25566 Federal Register / Vol. 61, No. 100 / Wednesday, May 22, 1996 / Rules and Regulations

and computer output products’ or

‘manual, maintained in paper files’ or

‘hybrid, maintained in paper files and in

computers’) should be stated. Storage

does not refer to the container or facility

in which the records are kept.

14. Retrievability: How records are

retrieved from the system (e.g., ‘by

name,’ ‘by SSN,’ or ‘by name and SSN’)

should be indicated.

15. Safeguards: The categories of

agency personnel who use the records

and those responsible for protecting the

records from unauthorized access

should be stated. Generally the methods

used to protect the records, such as

safes, vaults, locked cabinets or rooms,

guards, visitor registers, personnel

screening, or computer ‘fail-safe’

systems software should be identified.

Safeguards should not be described in

such detail as to compromise system

security.

16. Retention and disposal: Describe

how long records are maintained. When

appropriate, the length of time records

are maintained by the agency in an

active status, when they are transferred

to a Federal Records Center, how long

they are kept at the Federal Records

Center, and when they are transferred to

the National Archives or destroyed

should be stated. If records eventually

are destroyed, the method of destruction

(e.g., shredding, burning, pulping, etc.)

should be stated. If the agency rule is

cited, the applicable disposition

schedule shall also be identified.

17. System manager(s) and address.

The title (not the name) and address of

the official or officials responsible for

managing the system of records should

be listed. If the title of the specific

official is unknown, such as with a local

system, the local director or office head

as the system manager should be

indicated. For geographically separated

or organizationally decentralized

activities with which individuals may

correspond directly when exercising

their rights, the position or title of each

category of officials responsible for the

system or portion thereof should be

listed. Addresses that already are listed

in the agency address directory or

simply refer to the directory should not

be included.

18. Notification procedures. (1)

Notification procedures describe how an

individual can determine if a record in

the system pertains to him/her. If the

record system has been exempted from

the notification requirements of

subsection (f)(l) or subsection (e)(4)(G)

of the Privacy Act, it should be so

stated. If the system has not been

exempted, the notice must provide

sufficient information to enable an

individual to request notification of

whether a record in the system pertains

to him/her. Merely referring to a DFAS

regulation is not sufficient. This section

should also include the title (not the

name) and address of the official

(usually the Program Manager) to whom

the request must be directed; any

specific information the individual must

provide in order for DFAS to respond to

the request (e.g., name, SSN, date of

birth, etc.); and any description of proof

of identity for verification purposes

required for personal visits by the

requester.

19. Record access procedures. This

section describes how an individual can

review the record and obtain a copy of

it. If the system has been exempted from

access and publishing access procedures

under subsections (d)(1) and (e)(4)(H),

respectively, of the Privacy Act, it

should be so indicated. If the system has

not been exempted, describe the

procedures an individual must follow in

order to review the record and obtain a

copy of it, including any requirements

for identity verification. If appropriate,

the individual may be referred to the

system manager or another DFAS

official who shall provide a detailed

description of the access procedures.

Any addresses already listed in the

address directory should not be

repeated.

20. Contesting records procedures.

This section describes how an

individual may challenge the denial of

access or the contents of a record that

pertains to him or her. If the system of

record has been exempted from

allowing amendments to records or

publishing amendment procedures

under subsections (d)(1) and (e)(4)(H),

respectively, of the Privacy Act, it

should be so stated. If the system has

not been exempted, this caption

describes the procedures an individual

must follow in order to challenge the

content of a record pertaining to him/

her, or explain how he/she can obtain

a copy of the procedures (e.g., by

contacting the Program Manager or the

appropriate DFAS Privacy Act Officer).

21. Record source categories: If the

system has been exempted from

publishing record source categories

under subsection (e)(4)(I) of the Privacy

Act, it should be so stated. If the system

has not been exempted, this caption

must describe where DFAS obtained the

information maintained in the system.

Describing the record sources in general

terms is sufficient; specific individuals,

organizations, or institutions need not

be identified.

22. Exemptions claimed for the

system. If no exemption has been

established for the system, indicate

‘None.’ If an exemption has been

established, state under which provision

of the Privacy Act it is established (e.g.,

‘Portions of this system of records may

be exempt under the provisions of 5

U.S.C. 552a(k)(2).’)

Dated: May 15, 1996.

L. M. Bynum,

Alternate OSD Federal Register Liaison

Officer, Department of Defense.

[FR Doc. 96–12856 Filed 5–21–96; 8:45 am]

BILLING CODE 5000–04–F

ENVIRONMENTAL PROTECTION

AGENCY

40 CFR Part 50

[AD–FRL–5508–5]

RIN 2060–AA61

National Ambient Air Quality

Standards for Sulfur Oxides (Sulfur

Dioxide)—Final Decision

AGENCY: Environmental Protection

Agency (EPA).

ACTION: Final decision.

SUMMARY: In accordance with sections

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

EPA has reviewed and revised the air

quality criteria upon which the existing

national ambient air quality standards

(NAAQS) for sulfur oxides are based.

Based on that review, this document

announces EPA’s final decision under

section 109(d)(1) that revisions of the

NAAQS for sulfur oxides are not

appropriate at this time, aside from

several minor technical changes.

In lieu of the two alternatives to shortterm NAAQS proposed on November

15, 1994, EPA will shortly propose

revisions to 40 CFR part 51 to establish

concern and intervention levels under

section 303 of the Act and associated

guidance to assist States in addressing

short-term peaks of sulfur dioxide (SO2).

Final action will be taken on proposed

changes to 40 CFR parts 53 and 58 when

final action is taken on the 40 CFR part

51 proposal and associated guidance.

EFFECTIVE DATE: May 22, 1996.

ADDRESSES: A docket containing

information relating to EPA’s review of

the SO2 NAAQS (Docket No. A–84–25)

is available for public inspection in the

Air & Radiation Docket Information

Center, U.S. Environmental Protection

Agency, South Conference Center, Room

M–1500, 401 M Street, SW, Washington,

DC, telephone (202) 260–7548. The

docket may be inspected between 8 a.m.

and 5:30 p.m. on weekdays, and a

reasonable fee may be charged for
Federal Register / Vol. 61, No. 100 / Wednesday, May 22, 1996 / Rules and Regulations 25567

copying. For the availability of related

information, see SUPPLEMENTARY

INFORMATION.

FOR FURTHER INFORMATION CONTACT: Ms.

Susan Lyon Stone, Air Quality

Strategies and Standards Division (MD–

15), U.S. Environmental Protection

Agency, Research Triangle Park, NC

27711, telephone (919) 541-1146.

SUPPLEMENTARY INFORMATION:

Availability of Related Information

The 1982 revised criteria document,

Air Quality Criteria for Particulate

Matter and Sulfur Oxides (three

volumes, EPA–600/8–82–029af-cf,

December 1982; Volume I, NTIS # PB–

84–120401, $36.50 paper copy and

$9.00 microfiche; Volume II, NTIS # PB–

84–120419, $77.00 paper copy and

$9.00 microfiche; Volume III, NTIS #

PB–84–120427, $77.00 paper copy and

$20.50 microfiche); the 1986 criteria

document addendum, Second

Addendum to Air Quality Criteria for

Particulate Matter and Sulfur Oxides

(1982): Assessment of Newly Available

Health Effects Information (EPA/600/8–

86–020–F, NTIS # PB–87–176574,

$36.50 paper copy and $9.00

microfiche); the 1994 criteria document

supplement, Supplement to the Second

Addendum (1986) to Air Quality

Criteria for Particulate Matter and Sulfur

Oxides (1982): Assessment of New

Findings on Sulfur Dioxide Acute

Exposure Health Effects in Asthmatic

Individuals (1994) (EPA–600/FP–93/

002); the 1982 staff paper, Review of the

National Ambient Air Quality Standards

for Sulfur Oxides: Assessment of

Scientific and Technical Information

(EPA–450/5–82–007, November 1982;

NTIS # PB–84–102920, $36.50 paper

copy and $9.00 microfiche); the 1986

staff paper addendum, Review of the

National Ambient Air Quality Standards

for Sulfur Oxides: Updated Assessment

of Scientific and Technical Information

(EPA–450/05–86–013, December 1986;

NTIS # PB–87–200259, $19.50 paper

copy and $9.00 microfiche) and the

1994 staff paper supplement, Review of

the National Ambient Air Quality

Standards For Sulfur Oxides: Updated

Assessment of Scientific and Technical

Information, Supplement to the 1986

OAQPS staff paper addendum (1994)

(EPA–452/R–94–013, September 1994;

NTIS # PB–95–124160, $27.00 paper

copy and $12.50 microfiche) are

available from: U.S. Department of

Commerce, National Technical

Information Service, 5285 Port Royal

Road, Springfield, Virginia 22161, or

call 1–800–553–NTIS. (Add $3.00

handling charge per order.) Other

documents generated in connection

with this standard review are also

available in the EPA docket identified

above.

Table of Contents

I. Background

A. Legislative Requirements Affecting this

Decision

1. Primary Standards

2. Related Control Requirements

B. Sulfur Oxides and Existing Standards

for SO2

C. 1988 Proposal

D. 1994 Reproposal

E. Rulemaking Docket

II. Summary of Public Comments

A. Current 24-hour and Annual Standards

B. Regulatory Alternatives to Address

Short-term Peak SO2 Exposures

III. Rationale for Final Decision

A. Current 24-hour and Annual Standards

B. Short-term Peak SO2 Exposures

1. Assessment of Health Effects Associated

with Short-term SO2 Exposures

2. Air Quality and Exposure

Considerations

3. Conclusions

C. Final Decision on Primary Standards

D. Technical Changes

IV. Regulatory Impacts

A. Executive Order 12866

B. Regulatory Flexibility Analysis

C. Impact on Reporting Requirements

D. Unfunded Mandates Reform Act

E. Environmental Justice

References

Appendix I—1987 Clean Air Scientific

Advisory Committee (CASAC) Closure

Letter

Appendix II—1994 CASAC Closure Letter

I. Background

A. Legislative Requirements Affecting

This Decision

1. Primary Standards

Two sections of the Act govern the

establishment 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 or welfare’’

and to issue air quality criteria for them.

These air quality criteria are to ‘‘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’’ 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, [is] requisite to protect

the public health.’’ For a discussion of

the margin of safety requirement, see the

November 15, 1994 proposed rule (59

FR 58958).

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

7409(d)) requires periodic review and, if

appropriate, revision of existing criteria

and standards. The process by which

EPA has reviewed the criteria and

standards for sulfur oxides under

section 109(d) is described in a later

section of this notice.

2. Related Control Requirements

States are primarily responsible for

ensuring attainment and maintenance of

ambient air quality standards once the

EPA has established them. Under

section 110 (42 U.S.C. 7410) and part D

of title I of the Act (42 U.S.C. 7501–

7515), 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; new

source performance standards under

section 111 (42 U.S.C. 7411); national

emission standards for hazardous air

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

7412); and title IV of the Act

Amendments of 1990 (42 U.S.C. 7651–

76510), which specifically provides for

major reductions in SO2 emissions.

B. Sulfur Oxides and Existing Standards

for SO2

The focus of this standard review is

on the health effects of SO2, alone and

in combination with other pollutants.

Other sulfur oxide (SOx) vapors (e.g.,

sulfur trioxide, SO3) are not commonly

found in the atmosphere. Sulfur dioxide

is a rapidly-diffusing reactive gas that is

very soluble in water. It is emitted

principally from combustion or

processing of sulfur-containing fossil

fuels and ores. At elevated

concentrations, SO2 can adversely affect

human health.

