Regulatory Model (AERMOD)) to determine locations where monitoring
should be conducted.  Any screening or modeling would likely be carried
out by states by using EPA recommended models and techniques referenced
by 40 CFR Part 51, Appendix W, which provides guidance on air quality
modeling.  Such screening or modeling uses facility emission tonnage,
stack heights, stack diameters, emission temperatures, emission
velocities, and accounts for local terrain and meteorology in
determining where expected maximum hourly concentrations may occur.  In
using this approach, EPA would then require states to locate monitors at
the point of maximum concentration around sources identified as likely
causing NAAQS exceedances.

This approach could lead to monitors being required at a significantly
larger number of locations than under the proposed approach, as this
alternative approach would not distinctly use population as a factor for
where monitors should be placed.  For example, our NEI shows that 2,407
sources emit 50 tons per year or more of SO2, and 1,928 sources emit 100
tons per year or more of SO2.  If the state screening approach found
that a substantial fraction of those had a significant probability of
violating the NAAQS, states could be required to model, evaluate, and
potentially monitor a corresponding number of sources.  EPA solicits
comment on the resource implications for state, local, and tribal
agencies associated with this approach.

If EPA selects a standard level near the lower end of the proposed
range, it is likely that a greater number of areas would exceed the
NAAQS, leading to the need for additional monitors.  A facility
screening approach, as described above would explicitly account for the
specific parameters of a facility, air quality information, and the
stringency of the standard for determining the number of monitors, in
contrast to the proposed approach.  EPA solicits comment on how, in the
absence of a facility screening approach, the number of monitors
required nationwide could be adjusted if EPA finalizes a standard near
the lower end of the proposed range.

C.	Data Reporting

SO2 UV fluorescence FEMs are continuous gas analyzers, producing updated
data values on the order of every 20 seconds. Data values are typically
aggregated into minute averages and then compiled into hourly averages
for reporting purposes. EPA proposes to retain the existing requirement
that State and local monitoring agencies report hourly SO2 data to AQS
within 90 days of the end of each calendar quarter. EPA encourages
monitoring agencies to continue to voluntarily report their
pre-validated data on an hourly basis to EPA’s real time AIRNow data
system.

The definitive evidence for the ISA’s conclusion of causal association
between short-term SO2 exposure and respiratory morbidity was from
controlled human exposure studies of 5-10 minutes in exercising
asthmatics (ISA, section 5.2).  The REA therefore assessed exposure and
risks associated with 5-minute SO2 concentrations above 5-minute health
effect benchmark levels derived from these controlled human exposure
studies.  In performing these analyses, the REA noted that: 1) the
majority of the current SO2 monitoring network reported 1-hour SO2
concentrations (REA section 7.2.3); 2) because there was only a
voluntary request, very few state and local agencies in the U.S.
reported ambient 5-minute SO2 concentrations since such monitoring is
not required (REA, section <IP_ADDRESS>); and 3) the lack of 5-minute
monitoring data necessitated the use of statistically estimated 5-minute
SO2 concentrations derived from reported 1-hour SO2 levels (see REA
section 7.2.3) in order to expand the geographic scope of its exposure
and risk analyses. Thus given the demonstrated importance of 5-minute
SO2 concentrations, EPA proposes that State and local agencies shall
report the maximum 5-minute block average of SO2 each hour, out of the
twelve 5-minute blocks in the hour, in addition to the existing
requirement to report the hourly average. EPA solicits comment on the
proposed requirement for State and local monitoring agencies to report
both hourly average and maximum 5-minute average values for each hour.
EPA also solicits comment on the advantages and disadvantages of
requiring state, local, and tribal agencies to report all twelve
5-minute SO2 values for each hour.

As a part of the larger data quality performance requirements of the
ambient monitoring program, we are proposing to develop data quality
objectives (DQOs) for the proposed SO2 network.  The DQOs are meant to
identify measurement uncertainty for a given pollutant method.  We
propose a goal for acceptable measurement uncertainty for SO2 methods to
be defined for precision as an upper 90 percent confidence limit for the
coefficient of variation (CV) of 15 percent and for bias as an upper 95
percent confidence limit for the absolute bias of 15 percent.  We
solicit comment on the proposed goals for developing DQOs and on what
the acceptable measurement uncertainty should be.

IV. 	Proposed Appendix T--Interpretation of the Primary NAAQS for Oxides
of Sulfur and Proposed Revisions to the Exceptional Events Rule

	The EPA is proposing to add Appendix T, Interpretation of the Primary
National Ambient Air Quality Standards for Oxides of Sulfur, to 40 CFR
Part 50 in order to provide data handling procedures for the proposed
SO2 1-hour primary standard.  The proposed section 50.11 which sets the
averaging period, level, indicator and form of the NAAQS refers to this
Appendix T.  The proposed Appendix T would detail the computations
necessary for determining when the proposed 1-hour primary SO2 NAAQS is
met. The proposed Appendix T also would address data reporting, data
completeness considerations, and rounding conventions.

	Two versions of the proposed Appendix T are printed at the end of this
notice. The first applies to a 1-hour primary standard based on the
annual 4th high value form, while the second applies to a 1-hour primary
standard based on the 99th percentile daily value form.  (As explained
in section II.F. 3 above, EPA is proposing alternative forms here based
on technical analysis that they are equally effective.)  The discussion
here addresses the first of these versions, followed by a brief
description of the differences found in the second version.

	For the proposed 1-hour primary standard, EPA is proposing data
handling procedures, a proposed addition of a cross-reference to the
Exceptional Events Rule, a proposed addition to allow the Administrator
discretion to consider otherwise incomplete data to be complete, and a
proposed provision addressing the possibility of there being multiple
SO2 monitors at one site.

	The EPA is also proposing SO2-specific changes to the deadlines in 40
CFR 50.14, by which states must flag ambient air data that they believe
have been affected by exceptional events and submit initial descriptions
of those events, and to the deadlines by which states must submit
detailed justifications to support the exclusion of that data from EPA
determinations of attainment or nonattainment with the NAAQS. The
deadlines now contained in 40 CFR 50.14 are generic, and are not always
appropriate for SO2 given the anticipated schedule for the designations
of areas under the proposed SO2 NAAQS.

A.	 Background

	The general purpose of a data interpretation appendix is to provide the
practical details on how to make a comparison between multi-day and
possibly multi-monitor ambient air concentration data and the level of
the NAAQS, so that determinations of attainment and nonattainment are as
objective as possible. Data interpretation guidelines also provide
criteria for determining whether there are sufficient data to make a
NAAQS level comparison at all.	The regulatory language for the current
SO2 NAAQS, originally adopted in 1977, contains data interpretation
instructions only for the issue of data completeness. This situation
contrasts with the situations for ozone, PM2.5, PM10, and most recently
Pb for which there are detailed data interpretation appendices in 40 CFR
Part 50 addressing issues that can arise in comparing monitoring data to
the NAAQS. EPA has used its experience developing and applying these
other data interpretation appendices to develop the proposed text for
Appendix T.

	An exceptional event is defined in 40 CFR 50.1 as an event that affects
air quality, is not reasonably controllable or preventable, is an event
caused by human activity that is unlikely to recur at a particular
location or is a natural event, and is determined by the Administrator
in accordance with 40 CFR 50.14 to be an exceptional event. Air quality
data that is determined, under the procedural steps and substantive
criteria specified in section 50.14, to have been affected by an
exceptional event may be excluded from consideration when EPA makes a
determination that an area is meeting or not meeting the associated
NAAQS.  The key procedural deadlines in section 50.14 are that a State
must notify EPA that data have been affected by an event, i.e.,
“flag” the data in the Air Quality Systems (AQS) database, and
provide an initial description of the event by July 1 of the year after
the data are collected, and that the State must submit the full
justification for exclusion within 3 years after the quarter in which
the data were collected. However, if a regulatory decision based on the
data, for example a designation action, is anticipated, the schedule is
shortened and all information must be submitted to EPA no later than a
year before the decision is to be made. This generic schedule presents
problems when a NAAQS has been recently revised, as discussed below.

