PM10 standards.

Particle dosimetry and mechanistic

considerations developed in the current

review continue to support the view

that, for particles that typically occur in

the ambient air, those that are capable

of penetrating to the thoracic regions of

the respiratory tract are of greatest

concern to health (U.S. EPA, 1996b,

Section V).

Section V.F of the Staff Paper

summarizes the evidence regarding the

health effects associated with the fine

(PM2.5) and coarse (PM10–2.5) fractions of

PM10. Both fine and coarse fraction

particles can deposit in the thoracic

regions of the respiratory tract.

However, based on atmospheric

chemistry, exposure, and mechanistic

considerations, the Criteria Document

concludes it would be most appropriate

to ‘‘consider fine and coarse mode

particles as separate subclasses of

pollutants’’ (U.S. EPA, 1996a, p. 13–94),

and to measure them separately as a

basis for planning effective control

strategies.

Given the significant physical and

chemical differences between the two

subclasses of PM10 (U.S. EPA, 1996b,

pp. V–69–78), it is reasonable to expect

that differences may exist between fine

and coarse fraction particles in both the

nature of potential effects and the

relative concentrations required to

produce such effects. The Criteria

Document highlights a number of

specific components of PM that could

be of concern to health, including

components typically within the fine

fraction (e.g., acid aerosols including

sulfates, certain transition metals, diesel

particles, and ultrafine particles), and

other components typically within the

coarse fraction (e.g., silica, resuspended

dust, and bioaerosols). While

components of both fractions can

produce health effects, in general the

fine fraction appears to contain more of

the reactive substances potentially

linked to the kinds of effects observed

in the epidemiological studies. The fine

fraction also contains by far the largest

number of particles and a much larger

aggregate surface area than the coarse

fraction. The greater surface area of the

fine fraction increases the potential for

surface absorption of other potentially

toxic components of PM (e.g., metals,

acids, organic materials), and

dissolution or absorption of pollutant
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65649

12The 1986 Staff Paper cited PM studies

conducted in essentially 3 locations as a basis for

the 24-hour standard, and 4 studies involving a

total of 10 cities as a basis for the annual standard;

none measured PM10 directly (EPA, 1986b).

13As discussed in Chapter IV of the Staff Paper,

annual average background levels of PM2.5 are

estimated to range from approximately 1–4 μg/m3

in western areas and 2–5 μg/m3 in eastern areas,

with the maximum 24-hour levels estimated to

reach as high as about 15–20 μg/m3 over the course

of a year. Background PM is defined in the Staff

Paper as the distribution of PM concentrations that

Continued

gases and their subsequent deposition in

the thoracic region.

The Staff Paper presents the available

quantitative and qualitative information

on the effects of fine particles and its

constituents (U.S. EPA, 1996b, pp. V–

60–63). Because of the number of

pertinent studies published since the

last review, far more quantitative

epidemiological data exist today for

relating fine particles to mortality,

morbidity, and lung function changes in

sensitive subpopulations, in terms of

both short- and long-term ambient

concentrations, than was the case for

PM10 at the conclusion of the last

review.12 Like the more numerous PM10

studies, the fine particle studies (e.g.,

studies using PM2.5, sulfates) generally

find statistically significant positive

associations between fine particle

concentrations and mortality and

morbidity endpoints, with more than 20

studies conducted in a number of

geographic locations throughout the

world, including the U.S., Canada, and

Europe. More specifically, daily

mortality effects estimates reported for

PM2.5 fall within the range of

approximately 3 to 6 percent increases

in relative risk for a 25 μg/m3 increase

in 24-hour average PM2.5

concentrations, for those cities with

statistically significant positive

associations (U.S. EPA, 1996b, Table V–

12). This collection of studies shows

qualitative coherence in the types of

health effects associated with fine

particle exposure including mortality,

morbidity, symptoms, and changes in

lung function (U.S. EPA, 1996b, Tables

V–11 to V–13).

By contrast, the current review finds

much less direct epidemiological or

toxicological evidence regarding the

potential effects of coarse fraction

particles at typical ambient

concentrations. As discussed in the Staff

Paper, community epidemiological

studies directly comparing the effects of

fine and coarse fraction particles

provide evidence that reported PM

associations with mortality and

decreased lung function in children are

more likely associated with fine fraction

particles (U.S. EPA, 1996b, pp. V–63–

67). On the other hand, both past and

current reviews of occupational and

toxicological literature have found

ample qualitative reasons for concern

about higher-than-ambient

concentrations of coarse fraction

particles. At such elevated levels, coarse

fraction particles are linked to shortterm effects such as aggravation of

asthma and increased upper respiratory

illness, which are consistent with

enhanced deposition of coarse fraction

particles in the tracheobronchial region

(U.S. EPA, 1996a, p. 13–51). Children

may be particularly sensitive to such an

effect, since they typically spend more

time in outdoor activities, such that they

may encounter higher exposures and

doses of coarse fraction particles than

other potentially sensitive populations.

In addition, long-term deposition of

insoluble coarse fraction particles in the

alveolar region may have the potential

for enhanced toxicity, in part because

clearance from this region of the lung is

significantly slower than from the

tracheobronchial region. Limited

qualitative support for this concern is

found in autopsy studies of animals and

humans exposed to various ambient

crustal dusts at or slightly above

ambient levels typical in the Southwest.

Unlike the case for fine particles, the

clearest community epidemiological

evidence regarding coarse fraction

particles finds such effects only in areas

with numerous marked exceedances of

the current PM10 standard (U.S. EPA,

1996a, p. 13–51). In this regard, it

appears that the weight of the available

evidence allowing direct comparisons

between the two size fractions of PM10

suggests that ambient coarse fraction

particles are either less potent or a

poorer surrogate for community effects

of air pollution than are fine fraction

particles.

B. Quantitative Risk Assessment

The Staff Paper presents the results of

a quantitative assessment of health risks

for two example cities, including risk

estimates for several categories of health

effects associated with: (1) existing PM

air quality levels, (2) projected PM air

quality levels that would occur upon

attainment of the current PM10

standards, and (3) projected PM air

quality levels that would occur upon

attainment of alternative PM2.5

standards. As an integral part of this

assessment, qualitative and, where

possible, quantitative characterizations

of the uncertainties in the resulting risk

estimates have been developed, as well

as information on baseline incidence

rates for the health effects considered.

The risk assessment is intended as an

aid to the Administrator in judging

which alternative PM NAAQS would

reduce risks sufficiently to protect

public health with an adequate margin

of safety, recognizing that such

standards will not be risk-free.

As discussed in Section A above, the

Criteria Document concludes that the

overall consistency and coherence of the

epidemiological evidence suggests a

likely causal role of ambient PM in

contributing to adverse health effects.

An alternative interpretation is that PM

may be serving as an index for the

complex mixture of pollutants in urban

air. The manner in which the PM

epidemiological evidence is used in this

risk assessment is consistent with either

of these alternative interpretations of the

evidence.

Despite the consistency and

coherence of the epidemiological

evidence reporting health effects

associated with PM, EPA cautions that

quantitative risk estimates derived from

these studies include significant

uncertainty, and thus, should not be

viewed as demonstrated health impacts.

EPA believes, however, that they do

represent reasonable estimates as to the

possible extent of risk for these effects

given the available information.

1. Overview

The following discussion briefly

summarizes the scope of the risk

assessment and key components of the

risk model. A more detailed discussion

of the risk assessment methodology and

results is presented in the Staff Paper

and technical support documents (Abt

Associates, 1996a, b).

The risk assessment focused on

selected health effects endpoints

discussed above for which adequate

quantitative information is available

(U.S. EPA, 1996a, Table VI–2),

including increased daily mortality,

increased hospital admissions for

respiratory and cardiopulmonary

causes, and increased respiratory

symptoms in children. All

concentration-response relationships

used in the assessment were based on

findings from human epidemiological

studies, and consequently rely on fixedsite, population-oriented, ambient

monitors as a surrogate for actual PM

exposures.

Risk estimates were developed for the

urban centers of two example cities, one

eastern (Philadelphia County) and one

western (Southeast Los Angeles

County), for which sufficient PM10 and

PM2.5 air quality data were available.

Risk estimates were calculated only for

ambient PM levels in excess of

estimated annual average background

levels. 13 This approach of estimating
65650 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

would be observed in the U.S. in the absence of

anthropogenic emissions of PM and precursor

emissions of VOC, NOx, and SOx in North America.

14See Table VI–2 in the Staff Paper (U.S. EPA,

1996b) for information about the reported PM mean

and range of concentration levels observed in the

various epidemiological studies used in the risk

assessment.

15 In the examples presented here the ranges of

estimated incidences are based on the 90 percent

credible intervals from the risk analyses. The 90

percent credible interval represents the range from

the 5th percentile to the 95th percentile of the

estimated risk distribution, and provides a

reasonable characterization of the range of

estimated values that results from the various

uncertainties that could be incorporated

quantitatively in the risk analyses.

16 Incidence estimates of roughly 400 to 1,000

excess deaths per year represent roughly 2 to 4

percent of the total mortality incidence in Los

Angeles County.

risks in excess of background was

judged to be more relevant to policy

decisions regarding ambient air quality

standards than risk estimates that

include effects potentially attributable

to uncontrollable background PM

concentrations. For these analyses, an

estimate of the annual average

background level was used, rather than

a maximum 24-hour value, since

estimated risks were aggregated for each

day throughout the year. Risks have

been estimated for a recent year of PM

air quality data in each of the two

example cities. Risk estimates were

calculated for Los Angeles County with

PM levels adjusted downward to just

attain the current PM10 standards.

Finally, risk estimates were also

calculated for both example cities where

PM levels were further adjusted to just

attain various alternative PM2.5

standards.

As discussed in Chapter 13 of the

Criteria Document, the interpretation of

specific concentration-response

relationships is the most problematic

issue in conducting risk assessments for

PM-associated health effects at this

time, due to (1) the absence of clear

evidence regarding mechanisms of

action for the various health effects of

interest; (2) uncertainties about the

shape of the concentration-response

relationships; and (3) concern about

whether the use of ambient PM2.5 and

ambient PM10 fixed-site monitoring data

adequately reflects the relevant

population exposures to PM that are

responsible for the reported health

effects. The reported study results used

in this assessment are based on linear

concentration-response models

extending only down to the lowest PM

concentrations observed within each

study. 14 Thus, concentration-response

relationships were not extrapolated

below the range of the PM concentration

air quality data reported in any given

study. Alternatively, the data do not

rule out the possibility of an underlying

non-linear, threshold concentrationresponse relationship. Although these

alternative interpretations of study

results could significantly affect

estimated risks, only very limited

information is available to aid in

resolving this issue (U.S. EPA, 1996a,

section 13.6.5). Thus, the approach

taken in the PM risk assessment is to

address alternative concentrationresponse models through sensitivity and

integrated uncertainty analyses to

develop ranges of estimated risks, rather

than characterizing any particular set of

risk estimates as representing the ‘‘best’’

estimates.

Risk estimates for PM-associated

health effects in excess of background

PM levels (i.e., excess risk) were

initially developed based on a set of

‘‘base case’’ assumptions. These base

case assumptions reflect the use of: (1)

Mid-point estimates from the ranges of

estimated annual average background

concentrations for the eastern and

western regions of the U.S. to represent

typical background levels; (2)

essentially linear concentrationresponse relationships down to the

lowest PM level observed in each study;

and (3) annual distributions of 24-hour

PM10 and PM2.5 concentrations that

were obtained by taking a recent year of

PM air quality data in each example city

and adjusting all PM concentrations

exceeding the estimated background

concentration level by the same

percentage to simulate attainment of

alternative standards (referred to as a

‘‘proportional rollback’’ approach).

While there are many different methods

of adjusting PM air quality distributions

to reflect future attainment of alternative

standards, analysis of historical data

(Abt, 1996b) support the use of such a

proportional method for adjusting air

quality values.

For comparison with alternative

standards, it is desirable to estimate

health risks associated with PM air

quality that do not include the effect of

concentrations in excess of those

allowed by the current PM10 standards.

Since the air quality in one of the two

cities examined, Los Angeles, exceeded

the current PM10 standards, both PM10

and PM2.5 concentrations were

proportionally rolled back (preserving

the PM2.5/PM10 ratio) to air quality

concentrations that just attain the

current PM10 standards. While this

necessarily introduces additional

uncertainty into the risk estimates, it is

required in order to compare risks

associated with attaining the current

PM10 standards with risks associated

with attainment of alternative PM2.5

standards.

Sensitivity analyses have been

conducted to examine the impact on the

risk estimates of these and other

assumptions, by varying each

assumption independently. For

example, the impact of using alternative

estimates for background concentrations

was examined by replacing the midpoint estimate with the lower and the

upper end of the range of estimated

annual average background levels. In

addition, integrated uncertainty

analyses have been conducted

specifically for the excess mortality

associated with PM exposures to

examine the range of risk estimates

when several key assumptions and

uncertainties are considered

simultaneously, rather than one at a

time. The key issues examined in the

integrated uncertainty analyses include:

(1) Variability in the underlying

concentration-response relationship

resulting from combining the results of

PM2.5 mortality studies in six cities to

estimate the relative risks in the two

example cities; (2) consideration of

alternative potential threshold

concentrations; (3) inclusion of the

range of estimates for PM background

levels; and (4) use of alternative PM air

quality adjustment procedures to

simulate attainment of alternative

standards based on analysis of historical

data.

2. Key Observations

The discussion below highlights the

key observations and insights from the

risk assessment, together with important

caveats and limitations.

(1) Fairly wide ranges of estimates of the

incidence of PM-related mortality and

morbidity effects were calculated for the two

locations analyzed when the effects of key

uncertainties and alternative assumptions

were considered.

This point is illustrated below for

mortality estimates using base case and

alternative assumptions, as well as for

morbidity estimates using base case

assumptions alone.15 For example, the

incidence of mortality associated with

short-term PM2.5 exposures upon

attainment of the current PM10

standards was estimated to range from

approximately 400 to 1,000 deaths per

year in Los Angeles County (with a

population of 3.6 million) under base

case assumptions, and from

approximately 100 to 1,000 deaths using

alternative assumptions considered in

the integrated uncertainty analysis.16

For Philadelphia County (with a

population of 1.6 million), a city with

better air quality than Los Angeles and

already well below the current PM10
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65651

17 Incidence estimates of 200 to 500 excess deaths

per year associated with PM exposures represent

roughly 1 to 2.5 percent of total mortality in

Philadelphia County.

18 Incidence estimates of 250 to 1,600 respiratoryrelated hospital admissions associated with PM

exposures represent roughly 1.5 to 10 percent of

total respiratory-related hospital admissions in Los

Angeles County. Incidence estimates of 23,000 to

58,000 cases of respiratory symptoms represent

roughly 15 to 40 percent of total respiratory

symptom cases in Los Angeles County.

19 Incidence estimates of 70 to 450

cardiopulmonary-related hospital admissions

associated with PM exposures represent roughly 0.5

to 3.5 percent of total respiratory-related hospital

admissions in Philadelphia County. Incidence

estimates of 6,000 to 15,000 cases of respiratory

symptoms associated with PM exposures represent

roughly 10 to 30 percent of total respiratory

symptom cases in Philadelphia County.

20The annual standards analyzed were simulated

by adjusting the annual average concentration at the

population-oriented monitor in the study area with

the highest measured values to the standard level

under consideration.

21The alternative daily standards analyzed were

the 1-expected-exceedance form of the standard.

22 In Los Angeles County, a 45–50% reduction in

excess mortality and morbidity associated with

short-term PM2.5 exposures represents decreases of

roughly 320 excess deaths, 540 cardiopulmonaryrelated hospital admissions, and 22,000 cases of

respiratory symptoms; a 20–25% reduction

represents decreases of roughly 150 excess deaths,

250 cardiopulmonary-related hospital admissions,

and 11,000 cases of respiratory symptoms.

23 In Philadelphia County, a 15–20% reduction in

excess mortality and morbidity associated with

short-term PM2.5 exposures represents decreases of

roughly 60 excess deaths, 70 cardiopulmonaryrelated hospital admissions, and 2,000 cases of

respiratory symptoms.

24 In Los Angeles County, an 85% reduction in

excess mortality and morbidity associated with

short-term PM2.5 exposures represents decreases of

roughly 590 excess deaths, 1000 cardiopulmonaryrelated hospital admissions, and 37,000 cases of

respiratory symptoms; a 40–50% reduction

represents decreases of roughly 280 excess deaths,

480 cardiopulmonary-related hospital admissions,

and 20,000 cases of respiratory symptoms.

25 In Philadelphia County, a 70–75% reduction in

excess mortality and morbidity associated with

short-term PM2.5 exposures represents decreases of

roughly 260 excess deaths, 320 cardiopulmonaryrelated hospital admissions, and 8,000 cases of

respiratory symptoms; a 10% reduction represents

decreases of roughly 40 excess deaths, 50

cardiopulmonary-related hospital admissions, and

1,000 cases of respiratory symptoms.

standards, estimated mortality

associated with short-term PM2.5

exposures ranged from approximately

200 to 500 deaths per year under base

case assumptions, and from

approximately 20 to 500 deaths per year

under alternative assumptions

considered in the integrated uncertainty

analyses.17

Morbidity effects associated with

exposures to PM2.5 are estimated using

base case assumptions to range from

approximately 250 to 1,600 respiratoryrelated hospital admissions per year and

from 23,000 to 58,000 cases of

respiratory symptoms in children per

year for Los Angeles.18 For Philadelphia

County, morbidity effects associated

with exposures to PM2.5 are estimated

using base case assumptions to range

from about 70 to 450 respiratory-related

hospital admissions and from 6,000 to

15,000 cases of respiratory symptoms

per year.19

(2) Risk estimates associated with

attainment of alternative PM2.5 standards

described in the Staff Paper show highly

variable reductions in PM-associated risk

which are a function of the particular city

and the levels of the standards.

Risk estimates for PM-associated

mortality and morbidity health effects

have been estimated for alternative

annual PM2.5 standards 20 of 15 and 20

μg/m3, alone and in combination with

alternative daily standards 21 ranging

from 25 to 65 μg/m3. For two cases

considering only annual PM2.5

standards, the mean estimates (using

base case assumptions) of excess

mortality and morbidity associated with

short-term PM2.5 exposures in Los

Angeles County were reduced by

roughly 45–50% for attainment of an

annual PM2.5 standard level of 15 μg/m3,

and by roughly 20–25% for attainment

of an annual standard level of 20 μg/

m3.22 These estimates of risk reduction

are incremental to the risk reductions

associated with attainment of the

current PM10 standards as explained

above. Similarly, for an area already in

attainment with the current PM10

standards (Philadelphia County), mean

estimates of excess morbidity and

mortality associated with short-term

exposures to PM2.5 were not affected by

an annual standard of 20 μg/m3 but were

reduced by about 15–20% upon

attainment of an annual PM2.5 standard

of 15 μg/m3.23

As noted above, risk estimates for PMassociated mortality and morbidity

health effects also have been estimated

for alternative 24-hour PM2.5 standards

ranging from 25 to 65 μg/m3 (in

combination with an annual standard of

20 μg/m3). These combinations of

standards result in cases for which the

24-hour standard was generally

controlling the degree of risk reduction.

Mean estimates of excess mortality and

morbidity associated with short-term

PM2.5 exposures in Los Angeles County

were reduced by roughly 85% for a

daily standard of 25 μg/m3, and by

roughly 40–50% for a daily standard of

65 μg/m3, beyond the risks associated

with attainment of the current PM10

standards when base case assumptions

were used.24 Similarly, for Philadelphia

County, the mean estimates of excess

mortality and morbidity were reduced

by roughly 70–75% for a daily standard

of 25 μg/m3, and about 10% for a daily

standard of 65 μg/m3.25

(3) Based on the results from the sensitivity

analyses of key uncertainties and the

integrated uncertainty analyses, the single

most important factor influencing the

uncertainty associated with the risk estimates

is whether or not a threshold concentration

exists below which PM-associated health

risks are not likely to occur.

Alternative assumed threshold

concentrations considered in these

analyses result in as much as a 3- to 4-

fold difference in estimated risk

associated with PM exposures in Los

Angeles County (U.S. EPA, 1996b,

Figure VI–8; Abt Associates, 1996b,

Exhibits 7.19 and 7.20) depending on

the likelihood imputed to various PM2.5

threshold concentrations. In an area

with PM concentrations well below the

current PM standards (e.g., Philadelphia

County), differences in risk associated

with a recent year of PM air quality may

be even greater for alternative threshold

assumptions, since these locations

would be expected to have a greater

proportion of PM concentrations below

assumed threshold concentrations.

(4) Based on results from the sensitivity

analyses of key uncertainties and/or the

integrated uncertainty analyses, quantitative

consideration of the following uncertainties

is estimated to have a much more modest

impact on the risk estimates: (a) Inclusion of

individual co-pollutant species when

estimating PM effect sizes (based on reported

estimates of effects modification); (b) the

choice of approach to adjusting the slope of

the concentration-response relationship

when analyzing alternative possible

threshold concentrations; (c) the value

chosen to represent average background PM

concentrations; and (d) the choice of air

quality adjustment approaches for simulating

attainment of alternative PM standards.

(5) Additional sources of uncertainty

associated with risk analyses of alternative

PM2.5 standard scenarios which could not be

addressed quantitatively include: (a)

Uncertainty in the pattern of air quality

concentration reductions that would be

observed across the distribution of 24-hour

PM2.5 concentrations in areas attaining the

standards, and (b) uncertainty concerning the

degree to which PM concentration-response

relationships may reflect contributions from

other pollutants, or the particular

contribution of certain constituents of PM2.5,

and whether such constituents would be

reduced in similar proportion as the

reduction in PM2.5.

To the extent concentrations of other

combustion source co-pollutants are

reduced more or less than PM2.5

concentrations in attaining alternative

PM2.5 standards, estimates of health

effects reduced by such standards

would be expected to be related to the

degree to which these co-pollutants in

fact play a role in producing or

modifying PM-associated effects.

Similarly, if specific constituents of

PM2.5 mass have differing potencies in
65652 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

producing effects relative to other PM2.5

constituents, estimates of risk reduced

would be expected to vary if these

constituent concentrations are reduced

to different degrees by control strategies

designed to attain alternative PM2.5

standards.

(6) The peak 24-hour PM2.5 concentrations

appear to contribute a relatively small

amount to the total health risk posed by the

entire air quality distribution as compared to

the risks associated with the low to midrange concentrations.

Standards with a 24-hour averaging

time are traditionally based on the

highest 24-hour values observed in a

year, concentrations for which the risk

on an individual day is highest.

However, examining a typical

distribution of ambient 24-hour PM2.5

concentrations over the course of a year

in conjunction with PM2.5

concentration-response relationships, as

illustrated in Figures 2a, 2b, and 2c, the

peak PM2.5 concentrations contribute

much less to the total health risk over

a year than the low- to mid-range PM2.5

concentrations.

More specifically, Figures 2a, 2b, and

2c illustrate some of the characteristics

of the integration of air quality

distributions and concentrationresponse relationships as used to

predict total risk from ambient particle

exposures across a year. These figures

show the relative contribution of

different portions of a typical urban

ambient PM2.5 concentration

distribution to mortality risk from shortterm exposures. As shown in Figures 2b

and 2c, low- to mid-range

concentrations (e.g., 10–50 μg/m3)

account for the largest amount of

estimated mortality risk on an

annualized basis.

The portion of the air quality

distribution that contributes

significantly to total health risk over the

course of a year is, of course, smaller if

effects thresholds are assumed or if

much higher levels of estimated

background PM2.5 concentrations are

used (Figure 2c). However, even with

this assumption, most of the aggregate

risk associated with short-term

exposures likely results from the large

number of days during which the 24-

hour average concentrations are in the

low- to mid-range, below peak 24-hour

concentrations. Even though higher 24-

hour concentrations, including peaks

above 70 μg/m3, clearly contribute more

mortality per day than low- to midrange concentrations, the much larger

number of days within the low- to midranges results in this interval being

associated with the largest proportion of

the total risk.

BILLING CODE 6560–50–P

Figure 2a. Illustrative Air Quality Distribution of 24-Hour PM2.5 Concentrations—This figure shows an example of

a frequency distribution of the number of days exceeding various 24-hour average PM2.5 concentrations over a year.

Figure 2b. Estimated Mortality Risks Using A Non-Threshold Concentration-Response Relationship—This figure illustrates

the proportion of estimated mortality incidence, using a non-threshold concentration-response relationship, associated

with each concentration range shown above in Figure 2a.
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65653

BILLING CODE 6560–50–C

Figure 2c. Estimated Mortality Risks Using An Illustrative Threshold Concentration-Response Relationship—This figure

illustrates the proportion of estimated mortality incidence, using an example threshold concentration of 18 μg/m3

PM2.5, associated with each concentration range shown above in Figure 2a.

An annual PM2.5 standard would

almost certainly require areas whose air

quality concentrations are above those

necessary for attainment to reduce PM2.5

concentrations across a wide range of

the 24-hour air quality distribution

rather than just a few high 24-hour

values, thus resulting in more

significant risk reduction than would a

24-hour standard set so as to control the

peak concentrations. Further, an annual

standard would be expected to lead to

greater consistency in the risk reduced

in different geographic areas having

similar initial air quality than would a

24-hour standard of similar impact, in

terms of the number of areas affected.