Sulfur dioxide occurs in the

atmosphere with a variety of particles

and other gases and undergoes chemical

and physical interactions with them,

forming sulfates and other

transformation products. Information on

the effects of the principal atmospheric

transformation products of SO2 (i.e.,

sulfuric acid and sulfates) was
25568 Federal Register / Vol. 61, No. 100 / Wednesday, May 22, 1996 / Rules and Regulations

1The proposal notice contains a detailed history

of the process leading to the 1988 proposal.

2EPA also concluded that it was not appropriate

at that time to propose a separate secondary SOx

standard to provide increased protection against

acidic deposition-related effects of SOX.

3A final decision that revision of the secondary

standard was not appropriate was signed on April

15, 1993 and published in the Federal Register on

April 21, 1993 (58 FR 21351).

4 In a subsequent notice, EPA solicited comment

on proposed requirements for implementing each of

the alternatives (59 FR 12492, March 7, 1995).

considered in the review of the

particulate matter standards that

culminated in revision of the standards

on July 1, 1987 (52 FR 24634); it will be

considered again in the next review of

the particulate matter standards, the

commencement of which was

announced on April 12, 1994 (59 FR

17375).

On April 30, 1971, EPA promulgated

primary and secondary NAAQS for

sulfur oxides, measured as SO2, under

section 109 of the Act (36 FR 8186). The

existing primary standards for SO2 are

365 μg/m3 (0.14 ppm), averaged over a

period of 24 hours and not to be

exceeded more than once per year, and

80 μg/m3 (0.030 ppm) annual arithmetic

mean. The secondary standard was set

at 1300 μg/m3 (0.50 ppm) averaged over

a period of 3 hours and not to be

exceeded more than once per year. The

scientific and technical bases for the

current standards are contained in the

original criteria document, Air Quality

Criteria for Sulfur Oxides (DHEW,

1970). For a history of the effects of SO2

regulations on trends in SO2 emissions

and ambient concentrations, see the

November 15, 1994 proposed rule (59

FR 58958).

Annual average SO2 levels range from

less than 0.004 ppm in remote rural

sites to over 0.03 ppm in the most

polluted urban industrial areas. The

highest short-term values are found in

the vicinity (< 20 km) of major point

sources. In the absence of adequate

controls, maximum levels at such sites

for 24-hour, 3-hour, and 1-hour averages

can reach or exceed 0.4 ppm, 1.4 ppm,

and 2.3 ppm, respectively. The origins,

relevant concentrations and potential

effects of SO2 are discussed in greater

detail in the revised criteria document

(EPA, 1982a), in the staff paper (EPA,

1982b), in the criteria document

addendum (EPA, 1986a), the staff paper

addendum (EPA, 1986b), the criteria

document supplement (EPA, 1994a),

and the staff paper supplement (EPA,

1994b).

C. 1988 Proposal

Based on reviews of the original air

quality criteria and standards for sulfur

oxides, EPA published a proposed

decision not to revise the existing

primary and secondary standards on

April 26, 1988 (53 FR 14926).1 In

reaching the provisional conclusion that

the current standards provided adequate

protection against the health and

welfare effects associated with SO2, EPA

was mindful of uncertainties in the

available evidence concerning the risk

that elevated short-term (< 1-hour) SO2

concentrations might pose to asthmatic

individuals exercising in ambient air.

The EPA specifically requested broad

public comment on the alternative of

revising the current standards and

adding a new 1-hour primary standard

of 0.4 ppm. The notice also announced

that if a 1-hour primary standard were

adopted, consideration would be given

to replacing the current 3-hour

secondary standard (1,300 μg/m3 (0.50

ppm)) with a 1-hour secondary standard

set equal to the primary standard, and

adopting an expected-exceedance form

for all of the standards.2

In the same notice, EPA also proposed

minor technical revisions to the

standards, including restating the levels

for the primary and secondary standards

in terms of ppm rather than μg/m3,

adding explicit rounding conventions,

and specifying data completeness and

handling conventions. In addition, EPA

announced its intention to retain the

block averaging convention for the 24-

hour, annual, and 3-hour standards and

proposed to eliminate any future

questions in this regard by adding

clarifying language to 40 CFR 50.4 and

50.5. Based on its assessment of the SO2

health effects information, EPA also

proposed to revise the significant harm

levels for SO2 and the associated

example air pollution episode levels (40

CFR part 51). Finally, EPA proposed

some minor modifications to the

ambient air quality surveillance

requirements (40 CFR part 58).

D. 1994 Reproposal

As a result of public comments on the

1988 proposal and other post-proposal

developments, EPA published a second

proposal regarding revision of the

primary standards for sulfur oxides on

November 15, 1994 (59 FR 58958).3 The

1994 reproposal was based in part on

supplements to the criteria document

(EPA, 1994a) and staff paper (EPA,

1994b) that were prepared to take into

account recent health studies. Drafts of

these documents were made available

for review by the public and by the

Clean Air Scientific Advisory

Committee (CASAC) of EPA’s Science

Advisory Board, which provided its

advice and recommendations in a letter

dated June 1, 1994 (reprinted as

Appendix II to this preamble). These

and other aspects of the administrative

process leading to the 1994 reproposal

are described more fully in the

reproposal notice.

As in the 1988 proposal, EPA

proposed to retain the existing 24-hour

and annual standards. The EPA also

solicited comment on three regulatory

alternatives to further reduce the health

risk posed by exposure to high 5-minute

peaks of SO2 if additional protection

were judged to be necessary. The three

alternatives included: 1) Revising the

existing primary SO2 NAAQS by adding

a new 5-minute standard of 0.60 ppm

SO2, 1 expected exceedance; 2)

establishing a new regulatory program

under section 303 of the Act to

supplement protection provided by the

existing NAAQS, with a trigger level of

0.60 ppm SO2, 1 expected exceedance;

and 3) augmenting implementation of

existing standards by focusing on those

sources or source types likely to

produce high 5-minute peak

concentrations of SO2.4

In the reproposal notice, EPA

specifically requested public comment

in several key areas. First, EPA

requested the submittal of factual

information on the frequency of

occurrence of 5-minute peak SO2 levels

in the ambient air, as well as

information on the source or source

types and the nature of events that are

most likely to give rise to such peak SO2

levels. Second, EPA requested the

submission of data that would allow

better characterization of the asthmatic

population at risk and the frequency

that an asthmatic individual would

likely be exposed to peak concentrations

of 0.60 ppm SO2 and above, while at

elevated ventilation rates. Third, EPA

requested that asthma specialists in the

medical community submit their views

on the medical significance of the

reported SO2 effects, and on whether a

numerical value below or above 0.60

ppm SO2 would be more appropriate to

protect asthmatic individuals.

The technical changes to the SO2

NAAQS that were first proposed in

1988, including formally adopting the

block averaging convention, stating the

standards in ppm rather than μg/m3,

adopting explicit rounding and data

completeness conventions and other

technical changes, were reproposed in

this notice. Comments on this

reproposal were to be received by

February 13, 1995.

On December 29, 1994 (59 FR 67255),

EPA announced that a public hearing on

the reproposal would be held on

February 8, 1995, and that the public
Federal Register / Vol. 61, No. 100 / Wednesday, May 22, 1996 / Rules and Regulations 25569

comment period was being extended to

March 15, 1995. The public hearing was

held at the U.S. Environmental

Protection Agency’s Environmental

Research Center Auditorium in

Research Triangle Park, NC.

On March 14, 1995 (60 FR 13663), the

public comment period was extended

again, to April 14, 1995, to allow

additional time for commenters to

review the proposed requirements for

implementing the three regulatory

alternatives (59 FR 12492, March 7,

1995) before submitting comments on

the 1994 reproposal.

E. Rulemaking Docket

The EPA established a standard

review docket (Docket No. A–79–28) for

the sulfur oxides review in July 1979.

The EPA also established a rulemaking

docket (Docket No. A–84–25) for the

1988 proposal as required by section

307(d) of the Act. The standard review

docket and a separate docket established

for criteria document revision (Docket

No. ECAO–CD–79–1) have been

incorporated into the rulemaking

docket.

II. Summary of Public Comments

There were 95 written comments

received prior to the end of the

comment period on April 14, 1995. An

additional 10 written comments were

received after the close of the comment

period. Of the 105 submissions, 53 were

provided by individual industrial

companies or industrial associations, 16

by Federal, State and local government

agencies, 7 by environmental and public

interest groups, and 5 by interested

individuals, including one

neighborhood association. Comments

also were received from physicians and

other independent experts

knowledgeable about the health effects

described in the reproposal. Along with

its written comments, one

environmental group submitted

videotaped testimony.

In addition, 14 persons presented

testimony at the February 8, 1995 public

hearing. The written text of the

comments presented, as well as a

transcript of the hearing, may be found

in Docket No. A–84–25, Category VIII–

F, located in the Air and Radiation

Docket Information Center (see the

Addresses section above).

A general summary of the public

comments follows. Some of the most

significant comments are addressed,

explicitly or implicitly, in other sections

of this preamble. A more detailed

summary of the comments received and

EPA’s responses to them has been

placed in Docket No. A–84–25, Category

IX–C.

A. Current 24-hour and Annual

Standards

Most commenters concurred with

EPA’s conclusion that the existing 24-

hour and annual standards provide

adequate protection against SO2-

induced health effects associated with

those averaging periods.

B. Regulatory Alternatives To Address

Short-term Peak SO2 Exposures

Almost all commenters agreed on the

basic nature of the health effects

associated with short-term exposure to

SO2 in controlled human exposure

studies; that is, that brief (5-minute)

exposures to 0.5 to 1.0 ppm SO2 caused

a proportion of asthmatic subjects at

elevated ventilation rates to develop

measurable and statistically significant

bronchoconstriction, producing a range

of symptoms from barely perceptible to

severe enough to cause cessation of

activity and medication use. In contrast,

the comments were sharply divided on

whether the existing standards should

be supplemented by one of the three

regulatory alternatives identified in the

1994 reproposal.

In general, industry commenters and

affiliated physicians argued that

additional regulatory protection from

health effects associated with exposure

to short-term peaks of SO2 was

unnecessary. Two broad arguments

were made for this position. First, these

commenters typically argued that the

health effects associated with 5-minute

peaks in the range of 0.6 to 1.0 ppm SO2

are not significant because the effects

are transient, subsiding within 1 to 2

hours without medication, do not

include a late-phase inflammatory

response, can be avoided or ameliorated

with medication, and are similar

qualitatively and quantitatively to the

kinds of effects that asthmatic

individuals experience on an almost

daily basis as a result of exposure to

common stimuli. Second, these

commenters argued that exposures to 5-

minute peaks of SO2 are currently rare

and, with the advent of title IV

reductions in SO2 emissions, likely to

become even rarer. In this regard, some

commenters agreed with EPA’s

conclusion that the existing standards

markedly limit the occurrence of shortterm peaks of SO2.

Conversely, environmental and public

interest groups and affiliated

physicians, citizens and physicians

living in SO2-impacted areas, and

independent experts argued that health

effects that cause cessation of activity

and medication use are adverse health

effects, even if transient and preventable

or reversible with medication. Citizens

and physicians living in SO2-impacted

areas also argued that asthmatic

individuals living around industrial

sources of SO2 are repeatedly exposed to

short-term peaks of SO2, and that such

repeated exposures affect their health

adversely through exacerbation of their

asthma and reduction in their quality of

life. Some of these commenters

disagreed with EPA’s conclusion that

the existing standards limit the

occurrence of short-term peaks of SO2.

