EXCERPTS FROM: http://www.gpo.gov/fdsys/pkg/FR-2010-06-22/html/2010-13947.htm
[Federal Register Volume 75, Number 119 (Tuesday, June 22, 2010)]
[Rules and Regulations]
[Pages 35519-35603]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2010-13947]
[[Page 35519]]
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Part II
Environmental Protection Agency
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40 CFR Parts 50, 53, and 58
Primary National Ambient Air Quality Standard for Sulfur Dioxide; Final
Rule
Federal Register / Vol. 75 , No. 119 / Tuesday, June 22, 2010 / Rules
and Regulations
[[Page 35520]]
SUMMARY: Based on its review of the air quality criteria for oxides of
sulfur and the primary national ambient air quality standard (NAAQS)
for oxides of sulfur as measured by sulfur dioxide (SO2),
EPA is revising the primary SO2 NAAQS to provide requisite
protection of public health with an adequate margin of safety.
Specifically, EPA is establishing a new 1-hour SO2 standard
at a level of 75 parts per billion (ppb), based on the 3-year average
of the annual 99th percentile of 1-hour daily maximum concentrations.
The EPA is also revoking both the existing 24-hour and annual primary
SO2 standards.
DATES: This final rule is effective on August 23, 2010.
I. Background
A. Summary of Revisions to the SO2 Primary NAAQS
EPA is replacing the current 24-hour and
annual standards with a new short-term standard based on the 3-year
average of the 99th percentile of the yearly distribution of 1-hour
daily maximum SO2 concentrations. EPA is setting the level
of this new standard at 75 ppb. EPA is adding data handling conventions
for SO2 by adding provisions for this new 1-hour primary
standard. EPA is also establishing requirements for an SO2
monitoring network. These new provisions require monitors in areas
where there is an increased coincidence of population and
SO2 emissions. EPA is also making conforming changes to the
Air Quality Index (AQI).
B. Statutory Requirements
Section 109(a) of the Act directs the Administrator to promulgate
``primary'' and ``secondary'' NAAQS for pollutants for which air
quality criteria have been issued. 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 air quality] criteria and
allowing an adequate margin of safety, are requisite to protect the
public health.'' \1\ Section 109(b)(1). A secondary standard, in turn,
must ``specify a level of air quality the attainment and maintenance of
which, in the judgment of the Administrator, based on [the air quality]
criteria, is requisite to protect the public welfare from any known or
anticipated adverse effects associated with the presence of such
pollutant in the ambient air.'' \2\ Section 109(b)(2) This rule
concerns exclusively the primary NAAQS for oxides of sulfur.
\1\ The legislative history of section 109 indicates that a
primary standard is to be set at ``the maximum permissible ambient
air level * * * which will protect the health of any [sensitive]
group of the population,'' and that for this purpose ``reference
should be made to a representative sample of persons comprising the
sensitive group rather than to a single person in such a group.'' S.
Rep. No. 91-1196, 91st Cong., 2d Sess. 10 (1970). See also American
Lung Ass'n v. EPA, 134 F. 3d 388, 389 (DC Cir. 1998) (``NAAQS must
protect not only average healthy individuals, but also `sensitive
citizens'--children, for example, or people with asthma, emphysema,
or other conditions rendering them particularly vulnerable to air
pollution. If a pollutant adversely affects the health of these
sensitive individuals, EPA must strengthen the entire national
standard.'');
The requirement that primary standards include an adequate margin
of safety is intended to address uncertainties associated with
inconclusive scientific and technical information available at the time
of standard setting. It is also intended to provide a reasonable degree
of protection against hazards that research has not yet identified.
Lead Industries Association v. EPA, 647 F.2d 1130, 1154 (DC Cir 1980),
cert. denied, 449 U.S. 1042 (1980); American Petroleum Institute v.
Costle, 665 F.2d 1176, 1186 (DC Cir. 1981), cert. denied, 455 U.S. 1034
(1982). Both kinds of uncertainties are components of the risk
associated with pollution at levels below those at which human health
effects can be said to occur with reasonable scientific certainty.
Thus, in selecting primary standards that include an adequate margin of
safety, the Administrator is seeking not only to prevent pollution
levels that have been demonstrated to be harmful but also to prevent
lower pollutant levels that may pose an unacceptable risk of harm, even
if the risk is not precisely identified as to nature or degree. The CAA
does not require the Administrator to establish a primary NAAQS at a
zero-risk level or at background concentration levels, see Lead
Industries Association v. EPA, 647 F.2d at 1156 n. 51, but rather at a
level that reduces risk sufficiently so as to protect public health
with an adequate margin of safety.
In addressing the requirement for a margin of safety, EPA considers
such factors as the nature and severity of the health effects involved,
the size of the at-risk population(s), and the kind and degree of the
uncertainties that must be addressed. The selection of any particular
approach to providing an adequate margin of safety is a policy choice
left specifically to the Administrator's judgment. Lead Industries
Association v. EPA, 647 F.2d at 1161-62.