B. 	Interpretation of the primary NAAQS for Oxides of Sulfur

	The purpose of a data interpretation rule for the SO2  NAAQS is to give
effect to the form, level, averaging time, and indicator specified in
the proposed regulatory text at 40 CFR 50.11, anticipating and resolving
in advance various future situations that could occur. The proposed
Appendix T provides definitions and requirements that apply to the
proposed 1-hour primary standard for SO2. The requirements concern how
ambient data are to be reported, what ambient data are to be considered
(including the issue of which of multiple monitors’ data sets will be
used when more than one monitor has operated at a site), and the
applicability of the Exceptional Events Rule to the primary SO2  NAAQS.

1.	1-hour primary standard based on the annual 4th high value form

	With regard to data completeness for the proposed 1-hour primary
standard, the proposed Appendix follows past EPA practice for other
NAAQS pollutants by requiring that in general at least 75% of the
monitoring data that should have resulted from following the planned
monitoring schedule in a period must be available for the key air
quality statistic from that period to be considered valid. For the
proposed 1-hour primary SO2 NAAQS, the key air quality statistics are
the daily maximum 1-hour concentrations in three successive years. It is
important that sampling within a day encompass the period when
concentrations are likely to be highest and that all seasons of the year
are well represented.  Hence, the 75% requirement is proposed to be
applied at the daily and quarterly levels. EPA invites comment on the
proposed completeness requirements.

	Recognizing that there may be years with incomplete data, the proposed
text provides that a design value derived from incomplete data will
nevertheless be considered valid in either of two situations.

	First, if the design value calculated from at least four days of
monitoring observations in each of these years exceeds the level of the
1-hour primary standard, it would be valid.  This situation could arise
if monitoring was intermittent but high SO2 levels were measured on
enough hours and days for the mean of the three annual 4th highest
values to exceed the standard.  In this situation, more complete
monitoring could not possibly have indicated that the standard was
actually met.

	Second, we are proposing a diagnostic data substitution test which is
intended to identify those cases with incomplete data in which it
nevertheless is very likely, if not virtually certain, that the daily
1-hour design value would have been observed to be below the level of
the NAAQS if monitoring data had been minimally complete.

	The diagnostic test would be applied only if there is at least 50% data
capture in each quarter of each year and if the 3-year mean of the
observed annual 4th highest maximum hourly values in the incomplete data
is below the NAAQS level.  The test would substitute a high hypothetical
concentration for as much of the missing data as needed to meet the 100%
requirement in each quarter. The value that is substituted for the
missing values is the highest daily maximum 1-hour observed in the same
quarter, looking across all three years under evaluation. If the
resulting 3-year design value is below the NAAQS, it is highly likely
that the design value calculated from complete data would also have been
below the NAAQS, so the original design value indicating compliance
would be considered valid.

	It should be noted that one possible outcome of applying the proposed
substitution test is that a year with incomplete data may nevertheless
be determined to not have a valid design value and thus to be unusable
in making 1-hour primary NAAQS compliance determinations for that 3-year
period. EPA invites comment on incorporating the proposed substitution
test into the final rule.

	EPA is proposing that the Administrator have general discretion to use
incomplete data to calculate design values that would be treated as
valid for comparison to the NAAQS despite the incompleteness, either at
the request of a state or at her own initiative.  Similar provisions
exist already for the PM2.5 and lead NAAQS, and EPA has recently
proposed such provisions to accompany the proposed 1-hour NO2 and SO2
NAAQS.  The Administrator would consider monitoring site closures/moves,
monitoring diligence, and nearby concentrations in determining whether
to use such data.

2.	1-hour primary standard based on the annual 99th percentile daily
value form

	The second version of the proposed Appendix T appearing at the end of
this notice contains proposed interpretation procedures for a 1-hour
primary standard based on the 99th percentile daily value form.  The 4th
high daily value form and the 99th percentile daily value form would
yield the same design value in a situation in which every hour and day
of the year has reported monitoring data, since the 99th percentile of
365 daily values is the 4th highest value.  However, the two forms
diverge if data completeness is 82% or less, because in that case the
99th percentile value is the 3rd highest (or higher) value, to
compensate for the lack of monitoring data on days when concentrations
could also have been high.

	Logically, provisions to address possible data incompleteness under the
99th percentile daily value form should be somewhat different from those
for the 4th highest form.  With a 4th highest form, incompleteness
should not invalidate a design value that exceeds the standard, for
reasons explained above. With the 99th percentile form, however, a
design value exceeding the standard stemming from incomplete data should
not automatically be considered valid, because concentrations on the
unmonitored days could have been relatively low, such that the actual
99th percentile value for the year could have been lower, and the design
value could have been below the standard.  The second proposed version
of Appendix T accordingly has somewhat different provisions for dealing
with data incompleteness.  One difference is the addition of another
diagnostic test based on data substitution, which in some cases can
validate a design value based on incomplete data that exceeds the
standard.

	The second version of the proposed Appendix T provides a table for
determining which day’s maximum 1-hour concentration will be used as
the 99th percentile concentration for the year.  The proposed table is
similar to one used now for the 24-hour PM2.5 NAAQS, which is based on a
 98th percentile form, but adjusted to reflect a 99th percentile form
for the 1-hour primary SO2 standard.  The proposed Appendix T also
provides instructions for rounding (not truncating) the average of three
annual 99th percentile hourly concentrations before comparison to the
level of the primary NAAQS.

C.	 Exceptional events information submission schedule

The Exceptional Events Rule at 40 CFR 50.14 contains generic deadlines
for a state to submit to EPA specified information about exceptional
events and associated air pollutant concentration data.  A state must
initially notify EPA that data have been affected by an event by July 1
of the calendar year following the year in which the event occurred;
this is done by flagging the data in AQS and providing an initial event
description.  The state must also, after notice and opportunity for
public comment, submit a demonstration to justify any claim within 3
years after the quarter in which the data were collected.  However, if a
regulatory decision based on the data (for example, a designation
action) is anticipated, the schedule to flag data in AQS and submit
complete documentation to EPA for review is shortened, and all
information must be submitted to EPA no later than one year before the
decision is to be made.

These generic deadlines are suitable for the period after initial
designations have been made under a NAAQS, when the decision that may
depend on data exclusion is a redesignation from attainment to
nonattainment or from nonattainment to attainment.  However, these
deadlines present problems with respect to initial designations under a
newly revised NAAQS.  One problem is that some of the deadlines,
especially the deadlines for flagging some relevant data, may have
already passed by the time the revised NAAQS is promulgated.  Until the
level and form of the NAAQS have been promulgated a state does not know
whether the criteria for excluding data (which are tied to the level and
form of the NAAQS) were met on a given day.   Another problem is that it
may not be feasible for information on some exceptional events that may
affect final designations to be collected and submitted to EPA at least
one year in advance of the final designation decision.  This could have
the unintended consequence of EPA designating an area nonattainment
because of uncontrollable natural or other qualified exceptional events.

The Exceptional Events Rule at section 50.14(c)(2)(v) indicates “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
data for initial designation of areas for those NAAQS.”

For the specific case of SO2, EPA anticipates that the signature date
for the revised SO2 NAAQS will be June 2, 2010 (a date specified by
Consent Decree), that state/tribal  designations recommendations will be
due by June 2, 2011, and that initial designations under the revised
NAAQS will be made by June  1, 2012 (since June 2, 2012 would be on a
Saturday) and will be based on air quality data from the years 2008-2010
or 2009-2011 if there is sufficient data for these data years. (See
Section VI below for more detailed discussion of the designation
schedule and what data EPA intends to use.)    Under the current rule,
because final designations would be made by June 1, 2012, all events to
be considered during the designations process would have to be flagged
and fully documented by states one year prior to designations, by June
1, 2011.   A state would not be able to flag and submit documentation
regarding events that occurred between June to December 2011 by one year
before designations are made in June 2012.