In general, Federal, State and local

government agencies focused on the

same two broad issues as the other

commenters (significance of the health

effects and likelihood of exposure) as a

basis for supporting or not supporting

adoption of one of the three proposed

regulatory alternatives to address shortterm peaks of SO2. In addition, most

governmental agencies submitted

comments on implementation of the

alternatives and tended to favor one or

another based on the anticipated

efficiency and effectiveness of

implementing them. Of the 11 State

agencies that commented, four favored

adopting either the proposed 5-minute

NAAQS or the section 303 program.

One State agency recommended that

EPA not adopt any of the proposed

alternatives at this time but continue to

study the problem, adding that the

proposed level of the standard, 0.60

ppm SO2, might not be low enough to

include an adequate margin of safety.

Another State agency was not in favor

of adopting any of the proposed

regulatory alternatives because it

already had adequate authority to

eliminate short-term peaks of SO2 in

problem areas. The remaining five State

agencies opposed adoption of any of the

three proposed regulatory alternatives.

Of the two local agencies that

commented, one opposed any new

regulations. The other did not comment

on the need for new SO2 regulations but

provided 5-minute SO2 data from the

local SO2 surveillance network and

relevant information about the causes

and temporal distribution of 5-minute

peaks ≥0.60 ppm SO2. Of the three

Federal agencies that commented, all

supported adoption of a 5-minute

NAAQS or the section 303 program

alternative.

III. Rationale for Final Decision

A. Current 24-hour and Annual

Standards

In the 1994 reproposal, EPA proposed

to determine that revisions to the 24-

hour and annual standards were not

appropriate. As in the 1988 proposal,

EPA provisionally concluded that the

current 24-hour and annual standards
25570 Federal Register / Vol. 61, No. 100 / Wednesday, May 22, 1996 / Rules and Regulations

were both necessary and adequate to

protect public health against effects

associated with those averaging periods.

The EPA also provisionally concluded

that retaining the current 24-hour and

annual standards was consistent with

the scientific data assessed in the

criteria document and staff paper and

their addenda, and with the advice and

recommendations of the staff and

CASAC (Appendix I).

Most comments on the 1994

reproposal focused on whether or not

there was a need to adopt one of the

regulatory alternatives to limit shortterm peaks of SO2. Virtually every

commenter that mentioned the existing

primary standards agreed with EPA’s

conclusion that these standards were

necessary and adequate to protect the

public health against effects associated

with those averaging periods. No

commenter argued that the

concentrations of these standards

should be changed.

After taking into account the public

comments, the Administrator again

concludes, based on the scientific data

assessed in the criteria document and

staff paper and their addenda, and

consistent with the advice and

recommendations of the staff and

CASAC, that the 24-hour and annual

standards provide adequate protection

against the health effects associated

with 24-hour and annual SO2

concentrations. Accordingly, the

Administrator concludes that revisions

to the 24-hour and annual standards are

not appropriate at this time. In reaching

this decision, the Administrator notes

that the health effects information on

24-hour and annual SO2 exposures has

remained largely unchanged since 1988.

As newer information becomes available

and is incorporated into new criteria

documents, it will provide the basis for

future reviews of the 24-hour and

annual standards.

B. Short-Term Peak SO2 Exposures

As reflected in the 1994 reproposal

and in public comments on the

reproposal, the question of whether

revision of the existing NAAQS is

appropriate to address risks that may be

posed by short-term peaks of SO2

depends upon two factors: (1) The

nature and significance of the health

effects per se, and (2) the number of

people likely to be exposed under

conditions likely to produce such

effects. The next two sections address

these factors in turn, and the

Administrator’s overall conclusions are

discussed in section III.B.3.

1. Assessment of Health Effects

Associated With Short-term SO2

Exposures

This section focuses on the nature and

significance of health effects that have

been observed in controlled human

exposure studies, putting aside

temporarily, questions about the

likelihood of such effects occurring

under real-life conditions. Subsections

a.–c. are adopted from the summary

discussion in the 1994 reproposal of

several important aspects of the health

effects associated with short-term peak

concentrations of SO2. Additional

references on these subjects are

provided in the reproposal notice.

Public comments on the most important

and controversial aspects of the shortterm SO2 health effects are discussed in

subsection d., with some indication of

the Administrator’s conclusions on

particular issues. The last subsection

contains the Administrator’s overall

conclusions regarding the significance

of health effects associated with

exposure to short-term peaks of SO2.

a. Sensitive Populations. It is clear

that healthy, nonasthmatic individuals

are essentially unaffected by acute

exposures to SO2 at concentrations

below 2 ppm, and that the population

of concern for the effects of short-term

SO2 exposure consists of mild and

moderate asthmatic children,

adolescents and adults that are

physically active outdoors. This is a

subset of the approximately 10 million

people or 4 percent of the population of

the United States that are estimated to

have asthma (NIH, 1991). The true

prevalence may be as high as 7 to 10

percent of the population (Evans et al.,

1987), because some individuals with

mild asthma may be unaware that they

have the disease and thus go

unreported. The prevalence is higher

among African-Americans, older (8- to

11-year-old) children, and urban

residents (Schwartz et al., 1990).

b. Asthma. The Expert Panel Report

from the National Asthma Education

Program of the National Heart, Lung and

Blood Institute (NIH, 1991) has defined

asthma as ‘‘a lung disease with the

following characteristics: (1) airway

obstruction that is reversible (but not

completely so in some patients) either

spontaneously or with treatment, (2)

airway inflammation, and (3) increased

airway responsiveness to a variety of

stimuli.’’ Common symptoms include

cough, wheezing, shortness of breath,

chest tightness, and sputum production.

Asthma is characterized by an

exaggerated bronchoconstrictor

response to many physical challenges

(e.g., cold or dry air, exercise) and

chemical and pharmacologic agents

(e.g., histamine or methacholine).

Daily variability in lung function

measurements is a typical feature of

asthma, with the poorest function (i.e.,

lowest forced expiratory volume in 1

second (FEV1) and highest specific

airway resistance (SRaw)) being

experienced in the early morning hours

and the best function (i.e., highest FEV1

and lowest SRaw) occurring in the midafternoon.

The degree of exercise tolerance

varies with the severity of disease. Mild

asthmatic individuals have good

exercise tolerance but may not tolerate

vigorous exercise such as prolonged

running. Moderate asthmatic

individuals have diminished exercise

tolerance, and individuals with severe

disease have very poor exercise

tolerance that markedly limits physical

activity. Many asthmatic individuals

experience bronchoconstriction when

exercising, even in clean air. This

response, called exercise-induced

bronchoconstriction, is made worse by

cold, dry air. Exercise-induced

bronchoconstriction is followed by a

refractory period of several hours during

which an asthmatic individual is less

susceptible to bronchoconstriction

(Edmunds et al., 1978). This refractory

period may alter an asthmatic

individual’s responsiveness to SO2 or

other inhaled substances.

c. Short-term SO2 Health Effects. The

EPA’s concern about the potential

public health consequences of

exposures to short-term peaks of SO2

arose from the extensive literature

involving brief (2- to 10-min) controlled

exposures of persons with mild (and in

some cases more moderate) asthma to

concentrations of SO2 in the range of 0.1

ppm to 2 ppm while at elevated

ventilation rates. The major effect of SO2

on sensitive asthmatic individuals is

bronchoconstriction, usually evidenced

in these studies by increased SRaw or

decreased FEV1, and the occurrence of

clinical symptoms such as wheezing,

chest tightness, and shortness of breath.

The proportion of asthmatic individuals

who respond, the magnitude of the

response and the occurrence of

symptoms increase as SO2

concentrations and ventilation rates

increase. The health effects are

relatively transient. Numerous studies

have shown that lung function typically

returns to normal for most subjects

within an hour of exposure. No

substantial ‘‘late phase’’ responses have

been noted for SO2, unlike the case for

more specific stimuli (e.g., pollen, dust

mites, or other allergens) in which ‘‘late

phase’’ inflammatory responses often

occur 4–8 hours after exposure and are
Federal Register / Vol. 61, No. 100 / Wednesday, May 22, 1996 / Rules and Regulations 25571

5Since elevated ventilation sufficient for oronasal

breathing to occur is a requirement for most

asthmatic persons to respond to SO2, and because

many asthmatic individuals experience

bronchoconstriction responses to exercise alone, it

is useful to distinguish between the two different

effects. In this discussion, ‘‘total FEV1 (or SRaw)’’

refers to the total change in lung function

experienced by a subject as a result of an exposure

to SO2 while at exercise, while ‘‘the effect of

changes due to SO2 alone’’ refers to the total lung

function change observed minus the change seen

for that subject from a control exposure at exercise

in clean air. Both measures have their utility: total

FEV1 or SRaw indicates the magnitude of overall

lung function change actually experienced by the

subject, while the change due to SO2 alone

indicates how much of this total change is

attributable to the pollutant itself.

often much more severe and dangerous

than earlier immediate responses.

The available data also indicate that

most types of regularly administered

asthma medications are not very

effective in blocking the SO2 response.

The exception, however, is the most

commonly used class of asthma

medications, the β-sympathomimetic

drugs (beta-agonist bronchodilator),

which are usually highly effective in

preventing the SO2 response from

developing, if taken shortly before

exposure, or ameliorating the effect, if

taken after symptoms develop.

In assessing the results from the

controlled human exposure studies, it

should be noted that the individuals

who participate in such studies

typically have mild allergic asthma and

can go without medication altogether or

can discontinue medication for brief

periods of time if exposures are

conducted outside their normal allergy

season. In addition, the responses of

African-American and Hispanic

adolescents and young adults to shortterm SO2 exposures have not been

studied systematically. Finally, subjects

who participate in controlled exposure

studies are also generally self-selected

and this may introduce some bias. Thus,

the extent to which the participants in

the studies reflect the characteristics of

the asthmatic population at large is not

known. Nevertheless, the high degree of

consistency among studies suggests that

the subjects are generally representative

of the population at risk or that any

selection bias is consistently present

across a diverse group of laboratories

(EPA, 1994a).

The criteria document supplement

(EPA, 1994a) contains a summary of the

literature on the health effects

associated with brief exposures to SO2.

Recent studies have provided useful

information about the magnitude of

responses in the range of 0.4 to 1.0 ppm

SO2, the range of interest identified in

the 1988 proposal (53 FR 14948, April

26, 1988). Data from several of these

recent large-scale chamber studies were

reexamined in Appendix B of the

criteria document supplement (EPA,

1994a) to provide a better understanding

of the responses observed in more

sensitive subjects. Forced expiratory

volume in 1 second was used as a

measure of lung function, in addition to

specific airway resistance, and other

endpoints examined included

symptoms, alteration of workload, and

medication usage occurring as a

consequence of these exposures.

Table B–1 of the criteria document

supplement (EPA, 1994a) summarizes

the lung function changes in response to

SO2 concentrations in the range of 0.6–

1.0 ppm from controlled human

exposure studies. Because different

studies used different measures of lung

function (FEV1 or SRaw), and different

concentrations of SO2, the discussion

that follows describes group mean

changes first for the studies that used

the measure SRaw, then group mean

changes for studies that used FEV1, and

then finally the individual responses.

