and transit project activities are consistent with (``conform to'')
the purpose of the SIP. Transportation conformity applies to areas
that are designated nonattainment, and those areas redesignated to
attainment after 1990 (``maintenance areas'' with plans developed
under CAA section 175A) for transportation-related criteria
pollutants. Due to the relatively small amounts of sulfur in
gasoline and on-road diesel fuel, transportation conformity does not
apply to the SO2 NAAQS. 40 CFR 93.102(b)(1).
---------------------------------------------------------------------------

    The general conformity determination examines the impacts of direct
and indirect emissions related to federal actions. The general
conformity rule provides several options to satisfy air quality
criteria, such as modeling or offsets, and requires the federal action
to also meet any applicable SIP requirements and emissions milestones.
The general conformity rule also requires that notices of draft and
final general conformity determinations be provided directly to air
quality regulatory agencies and to the public by publication in a local
newspaper.

E. Transition from the existing SO2 NAAQS to a revised SO2 NAAQS

    As stated in section II.F.5 of this notice, in addition to
proposing a short-term 1-hour SO2 NAAQS, EPA is proposing to
revoke the current annual and 24-hour standards, (annual 0.03 ppm and
24-hour 0.14 ppm). Specifically, EPA is proposing that the level for
the 1-hour standard for SO2 be a range between 50-100 ppb,
and is taking comment on setting the level of the standard up to 150
ppb. If the Administrator sets the 1-hour standard at 100 ppb or lower,
EPA is proposing to revoke the current 24-hour standard. If the
Administrator sets the level of the 1-hour standard between a range of
100-150 ppb, then EPA would retain the current 24-hour standard.
    If EPA revises the SO2 NAAQS and revokes either the
current annual or 24-hour standard, EPA would need to promulgate
adequate anti-backsliding provisions. The CAA establishes anti-
backsliding requirements where EPA relaxes a NAAQS. Here, if EPA were
to replace the annual and/or 24-hour standard with a short term 1-hour
standard, EPA would need to address the section 172(e) anti-backsliding
provision of the CAA and determine whether it applies on its face or by
analogy, and what provisions would be appropriate to provide for
transition to the new standard. States would need to insure that the
health protection provided under the existing SO2 NAAQS
continues to be achieved as well as maintained as states begin to
implement a revised NAAQS. This means that states would be directed to
continue implementing attainment and maintenance SIPs associated with
the existing SO2 NAAQS until such time as they are subsumed
by any new planning and control requirements associated with a revised
NAAQS.
    Whether or not section 172(e) directly applies to EPA's final
action on the SO2 NAAQS, EPA has previously looked to other
provisions of the CAA to determine how to address anti-backsliding. The
CAA contains a number of provisions that indicate Congress's intent to
not allow provisions from implementation plans to be altered or removed
if the plan revision would jeopardize the air quality protection being
provided by the existing plan when EPA revises a NAAQS to make it more
stringent. For example, section 110(l) provides that EPA may not
approve a SIP revision if it interferes with any applicable requirement
concerning attainment and RFP, or any other applicable requirement
under the CAA. In addition, section 193 of the CAA prohibits the
modification of a control, or a control requirement, in effect or
required to be adopted as of November 15, 1990 (i.e., prior to the
promulgation of the Clean Air Act Amendments of 1990), unless such a
modification would

ensure equivalent or greater emissions reductions. Further, section
172(e) of the CAA specifies that if EPA revises a NAAQS to make it less
stringent than a previous NAAQS, control obligations that apply in
nonattainment area SIPs may not be relaxed, and adopting those controls
that have not yet been adopted as needed may not be avoided. The intent
of Congress, concerning the aforementioned sections of the CAA, was
confirmed in a recent DC Circuit Court opinion on the Phase I ozone
implementation rule. See South Coast Air Quality Management Dist. v.
EPA, 472 F.3d 882 (DC Cir. 2006).
    To ensure that the antibacksliding provisions and principles of
section 172(e) are met and applied if EPA revokes the current
standards, EPA is proposing that the current SO2 NAAQS would
remain in effect for one year following the effective date of the
initial designations under section 107(d)(1) for the revised
SO2 NAAQS before the current NAAQS are revoked in most
attainment areas. However, any existing SIP provisions under CAA
sections 110, 191 and 192 associated with the existing annual and 24-
hour SO2 NAAQS would remain in effect, including all
currently implemented planning and emissions control obligations,
including both those in the state's SIP and that have been promulgated
by EPA in FIPs. This would ensure that both the new nonattainment NSR
requirements and the general conformity requirements for a revised
standard are in place so that there will be no gap in the public health
protections provided by these two programs. It will also insure that
all nonattainment areas under the current NAAQS and all areas for which
SIP calls have been issued would continue to be protected by currently
required control measures.
    EPA is also proposing that the existing NAAQS remain in place for
any current nonattainment area, or any area for which a state has not
fulfilled the requirements of a SIP call, until the affected area
submits, and EPA approves, a SIP with an attainment demonstration which
fully addresses the attainment requirements of the revised
SO2 NAAQS. This, in combination with the CAA mechanisms
provided in sections 110(l), 193, and 172(e) will help to ensure that
continued progress is made toward timely attainment of the
SO2 NAAQS. Also, in light of the nature of the proposed
revision of the SO2 NAAQS, the lack of classifications (and
mandatory controls associated with such classifications pursuant to the
CAA), and the small number of current nonattainment areas, and areas
subject to SIP calls, EPA believes (subject to consideration of public
comment) that retaining the current standard for a limited period of
time until attainment SIPs are approved for the new standard in current
nonattainment areas and SIP call areas, and one year after designations
in other areas, will adequately serve the anti-backsliding requirements
and goals of the CAA.\44\
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    \44\ The areas that are currently designated as nonattainment
for the pre-existing SO2 primary NAAQS are Hayden, AZ;
Armstrong, PA; Laurel, MT; Piti, GU; and Tanguisson, GU. The areas
that are designated nonattainment for both the primary and the
secondary standards are East Helena, MT, Salt Lake Co, MT, Toole Co,
UT, and Warren Co, NJ. (See http://www.epa.gov/oar/oaqps/greenbk/
lnc.html). The Billings/Laurel, MT, area is the only area currently
subject to a SIP call.
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VII. Communication of Public Health Information

    Information on the public health implications of ambient
concentrations of criteria pollutants is currently made available
primarily through EPA's Air Quality Index (AQI) program. The current
Air Quality Index has been in use since its inception in 1999 (64 FR
42530). It provides accurate, timely, and easily understandable
information about daily levels of pollution (40 CFR 58.50). The AQI
establishes a nationally uniform system of indexing pollution levels
for NO2, carbon monoxide, ozone, particulate matter and
sulfur dioxide. The AQI converts pollutant concentrations in a
community's air to a number on a scale from 0 to 500. Reported AQI
values enable the public to know whether air pollution levels in a
particular location are characterized as good (0-50), moderate (51-
100), unhealthy for sensitive groups (101-150), unhealthy (151-200),
very unhealthy (201-300), or hazardous (300-500). The AQI index value
of 100 typically corresponds to the level of the short-term primary
NAAQS for each pollutant. An AQI value greater than 100 means that a
pollutant is in one of the unhealthy categories (i.e., unhealthy for
sensitive groups, unhealthy, very unhealthy, or hazardous) on a given
day; an AQI value at or below 100 means that a pollutant concentration
is in one of the satisfactory categories (i.e., moderate or good).
Decisions about the pollutant concentrations at which to set the
various AQI breakpoints, that delineate the various AQI categories,
draw directly from the underlying health information that supports the
review of the primary NAAQS.
    The Agency recognizes the importance of revising the AQI in a
timely manner to be consistent with any revisions to the primary NAAQS.
Therefore EPA proposes to finalize conforming changes to the AQI, in
connection with the Agency's final decision on the SO2 NAAQS
if revisions to the primary standard are promulgated. If EPA
promulgates a short-term primary SO2 NAAQS, conforming
changes would include setting the 100 level of the AQI at the same
level as the revised primary SO2 NAAQS. Conforming changes
also would include setting the other AQI breakpoints at the lower end
of the AQI scale (i.e., AQI values of 50 and 150). EPA does not propose
to change breakpoints at the higher end of the AQI scale (from 200 to
500), which would apply to state contingency plans or the Significant
Harm Level (40 CFR 51.16), because the information from this review
does not inform decisions about breakpoints at those higher levels.
    With regard to an AQI value of 50, the breakpoint between the good
and moderate categories, historically this value is set at the level of
the annual NAAQS, if there is one, or one-half the level of the short-
term NAAQS in the absence of an annual NAAQS (63 FR 67823, Dec. 12,
1998). Taking into consideration this practice, EPA is proposing to set
the AQI value of 50 to be between 25 and 50 ppb SO2, 1-hour
average. EPA anticipates that figures towards the lower end of this
range would be appropriate if the standard is set towards the lower end
of the range for the proposed standard (e.g. 50 ppb), while figures
towards the higher end of the range would be more appropriate for
standards set at the higher end of the range (e.g., 100 ppb). If the
short-term standard is set at a level above 100 ppb, and (contrary to
the proposal) the annual standard is not revoked, then consideration
could be given to setting an AQI value of 50 at the level of the annual
standard, or 30 ppb. EPA solicits comments on this range for an AQI of
50, and the appropriate basis for selecting an AQI of 50 both within
this range and, in light of EPA's solicitation of comment on 1-hour
standard levels above 100 ppb, above this range.
    With regard to an AQI value of 150, the breakpoint between the
unhealthy for sensitive groups and unhealthy categories, historically
values between the short-term standard and an AQI value of 500 are set
at levels that are approximately equidistant between the AQI values of
100 and 500 unless there is health evidence that suggests a specific
level would be appropriate (63 FR 67829, Dec. 12, 1998). For an AQI
value of 150, the range of 175 to 200 ppb SO2, 1-hour
average, represents the midpoint between the proposed range for the
short-term standard and the level

of an AQI value of 200 (300 ppb SO2, 1-hour average).

VIII Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

    Under section 3(f)(1) of Executive Order 12866 (58 FR 51735,
October 4, 1993), this action is an ``economically significant
regulatory action'' because it is likely to have an annual effect on
the economy of $100 million or more. Accordingly, EPA submitted this
action to the Office of Management and Budget (OMB) for review under EO
12866 and any changes made in response to OMB recommendations have been
documented in the docket for this action. In addition, EPA prepared a
Regulatory Impact Analysis (RIA) of the potential costs and benefits
associated with this action. However, the CAA and judicial decisions
make clear that the economic and technical feasibility of attaining the
national ambient standards cannot be considered in setting or revising
NAAQS, although such factors may be considered in the development of
State implementation plans to implement the standards. Accordingly,
although an RIA has been prepared, the results of the RIA have not been
considered by EPA in developing this proposed rule.