EPA is proposing revisions to 40 CFR 50.14 only to change submission
dates for information supporting claimed exceptional events affecting
SO2 data.  The proposed rule text at the end of this notice shows the
changes that would apply if a revised SO2 NAAQS is promulgated by June
2, 2010, and designations are made two years after such promulgation.
For air quality data collected in 2008, we propose to extend the generic
July 1, 2009 deadline for flagging data (and providing a brief initial
description of the event) to October 1, 2010.  EPA believes this
extension would provide adequate time for states to review the impact of
exceptional events from 2008 on the revised standard and notify EPA by
flagging the relevant data in AQS.  EPA is not proposing to change the
foreshortened deadline of June 1, 2011 for submitting documentation to
justify an SO2-related exceptional event from 2008.  We believe the
generic deadline provides adequate time for states to develop and submit
proper documentation.

For data collected in 2009, EPA proposes to extend generic deadline of
July 1, 2010 for flagging data and providing initial event descriptions
to October 1, 2010.  EPA is retaining the deadline of June 1, 2011 for
states to submit documentation to justify an SO2-related exceptional
event from 2009.  EPA plans to assist the states by providing at the
time of signature our assessment of which monitoring sites and days have
exceeded the NAAQS in 2008 and 2009.

For data collected in 2010, EPA is proposing a deadline of June 1, 2011
for flagging data and providing initial event descriptions and for
submitting documentation to justify exclusion of the flagged data.  EPA
believes that this deadline provides states with adequate time to review
and identify potential exceptional events that occur in calendar year
2010, even for those events that might occur late in the year.    EPA
believes these deadlines will be feasible because experience suggest
that exceptional events affecting SO2 data are few in number and easily
assessed, so no state is likely to have a large workload.

If a state intends 2011 data to be considered in SO2 designations, 2011
data must be flagged and detailed event documentation submitted 60 days
after the end of the calendar quarter in which the event occurred or by
March 31, 2011, whichever date occurs first.   Again, EPA believes these
deadlines will be feasible because experience suggest that exceptional
events affecting SO2 data are few in number and easily assessed, so no
state is likely to have a large workload.

Table 6 summarizes the proposed designation deadlines discussed in this
section and provides designation schedule information from recent,
pending or prior NAAQS revisions for other pollutants.  If the
promulgation date for a revised SO2 NAAQS occurs on a different date
than June 1, 2010 (i.e. if the consent decree should be amended –
which EPA does not presently anticipate), EPA will revise the final SO2
exceptional event flagging and documentation submission deadlines
accordingly, consistent with this proposal, to provide states with
reasonably adequate opportunity to review, identify, and document
exceptional events that may affect an area designation under a revised
NAAQS.  EPA invites comment on these proposed changes in the exceptional
event flagging and documentation submission deadlines for the revised
SO2 NAAQS shown in Table 6.

Table 6.  Schedule for Exceptional Event Flagging and Documentation
Submission for Data to be Used in Designations Decisions for New or
Revised NAAQS

NAAQS Pollutant/

Standard/(Level)/

Promulgation Date	Air Quality Data Collected for Calendar Year	Event
Flagging & Initial Description Deadline	Detailed Documentation
Submission Deadline

PM2.5/24-Hr Standard (35 µg/m3)  Promulgated October 17, 2006	2004-2006
October 1, 2007a	April 15, 2008a

Ozone/8-Hr Standard (0.075 ppm)Promulgated March 12, 2008	2005-2007	June
18, 2009a	June 18, 2009a

	2008	June 18, 2009a	June 18, 2009a

	2009	60 Days after the end of the calendar quarter in which the event
occurred or February 5, 2010, whichever date occurs firstb	60 Days after
the end of the calendar quarter in which the event occurred or February
5, 2010, whichever date occurs firstb

NO2/1-Hour Standard(80-100 PPB, final level TBD)	2008	July 1, 2010a
January 22, 2011a

	2009	July 1, 2010a 	January 22, 2011a

	2010	 April 1, 2011a	July 1, 2011 a

SO2/1-Hour Standard (50-100 PPB, final level TBD)	2008	October 1, 2010b
June 1, 2011b

	2009	October 1, 2010b	June 1, 2011 b

	2010	June 1, 2011 b	June 1, 2011 b

	2011	60 Days after the end of the calendar quarter in which the event
occurred or March 31, 2011, whichever date occurs firstb	60 Days after
the end of the calendar quarter in which the event occurred or March 31,
2011, whichever date occurs firstb

aThese 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.

bIndicates 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.

V.  	 Designations for the SO2 NAAQS

	After EPA establishes or revises a NAAQS, the CAA directs EPA and the
states to begin taking steps to ensure that the new or revised NAAQS is
met.  The first step is to identify areas of the country that do not
meet the new or revised NAAQS.  This step is known as the initial area
designations.

	Section 107(d)(1)(A) of the CAA provides that, "By such date as the
Administrator may reasonably require, but not later than 1 year after
promulgation of a new or revised NAAQS for any pollutant under section
109, the Governor of each state shall * * * submit to the Administrator
a list of all areas (or portions thereof) in the state" that designates
those areas as nonattainment, attainment, or unclassifiable.  The CAA
section 107(d)(1)(A)(i) defines an area as nonattainment if it is
violating the NAAQS or if it is contributing to a violation in a nearby
area.

	Section 107(d)(1)(B)(i) further provides, "Upon promulgation or
revision of a NAAQS, the Administrator shall promulgate the designations
of all areas (or portions thereof) * * * as expeditiously as
practicable, but in no case later than 2 years from the date of
promulgation.  Such period may be extended for up to one year in the
event the Administrator has insufficient information to promulgate the
designations within 2 years.  By no later than 120 days prior to
promulgating designations, EPA is required to notify states of any
intended modifications to their boundaries as EPA may deem necessary.
States then have an opportunity to comment on EPA's intended decisions.
(See section 107(d)(1)(B)(ii).)  Whether or not a state provides a
recommendation, EPA must promulgate the designation that the Agency
deems appropriate.

	Therefore, following promulgation of any revised SO2 NAAQS in June
2010, EPA must promulgate initial designations by June 2012, or, by June
2013 in the event that the Administrator has insufficient information to
promulgate initial designations within 2 years.  Along with the proposal
to set a new 1-hour primary SO2 NAAQS, elsewhere in this action, EPA is
proposing new SO2 ambient air monitoring network requirements.  As
proposed, any new monitors would be deployed no later than January 1,
2013.  Compliance with the proposed 1-hour SO2 NAAQS would be determined
based on 3 years of quality assured, certified monitoring data.  We do
not expect newly sited monitors for the proposed new network to generate
sufficient monitoring data for EPA to use in determining whether areas
are in compliance with the revised SO2 NAAQS by the statutory deadline
for EPA to complete initial designations, even if EPA were to take an
additional third year.  Therefore, EPA intends to complete the
designations on a 2-year schedule based on 3 years of quality assured,
certified air quality monitoring data from the current monitoring
network, where the monitors would be retained in the new network.  The
SO2 monitors in the current network were generally sited to measure the
highest 24-hour and annual average SO2 concentrations.  However, all of
the monitors report hourly data.  EPA estimates that around 488 monitors
operated in 2008.  EPA believes at least one third of the monitors meet
the proposed network design requirements and therefore would not need to
be moved.  Additional monitors may be retained in their current
locations if they are measuring high levels of SO2.  Thus, potentially
one third to one half of the current monitors could be used to generate
the necessary data for purposes of initial area designations.  In areas
where the current network would not generate data that are adequate to
determine whether an area is attaining or not attaining the revised SO2
NAAQS, EPA would designate such areas as "unclassifiable."

	Accordingly, state Governors would need to submit their initial
designation recommendations to EPA no later than June 2011.  If the
Administrator intends to modify any state recommendation, EPA would
notify the state's Governor no later than  February 2012, 120 days prior
to promulgating the final designations.  States would then have an
opportunity to comment on EPA's tentative decisions before EPA
promulgates the final designations in June 2012.