The data indicate that, in terms of

group mean changes, total SRaw

changes 5 were approximately twice as

great at 0.6 ppm and above as at 0.5 ppm

and below. The differences were even

more pronounced when the changes in

SRaw due to SO2 alone (i.e., after

correction for the effects of exercise)

were considered.

For FEV1, the differences in responses

between 0.4 ppm and 0.6 ppm SO2 were

not as pronounced. At 0.6 ppm SO2,

group mean decreases in total FEV1 of

approximately 20 percent were observed

in the mild and moderate asthmatics

studied. The changes in FEV1 due to

SO2 alone resulted in decreases in FEV1

of approximately 15 percent (EPA,

1994a, Table B–1).

In addition, at 0.6 ppm SO2, 25

percent or more of the subjects had

pronounced individual responses

(either a 200 percent or greater increase

in SRaw or a 20 percent or greater

decrease in FEV1) due to SO2 alone

(total changes in lung function for these

individuals would be expected to be

even greater). In contrast, at ≤0.5 ppm

SO2, these more pronounced individual

responses were less frequent, occurring

in fewer than 25 percent of the subjects

for both measures of lung function for

all but one group studied (EPA, 1994a,

p. B–2).

While not examined in as much detail

as lung function, other indicators of

severity also tend to increase with

increasing SO2 concentration. In one

study, for example, four of 24 moderate/

severe asthmatic subjects were required

to reduce their exercise level because of

asthma symptoms at 0.6 ppm SO2. This

occurred only once at each of the lower

concentrations (EPA, 1994a). Two

recent studies, which considered

medication used to mitigate the effects

of SO2 as a health endpoint and which

followed the subjects’ medication use in

detail, found approximately twice as

many subjects took medication

immediately after exposure to 0.6 ppm

SO2 than after exposure to 0.3 ppm SO2

(EPA, 1994a, Table 7, p. 40).

Considering the variety of endpoints

for which information is available,

clearly the effects beginning at 0.6 ppm

and up to 1.0 ppm are more pronounced

than those at lower concentrations. This

is in agreement with the conclusions

reached in the staff paper addendum

(EPA, 1986b), which stated that there

were ‘‘clearer indications of clinically or

physiologically significant effects at 0.6

to 0.75 ppm SO2 and above.’’

The staff also compared the effects of

SO2 observed in these recent controlled

human exposure studies to the effects of

moderate exercise, typical daily

variation in lung function, and the

severity of frequently-experienced

asthma symptoms. The effects of 0.6

ppm SO2 exposure at moderate exercise,

as measured by FEV1, exceeded either

the typical effect of exercise alone or

typical daily variations in FEV1 (EPA,

1994a, sections 4.3 and 5.3). For

symptomatic responses, two to eight

times as many subjects, after exposure at

exercise to 0.6 ppm SO2, experienced

symptoms of at least moderate severity

(13–62 percent of subjects) than after

exercise in clean air alone (4–19 percent

of subjects) (EPA, 1994a, p. B–12). In

addition, a significant portion of

subjects (approximately 15 to 60

percent, depending on asthma status)

participating in certain controlled

human exposure studies seemed to

experience symptoms more frequently

in response to 0.6 ppm SO2 than at any

other time during their participation in

the studies (EPA, 1994a, p. B–12).

Furthermore, the response seen in the

most sensitive 25 percent of responders

at 0.6 ppm equalled or exceeded

approximately a 30 percent decline in

FEV1 for mild asthmatic subjects, and

approximately a 40 percent decline for

moderate asthmatic individuals. By

comparison, during clinical

bronchoprovocation testing, changes are

not usually induced beyond a 20

percent decrease in FEV1.

In addition, while at least some

subjects can experience such a 20

percent decline without experiencing

symptoms, in recent studies focusing on

effects at 0.6 ppm SO2, from 33–43

percent of moderate asthmatics and

from 6–35 percent of mild asthmatics

experienced at least a 20 percent
25572 Federal Register / Vol. 61, No. 100 / Wednesday, May 22, 1996 / Rules and Regulations

decrease in total FEV1 in conjunction

with symptoms rated as being of

moderate severity or worse. It should be

noted that the asthmatic subjects with

moderate/severe disease started an

exposure with compromised lung

function compared to mild asthmatic

subjects. While the response to SO2 was

similar in the mild versus the moderate/

severe asthmatic subjects, similar

functional declines beginning from a

different baseline may have different

biological importance (EPA, 1994a, pp.

21–25).

In the staff paper addendum,

‘‘bronchoconstriction * * *

accompanied by at least noticeable

symptoms,’’ was seen as an appropriate

measure of concern (EPA, 1986b, p. 37).

However, a substantial proportion of

the subjects in these more recent studies

experienced greater effects,

bronchoconstriction with at least

moderate symptoms, beginning at 0.6

ppm SO2 (EPA, 1994a).

Considering the recent body of

evidence along with previous studies,

the criteria document supplement (EPA,

1994a) concluded that substantial

percentages (≥ 25 percent) of mild or

moderate asthmatic individuals exposed

to 0.6 to 1.0 ppm SO2 during moderate

exercise would be expected to have

respiratory function changes and

severity of symptoms distinctly

exceeding those experienced as typical

daily variation in lung function or in

response to other stimuli, such as

moderate exercise. The severity of

effects for many of the responders is

likely to be of sufficient concern to

cause disruption of ongoing activities,

use of bronchodilator medication, and/

or possible seeking of medical attention.

At most, only 10 to 20 percent of mild

or moderate asthmatic individuals are

likely to exhibit lung function

decrements in response to SO2

exposures of 0.2 to 0.5 ppm that would

be of distinctly larger magnitude than

typical diurnal variation in lung

function or changes in lung function

experienced by them in response to

other often-encountered stimuli.

Furthermore, it appears likely that only

the most sensitive responders might

experience sufficiently large lung

function changes and/or respiratory

symptoms of such severity as to be of

potential health concern; that is, leading

to the disruption of ongoing activities,

the need for bronchodilator medication,

or seeking of medical attention.

d. Public Comments on Significance

of Health Effects. In regard to the

measured changes in lung function

(expressed as FEV1 or SRaw),

commenters did not disagree with the

EPA’s summary of the available

literature contained in the November 15,

1994 (59 FR 58958) reproposal. Where

there continues to be a real divergence

of opinion among asthma specialists

and others is on interpretation of the

results, or on the medical significance of

the lung function changes that have

been measured in exercising asthmatic

subjects and summarized in the various

EPA documents. At issue are not the

published data about SO2-induced

bronchoconstriction, but how they are

interpreted.

As noted in the 1994 reproposal,

bronchoconstriction caused by brief

exposure to 0.6 to 1.0 ppm SO2 is

transient. Measurements of lung

function start to improve when the

exposure ceases, or when the subject

ceases to exercise and the ventilation

rate decreases to resting levels; after 5

minutes of exposure, the magnitude of

the response does not worsen even if

exposure and elevated ventilation rate

continue. Most often, lung function

returns to preexposure levels within 1

hour, occasionally taking up to 2 hours

to return to normal. A dose of one of the

most commonly used classes of

medication, inhaled beta2-agonists,

rapidly attenuates or prevents the

response. The transient nature of the

response led some commenters to argue

that the health effects are not

significant. These commenters stated

that although they would advise an

asthmatic individual to take medication,

cease activity or avoid the stimulus, this

behavior was an everyday part of an

asthmatic individual’s life and not cause

for medical concern. Other commenters

argued that any effect which may entail

bronchoconstriction severe enough to

limit activity or cause medication use is

a significant health effect.

Many commenters argued that the

documented effects are not medically

significant because, as one commenter

put it, ‘‘changes in lung function are not

meaningful endpoints in themselves,

but must be placed in the context of

asthmatics’ typical respiratory function,

which is both highly variable and

reactive to many stimuli and

conditions’’ (see Docket No. A–84–25,

VIII–D–71). In general, these

commenters argued that the responses

to short-term peaks of SO2 in the range

of 0.6 to 1.0 ppm are similar in nature

and magnitude to the well-tolerated

responses to a variety of non-specific

stimuli (cold, dry air, exercise, irritants

such as perfume) encountered on a daily

basis by most asthmatic individuals and

are not in themselves deleterious to the

asthmatic individual’s health. Other

commenters argued that this fact does

not justify the neglect of potential

ambient air SO2 effects, and that

unusual susceptibility to an inhaled

pollutant does not simply constitute a

problem for the susceptible individual.

Despite these opposing points of

view, there was some agreement that

frequency of occurrence of SO2-induced

health effects could make a difference in

the concern that a physician feels. That

is, some physicians felt that the

documented SO2-induced health effects

were well tolerated by asthmatic

individuals; however, if the effects

occurred frequently enough, then they

would be cause for medical concern

(public hearing transcript, 1995, p. 155).

Other physicians felt that such effects

are a cause for concern despite their

transient and reversible nature; if

exposures occurred rarely enough,

however, these physicians would be less

concerned (public hearing transcript,

1995, p. 89–90). Several commenters

also noted that cold air appears to act at

least additively with SO2, and that the

bronchoconstrictive effect of cold air

which contains SO2 is larger than that

of either exposure condition alone.

Some commenters took issue with

EPA’s assessment of the proportion of

asthmatic individuals who would

experience meaningful symptoms or

have any disruption of daily activities.

Based on personal experience, one

commenter stated that most asthmatics

do not begin to perceive

bronchoconstriction until FEV1 falls to

about 50 percent of its normal value and

SRaw increases about 400 percent (see

Docket No. A–84–25, VIII–D–71). Other

commenters agreed that the kinds of

symptomatic responses experienced by

asthmatic subjects exposed to SO2 in the

reviewed chamber studies are no more

than brief, perceptible reactions that

might temporarily disrupt activities, but

are well tolerated and do not endanger

the individuals’ health or cause them to

seek medical attention. On the other

hand, commenters who believed the

effects were significant argued that

transient and reversible decrements in

lung function are adverse if they cause

physical discomfort, interfere with

normal activity or impair the

performance of daily activities, or

aggravate chronic respiratory disease by

increasing the frequency or severity of

asthma attacks. Several commenters

argued that measurable effects have

occurred after brief exposures, with

elevated ventilation rates, to

concentrations as low as 0.25 to 0.28

ppm SO2, and thus that the proposed 5-

minute standard of 0.60 ppm SO2 leaves

no margin of safety. However, as stated

above, considering a variety of

endpoints for which information is

available, clearly the effects beginning at

0.6 ppm and up to 1.0 ppm are more
Federal Register / Vol. 61, No. 100 / Wednesday, May 22, 1996 / Rules and Regulations 25573

pronounced than at lower

concentrations.

As noted in the criteria document

supplement (EPA, 1994a), the staff

paper supplement (EPA, 1994b) and the

November 15, 1994 reproposal (59 FR

58958), unlike the effects of allergens

and viral infections, there is no

evidence that short-term exposure to

SO2 while at an elevated ventilation rate

leads to any ‘‘late phase’’ response.

‘‘Late-phase’’ bronchoconstriction is

indicative of a more serious

inflammatory reaction which takes

much longer to resolve and which can

lead to emergency room visits and/or

hospitalization. The ‘‘late phase’’

inflammatory response can also cause

the airways to become more sensitive to

other stimuli. Since this type of

response has not been observed with

brief exposures in the range of 0.6 to 1.0

ppm SO2, many commenters argued that

the health of asthmatic individuals is

not affected by such exposures.