B. Paperwork Reduction Act

    The information collection requirements in this proposed rule have
been submitted for approval to the Office of Management and Budget
(OMB) under the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. The
Information Collection Request (ICR) document prepared by EPA for these
proposed revisions to part 58 has been assigned EPA ICR number 2370.01
    The information collected under 40 CFR part 53 (e.g., test results,
monitoring records, instruction manual, and other associated
information) is needed to determine whether a candidate method intended
for use in determining attainment of the NAAQS in 40 CFR part 50 will
meet the design, performance, and/or comparability requirements for
designation as a Federal reference method (FRM) or Federal equivalent
method (FEM). We do not expect the number of FRM or FEM determinations
to increase over the number that is currently used to estimate burden
associated with SO2 FRM/FEM determinations provided in the
current ICR for 40 CFR part 53 (EPA ICR numbers 2370.01). As such, no
change in the burden estimate for 40 CFR part 53 has been made as part
of this rulemaking.
    The information collected and reported under 40 CFR part 58 is
needed to determine compliance with the NAAQS, to characterize air
quality and associated health impacts, to develop emissions control
strategies, and to measure progress for the air pollution program. The
proposed amendments would revise the technical requirements for
SO2 monitoring sites, require the siting and operation of
additional SO2 ambient air monitors, and the reporting of
the collected ambient SO2 monitoring data to EPA's Air
Quality System (AQS). The annual average reporting burden for the
collection under 40 CFR part 58 (averaged over the first 3 years of
this ICR) is $13,863,950. Burden is defined at 5 CFR 1320.3(b). State,
local, and tribal entities are eligible for State assistance grants
provided by the Federal government under the CAA which can be used for
monitors and related activities.
    An agency may not conduct or sponsor, and a person is not required
to respond to, a collection of information unless it displays a
currently valid OMB control number. The OMB control numbers for EPA's
regulations in 40 CFR are listed in 40 CFR part 9.
    To comment on the Agency's need for this information, the accuracy
of the provided burden estimates, and any suggested methods for
minimizing respondent burden, EPA has established a public docket for
this rule, which includes this ICR, under Docket ID number EPA-HQ-OAR-
2007-0352. Submit any comments related to the ICR to EPA and OMB. See
ADDRESSES section at the beginning of this notice for where to submit
comments to EPA. Send comments to OMB at the Office of Information and
Regulatory Affairs, Office of Management and Budget, 725 17th Street,
NW, Washington, DC 20503, Attention: Desk Office for EPA. Since OMB is
required to make a decision concerning the ICR between 30 and 60 days
after December 8, 2009, a comment to OMB is best assured of having its
full effect if OMB receives it by January 7, 2010. The final rule will
respond to any OMB or public comments on the information collection
requirements contained in this proposal.

C. Regulatory Flexibility Act

    The Regulatory Flexibility Act (RFA) generally requires an agency
to prepare a regulatory flexibility analysis of any rule subject to
notice and comment rulemaking requirements under the Administrative
Procedure Act or any other statute unless the agency certifies that the
rule will not have a significant economic impact on a substantial
number of small entities. Small entities include small businesses,
small organizations, and small governmental jurisdictions.
    For purposes of assessing the impacts of this rule on small
entities, small entity is defined as: (1) A small business that is a
small industrial entity as defined by the Small Business
Administration's (SBA) regulations at 13 CFR 121.201; (2) a small
governmental jurisdiction that is a government of a city, county, town,
school district or special district with a population of less than
50,000; and (3) a small organization that is any not-for-profit
enterprise which is independently owned and operated and is not
dominant in its field.
    After considering the economic impacts of this proposed rule on
small entities, I certify that this action will not have a significant
economic impact on a substantial number of small entities. This
proposed rule will not impose any requirements on small entities.
Rather, this rule establishes national standards for allowable
concentrations of SO2 in ambient air as required by section
109 of the CAA. American Trucking Ass'ns v. EPA, 175 F. 3d 1027, 1044-
45 (DC Cir. 1999) (NAAQS do not have significant impacts upon small
entities because NAAQS themselves impose no regulations upon small
entities). Similarly, the proposed amendments to 40 CFR Part 58 address
the requirements for States to collect information and report
compliance with the NAAQS and will not impose any requirements on small
entities. We continue to be interested in the potential impacts of the
proposed rule on small entities and welcome comments on issues related
to such impacts.

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. Unless otherwise prohibited by law,
under section 202 of the UMRA, EPA generally must prepare a written
statement, including a cost-benefit analysis, for proposed and final
rules with ``Federal mandates'' that may result in expenditures to
State, local, and tribal governments, in the aggregate, or to the
private sector, of $100 million or more in any one year. Before
promulgating an EPA rule for which a written statement is required
under section 202, section 205 of the UMRA generally requires EPA to
identify and consider a reasonable number of

regulatory alternatives and to adopt the least costly, most cost-
effective or least burdensome alternative that achieves the objectives
of the rule. The provisions of section 205 do not apply when they are
inconsistent with applicable law. Moreover, section 205 allows EPA to
adopt an alternative other than the least costly, most cost-effective
or least burdensome alternative if the Administrator publishes with the
final rule an explanation why that alternative was not adopted. Before
EPA establishes any regulatory requirements that may significantly or
uniquely affect small governments, including tribal governments, it
must have developed under section 203 of the UMRA a small government
agency plan. The plan must provide for notifying potentially affected
small governments, enabling officials of affected small governments to
have meaningful and timely input in the development of EPA regulatory
proposals with significant Federal intergovernmental mandates, and
informing, educating, and advising small governments on compliance with
the regulatory requirements.
    This action is not subject to the requirements of sections 202 and
205 of the UMRA. EPA has determined that this proposed rule does not
contain a Federal mandate that may result in expenditures of $100
million or more for State, local, and tribal governments, in the
aggregate, or the private sector in any one year. The revisions to the
SO2 NAAQS impose no enforceable duty on any State, local or
Tribal governments or the private sector. The expected costs associated
with the monitoring requirements are described in EPA's ICR document,
but those costs are not expected to exceed $100 million in the
aggregate for any year. Furthermore, as indicated previously, in
setting a NAAQS, EPA cannot consider the economic or technological
feasibility of attaining ambient air quality standards. Because the CAA
prohibits EPA from considering the types of estimates and assessments
described in section 202 when setting the NAAQS, the UMRA does not
require EPA to prepare a written statement under section 202 for the
revisions to the SO2 NAAQS.
    With regard to implementation guidance, the CAA imposes the
obligation for States to submit SIPs to implement the SO2
NAAQS. In this proposed rule, EPA is merely providing an interpretation
of those requirements. However, even if this rule did establish an
independent obligation for States to submit SIPs, it is questionable
whether an obligation to submit a SIP revision would constitute a
Federal mandate in any case. The obligation for a State to submit a SIP
that arises out of section 110 and section 191 of the CAA is not
legally enforceable by a court of law, and at most is a condition for
continued receipt of highway funds. Therefore, it is possible to view
an action requiring such a submittal as not creating any enforceable
duty within the meaning of U.S.C. 658 for purposes of the UMRA. Even if
it did, the duty could be viewed as falling within the exception for a
condition of Federal assistance under U.S.C. 658.
    EPA has determined that this proposed rule contains no regulatory
requirements that might significantly or uniquely affect small
governments because it imposes no enforceable duty on any small
governments. Therefore, this rule is not subject to the requirements of
section 203 of the UMRA.

E. Executive Order 13132: Federalism

    Executive Order 13132, entitled ``Federalism'' (64 FR 43255; August
10, 1999), requires EPA to develop an accountable process to ensure
``meaningful and timely input by State and local officials in the
development of regulatory policies that have federalism implications.''
``Policies that have federalism implications'' is defined in the
Executive Order to include regulations that have ``substantial direct
effects on the States, on the relationship between the national
government and the States, or on the distribution of power and
responsibilities among the various levels of government.''
    This proposed rule does not have federalism implications. It will
not have substantial direct effects on the States, on the relationship
between the national government and the States, or on the distribution
of power and responsibilities among the various levels of government,
as specified in Executive Order 13132. The rule does not alter the
relationship between the Federal government and the States regarding
the establishment and implementation of air quality improvement
programs as codified in the CAA. Under section 109 of the CAA, EPA is
mandated to establish NAAQS; however, CAA section 116 preserves the
rights of States to establish more stringent requirements if deemed
necessary by a State. Furthermore, this rule does not impact CAA
section 107 which establishes that the States have primary
responsibility for implementation of the NAAQS. Finally, as noted in
section E (above) on UMRA, this rule does not impose significant costs
on State, local, or tribal governments or the private sector. Thus,
Executive Order 13132 does not apply to this rule.
    However, EPA recognizes that States will have a substantial
interest in this rule and any corresponding revisions to associated air
quality surveillance requirements, 40 CFR part 58. Therefore, in the
spirit of Executive Order 13132, and consistent with EPA policy to
promote communications between EPA and State and local governments, EPA
specifically solicits comment on this proposed rule from State and
local officials.

F. Executive Order 13175: Consultation and Coordination With Indian
Tribal Governments

    Executive Order 13175, entitled ``Consultation and Coordination
with Indian Tribal Governments'' (65 FR 67249, November 9, 2000),
requires EPA to develop an accountable process to ensure ``meaningful
and timely input by tribal officials in the development of regulatory
policies that have tribal implications.'' This proposed rule does not
have tribal implications, as specified in Executive Order 13175. It
does not have a substantial direct effect on one or more Indian tribes,
on the relationship between the Federal government and Indian tribes,
or on the distribution of power and responsibilities between the
Federal government and tribes. The rule does not alter the relationship
between the Federal government and tribes as established in the CAA and
the TAR. Under section 109 of the CAA, EPA is mandated to establish
NAAQS; however, this rule does not infringe existing tribal authorities
to regulate air quality under their own programs or under programs
submitted to EPA for approval. Furthermore, this rule does not affect
the flexibility afforded to tribes in seeking to implement CAA programs
consistent with the TAR, nor does it impose any new obligation on
tribes to adopt or implement any NAAQS. Finally, as noted in section E
(above) on UMRA, this rule does not impose significant costs on tribal
governments. Thus, Executive Order 13175 does not apply to this rule.
However, EPA recognizes that tribes may be interested in this rule and
any corresponding revisions to associated air quality surveillance
requirements. Therefore, in the spirit of Executive Order 13175, and
consistent with EPA policy to promote communications between EPA and
tribes, EPA specifically solicits additional comment on this proposed
rule from tribal officials.

G. Executive Order 13045: Protection of Children From Environmental
Health & Safety Risks

    This action is subject to Executive Order (62 FR 19885, April 23,
1997) because it is an economically significant regulatory action as
defined by Executive Order 12866, and we believe that the environmental
health risk addressed by this action has a disproportionate effect on
children. The proposed rule will establish uniform national ambient air
quality standards for SO2; these standards are designed to
protect public health with an adequate margin of safety, as required by
CAA section 109. The protection offered by these standards may be
especially important for asthmatics, including asthmatic children,
because respiratory effects in asthmatics are among the most sensitive
health endpoints for SO2 exposure. Because asthmatic
children are considered a sensitive population, we have evaluated the
potential health effects of exposure to SO2 pollution among
asthmatic children. These effects and the size of the population
affected are discussed in chapters 3 and 4 of the ISA; chapters 3, 4,
7, 8, 9 of the REA, and sections II.A through II.E of this preamble.