	While CAA section 107 specifically addresses states, EPA intends to
follow the same process for tribes to the extent practicable, pursuant
to section 301(d) of the CAA regarding tribal authority, and the Tribal
Authority Rule (63 FR 7254;  February 12, 1998).  Pursuant to the Tribal
Authority Rule, Tribes are not subject to the schedule requirements that
apply to states.  However, EPA intends to promulgate designations for
Tribal land as well as state land according to the schedule mandated for
state land, so EPA encourages Tribes that wish to provide input on
EPA’s designations to provide this input on the schedule mandated for
states.

VI.  	Clean Air Act Implementation Requirements

This section of the preamble discusses the Clean Air Act (CAA)
requirements that states and emissions sources would need to address
when implementing new or revised SO2 NAAQS based on the structure
outlined in the CAA and existing rules.  The EPA believes that there are
sufficient guidance documents and regulations currently in place to
fully implement the proposed revision to the SO2 NAAQS.  However, EPA
may provide additional guidance in the future, as necessary, to assist
states and emissions sources to comply with the CAA provisions for
implementing a new or revised SO2 NAAQS.

The CAA assigns important roles to EPA, states and tribal governments to
achieve the NAAQS.  States have the primary responsibility for
developing and implementing state implementation plans (SIPs) that
contain state measures necessary to achieve the air quality standards in
each area once EPA has established the NAAQS.  EPA provides assistance
to states and tribes by providing technical tools, assistance, and
guidance, including information on the potential control measures that
may assist in helping areas attain the standards.

Under section 110 of the CAA, 42 U.S.C. § 7410, and related provisions,
states are directed to submit, for EPA approval, SIPs that provide for
the attainment and maintenance of such standards through control
programs directed at sources of SO2 emissions.  If a state fails to
adopt and implement the required SIPs by the time periods provided in
the CAA, EPA has the responsibility under the CAA to adopt a federal
implementation plan (FIP) to assure that areas attain the NAAQS in an
expeditious manner.  The states, in conjunction with EPA, also
administer the prevention of significant deterioration (PSD) program for
SO2.  See sections 160-169 of the CAA, 42 U.S.C. §§ 7470-7479.  In
addition, federal programs provide for nationwide reductions in
emissions of SO2 and other air pollutants under Title II of the Act, 42
U.S.C. §§7521–7574.  These programs involve limits on the sulfur
content of the fuel used by automobiles, trucks, buses, motorcycles,
non-road engines and equipment, marine vessels and locomotives.  EPA is
also in the process of establishing limits on the sulfur content of the
fuel used by ocean going vessels.  Emissions reductions for SO2 are also
obtained from implementation of the new source performance standards
(NSPS) for stationary sources under sections 111 and 129 of the CAA, 42
§§ U.S.C. 7411 and 7429; and the national emission standards for
hazardous air pollutants (NESHAP) for stationary sources under section
112 of the CAA, 42 U.S.C. § 7412.

A.  	How this rule applies to tribes

	CAA section 301(d) authorizes EPA to treat eligible Indian tribes in
the same manner as states (TAS) under the CAA and requires EPA to
promulgate regulations specifying the provisions of the statute for
which such treatment is appropriate.  EPA has promulgated these
regulations – known as the Tribal Authority Rule or TAR – at 40
C.F.R. Part 49.  See 63 Fed. Reg. 7254 (February 12, 1998).  The TAR
establishes the process for Indian tribes to seek TAS eligibility and
sets forth the CAA functions for which TAS will be available.  Under the
TAR, eligible tribes may seek approval for all CAA and regulatory
purposes other than a small number of functions enumerated at section
49.4.  Implementation plans under section 110 are included within the
scope of CAA functions for which eligible tribes may obtain approval.
Section 110(o) also specifically describes tribal roles in submitting
implementation plans.  Eligible Indian tribes may thus submit
implementation plans covering their reservations and other areas under
their jurisdiction.

	The CAA and TAR do not, however, direct tribes to apply for TAS or
implement any CAA program.  In promulgating the TAR EPA explicitly
determined that it was not appropriate to treat tribes similarly to
states for purposes of, among other things, specific plan submittal and
implementation deadlines for NAAQS-related requirements.  40 C.F.R. §
49.4(a).  In addition, where tribes do seek approval of CAA programs,
including section 110 implementation plans, the TAR provides flexibility
and allows them to submit partial program elements, so long as such
elements are reasonably severable – i.e., “not integrally related to
program elements that are not included in the plan submittal, and are
consistent with applicable statutory and regulatory requirements”.  40
C.F.R. § 49.7.

To date, very few tribes have sought TAS for purposes of section 110
implementation plans.  However, some tribes may be interested in
pursuing such plans to implement today’s proposed standard, once it is
promulgated.  In several sections of this preamble, EPA describes the
various roles and requirements states will address in implementing
today’s proposed standard.  Such references to states generally
include eligible Indian tribes to the extent consistent with the
flexibility provided to tribes under the TAR.  Where tribes do not seek
TAS for section 110 implementation plans, EPA under its discretionary
authority will promulgate FIPs as “necessary or appropriate to protect
air quality.”  40 C.F.R. § 49.11(a).  EPA also notes that some tribes
operate air quality monitoring networks in their areas.  For such
monitors to be used to measure attainment with the proposed revised
primary NAAQS for SO2, the criteria and procedures identified in this
proposed rule would apply.

B. 	Attainment dates

	The latest date by which an area is required to attain the SO2 NAAQS is
determined from the effective date of the nonattainment designation for
the affected area.  For areas designated nonattainment for the revised
SO2 NAAQS, SIPs must provide for attainment of the NAAQS as
expeditiously as practicable, but no later than 5 years from the
effective date of the nonattainment designation for the area.  See
section 192(a) of the CAA.  The EPA will determine whether an area has
demonstrated attainment of the SO2 NAAQS by evaluating air quality
monitoring data consistent with the form of the NAAQS for SO2, if
revised, which will be codified at 40 CFR part 50, Appendix T.

1.	Attaining the NAAQS

In order for an area to be redesignated as attainment, it must meet five
conditions provided under section 107(d)(3)(E) of the CAA.  This section
requires that:

EPA must have determined that the area has met the SO2 NAAQS;

EPA has fully approved the state’s implementation plan;

the improvement in air quality in the affected area is due to permanent
and enforceable reductions in emissions;

EPA has fully approved a maintenance plan for the area; and

the state(s) containing the area have met all applicable requirements
under section 110 and part D.

2.	Consequences of failing to attain by the statutory attainment date

	Any SO2 nonattainment area that fails to attain by its statutory
attainment date would be subject to the requirements of sections 179(c)
and (d) of the CAA.  EPA is required to make a finding of failure to
attain no later than 6 months after the specified attainment date and
publish a notice in the Federal Register.  The state would then need to
submit an implementation plan revision no later than one year following
the effective date of the Federal Register notice making the
determination of the area’s failure to attain.  This submission must
demonstrate that the standard will be attained as expeditiously as
practicable, but no later than 5 years from the effective date of
EPA’s finding that the area failed to attain.  In addition, section
179(d)(2) provides that the SIP revision must include any specific
additional measures as may be reasonably prescribed by EPA, including
“all measures that can be feasibly implemented in the area in light of
technological achievability, costs, and any nonair quality and other air
quality-related health and environmental impacts.”

C.	Section 110(a)(1) and (2) NAAQS infrastructure requirements

	Section 110(a)(2) of the CAA directs all states to develop and maintain
a solid air quality management infrastructure, including enforceable
emission limitations, an ambient monitoring program, an enforcement
program, air quality modeling capabilities, and adequate personnel,
resources, and legal authority.  Section 110(a)(2)(D) also requires
state plans to prohibit emissions from within the state which contribute
significantly to nonattainment or maintenance areas in any other state,
or which interfere with programs under part C of the CAA to prevent
significant deterioration of air quality or to achieve reasonable
progress toward the national visibility goal for Federal class I areas
(national parks and wilderness areas).