The ability of inhaled beta2-agonists,

the most commonly prescribed class of

asthma medications, to prevent or

ameliorate the effects of SO2 exposure

was frequently cited as one reason why

most asthmatic individuals are unlikely

to experience bronchoconstriction due

to exposure to short-term peaks of SO2.

These commenters argued that since

most asthmatic individuals experience

exercise-induced bronchoconstriction,

they are highly likely to premedicate

with an inhaled beta2-agonist

medication prior to exercise and

therefore be protected from SO2-induced

health effects. Further, these

commenters stated that the highly

variable compliance rates for medicine

usage cited by EPA in the criteria

document supplement (EPA, 1994a),

staff paper supplement (EPA, 1994b)

and November 15, 1994 reproposal (59

FR 58958) do not apply to physically

active asthmatic individuals, for whom

medication compliance rates are

significantly better.

Conversely, many other commenters

agreed with EPA that medication

compliance rates can be very poor, even

for individuals who are physically

active, like children, and that many

asthmatic individuals use medication

only after symptoms occur. These

individuals would be at risk for

experiencing SO2-induced

bronchoconstriction. Some commenters,

including one from a State’s Office of

Environmental Health Hazard

Assessment, which recently reviewed

that State’s 1-hour SO2 standard (see

Docket No. A–84–25, VIII–D–65),

commented that an optimal medication

regimen from the standpoint of reducing

SO2-induced bronchoconstriction may

result in undesirable side effects. Some

of these commenters also noted that SO2

exposure could cause asymptomatic,

exercise-induced bronchoconstriction to

become symptomatic, thereby causing

an asthmatic individual to take

medicine that would normally not be

needed. Several commenters argued that

relying on medication use instead of

regulation was poor public policy. Some

of these commenters also argued that

asthmatic individuals of lower

socioeconomic status may not be able to

afford medication or have limited access

to health care. In the Administrator’s

judgment, these concerns about

accessibility of medication and health

care, and the variability of medication

compliance rates, are legitimate ones.

Although the use of medication may

substantially reduce the incidence and/

or severity of SO2-induced

bronchoconstriction, the mere

availability of medication does not

necessarily mean that all asthmatic

individuals will necessarily be

protected from this effect. The

Administrator therefore concludes that

this factor should not be regarded as

dispositive in assessing the

appropriateness of regulatory action to

provide additional protection against

short-term SO2 peaks.

Many commenters argued that there

are no epidemiological studies which

show an association between short-term

peaks of SO2 and adverse health effects

such as asthma symptoms or increased

visits to physicians or hospital

emergency rooms. Some of these

commenters argued that the changes in

lung function and symptoms found in

some subjects in controlled human

exposure studies may not be indicative

of what would occur in real-world

situations. The reason that there are no

epidemiological studies showing an

association between short-term (5- to 10-

minute) peaks of SO2 and real-world

health effects is that apparently no

studies have been conducted to examine

the association or lack thereof of shortterm SO2 peaks and adverse health

effects. This is most likely because it

would be difficult to design and

conduct an epidemiological study that

could detect possible associations

between very brief (5- to 10-minute),

geographically localized, peak SO2

exposures and respiratory effects in

asthmatic individuals. Furthermore, the

responses of naturally-breathing

asthmatics exposed to SO2 under

controlled conditions in an

environmental chamber presumably

reflect responses that would be observed

in the ambient (‘‘real-world’’)

environment under similar conditions

of activity level, air temperature, and

humidity. Although there is evidence

that other inhaled materials that modify

airway responsiveness can influence the

response to SO2, there is no reason, at

the present time, to suggest that the

ambient pollutant mixture would cause

either a suppression or an augmentation

of SO2 effects through some, as yet

unrecognized, chemical interaction.

e. Significance of Health Effects.

Taking into account the available health

effects studies and the body of

comments on the health effects, the

Administrator agrees with the staff

assessment that a substantial percentage

(20 percent or more) of mild-tomoderate asthmatic individuals exposed

to 0.6 to 1.0 ppm SO2 for 5 to 10

minutes at elevated ventilation rates,

such as would be expected during

moderate exercise, would be expected to

have lung function changes and severity

of respiratory symptoms that clearly

exceed those experienced from typical

daily variation in lung function or in

response to other stimuli (e.g., moderate

exercise or cold/dry air). For many of

the responders, the effects are likely to

be both perceptible and thought to be of

some health concern; that is, likely to

cause some disruption of ongoing

activities, use of bronchodilator

medication, and/or possibly seeking of

medical attention. The EPA agrees with

other commenters that the frequency

with which such effects are experienced

may affect the public health concern

that is appropriate. Taking into account

the broad range of opinions expressed

by CASAC members, medical experts,

and the public, the Administrator

concludes that repeated occurrences of

such effects should be regarded as

significant from a public health

standpoint. Accordingly, the

Administrator also concurs with the

staff judgment that the likely frequency

of occurrence of such effects should be

a consideration in assessing the overall

public health risk in a given situation.

2. Air Quality and Exposure

Considerations

Another major basis for considering

whether additional regulatory measures

are appropriate to reduce the occurrence

of short-term peaks of SO2 has been the

estimation of the geographic extent and

the frequency of 5-minute peaks greater

than 0.60 ppm SO2 in the ambient air,

and the likelihood that these peaks

would result in exposure conditions

that could cause significant health

effects. As discussed in the staff paper

supplement (EPA, 1994b) and the 1994

reproposal, the occurrence of short-term

peaks of SO2 is relatively infrequent and

highly localized around point sources of
25574 Federal Register / Vol. 61, No. 100 / Wednesday, May 22, 1996 / Rules and Regulations

6The 5-minute concentrations ranged from 0 to >

2.5 ppm SO2. The number of observations recorded

at any monitor ranged from 308 to 48,795 hours,

with the mean number of observations equalling

7,646 hours (a complete year of hourly maximum

5-minute averages would contain 8,760

observations). There were 63 monitors, located in

16 States, with continuous data sets of either the

maximum 5-minute block average per hour or all

of the 5-minute block averages per hour. For data

sets containing all of the 5-minute block averages

per hour, the maximum 5-minute block average for

each hour was extracted and that parameter was

used throughout the analysis. Of the 63 monitors,

26 (41 percent) registered 1 or more concentrations

greater than the proposed short-term standard of

0.60 ppm SO2 during the time periods represented

for the monitors involved. For any given monitor,

the number of such exceedances ranged from 0 to

139, which corresponds to 0 to 3 percent of the

hours represented in the data. Of the 26 monitors

measuring at least 1 exceedance, 11 monitors

recorded from 1 to 5 exceedances, while 8 monitors

in 4 communities recorded from 25 to 139

exceedances. While these data came from

sourcebased monitors, the existing SO2 monitoring

network is designed to characterize ambient air

quality associated with 3-hour, 24-hour, and annual

SO2 concentrations rather than to detect short-term

peak SO2 levels. This could have resulted in

underestimates of the maximum 5-minute block

averages recorded. Therefore, changes in monitor

siting and density near SO2 sources most likely to

produce high 5-minute peaks could increase both

the number of exceedances and the concentrations

of the maximum 5-minute block averages recorded.

SO2. None of the air quality or exposure

information subsequently received by

EPA has changed this assessment.

In 1993 and again in 1994, EPA

requested that States collect and submit

5-minute SO2 ambient monitoring data

from source-based monitors. Data were

submitted from both industry and Staterun monitors and while much of this

information was considered in the 1994

staff paper supplement (EPA 1994b) and

in the 1994 reproposal, a few sites

subsequently provided more data.

Available data have been compiled and

statistical parameters calculated in a

report for EPA by Systems Applications

International or SAI (1996).6 In general,

the data confirm that a substantial

number of short-term peaks greater than

0.60 ppm can occur in the vicinity of

certain sources.

As indicated previously, an important

consideration is whether such shortterm peaks of SO2 are likely to cause

episodes of bronchoconstriction in

asthmatic individuals. Thus, one

method of assessing the public health

significance of SO2-induced effects is to

estimate the likelihood that asthmatic

individuals will be exposed to such

peaks while simultaneously at elevated

ventilation rates (EPA, 1994a, p.51). It

should be noted, however, that not all

asthmatic individuals who experience

such exposures will necessarily

experience SO2-induced health effects,

either because of individual variability

or other factors.

At the time of the 1994 reproposal,

three exposure analyses were available

that estimated the frequency of SO2

exposures that could result in

measurable health effects. Two of the

analyses estimated the potential

frequency of exposure events resulting

from operation of utility boilers

nationwide. For these two studies,

detailed information on actual

emissions was available on a plant-byplant basis (Burton et al., 1987;

Rosenbaum et al., 1992) to use in

estimating ambient SO2 concentrations

and then exposures. The utility analyses

estimated there would be 68,000

exposure events per year at ≥ 0.5 ppm

SO2, which would affect approximately

44,000 asthmatic individuals at elevated

ventilation rates. Taking into account

full implementation of the title IV

program of the Act, in the year 2015, the

number of exposure events at ≥ 0.5 ppm

SO2 attributable to the utility sector was

estimated to drop to 40,000 per year,

contingent on trading decisions.

The third exposure analysis available

at the time of the 1994 reproposal

estimated nationwide SO2 exposures

resulting from the operation of

nonutility sources. Because actual data

were not available, some conservative

assumptions had to be made about

operating parameters, which increased

the uncertainties in the analysis

(Stoeckenius et al., 1990). Probably the

largest single source of uncertainty in

this analysis was the emissions

estimates used for the nonutility

sources. The analysis estimated 114,000

to 326,000 exposures to 0.5 ppm SO2

per year around nonutility sources.

These exposures were estimated to

affect 24,000 to 122,000 asthmatic

individuals at elevated ventilation rates,

implying that exposed individuals may

be exposed more than four times a year,

on average.

Combining the utility and nonutility

exposure estimates results in a

prediction of 180,000 to 395,000 total

exposure events to 0.5 ppm SO2

nationwide, per year. These analyses

indicate that 68,000 to 166,000

asthmatic individuals (or 0.7 to 1.8

percent of the total asthmatic

population) potentially could be

exposed one or more times, while

outdoors at exercise, to 5 minute peaks

of SO2 ≥ 0.5 ppm. The number of

asthmatic individuals likely to be

exposed to ≥ 0.60 ppm SO2 under the

same conditions, of course, would be

smaller. The methodologies employed

in these analyses, together with the

associated uncertainties, are discussed

in some detail in the staff paper

supplement (EPA, 1994b, pp. 46–47,

Appendix B).

In response to the 1994 reproposal,

several industry associations sponsored

and submitted as a public comment a

revised analysis of exposures around

four types of nonutility sources

(industrial/commercial/institutional

boilers, kraft and sulfite process pulp

and paper mills, and copper smelters)

by Sciences International, Inc. (1995).

This study incorporated new data and

additional analyses designed to

eliminate the need for some of the more

conservative assumptions employed in

the Stoeckenius et al. (1990) study. A

principal feature of the new study is the

use of improved source and emissions

data for all four source categories

examined and especially for sulfite

process pulp mills and copper smelters.