H. Executive Order 13211: Actions That Significantly Affect Energy
Supply, Distribution or Use

    This rule is not a ``significant energy action'' as defined in
Executive Order 13211, ``Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use'' (66 FR
28355; May 22, 2001) because it is not likely to have a significant
adverse effect on the supply, distribution, or use of energy. The
purpose of this rule is to establish revised NAAQS for SO2.
The rule does not prescribe specific control strategies by which these
ambient standards will be met. Such strategies will be developed by
States on a case-by-case basis, and EPA cannot predict whether the
control options selected by States will include regulations on energy
suppliers, distributors, or users. Thus, EPA concludes that this rule
is not likely to have any adverse energy effects.

 I. National Technology Transfer and Advancement Act

    Section 12(d) of the National Technology Transfer and Advancement
Act of 1995 (NTTAA), Public Law 104-113, section 12(d) (15 U.S.C. 27)
directs EPA to use voluntary consensus standards in its regulatory
activities unless to do so would be inconsistent with applicable law or
otherwise impractical. Voluntary consensus standards are technical
standards (e.g., materials specifications, test methods, sampling
procedures, and business practices) that are developed or adopted by
voluntary consensus standards bodies. The NTTAA directs EPA to provide
Congress, through OMB, explanations when the Agency decides not to use
available and applicable voluntary consensus standards.
    This proposed rulemaking involves technical standards with regard
to ambient monitoring of SO2. The use of this voluntary
consensus standard would be impractical because the analysis method
does not provide for the method detection limits necessary to
adequately characterize ambient SO2 concentrations for the
purpose of determining compliance with the proposed revisions to the
SO2 NAAQS.
    EPA welcomes comments on this aspect of the proposed rule, and
specifically invites the public to identify potentially applicable
voluntary consensus standards and to explain why such standards should
be used in the regulation.

J. Executive Order 12898: Federal Actions To Address Environmental
Justice in Minority Populations and Low-Income Populations

    Executive Order 12898 (59 FR 7629; Feb. 16, 1994) establishes
federal executive policy on environmental justice. Its main provision
directs federal agencies, to the greatest extent practicable and
permitted by law, to make environmental justice part of their mission
by identifying and addressing, as appropriate, disproportionately high
and adverse human health or environmental effects of their programs,
policies, and activities on minority populations and low-income
populations in the United States.
    EPA has determined that this proposed rule will not have
disproportionately high and adverse human health or environmental
effects on minority or low-income populations because it increases the
level of environmental protection for all affected populations without
having any disproportionately high and adverse human health effects on
any population, including any minority or low-income population. The
proposed rule will establish uniform national standards for
SO2 in ambient air. EPA solicits comment on environmental
justice issues related to the proposed revision of the SO2
NAAQS.

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1987) (Unpublished EPA contractor report produced by Research
Triangle Institute).
Roger LJ, Kehrl HR, Hazucha M, Horstman DH. (1985).
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Allergy Asthma Immunol. 86:232-238.

List of Subjects

40 CFR Part 50

    Environmental protection, Air pollution control, Carbon monoxide,
Lead, Nitrogen dioxide, Ozone, Particulate matter, Sulfur oxides.

40 CFR Part 53

    Environmental protection, Administrative practice and procedure,
Air pollution control, Intergovernmental relations, Reporting and
recordkeeping requirements.

40 CFR Part 58

    Environmental protection, Administrative practice and procedure,
Air pollution control, Intergovernmental relations, Reporting and
recordkeeping requirements.

    Dated: November 16, 2009.
Lisa P. Jackson,
Administrator.
    For the reasons stated in the preamble, title 40, chapter I of the
Code of Federal Regulations is proposed to be amended as follows:

PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY
STANDARDS

    1. The authority citation for part 50 continues to read as follows:

    Authority:  42 U.S.C. 7401, et seq.

    2. Section 50.4 is amended by adding paragraph (e) to read as
follows:

Sec.  50.4  National primary ambient air quality standards for sulfur
oxides (sulfur dioxide).

* * * * *
    (e) The standards set forth in this section will remain applicable
to all areas notwithstanding the promulgation of SO2
national ambient air quality standards (NAAQS) in Sec.  50.17. The
SO2 NAAQS set forth in this section will no longer apply to
an area one year after the effective date of the designation of that
area, pursuant to section 107 of the Clean Air Act, for the
SO2 NAAQS set forth in Sec.  50.17; except that for areas
designated nonattainment for the SO2 NAAQS set forth in this
section as of the effective date of Sec.  50.17, and areas not meeting
the requirements of a SIP call with respect to requirements for the
SO2 NAAQS set forth in this section, the SO2
NAAQS set forth in this section will apply until that area submits,
pursuant to section 191 of the Clean Air Act, and EPA approves, an
implementation plan providing for attainment of the SO2
NAAQS set forth in Sec.  50.17.
    3. Section 50.14 is amended by revising paragraph (c)(2)(vi) to
read as follows:

Sec.  50.14  Treatment of air quality monitoring data influenced by
exceptional events.

* * * * *
    (c) * * *
    (2) * * *
    (vi) When EPA sets a NAAQS for a new pollutant or revises the NAAQS
for an existing pollutant, it may revise or set a new schedule for
flagging exceptional event data, providing initial data descriptions
and providing detailed data documentation in AQS for the initial
designations of areas for those NAAQS. Table 1 provides the schedule
for submission of flags with initial descriptions in AQS and detailed
documentation. These schedules shall apply for those data which will or
may influence the initial designation of areas for those NAAQS. EPA
anticipates revising Table 1 as necessary to accommodate revised data
submission schedules for new or revised NAAQS.

Table 1--Schedule or Exceptional Event Flagging and Documentation Submission for Data To Be Used in Designations
                                       Decisions for New or Revised NAAQS
----------------------------------------------------------------------------------------------------------------
                                         Air quality data
   NAAQS pollutant/ standard/(level)/      collected for   Event flagging and initial    Detailed documentation
           promulgation date               calendar year      description deadline        submission deadline
----------------------------------------------------------------------------------------------------------------
PM2.5/24-Hr Standard (35 [mu]g/m\3\)            2004-2006  October 1, 2007 \a\.......  April 15, 2008 \a\.
 Promulgated October 17, 2006.
Ozone/8-Hr Standard (0.075 ppm)                 2005-2007  June 18, 2009 \a\.........  June 18, 2009 \a\.
 Promulgated March 12, 2008.
                                                     2008  June 18, 2009 \a\.........  June 18, 2009 \a\.

                                                     2009  60 Days after the end of    60 Days after the end of
                                                            the calendar quarter in     the calendar quarter in
                                                            which the event occurred    which the event occurred
                                                            or February 5, 2010,        or February 5, 2010,
                                                            whichever date occurs       whichever date occurs
                                                            first \b\.                  first \b\.
NO2/1-Hour Standard (80-100 PPB, final               2008  July 1, 2010 \a\..........  January 22, 2011 \a\.
 level TBD).
                                                     2009  July 1, 2010 \a\..........  January 22, 2011 \a\.
                                                     2010  April 1, 2011 \a\.........  July 1, 2011 \ a\.
SO2/1-Hour Standard (50-100 PPB, final               2008  October 1, 2010 \b\.......  June 1, 2011 \b\.
 level TBD).
                                                     2009  October 1, 2010 \b\.......  June 1, 2011 \b\.
                                                     2010  June 1, 2011 \b\..........  June 1, 2011 \b\.
                                                     2011  60 Days after the end of    60 Days after the end of
                                                            the calendar quarter in     the calendar quarter in
                                                            which the event occurred    which the event occurred
                                                            or March 31, 2011,          or March 31, 2011,
                                                            whichever date occurs       whichever date occurs
                                                            first \b\.                  first \b\.
----------------------------------------------------------------------------------------------------------------
\a\ These dates are unchanged from those published in the original rulemaking, or are being proposed elsewhere
  and are shown in this table for informational purposes--the Agency is not opening these dates for comment
  under this rulemaking.
\b\ Indicates change from general schedule in 40 CFR 50.14.
Note: EPA notes that the table of revised deadlines only applies to data EPA will use to establish the final
  initial designations for new or revised NAAQS. The general schedule applies for all other purposes, most
  notably, for data used by EPA for redesignations to attainment.

* * * * *
    4. A new 50.17 is added to read as follows:

Sec.  50.17  National primary ambient air quality standards for sulfur
oxides (sulfur dioxide).

    (a) The level of the national primary 1-hour annual ambient air
quality standard for oxides of sulfur is (50-100) parts per billion
(ppb, which is 1 part in 1,000,000,000), measured in the ambient air as
sulfur dioxide (SO2).
    (b) The 1-hour primary standard is met when the three-year average
of the annual (99th percentile)(fourth highest) of the daily maximum 1-
hour average concentrations is less than or equal to (50-100) ppb, as
determined in accordance with Appendix T of this part.
    5. Add Appendix A-1 to Part 50 to read as follows:

Appendix A-1 to Part 50--Reference Measurement Principle and
Calibration Procedure for the Measurement of Sulfur Dioxide in the
Atmosphere (Ultraviolet Fluorescence Method)