Such a 24-hour standard would focus on

reducing the highest 24-hour

concentrations rather than on the entire

air quality distribution.

(7) There is greater uncertainty about

estimated excess mortality (and other effects)

associated with PM exposures as one

considers increasingly lower concentrations

approaching background levels.

As discussed in Section A above, one

of the most important uncertainties

related to estimating excess mortality

associated with PM exposures is the

shape of the concentration-response

relationship. The existing

epidemiological data reporting excess

mortality associated with PM exposures

do not rule out the possibility that there

may be a threshold concentration below

which excess mortality associated with

PM exposures does not occur. As one

considers progressively higher PM

concentrations it is increasingly

unlikely that there is a threshold at

these higher levels. In contrast, as one

considers increasingly lower PM

concentrations, there is increasing

uncertainty about the shape and

magnitude of the estimated

concentration-response relationship

over the lower range of concentrations.

This increasing uncertainty is due to

questions about: (1) The possible impact

of multiple co-pollutants on the

estimated concentration-response

relationships; (2) whether exposure

misclassification associated with the use

of ambient monitors as a measure of

population exposure might be masking

a non-linear relationship; and (3)

whether a biological threshold may exist

below which excess mortality associated

with PM exposures does not occur. In

addition, there is uncertainty about

background levels, and thus about the

extent to which effects associated with

PM exposures at concentrations

approaching estimated background

levels are attributable to controllable,

non-background sources of ambient PM.

C. Need for Revision of the Current

Primary PM Standards

The overarching issue in the present

review of the primary NAAQS is

whether, in view of the advances in

scientific knowledge reflected in the

Criteria Document and Staff Paper, the

existing standards should be revised

and, if so, what revised or new

standards would be appropriate. The

concluding section of the integrative

summary of health effects information

in the Criteria Document provides the

following summary of the science with

respect to this issue:

The evidence for PM-related effects from

epidemiologic studies is fairly strong, with

most studies showing increases in mortality,

hospital admissions, respiratory symptoms,

and pulmonary function decrements

associated with several PM indices. These

epidemiologic findings cannot be wholly

attributed to inappropriate or incorrect

statistical methods, misspecification of

concentration-effect models, biases in study

design or implementation, measurement

errors in health endpoint, pollution

exposure, weather, or other variables, nor

confounding of PM effects with effects of

other factors. While the results of the

epidemiology studies should be interpreted

cautiously, they nonetheless provide ample

reason to be concerned that there are

detectable health effects attributable to PM at

levels below the current NAAQS (U.S. EPA,

1996a, p. 13–92).

Given the nature of the health effects

in question, this finding clearly suggests

that revision of the current NAAQS is

appropriate. The extensive PM

epidemiological data base provides

evidence of serious health effects (e.g.,

mortality, exacerbation of chronic

disease, increased hospital admissions)

in sensitive subpopulations (e.g., the

elderly, individuals with

cardiopulmonary disease). Although the

increase in relative risk is small for the

most serious outcomes (see Figure 1), it
65654 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

26Epidemiological studies alone cannot be used

to demonstrate mechanisms of action, but they can

provide evidence useful in making inferences with

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

V–9).

is likely significant from an overall

public health perspective, because of

the large number of individuals in

sensitive subpopulations that are

exposed to ambient PM and the

significance of the health effects (U.S.

EPA, 1996a, p. 1–21).

While the lack of demonstrated

mechanisms that explain the range of

epidemiological findings is an

important caution, which presents

difficulties in providing an integrated

assessment of PM health effects

research, qualitative information from

laboratory studies of the effects of

particle components at high

concentrations and dosimetry

considerations suggest that the kinds of

effects observed in community studies

(e.g., respiratory- and cardiovascularrelated responses) are at least plausibly

related to PM.26 Indeed, the Criteria

Document and Section V.E of the Staff

Paper point to the consistency of the

results of the epidemiological studies

from a large number of different

locations and the coherent nature of the

observed effects as being suggestive of a

likely causal role of ambient PM in

contributing to the reported effects.

Given the evidence that such effects

may occur at levels below the current

standards, the serious nature and

potential magnitude of the public health

risks involved, and the need to consider

the fine and coarse fractions as distinct

classes of particles, the Staff Paper and

the CASAC (Wolff, 1996b) concluded

that revision of the current standards is

clearly appropriate. Moreover, at the

May 1996 public meeting (U.S. EPA,

1996e), and in separate written

comments (including Lippmann et al.,

1996), a majority of CASAC panel

members recommended revisions that

would strengthen the health protection

provided by the current PM standards.

Based on the rationale and

recommendations contained in the Staff

Paper and the CASAC closure letter, the

Administrator concludes that the

current PM standards should be revised.

D. Indicators of PM

In formulating alternative approaches

to establishing adequately protective,

effective, and efficient PM standards, it

is necessary to specify the fraction of

particles found in the ambient air that

should be used as the indicator(s) for

the standards. In this regard, the most

recent assessment of scientific

information in the Criteria Document,

summarized in Chapters IV and V of the

Staff Paper, continues to support past

staff and CASAC recommendations

regarding the selection of size-specific

indicators for PM standards. More

specifically, the Staff Paper finds that

the following conclusions reached in

the 1987 review remain valid:

(1) Health risks posed by inhaled

particles are influenced both by the

penetration and deposition of particles

in the various regions of the respiratory

tract and by the biological responses to

these deposited materials.

(2) The risks of adverse health effects

associated with deposition of ambient

fine and coarse fraction particles in the

thoracic (tracheobronchial and alveolar)

regions of the respiratory tract are

markedly greater than for deposition in

the extrathoracic (head) region.

Maximum particle penetration to the

thoracic region occurs during oronasal

or mouth breathing.

(3) The risks of adverse health effects

from extrathoracic deposition of general

ambient PM are sufficiently low that

particles which deposit only in that

region can safely be excluded from the

standard indicator.

(4) The size-specific indicator(s)

should represent those particles capable

of penetrating to the thoracic region,

including both the tracheobronchial and

alveolar regions.

These conclusions, together with

information on the dosimetry of

particles in humans, were the basis for

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

PM10, that includes particles with an

aerodynamic diameter smaller than or

equal to a nominal 10 μm. The recent

information on human particle

dosimetry contained in the Criteria

Document provides no basis for

changing 10 μm as the appropriate cut

point for particles capable of penetrating

to the thoracic regions.

The Staff Paper concludes, however,

that continued use of PM10 as the sole

indicator for the PM standards would

not provide the most effective and

efficient protection from the health

effects of particulate matter (U.S. EPA,

1996b, pp. VII–4–11). The recent health

effects evidence and the fundamental

physical and chemical differences

between fine and coarse fraction

particles have prompted consideration

of separate standards for the fine and

coarse fractions of PM10. In this regard,

the Criteria Document concludes that

fine and coarse fractions of PM10 should

be considered separately (U.S. EPA,

1996a, p. 13–93). Taking into account

such information, CASAC found

sufficient scientific and technical bases

to support establishment of separate

standards relating to these two fractions

of PM10. Specifically, CASAC advised

the Administrator that ‘‘there is a

consensus that retaining an annual PM10

NAAQS * * * is reasonable at this

time’’ and that there is ‘‘also a

consensus that a new PM2.5 NAAQS be

established’’ (Wolff, 1996b).

While it is difficult to distinguish the

effects of either fine or coarse fraction

particles from those of PM10,

comparisons between fine and coarse

fraction particles presented in the Staff

Paper suggest that fine particles are a

better surrogate for those components of

PM that are linked to mortality and

morbidity effects at levels below the

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

VII–18). Moreover, a regulatory focus on

fine particles would likely also result in

controls on gaseous precursors of fine

particles (e.g., SOX, NOX, VOC), which

are all components of the complex

mixture of air pollution that has most

generally been associated with mortality

and morbidity effects. The Staff Paper

concludes that, in contrast to fine

particles, coarse fraction particles are

more clearly linked with certain

morbidity effects at levels above those

allowed by the current 24-hour

standard.

The Administrator concurs with staff

and CASAC recommendations to

control particles of health concern (i.e.,

PM10) through separate standards for

fine and coarse fraction particles. The

following sections outline the basis for

the Administrator’s decision on specific

indicators for fine and coarse particle

standards.

1. Indicators for the Fine Fraction of

PM10

The Administrator concludes that it is

appropriate to control fine particles as a

group, as opposed to singling out

particular components or classes of fine

particles. The qualitative literature,

evaluated in Chapter 11 of the Criteria

Document and summarized in Section

V.C of the Staff Paper, has reported

various health effects associated with

high concentrations of a number of fine

particle components (e.g., sulfates,

nitrates, organics, transition metals),

alone or in some cases in combination

with gases. Community studies have

found significant associations between

fine particles or PM10 and health effects

in various areas across the U.S. where

such fine particle components correlate

significantly with particle mass. As

noted above, it is not possible to rule

out any one of these components as

contributing to fine particle effects.

Thus, the Administrator finds that the

present data more readily support a

standard based on the total mass of fine

particles.
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65655

27Some commentors have recommended the use

of a smaller cutpoint at 1 μm (PM1) to further

reduce coarse particle intrusion. PM1 has not been

used in health studies, although in most cases

collected mass should be similar to those for

cutpoints of 2.1 or 2.5 μm. While this indicator

could reduce intrusion of coarse particles, it might

also omit portions of hygroscopic acid sulfates in

high humidity environments. PM1 sampling

technologies have been developed; however, PM1

samplers have not been widely used in the field to

date, and there are some concerns about loss of

certain organic materials relative to an instrument

with a larger size cut.

In specifying a precise size range for

a fine particle standard, both the staff

and CASAC recommend PM2.5 as the

indicator of fine particles (Wolff,

1996b). The particle diameter reflecting

the mass minimum between the fine

and coarse modes typically lies between

1 and 3 μm, and the scientific data

support a sampling cut point to

delineate fine particles in this range.

Because of the potential overlap of fine

and coarse particle mass in this

intermodal region, EPA recognizes that

any specific sampling cut point would

result in only an approximation of the

actual fine-mode particle mass. Thus,

the choice of a specific diameter within

this size range is largely a policy

judgment. The staff and CASAC

recommendation for a 2.5 μm sampling

cut point is based on considerations of

consistency with the community health

studies, the limited potential for

intrusion of coarse fraction particles

into the fine fraction, and availability of

monitoring technology.27 PM2.5

encompasses all of the potential agents

of concern in the fine fraction, including

most sulfates, acids, fine particle

transition metals, organics, and ultrafine

particles, and includes most of the

aggregate surface area and particle

number in the entire distribution of

atmospheric particles.

The Administrator concurs with staff

and CASAC recommendations, and

concludes that PM2.5 is the appropriate

indicator for fine particle standards.

Details of this definition are further

specified in the Federal Reference

Method discussed in section V below

and proposed in a new Appendix L.

2. Indicators for the Coarse Fraction of

PM10

The Criteria Document and Staff

Paper conclude that epidemiological

information, together with dosimetry

and toxicological information, support

the need for a particle indicator that

addresses the health effects associated

with coarse fraction particles within

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

coarse fraction particles can deposit in

those sensitive regions of the lung of

most concern. Although the role of

coarse fraction particles in much of the

recent epidemiological results is

unclear, limited evidence from studies

where coarse fraction particles are the

dominant fraction of PM10 suggest that

significant short-term effects related to

coarse fraction particles include

aggravation of asthma and increased

upper respiratory illness. In addition,

qualitative evidence suggests potential

chronic effects associated with longterm exposure to high concentrations of

coarse fraction particles.

In selecting an indicator for coarse

fraction particles, the Administrator

took into account the views of several

CASAC panel members who suggested

using the coarse fraction directly (i.e.,

PM10¥2.5) as the indicator. However, the

Administrator notes that the existing

ambient data base for coarse fraction

particles is smaller than that for fine

particles, and that the only studies of

clear quantitative relevance to effects

most likely associated with coarse

fraction particles have used

undifferentiated PM10. In fact, it was the

consensus of CASAC that it is

reasonable to consider PM10 itself as a

surrogate for coarse fraction particles,

when used in conjunction with PM2.5

standards. The monitoring network

already in place for PM10 is large.

Therefore, in conjunction with the

decision to have separate standards for

PM2.5, the Administrator concludes,

consistent with CASAC

recommendations, that it is appropriate

to retain PM10 as the particle indicator

for standards intended to protect against

the effects most likely associated with

coarse fraction particles.

E. Averaging Time of PM2.5 Standards

As discussed above, the

Administrator has concluded that PM2.5

is an appropriate indicator for standards

intended to provide protection from

effects associated primarily with fine

particles. The recent health effects

information includes reported

associations with both short-term (from

less than 1 day to up to 5 days) and

long-term (from generally a year to

several years) measures of PM. On the

basis of this information, summarized in

Chapter V of the Staff Paper, the

Administrator has considered both

short- and long-term PM2.5 standards.

1. Short-term PM2.5 Standard

The current 24-hour averaging time is

consistent with the majority of

community epidemiological studies,

which have reported associations of

health effects with 24-hour

concentrations of various PM indicators

such as PM10, fine particles, and TSP.

Such health effects, including

premature mortality and increased

hospital admissions, have generally

been reported with same-day, previous

day, or longer lagged single-day

concentrations, although some studies

have reported stronger associations with

multiple-day average concentrations. In

any case, the Administrator recognizes

that a 24-hour PM2.5 standard can

effectively protect against episodes

lasting several days, since such a

standard would provide protection on

each day of a multi-day episode, while

also protecting sensitive individuals

who may experience effects after even a

single day of exposure.

Although most reported effects have

been associated with daily or longer

measures of PM, evidence also suggests

that some effects may be associated with

PM exposures of shorter durations. For

example, controlled human and animal

exposures to specific components of

fine particles, such as acid aerosols,

suggest that bronchoconstriction can

occur after exposures of minutes to

hours. Some epidemiological studies of

exposures to acid aerosols have also

found changes in respiratory symptoms

in children using averaging times less

than 24 hours. However, such reported

results do not provide a satisfactory

quantitative basis for setting a fine

particle standard with an averaging time

of less than 24 hours, nor do current

gravimetric mass monitoring devices

make such shorter durations generally

practical at present. Further, the

Administrator recognizes that a 24-hour

average PM2.5 standard which leads to

reductions in 24-hour average

concentrations is likely to lead as well

to reductions in shorter-term average

concentrations in most urban

atmospheres, thus providing some

degree of protection from potential

effects associated with shorter duration

exposures.

For these reasons, the Administrator

has concluded that a short-term PM2.5

standard with a 24-hour averaging time

can serve to control short-term ambient

PM2.5 concentrations, thus providing

protection from health effects associated

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

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

2. Long-Term PM2.5 Standard

Community epidemiological studies

have reported associations of annual

and multi-year average concentrations

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

an array of health effects, notably

premature mortality, increased

respiratory symptoms and illness (e.g.,

bronchitis and cough in children), and

reduced lung function. The relative

risks associated with such measures of

long-term exposures, although highly
65656 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

uncertain, appear to be larger than those

associated with short-term exposures.

Based on the available epidemiology,

and consistent with the limited relevant

toxicological and dosimetric

information, the Administrator

concludes that significant, and

potentially independent, health

consequences are likely associated with

long-term PM exposures.

The Administrator has considered

this evidence, which suggests that some

health endpoints reflect the cumulative

effects of PM exposures over a number

of years. In such cases, an annual

standard would provide effective

protection against persistent long-term

(several years) exposures to PM.

Requiring a much longer averaging time

would also complicate and

unnecessarily delay control strategies

and attainment decisions.

The Administrator has also

considered the seasonality of emissions

of fine particles and their precursors in

some areas (e.g., wintertime smoke from

residential wood combustion,

summertime regional acid sulfate and

ozone formation), which suggests that

some effects associated with annual

average concentrations might be the

result of repeated seasonally high

exposures. However, different seasons

are likely of concern in different parts

of the country, and the current evidence

does not provide a satisfactory

quantitative basis for setting a national

fine particle standard in terms of a

seasonal averaging time.

In addition, the Administrator

recognizes that an annual standard

would have the effect of controlling air

quality broadly across the yearly

distribution of 24-hour PM2.5

concentrations, although such a

standard would not as effectively limit

peak 24-hour concentrations as would a

24-hour standard. Thus, as discussed

above in Section B above (see especially

Figures 2a, 2b, 2c), an annual standard

could also provide protection from

health effects associated with short-term

exposures to PM2.5.

For these reasons, the Administrator

has concluded that a long-term PM2.5

standard with an annual averaging time

can serve to control both long- and

short-term ambient PM2.5

concentrations, thus providing

protection from health effects associated

with long-term (seasonal to several

years) and, to some degree, short-term

exposures to PM2.5.

3. Combined Effect of Annual and 24–

Hour Standards

Having concluded that both 24-hour

and annual PM2.5 standards are

appropriate, the Administrator

considered the potential combined

effects of such standards on PM

concentration levels and distributions

prior to considering the form and level

of each standard. The existing health

effects evidence could, of course, be

used to assess the form and level of each

standard independently, with shortterm health effects evidence being used

as the basis for a 24-hour standard and

the long-term health effects evidence as

the basis for an annual standard. Some

CASAC panel members apparently used

this approach as a basis for their views

on appropriate averaging times and

standard levels. In particular, a few

members focused only on a 24-hour

PM2.5 standard in light of the relative

strength of the short-term exposure

studies. On the other hand, two

members focused only on an annual

standard, recognizing that strategies to

meet an annual standard would provide

protection against effects of both shortand long-term exposures.

The Administrator has focused on a

policy approach that considers the

consistency and coherence, as well as

the limitations, of the body of evidence

as a whole, and recognizes that there are

various ways to combine two standards

to achieve an appropriate degree of

public health protection. Such an

approach to standard setting that

integrates the body of health effects

evidence and air quality analyses, and

considers the combined effect of the

standards, has the potential to result in

a more effective and efficient suite of

standards than an approach that only

considers short- and long-term

evidence, analyses, and standards

independently.

In considering the combined effect of

such standards, the Administrator notes

that while an annual standard focuses

on annual average PM2.5 concentrations,

it would also result in fewer and lower

24-hour peak concentrations.

Alternatively, a 24-hour standard which

focuses on peak concentrations would

also result in lower annual average

concentrations. Thus, either standard

could be viewed as providing both

short- and long-term protection, with

the other standard serving as a

‘‘backstop’’ in situations where the daily

peaks and annual averages are not

consistently correlated.

The Administrator believes that the

suite of PM2.5 standards can be most

effectively and efficiently defined by

treating the annual standard as the

generally controlling standard for

lowering both short- and long-term

PM2.5 concentrations. As a supplement

to the annual standard, the 24-hour

standard would serve as a backstop to

provide additional protection against

days with high peak PM2.5

concentrations, localized ‘‘hot spots,’’

and risks arising from seasonal

emissions that would not be well

controlled by a national annual

standard. In reaching this view, the

Administrator took into account the

factors discussed below.

(1) Based on one of the key

observations from the quantitative risk

assessment (Section B, Figures 2a, 2b,

2c), the Administrator notes that much

if not most of the aggregate annual risk

associated with short-term exposures

results from the large number of days

during which the 24-hour average

concentrations are in the low- to midrange, below the peak 24-hour

concentrations. As a result, lowering a

wide range of ambient 24-hour PM2.5

concentrations, as opposed to focusing

on control of peak 24-hour

concentrations, is the most effective and

efficient way to reduce total population

risk. Further, there is no evidence

suggesting that risks associated with

long-term exposures are likely to be

disproportionately driven by peak 24-

hour concentrations. Thus, an annual

standard that controls an area’s

attainment status is likely to reduce

aggregate risks associated with both

short- and long-term exposures with

more certainty than a 24-hour standard.

(2) The consistency and coherence of

the health effects data base is more

directly related to long-term measures of

air quality (e.g., the annual distributions

of 24-hour PM concentrations), rather

than to 24-hour concentrations on

individual days. More specifically,

judgments about the quantitative

consistency of the large number of

short-term exposure studies reporting

associations with 24-hour

concentrations arise from comparing the

relative risk results derived from

analyzing the associations across the

entire duration of the studies, which

typically spanned at least an annual

time frame.

(3) An annual average measure of air

quality is more stable over time than are

24-hour measures. Thus, a controlling

annual standard is likely to result in the

development of more consistent risk

reduction strategies over time, since an

area’s attainment status will be less

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

conditions that affect the formation of

fine particles, than under a controlling

24-hour standard.

Under this policy approach, the

annual PM2.5 standard would serve in

most areas as the target for control

programs designed to be effective in

lowering the broad distribution of PM2.5

concentrations, thus protecting not only
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65657

28Spatial averaging of monitoring data is also

discussed in the notice of a proposed decision on

the O3 NAAQS published today. Different

considerations apply in the two cases principally

because of differences between (1) the nature of the

health effects evidence for PM2.5 and O3; (2) the

proposed suite and annual and 24-hour PM2.5

standards, in contrast to a single proposed O3

standard; and (3) the existence of an established,

extensive O3 monitoring network, in contrast to the

absence at present of such a network for PM2.5.

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

with such an annual standard, the 24-

hour PM2.5 standard would be set so as

to protect against the occurrence of peak

24-hour concentrations and those that

present localized or seasonal effects of

concern in areas where the highest 24-

hour-to-annual mean PM2.5 ratios are

appreciably above the national average.

The Administrator recognizes that

this policy approach represents a new

way of thinking about the combined

effects of short- and long-term

standards, and that there are alternative

views about this approach. Accordingly,

the Administrator solicits comment on

this policy approach for defining the

most effective and efficient suite of

PM2.5 standards.

F. Form of PM2.5 Standards

1. Annual Standard

As discussed in some detail during

the last review of the PM NAAQS (see

49 FR 10408, March 20, 1984; 52 FR

24634, July 1, 1987), the expected

annual arithmetic mean (i.e., the annual

arithmetic mean averaged over 3 years)

is a relatively stable measure of air

quality that reflects the total cumulative

dose of PM to which an individual or

population is exposed. Short-term peaks

have an influence on the arithmetic

mean that is proportional to their

frequency, magnitude, and duration,

and, thus, their contribution to

cumulative exposure and risk. As a

result, the annual arithmetic mean form

of an annual standard provides

protection across a wide range of the air

quality distribution contributing to

exposure and risk, in contrast to other

forms, such as the geometric mean, that

deemphasize the effects of short-term

peak concentrations. On this basis, the

Administrator concurs with the Staff

Paper recommendation, supported by

CASAC, to use the 3-year average

annual arithmetic mean as the form for

an annual PM2.5 standard, consistent

with the current form of the annual

PM10 standard.

The Staff Paper and some CASAC

panel members also recommended that

consideration be given to calculating the

PM2.5 annual arithmetic mean for an

area by averaging the annual arithmetic

means derived from multiple, primarily

population-oriented monitoring sites

within a monitoring planning area. In

considering a calculation method for

annual arithmetic averages that involves

spatial averaging of monitoring data, the

Administrator specifically took into

account the following factors: 28

(1) Many of the community-based

epidemiological studies examined in

this review used spatial averages, when

multiple monitoring sites were

available, to characterize area-wide PM

exposure levels and the associated

population health risk. Even in those

studies that used only one monitoring

location, the selected site was chosen to

represent community-wide exposures,

not the highest value likely to be

experienced within the community.

Thus, spatial averages are most directly

related to the epidemiological studies

used as the basis for the proposed

revisions to the PM NAAQS.

(2) Under the policy approach

advanced earlier, the annual PM2.5

standard would be intended to reduce

aggregate population risk from both

long- and short-term exposures by

lowering the broad distribution of PM2.5

concentrations across the community.

An annual standard based on spatially

averaged concentrations would better

reflect area-wide PM exposure levels

than would a standard based on

concentrations from a single monitor

with the highest measured values.

(3) Under this policy approach, the

24-hour PM2.5 standard would be

intended to supplement a spatially

averaged annual PM2.5 standard by

providing protection against peak 24-

hour concentrations, localized ‘‘hot

spots,’’ and risk arising from seasonal

emissions that would not be as well

controlled by an annual standard.

Accordingly, the 24-hour PM2.5 standard

should be based on the single

population-oriented monitoring site

within the monitoring planning area

with the highest measured values.

Based on these considerations, the

Administrator believes that the form of

a PM2.5 annual standard should be

expressed as the annual arithmetic

mean, temporally averaged over 3 years

and spatially averaged over all

designated monitoring sites. Such

designations would be based on criteria

contained in the proposed revision to

the monitoring siting guidance in 40

CFR Part 58 that accompanies this

notice. In the Administrator’s judgment,

an annual PM2.5 standard expressed in

this form, established in conjunction

with a 24-hour PM2.5 standard, would

provide the most appropriate target for

reducing area-wide population exposure

to fine particle pollution.

On the other hand, the Administrator

is mindful that adoption of spatial

averaging for an annual PM2.5 standard

would add a degree of complexity to the

monitor siting requirements for a new

PM2.5 monitoring network and the

specification of those areas across which

spatial averaging should be permitted.