In setting standards that are ``requisite'' to protect public
health and welfare, as provided in section 109(b), EPA's task is to
establish standards that are neither more nor less stringent than
necessary for these purposes. In so doing, EPA may not consider the
costs of implementing the standards. Whitman v. American Trucking
[[Page 35522]]
C. Related SO2 Control Programs
States are primarily responsible for ensuring attainment and
maintenance of ambient air quality standards once EPA has established
them. Under section 110 of the Act, and related provisions, States are
to submit, for EPA approval, State implementation plans (SIPs) that
provide for the attainment and maintenance of such standards through
control programs directed to sources of the pollutants involved.
As noted in that
plan, SOX includes multiple gaseous (e.g., SO3)
and particulate (e.g., sulfate) species. Because the health effects
associated with particulate species of SOX have been
considered within the context of the health effects of ambient
particles in the Agency's review of the NAAQS for particulate matter
(PM), the current review of the primary SO2 NAAQS is focused
on the gaseous species of SOX and does not consider health
effects directly associated with particulate species
E. Summary of Proposed Revisions to the SO2 Primary NAAQS
For the reasons discussed in the preamble of the proposal for the
SO2 primary NAAQS, EPA proposed to make revisions to the
primary SO2 NAAQS (and to add SO2 data handling
conventions) so the standards provide requisite protection of public
health with an adequate margin of safety. Specifically, EPA proposed to
replace the current 24-hour and annual standards with a new short-term
SO2 standard. EPA proposed that this new short-term standard
would be based on the 3-year average of the 99th percentile (or 4th
highest) of the yearly distribution of 1-hour daily maximum
SO2 concentrations. EPA proposed to set the level of this
new 1-hour standard within the range of 50 to 100 ppb and solicited
comment on standard levels as high as 150 ppb. EPA also proposed to
establish requirements for an SO2 monitoring network at
locations where maximum SO2 concentrations are expected to
occur and to add a new Federal Reference Method (FRM) for measuring
SO2 in the ambient air. Finally, EPA proposed to make
corresponding changes to the Air Quality Index for SO2.
II. Rationale for Decisions on the Primary Standards
This section presents the rationale for the Administrator's
decision to revise the existing SO2 primary standards by
replacing the current 24-hour and annual standards with a new 1-hour
SO2 standard at a level of 75 ppb, based on the 3-year
average of the annual 99th percentile of 1-hour daily maximum
concentrations. As discussed more fully below, this rationale takes
into account: (1) Judgments and conclusions presented in the ISA and
the REA; (2) CASAC advice and recommendations as reflected in the CASAC
panel's discussions of drafts of the ISA and REA at public meetings, in
separate written comments, and in letters to the Administrator
(Henderson 2008a; Henderson 2008b; Samet, 2009); (3) public comments
received at CASAC meetings during the development of the ISA and the
REA; and (4) public comments received on the notice of proposed
rulemaking.
A. Characterization of SO2 Air Quality
1. Anthropogenic Sources and Current Patterns of SO2 Air
Quality
Anthropogenic SO2 emissions originate chiefly from point
sources, with fossil fuel combustion at electric utilities (~66%) and
other industrial facilities (~29%) accounting for the majority of total
emissions (ISA, section 2.1). Other anthropogenic sources of
SO2 include both the extraction of metal from ore as well as
the burning of high sulfur-containing fuels by locomotives, large
ships, and equipment utilizing diesel engines. SO2 emissions
and ambient concentrations follow a strong east to west gradient due to
the large numbers of coal-fired electric generating units in the Ohio
River Valley and upper Southeast regions. In the 12 Consolidated
Metropolitan Statistical Areas (CMSAs) that had at least four
SO2 regulatory monitors from 2003-2005, 24-hour average
concentrations in the continental U.S. ranged from a reported low of ~1
ppb in Riverside, CA and San Francisco, CA to a high of ~12 ppb in
Pittsburgh, PA and Steubenville, OH (ISA, section 2.5.1). In addition,
outside or inside all CMSAs from 2003-2005, the annual average
SO2 concentration was 4 ppb (ISA, Table 2-8). However,
spikes in hourly concentrations occurred. The mean 1-hour maximum
concentration outside or inside CMSAs was 13 ppb, with a maximum value
of greater than 600 ppb outside CMSAs and greater than 700 ppb inside
CMSAs (ISA, Table 2-8).
Temporal and spatial patterns of 5-minute peaks of SO2
are also important given that controlled human exposure studies have
demonstrated that exposure to these peaks can result in adverse
respiratory effects in exercising asthmatics (see section II.B below).