    1.0 Applicability.
    1.1 This ultraviolet fluorescence (UVF) method provides a
measurement of the concentration of sulfur dioxide (SO2)
in ambient air for determining compliance with the national primary
and secondary ambient air quality standards for sulfur oxides
(sulfur dioxide) as specified in Sec.  50.4 and Sec.  50.5 of this
chapter. The method is applicable to the measurement of ambient
SO2 concentrations using continuous (real-time) sampling.
Additional quality assurance procedures and guidance are provided in
part 58, appendix A, of this chapter and in Reference 3.
    2.0 Principle.
    2.1 This reference method is based on automated measurement of
the intensity of the characteristic fluorescence released by
SO2 in an ambient air sample contained in a measurement
cell of an analyzer when the air sample is irradiated by ultraviolet
(UV) light passed through the cell. The fluorescent light released
by the SO2 is also in the ultraviolet region, but at
longer wavelengths than the excitation light. Typically, optimum
instrumental measurement of SO2 concentrations is
obtained with an excitation wavelength in a band between
approximately 190 to 230 nm, and measurement of the SO2
fluorescence in a broad band around 320 nm, but these wavelengths
are not necessarily constraints of this reference method. Generally,
the measurement system (analyzer) also requires means to reduce the
effects of aromatic hydrocarbon species, and possibly other
compounds, in the air sample to control measurement interferences
from these compounds, which may be present in the ambient air.
References 1 and 2 describe UVF method.
    2.2. The measurement system is calibrated by referencing the
instrumental fluorescence measurements to SO2 standard
concentrations traceable to a National Institute of Science and
Technology (NIST) primary standard for SO2 (see
Calibration Procedure below).
    2.3. An analyzer implementing this measurement principle is
shown schematically in Figure 1. Designs should include a
measurement cell, a UV light source of appropriate wavelength, a UV
detector system with appropriate wave length sensitivity, a pump and
flow control system for sampling the ambient air and moving it into
the measurement cell, sample air conditioning components as
necessary to minimize measurement interferences, suitable control
and measurement processing capability, and other apparatus as may be
necessary. The analyzer must be designed to provide accurate,
repeatable, and continuous measurements of SO2
concentrations in ambient air, with measurement performance as
specified in subpart B of part 53 of this chapter.
    2.4. Sampling considerations: The use of a particle filter on
the sample inlet line of a UVF SO2 analyzer is required
to prevent interference, malfunction, or damage due to particles in
the sampled air.
    3.0 Interferences.
    3.1 The effects of the principal potential interferences may
need to be mitigated to meet the interference equivalent
requirements of part 53 of this chapter. Poly-nuclear aromatic (PNA)
hydrocarbons such as xylene and naphthalene can fluoresce and act as
strong positive interferences. These gases can be removed by using a
permeation type scrubber (hydrocarbon ``kicker''). Nitrogen oxide
(NO) in high concentrations can also fluoresce and cause positive
interference. Optical filtering can be employed to improve the
rejection of interference from high NO. Ozone can absorb UV light
given off by the SO2 molecule and cause a measurement
offset. This effect can be reduced by minimizing the measurement
path length between the area where SO2 fluorescence
occurs and the photomultiplier tube detector (e.g. <5 cm). A
hydrocarbon scrubber, optical filter and appropriate distancing of
the measurement path length may be required method components to
reduce interference.
    4.0 Calibration Procedure. Atmospheres containing accurately
known concentrations of sulfur dioxide are prepared using a
compressed gas transfer standard diluted with accurately metered
clean air flow rates.
    4.1 Apparatus: Figure 2 shows a typical generic system suitable
for diluting a SO2 gas cylinder concentration standard
with clean air through a mixing chamber to produce the desired
calibration concentration standards.

A valve may be used to conveniently divert the SO2 from
the sampling manifold to provide clean zero air at the output
manifold for zero adjustment. The system may be made up using common
laboratory components, or it may be a commercially manufactured
system. In either case, the principle components are as follows:
    4.1.1 Air and standard gas flow controllers, capable of
maintaining constant gas flow rates to within  2
percent.
    4.1.2 Air and standard gas flow meters, capable of measuring and
monitoring air or N2 (standard gas) flow rates to within
 2 percent and properly calibrated to a NIST-traceable
standard.
    4.1.3 Mixing chamber, of an inert material such as glass and of
proper design to provide thorough mixing of pollutant gas and
diluent air streams.
    4.1.4 Sampling manifold, constructed of glass,
polytetrafluoroethylene (PTFE TeflonTM), or other
suitably inert material and of sufficient diameter to insure a
minimum pressure drop at the analyzer connection, with a vent
designed to insure a minimum over-pressure (relative to ambient air
pressure) at the analyzer connection and to prevent ambient air from
entering the manifold.
    4.1.5 Standard gas pressure regulator, of clean stainless steel
with a stainless steel diaphragm, suitable for use with a high
pressure SO2 gas cylinder.
    4.1.6 Reagents.
    <IP_ADDRESS> SO2 gas transfer standard, in N2,
with the concentration traceable to a NIST Standard Reference
Material (SRM) such as SRM 1693a (50 [mu]mole/mole) or SRM 1694a
(100 [mu]mole/mole) Since UVF analyzers may be sensitive to
O2-to-N2 ratios, it is important that the
SO2 standard concentration be sufficiently high (50 to
100 ppm) such that the O2 content in the diluent air is
not significantly changed by the added standard gas.
    <IP_ADDRESS> Clean zero air, free of contaminants that could cause a
detectable response or a change in sensitivity of the analyzer.
Since ultraviolet fluorescence analyzers may be sensitive to
aromatic hydrocarbons and O2-to-N2 ratios, it
is important that the clean zero air contains less than 0.1 ppm
aromatic hydrocarbons and O2 and N2
percentages approximately the same as in ambient air. A procedure
for generating zero air is given in reference 1.
    4.2 Procedure
    4.2.1 Obtain a suitable calibration apparatus, such as the one
shown schematically in Figure 1, and verify that all materials in
contact with the pollutant are of glass, Teflon\TM\, or other
suitably inert material and completely clean.
    4.2.2 Purge the SO2 standard gas lines and pressure
regulator to remove any residual air.
    4.2.3 Ensure that there are no leaks in the system and that the
flow measuring devices are properly and accurately calibrated under
the conditions of use against a reliable volume or flow rate
standard such as a soap-bubble meter or a wet-test meter traceable
to a NIST standard. All volumetric flow rates should be corrected to
the same reference temperature and pressure by using the formula
below:
[GRAPHIC] [TIFF OMITTED] TP08DE09.004

Where:
Fc = corrected flow rate (L/min at 25[deg] C and 760 mm Hg),
Fm = measured flow rate, (at temperature, Tm and
pressure, Pm),
Pm = measured pressure in mm Hg, (absolute), and
Tm = measured temperature in degrees Celsius.

    4.2.4 Allow the SO2 analyzer under calibration to
sample zero air until a stable response is obtained, then make the
proper zero adjustment.
    4.2.5 Adjust the airflow to provide an SO2
concentration of approximately 80 percent of the upper measurement
range limit of the SO2 instrument and verify that the
total air flow of the calibration system exceeds the demand of all
analyzers sampling from the output manifold (with the excess
vented).
    4.2.6 Calculate the actual SO2 calibration
concentration standard as:
[GRAPHIC] [TIFF OMITTED] TP08DE09.005

Where:
C = the concentration of the SO2 gas standard
Fp = the flow rate of SO2 gas standard
Ft = the total air flow rate of pollutant and diluent
gases

    4.2.7 When the analyzer response has stabilized, adjust the
SO2 span control to obtain the desired response
equivalent to the calculated standard concentration. If substantial
adjustment of the span control is needed, it may be necessary to re-
check the zero and span adjustments by repeating steps 4.2.4 through
4.2.7 until no further adjustments are needed.
    4.2.8 Adjust the flow rate(s) to provide several other
SO2 calibration concentrations over the analyzer's
measurement range. At least five different concentrations evenly
spaced throughout the analyzer's range are suggested.
    4.2.9 Plot the analyzer response (vertical or Y-axis) versus
SO2 concentration (horizontal or X-axis). Compute the
linear regression slope and intercept and plot the regression line
to verify that no point deviates from this line by more than 2
percent of the maximum concentration tested.

    Note: Additional information on calibration and pollutant
standards is provided in Section 12 of Reference 3.

    5.0 Frequency of calibration.
    The frequency of calibration, as well as the number of points
necessary to establish the calibration curve and the frequency of
other performance checking will vary by analyzer; however, the
minimum frequency, acceptance criteria, and subsequent actions are
specified in Reference 3, Appendix D: Measurement Quality Objectives
and Validation Template for SO2 (page 9 of 30). The
user's quality control program should provide guidelines for initial
establishment of these variables and for subsequent alteration as
operational experience is accumulated. Manufacturers of analyzers
should include in their instruction/operation manuals information
and guidance as to these variables and on other matters of
operation, calibration, routine maintenance, and quality control.
    6.0 References for SO2 Method.
1. H. Okabe, P.L. Splitstone, and J.J. Ball, ``Ambient and Source
SO2 Detector Based on a Fluorescence Method'', Journal of
the Air Control Pollution Association, vol. 23, p. 514-516 (1973).
2. F.P. Schwarz, H. Okabe, and J.K. Whittaker, ``Fluorescence
Detection of Sulfur Dioxide in Air at the Parts per Billion Level,''
Analytical Chemistry, vol. 46, pp. 1024-1028 (1974).
3. QA Handbook for Air Pollution Measurement Systems--Volume II.
Ambient Air Quality Monitoring Programs. U. S. EPA. EPA-454/B-08-003
(2008). (Available at http://www.epa.gov/ttn/amtic/qabook.html.)

[GRAPHIC] [TIFF OMITTED] TP08DE09.006

[GRAPHIC] [TIFF OMITTED] TP08DE09.007

    6. Appendix A to Part 50 is redesignated as Appendix A-2 to Part
50.
    7. Appendix T to Part 50 is added to read as follows:

Option 1 for Appendix T to Part 50

Appendix T to Part 50--Interpretation of the Primary National Ambient
Air Quality Standards for Oxides of Sulfur (Sulfur Dioxide) [1-hour
primary standard based on the 4th highest daily maximum value form]