These issues are addressed more fully in

the accompanying proposed revisions to

40 CFR Part 58. Of particular concern is

whether appropriate and effective

criteria can be developed and

implemented for determining areas

within which spatial averaging would

be reflective of the area-wide population

risk. The EPA recognizes that some

monitoring planning areas may have to

be subdivided into smaller subareas to

reflect gradients in particle levels (e.g.,

upwind suburban sites, central city

sites, downwind sites) as well as

topographical barriers or other factors

that may result in a monitoring planning

area having several distinct air quality

regimes.

Because of the importance of this

issue, the notice of proposed revisions

to 40 CFR Part 58 specifically requests

broad public input on the approaches

advanced in that notice with respect to

the selection of sites and designation of

areas for spatial averaging. Recognizing

the complexities that spatial averaging

may introduce into risk management

programs and that unforeseen issues

may arise from public comment on the

40 CFR Part 58 notice, the

Administrator also requests comment on

the alternative of basing the annual

standard for PM2.5 on the populationoriented monitor site within the

monitoring planning area with the

highest 3-year average annual mean.

Based on comments received, the

Administrator may choose either of

these two approaches for specifying the

form of the annual PM2.5 standard at the

time of promulgation of any revisions to

the PM standards. Proposed methods for

using monitored concentrations to make

a comparison with a spatially averaged

annual mean standard, as well as

associated calculations and other data

handling conventions, are presented

below in the section on proposed

revisions to Appendix K.

2. 24-Hour Standard

The current 24-hour PM10 standard is

expressed in a ‘‘1-expected-exceedance’’

form. That is, the standard is formulated

on the basis of the expected number of

days per year (averaged over 3 years) on

which the level of the standard will be

exceeded. The test for determining

attainment of the current 24-hour
65658 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

standard is presented in Appendix K to

40 CFR Part 50.

Since promulgation of the current 24-

hour PM10 standard in 1987, a number

of concerns have been raised about the

1-expected-exceedance form. These

include, in particular, the year-to-year

stability of the number of exceedances,

the stability of the attainment status of

an area, and the complex data handling

conventions specified in Appendix K,

including the procedures for making

adjustments for missing data and lessthan-every-day monitoring.

In light of these concerns, the Staff

Paper and several CASAC panel

members (Wolff, 1996b) recommended

that consideration be given to adoption

of a more stable and robust form for 24-

hour PM standards. In considering this

recommendation, the Administrator

noted that the use of a concentrationbased percentile form would have

several advantages over the current 1-

expected-exceedance form:

(1) Such a concentration-based form is

more directly related to the ambient PM

concentrations that are associated with

health effects. Given that there is a

continuum of effects associated with

exposures to varying levels of PM, the

extent to which public health is affected

by exposure to ambient PM is related to

the actual magnitude of the PM

concentration, not just whether the

concentration is above a specified level.

With an exceedance-based form, days

on which the ambient PM concentration

is well above the level of the standard

are given equal weight to those days on

which the PM concentration is just

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

counted as one exceedance), even

though the public health impact on the

two days is significantly different. With

a concentration-based form, days on

which higher PM concentrations occur

would weigh proportionally more than

days with lower PM concentrations for

the design value, since the actual

concentrations are used directly in

determining whether the standard is

attained.

(2) More specifically, a concentrationbased percentile form would also

compensate for missing data and lessthan-every-day monitoring, thereby

reducing or eliminating the need for

complex data handling procedures in

the Appendix K test for attainment. As

a result, an area’s attainment status

would be based directly on monitoring

data rather than on a calculated value

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

(3) Further, a concentration-based

form, averaged over 3 years, also has

greater stability than the expected

exceedance form and, thus, would

facilitate the development of more

stable implementation programs by the

States.

In light of these advantages, and

taking into account the CASAC

recommendation as well as concerns

regarding adjustments for missing data

and less-than-every-day monitoring, the

Administrator believes that adoption of

a concentration percentile form for the

24-hour PM2.5 standard would be

appropriate.

Having reached this view, the

Administrator considered various

specific percentile values for such a

form. In doing so, she took into account

two factors. First, the 24-hour PM2.5

standard is intended to supplement the

annual PM2.5 standard by providing a

‘‘back stop’’ to provide additional

protection against extremely high peak

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

arising from seasonal emissions.

Second, the form of the 24-hour PM2.5

standard should provide an appropriate

degree of increased stability relative to

the current form. A more stable statistic

would reduce the impact of a single

high exposure event that may be due to

unusual meteorological conditions

alone, and thus would provide a more

stable basis upon which to design

effective control programs.

With these purposes in mind, the

Administrator observed that while a

percentile value such as the 90th or 95th

would provide substantially increased

stability when compared to a more

extreme air quality statistic (e.g., the

current 1-expected-exceedance form), it

would likely not serve as an effective

‘‘back stop,’’ because it would allow a

large number of days with peak PM2.5

concentrations above the standard level.

For example, in a 365 day data base, the

90th and 95th percentiles would equal

the 37th and 19th highest 24-hour

concentrations, respectively. On the

other hand, a percentile value selected

much closer to the tail of the air quality

distribution (e.g., a 99th or greater

percentile) would not likely provide

significantly more health protection nor

significantly increased stability as

compared to the current form. In

balancing these issues, the

Administrator believes that a 98th

percentile value form of a standard, set

at an appropriate level, would achieve

the desired outcomes of both a 24-hour

standard that would serve as an

effective supplement to the PM2.5

annual standard and a more stable form.

Proposed methods for using monitored

concentrations to make a comparison

with a concentration percentile form of

a 24-hour standard, averaged over 3

years, as well as associated calculations

and other data handling conventions,

are presented below in the section on

proposed revisions to Appendix K.

G. Levels for the Annual and 24-Hour

PM2.5 Standards

As discussed in Section E above, the

Administrator believes that an annual

PM2.5 standard can provide the requisite

reduction in risk associated with both

annual and 24-hour averaging times in

most areas of the U.S. Under this

approach, the 24-hour standard would

be intended to provide supplemental

protection against extreme peak fine

particle levels that may occur in some

localized situations or in areas with

distinct variations in seasonal fine

particle levels. In reaching judgments as

to appropriate levels to propose for both

the annual and 24-hour PM2.5 standards,

the Administrator has considered the

combined protection afforded by both

the annual and 24-hour standards,

taking into account the forms discussed

above in Section F.

With this approach in mind, the

Administrator has considered the

available health effects evidence and

related air quality information presented

in the Criteria Document and

summarized in Chapters IV–VII of the

Staff Paper and in Section A above,

which provides the basis for decisions

on standard levels that would reduce

risk sufficiently to protect public health

with an adequate margin of safety,

recognizing that such standards will not

be risk free. In so doing, the

Administrator has considered both the

strengths and the limitations of the

available evidence and information, as

well as alternative interpretations of the

scientific evidence advanced by various

CASAC panel members (Wolff, 1996b;

Lippmann et al., 1996) and public

commenters, arising primarily from the

inherent uncertainties and limitations in

the health effects studies.

Beyond those factors, but clearly

related to them, a range of views have

been expressed by CASAC panel

members and the public as to the

appropriate policy response to the

available health effects evidence and

related air quality information. Toward

one end of the spectrum, the view has

been expressed that only a very limited

policy response is appropriate in light of

the many key uncertainties and

unanswered questions that, taken

together, call into question the

fundamental issue of causality in the

reported associations between ambient

levels of PM2.5 and mortality and other

serious health effects. Toward the other

end, the view has been expressed that

the consistency and coherence of the

epidemiological evidence can

appropriately be interpreted as
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65659

29Nationwide PM2.5 estimates have been derived

from the nationwide PM10 air quality data base but

reflect a significant degree of uncertainty due to the

highly variable relationship between PM2.5 and

PM10 air quality values across locations and seasons

(Fitz-Simons et al., 1996).

30 In presenting their opinions on the appropriate

policy choice for PM2.5 standards, several CASAC

panel members supported levels consistent with

this approach. In addition, three CASAC members

expressed a preference for standards that would be

equivalent in stringency to the current PM10

standards; with the suggestion that standard levels

of 25 to 30 μg/m3, annual average, and ≥75 μg/m3,

24-hour average (presumably for the same 1-

expected-exceedence form used for comparison of

options in the Staff Paper), would approximate

equivalence (Wolff, 1996b). As CASAC recognized,

the wide variability in PM2.5/PM10 ratios in time

and location precludes defining uniform PM2.5

standards that would provide close to ‘‘equivalent’’

protection to the current standard in all or even

most areas. However, based on estimated PM2.5 data

for 1993–95, the combination of 20 μg/m3, annual

spatially averaged mean, and 65 μg/m3, 24-hour,

98th percentile, standards is likely to be less

stringent than the current standards in terms of the

numbers of counties predicted not to meet that

alternative.

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

standard is consistent with the levels recommended

by four CASAC panel members, although no

members supported an annual PM2.5 standard as

low as 12 μg/m3.

demonstrating causality in the

relationships between PM2.5 and health

endpoints that are clearly adverse, and

that uncertainties in the underlying

health effects information should be

treated, regardless of their nature, as

warranting a maximally precautionary

policy response. A third view would

suggest an intermediate policy response,

taking into account not only the

consistency and coherence of the health

effects evidence, but also the

recognition of key uncertainties and

unanswered questions that increasingly

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

decrease below the mean values in areas

where effects have been observed and/

or as such concentrations approach

background levels.

Reflecting these divergent views, both

of the science itself and of how the

science should be used in making policy

decisions on proposed standards, the

Administrator has considered three

alternative approaches to selecting

appropriate standard levels, as

described below.

(1) One approach would place great

weight on the uncertainties and

limitations in the available health

effects studies considered individually,

such as the possible existence of effects

thresholds and unanswered questions

regarding the causal agent(s) responsible

for the reported health effects, and on

the limited amount of research currently

available that has measured PM2.5

directly. This approach would recognize

PM2.5 as a component of air pollution

that should be addressed through a

NAAQS, since serious health effects

have been linked to the complex mix of

urban air pollution containing PM (or

some subset of particles within the fine

fraction for which PM2.5 appears to be

a reasonable surrogate). Beyond that

recognition, however, this approach

would reflect the judgment that

significant new regulatory programs

directed toward fine particle

concentrations well below those

permitted under the current PM10

standards may be premature until

additional research has addressed the

key uncertainties and unanswered

questions especially with regard to

plausible physiological mechanisms for

effects at such low exposure levels.

Such an approach would be based on

the judgment that the current scientific

evidence has not demonstrated adverse

public health effects from fine particle

concentrations well below those

corresponding to the current standard

and that it would be difficult to target

regulatory programs toward the specific

pollutants that may be responsible for

the health effects of concern in the

absence of an understanding of the

mechanism(s) by which these effects are

produced. Although there is currently

significant uncertainty regarding

nationwide ambient concentrations of

PM2.5,29 since little actual monitoring

data are available, the Administrator

believes that such an approach could be

reflected by setting a standard near the

upper end of the range recommended in

the Staff Paper; i.e., an annual standard

level up to 20 μg/m3 in combination

with a 24-hour standard of up to 65

μg/m3.30

A policy decision to set PM2.5

standards at these levels would

recognize that, while the scientific

evidence demonstrating adverse effects

from fine particles specifically is not

conclusive, fine particles should

nonetheless be regulated separately

through PM2.5 standards, to provide

public health protection with an

adequate margin of safety, as specified

in the Act. Such standards would result

in the establishment of new regulatory

programs to reduce potential health

risks in areas where current levels are

high enough to warrant serious concern.

Such standards would also result in the

establishment of a new monitoring

network to better characterize fine

particle levels and composition in major

population areas throughout the U.S.

This would in turn facilitate further

research into health effects associated

with ambient PM2.5 levels, which would

likely lead to a better understanding in

the future of the key uncertainties and

unanswered questions that currently

exist, especially with regard to

mechanisms and the identification of

components of urban air pollution, and

specifically of fine particles, on which

to focus future regulatory efforts.

(2) In sharp contrast, a second

approach would place great weight on

the consistency and coherence of the

entire body of epidemiological

evidence, the seriousness of the

associated health effects (e.g., premature

mortality and increased hospital

admissions), and the magnitude of the

incidence of such effects that can be

estimated from plausible assumptions in

an analysis of the quantitative effects

evidence. While recognizing that

uncertainties and unanswered questions

remain, this approach would suggest

policy decisions that would result in

major new regulatory programs directed

at fine particles even as additional

research is ongoing.

Such an approach could be viewed as

a maximally precautionary response,

reflecting judgments that the likely

effects are as serious and potentially

adverse to large numbers of sensitive

individuals as the reported evidence

might suggest, and that uncertainties in

the evidence should be treated,

regardless of their nature, as warranting

greater protection. Such an approach

would be predicated on interpreting the

epidemiological evidence as sufficient

to have made a compelling case for

causality in relationships between PM2.5

and health effects at the lower

concentrations observed in these

studies. Based on uncertain estimates of

PM2.5 air quality, such an approach

could be reflected by an annual

standard level at the lower end of the

range recommended in the Staff Paper,

i.e., an annual standard level down to

about 12 μg/m3, in combination with a

24-hour standard set within the lower

part of the range recommended in the

Staff Paper, from 20 μg/m3, at which the

24-hour standard might primarily

control, up to about 50 μg/m3, where the

annual standard might primarily

control.31

A policy decision to set PM2.5

standards at these levels would not only

result in a new monitoring network and

facilitate additional health effects

research, but would likely result in

major reductions in PM2.5 levels

throughout the U.S., with associated

reductions in risks to public health.

Commensurate reductions in health

risks would result only if, in fact, there

is a continuum of health risk down to

the lower end of the ranges of air quality

observed in the key epidemiological

studies, and if the reported associations
65660 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

32As discussed in Appendix E of the Staff Paper

(U.S. EPA, 1996b, p. E–4), there is generally the

greatest statistical confidence in the association at

and above the mean concentration.

are, in fact, causally related to PM2.5. By

setting standards at levels where the

possibility of effects thresholds are more

likely and there is greater potential that

other elements in the air pollution mix

(or some subset of particles within the

fine fraction) are at least in part

responsible for or modifying the effects

being causally attributed to PM2.5, such

standards might result in regulatory

programs that go beyond those that are

needed to effectively reduce risks to

public health. The policy goal of such

an approach would be to focus maximal

regulatory efforts on controlling

potential risks to public health, with a

large margin of safety that takes into

account the uncertainties and

limitations in the available evidence or

treating them as warranting increased

protection in all cases.

In assessing these two sharply

contrasting alternative approaches, the

Administrator is mindful that the

proponents of each, both within the

scientific community and in the public

at large, can advance reasoned and

potentially persuasive arguments in

support of their preferred policy

approaches. In considering the bases for

these two contrasting views, however,

the Administrator was drawn to

consider a third approach representing

an intermediate policy response, as

discussed below.

(3) The third approach would focus

primarily on standard levels designed to

limit annual PM2.5 concentrations to

somewhat below those where the body

of epidemiological evidence is most

consistent and coherent. Such an

approach would recognize both the

strengths and the limitations of the full

range of scientific and technical

information on the health effects of PM,

as well as associated uncertainties, as

interpreted by the Criteria Document,

Staff Paper, and CASAC. The

Administrator believes that such an

approach would appropriately reflect

the weight of the evidence as a whole.

In identifying PM2.5 standard levels

consistent with this overall approach,

the Administrator has placed greatest

weight on those epidemiological studies

reporting associations between health

effects and direct measures of fine

particles, most notably those recent

studies conducted in North America

(summarized in Tables V–12 to V–14 of

the Staff Paper). Key considerations and

study results upon which this approach

is based are presented below.

As previously discussed, the

Administrator is proposing to select the

level of the annual standard so as to

protect against the range of effects

associated with both short- and longterm exposures to PM, with the 24-hour

standard level selected to provide

supplemental protection against peak

concentrations that might occur over

limited areas and/or for limited time

periods. In selecting the level of an

annual standard, therefore, the

Administrator has considered

epidemiological studies of both shortand long-term exposures to fine

particles.

The effects estimates from the daily

studies (in Table V–12 of the Staff

Paper) are based on analyses of daily

PM2.5 concentrations that occurred over

the course of the year(s) studied. While

effects may occur over the full range of

concentrations observed in the studies,

the strongest evidence for daily PM2.5

effects is associated with annual

concentrations at or above the mean

levels reported for these studies.32 Given

the serious nature of the potential

effects, the Administrator believes it is

both prudent and appropriate to select

a level for an annual standard at or

below such concentrations. An

examination of the annual means from

the combined Six City analysis of daily

mortality and respiratory symptoms

(Schwartz et al., 1996a), together with

those from studies in individual cities

for which statistically significant PMeffects associations are reported (from

Table V–12 in the Staff Paper), finds

mean concentrations ranging from about

16 to 21 μg/m3. In addition, the mean

concentrations in cities where shortterm exposure associations

characterized in the Criteria Document

as nearly statistically significant (U.S.

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

11 μg/m3 to 30 μg/m3. Taken together,

this evidence suggests that an annual

standard level of about 15 μg/m3 may be

appropriate to reduce the risk of shortterm effects of fine particles.

The Administrator also examined this

level in light of the effects reported in

epidemiological studies of long-term

exposures to fine particles (Table V–13

in the Staff Paper), which may reflect

the accumulation of daily effects over

time as well as potential effects

uniquely associated with long-term

exposures. Even though subject to

additional uncertainties, the long-term

studies provide important insights with

respect to the overall protection

afforded by an annual standard. The

most direct comparison with the daily

fine particle mortality studies is

provided by two long-term cohort

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

1995). The annual mean PM2.5

concentration for the multiple cities

included in both of these studies (6 and

47 cities, respectively) was 18 μg/m3

each study (U.S. EPA, 1996b, p. E–10).

The Staff Paper assessment of the

concentration-response results from

these studies concluded that the

evidence for increased risk was more

apparent at annual concentrations at or

above 15 μg/m3 (Table E–3 in the Staff

Paper). As noted in the Staff Paper and

the Criteria Document, however, the

estimated magnitude of effects may be

related to somewhat higher historical

concentrations than the affected

communities experienced during the

time period of the studies; this

consideration suggests that a level of 15

μg/m3 would incorporate a margin of

safety.

Taking the epidemiological studies of

both short- and long-term exposures

together, the Administrator believes the

concordance of evidence for PM effects

and associated levels provides clear

support for an annual PM2.5 standard

level of about 15 μg/m3. This level is

below the range of annual data most

strongly associated with both short- and

long-term effects, and because even

small changes in annual means in this

concentration range can make

significant differences in overall risk

reduction and total population

exposures, the Administrator believes it

would provide an adequate margin of

safety. Moreover, the means in areas

where PM2.5 concentrations were

statistically significantly associated with

daily mortality (about 16 to 21 μg/m3)

reflect an 8-year average; thus, the

proposed use of a 3-year average mean

would provide additional protection.

Although the possibility of effects at

lower annual concentrations cannot be

excluded, the evidence for that

possibility is highly uncertain and, as

previously discussed, the likelihood of

significant health risk, if any, becomes

smaller as concentrations approach the

lower end of the range of air quality

observed in the key epidemiological

studies and/or background levels.

For the reasons specified above,

however, an annual, spatially averaged

standard cannot be expected to offer

fully effective and efficient protection

against all potential short-term effects in

areas with strong local or seasonal

sources. The broad-based community

studies considered in this review

generally could not evaluate such peak

exposure conditions directly. Given the

public health purposes of the 24-hour

standard, the Administrator believes it

should be set at a level that generally

supplements the control provided by an

annual standard and reasonably reflects

the peak levels observed in
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65661

communities where health effects have

been associated with daily levels of fine

particles.

An examination of air quality in cities

where short-term exposure associations

are characterized in the Criteria

Document as statistically significant or

nearly so (U.S. EPA, 1996a, p. 13–40)

shows that the 98th percentile 24-hour

average PM2.5 concentrations ranged

from approximately 35 μg/m3 to 90 μg/

m3 (Koman, 1996), with the majority of

cities ranging from above 40 to above 50

μg/m3. Based on this examination of

relevant air quality information, the

Administrator believes that a 98th

percentile 24-hour PM2.5 standard of 50

μg/m3 (at the monitoring site within the

monitoring planning area with the

highest 3-year average) would provide

an appropriate supplement or

‘‘backstop’’ to a spatially averaged

annual mean standard of 15 μg/m3.

In the Administrator’s judgment, the

factors discussed above provide ample

reason to believe that both annual and

24-hour PM2.5 standards are appropriate

to protect public health from adverse

health effects associated with short- and

long-term exposures to ambient fine

particles. Further, she believes these

factors provide a clear basis for judging

that an annual standard set at 15 μg/m3,

in combination with a 24-hour standard

set at 50 μg/m3, would protect public

health with an adequate margin of

safety.

The Administrator is mindful,

however, that in assessing these factors

a series of judgments had to be made

with respect to both the interpretation of

the underlying scientific evidence and

the treatment of inherent uncertainties

and limitations in the available

information in making policy choices.

Accordingly, the Administrator solicits

broad public comment, not only on her

proposed decision to establish new

PM2.5 standards of 15 μg/m3, annual

average, and 50 μg/m3, 24-hour average,

but also on the two alternative

approaches described above. Based on

the comments received and the

accompanying rationale, the

Administrator may choose at the time of

final promulgation to adopt other

standards within the range of these

alternative approaches in lieu of the

standards she is proposing today.

H. Conclusions Regarding the Current

PM10 Standards

1. Averaging Time and Form

In conjunction with the proposed

PM2.5 standards, the new function of

PM10 standard(s) would be to protect

against potential effects associated with

coarse fraction particles in the size

range of 2.5 to 10 μm. As noted above,

coarse fraction particles are plausibly

associated with certain effects from both

long- and short-term exposures. Based

on qualitative considerations,

deposition of coarse fraction particles in

the respiratory system could be

expected to aggravate effects in

individuals with asthma. The Criteria

Document and Staff Paper found

support for this expectation in limited

epidemiological evidence on the effects

of coarse fraction particles, suggesting

that aggravation of asthma and

respiratory infections and symptoms

may be associated with daily or episodic

increases in PM10 that is dominated by

coarse fraction particles. The potential

buildup of insoluble coarse fraction

particles in the lung after long-term

exposures to high levels should also be

considered.

Based on assessments of the available

information in the Criteria Document

and Staff Paper, both the staff and

CASAC recommended retention of an

annual PM10 standard. The staff, with

CASAC concurrence, recommended

retention of the current expected annual

mean form of the standard, which is the

same form being proposed for the

annual PM2.5 standard. As noted in the

staff assessment, the current annual

PM10 standard offers substantial

protection against both long- and shortterm effects of coarse fraction particles.

The staff and CASAC also

recommended that consideration be

given to retention of a 24-hour standard

to provide additional protection against

potential effects of short-term exposures

to coarse fraction particles. The staff,

with CASAC concurrence, also

recommended that if a 24-hour standard

is retained, the form of the standard

should be revised to provide a more

robust target for practical coarse particle

controls. For the reasons outlined above

regarding the form of the 24-hour PM2.5

standard, the Administrator believes the

98th percentile concentration based

form would also be an appropriate form

for a 24-hour PM10 standard.

2. Levels for Alternative Averaging

Times

a. Annual PM10 Standard

As a result of the more limited

information for coarse fraction particles,

the Administrator’s approach for

selecting a level of the standard is

directly related to the approach taken in

the last review of the PM NAAQS. In

that review, evidence from limited

quantitative studies was used in

conjunction with support from the

qualitative literature in selecting the

level of the current annual PM10

standard. The staff assessment of the

major quantitative basis for the level of

that standard (Ware et al., 1986),

together with a more recent related

study (Dockery et al., 1989), now finds

the same range of levels of concern (40–

50 μg/m 3) as was found in the previous

standard review. The staff finds that it

is possible, but not certain, that coarse

fraction particles, in combination with

fine particles, may have influenced the

observed effects at these levels. Based

on particle deposition considerations, it

is possible that cumulative deposition of

coarse fraction particles could be of

concern in children, who are more

prone to be active outdoors than

sensitive adult subpopulations.

Qualitative evidence of other longterm coarse particle effects, most

notably from long-term buildup of

silica-containing materials, supports the

need for a long-term standard, but does

not provide evidence of effects below

the range of 40–50 μg/m3 (U.S. EPA,

1996a, p. 13–79). The staff concludes

that the qualitative evidence with

respect to biological aerosols also

supports the need to limit coarse

materials, but should not form the major

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

1996a, p. 13–79). In addition, the nature

and distribution of such materials,

which vary from endemic fungi (e.g.,

valley fever) to pollens larger than 10

μm, are not appropriately addressed by

traditional air pollution control

programs.