	Under sections 110(a)(1) and (2) of the CAA, all states are directed to
submit SIPs to EPA which demonstrate that basic program elements have
been addressed within 3 years of the promulgation of any new or revised
NAAQS.  Subsections (A) through (M) of section 110(a)(2)  set forth the
elements that a state’s program must contain in the SIP.  The list of
section 110(a)(2) NAAQS implementation requirements are the following:

Ambient air quality monitoring/data system:  Section 110(a)(2)(B)
requires SIPs to provide for setting up and operating ambient air
quality monitors, collecting and analyzing data and making these data
available to EPA upon request.

Program for enforcement of control measures:  Section 110(a)(2)(C)
requires SIPs to include a program providing for enforcement of SIP
measures and the regulation and permitting of new/modified sources.

Interstate transport:  Section 110(a)(2)(D) requires SIPs to include
provisions prohibiting any source or other type of emissions activity in
the state from contributing significantly to nonattainment or
interfering with maintenance of the NAAQS in another state, or from
interfering with measures required to prevent significant deterioration
of air quality or to protect visibility.

Adequate resources:  Section 110(a)(2)(E) directs states to provide
assurances of adequate funding, personnel and legal authority to
implement their SIPs.

Stationary source monitoring system:  Section 110(a)(2)(F) directs
states to establish a system to monitor emissions from stationary
sources and to submit periodic emissions reports to EPA.

Emergency power:  Section 110(a)(2)(G) directs states to include
contingency plans, and adequate authority to implement them, for
emergency episodes in their SIPs.

Provisions for SIP revision due to NAAQS changes or findings of
inadequacies:  Section 110(a)(2)(H) directs states to provide for
revisions of their SIPs in response to changes in the NAAQS,
availability of improved methods for attaining the NAAQS, or in response
to an EPA finding that the SIP is inadequate.

Consultation with local and Federal government officials:  Section
110(a)(2)(J) directs states to meet applicable local and Federal
government consultation requirements when developing SIPs and reviewing
preconstruction permits.

Public notification of NAAQS exceedances:  Section 110(a)(2)(J) directs
states to adopt measures to notify the public of instances or areas in
which a NAAQS is exceeded.

PSD and visibility protection:  Section 110(a)(2)(J) also directs states
to adopt emissions limitations, and such other measures, as may be
necessary to prevent significant deterioration of air quality in
attainment areas and protect visibility in Federal Class I areas in
accordance with the requirements of CAA Title I, part C.

Air quality modeling/data:  Section 110(a)(2)(K) requires that SIPs
provide for performing air quality modeling for predicting effects on
air quality of emissions of any NAAQS pollutant and submission of data
to EPA upon request.

Permitting fees:  Section 110(a)(2)(L) requires the SIP to include
requirements for each major stationary source to pay permitting fees to
cover the cost of reviewing, approving, implementing and enforcing a
permit.

Consultation/participation by affected local government:  Section
110(a)(2)(M) directs states to provide for consultation and
participation by local political subdivisions affected by the SIP.

D.  	Attainment planning requirements

1.	SO2 nonattainment area SIP requirements

Any state containing an area designated as nonattainment with respect to
the SO2 NAAQS would need to develop for submission to EPA a SIP meeting
the requirements of part D, Title I, of the CAA, providing for
attainment by the applicable statutory attainment date.  See sections
191(a) and 192(a) of the CAA.  As indicated in section 191(a), all
components of the SO2 part D SIP must be submitted within 18 months of
the effective date of an area’s designation as nonattainment.

Section 172 of the CAA addresses the general requirements for areas
designated as nonattainment.  Section 172(c) directs states with
nonattainment areas to submit a SIP which contains an attainment
demonstration showing that the affected area will attain the standard by
the applicable statutory attainment date.  The SIP must show that the
area will attain the standard as expeditiously as practicable, and must
“provide for the implementation of all Reasonably Available Control
Measures (RACM) as expeditiously as practicable (including such
reductions in emissions from existing sources in the area as may be
obtained through the adoption, at a minimum, of Reasonably Available
Control Technology (RACT)).”

	SIPs required under Part D of the CAA must also provide for reasonable
further progress (RFP).  See section 172(c)(2) of the CAA.  The CAA
defines RFP as “such annual incremental reductions in emissions of the
relevant air pollution as are required by part D, or may reasonably be
required by the Administrator for the purpose of ensuring attainment of
the applicable NAAQS by the applicable attainment date.”  See section
171 of the CAA.  Historically, for some pollutants, RFP has been met by
showing annual incremental emission reductions sufficient to maintain
generally linear progress toward attainment by the applicable attainment
date.

All SO2 nonattainment area SIPs must include contingency measures which
must be implemented in the event that an area fails to meet RFP or fails
to attain the standards by its attainment date.  See section 172(c)(9)
of the CAA.  These contingency measures must be fully adopted rules or
control measures that take effect without further action by the state or
the Administrator.  The EPA interprets this requirement to mean that the
contingency measures must be implemented with only minimal further
action by the state or the affected sources with no additional
rulemaking actions such as public hearings or legislative review.

	Emission inventories are also critical for the efforts of state, local,
and federal agencies to attain and maintain the NAAQS that EPA has
established for criteria pollutants including SO2.  Section 191(a) in
conjunction with section 172(c) requires that areas designated as
nonattainment for SO2 submit an emission inventory to EPA no later than
18 months after designation as nonattainment.  In the case of SO2,
sections 191(a) and 172(c) also direct states to submit periodic
emission inventories for nonattainment areas.  The periodic inventory
must include emissions of SO2 for point, nonpoint, mobile, and area
sources.

2.	New source review and prevention of significant deterioration
requirements

The Prevention of Significant Deterioration (PSD) and nonattainment New
Source Review (NSR) programs contained in parts C and D of Title I of
the CAA govern preconstruction review of any new or modified major
stationary sources of air pollutants regulated under the CAA as well as
any precursors to the formation of that pollutant when identified for
regulation by the Administrator.  The EPA rules addressing these
programs can be found at 40 CFR 51.165, 51.166, 52.21, 52.24, and Part
51, appendix S.

The PSD program applies when a major source located in an area that is
designated as attainment or unclassifiable for any criteria pollutant is
constructed or undergoes a major modification.  The nonattainment NSR
program applies on a pollutant-specific basis when a major source
constructs or modifies in an area that is designated as nonattainment
for that pollutant.  The minor NSR program addresses major and minor
sources that undergo construction or modification activities that do not
qualify as major, and it applies, as necessary to assure attainment,
regardless of the designation of the area in which a source is located.

	PSD permit requirements are effective on the promulgation date of a new
or revised standard.  SIPs that address the PSD requirements related to
attainment areas are due no later than 3 years after the promulgation of
a revised NAAQS for SO2.  The PSD requirements include but are not
limited to the following:

installation of Best Available Control Technology (BACT);

air quality monitoring and modeling analyses to ensure that a
project’s emissions will not cause or contribute to a violation of any
NAAQS or maximum allowable pollutant increase (PSD increment);

notification of Federal Land Manager of nearby Class I areas; and

public comment on the permit.

	If EPA establishes a 1-hour NAAQS for SO2, the owner or operator of any
major stationary source or major modification locating in an attainment
or unclassifiable area for SO2 will be required, as a prerequisite for a
PSD permit, to demonstrate that the emissions increases from the new or
modified source will not cause or contribute to a violation of the that
new NAAQS.  The EPA does not anticipate that this will pose a technical
problem, since the modeling capability and SO2 emissions input data
already exist.  Depending on the final form of the 1-hour NAAQS, it may
be necessary to make adjustments to the AERMOD modeling system to
accommodate the form of the standard; however, EPA anticipates that any
such adjustments can be readily accomplished in coordination with the
promulgation of any new NAAQS for SO2 in time to enable states to
implement such standard via the PSD program.  The analyses for the
1-hour NAAQS will be in addition to the existing demonstration of
compliance for the annual and 24-hour SO2 NAAQS, which will continue to
be required unless EPA revokes these standards in conjunction with its
promulgation of a new 1-hour NAAQS for SO2.