The new analysis estimated

significantly fewer expected exposure

events for the four source categories

examined. In the original study, the four

categories were estimated to contribute

a total of 73,000 to 259,000 exposure

events (Stoeckenius et al., 1990). In the

revised analysis, this range decreased by

an order of magnitude, to between 7,892

and 23,099 events. The same basic

procedures were used to calculate

expected exposures in both the 1990

and 1995 studies. However, a direct

comparison of the results of the two

exposure analyses may not be possible

due to differences in some key details

between the two studies, which are

highlighted in a technical review by

Stoeckenius (1995) of the Sciences

International, Inc. (1995) exposure

analysis. In general, that review

indicates that while the Stoeckenius et

al. (1990) study utilized several very

conservative assumptions, which most

likely led to an overestimate of

exposures for these three source

categories. The Sciences International,

Inc. (1995) reanalysis did not provide

reliable estimates of the degree of

conservatism resulting from the original

assumptions which could then be used

for the purpose of comparison. In

contrast, the updated information and

data for copper smelters used in the

Sciences International, Inc. (1995)

reanalysis most likely resulted in a more

accurate estimate of exposures for that

source category than did previously

available estimates (Stoeckenius, 1995).

Another industry commenter

submitted an exposure analysis (see

Docket No. A–84–25, VIII–G–08) that

utilized actual SO2 ambient air

monitoring and demographic data from

a community located near a coppersmelting facility. The results of this

analysis indicate that the probability of

SO2-related episodes of

bronchoconstriction in the sensitive
Federal Register / Vol. 61, No. 100 / Wednesday, May 22, 1996 / Rules and Regulations 25575

population of asthmatic individuals in

the community is very low. There was

no evidence of an association between

5-minute concentrations of SO2 > 0.60

ppm and episodes of

bronchoconstriction in the sensitive

population.

These exposure analyses and the body

of 5-minute SO2 monitoring data

underscore the views of the

Administrator, the staff and the CASAC,

reflected in the 1994 reproposal, that the

likelihood that asthmatic individuals

will be exposed to 5-minute peak SO2

concentrations of concern, while

outdoors and at elevated ventilation

rates, is very low when viewed from a

national perspective. Even in

communities where frequent 5-minute

peaks have been recorded, the

likelihood of exposure is highly

variable. One county public health

agency submitted 5-minute SO2

monitoring data (see Docket No. A–84–

25, VIII–D–15), for the years 1993–1994,

from the 10 continuous SO2 monitors in

the local surveillance network. Only

monitors located near large industrial

sources of SO2 measured exceedances of

0.60 ppm SO2. Of 29 exceedances

measured over a 2-year period,

approximately half of the exceedances

were associated with breakdowns of the

desulfurization equipment used to

control SO2 emissions from coke plants

in the county. The agency noted that

more than 70 percent of the hours in

which exceedances were measured

occurred very late at night or early in

the morning, which would reduce the

likelihood of the exceedances affecting

the sensitive population.

Nonetheless, the 5-minute monitoring

data indicate that some communities in

proximity to SO2 sources are repeatedly

subjected to high short-term

concentrations of SO2 in the ambient

air. Asthmatic individuals who reside in

proximity to certain individual sources

may be at greater risk of being exposed

to such peak SO2 levels while at

elevated ventilation rates, and,

therefore, at greater risk of suffering

health effects than the asthmatic

population as a whole. This conclusion

is supported by the comments of

citizens and physicians living in areas

where high 5-minute peaks of SO2 have

been recorded. Citizens have reported,

for example, that they developed asthma

upon moving to an SO2-impacted area;

that their asthma is better, both in terms

of symptoms and indicators such as

peak flow measurements when they

leave the SO2-impacted area on vacation

or for medical treatment; and that their

peak flow measurements decrease when

the wind is blowing from the direction

of the local SO2 source(s). These citizens

express the belief that ambient SO2

concentrations are responsible for their

symptoms. Physicians have commented

that they believe that ambient air SO2

concentrations in their communities are

negatively affecting the health of their

patients. Most of these comments came

from two of the six communities for

which SO2 monitoring data show

repeated high 5-minute peaks greater

than 0.60 ppm SO2.

The data also indicate that asthmatic

individuals living in communities in

which 5-minute peaks greater than 0.60

ppm SO2 rarely occur may be subject to

much less risk of experiencing health

effects that cause cessation of activities

or increased medication use. Even when

monitors record a substantial number of

such peaks, the likelihood that a

significant number of asthmatic

individuals will be exposed to such

peaks with some frequency while at

elevated ventilation rates may range

from nonexistent to fairly high

depending upon such localized factors

as the magnitude and frequency of the

peaks, the times of occurrence,

meteorological conditions in the area,

the density of the population near the

source(s) involved, and daily activity

patterns. Thus, estimation of risk must

be done on a case-by-case basis and be

based on site-specific factors. In short,

the data clearly show that 5-minute

peaks greater than 0.60 ppm SO2 can

occur around particular industrial point

sources of SO2, that such peaks are not

ubiquitous from a national perspective

but instead appear to occur only in the

vicinity of such sources, and that the

risk of exposures that could cause

significant health effects in asthmatic

individuals cannot be estimated based

solely on the number of recorded high

5-minute peaks of SO2, but instead must

be estimated using site-specific factors.

3. Conclusions

For reasons discussed above, based on

her assessment of the relevant scientific

and technical information and taking

into account public comment, it is the

Administrator’s judgment that 5-minute

peak SO2 levels do not pose a broad

public health problem when viewed

from a national perspective. As

discussed in some detail in the 1994

reproposal, the existing suite of SO2

standards and associated control

strategies clearly limit both the

occurrence of high 5-minute peak SO2

levels, and the likelihood that asthmatic

individuals will be exposed to them

while outdoors and at elevated

ventilation rates.

In considering the residual risk posed

by such peak concentrations, the

Administrator has taken a number of

factors into account. As discussed in the

criteria document and staff paper

supplements (EPA 1994a, p. 51, EPA

1994b, p. 59), an important

consideration in determining the public

health risk posed by 5-minute

concentrations in the range of 0.60 to

1.0 ppm SO2 is the frequency with

which an asthmatic individual may be

exposed while at an elevated ventilation

rate. As discussed earlier, there is some

agreement that infrequent exposures in

this range may not be a cause for

significant concern. As the frequency of

exposure increases, so does concern

about the associated public health risk.

Asthmatic individuals living in

communities in which 5-minute peaks

in the range of 0.60 to 1.0 ppm SO2

rarely occur may be unlikely to

experience exposure events that would

cause them to cease their activities or

increase medication use. In particular

locations, of course, the concentrations

involved in exposure events can exceed

1.0 ppm SO2, and could induce a greater

response in an exposed asthmatic

individual than lower concentrations.

Thus, frequency of exposure events

alone is not an adequate indicator of the

risk to public health. As discussed

above, factors such as the magnitude of

5-minute SO2 peaks, time of day,

activity patterns, and the size of the

population exposed are also relevant. As

a result, whether 5-minute peak SO2

concentrations will pose a significant

public health risk depends largely on

highly localized factors.

Given the localized, infrequent and

site-specific nature of the risk involved,

the Administrator has concluded that

short-term peak concentrations of SO2

do not constitute the type of ubiquitous

public health problem for which

establishing a NAAQS would be

appropriate. For similar reasons, the

Administrator concludes that adoption

of a section 303 program employing a

uniform, nationwide trigger level would

not be an appropriate response. With

respect to the third alternative identified

in the 1994 reproposal (augmenting

implementation of existing SO2

NAAQS), it has become increasingly

clear that even full attainment of the

existing SO2 standards would not

preclude the occurrence of high 5-

minute SO2 peaks in particular

locations. Moreover, given the sitespecific nature of the problem, States

can more effectively identify for

monitoring purposes, sources that may

be causing or contributing to high 5-

minute SO2 concentrations.

For the reasons discussed previously,

the Administrator has concluded that

repeated exposures to 5-minute peak

SO2 levels of 0.60 ppm and above could
25576 Federal Register / Vol. 61, No. 100 / Wednesday, May 22, 1996 / Rules and Regulations

pose a risk of significant health effects

for asthmatic individuals at elevated

ventilation rates in some localized

situations. The Administrator has also

concluded that the residual health risks

posed by short-term concentrations are

most appropriately addressed at the

State level. In the Administrator’s

judgment, the States are in a far better

position than EPA to assess the highly

localized and site-specific factors that

determine whether the occurrence of

such concentrations in a given area

poses a significant public health risk to

the local population, and if so, to

fashion an appropriate remedial

response. This view was also advanced

by some States in their comments on the

1994 reproposal.

To assist the States in addressing

short-term peak SO2 levels, EPA will

publish a reproposal notice superseding

the March 1995 notice (59 FR 12492)

that proposed revisions to 40 CFR part

51 establishing a new program under

section 303 of the Act that would differ

from that contemplated in the 1994

reproposal. The new program would

also differ from existing programs under

section 303 that are designed to protect

against episodic events.

In particular, EPA plans to propose

two new levels as guides to State action:

A ‘‘concern level’’ at 0.60 ppm SO2, 5-

minute block average; and an

‘‘intervention level’’ at 2.0 ppm SO2, 5-

minute block average. Under the

program to be proposed, the States

would determine whether 5-minute

peak SO2 levels recorded in the range of

0.60 to 2.0 ppm SO2 posed a significant

public health risk and, if so, the

appropriate remedial response. To assist

the States in reaching such

determinations, the proposal will

identify, in the form of guidance, factors

that EPA believes should be considered

in assessing whether recorded peaks

pose a significant health risk to the local

population. Among other things, the

factors would include the frequency and

magnitude of observed 5-minute peaks,

and the likelihood and frequency of

exposures for asthmatic individuals at

elevated ventilation rates. In assessing

whether observed 5-minute peaks in

this range posed a significant public

health risk, thus warranting

intervention, the States would be

advised to take into account the above

factors, as well as others they might

deem appropriate. It is the

Administrator’s judgment that

establishing such a program, in which

the States would determine at the local

level whether peak SO2 levels in the

range of 0.60 to 2.0 ppm SO2 posed a

significant public health risk and, if so,

the appropriate remedial response, is

the most effective approach for

addressing this potential public health

problem.

C. Final Decision on Primary Standards

For the reasons discussed above, and

in the November 15, 1994 reproposal

notice (58 FR 58958), it is the

Administrator’s judgment under section

109(d)(1) that revisions to the existing

primary SO2 NAAQS are not

appropriate at this time. As provided for

under the Act, the EPA will continue to

assess the scientific information on

health effects associated with 5-minute,

24-hour and annual SO2 exposures as it

emerges from research and ongoing SO2

monitoring programs, and will update

the air quality criteria for sulfur oxides

accordingly. The revised criteria will

provide the basis for the next review of

the primary NAAQS for SO2.

D. Technical Changes

There were relatively few comments

on the proposed technical changes.

Several environmental and public

interest groups and one State preferred

the running averaging convention, while

industry comments supported the block

averaging convention. A small number

of comments were also received both for

and against the change from μmg/m3 to

ppm. Taking these comments into

account, EPA has decided to promulgate

the technical changes set forth in the

1994 reproposal. First, the block

averaging convention will be retained,

and language clarifying this point will

be adopted in the regulation (40 CFR

50.4 and 50.5). Under the block

convention, periods such as 24 hours

and 3 hours are measured sequentially

and do not overlap; when one averaging

period ends, the next begins.

Although the wording of the original

24-hour, 3-hour, and annual SO2

standards may have been ambiguous on

the matter, the earliest actions of the

EPA signify that the block averaging

convention was intended for these

standards (OAQPS, l986), and block

averages have generally been used in

implementing the standards. Given a

fixed standard level, the use of the

alternative, running averages, would

represent a tightening of the standards

(Faoro, 1983; Possiel, 1985). For reasons

explained in this notice and in the April

21, 1993, notice on the secondary

NAAQS (58 FR 21351), the

Administrator has already determined

that protection of the public health and

welfare does not require tightening the

existing standards. Therefore, EPA will

retain the block averaging convention

for the 24-hour, 3-hour, and annual

standards.