Based on its review of the available

information, CASAC found ‘‘a

consensus that retaining an annual PM10

NAAQS at the current level is

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

Taking into account the above

considerations, as more fully detailed in

the Staff Paper and the CASAC

recommendations, the Administrator

proposes to retain the current annual

PM10 standard of 50 μg/m3 to protect

against the long- and short-term effects

of coarse fraction particles.

b. 24–Hour PM10 Standard

As discussed above, EPA staff and

CASAC also recommended that

consideration should be given to a 24-

hour standard for coarse fraction

particles as measured by PM10. Unlike

the case for the annual standard,

however, the staff found that the

original quantitative basis for the level

of the current 24-hour PM10 standard

(150 μg/m3) is no longer appropriate.

Instead, the staff found the main

quantitative basis for a short-term

standard is provided by the two

community studies of exposure to

fugitive dust referenced above. Because

these studies reported multiple large
65662 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

33Congress adopted section 169A of the Act

because of concern that the NAAQS and Prevention

of Significant Deterioration programs may not

provide adequate visibility protection nationally,

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

See H.R. Rep. No. 294, 95th Congress, 1st Session,

203–205 (1977).

34There are 156 mandatory class I Federal areas

protected by the visibility provisions in sections

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

in section 162 of the Act as those national parks

exceeding 6000 acres, wilderness areas and

memorial parks exceeding 5000 acres, and all

international parks which were in existence on

August 7, 1977.

exceedences of the current 24-hour

standard, and because of limitations in

the studies themselves, they provide no

basis to lower the level of the standard

below 150 μg/m3. Moreover, none of the

qualitative literature regarding the

potential short-term effects of coarse

particles provides a basis for a lower

standard level. Both EPA staff and

CASAC recommended that if a 24-hour

PM10 standard is retained, the level of

the standard should be maintained at

150 μg/m3, although with a revised

form.

In the judgment of the Administrator,

retention of a 24-hour PM10 standard at

the level of 150 μg/m3 with a 98th

percentile form would provide adequate

protection against the short-term effects

of coarse particles that have been

identified to date in the scientific

literature. However, analyses of the

available air quality relationships show

that such a standard might not add

greatly to the protection afforded by the

current PM10 annual standard (FitzSimons et al., 1996). As noted in the

Staff Paper and by some CASAC panel

members, it is possible that the current

annual standard might provide adequate

protection against both long- and shortterm effects of coarse particles,

especially when viewed in conjunction

with the overall proposal to add new

annual and 24-hour PM2.5 standards.

Therefore, the Administrator also

solicits comment on the alternative of

retaining the current annual PM10

standard and revoking the current 24-

hour PM10 standard.

I. Proposed Decisions on Primary

Standards

For the reasons discussed above, and

taking into account the information and

assessments presented in the Criteria

Document and the Staff Paper, the

advice and recommendations of

CASAC, and public comments to date,

the Administrator proposes to amend

the current suite of PM10 standards by

adding new PM2.5 standards and by

revising the form of the current 24-hour

PM10 standard. Specifically, the

Administrator proposes to add two new

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

annual mean, and 50 μg/m3, 24-hour

average. The proposed new annual

PM2.5 standard would be met when the

3-year average of the annual arithmetic

mean PM2.5 concentrations, spatially

averaged across an area, is less than or

equal to 15 μg/m3, with fractional parts

of 0.05 or greater rounding up. The

Administrator solicits comment on the

alternative of using the 3-year average of

the annual arithmetic mean PM2.5

concentrations at each monitor within

an area rather than a spatially averaged

value. The proposed new 24-hour PM2.5

standard would be met when the 3-year

average of the 98th percentile of 24-hour

PM2.5 concentrations at each monitor

within an area is less than or equal to

50 μg/m3, with fractional parts of 0.5 or

greater rounding up. Data handling

conventions are specified in proposed

revisions to Appendix K, as discussed

in Section IV below, and a reference

method for monitoring PM as PM2.5 is

specified in a proposed new Appendix

L, as discussed in Section V below.

In recognition of alternative views as

to the appropriate policy response, the

Administrator also solicits comments on

two alternative sets of new annual and

24-hour PM2.5 standards: (1) An annual

standard set at a level up to 20 μg/m3,

in combination with a 24-hour standard

set at a level up to 65 μg/m3; and (2) an

annual standard set at a level as low as

12 μg/m3, in combination with a 24-

hour standard set at a level within the

range of 20 to 50 μg/m3.

The Administrator also proposes to

retain the current annual PM10 standard

at the level of 50 μg/m3, which would

be met when the 3-year average of the

annual arithmetic mean PM10

concentrations at each monitor within

an area is less than or equal to 50 μg/

m3, with fractional parts of 0.5 or greater

rounding up. Further, the Administrator

proposes to retain the current 24-hour

PM10 standard at the level of 150 μg/m3,

but to revise the form such that the

standard would be met when the 3-year

average of the 98th percentile of the

monitored concentrations at the highest

monitor in an area is less than or equal

to 150 μg/m3, rounding to the nearest 10

μg/m3. Data handling conventions are

specified in proposed revisions to

Appendix K, as discussed in Section IV

below, and revisions to the reference

method for monitoring PM as PM10

(Appendix J) are proposed as discussed

in Section V below. The Administrator

also solicits comment on the alternative

of revoking the current 24-hour PM10

standard.

III. Rationale for Proposed Decision on

the Secondary Standards

The Criteria Document and Staff

Paper examined the effects of PM on

such aspects of public welfare as

visibility, materials damage, and soiling.

The following discussion of the

rationale for the proposed secondary

standards focuses on those

considerations most influential in the

Administrator’s proposed decision.

A. Visibility Impairment

This section of the notice presents the

Administrator’s proposed decision to

address the effects of PM on visibility by

setting secondary standards identical to

the suite of proposed primary standards,

in conjunction with the establishment of

a regional haze program under section

169A of the Act.33 In the

Administrator’s judgment, this approach

is the most effective way to address

visibility impairment given the sharp

regional variations in concentrations of

non-anthropogenic PM as well as other

factors (e.g., humidity) that affect

visibility. By augmenting the protection

provided by secondary standards set

identical to the proposed suite of

primary standards with a regional haze

program, the Administrator believes that

an appropriate degree of visibility

protection can be achieved in the

various regions of the country.

In coming to this proposed decision,

the Administrator took into account

several factors, including: (1) Staff

assessments of the most policy-relevant

information in the Criteria Document

and Staff Paper; (2) the degree of

visibility improvement expected

through attainment of the recommended

primary standards; (3) the regional

variation of naturally occurring levels of

PM and visual range; (4) difficulties

inherent in attempting to address

visibility impairment by setting national

secondary standards; and (5) EPA’s

authority to develop a national regional

haze program under section 169A of the

Act that can allow for regionallyspecific approaches to protecting

visibility. The Administrator’s

consideration of each of these factors is

discussed below.

The Administrator first concluded,

based on information presented in the

Criteria Document and Staff Paper, that

impairment of visibility is an important

effect of PM on public welfare, and that

it is experienced throughout the U.S., in

multi-state regions, urban areas, and

remote class I Federal areas 34 alike.

Visibility is an important welfare effect

because it has direct significance to

people’s enjoyment of daily activities in

all parts of the country. Individuals

value good visibility for the well-being

it provides them directly, both where

they live and work, and in places where
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65663

35 Visual range can be defined as the maximum

distance at which one can identify a black object

against the horizon sky. It is typically described in

miles or kilometers. Light extinction is the sum of

light scattering and absorption by particles and

gases in the atmosphere. It is typically expressed in

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

values representing poorer visibility. The deciview

metric describes perceived visual changes in a

linear fashion over its entire range, analogous to the

decibel scale for sound. A deciview of 0 represents

pristine conditions. Under many scenic conditions,

a change of 1 deciview is considered perceptible by

the average person.

36Estimates of annual average visibility

improvements assume (1) that the % reduction for

each fine particle constituent is equal to the %

reduction in the mass of fine particles, and (2) the

overall light extinction efficiency of the fine particle

pollutant mix does not change. (Damberg and

Polkowsky, 1996)

37 IMPROVE (Interagency Monitoring of

PROtected Visual Environments) is a visibility

monitoring network managed cooperatively by EPA,

Federal land management agencies, and State

representatives. An analysis of IMPROVE data for

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

they enjoy recreational opportunities.

Visibility is highly valued in significant

natural areas, such as national parks and

wilderness areas, because of the special

emphasis given to protecting these lands

now and for future generations.

Visibility conditions are determined

by the scattering and absorption of light

by particles and gases, from both natural

and anthropogenic sources. Visibility is

often described in terms of visual range,

light extinction, or deciviews.35 The

classes of fine particles principally

responsible for visibility impairment are

sulfates, nitrates, organic matter,

elemental carbon (soot), and soil dust.

Fine particles are more efficient per unit

mass at scattering light than coarse

particles. The scattering efficiency of

certain classes of fine particles, such as

sulfates, nitrates, and some organics,

increases as relative humidity rises

because these particles can absorb water

and grow to sizes comparable to the

wavelength of visible light. In addition

to limiting the distance that one can see,

the scattering and absorption of light

caused by air pollution can also degrade

the color, clarity, and contrast of scenes.

The Administrator also considered

the information in the Criteria

Document and Staff Paper describing

estimated background levels of PM and

natural light extinction. In the United

States, estimated annual average

background levels of PM2.5 are lower in

the West than in the East. Because

visibility in a pristine environment is

very sensitive to an additional 1 or 2

μg/m3 of PM2.5 in the atmosphere,

estimated light extinction due to natural

background levels of PM2.5 varies fairly

significantly between the East and the

West. Based on estimated background

light extinction levels summarized in

Table VIII–2 of the Staff Paper, naturally

occurring visual range in the East is

approximately 105 to 195 kilometers,

whereas in the West it is approximately

190 to 270 kilometers. Increased light

scattering of certain particles due to

higher average relative humidity in the

East is an important factor leading to

this regional difference.

The Administrator also assessed

potential visibility improvements 36 on

urban and regional scales that would

result from attainment of the proposed

primary standards for PM2.5 are attained.

In many cities having annual average

PM2.5 concentrations exceeding 17 μg/

m3, improvements in annual average

visibility resulting from attainment of

the proposed primary standards are

expected to be perceptible (i.e., to

exceed 1 deciview). Based on annual

average PM2.5 data reported in Table 12–

2 of the Criteria Document and Table V–

12 in the Staff Paper, many cities in the

Northeast, Midwest, and Southeast, as

well as Los Angeles, would be expected

to see perceptible improvement in

visibility.

In Washington, D.C., for example,

where the IMPROVE network 37 shows

average PM2.5 levels at about 19 μg/m3

during 1992–1995, approximate annual

average visibility would be expected to

improve from 21 km visual range (29

deciview) to 27 km (27 deciview).

Annual average visibility in

Philadelphia, where annual PM2.5 levels

have been recently measured at 17 μg/

m3, would be expected to change from

about 24 to 27 km, an improvement of

about 1 deciview. In Los Angeles, where

recent data shows annual average PM2.5

levels at approximately 30 μg/m3,

visibility would be expected to improve

from about 19 to 34 km (30 to 24

deciview) if the proposed annual

standard is attained.

It is important to note that some urban

areas would be expected to have annual

average PM2.5 concentrations reduced

below the proposed primary standard

level of 15 μg/m3 when implementation

of regional control strategies for PM and

other air quality programs, such as those

addressing acid rain and mobile

sources, are taken into account together.

On the other hand, some urban areas

with annual PM2.5 levels at or below the

15 μg/m3 level would be expected to see

little, if any, improvement in annual

average visibility. This may be

particularly true of certain western

urban areas that are dominated by

coarse rather than fine particles.

The Administrator also considered

the potential effect on urban visibility

when the proposed 24-hour PM2.5

standard of 50 μg/m3 is attained. In

some urban areas, attainment of the 24-

hour standard would be expected to

reduce to some degree the number and

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

the 20% of days having the greatest

impairment over the course of a year).

For example, maximum 24-hour PM2.5

concentrations have been recorded in

recent years at over 140 μg/m3 at several

California locations, and at over 70

μg/m3 in Philadelphia. If the level and

frequency of peak PM concentrations

are reduced, improvements would be

expected in those days where visibility

is worst. Some of these improvements in

peak concentrations may even be

experienced in urban areas having

annual averages below the annual

standard.

Having concluded that attainment of

the proposed annual and 24-hour PM2.5

standards would lead to visibility

improvements in many eastern and

some western urban areas, the

Administrator also considered potential

improvements to visibility on a regional

scale. In the rural East, attainment of the

proposed PM2.5 standards could result

in regional visibility improvement (e.g.,

in certain mandatory Federal Class I

areas such as Shenandoah and Great

Smoky Mountains National Parks) if

regional control strategies are adopted

and carried out in order to reduce the

impact of long-range transport of fine

particles such as sulfates. It is important

to recognize that fine particle emission

reductions achieved by other air quality

programs, such as those to reduce acid

rain or mobile source emissions, are also

expected to improve Eastern regional

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

In the West, strategies to attain the

recommended standards are less likely

to significantly improve visibility on a

regional basis. However, areas

downwind from large urban areas, such

as Southern California, would likely see

some improvement in annual average

visibility.

Based on the foregoing, the

Administrator concludes that

attainment of secondary standards set at

the level of the proposed primary

standards for PM2.5 would be expected

to result in visibility improvements in

the eastern U.S. at both urban and

regional scales, but little or no change

in the western U.S. except in and near

selected urban areas.

The Administrator also considered

whether establishment of a more

stringent national secondary standard or

standards would be effective and

efficient in providing increased

visibility protection in the western U.S.

Table VIII–4 of the Staff Paper indicates
65664 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

that the current level of annual average

light extinction (resulting from both

anthropogenic and background sources

of PM) in several western locations,

such as the Colorado Plateau, is about

equal to the level of background light

extinction (i.e., the level representing

nonanthropogenic sources only) in the

East. This regional difference is due to

higher background particle

concentrations in the East, the greater

light scattering associated with higher

humidity levels in the East, and

significantly lower concentrations of

anthropogenic PM in remote western

locations as compared with remote

eastern sites.

Because of these regional differences,

it is the Administrator’s judgment that

national secondary standards intended

to maintain or improve visibility

conditions on the Colorado Plateau

would have to be set at or even below

natural background levels in the East,

the attainment of which would

effectively require elimination of all

eastern anthropogenic emissions.

Conversely, national secondary

standards that would achieve an

appropriate degree of visibility

improvement in the East would permit

further degradation in the West. Due to

this regional variability in visibility

conditions created by differing

background fine particle levels and the

effect of humidity on these background

levels, the Administrator concludes that

proposing more stringent national

secondary standards would not be an

effective or appropriate means to protect

the public welfare from adverse impacts

of PM on visibility in all parts of the

country.

The Administrator then considered

the potential effectiveness of a regional

haze program in addressing regional

differences in visibility impairment and

thereby supplementing the protection

that would be achieved by setting the

secondary standards identical to the

suite of proposed primary standards. A

program to address this widespread,

regionally uniform type of haze caused

by a multitude of sources is required by

sections 169A and 169B of the Act. In

1977, Congress established as a national

goal ‘‘the prevention of any future, and

the remedying of any existing, manmade

impairment of visibility in mandatory

Class I areas.’’ EPA is required by

section 169A(b)(2) of the Act to ensure

that ‘‘reasonable progress’’ is achieved

toward meeting the national goal. The

structure and requirements of sections

169A and 169B, to be implemented by

the States, make it clear that visibility

protection programs can be specific to

each affected region, in contrast with

the national applicability of a secondary

NAAQS. The EPA is currently engaged

in efforts to develop a regional haze

program, and will have the benefit of

the June 1996 recommendations from

the Grand Canyon Visibility Transport

Commission as well as

recommendations from the Federal

Advisory Committee Act (FACA)

Subcommittee on Ozone, Particulate

Matter, and Regional Haze

Implementation Programs which are

expected by the end of the year.

An important factor considered in this

review is whether a regional haze

program, in conjunction with secondary

standards set identical to the suite of

proposed primary standards for PM,

would provide appropriate protection

for visibility in non-Class I areas. Based

on the following recommendation from

the 1993 report of the National Research

Council, Protecting Visibility in

National Parks and Wilderness Areas,

the Administrator believes such

protection would be provided:

Efforts to improve visibility in Class I areas

also would benefit visibility outside these

areas. Because most visibility impairment is

regional in scale, the same haze that degrades

visibility within or looking out from a

national park also degrades visibility outside

it. Class I areas cannot be regarded as

potential islands of clean air in a polluted

sea.

The Administrator recognizes,

however, that people living in certain

urban areas may place a high value on

unique scenic resources in or near these

areas, yet could have visibility problems

attributable to local sources that would

not necessarily be addressed by the

combined effects of a regional haze

program and secondary standards

identical to the proposed suite of

primary standards for PM. This may be

particularly true of certain cities located

near scenic vistas in the West. In the

Administrator’s judgment, State or local

regulatory approaches, such as recent

action by Colorado to establish a local

visibility standard for the city of Denver,

would be more appropriate and effective

in addressing these special situations

because of the localized and unique

characteristics of the problems involved.

Visibility in an urban area located near

a Class I area can also be improved

through State implementation of the

current visibility regulations, by which

emission limitations can be imposed on

a source or group of sources found to be

contributing to ‘‘reasonably

attributable’’ impairment in the Class I

area.

Based on the above considerations,

the Administrator proposes to set

secondary standards identical to the

proposed suite of primary standards, in

conjunction with a regional haze

program under sections 169A and 169B

of the Act, as the most appropriate and

effective means of addressing the

welfare effects associated with visibility

impairment. Together, the two programs

and associated control strategies should

provide appropriate protection against

the effects of PM on visibility and allow

all regions of the country to make

reasonable progress toward the national

visibility goal.

B. Materials Damage and Soiling Effects

Annual and 24-hour secondary

standards for PM10 effects on materials

damage and soiling were established in

1987 at levels equal in all respects to the

primary standards. As discussed in the

Criteria Document and Staff Paper,

particles affect materials by promoting

and accelerating the corrosion of metals,

by degrading paints, and by

deteriorating building materials such as

concrete and limestone. Soiling is found

to reduce the aesthetic quality of

buildings and objects of historical or

social interest. Past studies have found

that residential properties in highly

polluted areas typically have lower

values than those in less polluted areas.

Thus, at high enough concentrations,

particles become a nuisance and result

in increased cost and decreased

enjoyment of the environment.

After reviewing the extent of relevant

studies and other information provided

since the 1987 review of the PM

standards, the Administrator concurs

with staff and CASAC conclusions that

the available data do not provide a

sufficient basis for establishing a

secondary standard based on soiling or

materials damage alone. In the

Administrator’s judgment, however,

setting secondary standards identical to

the suite of proposed PM2.5 and PM10

primary standards, as discussed above,

would provide increased protection

against the effects of fine particles and

retain an appropriate degree of control

on coarse particles. Accordingly, the

Administrator proposes to set the

secondary standards identical to the

suite of proposed primary standards to

protect against materials damage and

soiling effects of PM.

C. Proposed Decision on the Secondary

Standards

The Administrator proposes to set

secondary standards identical to the

suite of proposed primary standards, in

conjunction with establishment of a

regional haze program. In her judgment,

such an approach would provide

appropriate protection against the

welfare effects associated with particle

pollution.
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65665

If at the time of final promulgation the

most stringent approach to setting the

PM2.5 primary standards were to be

adopted, the Administrator would

propose to set the secondary standards

identical to the final suite of primary

standards. However, even if the levels of

the PM2.5 standards were to be set as

low as 12 μg/m3 and 25 μg/m3,

respectively, for the annual and 24-hour

PM2.5 standards, the Administrator

would still foresee the need for a

regional haze program to supplement

the visibility protection afforded by

such standards. If, on the other hand,

the levels of the PM2.5 primary

standards were to be set at up to 20 μg/

m3, annual average, and up to 65 μg/m3,

24-hour average, the Administrator

would find it necessary to re-examine

whether a separate lower secondary

standard would have to be established

to protect against the welfare effects

associated with particle pollution.

Based on the above discussion, the

Administrator would consider setting

separate secondary standards for PM2.5

at 15 μg/m3, annual average, and 50 μg/

m3, 24-hour average, with PM10

standards set identical to the final

primary PM10 standards. In her

judgment, such a suite of secondary

standards, in conjunction with the

establishment of a regional haze

program, would appropriately protect

public welfare from the effects of

particle pollution.

IV. Revisions to Appendix K—

Interpretation of the PM NAAQS

The EPA is proposing to revise

Appendix K to 40 CFR part 50 to reflect

the proposed forms for the annual and

24-hour standards for PM2.5 and PM10.

The proposed revisions to Appendix K

explain the computations necessary for

determining when the proposed primary

and secondary standards are met. More

specifically, the proposed revisions

address data reporting, handling, and

rounding conventions, with example

calculations. The proposed revisions do

not address the treatment of exceptional

events data. Policies for addressing

exceptional and natural events are part

of the standards implementation

process.

Key elements of the proposed

revisions to Appendix K are outlined

below.

A. PM2.5 Computations and Data

Handling Conventions

As discussed in section II.F above,

EPA is proposing a spatially averaged

annual mean as the form of the annual

PM2.5 and a 98th percentile

concentration form of the 24-hour PM2.5

standard. The proposed Appendix K

explains the data handling conventions

and computations for the annual and

24-hour forms of the PM2.5 standards in

sections 2.1 and 2.2, respectively; data

rounding conventions in section 2.3;

monitoring considerations in section

2.4; and formulas for calculating the

annual and 24-hour forms in sections

2.5 and 2.6, respectively.

With regard to the annual PM2.5

standard, EPA is proposing to spatially

average the annual mean values in areas

designated to represent population

exposures. The spatial average is to be

carried out using data from monitoring

sites designated in a State monitoring

plan in accordance with the proposed

revisions to 40 CFR Part 58. Also, EPA

is proposing that the requirements for 3

years of data for comparison with the

standard be fulfilled by the spatial

averaging network as a whole, not by

individual monitors within the network.

The EPA also proposes that

intermediate averaging over calendar

quarters be retained for the annual

average form of the standard. Quarterly

averages may be important to ensure

representative sampling in areas with

extreme seasonal variation; however,

this extra calculation has little effect on

the calculated 3-year average value (SAI,

1996, pp. 6–9). Thus, EPA solicits

comments on whether or not the

calculation of quarterly means as an

intermediate step in deriving the annual

mean should be retained.

With regard to the 24-hour PM2.5

standard, the proposed Appendix K

defines the 98th percentile as the daily

value out of a year of monitoring data

below which 98 percent of all values in

the group fall.

State and local agencies are expected

to report daily PM2.5 concentrations to

the nearest 0.1 μg/m3 for concentrations

less than 100 μg/m3 and to the nearest

1 μg/m3 for higher values. The

incremental sensitivity of proposed

PM2.5 monitors is better than that for

PM10, and PM2.5 measurements can be

reported to 3 significant digits.

In addition to instrument sensitivity,

the number of measured values used to

calculate an averaged value affects the

precision of the value to be compared

with the level of the standard. In

calculating a 3-year average of annual

means, many values (typically 144

values to as many as 1095 values) are

used to calculate the annual mean,

whereas only 3 values are averaged to

calculate the 24-hour standard. As a

result, the annual and 24-hour standards

are expressed with different degrees of

precision and, thus, different rounding

conventions are appropriate.

Specifically, when calculating a 3-year

average of annual mean values, the

second decimal place shall be rounded

(0.05 to be rounded up) to fall within

the ±15% precision goal for the PM2.5

measurements. When calculating the 3-

year average of the 98th percentile

values, only two significant digits are

retained at levels near the standard,

with the non-significant first decimal

place rounded (0.5 μg/m3 to be rounded

up to the next highest 1 μg/m3).

To determine whether the proposed

standards are met, the calculated value

of the 3-year average of the annual

means and the 3-year average of the

98th percentile values would be

compared to the level of the relevant

standard. The proposed annual standard

of 15.0 μg/m3 is expressed to the nearest

0.1 μg/m3, while the 24-hour standard of

50 μg/m3 is expressed to the nearest 1

μg/m3, reflective of the quantitative

uncertainties in the health effects

evidence upon which these standards

are based. More specifically, these

uncertainties include the measurement

uncertainty inherent in the ambient

PM2.5 concentrations used in

epidemiological studies upon which

consideration of the levels of the

standards have been based. Because the

measurement precision is expressed as

a percentage of the measured value

(±15%), the magnitude of the target

concentration affects the appropriate

number of significant digits for the

purpose of comparison to the standard.

The EPA believes that expressing the

proposed annual standard to the nearest

0.1 μg/m3 and the 24-hour standard to

the nearest 1 μg/m3 is consistent with

the quality assurance goal for PM2.5

measurements, as stated in the proposed

Appendix A of 40 CFR Part 58, to be

within ±15%.

B. PM10 Computations and Data

Handling Conventions

As discussed in section II.H above,

the EPA is proposing to retain the

annual mean as the form of the annual

PM10 standard, and to revise the form of

the 24-hour PM10 standard to a 98th

percentile form. The 98th percentile for

the 24-hour PM10 standard would be

calculated in the same manner as

described in section A above for the

PM2.5 standard. The proposed Appendix

K explains the data handling

conventions and computations for the

annual and 24-hour forms of the PM10

standards in sections 3.1 and 3.2,

respectively; rounding conventions in

section 3.3; monitoring considerations

in section 3.4; and formulas for

calculating the annual and 24-hour

forms in sections 3.5 and 3.6,

respectively.