2. SO2 Monitoring
Although EPA established the SO2 standards in 1971,
uniform minimum monitoring network requirements for SO2
monitoring were only adopted in May 1979. From the time of the
implementation of the 1979 monitoring rule through 2008, the
SO2 monitoring network has steadily decreased in size from
approximately 1496 sites in 1980 to the approximately 488 sites
operating in 2008. At present, except for SO2 monitoring
required at National Core Monitoring Stations (NCore stations), there
are no minimum monitoring requirements for SO2 in 40 CFR
part 58 Appendix D, other than a requirement for EPA Regional
Administrator approval before removing any existing monitors and a
requirement that any ongoing SO2 monitoring must have at
least one monitor sited to measure the maximum concentration of
SO2 in that area. EPA removed the specific minimum
monitoring requirements for SO2 in the 2006 monitoring rule
revisions, except for monitoring at NCore stations, based on the fact
that there were no SO2 nonattainment areas at that time,
coupled with trends showing an increasing gap between national average
SO2 concentrations and the current 24-hour and annual
standards. The rule was also intended to provide State, local, and
Tribal air monitoring agencies flexibility in meeting perceived higher
priority monitoring needs for other pollutants, or to implement the new
multi-pollutant sites (NCore network) required by the 2006 rule
revisions (71 FR 61236, (October 6, 2006)). More information on
SO2 monitoring can be found in section IV.
1. Short-Term (5-minute to 24-hour) SO2 Exposure and
Respiratory Morbidity Effects
The ISA examined numerous controlled human exposure studies and
found that moderate or greater decrements in lung function (i.e.,
[gteqt] 15% decline in Forced Expiratory Volume (FEV1) and/
or [gteqt] 100% increase in specific airway resistance (sRaw)) occur in
some exercising asthmatics exposed to SO2 concentrations as
low as 200-300 ppb for 5-10 minutes. The ISA also found that among
asthmatics, both the percentage of individuals affected, and the
severity of the response increased with increasing SO2
concentrations. That is, at 5-10 minute concentrations ranging from
200-300 ppb, the lowest levels tested in free breathing chamber
studies, approximately 5-30% percent of exercising asthmatics
experienced moderate or greater decrements in lung function (ISA, Table
3-1). At concentrations of 400-600 ppb, moderate or greater decrements
in lung function occurred in approximately 20-60% of exercising
asthmatics, and compared to exposures at 200-300 ppb, a larger
percentage of asthmatics experienced severe decrements in lung function
(i.e., [gteqt] 20% decrease in FEV1 and/or [gteqt] 200%
increase in sRaw; ISA, Table 3-1). Moreover, at SO2
concentrations [gteqt] 400 ppb (5-10 minute exposures), moderate or
greater decrements in lung function were often statistically
significant at the group mean level and frequently accompanied by
respiratory symptoms. Id.
The immediate effect of SO2 on the
respiratory system is bronchoconstriction. This response is mediated by
chemosensitive receptors in the tracheobronchial tree. Activation of
these receptors triggers central nervous system reflexes that result in
[[Page 35526]]
bronchoconstriction and respiratory symptoms that are often followed by
rapid shallow breathing (id). The ISA noted that asthmatics are likely
more sensitive to the respiratory effects of SO2 due to pre-
existing inflammation associated with the disease. For example, pre-
existing inflammation may lead to enhanced release of inflammatory
mediators, and/or enhanced sensitization of the chemosensitive
receptors (id).
Taken together, the ISA concluded that the controlled human
exposure, epidemiologic, and toxicological evidence supported its
determination of a causal relationship between respiratory morbidity
and short-term (5-minutes to 24-hours) exposure to SO2.
1. Rationale for Proposed Decision
In the proposal, the Administrator initially concluded that the
current 24-hour and annual SO2 NAAQS were not adequate to
protect public health with an adequate margin of safety (see section
II.E.4, 74 FR at 64829). In reaching this conclusion, she considered
the: (1) Scientific evidence and conclusions in the ISA; (2) exposure
and risk information presented in the REA; (3) conclusions of the
policy assessment chapter of the REA; and (4) views expressed by CASAC.
These considerations are discussed in detail in the proposal (see
section II.E., 74 FR at 64826) and are summarized in this section.
[[Page 35530]]
CASAC advice ``that the current 24-hour and annual
standards are not adequate to protect public health, especially in
relation to short term exposures to SO2 (5-10 minutes) by
exercising asthmatics'' (Samet, 2009, p. 15).
Based on these considerations (discussed in more detail in the
proposal, see sections II.E.1 and II.E.2), the Administrator proposed
that the current 24-hour and annual SO2 standards are not
requisite to protect public health with an adequate margin of safety
against adverse respiratory effects associated with short-term (5-
minute to 24-hour) SO2 exposures. In considering approaches
to revising the current standards, the Administrator initially
concluded it appropriate to consider setting a new 1-hour standard. The
Administrator noted that a 1-hour standard would likely provide
increased public health protection, especially for members of at-risk
groups, from the respiratory effects described in both epidemiologic
and controlled human exposure studies.