    1. General.
    (a) This appendix explains the data handling conventions and
computations necessary for determining when the primary national
ambient air quality standards for Oxides of Sulfur as measured by
Sulfur Dioxide (``SO2 NAAQS'') specified in Sec.  50.4
are met. Sulfur Dioxide (SO2) is measured in the ambient
air by a Federal reference method (FRM) based on appendix A to this
part or by a Federal equivalent method (FEM) designated in
accordance with part 53 of this chapter. Data handling and
computation procedures to be used in making comparisons between
reported SO2 concentrations and the levels of the
SO2 NAAQS are specified in the following sections.
    (b) Decisions to exclude, retain, or make adjustments to the
data affected by exceptional events, including natural events, are
made according to the requirements and process deadlines specified
in Sec. Sec.  50.1, 50.14 and 51.930 of this chapter.
    (c) The terms used in this appendix are defined as follows:
    Annual 4th highest daily maximum 1-hour value refers to the 4th
highest daily 1-hour maximum value at a site in a particular year.
    Daily maximum 1-hour values for SO2 refers to the
maximum 1-hour SO2 concentration values measured from
midnight to midnight (local standard time) that are used in NAAQS
computations.
    Design values are the metrics (i.e., statistics) that are
compared to the NAAQS levels to determine compliance, calculated as
specified in section 5 of this appendix. The design value for the
primary NAAQS is the 3-year average of annual 4th highest daily
maximum 1-hour values for a monitoring site (referred to as the ``1-
hour primary standard design value'').
    Quarter refers to a calendar quarter.
    Year refers to a calendar year.
    2. Requirements for Data Used for Comparisons With the
SO2 NAAQS and Data Reporting Considerations.
    (a) All valid FRM/FEM SO2 hourly data required to be
submitted to EPA's Air Quality System (AQS), or otherwise available
to EPA, meeting the requirements of part 58 of this chapter
including appendices A, C, and E shall be used in design value
calculations. Multi-hour average concentration values collected by
wet chemistry methods shall not be used.
    (b) When two or more SO2 monitors are operated at a
site, the state may in advance designate one of them as the primary
monitor. If the state has not made this designation in advance, the
Administrator will make the designation, either in advance or
retrospectively. Design values will be developed using only the data
from the primary monitor, if this results in a valid design value.
If data from the primary monitor do not allow the development of a
valid design value, data solely from the other monitor(s) will be
used in turn to develop a valid design value, if this results in a
valid design value. If there are three or more monitors, the order
for such comparison of the other monitors will be determined by the
Administrator. The Administrator may combine data from different
monitors in different years for the purpose of developing a valid 1-
hour primary standard design value, if a valid design value cannot
be developed solely with the data from a single monitor. However,
data from two or more monitors in the same year at the same site
will not be combined in an attempt to meet data completeness
requirements, except if one monitor has physically replaced another
instrument permanently, in which case the two instruments will be
considered to be the same monitor, or if the state has switched the
designation of the primary monitor from one instrument to another
during the year.
    (c) Hourly SO2 measurement data shall be reported to
AQS in units of parts per billion (ppb), to at most one place after
the decimal, with additional digits to the right being truncated
with no further rounding.
    3. Comparisons with the 1-hour Primary SO2 NAAQS.
    (a) The 1-hour primary SO2 NAAQS is met at a site
when the valid 1-hour primary standard design value is less than or
equal to [50-150] parts per billion (ppb).
    (b) An SO2 1-hour primary standard design value is
valid if it encompasses three consecutive calendar years of complete
data. A year meets data completeness requirements when all 4
quarters are complete. A quarter is complete when at least 75
percent of the sampling days for each quarter have complete data. A
sampling day has complete data if 75 percent of the hourly
concentration values are reported.
    (c) In the case of one, two, or three years that do not meet the
completeness requirements of section 3(b) of this appendix and thus
would normally not be usable for the calculation of a valid 3-year
1-hour primary standard design value, the 3-year 1-hour primary
standard design value shall nevertheless be considered valid if
either of the following conditions is true:
    (i) If there are at least four days in each of the 3 years that
have at least one reported hourly value, and the resulting 3-year 1-
hour primary standard design value exceeds the 1-hour primary NAAQS.
In this situation, more complete data capture could not possibly
have resulted in a design value below the 1-hour primary NAAQS:
    (ii)(A) A 1-hour primary standard design value that is below the
level of the NAAQS can be validated if the substitution test in
section 3(c)(ii)(B) results in a ``test design value'' that is below
the level of the NAAQS. The test substitutes actual ``high''
reported daily maximum 1-hour values from the same site at about the
same time of the year (specifically, in the calendar quarter) for
unknown hourly values that were not successfully measured. Note that
the test is merely diagnostic in nature, intended to confirm that
there is a very high likelihood that the original design value (the
one with less than 75 percent data capture of hours by day and of
days by quarter) reflects the true under-NAAQS-level status for that
3-year period; the result of this data substitution test (the ``test
design value,'' as defined in section 3(c)(ii)(B)) is not considered
the actual design value. For this test, substitution is permitted
only if there are at least 200 days across the three matching
quarters of the three years under consideration (which is about 75
percent of all possible daily values in those three quarters) for
which 75 percent of the hours in the day have reported
concentrations. However, maximum 1-hour values from days with less
than 75 percent of the hours reported shall also be considered in
identifying the high value to be used for substitution.
    (B) The substitution test is as follows: Data substitution will
be performed in all quarter periods that have less than 75 percent
data capture but at least 50 percent data capture; if any quarter
has less than 50 percent data capture, then this substitution test
cannot be used. Identify for each quarter (e.g., January-March) the
highest reported daily maximum 1-hour value for that quarter,
looking across those three months of all three years under
consideration. All daily maximum 1-hour values from all days in the
quarter period shall be considered when identifying this highest
value, including days with less than 75 percent data capture. If
after substituting the highest reported daily maximum 1-hour value
for a quarter for as much of the missing daily data in the matching
deficient quarter(s) as is needed to make them 100 percent complete,
the procedure in section 5 yields a recalculated 3-year 1-hour
standard ``test design value'' below the level of the standard, then
the 1-hour primary standard design value is deemed to have passed
the diagnostic test and is valid, and the level of the standard is
deemed to have been met in that 3-year period. As noted in section
3(c)(i), in such a case, the 3-year design value based on the data
actually reported, not the ``test design value,'' shall be used as
the valid design value.
    (d) A 1-hour primary standard design value based on data that do
not meet the completeness criteria stated in 3(b) and also do not
satisfy section 3(c), may also be considered valid with the approval
of, or at the initiative of, the Administrator, who may consider
factors such as monitoring site closures/moves, monitoring
diligence, the consistency and levels of the valid concentration
measurements that are available, and nearby concentrations in
determining whether to use such data.
    (e) The procedures for calculating the 1-hour primary standard
design values are given in section 5 of this appendix.
    4. Rounding Conventions for the 1-hour Primary SO2
NAAQS.
    (a) Hourly SO2 measurement data shall be reported to
AQS in units of parts per billion (ppb), to at most one place after
the decimal, with additional digits to the right being truncated
with no further rounding.

    (b) Daily maximum 1-hour values, including the annual 4th
highest of those daily values, are not rounded.
    (c) The 1-hour primary standard design value is calculated
pursuant to section 5 and then rounded to the nearest whole number
or 1 ppb (decimals 0.5 and greater are rounded up to the nearest
whole number, and any decimal lower than 0.5 is rounded down to the
nearest whole number).
    5. Calculation Procedures for the 1-hour Primary SO2
NAAQS.
    (a) When the data for a particular site and year meet the data
completeness requirements in section 3(b), or if one of the
conditions of section 3(c) is met, or if the Administrator exercises
the discretionary authority in section 3(d), calculation of the 4th
highest daily 1-hour maximum is accomplished as follows.
    (i) For each year, select from each day the highest hourly
value. All daily maximum 1-hour values from all days in the quarter
period shall be considered at this step, including days with less
than 75 percent data capture.
    (ii) For each year, order these daily values and take the 4th
highest.
    (iii) The 1-hour primary standard design value for a site is
mean of the three annual 4th highest values, rounded according to
the conventions in section 4.

Option 2 for Appendix T to Part 50

Appendix T to Part 50--Interpretation of the Primary National Ambient
Air Quality Standards for Oxides of Sulfur (Sulfur Dioxide) [1-hour
primary standard based on the 99th percentile form]

    1. General.
    (a) This appendix explains the data handling conventions and
computations necessary for determining when the primary national
ambient air quality standards for Oxides of Sulfur as measured by
Sulfur Dioxide (``SO2 NAAQS'') specified in Sec.  50.4
are met. Sulfur Dioxide (SO2) is measured in the ambient
air by a Federal reference method (FRM) based on appendix A to this
part or by a Federal equivalent method (FEM) designated in
accordance with part 53 of this chapter. Data handling and
computation procedures to be used in making comparisons between
reported SO2 concentrations and the levels of the
SO2 NAAQS are specified in the following sections.
    (b) Decisions to exclude, retain, or make adjustments to the
data affected by exceptional events, including natural events, are
made according to the requirements and process deadlines specified
in Sec. Sec.  50.1, 50.14 and 51.930 of this chapter.
    (c) The terms used in this appendix are defined as follows:
    Daily maximum 1-hour values for SO2 refers to the
maximum 1-hour SO2 concentration values measured from
midnight to midnight (local standard time) that are used in NAAQS
computations.
    Design values are the metrics (i.e., statistics) that are
compared to the NAAQS levels to determine compliance, calculated as
specified in section 5 of this appendix. The design value for the
primary 1-hour NAAQS is the 3-year average of annual 99th percentile
daily maximum 1-hour values for a monitoring site (referred to as
the ``1-hour primary standard design value'').
    99th percentile daily maximum 1-hour value is the value below
which nominally 99 percent of all daily maximum 1-hour concentration
values fall, using the ranking and selection method specified in
section 5 of this appendix.
    Quarter refers to a calendar quarter.
    Year refers to a calendar year.
    2. Requirements for Data Used for Comparisons With the
SO2 NAAQS and Data Reporting Considerations.
    (a) All valid FRM/FEM SO2 hourly data required to be
submitted to EPA's Air Quality System (AQS), or otherwise available
to EPA, meeting the requirements of part 58 of this chapter
including appendices A, C, and E shall be used in design value
calculations. Multi-hour average concentration values collected by
wet chemistry methods shall not be used.
    (b) When two or more SO2 monitors are operated at a
site, the state may in advance designate one of them as the primary
monitor. If the state has not made this designation, the
Administrator will make the designation, either in advance or
retrospectively. Design values will be developed using only the data
from the primary monitor, if this results in a valid design value.
If data from the primary monitor do not allow the development of a
valid design value, data solely from the other monitor(s) will be
used in turn to develop a valid design value, if this results in a
valid design value. If there are three or more monitors, the order
for such comparison of the other monitors will be determined by the
Administrator. The Administrator may combine data from different
monitors in different years for the purpose of developing a valid 1-
hour primary standard design value, if a valid design value cannot
be developed solely with the data from a single monitor. However,
data from two or more monitors in the same year at the same site
will not be combined in an attempt to meet data completeness
requirements, except if one monitor has physically replaced another
instrument permanently, in which case the two instruments will be
considered to be the same monitor, or if the state has switched the
designation of the primary monitor from one instrument to another
during the year.
    (c) Hourly SO2 measurement data shall be reported to
AQS in units of parts per billion (ppb), to at most one place after
the decimal, with additional digits to the right being truncated
with no further rounding.
    3. Comparisons with the 1-hour Primary SO2 NAAQS.
    (a) The 1-hour primary SO2 NAAQS is met at a site
when the valid 1-hour primary standard design value is less than or
equal to [50-150] parts per billion (ppb).
    (b) An SO2 1-hour primary standard design value is
valid if it encompasses three consecutive calendar years of complete
data. A year meets data completeness requirements when all 4
quarters are complete. A quarter is complete when at least 75
percent of the sampling days for each quarter have complete data. A
sampling day has complete data if 75 percent of the hourly
concentration values are reported.
    (c) In the case of one, two, or three years that do not meet the
completeness requirements of section 3(b) of this appendix and thus
would normally not be useable for the calculation of a valid 3-year
1-hour primary standard design value, the 3-year 1-hour primary
standard design value shall nevertheless be considered valid if one
of the following conditions is true.
    (i) At least 75 percent of the days in each quarter of each of
three consecutive years have at least one reported hourly value, and
the design value calculated according to the procedures specified in
section 5 is above the level of the primary 1-hour standard.
    (ii) (A) A 1-hour primary standard design value that is below
the level of the NAAQS can be validated if the substitution test in
section 3(c)(ii)(B) results in a ``test design value'' that is below
the level of the NAAQS. The test substitutes actual ``high''
reported daily maximum 1-hour values from the same site at about the
same time of the year (specifically, in the same calendar quarter)
for unknown values that were not successfully measured. Note that
the test is merely diagnostic in nature, intended to confirm that
there is a very high likelihood that the original design value (the
one with less than 75 percent data capture of hours by day and of
days by quarter) reflects the true under-NAAQS-level status for that
3-year period; the result of this data substitution test (the ``test
design value'', as defined in section 3(c)(ii)(B)) is not considered
the actual design value. For this test, substitution is permitted
only if there are at least 200 days across the three matching
quarters of the three years under consideration (which is about 75
percent of all possible daily values in those three quarters) for
which 75 percent of the hours in the day have reported
concentrations. However, maximum 1-hour values from days with less
than 75 percent of the hours reported shall also be considered in
identifying the high value to be used for substitution.
    (B) The substitution test is as follows: Data substitution will
be performed in all quarter periods that have less than 75 percent
data capture but at least 50 percent data capture; if any quarter
has less than 50 percent data capture then this substitution test
cannot be used. Identify for each quarter (e.g., January-March) the
highest reported daily maximum 1-hour value for that quarter,
looking across those three months of all three years under
consideration. All daily maximum 1-hour values from all days in the
quarter period shall be considered when identifying this highest
value, including days with less than 75 percent data capture. If
after substituting the highest reported daily maximum 1-hour value
for a quarter for as much of the missing daily data in the matching
deficient quarter(s) as is needed to make them 100 percent complete,
the procedure in section 5 yields a recalculated 3-year 1-hour
standard ``test design value'' below the level of the standard, then
the 1-hour primary standard design value is deemed to have passed
the diagnostic test and is valid, and the level of