State and local agencies report daily

PM10 concentrations to the nearest 1 μg/
65666 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

m3 since the typical incremental

sensitivity of currently PM10 monitors is

1 μg/m3. As with the PM2.5 standards,

the number of measured values used to

calculate an averaged value affects the

precision of the value to be compared

with the level of the standard. As a

result, the annual and 24-hour standards

are expressed with different degrees of

precision and different rounding

conventions. Specifically, when

calculating the annual mean

concentration (i.e., typically with 144

values or greater), the non-significant

first decimal place shall be rounded

(with 0.5 rounded up) to preserve the

number of significant digits in the

reported data. When calculating the 3-

year average of the annual 98th

percentile values (i.e., 3 values are

averaged), only two significant digits are

retained at levels near the standard,

with the non-significant units digit

rounded (5 μg/m3 to be rounded up to

the next highest 10 μg/m3).

To determine whether the proposed

standards are met, the calculated value

of the 3-year average of the annual

means and the 3-year average of the

annual 98th percentile values would be

compared to the levels of the respective

standards. The proposed annual

standard of 50 μg/m3 is expressed to the

nearest 1 μg/m3, while the 24-hour

standard of 150 μg/m3 is expressed to

the nearest 10 μg/m3, reflective of the

quantitative uncertainties in the health

effects evidence upon which these

standards are based. More specifically,

these uncertainties include the

measurement uncertainty inherent in

the ambient PM10 concentrations used

in epidemiological studies upon which

consideration of the levels of the

standards have been based. Because the

measurement precision is expressed as

a percentage of the measured values

(±15%), the magnitude of the target

concentration affects the number of

significant digits for the purpose of

comparison to the standard. The EPA

believes that expressing the proposed

annual standard to the nearest 1 μg/m3

and the 24-hour standard to the nearest

10 μg/m3 is consistent with the quality

assurance guidelines that indicate that

the precision for PM10 measurements

shall be within ±15%.

V. Reference Methods for the

Determination of Particulate Matter as

PM2.5 and PM10 in the Atmosphere

A. Revisions to Appendix J—Reference

Method for PM10

During the course of this review, EPA

has received a number of comments

regarding the appropriateness of the

current practice of adjusting measured

PM10 concentrations to reflect standard

conditions of temperature and pressure

(25 °C and 760 mm Hg, respectively), as

required by Appendix J to Part 50. The

practice was originally adopted to

provide a standard basis for comparing

all pollutants measured in terms of mass

per unit volume (e.g., μg/m3). As EPA

has reviewed the ambient standards for

gaseous pollutants, however, technical

changes have been made to express

them on a pollutant volume/air volume

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

differences in altitude and temperature.

Such an approach is not applicable to

particulate pollutants. The question

arises whether continuing the past

practice of making temperature and

pressure adjustments for PM is

appropriate or necessary.

Information in the Criteria Document

on the health and welfare effects of PM

provides no clear basis for making such

adjustments. Recent health effects

studies have been conducted in cool

and warm climates, and in cities at high

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

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

1996a). These studies provide no

evidence that risk associated with PM

exposures is affected by variations in

altitude. Accordingly, any effect that

would be accounted for by temperature

and pressure adjustments would be

below the detection limits of

epidemiological studies. While extremes

of altitude might be expected to increase

the delivered dose of PM in those not

acclimatized to such locations, the

dosimetric studies summarized in the

Criteria Document provide no clear

support for any quantitative adjustment

to standard conditions. With respect to

welfare effects, visibility is directly

related to the actual mass of fine

particles in the atmosphere. Adjustment

of PM concentrations collected at higher

altitudes to standard conditions would

therefore lead to an overstatement of the

effect of PM on visibility in such

locations. Similarly, there is no

evidence in the Criteria Document

suggesting that effects on materials

damage and soiling are dependent on

altitude.

Based on this assessment, EPA

concludes that a continuation of the

practice of adjusting PM10

concentrations to standard conditions of

temperature and pressure is not

warranted or appropriate. Accordingly,

EPA proposes to delete this requirement

from Appendix J and to make

corresponding revisions in 40 CFR Part

50.3. In addition, EPA proposes to make

minor modifications to update

Appendix J.

B. Appendix L—New Reference Method

for PM2.5

A new reference method for the

measurement of fine particles (as PM2.5)

in the ambient air has been developed

for the primary purpose of determining

attainment of the new PM2.5 standards.

The proposed method is described in a

new Appendix L to part 50, and would

join the other reference methods (or

measurement principles) specified for

other criteria pollutants in other

appendices to part 50.

In developing a new reference method

for PM2.5, EPA staff consulted with a

number of individuals and groups in the

monitoring community, including

instrument manufacturers, academics,

consultants, and experts in State and

local agencies. The approach and key

specifications were submitted to the

CASAC Technical Subcommittee for

Fine Particle Monitoring, which held a

public meeting to discuss the FRM and

related monitoring issues on March 1,

1996. Comments on the proposed

method were provided orally and in

writing by interested parties. The

Technical Subcommittee indicated their

overall satisfaction with the FRM

approach in a letter (Price, 1996)

forwarded by CASAC to the

Administrator.

1. Approach

In addition to the primary purpose of

the new PM2.5 reference method

(determining attainment of the

standards), the EPA considered a variety

of possible secondary goals and

objectives that this measurement

method might also fulfill. Subsequently,

various alternative PM2.5 measurement

techniques were evaluated. From this

analysis, the EPA determined that the

new reference method should be based

on a conventional type ambient air

sampler that collects 24-hour integrated

PM2.5 samples on a filter that is

subsequently moisture and temperature

equilibrated and analyzed

gravimetrically.

This type of sampler is relatively

inexpensive and easy to use by

monitoring agency personnel, operates

over a wide range of ambient

conditions, produces a measurement

that is comparable to large sets of

previously collected PM data in existing

data bases, and provides a physical

sample that can be further analyzed for

chemical composition. The proposed

PM2.5 sampler is a low volume sampler

operating at 1 cubic meter per hour, for

a total sample volume of 24 m3 for the

specified 24-hour sample collection

period. The sample is collected on a 47

mm Teflon filter.
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65667

2. PM Concentrations Based on Actual

Air Volume

In accordance with the proposed

change to the PM10 reference method in

Appendix J, ambient concentrations

measured with the new reference

method would be expressed as

micrograms of PM mass per actual cubic

meter of air sampled (μg/m3), rather

than mass per cubic meter of air

adjusted to standard temperature and

pressure (25 °C and 760 mm Hg,

respectively). This convention would

provide PM concentration

measurements that are more

representative of the actual mass of

PM2.5 present in conditions of cold

temperatures and for monitoring sites at

high altitude.

3. Sampler

Although the sampler is conventional

in configuration, its design is more

sophisticated than previous samplers

used for collection of PM samples. This

more sophisticated sampler, together

with improved manufacturing and

operational quality assurance, is

necessary to achieve the more stringent

data quality objectives established for

PM2.5 monitoring data.

To meet precision requirements, the

critical mechanical components of the

inlet, particle size separator, downtube,

and upper filter holder are proposed to

be specified by design, in the form of

manufacturing drawings. Performance

specifications for these components

would be quite extensive, and the

performance tests that would be

required are difficult and require very

costly test facilities. All other aspects of

the sampler would be described by

performance-based specifications.

Sample air flow rate would have to be

carefully controlled and accurately

measured. Ambient temperature and

barometric pressure sensors would be

required for accurate measurement of

actual volumetric sample flow rate and

to provide archival documentation of

these conditions associated with the

PM2.5 measurements. Loss of semivolatile components of PM2.5 would be

reduced by temperature control of the

sample filter. The allowable rise of the

temperature of the filter above ambient

temperature is proposed to be limited to

3 degrees C above ambient temperature

during sampling as well as after sample

collection while the sample is retained

in the sampler awaiting retrieval.

The sampler would be required to

have a variety of other timing, control,

and diagnostic functions and to report

any abnormal operational conditions to

the sampler operator. Flow rate, sample

volume, sample time, and other sample,

site, and diagnostic information would

also be downloadable to a portable data

retrieval device through an electronic

port connection for fast and accurate

documentation of the sample

parameters and site conditions. A builtin sampler leak-check capability would

allow frequent checking of this

potentially important source of

measurement error. Filters would be

mounted in filter cassettes to facilitate

protected installation and retrieval from

the sampler, and sampler manufacturers

would be free to develop innovative

filter holder opening/closing

mechanisms to make filter changing fast

and reliable.

VI. Implementation Program

Recognizing that potential adoption of

new or revised NAAQS for PM and O3,

as well as potential new regulations for

regional haze, could have profound

implications for existing State

implementation programs, EPA

established a subcommittee under the

Clean Air Act Advisory Committee

(CAAAC) in 1995 to consider how such

actions might be implemented. The

Subcommittee, comprised of some 58

members representing environmental

organizations, State and local air

pollution control agencies, Federal

agencies, academia, industry, and other

public interests, was asked to provide

advice and recommendations to EPA on

developing new, integrated approaches

for implementing potential new NAAQS

for PM and O3, as well as a potential

new regional haze reduction program.

The Subcommittee, through several

work groups made up of Subcommittee

members and other designees

recommended by the Subcommittee, is

examining key aspects of the existing

implementation programs for PM and

O3, to provide for more effective

implementation of the potential new

NAAQS, as well as to provide new

approaches to better integrate broad

regional and national control strategies

with more localized efforts.

Upon completion of its work, the

Subcommittee will present its findings

and recommendations to the CAAAC.

These recommendations will then assist

EPA’s development of appropriate

policies and regulations for

implementing the potential new PM and

O3 NAAQS and regional haze

regulations in the most efficient and

environmentally effective manner.

These policies and regulations will then

be published in the Federal Register for

further input from the public.

As discussed in the advance notice of

proposed rulemaking, EPA also intends

to release an interim implementation

policy that would take effect at the time

the new or revised NAAQS for PM and

O3 are promulgated. The interim

implementation policy is intended to

provide for an effective transition from

the existing implementation

requirements and control strategies for

PM and O3 to new ones that are under

development. Among other things, the

policy will address such issues as the

continuation of existing control

requirements during the transition

period, continued classification of areas,

substitution of progress requirements, as

well as the timing of the applicability of

certain provisions of new source review

requirements.

VII. Regulatory and Environmental

Impact Analyses

The EPA has judged this proposal to

be a significant action, and has prepared

a draft Regulatory Impact Analysis (RIA)

for it as discussed below. Neither the

draft RIA nor the associated contractor

reports have been considered in issuing

this proposal. Judicial decisions make

clear that the economic and

technological feasibility of attaining

ambient standards are not to be

considered in setting them, although

such factors may be considered to a

degree in the development of State

plans to implement the standards.

As discussed above, EPA has

established a Subcommittee of the

CAAAC to examine the existing

implementation programs for PM and

O3, and provide advice and

recommendations to assist EPA in

developing new, integrated approaches

for implementing potential new or

revised NAAQS for PM and O3, as well

as a potential new regional haze

reduction program. Because the work of

the Subcommittee is still in progress,

the draft RIA and associated regulatory

flexibility assessment that accompany

this notice do not reflect its advice and

recommendations or any resulting

implementation strategies for PM. The

EPA anticipates that such strategies will

be more efficient and environmentally

effective than the ones analyzed. While

the draft RIA and flexibility assessment

should be useful in generally informing

the public about potential costs and

benefits associated with implementation

of the proposed revisions, they do not

reflect any new implementation

requirements or policies that may be

proposed after consideration of the

Subcommittee’s advice and

recommendations. As EPA develops and

elaborates such requirements or

policies, it will continue to consult with

the Subcommittee and will prepare

further regulatory analyses as

appropriate.
65668 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

A. Executive Order 12866

Under Executive Order 12866, the

Agency must determine whether a

regulatory action is ‘‘significant’’ and,

therefore, subject to Office of

Management and Budget (OMB) review

and other requirements of the Executive

Order. The order defines ‘‘significant

regulatory action’’ as one that may:

(1) Have an annual effect on the

economy of $100 million or more or

adversely affect in a material way the

economy, a sector of the economy,

productivity, competition, jobs, the

environment, public health or safety, or

State, local, or tribal governments or

communities;

(2) create a serious inconsistency or

otherwise interfere with an action taken

or planned by another Agency;

(3) materially alter the budgetary

impact of entitlements, grants, user fees,

or loan programs or the rights and

obligations or recipients thereof; or

(4) raise novel legal or policy issues

arising out of legal mandates, the

President’s priorities, or the principles

set forth in the Executive Order.

In view of its important policy

implications, this proposal has been

judged to be a ‘‘significant regulatory

action’’ within the meaning of the

Executive Order, and EPA has

submitted it to OMB for review.

Changes made in response to OMB

suggestions or recommendations will be

documented in the public docket and

made available for public inspection at

EPA’s Air and Radiation Docket

Information Center (Docket No. A–95–

54).

The EPA has prepared and entered

into the docket a draft RIA entitled

‘‘Regulatory Impact Analysis for

Proposed Particulate Matter National

Ambient Air Quality Standard

(November 1996).’’ This draft RIA

assesses the costs, economic impacts,

and benefits associated with the

implementation of the current and

several alternative NAAQS for PM as

discussed above. As discussed in the

draft RIA, there are an unusually large

number of limitations and uncertainties

associated with the analyses and

resulting cost impacts and benefit

estimates. Below are the estimated costs

and benefits associated with partial

attainment of the alternative levels in

2007. Because judicial decisions make

clear that cost can not be considered in

setting NAAQS, the results of the draft

RIA have not been considered in

developing this proposal.

COMPARISON OF ANNUAL BENEFITS

AND COSTS OF PM2.5 ALTERNATIVES

IN 2007 a (BILLIONS 1990$)

PM2.5 alternative (μg/m3)

Monetized

annual benefits of partial

attainmentb c

Annual costs

of partial attainment

*20/65 22–44 2

15/50d 58–119 6

12.5/50 94–192 14

* Does not include the reductions in costs

and benefits associated with revised PM10

studies. This alternative requires less reductions than current PM10 standards. aAll estimates are measured incremental to

the baseline PM10 alternative (PM10 μg/m3 annual/150 μg/m3 daily, 1 expected exceedance

per year). b Lower and upper end of benefit range reflects benefits of including the short-term and

long-term mortality risk reduction measure, respectively. cPartial attainment benefits based upon

post-control air quality as defined in the control cost analysis. dProposed PM2.5 alternative.

As discussed in the RIA itself, there

are a large number of limitations and

uncertainties inherent in estimating

these national costs and benefits over

extended periods of time. Results are

limited by the inability to monetize

certain health or welfare benefits for

comparison with projections of control

costs that are usually more complete,

but are sometimes overstated due to an

inability to forecast advances in

pollution prevention and control. The

approaches used for the RIA did not

attempt to take advantage of flexibilities

and savings possible in consideration of

combined air quality management

programs for PM and O3. Further, they

were limited by availability of

emissions, air quality monitoring, and

related information. Indeed, the suite of

control measures available to be

considered in the cost analysis was not

sufficient to achieve full attainment in

2007. It is for this reason we have only

presented the costs and benefits for this

‘‘partial attainment’’ scenario. In the

partial attainment scenario, there would

be 57 residual nonattainment counties

representing 29 million people in 2007

for the proposed level. One implication

of this scenario is that more time will be

needed to attain the standards in the

areas remaining in nonattainment.

Moreover, based on past experience,

improvements in technologies and

creative implementation programs are

likely to result in more effective

programs than can now be forecasted.

The EPA is planning to improve and

expand its analysis of the integrated

costs and benefits of attaining both the

PM and ozone standards in association

with developing implementation

guidance.

B. Regulatory Flexibility Analysis

The Regulatory Flexibility Act (RFA),

5 U.S.C. 601 et seq., provides that,

whenever an agency is required to

publish a general notice of rulemaking

for a proposed rule, the agency must

prepare regulatory flexibility analyses

for the proposed and final rule unless

the head of the agency certifies that it

will not have a significant economic

impact on a substantial number of small

entities. In judging what kinds of

economic impacts are relevant for this

determination, it is appropriate to

consider the purposes and requirements

of the RFA. Mid-Tex Electrical Co-op v.

FERC, 773 F.2d 327, 341–42 (D.C. Cir.

1985).

Review of the findings and purposes

section of the RFA makes clear that

Congress enacted the RFA to address the

economic impact of rules on small

entities subject to the rule’s

requirements. Pub. L. 96–354, section 2

(1980); see also 126 Cong. Rec. 21,452,

21,453 (1980). In explaining the need for

the RFA, Congress generally expressed

concern about the problematic

consequences of applying regulations

uniformly to large and small entities.

Specifically, Congress stated that ‘‘laws

and regulations designed for application

to large scale entities have been applied

uniformly to small [entities] even

though the problems that gave rise to

government action may not have been

caused by those small entities,’’ that

‘‘uniform Federal regulatory and

reporting requirements have in

numerous instances imposed

unnecessary and disproportionately

burdensome demands . . . upon small

[entities] with limited resources,’’ that

‘‘the failure to recognize differences in

the scale and resources of regulated

entities has in numerous instances

adversely affected competition in the

marketplace,’’ and that ‘‘the practice of

treating all regulated [entities] as

equivalent may lead to inefficient use of

regulatory agency resources.’’ Id. To

address these concerns, Congress

enacted the RFA ‘‘to establish as a

principle of regulatory issuance that

agencies shall endeavor, consistent with

the objectives of the rule and of

applicable statutes, to fit regulatory and

informational requirements to the scale

of the [entity] subject to regulation’’

(emphasis added). Id.

The statutory requirements for

regulatory flexibility analyses confirm

that the economic impact to be analyzed

is the impact of the rule on small

entities that will have to comply with

the rule’s requirements. In both initial
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65669

38Because the proposed rule would not establish

requirements applicable to small entities, EPA

cannot in fact perform the analyses contemplated

by the RFA.

and final regulatory flexibility analyses,

for example, the agency issuing the rule

is required to describe and (where

feasible) estimate the number of small

entities ‘‘to which the proposed rule

will apply’’; describe the reporting,

recordkeeping and other ‘‘compliance

requirements’’ of the proposed rule; and

estimate the classes of small entities that

‘‘will be subject to the requirement.’’

See RFA sections 603 and 604. The

agency must also discuss and address

significant regulatory alternatives that

are consistent with the applicable

statutes and would minimize any

significant economic impact on small

entities. Among the possible alternatives

listed by the RFA are the establishment

of differing compliance and reporting

requirements that take into account the

resources available to small entities and

partial or total exemptions from the rule

for small entities. See RFA section

603(c). The RFA’s requirements for

regulatory flexibility analyses thus

establish that the focus of such analyses

are the regulatory requirements small

entities will be required to meet as a

result of the rule and ways to tailor

those requirements to reduce the burden

on small entities. Mid-Tex Electrical Coop, 773 F.2d at 342 (‘‘[I]t is clear that

Congress envisioned that the relevant

‘economic impact’ was the impact of

compliance with the proposed rule on

regulated small entities’’).

The scope of regulatory flexibility

analyses in turn informs the scope of the

analysis necessary to support a

certification that a rule will not have ‘‘a

significant economic impact on a

substantial number of small entities.’’

Thus, ‘‘an agency may properly certify

that no regulatory flexibility analysis is

necessary when it determines that the

rule will not have a significant

economic impact on a substantial

number of small entities that are subject

to the requirements of the rule.’’ Id.

(emphasis added); see also United

Distribution Companies v. FERC, 88

F.3d 1105, 1170 (D.C. Cir. 1996).

In view of the RFA’s purposes and the

requirements it establishes for

regulatory flexibility analyses, EPA

believes that today’s proposal to revise

the PM NAAQS will not have a

significant economic impact on small

entities within the meaning of the RFA.

The proposed rule, if promulgated, will

not establish requirements applicable to

small entities. Instead, it will establish

a standard of air quality that other Clean

Air Act provisions will call on states (or

in case of state default, the federal

government) to achieve by adopting

implementation plans containing

specific control measures for that

purpose. In other words, state (or

federal) regulations implementing the

NAAQS might establish requirements

applicable to small entities, but the

NAAQS itself would not.38

For these reasons, the Administrator

certifies that this proposed rule will not

have a significant economic impact on

a substantial number of small entities.

While the statutory requirements for

regulatory flexibility analyses are thus

inapplicable to NAAQS standardsetting, EPA is nonetheless interested in

assessing to the extent possible the

potential impact on small entities of

implementing a revised PM NAAQS.

EPA has accordingly conducted a more

general analysis of the potential cost

impacts on small entities of control

measures that states might adopt to

attain and maintain a revised NAAQS,

and has included that analysis in the

RIA cited above.

That analysis examines industry-wide

cost and economic impacts for those

sectors likely to be affected when the

proposed revisions to the PM NAAQS

are implemented by States. As part of

the draft RIA, the EPA has analyzed

various industries for the existence of

small entities to ascertain whether small

entities within a given industry category

are likely to be differentially affected

when compared to the industry category

as a whole. This information will serve

to inform potentially affected small

entities, thus enabling them to

participate more effectively in EPA’s

review and potential revision of existing

implementation requirements and

policies and in development of any

necessary State implementation plan

revisions. As indicated previously, EPA

will prepare further analyses as

appropriate as it develops new

implementation requirements or

policies.

EPA’s finding that today’s proposal

will not have a significant economic

impact on small entities also entails that

the new small-entity provisions in

Section 244 of the Small Business

Regulatory Enforcement Fairness Act

(SBREFA) do not apply. Nevertheless,

EPA intends to fulfill the spirit of

SBREFA on a voluntary basis. To

accomplish this, following the proposal

of new air quality standards for O3 and

PM, EPA intends to work with the Small

Business Administration (SBA) to hold

two separate panel exercises to collect

comments, advice and

recommendations from representatives

of small businesses, small governments,

and other small organizations. The first

panel, soliciting comments on the new

standards themselves, will be held

shortly after proposal. The second

panel, covering implementation of the

standards, will be held a few months

later. Both panel exercises will be

carried out using a panel process

modeled on the ‘‘Small Business

Advocacy Review Panel’’ provisions in

Section 244 of SBREFA. We are also

adding a number of small-entity

representatives to our Federal advisory

committee focusing on NAAQS

implementation; we expect the smallentity advice from this committee will

help the aforementioned

implementation panel accomplish its

purpose.

C. Impact on Reporting Requirements

There are no reporting requirements

directly associated with an ambient air

quality standard proposed under section

109 of the Act (42 U.S.C. 7400). There

are, however, reporting requirements

associated with related sections of the

Act, particularly sections 107, 110, 160,

and 317 (42 U.S.C. 7407, 7410, 7460,

and 7617). In EPA’s proposed revisions

to the air quality surveillance

requirements (40 CFR part 58) for PM,

the associated RIA addresses the

Paperwork Reduction Act requirements

through an Information Collection

Request.

D. Unfunded Mandates Reform Act

Title II of the Unfunded Mandates

Reform Act of 1995 (UMRA), Pub. L.

104–4, establishes requirements for

Federal agencies to assess the effects of

their regulatory actions on State, local,

and tribal governments and the private

sector. Under section 202 of the UMRA,

EPA generally must prepare a written

statement, including a cost-benefit

analysis, for proposed and final rules

with ‘‘Federal mandates’’ that may

result in expenditures to State, local,

and tribal governments, in the aggregate,

or to the private sector, of $100 million

or more in any one year. This

requirement does not apply if EPA is

prohibited by law from considering

section 202 estimates and analyses in

adopting the rule in question. Before

promulgating an EPA rule for which a

written statement is needed, section 205

of the UMRA generally requires EPA to

identify and consider a reasonable

number of regulatory alternatives and

adopt the least costly, most costeffective, or least burdensome

alternative that achieves the objectives

of the rule. These requirements do not

apply when they are inconsistent with

applicable law. Moreover, section 205

allows EPA to adopt an alternative other

than the least costly, most cost-effective,
65670 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

or least burdensome alternative if the

Administrator publishes with the final

rule an explanation of why that

alternative was not adopted. Before EPA

establishes any regulatory requirements

that may significantly or uniquely affect

small governments, including tribal

governments, it must have developed

under section 203 of the UMRA a small

government agency plan. The plan must

provide for notifying potentially

affected small governments, enabling

officials of affected small governments

to have meaningful and timely input in

the development of EPA regulatory

proposals with significant Federal

intergovernmental mandates, and

informing, educating, and advising

small governments on compliance with

the regulatory requirements.

As indicated previously, EPA cannot

consider in setting a NAAQS the

economic or technological feasibility of

attaining ambient air quality standards,

although such factors may be

considered to a degree in the

development of State plans to

implement the standards. Moreover, the

proposed revisions to the PM NAAQS,

if adopted, will not in themselves

impose any new expenditures on

governments or on the private sector, or

establish any new regulatory

requirements affecting small

governments. Accordingly, EPA has

determined that the provisions of

sections 202, 203, and 205 of the UMRA

do not apply to this proposed decision.