The owner of operator of a new or modified source will still be required
to demonstrate compliance with the annual and 24-hour SO2 increments,
even if their counterpart NAAQS are revoked.  The annual and 24-hour
increments are established in the CAA and will need to remain in the PSD
regulations because EPA does not interpret the Clean Air Act to
authorize EPA to remove them.  It appears necessary for Congress to
amend the Act to make appropriate changes to the statutory SO2
increments, perhaps similar to the way the Act was amended to
accommodate PM10 increments in lieu of the statutory TSP increments.  If
we establish a new 1-hour SO2 NAAQS, EPA will consider the need to adopt
new 1-hour SO2 increments.

In association with the requirement to demonstrate compliance with the
NAAQS and increments, the owner or operator of a new or modified source
must submit for review and approval a source impact analysis and an air
quality analysis.  The source impact analysis, primarily a modeling
analysis, must demonstrate that allowable emissions increases from the
proposed source or modification, in conjunction with emissions from
other existing sources will not cause or contribute to either a NAAQS or
increment violation.  The air quality analysis must assess the ambient
air quality in the area that the proposed source or modification would
affect.

For the air quality analysis, the owner or operator must submit in its
permit application air quality monitoring data that shall have been
gathered over a period of one year and is representative of air quality
in the area of the proposed project.  If existing data representative of
the area of the proposed project is not available, new data may need to
be collected by the owner or operator of the source or modification.
Where data is already available, it might be necessary to evaluate the
location of the monitoring sites from which the SO2 data were collected
in comparison to any new siting requirements associated with the 1-hour
NAAQS.  If existing sites are inappropriate for providing the necessary
representative data, then new monitoring data will need to be collected
by the owner or operator of the proposed project.

	Historically, EPA has allowed the use of several screening tools to
help facilitate the implementation of the new source review program by
reducing the permit applicant’s burden, and streamlining the
permitting process for de minimis circumstances.  These screening tools
include a significant emissions rate (SER), significant impact levels
(SILs), and a significant monitoring concentration (SMC).  The SER, as
defined in tons per year for each regulated pollutant, is used to
determine whether any proposed source or modification will emit
sufficient amounts of a particular pollutant to require the review of
that pollutant under the NSR permit program.  EPA will consider whether
to evaluate the existing significant emissions rate (SER) for SO2 to see
if it would change substantially based on the NAAQS levels for the
1-hour averaging period.  Historically, we have defined a de minimis
pollutant impact as one that results in a modeled ambient impact of less
than approximately 4% of the short-term NAAQS.  The current SER for SO2
(40 tpy) is based on the impact on the 24-hour SO2 NAAQS.  See, 45 FR
52676, 52707 (August 7, 1980).  We have typically used the most
sensitive averaging period to calculate the SER, and we may want to
evaluate the new 1-hour period for SO2 because it is likely to represent
most sensitive averaging period for SO2.

The SIL, expressed as an ambient pollutant concentration (ug/m3), is
used to determine whether the impact of a particular pollutant is
significant enough to warrant a complete air quality impact analysis for
any applicable NAAQS and increments.  EPA has promulgated regulations
under 40 CFR 51.165(b) which include SILs for SO2 to determine whether a
source’s impact would be considered to cause or contribute to a NAAQS
violation for either the 3-hour, 24-hour or annual averaging periods.
These SILs were originally developed in 1978 to limit the application of
air quality dispersion models to a downwind distance of no more than 50
kilometers or to “insignificant levels.”  See, 43 FR 26398, June 19,
1978.  Through guidance, EPA has also allowed the use of SILs to
determine whether or not it is necessary for a source to carry out a
comprehensive source impact analysis and to determine the extent of the
impact area in which the analysis will be carried out.  The existing
SILs for SO2 were not developed on the basis of specific SO2 NAAQS
levels, so if the existing NAAQS are not being revised, there is
probably no need to revise the existing SILs.  Even if we decide to
revoke any of the existing NAAQS, the corresponding SIL should still be
useful for increment assessment.  A SIL for the 1-hour averaging period
does not exist, and would need to be developed for use with modeling for
1-hour SO2 NAAQS and increments (if and when developed).

	Finally, the SMC, also measured as an ambient pollutant concentration
(ug/m3), is used to determine whether it may be appropriate to exempt a
proposed project from the requirement to collect ambient monitoring data
for a particular pollutant as part of a complete permit application.
EPA first defined SMCs for regulated pollutants under the PSD program in
1980.  See, 45 FR 52676, 52709-10 (August 7, 1980).  The existing SMC
for SO2, based on a 24-hour averaging period, may need to be
re-evaluated to consider the effect of basing the SMC on the 1-hour
averaging period, especially in light of the fact that we may revoke the
NAAQS for the 24-hour averaging period.  Third, even if the 1-hour
averaging period does not indicate the need for a revised SMC for SO2,
the fact that the original SMC for SO2 is based on 1980 monitoring data
(Lowest Detectable Level, correction factor of “5”), could be a
basis for revising the existing value.  More up-to-date monitoring data
and statistical analyses of monitoring accuracy may yield a
different—possibly lower—correction factor today.  A new 1-hour
NAAQS would not necessarily cause this result, but may provide a
“window of opportunity” to re-evaluate the SMC for SO2.  See
sections II. E. 2 and II.F. 2 above.

As a means of reducing the permit applicant’s burden, and to
streamline permitting, permit authorities use screening tools referred
to as significant impact levels (SILs) and a significant monitoring
concentration (SMC).  EPA issued unofficial SO2 SILs for the 3-hour
(secondary standard), 24-hour and annual averaging periods.  These SILs
were developed in 1978 to limit the application of air quality
dispersion models to a downwind distance of no more than 50 kilometers
or to “insignificant levels.”  See, 43 FR 263--, 26398, (June 19,
1978).  These values were not developed on the basis of specific SO2
NAAQS levels, so if the existing NAAQS are not being revised, there is
probably no need to revise the existing SILs.  Even if we decide to
revoke any of the existing NAAQS, the corresponding SIL should still be
useful for increment assessment.  A SIL for the 1-hour averaging period
does not exist, and would need to be developed for use with modeling for
the 1-hour SO2 NAAQS and increments (if and when developed).

States which have areas designated as nonattainment for the  SO2 NAAQS
are directed to submit, as a part of the SIP due 18 months after an area
is designated as nonattainment, provisions requiring permits for the
construction and operation of new or modified stationary sources
anywhere in the nonattainment area.  Prior to adoption of the SIP
revision addressing major source nonattainment NSR for SO2 nonattainment
areas, the requirements of 40 CFR part 51, appendix S will apply.
Nonattainment NSR requirements include but are not limited to:

installation of Lowest Achievable Emissions Rate (LAER) control
technology;

offsetting new emissions with creditable emissions reductions;

a certification that all major sources owned and operated in the state
by the same owner are in compliance with all applicable requirements
under the CAA;

an alternative siting analysis demonstrating that the benefits of a
proposed source significantly outweigh the environmental and social
costs imposed as a result of its location, construction, or
modification; and

public comment on the permit.

Minor NSR programs must meet the statutory requirements in section
110(a)(2)(C) of the CAA which requires “…regulation of the
modification and construction of any stationary source …as necessary
to assure that the [NAAQS] are achieved.”  These programs must be
established in each state within 3 years of the promulgation of a new or
revised NAAQS.