the standard is deemed to have been met in that 3-year period. As
noted in section 3(c)(i), in such a case, the 3-year design value
based on the data actually reported, not the ``test design value'',
shall be used as the valid design value.
    (iii) (A) A 1-hour primary standard design value that is above
the level of the NAAQS can be validated if the substitution test in
section 3(c)(iii)(B) results in a ``test design value'' that is
above the level of the NAAQS. The test substitutes actual ``low''
reported daily maximum 1-hour values from the same site at about the
same time of the year (specifically, in the same three months of the
calendar) for unknown hourly values that were not successfully
measured. Note that the test is merely diagnostic in nature,
intended to confirm that there is a very high likelihood that the
original design value (the one with less than 75 percent data
capture of hours by day and of days by quarter) reflects the true
above-NAAQS-level status for that 3-year period; the result of this
data substitution test (the ``test design value'', as defined in
section 3(c)(iii)(B)) is not considered the actual design value. For
this test, substitution is permitted only if there are a minimum
number of available daily data points from which to identify the low
quarter-specific daily maximum 1-hour values, specifically if there
are at least 200 days across the three matching quarters of the
three years under consideration (which is about 75 percent of all
possible daily values in those three quarters) for which 75 percent
of the hours in the day have reported concentrations. Only days with
at least 75 percent of the hours reported shall be considered in
identifying the low value to be used for substitution.
    (B) The substitution test is as follows: Data substitution will
be performed in all quarter periods that have less than 75 percent
data capture. Identify for each quarter (e.g., January-March) the
lowest reported daily maximum 1-hour value for that quarter, looking
across those three months of all three years under consideration.
All daily maximum 1-hour values from all days with at least 75
percent capture in the quarter period shall be considered when
identifying this lowest value. If after substituting the lowest
reported daily maximum 1-hour value for a quarter for as much of the
missing daily data in the matching deficient quarter(s) as is needed
to make them 75 percent complete, the procedure in section 5 yields
a recalculated 3-year 1-hour standard ``test design value'' above
the level of the standard, then the 1-hour primary standard design
value is deemed to have passed the diagnostic test and is valid, and
the level of the standard is deemed to have been exceeded in that 3-
year period. As noted in section 3(c)(i), in such a case, the 3-year
design value based on the data actually reported, not the ``test
design value'', shall be used as the valid design value.
    (d) A 1-hour primary standard design value based on data that do
not meet the completeness criteria stated in 3(b) and also do not
satisfy section 3(c), may also be considered valid with the approval
of, or at the initiative of, the Administrator, who may consider
factors such as monitoring site closures/moves, monitoring
diligence, the consistency and levels of the valid concentration
measurements that are available, and nearby concentrations in
determining whether to use such data.
    (e) The procedures for calculating the 1-hour primary standard
design values are given in section 5 of this appendix.
    4. Rounding Conventions for the 1-hour Primary SO2
NAAQS.
    (a) Hourly SO2 measurement data shall be reported to
AQS in units of parts per billion (ppb), to at most one place after
the decimal, with additional digits to the right being truncated
with no further rounding.
    (b) Daily maximum 1-hour values and therefore the annual 4th
highest of those daily values are not rounded.
    (c) The 1-hour primary standard design value is calculated
pursuant to section 5 and then rounded to the nearest whole number
or 1 ppb (decimals 0.5 and greater are rounded up to the nearest
whole number, and any decimal lower than 0.5 is rounded down to the
nearest whole number).
    5. Calculation Procedures for the 1-hour Primary SO2
NAAQS.
    (a) Procedure for identifying annual 99th percentile values.
When the data for a particular site and year meet the data
completeness requirements in section 3(b), or if one of the
conditions of section 3(c) is met, or if the Administrator exercises
the discretionary authority in section 3(d), identification of
annual 99th percentile value is accomplished as follows.
    (i) The annual 99th percentile value for a year is the higher of
the two values resulting from the following two procedures.
    (1) Procedure 1. For the year, determine the number of days with
at least 75 percent of the hourly values reported.
    (A) For the year, from only the days with at least 75 percent of
the hourly values reported, select from each day the maximum hourly
value.
    (B) Sort all these daily maximum hourly values from a particular
site and year by descending value. (For example: (x[1], x[2], x[3],
* * *, x[n]). In this case, x[1] is the largest number and x[n] is
the smallest value.) The 99th percentile is determined from this
sorted series of daily values which is ordered from the highest to
the lowest number. Using the left column of Table 1, determine the
appropriate range (i.e., row) for the annual number of days with
valid data for year y (cny). The corresponding ``n''
value in the right column identifies the rank of the annual 99th
percentile value in the descending sorted list of daily site values
for year y. Thus, P0.99, y = the nth largest value.
    (2) Procedure 2. For the year, determine the number of days with
at least one hourly value reported.
    (A) For the year, from all the days with at least one hourly
value reported, select from each day the maximum hourly value.
    (B) Sort all these daily maximum values from a particular site
and year by descending value. (For example: (x[1], x[2], x[3], * *
*, x[n]). In this case, x[1] is the largest number and x[n] is the
smallest value.) The 99th percentile is determined from this sorted
series of daily values which is ordered from the highest to the
lowest number. Using the left column of Table 1, determine the
appropriate range (i.e., row) for the annual number of days with
valid data for year y (cny). The corresponding ``n''
value in the right column identifies the rank of the annual 99th
percentile value in the descending sorted list of daily site values
for year y. Thus, P0.99, y = the nth largest value.
    (b) The 1-hour primary standard design value for a site is mean
of the three annual 99th percentile values, rounded according to the
conventions in section 4.

                                 Table 1
------------------------------------------------------------------------
                                       P0.99, y is the nth maximum value
Annual number of days with valid data     of the year, where n is the
         for year ``y'' (cny)                    listed number
------------------------------------------------------------------------
1-100................................  1
101-200..............................  2
201-300..............................  3
301-366..............................  4
------------------------------------------------------------------------

PART 53--AMBIENT AIR MONITORING REFERENCE AND EQUIVALENT METHODS

    8. The authority citation for part 53 continues to read as follows:

    Authority:  Sec. 301(a) of the Clean Air Act (42 U.S.C. sec.
1857g(a)), as amended by sec. 15(c)(2) of Public Law 91-604, 84
Stat. 1713, unless otherwise noted.

Subpart A--[Amended]

    9. Section 53.2 is amended by revising paragraphs (a)(1) and (b) to
read as follows:

Sec.  53.2.  General requirements for a reference method determination.

* * * * *
    (a) Manual methods--(1) Sulfur dioxide (SO2) and Lead. For
measuring SO2 and lead, Appendixes A-2 and G of part 50 of
this chapter specify unique manual FRM for measuring those pollutants.
After [effective date of Appendix A-1], a new FRM for SO2
must be an automated method that utilizes the measurement principle and
calibration procedure specified in Appendix A-1 to part 50 of this
chapter and must meet applicable requirements of this part, as
specified in paragraph (b) of this section. Except as provided in Sec.
53.16, other manual methods for lead will not be considered for a
reference method determination under this part.
* * * * *
    (b) Automated methods. An automated FRM for measuring
SO2, CO, O3, or NO2 must utilize the
measurement principle and calibration procedure specified in the
appropriate appendix to part 50 of this chapter (appendix A-1 only for
SO2 methods) and must have been shown in accordance with
this part to meet the

requirements specified in this subpart A and subpart B of this part.
    10. Section 53.8 is amended by revising paragraph (c) to read as
follows:

Sec.  53.8  Designation of reference and equivalent methods.

* * * * *
    (c) The Administrator will maintain a current list of methods
designated as FRM or FEM in accordance with this part and will send a
copy of the list to any person or group upon request. A copy of the
list will be available via the Internet and may be available from other
sources.
    11. Table A-1 to Subpart A is revised to read as follows:

  Table A-1 to Subpart A of Part 53--Summary of Applicable Requirements for Reference and Equivalent Methods for Air Monitoring of Criteria Pollutants
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Applicable subparts of part 53
     Pollutant          Reference or       Manual or automated   Applicable part 50 appendix -----------------------------------------------------------
                         equivalent                                                               A         B         C         D         E         F
--------------------------------------------------------------------------------------------------------------------------------------------------------
SO2...............  Reference...........  Manual..............  A-2
                                          Automated...........  A-1                           [check]   [check]
                    Equivalent..........  Manual..............  A-1                           [check]   ........  [check]
                                          Automated...........  A-1                           [check]   [check]   [check]
CO................  Reference...........  Automated...........  C                             [check]   [check]
                    Equivalent..........  Manual..............  C                             [check]   ........  [check]
                                          Automated...........  C                             [check]   [check]   [check]
O3................  Reference...........  Automated...........  D                             [check]   [check]
                    Equivalent..........  Manual..............  D                             [check]   ........  [check]
                                          Automated...........  D                             [check]   [check]   [check]
NO2...............  Reference...........  Automated...........  F                             [check]   [check]
                    Equivalent..........  Manual..............  F                             [check]   ........  [check]
                                          Automated...........  F                             [check]   [check]   [check]
Pb................  Reference...........  Manual..............  G
                    Equivalent..........  Manual..............  G                             [check]   ........  [check]
                                          Automated...........  G                             [check]   ........  [check]
PM10-Pb...........  Reference...........  Manual..............  Q
                    Equivalent..........  Manual..............  Q                             [check]   ........  [check]
                                          Automated...........  Q                             [check]   ........  [check]
PM10..............  Reference...........  Manual..............  J                             [check]   ........  ........  [check]   ........  ........
                    Equivalent..........  Manual..............  J                             [check]   ........  [check]   [check]   ........  ........
                                          Automated...........  J                             [check]   ........  [check]   [check]   ........  ........
PM2.5.............  Reference...........  Manual..............  L                             [check]   ........  ........  ........  [check]   ........
                    Equivalent Class I..  Manual..............  L                             [check]   ........  [check]   ........  [check]   ........
                    Equivalent Class II.  Manual..............  L \1\                         [check]   ........  [check]   ........  [check]   [check]
                                                                                \2\                           1 2
                    Equivalent Class III  Automated...........  L \1\                         [check]   ........  [check]   ........  [check]   [check]
                                                                                \1\
PM10	2.5..........  Reference...........  Manual..............  L, O                          [check]   ........  ........  ........  [check]   ........
                    Equivalent Class I..  Manual..............  L, O                          [check]   ........  [check]   ........  [check]   ........
                    Equivalent Class II.  Manual..............  L, O                          [check]   ........  [check]   ........  [check]   [check]
                                                                                \2\                           1 2
                    Equivalent Class III  Automated...........  L \1\, O \1\                  [check]   ........  [check]   ........  [check]   [check]
                                                                                \1\
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Some requirements may apply, based on the nature of each particular candidate method, as determined by the Administrator.
\2\ Alternative Class III requirements may be substituted.