The EPA acknowledges, however, that

any corresponding revisions to

associated State implementation plan

requirements and air quality

surveillance requirements, 40 CFR part

51 and 40 CFR part 58, respectively,

might result in such effects.

Accordingly, EPA has addressed

unfunded mandates in the notice that

announces the proposed revisions to 40

CFR part 58, and will, as appropriate,

when it proposes any revisions to 40

CFR part 51.

E. Environmental Justice

Executive Order 12848 requires that

each Federal agency make achieving

environmental justice part of its mission

by identifying and addressing, as

appropriate, disproportionately high

and adverse human health or

environmental effects of its programs,

policies, and activities on minorities

and low-income populations. These

requirements have been addressed to

the extent practicable in the draft RIA

cited above.

List of Subjects in 40 CFR Part 50

Environmental protection, Air

pollution control, Carbon monoxide,

Lead, Nitrogen dioxide, Ozone,

Particulate matter, Sulfur oxides.

Dated: November 27, 1996.

Carol M. Browner,

Administrator.

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Damberg, R.; Polkowsky, B. (1996)

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Carol M. Browner. Closure letter on draft

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(A&WMA publication VIP–49).

For the reasons set forth in the

preamble, Part 50 of Chapter I of Title

40 of the Code of Federal Regulations is

proposed to be amended as follows:

PART 50—NATIONAL PRIMARY AND

SECONDARY AMBIENT AIR QUALITY

STANDARDS

1. The authority citation for Part 50

continues to read as follows:

Authority: Secs. 109 and 301(a), Clean Air

Act, as amended (42 U.S.C. 7409, 7801(a)).

2. Section 50.3 is revised to read as

follows:

§ 50.3 Reference conditions.

All measurements of air quality that

are expressed as mass per unit volume

(e.g., micrograms per cubic meter) other

than for particulate matter (PM10 and

PM2.5) shall be corrected to a reference

temperature of 25 °C and a reference

pressure of 760 millimeters of mercury

(1,013.2 millibars). Measurements of

PM10 and PM2.5 shall be reported based

on actual air volume measured at the

actual temperature and pressure at the

monitoring site during the measurement

period.

3. Section 50.6 is revised to read as

follows:

§ 50.6 National primary and secondary

ambient air quality standards for particulate

matter.

(a) The national primary and

secondary ambient air quality standards

for particulate matter are:

(1) 15.0 micrograms per cubic meter

(μg/m3) annual arithmetic mean

concentration, and 50 μg/m3 24-hour

average concentration measured in the

ambient air as PM2.5 (particles with an

aerodynamic diameter less than or equal

to a nominal 2.5 micrometers) by:
65672 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

(i) A reference method based on

Appendix L and designated in

accordance with Part 53 of this chapter,

or

(ii) An equivalent method designated

in accordance with Part 53 of this

chapter.

(2) 50 micrograms per cubic meter

(μg/m3) annual arithmetic mean

concentration, and 150 μg/m3 24-hour

average concentration measured in the

ambient air as PM10 (particles with an

aerodynamic diameter less than or equal

to a nominal 10 micrometers) by:

(i) A reference method based on

Appendix J and designated in

accordance with Part 53 of this chapter,

or

(ii) An equivalent method designated

in accordance with Part 53 of this

chapter.

(b) The annual primary and secondary

PM2.5 standards are met when the

annual arithmetic mean concentration,

as determined in accordance with

Appendix K to this part, is less than or

equal to 15.0 micrograms per cubic

meter.

(c) The 24-hour primary and

secondary PM2.5 standards are met when

the 98th percentile 24-hour

concentration, as determined in

accordance with Appendix K to this

part, is less than or equal to 50

micrograms per cubic meter.

(d) The annual primary and secondary

PM10 standards are met when the

annual arithmetic mean concentration,

as determined in accordance with

Appendix K of this part, is less than or

equal to 50 micrograms per cubic meter.

(e) The 24-hour primary and

secondary PM10 standards are met when

the 98th percentile 24-hour

concentration, as determined in

accordance with Appendix K of this

part, is less than or equal to 150

micrograms per cubic meter.

4. Appendix J is amended as follows:

a. Section 2.2 is revised.

b. The last sentence of Section 3.1 is

revised.

c. The first sentence of Section 7.3 is

revised.

d. The last sentence of Section 8.1.2

is removed.

e. Section 8.2.1 is revised.

f. The first sentence of Section 8.2.2

is revised.

g. Section 11.1 is revised.

h. Section 11.2 is revised.

i. Section 11.3 is removed.

Appendix J to Part 50—Reference

Method for the Determination of

Particulate Matter as PM10 in the

Atmosphere

* * * * *

2.2 Each filter is weighed (after moisture

equilibration) before and after use to

determine the net weight (mass) gain due to

collected PM10. The total volume of air

sampled, measured at the actual ambient

temperature and pressure, is determined

from the measured flow rate and the

sampling time. The mass concentration of

PM10 in the ambient air is computed as the

total mass of collected particles in the PM10

size range divided by the volume of air

sampled, and is expressed in micrograms per

actual cubic meter (μg/m3).

* * * * *

3.1 * * * Nevertheless, all samplers

should be capable of measuring 24-hour PM10

mass concentrations of at least 300 μg/m3

while maintaining the operating flow rate

within the specified limits.

* * * * *

7.3 Flow Rate Transfer Standard. The

flow rate transfer standard must be suitable

for the sampler’s operating flow rate and

must be calibrated against a primary flow or

volume standard that is traceable to the

National Institute of Standards and

Technology (NIST).

* * * * *

8.2.1 PM10 samplers employ various

types of flow control and flow measurement

devices. The specific procedure used for flow

rate calibration or verification will vary

depending on the type of flow controller and

flow rate indicator employed. Calibration is

in terms of actual volumetric flow rates (Qa)

to meet the requirements of section 8.1. The

general procedure given here serves to

illustrate the steps involved in the

calibration. Consult the sampler

manufacturer’s instruction manual and

Reference 2 for specific guidance on

calibration. Reference 14 provides additional

information on various other measures of

flow rate and their interrelationships.

8.2.2 Calibrate the flow rate transfer

standard against a primary flow or volume

standard traceable to NIST.

* * * * *

11.1 Calculate the total volume of air

sampled as:

V=Qa×t

Where:

V=total air sampled, at ambient temperature

and pressure, m3,

Qa=average sample flow rate at ambient

temperature and pressure, m3/min, and

t=sampling time, min.

11.2 Calculate the PM10 concentration as:

PM10=(Wf ¥ Wi) × 106/V

Where:

PM10=mass concentration of PM10, μg/m3,

Wf, Wi=final and initial weights of filter

collecting PM10 particles, g, and

106 = conversion of g to μg.

Note: If more than one size fraction in the

PM10 size range is collected by the sampler,

the sum of the net weight gain by each

collection filter [∑S(Wf ¥ Wi)] is used to

calculate the PM10 mass concentration.

* * * * *

5. Appendix K is revised in its

entirety to read as follows:

Appendix K to Part 50—Interpretation

of the National Ambient Air Quality

Standards for Particulate Matter

1.0 General

This appendix explains the data handling

conventions and computations necessary for

determining whether the annual and 24-hour

primary and secondary national ambient air

quality standards for particulate matter

specified in part 50.6 of this chapter are met.

Particulate matter is measured in the ambient

air as PM10 and PM2.5 (particles with an

aerodynamic diameter less than or equal to

a nominal 10 and 2.5 micrometers,

respectively) by a reference method based on

appendix J of this part for PM10 and on

appendix L for PM2.5, as applicable, and

designated in accordance with part 53 of this

chapter, or by an equivalent method

designated in accordance with part 53 of this

chapter. Data reporting, data handling, and

computation procedures to be used in

making comparisons between reported PM10

and PM2.5 concentrations and the levels of

the PM standards are specified in the

following sections.

Several terms used throughout this

appendix are defined here. A ‘‘daily value’’

for PM refers to the 24-hour average

concentration of PM calculated or measured

from midnight to midnight (local time) for

PM10 or PM2.5. The term ‘‘98th percentile’’

means the daily value out of a year of

monitoring data below which 98% of all

values in the group fall. The terms ‘‘average’’

and ‘‘mean’’ refer to an arithmetic mean. All

particulate matter standards are expressed in

terms of 3-year averages of annual values: the

3-year average of the annual means for the

annual standards, and the 3-year average of

the 98th percentile values for each year for

the 24-hour standards. The term ‘‘year’’ refers

to a calendar year. ‘‘Designated monitors’’ are

those monitoring sites designated in a State

monitoring plan for spatial averaging in areas

designated for spatial averaging in

accordance with part 58 of this chapter.

2.0 Comparisons With the PM2.5 Standards

2.1 Annual PM2.5 Standard

The annual PM2.5 standard is met when the

3-year average of the spatially averaged

annual means is less than or equal to 15.0 μg/

m3. The 3-year average of the spatially

averaged annual means is determined by

averaging quarterly means at each monitor to

obtain the annual mean PM2.5 concentrations

at each monitor, then averaging across all

designated monitors, and finally averaging

for three consecutive years.

The steps can be summarized as follows:

(a) Average 24-hour measurements to

obtain quarterly means at each monitor,

(b) Average quarterly means to obtain

annual means at each monitor,

(c) Average across designated monitoring

sites to obtain an annual spatial mean for an

area, and

(d) Average 3 years of annual spatial means

to obtain a 3-year average of spatially

averaged annual means.

For the annual PM2.5 standard, a year meets

data completeness requirements when at
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65673

least 75 percent of the scheduled sampling

days for each quarter have valid data. Three

years of spatial averages are required to

demonstrate that the standard has been met.

Sites with less than 3 years of data shall be

included in spatial averages for those years

that data completeness requirements are met.

The formulas for calculating the 3-year

average annual mean of the PM2.5 standard

are given in Section 2.5.

Although 3 complete years of data are

required to demonstrate that the standard has

been met, years with high concentrations

shall not be ignored just because they have

less than complete data. Thus, in computing

annual spatially averaged means, sites with

less than 75 percent data completeness for

each quarter in a year shall be included in

the computation if the resulting annual mean

concentration is greater than the level of the

standard.

2.2 24–Hour PM2.5 Standard

The 24-hour PM2.5 standard for is met

when the 3-year average of the 98th

percentile values at each monitoring site is

less than or equal to 50 μg/m3. This

comparison shall be based on three

consecutive, complete years of air quality

data. A year meets data completeness criteria

when at least 75 percent of the scheduled

sampling days have valid data for each

quarter. The formula for calculating the 3-

year average of the annual 98th percentile

values is given in Section 2.6.

Although three complete years of data are

required to demonstrate that the standard has

been met, years with high concentrations

shall not be ignored just because they have

less than complete data. Thus, in computing

the 3-year average 98th percentile value,

years with less than 75 percent data

completeness shall be included in the

computation if the annual 98th percentile

value is greater than the level of the standard.

2.3 Rounding Conventions

For the purposes of comparing calculated

values to the applicable level of the standard,

it is necessary to round the final results of

the calculations described in sections 2.5 and

2.6. For the annual PM2.5 standard, the 3-year

average of the spatially averaged annual

means shall be rounded to the nearest 0.1 g/

m3 (decimals 0.05 and greater are rounded up

to the next 0.1, and any decimal lower than

0.05 is rounded down to the nearest 0.1). For

the 24-hour PM2.5 standard, the 3-year

average of the annual 98th percentile values

shall be rounded to the nearest 1 μg/m3

(decimals 0.5 and greater are rounded up to

nearest whole number, and any decimal

lower than 0.5 is rounded down to the

nearest whole number).

2.4 Monitoring Considerations

Part 58.13 of this chapter specifies the

required minimum frequency of sampling for

PM2.5. Part 58 also specifies which monitors

shall be used in making comparisons with

the particulate matter standards.

For the annual PM2.5 standard, when

designated monitors are located at the same

site and are reporting PM2.5 values for the

same time periods, their concentrations shall

be averaged before an area-wide spatial

average is calculated, and such monitors will

then be considered as one monitor.

2.5 Formulas for the Annual PM2.5 Standard

(a) An annual mean value for PM2.5 is

determined by first averaging the daily values

of a calendar quarter.

X

n

q y s X

q

i q y s

i

nq

, , , , , = [ ] =

∑1

1

1

Where:

xq, y, s=the mean for quarter q of year y for

site s,

nq=the number of monitored values in the

quarter, and

xi, q, y, s=the ith value in quarter q for year y

for site s.

(b) The following formula is then to be

used for calculation of the annual mean:

X X y s q y s

q

, , , = [ ] =

∑

1

4

2

1

4

Where:

xy, s=the annual mean concentration for year

y (y=1, 2, or 3) and for site s, and

xq, y, s=the mean for quarter q of year y for

site s.

(c) The spatially averaged annual mean for

year y is computed by first calculating the

annual mean for each site designated to be

included in a spatial average, xy,s and then

computing the average of these values across

sites:

x

n

x y

s

y s

s

ns

= [ ] =

∑1 3

1

,

Where:

xy=the spatially averaged mean for year y,

xy,s=the annual mean for year y and site s,

and

ns=the number of sites designated to be

averaged.

In the event that an area designated for

spatial averaging has one or more sites at the

same location producing data for the same

time periods, the sites are averaged together

before using formula [3] by:

x

n

x y s*

c

y s

s

nc

, , = [ ] =

∑1 4

1

Where:

xy,s*=the annual mean for year y for the sites

at the same location (which will now be

considered one site),

nc=the number of sites at the same location

designated to be included in the spatial

average, and

xy,s=the annual mean for year y and site s.

(d) The 3-year average of the spatially

averaged annual means is calculated by using

the following formula:

x xy

y

= [ ] =

∑

1

3

5

1

3

Where:

x=the 3-year average of the spatially averaged

annual means, and

xy=the spatially averaged annual mean for

year y.

Example 1. Area designated for spatial

averaging that meets the primary annual

PM2.5 standard.

In an area designated for spatial averaging,

four designated monitors recorded data in at

least 1 year of a particular 3-year period.

Using formulas [1] and [2], the annual means

for PM2.5 at each site are calculated for each

year. The following table can be created from

the results. Data completeness percentages

are also shown.

Site #1 Site #2 Site #3 Site #4 Spatial mean

Year 1 .............................. Annual mean (μg/m3) ....................... 12.7 ...................... ...................... ...................... 12.7

% data completeness ....................... 80 0 0 0 ......................

Year 2 .............................. Annual mean (μg/m3) ....................... 13.3 17.4 9.8 ...................... 15.35

% data completeness ....................... 90 63 40 0 ......................

Year 3 .............................. Annual mean (μg/m3) ....................... 12.9 16.7 12.3 20.1 15.50

% data completeness ....................... 90 80 85 50 ......................

3-year mean ..................... ........................................................... ...................... ...................... ...................... ...................... 14.52

The data from these sites are averaged in

the order described in section 2.1. Note that

the annual mean from site #3 in year 2 does

not enter in the spatial mean since the data

completeness criteria are not met. However,

the annual means from site #2 in year 2 and

from site #4 in year 3 are included, even

though the data completeness criteria are not

met, since they are above the level of the

standard. The 3-year mean is rounded to 14.5

μg/m3, indicating that this area meets the

annual PM2.5 standard.

Example 2. Area with two monitors at the

same location that meets the primary

annual PM2.5 standard.

In an area designated for spatial

monitoring, six designated monitors, with
65674 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

two monitors at the same location (#5 and

#6), recorded data in a particular 3-year

period.

Using formulas [1] and [2], the annual

means for PM2.5 at each site are calculated

for each year. The following table can be

created from the results.

Annual mean (μg/m3) Site #1 Site #2 Site #3 Site #4 Site #5 Site #6 Average of

#5 and #6

Spatial

mean

Year 1 .................................... 14.2 11.5 8.7 10.9 16.9 14.5 15.70 12.21

Year 2 .................................... 16.4 13.3 10.3 12.3 15.5 13.8 14.65 13.39

Year 3 .................................... 12.9 12.4 9.5 11.2 15.1 13.3 14.20 12.04

3-Year mean .......................... .................... .................... .................... .................... .................... .................... .................. 12.55

The annual means for sites #5 and #6 are

averaged together using formula [4] before

the spatial average is calculated using

formula [3] since they are in the same

location. The 3-year mean is rounded to 12.6

μg/m3, indicating that this area meets the

annual PM2.5 standard.

Example 3. Area with a single monitor that

meets the primary annual PM2.5

standard.

Given data from a single monitor in an area

designated for spatial averaging, the

calculations are as follows. Using formulas

[1] and [2], the annual means for PM2.5 are

calculated for each year. If the annual means

are 10.28, 17.38, and 12.25 μg/m3, then the

3-year mean is:

X=(1⁄3)×(10.28+17.38+12.25)=13.303 μg/m3.

This value is rounded to 13.3, indicating

that this area meets the annual PM2.5

standard.

2.6 Formulas for the 24-Hour PM2.5

Standard

When the data for a particular site and year

meet the data completeness requirements in

section 2.2, calculation of the 98th percentile

is accomplished by the following steps. All

the daily values from a particular site and

year comprise a series of values (X1, X2, X3,

. . ., Xn), that can be sorted into a series

where each number is equal to or larger than

the preceding number (X[1], X[2], X[3], . . .,

X[n]). In this case, X[1] is the smallest number

and X[n] is the largest value. The 98th

percentile is found from the sorted series of

daily values which is ordered from the

lowest to the highest number. Compute

(0.98)×(n) as the number ‘‘i.d’’, where ‘‘i’’ is

the integer part of the result and ‘‘d’’ is the

decimal part of the result. The 98th

percentile value for year y, P0.98, y, is given

by formula [6]:

P X if d and

P

X X

if d

y j

y

j j

0 98 1

0 98

1

0

6

2

0

. ,

. ,

= ≠

[ ]

= + =

[ ] +

[ ] [ ] +

where:

P0.98,y=98th percentile for year y,

X[j]=the jth number in the ordered series of

numbers,

‘‘i’’=the integer part of the product of 0.98

and n (the number of values in the

series), and

‘‘d’’=the decimal part of the product of 0.98

and n.

The 3-year average 98th percentile is then

calculated by averaging the annual 98th

percentiles:

P

P y

y

0 98

0 98

1

3

3 . 7

. ,

= [ ] =

∑

The 3-year average 98th percentile is

rounded according to the conventions in

section 2.3 before a comparison with the

standard is made.

Example 4. Ambient monitoring site with

every-day sampling that meets the primary

24-hour PM2.5 standard.

In each year of a particular 3 year period,

varying numbers of daily PM2.5 values (e.g.,

278, 300, and 293) out of a possible 365

values were recorded at a particular site with

the following ranked values (in μg/m 3):

Year 1 Year 2 Year 3

j rank Xj value j rank Xj value j rank Xj value

* * * * * * * * * * * * * * * * * *

272 44.1 293 41.4 287 50.3

273 45.0 294 43.5 288 52.1

274 47.4 295 48.0 289 53.2

* * * * * * * * * * * * * * * * * *

Using formula [6], the 98th percentile values for each year are calculated as follows:

0 98 278 272 45 0

0 98 300 294

2

43 5 48 0

2

45 75

0 98 293 28714 52 1

0 98 1 273

3

0 98 2

294 295

0 98 3 288

3

. * .44 . /

. * . . .

. * . . / .

. ,

. ,

. ,

= ⇒ = =

= ⇒ =

+ = ( ) + =

= ⇒ = =

[ ]

[ ] [ ]

[ ]

P X g m

P

X X

P X g m

μ

μ

Using formula [7], the 3-year average 98th percentile is calculated as follows:

P g m which rounds to g m 0 98

45 0 45 75 52 7 3 3

3 . 47 6 48 . . . = . / , / + + = μ μ

Therefore, this site meets the 24-hour PM2.5 standard.
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65675

3.0 Comparisons with the PM10 Standards

3.1 Annual PM10 Standard

The annual PM10 standard is met when the

3-year average of the annual mean PM10

concentrations at each monitoring site is less

than or equal to 50 μg/m 3. The 3-year average

of the annual means is determined by

averaging quarterly means to obtain annual

mean PM10 concentrations for 3 consecutive,

complete years at each monitoring site. The

steps can be summarized as follows:

(a) Average 24-hour measurements to

obtain a quarterly mean,

(b) Average quarterly means to obtain an

annual mean, and

(c) Average annual means to obtain a 3-

year mean.

For the annual PM10 standard, a year meets

data completeness requirements when at

least 75 percent of the scheduled sampling

days for each quarter have valid data. The

formulas for calculating the 3-year average

annual mean of the PM10 standard are given

in Section 3.5.

Although 3 complete years of data are

required to demonstrate that the standard has

been met, years with high concentrations

shall not be ignored just because they have

less than complete data. Thus, in computing

the 3-year average annual mean

concentration, years with less than 75

percent data completeness shall be included

in the computation if the annual mean

concentration is greater than the level of the

standard.

3.2 24-Hour PM10 Standard

The 24-hour PM10 standard is met when

the 3-year average of the annual 98th

percentile values at each monitoring site is

less than or equal to 150 μg/m 3. This

comparison shall be based on 3 consecutive,

complete years of air quality data. A year

meets data completeness criteria when at

least 75 percent of the scheduled sampling

days have valid data each quarter. The

formula for calculating the 3-year average of

the annual 98th percentile values is given in

Section 3.6.

Although 3 complete years of data are

required to demonstrate that the standard has

been met, years with high concentrations

shall not be ignored just because they have

less than complete data. Thus, in computing

the 3-year average of the annual 98th

percentile values, years with less than 75

percent data completeness shall be included

in the computation if the annual 98th

percentile value is greater than the level of

the standard.

3.3 Rounding Conventions

For the annual PM10 standard, the 3-year

average of the annual PM10 means shall be

rounded to the nearest 1 μg/m 3 (decimals 0.5

and greater are rounded up to the next whole

number, and any decimal less than 0.5 is

rounded down to the nearest whole number).

For the 24-hour PM10 standard, the 3-year

average of the annual 98th percentile values

of PM10 shall be rounded to the nearest 10

μg/m 3 (155 μg/m 3 and greater would be

rounded to 160 μg/m 3 and 154 μg/m 3 and

less would be rounded to 150 μg/m 3).

3.4 Monitoring Considerations

Part 58.13 of this chapter specifies the

required minimum frequency of sampling for

PM10. For making comparisons with the PM10

NAAQS, all sites meeting applicable

requirements in part 58 of this chapter would

be used.

3.5 Formulas for the Annual PM10 Standard

(a) An annual arithmetic mean value for

PM10 is determined by first averaging the 24-

hour values of a calendar quarter using the

following formula:

X

n q y X

q

i q y

i

nq

, , , = [ ] =

∑1 9

1

Where:

X ̄ q, y=the mean for quarter q of year y,

nq=the number of monitored values in the

quarter, and

xi, q, y=the ith value in quarter q for year y.

(b) The following formula is then to be

used for calculation of the annual mean:

X Xq y

q

= [ ] =

∑

1

4

10

1

4

,

Where:

Xy=the annual mean concentration for year y,

(y=1, 2, or 3), and

xq,y=the mean for a quarter q of year y.

(c) The 3-year average of the annual means

is calculated by using the following formula:

x xy

y

= [ ] =

∑

1

3

11

1

3

Where:

x ̃=the 3-year average of the annual means,

and

x ̃ y=the annual mean for calendar year y.

Example 5. Ambient monitoring site that

does not meet the annual PM10 standard.

Given data from a PM10 monitor and using

formulas [9] and [10], the annual means for

PM10 are calculated for each year. If the

annual means are 52.42, 82.17, and 63.23

μg/m 3, then the 3-year average annual mean

is

x ̃=(1⁄3) • (52.42 + 82.17 + 63.23)=65.94 which

is rounded to 66 μg/m3. Therefore, this

site does not meet the annual PM10

standard.

3.6 Formula for the 24-Hour PM10 Standard

When the data for a particular site and year

meet the data completeness requirements in

section 3.2, calculation of the 98th percentile

is accomplished by the following steps. All

the daily values from a particular site and

year comprise a series of values (X1, X2, X3,

. . ., Xn) that can be sorted into a series

where each number is equal to or larger than

the preceding number (X[1], X[2], X[3], . . .,

X[n]). In this case, X[1] is the smallest number

and X[n] is the largest value. The 98th

percentile is found from the sorted series of

daily values which is ordered from the

lowest to the highest number. Compute (0.98)

× (n) as the number ‘‘i.d’’, where ‘‘i’’ is the

integer part of the result and ‘‘d’’ is the

decimal part of the result. The 98th

percentile value for year y, P0.98,y, is given by

formula [12]:

P X if d and

P

X X

if d

y j

y

j j

0 98 1

0 98

1

0

12

2

0

. ,

. ,

= ≠

[ ]

=

+

=

[ ] +

[ ] [ ] +

Where:

P0.098,y=the 98th percentile for year y,

X[j]=the jth number in the ordered series of

numbers,

‘‘i’’=the integer part of the product of 0.98

and n (the number of observations in the

series), and

‘‘d’’=the decimal part of the product of 0.98

and n.

The 3-year average 98th percentile value is

then calculated by averaging the annual 98th

percentiles:

P

P y

y

0 98

0 98

1

3

3 . 13

. ,

= [ ] =

∑

The 3-year average 98th percentile is

rounded according to the conventions in

section 3.3 before a comparison with the

standard is made.