The second technical change to be

adopted is that the levels for the

primary and secondary NAAQS will be

stated in ppm rather than μg/m3 (40 CFR

50.4 and 50.5). This will be done to

make the SO2 NAAQS consistent with

those for other pollutants and to

facilitate public understanding of the

standards. Although the ppm levels are

slightly less than their current μg/m3

counterparts, the differences are

considered negligible (Frank, 1988).

Finally, the explicit rounding

conventions and the data completeness

and handling conventions put forth in

the reproposal will be adopted.

IV. Regulatory Impacts

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 the 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.

Pursuant to the terms of Executive

Order 12866, OMB has notified EPA

that it considers this a ‘‘significant

regulatory action’’ within the meaning

of the Executive Order. The EPA has

submitted this action 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–84–25).

The EPA has judged that today’s

decision on the SO2 primary NAAQS is

not an economically-significant

regulatory action as defined by

Executive Order 12866 because there are

no additional costs or other impacts as

a result of not revising the standards.

The EPA, therefore, has deemed

unnecessary the preparation of a final

regulatory impact statement.
Federal Register / Vol. 61, No. 100 / Wednesday, May 22, 1996 / Rules and Regulations 25577

B. Regulatory Flexibility Analysis

Pursuant to section 605(b) of the

Regulatory Flexibility Act, 5 U.S.C.

605(b), the Administrator certifies that

this rule will not have a significant

impact on a substantial number of small

entities. The Regulatory Flexibility Act

requires that all Federal agencies

consider the impacts of final regulations

on small entities, which are defined to

be small businesses, small

organizations, and small governmental

jurisdictions (5 U.S.C. 601 et seq.). A

decision not to revise the existing

primary NAAQS for SO2 would, of

course, impose no new requirements on

small entities. In addition, the SIPs

necessary to implement the existing

primary standards have been

substantially adopted and implemented.

Additional SIP requirements will be

needed only for those areas or sources

which are designated as nonattainment

for the existing primary standards now

or in the future. Given the current air

quality and attainment status, however,

it is very unlikely that new SIP

requirements would be required that

would significantly affect a substantial

number of small entities.

C. Impact on Reporting Requirements

There are no reporting requirements

directly associated with an ambient air

quality standard promulgated 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). This final action

will not result in any changes in these

reporting requirements since it would

retain the existing levels and averaging

times for the primary standards. The

current standards are covered under

EPA Information Collection Request

Number 940.13.

D. Unfunded Mandates Reform Act

Title II of the Unfunded Mandates

Reform Act of 1995 (UMRA), Public

Law 104–4, establishes requirements for

Federal agencies to assess the effects of

their regulatory actions on State, local,

and tribal governments and the private

sector. Under sections 202, 203, and

205, respectively, of the UMRA, EPA

generally must: (1) 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; (2) develop a

small government agency plan; and (3)

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.

Because the Administrator has

decided not to revise the existing

primary NAAQS for SO2, this action

will not 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 final decision.

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, disproportionally high and

adverse human health or environmental

effects of its programs, policies, and

activities on minorities and low-income

populations. These requirements were

addressed in the draft Regulatory Impact

Analysis (59 FR 58958; November 15,

1994) and taken into account by EPA in

reaching its determination that revisions

to the existing primary SO2 NAAQS are

not appropriate at this time.

List of Subjects in 40 CFR Part 50

Environmental protection, Air

pollution control, Carbon monoxide,

Lead, Nitrogen dioxide, Ozone,

Particulate matter, Sulfur oxides.

Dated: May 14, 1996.

Carol M. Browner,

Administrator.

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class, perinatal events, and race, Am.

Rev. Respir. Dis. 142: 555–562.

Sciences International, Inc. (1995), Estimate

of the Nationwide Exercising Asthmatic

Exposure Frequency to Short-Term Peak

Sulfur Dioxide Concentrations in the

Vicinity of Non-Utility Sources.

Alexandria, VA, Docket No. A–84–25,

VIII–D–71.

Stoeckenius, T.E. (1995), Technical Review

of NMA’s Report on: ‘Estimate of the

Nationwide Exercising Asthmatic

Exposure Frequency to Short-Term Peak

Sulfur Dioxide Concentrations in the

Vicinity of Non-Utility Sources.’

ENVIRON International Corporation,

Novato, CA, Docket No. A–84–25, VIII–

A–01.

Stoeckenius, T.E.; Garelick, B.; Austin, B.S.;

O’Connor, K.; Pehling, J.R. (1990).

Estimates of Nationwide Asthmatic

Exposures to Short-term Sulfur Dioxide

Concentrations in the Vicinity of NonUtility Sources. Systems Applications

Inc., San Rafael, CA, Pub. No. SYSAPP–

90/129, December 6, 1990.

Systems Applications International (1996)

Summary of 1988–1995 Ambient 5–

Minute SO2 Concentration Data. Systems

Applications International, Research

Triangle Park, NC, Docket No. A–84–25,

VIII–A–02.

Appendix I to the Preamble

February 19, 1987

The Honorable Lee M. Thomas,

Administrator U.S. Environmental Protection

Agency, Washington, DC 20460

Dear Mr. Thomas: The Clean Air Scientific

Advisory Committee (CASAC) has completed

its review of the 1986 Addendum to the 1982

Staff Paper on Sulfur Oxides (Review of the

National Ambient Air Quality Standards for

Sulfur Oxides: Updated Assessment of

Scientific and Technical Information)

prepared by the Agency’s Office of Air

Quality Planning and Standards (OAQPS).

The Committee unanimously concludes

that this document is consistent in all

significant respects with the scientific

evidence presented and interpreted in the

combined Air Quality Criteria Document for

Particulate Matter/Sulfur Oxides (1982) and

its 1986 Addendum, on which CASAC issued

its closure letter on December 15, 1986. The

Committee believes that the 1986 Addendum

to the 1982 Staff Paper on Sulfur Oxides

provides you with the kind and amount of

technical guidance that will be needed to

make appropriate decisions with respect to

the standards. The Committee’s major

findings and conclusions concerning the

various scientific issues and studies

discussed in the staff paper addendum are

contained in the attached report.

Thank you for the opportunity to present

the Committee’s views on this important

public health and welfare issue.

Sincerely,

Morton Lippmann, Ph.D.,

Chairman, Clean Air Scientific Advisory

Committee.

cc: A. James Barnes

Gerald Emison

Lester Grant

Vaun Newill

John O’Connor

Craig Potter

Terry Yosie

Summary of Major Scientific Issues and

CASAC Conclusions on the 1986 Draft

Addendum to the 1982 Sulfur Oxides

Staff Paper

The Committee found the technical

discussions contained in the staff paper

addendum to be scientifically thorough

and acceptable, subject to minor

editorial revisions. This document is

consistent in all significant respects

with the scientific evidence presented

in the 1982 combined Air Quality

Criteria Document for Particulate

Matter/Sulfur Oxides and its 1986

Addendum, on which the Committee

issued its closure letter on December 15,

1986.

Scientific Basis for Primary Standards

The Committee addressed the

scientific basis for a 1-hour, 24-hour,

and annual primary standards at some

length in its August 26, 1983 closure

letter on the 1982 Sulfur Oxides Staff

Paper. That letter was based on the

scientific literature which had been

published up to 1982. The present

review has examined the more recently

published studies.

It is clear that no single study of SO2

can fully address the range of public

health issues that arise during the

standard setting process. The Agency

has completed a thorough analysis of

the strengths and weaknesses of various

studies and has derived its

recommended ranges of interest by

evaluating the weight of the evidence.

The Committee endorses this approach.

The Committee wishes to comment on

several major issues concerning the

scientific data that are available. These

issues include:

• Recent studies more clearly

implicate particulate matter than SO2 as

a longer-term public health concern at

low exposure levels.

• A majority of Committee members

believe that the effects reported in the

clinical studies of asthmatics represent

effects of significant public health

concern.

• The exposure uncertainties

associated with a 1-hour standard are

quite large. The relationship between

the frequency of short-term peak

exposures and various scenarios of

asthmatic responses is not well

understood. Both EPA and the electric

power industry are conducting further

analyses of a series of exposure

assessment issues. Such analyses have

the potential to increase the collective

understanding of the relationship

between SO2 exposures and responses

observed in subgroups of the general

population.

• The number of asthmatics

vulnerable to peak exposures near

electric power plants, given the

protection afforded by the current

standards, represents a small number of

people. Although the Clean Air Act

requires that sensitive population

groups receive protection, the size of

such groups has not been defined.

CASAC believes that this issue

represents a legal/policy matter and has

no specific scientific advice to provide

on it.

CASAC’s advice on primary standards

for three averaging times is presented

below:

1-Hour Standard—It is our conclusion

that a large, consistent data base exists

to document the bronchoconstrictive

response in mild to moderate asthmatics

subjected in clinical chambers to shortterm, low levels of sulfur dioxide while

exercising. There is, however, no

scientific basis at present to support or

dispute the hypothesis that individuals

participating in the SO2 clinical studies

are surrogates for more sensitive

asthmatics. Estimates of the size of the

asthmatic population that experience

exposures to short-term peaks of SO2

(0.2–0.5 parts per million (ppm) SO2 for

5–10 minutes) during light to moderate

exercise, and that can be expected to

exhibit a bronchoconstrictive response,

varies from 5,000 to 50,000.

The majority of the Committee

believes that the scientific evidence

supporting the establishment of a new

1-hour standard is stronger than it was

in 1983. As a result, and in view of the

significance of the effects reported in
Federal Register / Vol. 61, No. 100 / Wednesday, May 22, 1996 / Rules and Regulations 25579

these clinical studies, there is strong,

but not unanimous support for the

recommendation that the Administrator

consider establishing a new 1-hour

standard for SO2 exposures. The

Committee agrees that the range

suggested by EPA staff (0.2—0.5 ppm) is

appropriate, with several members of

the Committee suggesting a standard

from the middle of this range. The

Committee concludes that there is not a

scientifically demonstrated need for a

wide margin of safety for a 1-hour

standard.

24-Hour Standard—The more recent

studies presented and analyzed in the

1986 staff paper addendum, in

particular, the episodic lung function

studies in children (Dockery et al., and

Dassen et al.) serve to strengthen our

previous conclusion that the rationale

for reaffirming the 24-hour standard is

appropriate.

Annual Standard—The Committee

reaffirms its conclusion, voiced in its

1983 closure letter, that there is no

quantitative basis for retaining the

current annual standard. However, a

decision to abolish the annual standard

must be considered in the light of the

total protection that is to be offered by

the suite of standards that will be

established.

The above recommendations reflect

the consensus position of CASAC. Not

all CASAC reviewers agree with each

position adopted because of the

uncertainties associated with the

existing scientific data. However, a

strong majority supports each of the

specific recommendations presented

above, and the entire Committee agrees

that this letter represents the consensus

position.

Secondary Standards

The 3-hour secondary standard was

not addressed at this review.

Appendix II to the Preamble

June 1, 1994.