3.	General conformity

Section 176(c) of the CAA requires that all federal actions conform to
an applicable implementation plan developed pursuant to section 110 and
part D of the CAA.  The EPA rules developed under section 176(c)
prescribe the criteria and procedures for demonstrating and assuring
conformity of federal actions to a SIP.  Each federal agency must
determine that any actions covered by the general conformity rule
conform to the applicable SIP before the action is taken.  The criteria
and procedures for conformity apply only in nonattainment areas and
those areas redesignated attainment since 1990 (“maintenance areas”)
with respect to the criteria pollutants under the CAA:  carbon monoxide
(CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3), particulate matter
(PM2.5 and PM10), and sulfur dioxide (SO2).  The general conformity
rules apply one year following the effective date of designations for
any new or revised NAAQS.

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 D.C. Circuit Court opinion on the Phase I ozone implementation
rule.  See South Coast Air Quality Management Dist. v. EPA, 472 F.3d 882
(D.C. 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.

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 (to be determined).  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 [Insert date of publication in the Federal Register], a comment to
OMB is best assured of having its full effect if OMB receives it by
[Insert date 30 days after publication in the Federal Register.].  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 (D.C.
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.

References

American Lung Association.  (2001).  Urban air pollution and health
inequities: a workshop report.  Environ Health Perpect.
109(S3):357-374.

American Thoracic Society.  (1985).  Guidelines as to what constitutes
an adverse respiratory health effect, with special reference to
epidemiologic studies of air pollution. Am Rev Respir Dis.  131:666-668.

American Thoracic Society.  (2000).  What constitutes an adverse health
effect of air pollution? Am J Respir Crit Care Med.  161:665-673.

Bethel RA, Sheppard D, Geffroy B, Tam E, Nadel JA, Boushey HA.  (1985).
Effect of 0.25 ppm sulfur dioxide on airway resistance in freely
breathing, heavily exercising, asthmatic subjects.  Am Rev Respir Dis.
131:659-61.

Balmes JR, Fine JM, Sheppard D.  (1987).  Symptomatic
bronchoconstriction after short-term inhalation of sulfur dioxide.  Am
Rev Respir Dis.  136:1117-21.

Chapmann RS, Calafiore DC, Hasselblad V.  (1985).  Prevalence of
persistent cough and phlegm in young adults in relation to long-term
ambient sulfur dioxide exposure.  Am Rev Respir Dis.  132:261-267.

Delfino RJ, Gone H, Linn WS, Pellizzari ED, Hu Y.  (2003).  Asthma
symptoms in hispanic children and daily ambient exposures to toxic and
criteria air pollutants.  Environ Health Perspect.  111:647-656.

Dodge R. et al. (1985).  A longitudinal study of children exposed to
sulfur oxides.  Am J Epidemiology.  121:720-736.

EPA.  (1982).  Air Quality Criteria for Particulate Matter and Sulfur
Oxides. US EPA, Research Triangle Park, NC: Office of Health and
Environmental Assessment.

EPA.  (1986).  Second Addendum to Air Quality Criteria for Particulate
Matter and Sulfur Oxides (1982): Assessment of Newly Available Health
Effects Information. US EPA, Research Triangle Park, NC: Office of
Health and Environmental Assessment.

EPA.  (1994a).  Supplement to the Second Addendum (1986) to Air Quality
Criteria for Particulate Matter and Sulfur Oxides (1982).  Research
Triangle Park, NC: Office of Health and Environmental Assessment,
Environmental Criteria and Assessment Office.  EPA-600/FP-93/002.

EPA.  (1994b).  Review of the National Ambient Air Quality Standards for
Sulfur Oxides:  Assessment of Scientific and Technical Information,
Supplement to the 1986 OAQPS Staff Paper Addendum.  Research Triangle
Park, NC: Office of Air Quality Planning and Standards.
EPA-452/R-94/013.

EPA.  (2005).  Review of the National Ambient Air Quality Standards for
Particulate Matter:  Policy Assessment of Scientific and Technical
Information – OAQPS Staff Paper.  Research Triangle Park, NC: Office
of Air Quality Planning and Standards.  EPA-452/R-05-005a. Available at:
http://www.epa.gov/ttn/naaqs/standards/pm/data/pmstaffpaper_20051221.pdf

EPA (2006). Air Quality Criteria for Ozone and Related Photochemical
Oxidants (Final); Available at:
http://www.epa.gov/ttn/naaqs/standards/ozone/s_o3_cr_cd.html

EPA.  (2007a).  SO2 NAAQS Review Plan - Draft.  US EPA, Research
Triangle Park, NC: National Center for Environmental Assessment.
Available at http://www.epa.gov/ttn/naaqs/standards/so2/s_so2_cr_pd.html

EPA.  (2007b).  Sulfur Dioxide Health Assessment Plan: Scope and Methods
for Exposure and Risk Assessment.  US EPA Research Triangle Park, NC:
Office of Air Quality Planning and Standards, Research Triangle Park.
Available at:
http://www.epa.gov/ttn/naaqs/standards/so2/s_so2_cr_pd.html.

EPA (2007c).  Review of the National Ambient Air Quality Standards for
Pb: Policy Assessment of Scientific and Technical Information. OAQPS
Staff paper.  Office of Air Quality Planning and Standards, Research
Triangle Park, NC.  EPA-452/R-07-013.  Available at:
http://www.epa.gov/ttn/naaqs/standards/pb/data/20071101_pb_staff.pd

EPA.  (2007d).  Review of the National Ambient Air Quality Standards for
Ozone: Assessment of Scientific and Technical Information, OAQPS Staff
paper. Office of Air Quality Planning and Standards, Research Triangle
Park, NC.  EPA-452/R-07-007a.  Available at:
http://epa.gov/ttn/naaqs/standards/ozone/s_o3_cr_sp.html.

EPA.  (2008a).  Integrated Science Assessment (ISA) for Sulfur Oxides
– Health Criteria (Final Report).  EPA/600/R-08/047F.  Available at:
http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=198843.

EPA.  (2008b).  Integrated Science Assessment (ISA) for Oxides of
Nitrogen – Health Criteria (Final Report). EPA/600/R-08/071 .
Available at:
http://www.epa.gov/ttn/naaqs/standards/nox/s_nox_cr_isi.html.

EPA.  (2008c).  Risk and Exposure Assessment to Support the Review of
the NO2 Primary National Ambient Air Quality Standard.
EPA-452/R-08-008a; Available at:
http://www.epa.gov/ttn/naaqs/standards/nox/s_nox_cr_rea.html

EPA.  (2009).  Risk and Exposure Assessment to Support the Review of the
SO2 Primary National Ambient Air Quality Standards- Final Report.
EPA-452/R-09-007; Available at:
http://www.epa.gov/ttn/naaqs/standards/so2/s_so2_cr_rea.html

Finkelstein MM, Jerrett M, DeLuca P, Finkelstein N, Verma DK, Chapman K,
Sears MR. (2003).  Relation between income, air pollution and mortality:
a cohort study.  CMAJ.  169: 397-402.

Finkelstein MM, Jerrett M, DeLuca P, Finkelstein N, Verma DK, Chapman K,
Sears MR. (2003).  Relation between income, air pollution and mortality:
a cohort study.  CMAJ.  169: 397-402.

Gong H, Jr., Lachenbruch PA, Harber P, Linn WS.  (1995).  Comparative
short-term health responses to sulfur dioxide exposure and other common
stresses in a panel of asthmatics. Toxicol Ind Health.  11:467-487

Henderson.  (2006).  Letter to EPA Administrator Stephen Johnson: Clean
Air Scientific Advisory Committee’s (CASAC) Peer Review of the
Agency’s 2nd Draft Ozone Staff Paper.  EPA-CASAC-07-001.  October 24,
2006.  Sulfur Dioxide Review Docket.  Docket ID No.
EPA-HQ-OAR-2007-0352.  Available at www.regulations.gov.

Henderson.  (2008).  Letter to EPA Administrator Stephen Johnson:  Clean
Air Scientific Advisory Committee’s (CASAC) Peer Review of EPA’s
Risk and Exposure Assessment to Support the Review of the SO2 Primary
National Ambient Air Quality Standards (First Draft, July 2008).
EPA-CASAC-08-019.  August 22, 2008.  Sulfur Dioxide Review Docket.
Docket ID No.  EPA-HQ-OAR-2007-0352.  Available at www.regulations.gov.