Example 6. Ambient monitoring site with

sampling every sixth day that meets the

primary 24-hour PM10 standard.

In each year of a particular three year

period, varying numbers of PM10 daily values

(e.g., 55, 49, and 50) out of a possible 61 daily

values were recorded at a particular site with

the following ranked values (in μg/m3):
65676 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

Year 1 Year 2 Year 3

j rank Xj value j rank Xj value j rank Xj value

* * * * * * * * * * * * * * * * * *

53 120 47 143 48 140

54 128 48 148 49 144

55 130 49 150 50 147

* * * * * * * * * * * * * * * * * *

Using formula [12], the 98th percentile values for each year are calculated as follows:

0 98 55 53 9 128

0 98 49 48 02 150

0 98 50 49

2

144 147

2

145 5

0 98 1 54

3

0 98 2 49

3

0 98 3

49 50 3

. * . /

. * . /

. * . /

. ,

. ,

. ,

= ⇒ = =

= ⇒ = =

= ⇒ =

+ = + =

[ ]

[ ]

[ ] [ ]

P X g m

P X g m

P

X X

g m

μ

μ

μ

Using formula [3], the 3-year average 98th percentile is calculated as follows:

128 150 145 5

3

141 2 140 + + 3 3 = . . / / . μ μ g m rounds to g m

Therefore, this site meets the 24-hour PM10

standard.

6. Appendix L is added to read as

follows:

Appendix L—Reference Method for the

Determination of Fine Particulate

Matter as PM2.5 in the Atmosphere

1.0 Applicability.

1.1 This method provides for the

measurement of the mass concentration of

fine particulate matter having an

aerodynamic diameter less than or equal to

a nominal 2.5 micrometers (PM2.5) in ambient

air over a 24-hour period for purposes of

determining whether the primary and

secondary national ambient air quality

standards for fine particulate matter specified

in Sec. 50.6 of this chapter are met. The

measurement process is considered to be

nondestructive, and physical or chemical

analyses. Quality assessment procedures are

provided in part 58, Appendices A and B, of

this chapter and quality assurance

procedures and guidance are provided in

References 1 and 2.

1.2 This method will be considered a

reference method for purposes of part 58 of

this chapter only if:

(a) the associated sampler meets the

requirements specified in this appendix and

the applicable requirements in part 53 of this

chapter,

(b) the method and associated sampler

have been designated as a reference method

in accordance with part 53 of this Chapter,

and

(c) the national operating performance of

the associated sampler, as determined in

accordance with part 58, Appendix A,

section 6 of this chapter, continue to meet the

specifications set forth in part 58, Appendix

A, section 6.3.3 of this chapter.

1.3 PM2.5 samplers that meet all

specifications set forth in this method but

have minor deviations and/or modifications

of the reference method sampler necessary to

obtain sequential operation will be

designated as ‘‘Class I’’ equivalent methods

for PM2.5 in accordance with part 53 of this

Chapter.

2.0 Principle

2.1 An electrically powered air sampler

draws ambient air at a constant volumetric

flow rate into a specially shaped inlet and

through an inertial particle size separator

(impactor) where the suspended particulate

matter in the PM2.5 size range is separated for

collection on a polytetrafluoroethylene

(PTFE) filter over the specified sampling

period. The air sampler and other aspects of

this reference method are specified either

explicitly in this appendix or generally with

reference to other applicable regulations or

quality assurance guidance.

2.2 Each filter is weighed (after moisture

and temperature equilibration) before and

after sample collection to determine the net

weight (mass) gain due to collected PM2.5.

The total volume of air sampled is

determined by the sampler from the

measured flow rate at actual ambient

temperature and pressure and the sampling

time. The mass concentration of PM2.5 in the

ambient air is computed as the total mass of

collected particles in the PM2.5 size range

divided by the actual volume of air sampled,

and is expressed in micrograms per actual

cubic meter of air (μg/m 3).

3.0 PM2.5 Measurement Range

3.1 Lower concentration limit. The lower

limit of the mass concentration range should

be 1 μg/m3 or less and is determined

primarily by the repeatability (precision) of

filter blanks, based on the 24 m3 nominal

total air sample volume specified for the 24-

hour sample.

3.2 Upper concentration limit. The upper

limit of the mass concentration range is

determined by the filter mass loading beyond

which the sampler can no longer maintain

the operating flow rate within specified

limits due to increased pressure drop across

the loaded filter. This upper limit cannot be

specified precisely because it is a complex

function of the ambient particle size

distribution and type, humidity, the

individual filter used, the capacity of the

sampler flow rate control system, and

perhaps other factors. Nevertheless, all

samplers should be capable of measuring 24-

hour PM2.5 mass concentrations of at least

200 μg/m3 while maintaining the operating

flow rate within the specified limits.

3.3 Sample period. The required sample

period for PM2.5 concentration measurements

by this method shall be 1380 to 1500 minutes

(23 to 25 hours). However, when a sample

period is less than 1380 minutes, the

measured concentration (as determined by

the collected PM2.5 mass divided by the

actual sampled air volume), multiplied by

the actual number of minutes in the sample

period and divided by 1440, may be used as

a valid concentration measurement for

purposes of determining violations of the

NAAQS. This number represents the

minimum concentration that would have

been measured for the full 24-hour sample

period. When reported to AIRS, this data

value should receive a special code.

4.0 Accuracy

4.1 Because the size and volatility of the

particles making up ambient particulate

matter vary over a wide range and the mass

concentration of particles varies with particle

size, it is difficult to define the accuracy of

PM2.5 samplers in an absolute sense. The

accuracy of PM2.5 measurements is therefore

defined in a relative sense, referenced to

measurements provided by this reference

method. Accordingly, accuracy for other

(equivalent) methods for PM2.5 shall be

defined as the degree of agreement between

a subject field PM2.5 sampler and a collocated

PM2.5 reference method audit sampler

operating simultaneously at the monitoring

site location of the subject sampler. This field

sampler audit procedure is set forth in

section 6 of part 58, Appendix A of this

chapter.

4.2.1 Test of concordance

(reproducibility). Annual assessment of

reproducibility for each designated reference
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65677

method sampler is required under the

provisions of Appendix A of Part 58 of this

chapter. This assessment is based on the

concordance correlation, using 6

measurements per year at regular intervals of

each reference method sampler operated in a

SLAMS network to a collocated audit

reference sampler. The assessment audits

may be performed by either the reporting

agency itself or by a third party and must

meet criteria specified in Appendix A of part

58 of this Chapter. A test procedure is

described in section 6.1 of part 58, Appendix

A that determines the bias in the primary

sampler as compared to the reference method

sampler under actual network operational

sampling conditions. The lower 95 percent

probability limit of the concordance

correlation for PM2.5 samplers, as determined

by this procedure, must be equal to or greater

than 0.94 for each designated reference

method sampler to retain its designation.

4.2.2 Annual assessment of the bias of

each designated reference method sampler is

required under the provisions of part 58 of

this chapter. This assessment is based on

comparisons made six times per year at

regular intervals of each reference method

sampler operated in a SLAMS network to a

collocated audit sampler. The assessment

audits may be performed by either the

reporting agency itself or by a third party and

must meet criteria specified in Appendix A

of part 58 of this chapter. A screening test

procedure is described in section 6.2 of part

58, Appendix A that examines for bias

between the primary sampler and the

reference method sampler under actual

network operational sampling conditions.

The test uses a simple counting procedure

and leads to a conclusion of bias only when

the evidence is quite strong (p=0.01).

4.3 In addition, part 58, Appendix A of

this chapter requires that the flow rate

accuracy of PM2.5 samplers used in SLAMS

monitoring networks be assessed periodically

via audits of the sampler’s operational flow

rate.

5.0 Precision.

5.1 Tests to establish initial operational

precision for each reference method sampler

are specified as a part of the requirements for

designation as a reference method under part

53 of this chapter (§ 53.56).

5.2 Annual assessments of routine

operational precision are also required.

5.2.1 Annual assessment of the pooled

operational precision of each designated

reference method sampler is required under

the provisions of part 58 of this chapter. This

assessment is based on comparisons made six

times per year at regular intervals of each

reference method sampler operated in a

SLAMS network to a collocated audit

sampler. The assessment audits may be

performed by either the reporting agency

itself or by a third party and must meet

criteria specified in Appendix A of part 58

of this Chapter. A test procedure is described

in section 6.1 of part 58, Appendix A that

determines the variation in the PM2.5

concentration measurements of reference

method samplers under the actual network

operational sampling conditions. The pooled

operational precision of PM2.5 samplers, as

determined by this procedure, must meet the

specification in section 6 of Appendix A, part

58 for each designated reference method

sampler to retain its designation.

5.2.2 A screening test for bias and

excessive imprecision is required under the

provisions of part 58 of this chapter. This

assessment is based on comparisons made six

times per year at regular intervals of each

reference method sampler operated in a

SLAMS network to a collocated audit

sampler. The assessment audit may be

performed by either the reporting agency

itself or by a third party and must meet

criteria specified in Appendix A section 6.2

of part 58 of this Chapter. A screening test

procedure is described in section 6 of part 58,

Appendix A that examines for excessive

imprecision (>15%) in one or both of the

samplers. The test uses a simple counting

procedure and leads to a conclusion of

excessive imprecision only when evidence is

quite strong (p¥0.01) under the actual

network operational sampling conditions.

6.0 Filter for PM2.5 Sample Collection

6.1 Size: Circular, 47 mm diameter.

6.2 Medium: Polytetrafluoroethylene

(PTFE) with integral 0.38 ±0.04 mm thick

polymethylpentene (PMP) or equivalent

support ring.

6.3 Pore size: 2 μm as measured by ASTM

F 316–80

6.4 Thickness: 20–60 μm

6.5 Maximum pressure drop: 30 cm H2O

column @ 16.67 L/min clean air flow.

6.6 Maximum moisture pickup: 0.0%

weight increase after 24-hour exposure at

48% relative humidity at 23 °C.

6.7 Collection efficiency. Greater than

99.7 percent, as measured by the DOP test

(ASTM D 2986–91) with 0.3 μm particles at

the sampler’s operating face velocity.

6.8 Filter weight stability. Filter weight

loss ≤ 20 μg, measured as specified in the

following two tests. Filter weight loss shall

be the average difference between the initial

and the final weights of a random sample of

test filters selected from each lot prior to

shipment. The number of filters tested shall

be not less than 0.1% of the filters of each

manufacturing lot, or 10 filters, whichever is

greater. The filters shall be weighed under

laboratory conditions and shall have had no

air sample passed through them (i.e., filter

blanks). Each test procedure must include

initial equilibration and weighing, the test,

and final equilibration and weighing.

Equilibration and weighing shall be in

accordance with section 8 and guidance

provided in Reference 2.

6.8.1 Test for surface particle

contamination. Install each test filter in a

filter cassette (Drawing numbers L–25, L–26)

and drop the cassette from a height of 25 cm

to a flat hard surface, such as a particle-free

wood bench. Repeat three times. Remove the

test filter from the cassette and weigh the

filter. The average change in weight must be

less than 20 μg.

6.8.2 Test of temperature stability. Place

randomly selected test filters in a drying

oven set at 40°C ±2 °C for not less than 48

hours. Remove, equilibrate, and reweigh each

test filter. The average change in weight must

be less than 20 μg.

6.9 Alkalinity. Less than 25

microequivalents/gram of filter, as measured

by the procedure given in Reference 2.

6.10 Supplemental Requirements.

Although not required for determination of

PM2.5 mass concentration under this

reference method, additional specifications

for the filter must be developed by users who

intend to subject PM2.5 filter samples to

subsequent chemical analysis. These

supplemental specifications include

background chemical contamination of the

filter and any other filter parameters that may

be required by the method of chemical

analysis. All such supplemental filter

specifications must be compatible with and

secondary to the primary filter specifications

given in this section 6.

7.0 PM2.5 Sampler.

7.1 Configuration. The sampler shall

consist of a sample air inlet, downtube,

particle size separator (impactor), filter

holder assembly, air pump and flow rate

control system, flow rate measurement

device, ambient and filter temperature

monitoring system, timer, outdoor

environmental enclosure, and suitable

mechanical, electrical, or electronic control

capability to provide the design and

functional performance as specified in this

section 7. The performance specifications

require that the sampler:

(a) provide automatic control of sample

flow rate and other operational parameters,

(b) monitor these operational parameters as

well as ambient temperature and pressure,

and

(c) provide this information to the sampler

operator at the end of each sample period in

digital form, either visually or as electronic

data available for output through a data

output port connection.

7.2 Nature of specifications. The PM2.5

sampler is specified by a combination of

design and performance requirements. The

sample inlet, downtube, particle size

discriminator, and the internal configuration

of the filter holder assembly are specified

explicitly by design drawings and associated

mechanical dimensions, tolerances,

materials, surface finishes, assembly

instructions, and other necessary

specifications. All other aspects of the

sampler are specified by required operational

function and performance, and the design of

these other aspects (including the design of

the lower portion of the filter holder

assembly) is optional, subject to acceptable

operational performance. Test procedures to

demonstrate compliance with both the design

and performance requirements are set forth

in subpart E of part 53 of this Chapter.

7.3 Design specifications. These

components must be manufactured or

reproduced exactly as specified in an ISO

9001-registered facility, with registration

initially approved and subsequently

maintained.

7.3.1 Sample inlet assembly. The sample

inlet assembly, consisting of the inlet,

downtube, and impactor shall be assembled

as indicated in drawing No. L–1 and shall

meet all associated requirements. A portion

of this assembly shall also be subject to the

maximum overall sampler leak rate

specification (see section 7.4.6).
65678 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

7.3.2 Inlet. The sample inlet shall be

fabricated as indicated in drawing Nos. L–2

through L–18 and shall meet all associated

requirements.

7.3.3 Downtube. The downtube shall be

fabricated as indicated in drawing No. L–19

and shall meet all associated requirements.

7.3.4 Impactor.

7.3.4.1 The impactor (particle size

separator) shall be fabricated as indicated in

drawing Nos. L–20 through L–24 and shall

meet all associated requirements.

7.3.4.2 Impactor filter specifications:

(a) Size: Circular, 35 to 37 mm diameter

(b) Medium: Borosilicate glass fiber,

without binder

(c) Pore size: 1 to 1.5 micrometer, as

measured by ASTM F 316–80

(d) Thickness: 300 to 500 micrometers

7.3.4.3 Impactor oil specifications:

(a) Composition:

Tetramethyltetraphenyltrisiloxane, single

compound diffusion oil

(b) Vapor pressure: Maximum 2 × 10 –8 mm

Hg at 25 °C

(c) Viscosity: 36 to 40 centistokes at 25 °C

(d) Density: 1.06 to 1.07 g/cm 3 at 25 °C

(e) Quantity: 1 mL

7.3.5 Filter holder assembly. The sampler

shall have a sample filter holder assembly to

adapt and seal to the down tube and to hold

and seal the specified filter (section 6) in the

sample air stream in a horizontal position

below the downtube such that the sample air

passes downward through the filter at a

uniform face velocity. The upper portion of

this assembly shall be fabricated as indicated

in drawing Nos. L–25 and L–26 and shall

accept and seal with the filter cassette, which

shall be fabricated as indicated in drawing

Nos. L–27 through L–29.

(a) The lower portion of the filter holder

assembly shall be of a design and

construction that:

(1) mates with the upper portion of the

assembly to complete the filter holder

assembly,

(2) completes both the external air seal and

the internal filter cassette seal such that all

seals are reliable over repeated filter

changings, and

(3) facilitates repeated changing of the filter

cassette by the sampler operator.

(b) Leak-test performance requirements for

the filter holder assembly are included in

section 7.4.6 below.

7.3.6 Flow rate measurement adapter. A

flow rate measurement adapter as specified

in drawing No. L–30 shall be furnished with

each sampler.

7.3.7 Surface finish. All internal surfaces

exposed to sample air prior to the filter shall

be treated electrolytically in a sulfuric acid

bath to produce a clear, uniform anodized

surface finish of not less than 1000 mg/ft 2

(1.08 mg/cm 2) in accordance with military

standard specification (mil. spec.) 8625F,

Type II, Class 1 (Reference 3). This anodic

surface coating shall not be dyed or

pigmented. Following anodization, the

surfaces shall be sealed by immersion in

boiling deionized water for 15 minutes.

7.4 Performance specifications.

7.4.1 Sample flow rate. Proper operation

of the impactor requires that specific air

velocities be maintained through the device.

Therefore, the sample air flow rate through

the inlet, downtube, impactor, and filter shall

be 16.67 L/min (1.000 m 3/hour) ±5%,

measured as actual volumetric flow rate at

the temperature and pressure of the sample

air entering the impactor.

7.4.2 Sample air flow rate control system.

The sampler shall have a sample air flow rate

control system which shall be capable of

providing a sample air volumetric flow rate

within the specified range (section 7.4.1) for

the specified filter (section 6), at any

atmospheric conditions specified (section

7.4.7), at a filter pressure drop equal to that

of a clean filter plus up to 75 cm water

column (55 mm Hg), and over the specified

range of supply line voltage (section

7.4.15.1). This flow control system shall

allow for operator adjustment of the

operational flow rate of the sampler over a

range of at least ±10 percent of the flow rate

specified in section 7.4.1.

7.4.3 Sample flow rate regulation. The

sample flow rate shall be regulated such that

for the specified filter (section 6), at any

atmospheric conditions specified (section

7.4.7), at a filter pressure drop equal to that

of a clean filter plus up to 75 cm water

column ( 55 mm Hg), and over the specified

range of supply line voltage (section

7.4.15.1), the flow rate is regulated as

follows:

7.4.3.1 The volumetric flow rate,

measured or averaged over intervals of not

more than 5 minutes over a 24-hour period,

shall not vary more than ±5 percent from the

specified 16.67 L/min flow rate over the

entire sample period; and

7.4.3.2 The coefficient of variation

(sample standard deviation divided by the

average) of the flow rate, measured at

intervals of not more than 5 minutes over a

24-hour period, shall not be greater than 4

percent.

7.4.4 Flow rate cut off. The sampler’s

sample air flow rate control system shall

terminate sample collection and stop all

sample flow for the remainder of the sample

period in the event that the sample flow rate

deviates by more than 10 percent from the

nominal (or cumulative average) sampler

flow rate specified in section 7.4.1 for more

than 60 seconds. However, this sampler cutoff provision shall not apply during periods

when the sampler is inoperative due to a

temporary power interruption and the

elapsed time of the inoperative period will

not be included in the total sample time

measured and reported by the sampler (see

section 7.4.13).

7.4.5 Flow rate measurement.

7.4.5.1 The sampler shall provide a

means to measure and indicate the

instantaneous sample air flow rate, which

shall be measured as volumetric flow rate at

the temperature and pressure of the sample

air entering the impactor, with an accuracy

of ±2 percent. The sampler shall also provide

a simple means by which the sampler

operator can manually start the sample flow

temporarily during non-sampling modes of

operation, for the purpose of checking the

sample flow rate or the flow rate

measurement system.

7.4.5.2 During each sample period, the

sampler’s flow rate measurement system

shall automatically monitor the sample

volumetric flow rate, obtaining flow rate or

average flow rate measurements at intervals

of not greater than 5 minutes.

(a) Using these interval flow rate

measurements, the sampler shall determine

or calculate the following flow-related

parameters, scaled in the specified

engineering units:

(1) the instantaneous or interval-average

flow rate, in L/min;

(2) the value of the average sample flow

rate for the sample period, in L/min;

(3) the value of the coefficient of variation

(sample standard deviation divided by the

average) of the sample flow rate for the

sample period, in percent;

(4) any time during the sample period in

which the sample flow rate measured

exceeds a range of ±5 percent of the average

flow rate for the sample period for more than

5 minutes, in which case a warning flag

indicator shall be set; and

(5) the value of the integrated total sample

volume for the sample period, in m 3.

(b) Determination or calculation of these

values shall properly exclude periods when

the sampler is inoperative due to temporary

interruption of electrical power (see section

7.4.13). These parameters shall be accessible

to the sampler operator as specified in Table

L–1, section 7.4.19.

7.4.6 Leak test capability.

7.4.6.1 External leakage: The sampler

shall include components, accessory

hardware, operator interface controls, a

written procedure in the associated

Operation/Instruction Manual (section

7.4.18), and all other necessary functional

capability to permit and facilitate the sampler

operator to conveniently carry out a leak test

of the sampler at a field monitoring site

without additional equipment.

(a) The suggested technique for this leak

test is as follows: The operator:

(1) removes the sampler inlet and installs

the flow rate measurement adapter supplied

with the sampler (see section 7.3.6),

(2) closes the valve on the flow rate

measurement adapter and uses the sampler

air pump to draw a partial vacuum in the

sampler, including (at least) the impactor,

filter holder assembly (filter in place), flow

measurement device, and interconnections

between these devices, of at least 55 mm Hg

(75 cm water column),

(3) plugs the flow system downstream of

these components to isolate the components

under vacuum from the pump, such as with

a built-in valve,

(4) stops the pump,

(5) measures the trapped vacuum in the

sampler with a built-in pressure measuring

device, and

(6) measures the vacuum in the sampler

with the built-in pressure measuring device

again at a later time at least 10 minutes after

the first pressure measurement, and

(7) removes the plugs and restores the

sampler to the normal operating

configuration.

(b) The associated leak test procedure shall

require that for successful passage of this test,

the difference between the two pressure

measurements shall not be greater than

either:
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65679

(1) 10 mm Hg or

(2) an alternative number of mm of Hg

specified for the sampler by the manufacturer

based on the actual internal volume of the

sampler that indicates a leak of less than 80

mL/min.

(c) The specific proposed external leak test

procedure, or particularly a proposed

alternative leak test technique such as may be

required for samplers whose design or

configuration would make the suggested

technique impractical, may be described and

submitted for specific individual

acceptability either as part of a reference or

equivalent method application under part 53

of this chapter or in writing in advance of

such application.

7.4.6.2 Internal (filter bypass) leakage:

The sampler shall include components,

accessory hardware, operator interface

controls, a written procedure in the

Operation/Instruction Manual, and all other

necessary functional capability to permit and

facilitate the sampler operator to

conveniently carry out a test for internal filter

bypass leakage in the sampler at a field

monitoring site without additional

equipment.

(a) The suggested technique for this leak

test is as follows: The operator:

(1) Carries out an external leak test as

provided under the paragraph 7.4.6.1 which

indicates successful passage of the prescribed

external leak test,

(2) Installs a flow-impervious membrane

material in the filter cassette, either with or

without a filter, as appropriate, which

effectively prevents air flow through the filter

holder,

(3) Uses the sampler air pump to draw a

partial vacuum in the sampler, downstream

of the filter holder assembly, of at least 55

mm Hg (75 cm water column),

(4) Plugs the flow system downstream of

the filter holder to isolate the components

under vacuum from the pump, such as with

a built-in valve,

(5) Stops the pump,

(6) Measures the trapped vacuum in the

sampler with a built-in pressure measuring

device,

(7) Measures the vacuum in the sampler

with the built-in pressure measuring device

again at a later time at least 10 minutes after

the first pressure measurement, and

(8) removes the membrane and plugs and

restores the sampler to the normal operating

configuration.

(b) The associated leak test procedure shall

require that for successful passage of this test,

the difference between the two pressure

measurements shall not be greater than either

10 mm Hg or an alternative number of mm

of Hg specified for the sampler by the

manufacturer based on the actual internal

volume of the portion of the sampler under

vacuum that indicates a leak of less than 80

mL/min. The specific proposed internal leak

test procedure, or particularly a proposed

alternative internal leak test technique such

as may be required for samplers whose

design or configuration would make the

suggested technique impractical, may be

described and submitted for specific

individual acceptability either as part of a

reference or equivalent method application

under part 53 of this chapter or in writing in

advance of such application.

7.4.7 Range of Operational Conditions.

The sampler is required to operate properly

and meet all requirements specified herein

over the following operational ranges:

7.4.7.1 Ambient temperature: ¥30 to +45

degrees Celsius (Note: Although for practical

reasons, the temperature range over which

samplers are required to be tested under part

53 of this chapter is ¥20 to +40 degrees

Celsius, the sampler should be designed to

operate properly over this wider temperature

range.);

7.4.7.2 Ambient relative humidity: 0 to

100 percent;

7.4.7.3 Barometric pressure range: 600 to

800 mm Hg.

7.4.8 Ambient temperature sensor. The

sampler shall have capability to measure the

temperature of the ambient air surrounding

the sampler over the range of ¥20 to +40 ,

with a resolution of 0.1 C and accuracy of

±2.00 C (referenced to National Weather

Service (NWS) requirements; see part 53,

subpart E), with or without maximum solar

insolation. This ambient temperature

measurement shall be updated at least every

5 minutes during both sampling and standby

(non-sampling) modes of operation. A visual

indication of the current (most recent) value

of the ambient temperature measurement

shall be available to the sampler operator

during both sampling and standby (nonsampling) modes of operation, as specified in

Table L–1. This ambient temperature

measurement shall be used for the purpose

of monitoring filter temperature deviation

from ambient temperature, as required by

section 7.4.11.4, and may be used for

purposes of effecting filter temperature

control (section 7.4.10) or computation of

volumetric flow rate (sections 7.4.1 to 7.4.5).