Subpart B--[Amended]

    12. Section 53.20 is amended as follows:
    A. By revising paragraph (b).
    B. In paragraph (c), by revising Table B-1.
    The revisions read as follows:

Sec.  53.20  General provisions.

* * * * *
    (b) For a candidate method having more than one selectable
measurement range, one range must be that specified in table B-1
(standard range for SO2), and a test analyzer representative
of the method must pass the tests required by this subpart while
operated in that range. The tests may be repeated for one or more
broader ranges (i.e., ones extending to higher concentrations) than the
range specified in table B-1, provided that the range does not extend
to concentrations more than four times the upper range limit specified
in table B-1. For broader ranges, only the tests for range
(calibration), noise at 80% of the upper range limit, and lag, rise and
fall time are required to be repeated. The tests may be repeated for
one or more narrower ranges (ones extending to lower concentrations)
than that specified in table B-1. For SO2 methods, table B-1
specifies special performance requirements for narrower (lower) ranges.
For methods other than SO2, only the tests for range
(calibration), noise at 0% of the measurement range, and lower
detectable limit are required to be repeated. If the tests are
conducted or passed only for the specified range (standard range for
SO2), any FRM or FEM method determination with respect to
the method will be limited to that range. If the tests are passed for
both the specified range and one or more broader ranges, any such
determination will include the additional range(s) as well as the
specified range, provided that the tests required by subpart C of this
part (if applicable) are met for the broader range(s). If the tests are
passed for both the specified range and one or more narrower ranges,
any FRM or FEM method determination for the method will include the
narrower range(s) as well as the specified range. Appropriate test data
shall be submitted for each range sought to be included in a FRM or FEM
method determination under this paragraph (b).
    (c) * * *

                                               Table B-1--Performance Specifications for Automated Methods
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                         SO2
                                                            ----------------------------
       Performance parameter                Units \1\                           Lower        O3           CO          NO2        Definitions and test
                                                             Std. range \3\   range \2\                                               procedures
                                                                                \3\
--------------------------------------------------------------------------------------------------------------------------------------------------------
1. Range...........................  ppm...................         0-0.5       <0.5        0-0.5           0-50     0-0.5    Sec. 53.23(a).
2. Noise...........................  ppm...................           0.001      0.0005       0.005           50       0.005  Sec. 53.23(b).
3. Lower detectable limit..........  ppm...................           0.002      0.001        0.010          1.0       0.010  Sec. 53.23(c).
4. Interference equivalent
    Each interferent...............  ppm...................      0.005  minus>0.00  minus>0.02    minus>1.0  minus>0.02
                                                                                5
    Total, all interferents........  ppm...................           0.020      0.020        0.06           1.5       0.04   Sec. 53.23(d).
5. Zero drift, 12 and 24 hour......  ppm...................      0.004  minus>0.00  minus>0.02    minus>1.0  minus>0.02
                                                                                2
7. Span drift, 24 hour:
    20% of upper range limit.......  Percent...............  ..............  ..........  20.0   minus>10.0  minus>20.0
    80% of upper range limit.......  Percent...............      5.0    minus>5.0   minus>5.0     minus>2.5  minus>5.0
8. Lag time........................  Minutes...............           2          2           20               10      20      Sec. 53.23(e).
9. Rise time.......................  Minutes...............           2          2           15                5      15      Sec. 53.23(e).
10. Fall time......................  Minutes...............           2          2           15                5      15      Sec. 53.23(e).
11. Precision:
    20% of upper range limit.......  ppm...................  ..............  ..........       0.010          0.5       0.020  Sec. 53.23(e).
                                     Percent...............           2          2       ..........  ...........  ..........  Sec. 53.23(e).
    80% of upper range limit.......  ppm...................  ..............  ..........       0.010          0.5       0.030  Sec. 53.23(e).
                                     Percent...............           2          2       ..........  ...........  ..........  Sec. 53.23(e).
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ To convert from parts per million (ppm) to [mu]g/m\3\ at 25 [deg]C and 760 mm Hg, multiply by M/0.02447, where M is the molecular weight of the gas.
  Percent means percent of the upper range limit.
\2\ Tests for interference equivalent and lag time do not need to be repeated for any lower SO2 range provided the test for the standard range shows
  that the lower range specification is met for each of these test parameters.
\3\ For candidate analyzers having automatic or adaptive time constants or smoothing filters, describe their functional nature, and describe and conduct
  suitable tests to demonstrate their function aspects and verify that performances for calibration, noise, lag, rise, fall times, and precision are
  within specifications under all applicable conditions. For candidate analyzers with operator-selectable time constants or smoothing filters, conduct
  calibration, noise, lag, rise, fall times, and precision tests at the highest and lowest settings that are to be included in the FRM or FEM
  designation.

* * * * *
    13. Section 53.21 is amended by revising paragraph (a) to read as
follows:

Sec.  53.21  Test conditions.

    (a) Set-up and start-up of the test analyzer shall be in strict
accordance with the operating instructions specified in the manual
referred to in Sec.  53.4(b)(3). Allow adequate warm-up or
stabilization time as indicated in the operating instructions before
beginning the tests. The test procedures assume that the test analyzer
has an analog measurement signal output that is connected to a suitable
strip chart recorder of the servo, null-balance type. This recorder
shall have a chart width of a least 25 centimeters, chart speeds up to
10 cm per hour, a response time of 1 second or less, a deadband of not
more than 0.25 percent of full scale, and capability either of reading
measurements at least 5 percent below zero or of offsetting the zero by
at least 5 percent. If the test analyzer does not have an analog signal
output, or if other types of measurement data output are used, an
alternative measurement data recording device (or devices) may be used
for the tests, provided it is reasonably suited to the nature and
purposes of the tests and an analog representation of the analyzer
measurements for each test can be plotted or otherwise generated that
is reasonably similar to the analog measurement recordings that would
be produced by a conventional chart recorder.
* * * * *
    14. Section 53.22(d) is amended by revising Table B-2 to read as
follows:

Sec.  53.22  Generation of test atmospheres.

* * * * *
    (d) * * *

                       Table B-2--Test Atmospheres
------------------------------------------------------------------------
           Test gas                  Generation          Verification
------------------------------------------------------------------------
Ammonia.......................  Permeation device.   Indophenol method,
                                 Similar to system    reference 3.
                                 described in
                                 references 1 and 2.
Carbon dioxide................  Cylinder of zero     Use NIST-certified
                                 air or nitrogen      standards whenever
                                 containing CO2 as    possible. If NIST
                                 required to obtain   standards are not
                                 the concentration    available, obtain
                                 specified in table   2 standards from
                                 B-3.                 independent
                                                      sources which
                                                      agree within 2
                                                      percent, or obtain
                                                      one standard and
                                                      submit it to an
                                                      independent
                                                      laboratory for
                                                      analysis, which
                                                      must agree within
                                                      2 percent of the
                                                      supplier's nominal
                                                      analysis.
Carbon monoxide...............  Cylinder of zero     Use a FRM CO
                                 air or nitrogen      analyzer as
                                 containing CO as     described in
                                 required to obtain   reference 8.
                                 the concentration
                                 specified in table
                                 B-3.
Ethane........................  Cylinder of zero     Gas chromatography,
                                 air or nitrogen      ASTM D2820,
                                 containing ethane    reference 10. Use
                                 as required to       NIST-traceable
                                 obtain the           gaseous methane or
                                 concentration        propane standards
                                 specified in table   for calibration.
                                 B-3.
Ethylene......................  Cylinder of pre-     Do.
                                 purified nitrogen
                                 containing
                                 ethylene as
                                 required to obtain
                                 the concentration
                                 specified in table
                                 B-3.