Honorable Carol M. Browner,

Administrator, U.S. Environmental

Protection Agency, 401 M Street, SW.,

Washington, D.C. 20460

Subject: Clean Air Scientific Advisory

Committee Closure on the Supplements

to Criteria Document and Staff Position

Papers for SO2

Dear Ms. Browner: The Clean Air Scientific

Advisory Committee (CASAC) at a meeting

on April 12, 1994, completed its review of

the documents: Supplement to the Second

Addendum (1986) to Air Quality Criteria for

Particulate Matter and Sulfur Oxides;

Assessment of New Findings on Sulfur

Dioxide and Acute Exposure Health Effects

in Asthmatics; and Review of the National

Ambient Air Quality Standards for Sulfur

Oxides: Updated Assessment of Scientific

and Technical Information, Supplement to

the 1986 OAQPS Staff Paper Addendum. The

Committee notes, with satisfaction, the

improvements made in the scientific quality

and completeness of the documents.

With the changes recommended at our

March 12 session, written comments

submitted to the Agency subsequent to the

meeting, and the major points provided

below, the documents are consistent with the

scientific evidence available for sulfur

dioxide. They have been organized in a

logical fashion and should provide an

adequate basis for a regulatory decision.

Nevertheless, there are four major points

which should be called to your attention

while reviewing these materials:

1. A wide spectrum of views exists among

the asthma specialists regarding the clinical

and public health significance of the effects

of 5 to 10 minute concentrations of sulfur

dioxide on asthmatics engaged in exercise.

On one end of the spectrum is the view that

spirometric test responses can be observed

following such short-term exposures and

they are a surrogate for significant health

effects. Also, there is some concern that the

effects are underestimated because moderate

asthmatics, not severe asthmatics, were used

in the clinical tests. At the other end of the

spectrum, the significance of the spirometric

test results are questioned because the

response is similar to that evoked by other

commonly encountered, non-specific stimuli

such as exercise alone, cold, dry air

inhalation, vigorous coughing, psychological

stress, or even fatigue. Typically, the

bronchoconstriction reverses itself within

one or two hours, is not accompanied by a

late-phase response (often more severe and

potentially dangerous than the immediate

response), and shows no evidence of

cumulative or long-term effects. Instead, it is

characterized by a short-term period of

bronchoconstriction, and can be prevented or

ameliorated by beta-agonist aerosol

inhalation.

2. It was the consensus of CASAC that the

exposure scenario of concern is a rare event.

The sensitive population in this case is an

unmedicated asthmatic engaged in moderate

exercise who happens to be near one of the

several hundred sulfur dioxide sources that

have the potential to produce high groundlevel sulfur dioxide concentrations over a

small geographical area under rare adverse

meteorological conditions. In addition,

CASAC pointed out that sulfur dioxide

emissions have been significantly reduced

since EPA conducted its exposure analysis

and emissions will be further reduced as the

1990 Clean Air Act Amendments are

implemented. Consequently, such exposures

will become even rarer in the future.

3. It was the consensus of CASAC that any

regulatory strategy to ameliorate such

exposures be risk-based—targeted on the

most likely sources of short-term sulfur

dioxide spikes rather than imposing shortterm standards on all sources. All of the nine

CASAC Panel members recommended that

Option 1, the establishment of a new 5-

minutes standard, not be adopted. Reasons

cited for this recommendation included: the

clinical experiences of many ozone experts

which suggest that the effects are short-term,

readily reversible, and typical of response

seen with other stimuli. Further, the

committee viewed such exposures as rare

events which will even become rarer as

sulfur dioxide emissions are further reduced

as the 1990 amendments are implemented. In

addition, the committee pointed out that

enforcement of a short-term NAAQS would

require substantial technical resources.

Furthermore, the committee did not think

that such a standard would be enforceable

(see below).

4. CASAC questioned the enforceability of

a 5-minute NAAQS or ‘‘target level.’’

Although the Agency has not proposed an air

monitoring strategy, to ensure that such a

standard or ‘‘target level’’ would not be

exceeded, we infer that potential sources

would have to be surrounded by concentric

circles of monitors. The operation and

maintenance of such monitoring networks

would be extremely resource intensive.

Furthermore, current instrumentation used to

routinely monitor sulfur dioxide does not

respond quickly enough to accurately

characterize 5-minute spikes.

The Committee appreciates the

opportunity to participate in this review and

looks forward to receiving notice of your

decision on the standard. Please do not

hesitate to contact me if CASAC can be of

further assistance on this matter.

Sincerely,

George T. Wolff, Ph.D.,

Chair, Clean Air Scientific Advisory

Committee.

For the reasons set forth in the

preamble, chapter I of title 40 of the

Code of Federal Regulations is 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, 7601(a)).

2. Section 50.4 is revised to read as

follows:

§ 50.4 National primary ambient air quality

standards for sulfur oxides (sulfur dioxide).

(a) The level of the annual standard is

0.030 parts per million (ppm), not to be

exceeded in a calendar year. The annual

arithmetic mean shall be rounded to

three decimal places (fractional parts

equal to or greater than 0.0005 ppm

shall be rounded up).

(b) The level of the 24-hour standard

is 0.14 parts per million (ppm), not to

be exceeded more than once per

calendar year. The 24-hour averages

shall be determined from successive

nonoverlapping 24-hour blocks starting

at midnight each calendar day and shall

be rounded to two decimal places

(fractional parts equal to or greater than

0.005 ppm shall be rounded up).
25580 Federal Register / Vol. 61, No. 100 / Wednesday, May 22, 1996 / Rules and Regulations

(c) Sulfur oxides shall be measured in

the ambient air as sulfur dioxide by the

reference method described in

Appendix A to this part or by an

equivalent method designated in

accordance with part 53 of this chapter.

(d) To demonstrate attainment, the

annual arithmetic mean and the secondhighest 24-hour averages must be based

upon hourly data that are at least 75

percent complete in each calendar

quarter. A 24-hour block average shall

be considered valid if at least 75 percent

of the hourly averages for the 24-hour

period are available. In the event that

only 18, 19, 20, 21, 22, or 23 hourly

averages are available, the 24-hour block

average shall be computed as the sum of

the available hourly averages using 18,

19, etc. as the divisor. If fewer than 18

hourly averages are available, but the

24-hour average would exceed the level

of the standard when zeros are

substituted for the missing values,

subject to the rounding rule of

paragraph (b) of this section, then this

shall be considered a valid 24-hour

average. In this case, the 24-hour block

average shall be computed as the sum of

the available hourly averages divided by

24.

3. Section 50.5 is revised to read as

follows:

§ 50.5 National secondary ambient air

quality standard for sulfur oxides (sulfur

dioxide).

(a) The level of the 3-hour standard is

0.5 parts per million (ppm), not to be

exceeded more than once per calendar

year. The 3-hour averages shall be

determined from successive

nonoverlapping 3-hour blocks starting at

midnight each calendar day and shall be

rounded to 1 decimal place (fractional

parts equal to or greater than 0.05 ppm

shall be rounded up).

(b) Sulfur oxides shall be measured in

the ambient air as sulfur dioxide by the

reference method described in appendix

A of this part or by an equivalent

method designated in accordance with

Part 53 of this chapter.

(c) To demonstrate attainment, the

second-highest 3-hour average must be

based upon hourly data that are at least

75 percent complete in each calendar

quarter. A 3-hour block average shall be

considered valid only if all three hourly

averages for the 3-hour period are

available. If only one or two hourly

averages are available, but the 3-hour

average would exceed the level of the

standard when zeros are substituted for

the missing values, subject to the

rounding rule of paragraph (a) of this

section, then this shall be considered a

valid 3-hour average. In all cases, the 3-

hour block average shall be computed as

the sum of the hourly averages divided

by 3.

[FR Doc. 96–12863 Filed 5–21–96; 8:45 am]

BILLING CODE 6560–50–P

40 CFR Part 75

[FRL–5506–6]

Acid Rain Program: Continuous

Emission Monitoring

AGENCY: Environmental Protection

Agency (EPA).

ACTION: Amendment to final rule;

correction.

SUMMARY: On May 17, 1995, EPA

published direct final amendments to

the Continuous Emission Monitoring

(CEM) rule in the Acid Rain Program for

the purpose of making implementation

of the program simpler, streamlined,

and more efficient. The amendments to

the original January 11, 1993 rule

became final and effective on July 17,

1995. During the public comment

period on the direct final rule and its

companion proposed rule, EPA received

significant, adverse comments on those

amended provisions that related to

notifications for periodic relative

accuracy test audits. EPA is removing

the provisions added in the direct final

rule related to notifications. EPA will

address the removed provisions in a

future final rule. EPA is also extending

the public comment period on the

removed provisions for 15 days to allow

the public to respond to the significant,

adverse comments. All other provisions

of the direct final rule remain final.

In addition, EPA is publishing

technical corrections of typographical

and similar inadvertent errors in the

final rule, as promulgated May 17, 1995.

DATES: Effective date: The effective date

of the amended rule provisions and

corrections is May 22, 1996.

Comment date: Comments in

response to the significant, adverse

comments on the direct final rule must

be received on or before June 6, 1996.

ADDRESSES: Any written comments in

response to the significant, adverse

comments on the direct final rule must

be identified as being in response to

such comments in Docket No. A–94–16

and must be submitted in duplicate to:

EPA Air Docket (6102), U.S.

Environmental Protection Agency, 401

M Street SW., Washington, D.C. 20460.

The docket is available for public

inspection and copying between 8:30

a.m. and 3:30 p.m., Monday through

Friday, at the above address. A

reasonable fee may be charged for

copying.

FOR FURTHER INFORMATION CONTACT:

Margaret Sheppard, Acid Rain Division

(6204J), U.S. Environmental Protection

Agency, 401 M Street SW., Washington,

D.C. 20460, (202) 233–9180.

SUPPLEMENTARY INFORMATION: EPA

received significant, adverse comments

on certain provisions of the direct final

rule amending part 75 from a group of

utilities called the Texas Subgroup.

These comments were apparently

submitted on time, but EPA became

aware of this only after the provision

became final. After the close of the

comment period, the Texas Subgroup

submitted a letter, dated November 2,

1995, clarifying its comments. The

comments and the November 28, 1995

letter are found in Docket No. A–94–16,

items V–D–23 and V–D–24. The Texas

Subgroup made significant, adverse

comments on the provisions of

§§ 75.21(d)and 75.61(a)(5). Therefore,

those provisions in the direct final rule

are being removed and are considered

proposed provisions until EPA takes

further comment and addresses the

comments in a future final rule.

The Texas Subgroup commented

adversely upon the requirements in

§§ 75.21(d) and 75.51(a)(5) for

notifications of the date on which

periodic Relative Accuracy Test Audits

(RATAs) will be performed. The direct

final provisions require submission of

written notification to the

Administrator, the appropriate EPA

Regional Office, and the applicable State

or local air pollution control agency at

least 21 days before the scheduled date

of a RATA. The date may be

rescheduled if written or oral notice is

provided to EPA and to the appropriate

State or local air quality agency at least

seven days before the earlier of the

original scheduled date or the new test

date. The Texas Subgroup felt that this

provision created additional paperwork.

In addition, they felt the provisions

could force utilities to delay

rescheduled RATAs unnecessarily for

seven days simply to meet the

notification requirement.

In discussions with EPA, the Texas

Subgroup suggested that perhaps the

provisions are not needed or the

provisions could be revised to provide

more flexibility in the case where a

RATA is rescheduled. Some

possibilities that the Texas Subgroup

discussed with EPA included: allowing

utilities to receive permission from EPA,

State and local agency Acid Rain

Program contacts to proceed with

testing in less than seven days from the

date of notification; creating an

‘‘emergency’’ notification two days after

the new testing date is known, similar