Following the end of each sample period, the

sampler shall report the maximum,

minimum, and average temperature for the

sample period, as specified in Table L–1.

7.4.9 Ambient barometric sensor. The

sampler shall have capability to measure the

barometric pressure of the air surrounding

the sampler over a range of 600 to 800 mm

Hg (referenced to National Weather Service

(NWS) requirements; see part 53, subpart E).

(The barometric pressure of the air entering

the impactor when sampling will be assumed

to be the same as the barometric pressure of

the air surrounding the sampler.) This

barometric pressure measurement shall have

a resolution of 5 mm Hg and an accuracy of

±10 mm Hg and shall be updated at least

every 5 minutes. A visual indication of the

value of the current (most recent) barometric

pressure measurement shall be available to

the sampler operator during both sampling

and standby (non-sampling) modes of

operation, as specified in Table L–1. This

barometric pressure measurement may be

used for purposes of computation of

volumetric flow rate (sections 7.4.1 to 7.4.5),

if appropriate. Following the end of a sample

period, the sampler shall report the

maximum, minimum, and average barometric

pressures for the sample period, as specified

in Table L–1.

7.4.10 Filter temperature control

(sampling and post-sampling). The sampler

shall provide a means to limit the

temperature rise of the sample filter, from

insolation and other sources, to no more than

3 °C above the temperature of the ambient air

surrounding the sampler, during both

sampling and post-sampling periods of

operation. The post-sampling period is the

non-sampling period between the end of the

active sampling period and the time of

retrieval of the sample filter by the sampler

operator.

7.4.11 Filter temperature sensor. The

sampler shall have the capability to monitor

the sample filter temperature via a

temperature sensor located within 1 cm of

the center of the filter downstream of the

filter and to provide a visual indication of the

filter temperature to the operator, as specified

in Table L–1. The sampler shall also provide

a warning flag indicator following any

occurrence in which the filter temperature

exceeds the ambient temperature by more

than 3 °C for more than 10 consecutive

minutes during either the sampling or postsampling periods of operation, as specified in

Table L–1. It is further recommended (not

required) that the sampler be capable of

recording the maximum differential between

the measured filter temperature and the

ambient temperature and its time and date of

occurrence during both sampling and postsampling (non-sampling) modes of operation

and providing those data to the sampler

operator following the end of the sample

period, as suggested in Table L–1.

7.4.12 Clock/Timer System. (a) The

sampler shall have a programmable real-time

clock timing/control system that:

(1) Is capable of maintaining local time and

date, including year, month, day-of-month,

hour, minute, and second to an accuracy of

±1.0 minute per month;

(2) Provides a visual indication of the

current system time, including year, month,

day-of-month, hour, and minute, updated at

least each minute, for operator verification;

(3) Provides appropriate operator controls

for setting the correct local time and date;

and

(4) Is capable of starting the sample

collection period and sample air flow at a

specific, operator-settable time and date, and

stopping the sample air flow and terminating

the sampler collection period 24 hours (1440

minutes) later, or at a specific, operatorsettable time and date.

(b) These start and stop times shall be

readily settable by the sampler operator to

within ±1.0 minute. The system shall provide

a visual indication of the current start and

stop time settings, readable to ±1.0 minute,

for verification by the operator, and the start

and stop times shall also be available via the

data output port, as specified in Table L–1.

Upon execution of a programmed sample

period start, the sampler shall automatically

reset all sample period information and

warning indications pertaining to a previous

sample period. Refer also to section 7.4.15.4

regarding retention of current date and time

and programmed start and stop times during

a temporary electrical power interruption.

7.4.13 Sampling sample time

determination. The sampler shall be capable

of determining the elapsed sample collection

time for each PM2.5 sample, accurate to
65680 Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules

within ±1.0 minute, measured as the time

between the start of the sampling period (sec.

7.4.12) and the termination of the sample

period (sec. 7.4.12 or sec. 7.4.4). This elapsed

sample time shall not include periods when

the sampler is inoperative due to a temporary

interruption of electrical power (section

7.4.15.4). In the event that the elapsed

sample time determined for the sample

period is not within the range specified for

the required sample period in section 3.3, the

sampler shall set a warning flag indicator.

The date and time of the start of the sample

period, the value of the elapsed sample time

for the sample period, and the flag indicator

status shall be available to the sampler

operator following the end of the sample

period, as specified in Table L–1.

7.4.14 Outdoor environmental enclosure.

The sampler shall have an outdoor enclosure

(or enclosures) suitable to protect the filter

and other non-weatherproof components of

the sampler from precipitation, wind, dust,

extremes of temperature and humidity; to

help maintain temperature control of the

filter; and to provide reasonable security for

sampler components and settings.

7.4.15 Electrical power supply.

7.4.15.1 The sampler shall be operable

and function as specified herein when

operated on an electrical power supply

voltage of 105 to 125 volts AC (RMS) at a

frequency of 59 to 61 Hz. Optional operation

as specified at additional power supply

voltages and/or frequencies shall not be

precluded by this requirement.

7.4.15.2 The design and construction of

the sampler shall comply with all applicable

National Electrical Code and Underwriters

Laboratories electrical safety requirements.

7.4.15.3 The design of all electrical and

electronic controls shall be such as to

provide reasonable resistance to interference

or malfunction from ordinary or typical

levels of stray electromagnetic fields (EMF)

as may be found at various monitoring sites

and from typical levels of electrical transients

or electronic noise as may often or

occasionally be present on various electrical

power lines.

7.4.15.4 In the event of temporary loss of

electrical supply power to the sampler, the

sampler shall not be required to sample or

provide other specified functions during

such loss of power, except that the internal

clock/timer system shall maintain its local

time and date setting within ±1 minute per

week, and the sampler shall retain all other

time and programmable settings and all data

required to be available to the sampler

operator following each sample period for at

least 7 days without electrical supply power.

When electrical power is absent at the

operator-set time for starting a sample period

or is interrupted during a sample period, the

sampler shall automatically start or resume

sampling when electrical power is restored,

if such restoration of power occurs before the

operator-set stop time for the sample period.

7.4.15.5 The sampler shall have the

capability to record and retain a record of the

year, month, day-of-month, hour, and minute

of the start of each power interruption of

more than 1 minute duration, up to 10 such

power interruptions per sample period.

(More than 10 such power interruptions shall

invalidate the sample, except where an

exceedance is measured see section 3.3.) The

sampler shall provide for these power

interruption data to be available to the

sampler operator following the end of the

sample period, as specified in Table L–1.

7.4.16 Control devices and operator

interface. The sampler shall have

mechanical, electrical, or electronic controls,

control devices, electrical or electronic

circuits as necessary to provide the timing,

flow rate measurement and control,

temperature control, data storage and

computation, operator interface, and other

functions specified. Operator-accessible

controls, data displays, and interface devices

shall be designed to be simple,

straightforward, reliable, and easy to learn,

read, and operate under field conditions. The

sampler shall have provision for operator

input and storage of up to 64 characters of

numeric (or alphanumeric) data for purposes

of site, sampler, and sample identification.

This information shall be available to the

sampler operator for verification and change

and for output via the data output port along

with other data following the end of a sample

period, as specified in Table L–1. All data

required to be available to the operator

following a sample collection period or

obtained during standby mode in a postsampling period shall be retained by the

sampler until reset, either manually by the

operator or automatically by the sampler

upon initiation of a new sample collection

period.

7.4.17 Data output port requirement. The

sampler shall have a standard RS–232C data

output connection through which digital data

may be exported to an external data storage

or transmission device. All information

which is required to be available at the end

of each sample period shall be accessible

through this data output connection. The

information that shall be accessible though

this output port is summarized in Table

L–1.

7.4.18 Operation/Instruction Manual. The

sampler shall include an associated

comprehensive operation or instruction

manual, as required by part 53 of this

chapter, which includes detailed operating

instructions on the setup, operation,

calibration, and maintenance of the sampler.

This manual shall provide complete and

detailed descriptions of the operational and

calibration procedures prescribed for field

use of the sampler and all instruments

utilized as part of this reference method. The

manual shall include adequate warning of

potential safety hazards that may result from

normal use or malfunction of the method and

a description of necessary safety precautions.

The manual shall also include a clear

description of all procedures pertaining to

installation, operation, periodic and

corrective maintenance, and troubleshooting,

and shall include parts identification

diagrams.

TABLE L–1.—SUMMARY OF INFORMATION TO BE PROVIDED BY THE SAMPLER

Information to be provided

Appendix

L section

reference

Availability Format

Anytime 1 End of period 2

Visual display 3Data output 4 Digital reading 5 Units

Flow rate, instantaneous.7.4.5.1 ✔ ✔ XX.X ........................... L/min

Flow rate, average for

the sample period.

7.4.5.2 * ✔ * ✔ XX.X ........................... L/min

Flow rate, CV, for

sample period.

7.4.5.2 * ✔ * ✔0 XX.X ........................... %

Flow rate, 5-min average out of spec.

(FLAG 6).

7.4.5.2 ✔ ✔ ✔ ✔0 On/Off ........................

Sample volume, total 7.4.5.2 * ✔ ✔ ✔0 XX.X ........................... m 3

Temperature, ambient,

instantaneous or 5-

minute average.

7.4.8 ✔ ✔ XX.X ........................... °C

Temperature, ambient,

min., max., average

for the sample period.

7.4.8 * ✔ ✔ ✔0 XX.X ........................... °C
Federal Register / Vol. 61, No. 241 / Friday, December 13, 1996 / Proposed Rules 65681

TABLE L–1.—SUMMARY OF INFORMATION TO BE PROVIDED BY THE SAMPLER

Information to be provided

Appendix

L section

reference

Availability Format

Anytime 1 End of period 2

Visual display 3Data output 4 Digital reading 5 Units

Baro pressure, ambient, instantaneous

or 5-minute average.

7.4.9 ✔ ✔ XXX ............................ mm Hg

Baro pressure, ambient, min, max, average for the sample

period.

7.4.9 * ✔ ✔ ✔0 XXX ............................ mm Hg

Filter temperature, instantaneous.7.4.11 ✔ ✔ XX.X ........................... °C

Filter temperature, instantaneous differential out of spec.

(FLAG 1).

7.4.11 * ✔ ✔ ✔0 On/Off ........................

Filter temp, maximum

differential from ambient, date, time of

occurrence.

7.4.11 * * * * X.X, YY/MM/DD

HH.mm.

°C, Yr/Mon/Day

Hrs.min

Date and Time ........... 7.4.12 ✔ ✔ YY/MM/DD HH.mm .... Yr/Mon/Day Hrs.min

Sample start and stop

time settings.

7.4.12 ✔ ✔ ✔ ✔ YY/MM/DD HH.mm .... Yr/Mon/Day Hrs.min

Sample period start

time.

7.4.12 ✔ ✔ ✔0 YYYY/MM/DD HH.mm Yr/Mon/Day Hrs.min

Elapsed sample time 7.4.13 * ✔ ✔ ✔0 HH.mm ....................... Hrs.min

Elapsed sample time,

out of spec.

(FLAG6).

7.4.13 ✔ ✔ ✔0 On/Off ........................

Power interruptions >1

min, start time of

first 10.

7.4.15.5 * ✔ * ✔ 1HH.mm 2HH.mm ... Hrs.min

User-entered information, such as sampler and site identification.7.4.16 ✔ ✔ ✔ ✔0 As entered .................

1 Information is required to be available to the operator at any time the sampler is operating, whether sampling or not.

2 Information relates to the entire sampler period and must be provided following the end of the sample period until reset manually by the operator or automatically by the sampler upon the start of a new sample period. 3 Information shall be available to the operator visually.

4 Information is to be available as digital data at the sampler’s data output port specified in section 7.4.16 following the end of the sample period until reset manually by the operator or automatically by the sampler upon the start of a new sample period. 5 Digital readings, both visual and data output, shall have not less than the number of significant digits and resolution specified.

6Flag warnings may be displayed to the operator by a single flag indicator or each flag may be displayed individually. Only a set (on) flag

warning must be indicated; an off (unset) flag may be indicated by the absence of a flag warning. The occurrence of a flag warning during a

sample period shall not necessarily indicate an invalid sample but shall indicate the need for specific review of the QC data by a quality assurance officer to determine sample validity.

*Provision of this information is optional. If information related to the entire sample period is optionally provided prior to the end of the sample

period, the value provided should be the value calculated for the portion of the sampler period completed up to the time the information is provided.

0Indicates that this information is also required to be provided to the AIRS data bank; see § 58.26 and § 58.35 of part 58 of this Chapter.

7.4.19 Data reporting requirements. The

various information that the sampler is

required to provide and how it is to be

provided is summarized in Table L–1.

8.0 Filter weighing.

See Reference 2 for additional, more

detailed guidance.

8.1 Analytical balance. The analytical

balance used to weigh filters must be suitable

for weighing the type and size of filters

specified (section 6) and have a readability of

±1 μg. The balance shall be calibrated as

specified by the manufacturer at installation

and recalibrated immediately prior to each

weighing session, but not less often than

once per year. See Reference 2 for additional

guidance.

8.2 Filter conditioning/equilibration. All

filters used are to be conditioned or

equilibrated immediately before both the preand post-sampling weighings as specified

below. See Reference 2 for additional

guidance.

8.2.1 Mean temperature: 20–23 °C.

8.2.2 Temperature control: ±2 °C over 24

hours.

8.2.3 Mean humidity: 30–40 percent

relative humidity.

8.2.4 Humidity control: ±5 relative

humidity percent over 24 hours.

8.2.5 Conditioning time: not less than 24

hours.

8.3 Weighing procedure.

8.3.1 New filters should be placed in the

conditioning environment immediately upon

arrival and stored there until the presampling weighing. See Reference 2 for

additional guidance.

8.3.2 The analytical balance shall be

located in the same environment in which

the filters are conditioned or equilibrated,

such that the filters can be weighed

immediately following the conditioning

period without intermediate or transient

exposure to nonequilibration conditions.

8.3.3 Filters must be equilibrated at the

same conditions before both the pre- and

post-sampling weighings.

8.3.4 Both the pre- and post-sampling

weighings should be carried out by the same

analyst on the same analytical balance, using

an effective technique to neutralize static

charges on the filter.
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8.3.5 The pre-sampling (tare) weighing

shall be within 30 days of the sampling

period.

8.3.6 The post-sampling equilibration and

weighing shall be completed within 240

hours (10 days) after the end of the sample

period.

8.3.7 New blank filters shall be weighed

along with the pre-sampling (tare) weighing

of each lot of PM2.5 filters. These blank filters

shall be transported to the sampling site,

installed in the sampler, retrieved from the

sampler without sampling, and reweighed as

a quality control check.

8.3.8 Additional guidance for proper

filter weighing is provided in Reference 2.

See also section 10.17 concerning filter

archiving.

9.0 Calibration

See Reference 2 for additional guidance.

9.1 General Requirements

9.1.1 Multipoint calibration and singlepoint verification of the sampler’s flow rate

measurement device must be performed

periodically to establish traceability of

subsequent flow measurements to a flow rate

standard.

9.1.2 An authoritative flow rate standard

shall be used for calibrating or verifying the

sampler’s flow rate measurement device with

an accuracy of ±2 percent. The flow rate

standard shall be a separate stand-alone

device designed to connect to the flow rate

measurement adapter, drawing L–30. This

flow rate standard must have its own

certification and be traceable to National

Institute of Standards and Technology (NIST)

primary standards for volume or flow rate. If

adjustments to the sampler’s flow calibration

are to be made in conjunction with an audit

of the sampler, such adjustments shall be

made following the audit. See Reference 2 for

additional guidance.

9.1.3 The sampler’s flow rate

measurement device shall be re-calibrated

after electromechanical maintenance or

transport of the sampler.

9.2 Flow Rate Calibration/Verification

Procedure

9.2.1 PM2.5 samplers may employ various

types of flow control and flow measurement

devices. The specific procedure used for

calibration or verification of the flow rate

measurement device will vary depending on

the type of flow rate controller and flow rate

measurement employed. Calibration shall be

in terms of actual ambient volumetric flow

rates (Qa). The generic procedure given here

serves to illustrate the general steps involved

in the calibration of a PM2.5 sampler. The

sampler operation/instruction manual

(required under section 7.4.18) and the

Quality Assurance Handbook (Reference 2)

provide more specific and detailed guidance

for calibration.

9.2.2 The flow rate standard used for flow

rate calibration shall have its own

certification and be traceable to National

Institute of Standards and Technology (NIST)

primary standards for volume or flow rate. A

calibration relationship for the flow rate

standard (e.g., an equation, curve, or family

of curves) shall be established that is accurate

to within 2 percent over the expected range

of ambient temperatures and pressures at

which the flow rate standard may be used.

The flow rate standard must be re-calibrated

or re-verified at least annually.

9.2.3 The sampler flow rate measurement

device shall be calibrated or verified by

removing the sampler inlet and connecting

the flow rate standard to the sampler in

accordance with the operation/instruction

manual, such that the flow rate standard

accurately measures the sampler’s flow rate.

The sampler operator shall verify that no

leaks exist between the flow rate standard

and the sampler.

9.2.4 The calibration relationship

between the flow rate (in actual L/min)

indicated by the flow rate standard and by

the sampler’s flow rate measurement device

shall be established or verified in accordance

with the sampler operation/instruction

manual. Temperature and pressure

corrections to the flow rate indicated by the

flow rate standard may be required for

certain types of flow rate standards.

Calibration of the sampler’s flow rate

measurement device shall consist of at least

three separate flow rate measurements

(multipoint calibration) evenly spaced within

the range of ¥10% to +10% of the sampler’s

operational flow rate (see section 7.4.1).

Verification of the sampler’s flow rate shall

consist of one flow rate measurement at the

sampler’s operational flow rate. The sampler

operation/instruction manual and Reference

2 provide additional guidance.

9.2.5 If during a flow rate verification the

reading of the sampler’s flow rate indicator

or measurement device differs by ±4 percent

or more from the flow rate measured by the

flow rate standard, a new multipoint

calibration shall be performed and the flow

rate verification must then be repeated.

9.2.6 Following the calibration or

verification, the flow rate standard shall be

removed from the sampler and the sampler

inlet shall be reinstalled. Then the sampler’s

normal operating flow rate (in L/min) shall

be determined with a clean filter in place. If

the sampler flow rate differs by ±2 percent or

more from the required sampler flow rate, the

sampler flow rate must be adjusted to the

required flow rate (see section 7.4.1).

10.0 PM2.5 Measurement Procedure

The detailed procedure for obtaining valid

PM2.5 measurements with each specific

sampler designated as part of a reference

method for PM2.5 under part 53 of this

chapter shall be provided in the samplerspecific operation or instruction manual

required by section 7.4.18. Supplemental

guidance is provided in section 2.12 of the

QA Handbook (Reference 2). The generic

procedure given here serves to illustrate the

general steps involved in the PM2.5 sample

collection and measurement, using a PM2.5

reference method sampler.

10.1 The sampler shall be set up,

calibrated, and operated in accordance with

the specific, detailed guidance provided in

the specific sampler’s operation or

instruction manual and in accordance with a

specific quality assurance program developed

and established by the user, based on

applicable supplementary guidance provided

in Reference 2.

10.2 Each new filter shall be inspected for

correct type and size and for pinholes,

particles, and other imperfections. A filter

information record shall be established for,

and an identification number assigned to,

each filter.

10.3 Each filter shall be equilibrated in

the conditioning environment in accordance

with the requirements specified in section

8.2.

10.4 Following equilibration, each filter

shall be weighed in accordance with the

requirements specified in section 8 and the

presampling weight recorded with the filter

identification number.

10.5 A numbered and preweighed filter

shall be installed in the sampler following

the instructions provided in the sampler

operation or instruction manual.

10.6 The sampler shall be checked and

prepared for sample collection in accordance

with instructions provided in the sampler

operation or instruction manual and with the

specific quality assurance program

established for the sampler by the user.

10.7 The sampler’s timer shall be set to

start the sample collection at the beginning

of the desired sample period and stop the

sample collection 24 hours later.

10.8 Information related to the sample

collection (site location or identification

number, sample date, filter identification

number, and sampler model and serial

number) shall be recorded and, if

appropriate, entered into the sampler.

10.9 The sampler shall be allowed to

collect the PM 2.5 sample during the set 24-

hour time period.

10.10 Within 96 hours of the end of the

sample collection period, the filter, while

still contained in the filter cassette, shall be

carefully removed from the sampler,

following the procedure provided in the

sampler operation or instruction manual and

the quality assurance program, and placed in

a protective container. The protective

container shall hold the filter cassette

securely. The cover shall not come in contact

with the filter’s surfaces. The protective

container shall be made of metal and contain

no loose material that could be transferred to

the filter. (See reference 2 for additional

information.)

10.11 The total sample volume in actual

m 3 for the sampling period and the elapsed

sample time shall be obtained from the

sampler and recorded in accordance with the

instructions provided in the sampler

operation or instruction manual. All sampler

warning flag indications and other

information required by the local quality

assurance program shall also be recorded.

10.12 All factors related to the validity or

representativeness of the sample, such as

sampler tampering or malfunctions, unusual

meteorological conditions, construction

activity, fires or dust storms, etc. shall be

recorded as required by the local quality

assurance program.

10.13 After retrieval from the sampler, the

exposed filter containing the PM2.5 sample

should be transported to the filter

conditioning environment as soon as

possible—ideally within 24 hours—for

equilibration and subsequent weighing.

During the period between filter retrieval
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from the sampler and the start of the

conditioning or equilibration, the filter shall

not be exposed to temperatures over 32 °C.

10.14 The exposed filter containing the

PM2.5 sample shall be re-equilibrated in the

conditioning environment in accordance

with the requirements specified in section

8.2.

10.15 The filter shall be reweighed

immediately after equilibration in accordance

with the requirements specified in section 8,

and the postsampling weight shall be

recorded with the filter identification

number.

10.16 The PM2.5 concentration shall be

calculated as specified in section 12.

10.17 Filter archiving. Following the postsampling weighing or other non-destructive

analysis, air pollution control agencies shall

archive all routinely collected PM2.5 filter

samples from all SLAMS sites, as well as

appropriate, associated laboratory and field

blanks and other quality assurance replicate

samples, for a period of not less than 1 year

after collection. All PM2.5 filters from core

NAMS sites shall be archived for a period of

not less than 5 years after collection. These

archived filters shall be made available for

supplemental analyses at the request of the

EPA or to provide information to State and

local agencies on the composition and trends

for PM2.5. Archived filter samples shall be

stored in clean, dust-proof, covered

containers at a temperature of 4 ±3 °C; see

Reference 2 for additional guidance.

11.0 Sampler Maintenance

The sampler shall be maintained as

described by the sampler’s manufacturer in

the sampler-specific operation or instruction

manual required under section 7.4.18 and in

accordance with the specific quality

assurance program developed and

established by the user based on applicable

supplementary guidance provided in

Reference 2.

12.0 Calculations.

12.1 The PM2.5 concentration is calculated

as:

PM2.5 = (Wf¥Wi)/Va

Where:

PM2.5 = mass concentration of PM2.5,

μg/m3;

Wf, Wi = final and initial weights,

respectively, of the filter used to collect the

PM2.5 particle sample, μg;

V a = total air volume sampled in actual

volume units, as provided by the

sampler, m3.

Note: Total sample time must be between

1380 and 1500 minutes (23 and 25 hrs) for

a fully valid PM 2.5 sample; however, see also

section 3.3.

13.0 References

1. Quality Assurance Handbook for Air

Pollution Measurement Systems, Volume I,

Principles. EPA/600/R–94/038a, April 1994.

Available from CERI, ORD Publications, U.S.

Environmental Protection Agency, 26 West

Martin Luther King Drive, Cincinnati, Ohio

45268.

2. Quality Assurance Handbook for Air

Pollution Measurement Systems, Volume II,

Ambient Air Specific Methods (Interim

Edition), section 2.12. EPA/600/R–94/038b,

April 1994. Available from CERI, ORD

Publications, U.S. Environmental Protection

Agency, 26 West Martin Luther King Drive,

Cincinnati, Ohio 45268. [Section 2.12 is

currently under development and will not be

available from the previous address until it

is published as an addition to EPA/600/R–

94/038b. Prepublication draft copies of

section 2.12 will be available from

Department E (MD–77B), U. S. EPA, Research

Triangle Park, NC 27711 or from the contact

identified at the beginning of this proposed

rule].

3. Military standard specification (mil.

spec.) 8625F, Type II, Class 1 as listed in

Department of Defense Index of

Specifications and Standards (DODISS),

available from DODSSP-Customer Service,

Standardization Documents Order Desk, 700

Robbins Avenue, Building 4D, Philadelphia,

PA 1911–5094.

14.0 Figures

Figures L–1 through L–30 are included as

part of this appendix L.

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[FR Doc. 96–30897 Filed 12–12–96; 8:45 am]

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