Hydrogen chloride.............  Cylinder \1\ of pre- Collect samples in
                                 purified nitrogen    bubbler containing
                                 containing           distilled water
                                 approximately 100    and analyze by the
                                 ppm of gaseous       mercuric
                                 HCL. Dilute with     thiocyante method,
                                 zero air to          ASTM (D612), p.
                                 concentration        29, reference 4.
                                 specified in table
                                 B-3.
Hydrogen sulfide..............  Permeation device    Tentative method of
                                 system described     analysis for H2S
                                 in references 1      content of the
                                 and 2.               atmosphere, p.
                                                      426, reference 5.
Methane.......................  Cylinder of zero     Gas chromatography
                                 air containing       ASTM D2820,
                                 methane as           reference 10. Use
                                 required to obtain   NIST-traceable
                                 the concentration    methane standards
                                 specified in table   for calibration.
                                 B-3.
Nitric oxide..................  Cylinder\1\ of pre-  Gas phase titration
                                 purified nitrogen    as described in
                                 containing           reference 6,
                                 approximately 100    section 7.1.
                                 ppm NO. Dilute
                                 with zero air to
                                 required
                                 concentration.
Nitrogen dioxide..............  1. Gas phase         1. Use an FRM NO2
                                 titration as         analyzer
                                 described in         calibrated with a
                                 reference 6.         gravimetrically
                                2. Permeation         calibrated
                                 device, similar to   permeation device.
                                 system described    2. Use an FRM NO2
                                 in reference 6.      analyzer
                                                      calibrated by gas-
                                                      phase titration as
                                                      described in
                                                      reference 6.
Ozone.........................  Calibrated ozone     Use an FEM ozone
                                 generator as         analyzer
                                 described in         calibrated as
                                 reference 9.         described in
                                                      reference 9.
Sulfur dioxide................  1. Permeation        Use an SO2 FRM or
                                 device as            FEM analyzer as
                                 described in         described in
                                 references 1 and 2.  reference 7.
                                2. Dynamic dilution
                                 of a cylinder
                                 containing
                                 approximately 100
                                 ppm SO2 as
                                 described in
                                 reference 7.
Water.........................  Pass zero air        Measure relative
                                 through distilled    humidity by means
                                 water at a fixed     of a dew-point
                                 known temperature    indicator,
                                 between 20 [deg]     calibrated
                                 and 30 [deg]C such   electrolytic or
                                 that the air         piezo electric
                                 stream becomes       hygrometer, or wet/
                                 saturated. Dilute    dry bulb
                                 with zero air to     thermometer.
                                 concentration
                                 specified in table
                                 B-3.
Xylene........................  Cylinder of pre-     Use NIST-certified
                                 purified nitrogen    standards whenever
                                 containing 100 ppm   possible. If NIST
                                 xylene. Dilute       standards are not
                                 with zero air to     available, obtain
                                 concentration        2 standards from
                                 specified in table   independent
                                 B-3.                 sources which
                                                      agree within 2
                                                      percent, or obtain
                                                      one standard and
                                                      submit it to an
                                                      independent
                                                      laboratory for
                                                      analysis, which
                                                      must agree within
                                                      2 percent of the
                                                      supplier's nominal
                                                      analysis.
Zero air......................  1. Ambient air
                                 purified by
                                 appropriate
                                 scrubbers or other
                                 devices such that
                                 it is free of
                                 contaminants
                                 likely to cause a
                                 detectable
                                 response on the
                                 analyzer.
                                2. Cylinder of
                                 compressed zero
                                 air certified by
                                 the supplier or an
                                 independent
                                 laboratory to be
                                 free of
                                 contaminants
                                 likely to cause a
                                 detectable
                                 response on the
                                 analyzer.
------------------------------------------------------------------------
\1\ Use stainless steel pressure regulator dedicated to the pollutant
  measured.
Reference 1. O'Keefe, A. E., and Ortaman, G. C. ``Primary Standards for
  Trace Gas Analysis,'' Anal. Chem. 38, 760 (1966).
Reference 2. Scaringelli, F. P., A. E. Rosenberg, E*, and Bell, J. P.,
  ``Primary Standards for Trace Gas Analysis.'' Anal. Chem. 42, 871
  (1970).
Reference 3. ``Tentative Method of Analysis for Ammonia in the
  Atmosphere (Indophenol Method)'', Health Lab Sciences, vol. 10, No. 2,
  115-118, April 1973.
Reference 4. 1973 Annual Book of ASTM Standards, American Society for
  Testing and Materials, 1916 Race St., Philadelphia, PA.
Reference 5. Methods for Air Sampling and Analysis, Intersociety
  Committee, 1972, American Public Health Association, 1015.
Reference 6. 40 CFR 50 Appendix F, ``Measurement Principle and
  Calibration Principle for the Measurement of Nitrogen Dioxide in the
  Atmosphere (Gas Phase Chemiluminescence).''
Reference 7. 40 CFR 50 Appendix A-1, ``Measurement Principle and
  Calibration Procedure for the Measurement of Sulfur Dioxide in the
  Atmosphere (Ultraviolet Fluorescence).''
Reference 8. 40 CFR 50 Appendix C, ``Measurement Principle and
  Calibration Procedure for the Measurement of Carbon Monoxide in the
  Atmosphere'' (Non-Dispersive Infrared Photometry)''.
Reference 9. 40 CFR 50 Appendix D, ``Measurement Principle and
  Calibration Procedure for the Measurement of Ozone in the
  Atmosphere''.
Reference 10. ``Standard Test Method for C, through C5 Hydrocarbons in
  the Atmosphere by Gas Chromatography'', D 2820, 1987 Annual Book of
  Aston Standards, vol 11.03, American Society for Testing and
  Materials, 1916 Race St., Philadelphia, PA 19103.

* * * * *
    15. Section 53.23(d) is amended by revising Table B-3 to read as
follows:

Sec.  53.23  Test procedures.

* * * * *
    (d) * * *

                                                                 Table B-3--Interferent Test Concentration,\1\ Parts Per Million
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                       Hydro-            Hydro-                                                                                Carbon
        Pollutant                Analyzer type        chloric   Ammo-     gen     Sulfur  Nitrogen   Nitric   Carbon   Ethy-    Ozone      M-    Water vapor    mon-    Meth-    Ethane   Naph-
                                                        acid     nia    sulfide  dioxide   dioxide   oxide   dioxide    lene             xylene                oxide     ane             thalene
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SO2.....................  Ultraviolet fluorescence..  .......  .......  \5\ 0.1      \4\       0.5      0.5  .......  .......      0.5      0.2       20,000  .......  .......  .......      \6\
                                                                                0.14                                                                                0.05
SO2.....................  Flame photometric.........  .......  .......     0.01      \4\  ........  .......      750  .......  .......  .......   \3\ 20,000       50  .......  .......  .......
                                                                                0.14
SO2.....................  Gas chromatography........  .......  .......      0.1      \4\  ........  .......      750  .......  .......  .......   \3\ 20,000       50  .......  .......  .......
                                                                                0.14
SO2.....................  Spectrophotometric-wet          0.2      0.1      0.1      \4\       0.5  .......      750  .......      0.5  .......  ...........  .......  .......  .......  .......
                           chemical (pararosanaline).                               0.14
SO2.....................  Electrochemical...........      0.2      0.1      0.1      \4\       0.5      0.5  .......      0.2      0.5  .......   \3\ 20,000  .......  .......  .......  .......
                                                                                0.14
SO2.....................  Conductivity..............      0.2      0.1  .......      \4\       0.5  .......      750  .......  .......  .......  ...........  .......  .......  .......  .......
                                                                                0.14
SO2.....................  Spectrophotometric-gas      .......  .......  .......      \4\       0.5  .......  .......  .......      0.5      0.2  ...........  .......  .......  .......  .......
                           phase, including DOAS.                                   0.14
O3......................  Chemiluminescent..........  .......  .......  \3\ 0.1  .......  ........  .......      750  .......      \4\  .......   \3\ 20,000  .......  .......  .......  .......
                                                                                0.08
O3......................  Electrochemical...........  .......  \3\ 0.1  .......      0.5       0.5  .......  .......  .......      \4\  .......  ...........  .......  .......  .......  .......
                                                                                0.08

O3......................  Spectrophotometric-wet      .......  \3\ 0.1  .......      0.5       0.5  \3\ 0.5  .......  .......      \4\  .......  ...........  .......  .......  .......  .......
                           chemical (potassium                                                                                0.08
                           iodide).
O3......................  Spectrophotometric-gas      .......  .......  .......      0.5       0.5      0.5  .......  .......      \4\     0.02       20,000  .......  .......  .......  .......
                           phase, including                                                                                0.08
                           ultraviolet absorption
                           and DOAS).
CO......................  Infrared..................  .......  .......  .......  .......  ........  .......      750  .......  .......  .......       20,000   \4\ 10  .......  .......  .......
CO......................  Gas chromatography with     .......  .......  .......  .......  ........  .......  .......  .......  .......  .......       20,000   \4\ 10  .......      0.5  .......
                           flame ionization detector.
CO......................  Electrochemical...........  .......  .......  .......  .......  ........      0.5  .......      0.2  .......  .......       20,000   \4\ 10  .......  .......  .......
CO......................  Catalytic combustion-       .......      0.1  .......  .......  ........  .......      750      0.2  .......  .......       20,000   \4\ 10      5.0      0.5  .......
                           thermal detection.
CO......................  IR fluorescence...........  .......  .......  .......  .......  ........  .......      750  .......  .......  .......       20,000   \4\ 10  .......      0.5  .......
CO......................  Mercury replacement-UV      .......  .......  .......  .......  ........  .......  .......      0.2  .......  .......  ...........   \4\ 10  .......      0.5  .......
                           photometric.
NO2.....................  Chemiluminescent..........  .......  \3\ 0.1  .......      0.5   \4\ 0.1      0.5  .......  .......  .......  .......       20,000  .......  .......  .......  .......
NO2.....................  Spectrophotometric-wet      .......  .......  .......      0.5   \4\ 0.1      0.5      750  .......      0.5  .......  ...........  .......  .......  .......  .......
                           chemical (azo-dye
                           reaction).
NO2.....................  Electrochemical...........      0.2  \3\ 0.1  .......      0.5   \4\ 0.1      0.5      750  .......      0.5  .......       20,000       50  .......  .......  .......
NO2.....................  Spectrophotometric-gas      .......  \3\ 0.1  .......      0.5   \4\ 0.1      0.5  .......  .......      0.5  .......       20,000       50  .......  .......  .......
                           phase.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Concentrations of interferent listed must be prepared and controlled to 10 percent of the stated value.
\2\ Analyzer types not listed will be considered by the Administrator as special cases.
\3\ Do not mix with the pollutant.
\4\ Concentration of pollutant used for test. These pollutant concentrations must be prepared to 10 percent of the stated value.
\5\ If candidate method utilizes an elevated-temperature scrubber for removal of aromatic hydrocarbons, perform this interference test.
\6\ If naphthalene test concentration cannot be accurately quantified, remove the scrubber, use a test concentration that causes a full scale response, reattach the scrubber, and evaluate
  response for interference.

* * * * *

Subpart C--[Amended]

    16. Section 53.32 is amended by revising paragraph (e)(2) to read
as follows:

Sec.  53.32  Test procedures for methods for SO2, CO, O3, and NO2.

* * * * *
    (e) * * *
    (2) For a candidate method having more than one selectable range,
one range must be that specified in table B-1 of subpart B of this
part, and a test analyzer representative of the method must pass the
tests required by this subpart while operated on that range. The tests
may be repeated for one or more broader ranges (i.e., ones extending to
higher concentrations) than the one specified in table B-1 of subpart B
of this part, provided that such a range does not extend to
concentrations more than four times the upper range limit specified in
table B-1 of subpart B of this part and that the test analyzer has
passed the tests required by subpart B of this part (if applicable) for
the broader range. If the tests required by this subpart are conducted
or passed only for the range specified in table B-1 of subpart B of
this part, any equivalent method determination with respect to the
method will be limited to that range. If the tests are passed for both
the specified range and a broader range (or ranges), any such
determination will include the broader range(s) as well as the
specified range. Appropriate test data shall be submitted for each
range sought to be included in such a determination.
* * * * *
    17. Table C-1 to Subpart C is revised to read as follows:

          Table C-1 to Subpart C of Part 53--Test Concentration Ranges, Number of Measurements Required, and Maximum Discrepancy Specifications
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Simultaneous measurements required               Maximum
                                                                                ----------------------------------------------------    discrepancy
                   Pollutant                       Concentration range, parts per            1-hour                    24-hour           specification,
                                                           million (ppm)           ----------------------------------------------------     parts per
                                                                                First set    Second set   First set    Second set       million
--------------------------------------------------------------------------------------------------------------------------------------------------------