Ito K.  (2007).  Characterization of PM2.5, gaseous pollutants, and
meteorological interactions in the context of time-series health effects
models.  J Expos Sci Environ Epidemiol. 17:S45-S60.

Jaffe DH, Singer ME, Rimm AA.  (2003).  Air pollution and emergency
department visits for asthma among Ohio medicaid recipients, 1991-1996.
Environ Res.  91:21-28.

Johns and Simmons (2009).  Memorandum to the Sulfur Oxides NAAQS Review
Docket.  Quality Assurance Review of Individual Subject Data Presented
in Table 3-1 of the 2008 Integrated Science Assessment (ISA) for Sulfur
Oxides.  Air Quality Criteria for Sulfur Oxides Docket.  Docket ID No.
EPA-HQ-ORD-2006-0260-0036.  Available at www.regulations.gov.

Koenig JQ, Covert DS, Hanley QS, van Belle G, Pierson WE.  (1990).
Prior exposure to ozone potentiates subsequent response to sulfur
dioxide in adolescent asthmatic subjects.  Am Rev Respir Dis.
141:377-380.

Lin M, Chen Y, Burnett RT, Villeneuve PJ, Krewski D.  (2004).  Effect of
short-term exposure to gaseous pollution on asthma hospitalizations in
children: a bi-directional case-crossover analysis.  J Epidemiol
Community Health.  57:50-55.

Linn WS, Venet TG, Shamoo DA, Valencia LM, Anzar UT, Spier CE, Hackney
JD.  (1983).  Respiratory effects of sulfur dioxide in heavily
exercising asthmatics. A dose-response study. Am Rev Respir Dis.
127:278-83.

Linn WS, Avol EL, Peng RC, Shamoo DA, Hackney JD.  (1987).  Replicated
dose-response study of sulfur dioxide effects in normal, atopic, and
asthmatic volunteers.  Am Rev Respir Dis.  136:1127-1134.

Linn WS, Avol EL, Shamoo DA, Peng RC, Spier CE, Smith MN, Hackney JD.
(1988).  Effect of metaproterenol sulfate on mild asthmatics’ response
to sulfur dioxide exposure and exercise.  Arch Environ Health.
43:399-406.

Linn WS, Shamoo DA, Peng RC, Clark KW, Avol EL, Hackney JD.  (1990).
Responses to sulfur dioxide and exercise by medication-dependent
asthmatics: effect of varying medication levels.  Arch Environ Health.
45:24-30.

Lunn JE, Knowelden J, Handyside AJ.  (1967).  Patterns of respiratory
illness in Sheffield infant schoolchildren.  Br J Prev Soc Med.  21:7-16

Mortimer KM, Neas LM, Dockery DW, Redline S, Tager IB.  (2002).  The
effect of air pollution on inner-city children with asthma.  Eur Respir
J.  19:699-705.

Neas LM, Dockery DW, Koutrakis P, Tollerud DJ, Speizer FE.  (1995).  The
association of ambient air pollution with twice daily peak expiratory
flow rate measurements in children.  Am J Epidemiol.  141:111-122.

NY DOH.  (2006).  A Study of Ambient Air Contaminants and Asthma in New
York City.  ATSDR Final Report #NTIS PB2006-113523.  Albany, NY; New
York State Energy Research and Development Authority; New York State
Department of Health, for Atlanta, GA; Agency for Toxic Substances and
Disease Registry; U.S. Department of Health and Human Services.

Peel JL, Tolbert PE, Klein M, Metzger KB, Flanders WD, Knox T,
Mulholland JA, Ryan PB, Frumkin H.  (2005).  Ambient air pollution and
respiratory emergency department visits.  Epidemiology. 16:164-174.

Roger LJ, Kehrl HR, Hazucha M, Horstman DH.  (1985).
Bronchoconstriction in asthmatics exposed to sulfur dioxide during
repeated exercise.  J Appl Physiol.  59:784-91.

Samet JM.  (2009).  Letter to EPA Administrator Lisa P. Jackson: Clean
Air Scientific Advisory Committee’s (CASAC) Review of EPA’s Risk and
Exposure Assessment to Support the Review of the SO2 Primary National
Ambient Air Quality Standards: Second Draft.  EPA-CASAC-09-0007, May 18,
2008.  Sulfur Dioxide Review Docket.  Docket ID No.
EPA-HQ-OAR-2007-0352.  Available at   HYPERLINK
"http://www.regulations.gov"  www.regulations.gov .

Schildcrout JS, Sheppard L, Lumley T, Slaughter JC, Koenig JQ, Shapiro
GG.  (2006).  Ambient air pollution and asthma exacerbations in
children: an eight-city analysis.  Am J Epidemiol.  164:505-517.

Schwartz J, Dockery DW, Neas LM, Wypij D, Ware JH, Spengler JD,
Koutrakis P, Speizer FE, Ferris BG, Jr.  (1994).  Acute effects of
summer air pollution on respiratory symptom reporting in children.  Am J
Respir Crit Care Med.  150:1234-1242.

Schwartz J.  (1995).  Short term fluctuations in air pollution and
hospital admissions of the elderly for respiratory disease.  Thorax.
50:531-538.

Schwartz J.  (1996).  Air pollution and hospital admissions for
respiratory disease.  Epidemiology.  7:20-28.

Sheppard D, Saisho A, Nadel JA, Boushey HA.  (1981).  Exercise increases
sulfur dioxide-    induced bronchoconstriction in asthmatic subjects.
Am Rev Respir Dis. 123:486-491.

Sheppard reanalysis (2003).  Ambient Air Pollution and Nonelderly Asthma
Hospital Admissions in Seattle, Washington, 1987-1994.  In: Revised
Analyses of Time-Series Studies of Air Pollution and Health.  Special
report.  Boston, MA: Health Effects Institute; pp. 227-230.

Smith E.  (1993).  Subject Data Supplied by the Researchers for the
Recent Controlled Human Studies Analyzed in the Staff Paper Supplement
and Accompanying Memorandum.  Memorandum to Docket No.  A-84-25, Item
IV-B-5

Thompson R.  (2009).  Sulfur Dioxide Descriptive Statistics Tables.
Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC.  Sulfur Dioxide Review
Docket.  Docket ID No. EPA-HQ-OAR-2007-0352.  Available at
www.regulations.gov.

Thompson R and Stewart MJ.  (2009).   Air Quality Statistics for Cities
Referenced in Key U.S. and Canadian Hospital Admission and Emergency
Department Visits for All Respiratory Causes and Asthma.  Office of Air
Quality Planning and Standards, U.S. Environmental Protection Agency,
Research Triangle Park, NC.  Sulfur Dioxide Review Docket.  Docket ID
No. EPA-HQ-OAR-2007-0352.  Available at   HYPERLINK
"http://www.regulations.gov"  www.regulations.gov .

Tolbert PE, Klein M, Peel JL, Sarnat SE, Sarnat JA.  (2007).
Multipollutant modeling issues in a study of ambient air quality and
emergency department visits in Atlanta.  J Expos Sci Environ Epidemiol.
17:S29–S35

Trenga CA, Koenig JQ, Williams PV.  (1999).  Sulphur dioxide sensitivity
and plasma antioxidants in adult subjects with asthma.  Occup Environ
Med.  56:544-547.

Watkins and Thompson.  (2009).  SO2 Network Review and Background;
OAQPS; Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, Research Triangle Park, NC.  Sulfur Dioxide NAAQS
Review Docket. (OAR-2005-0352). Sulfur Dioxide Review Docket.  Docket ID
No. EPA-HQ-OAR-2007-0352.  Available at   HYPERLINK
"http://www.regulations.gov"  www.regulations.gov .

Wilson AM, Wake CP, Kelly T, Salloway JC. (2005).  Air pollution,
weather, and respiratory emergency room visits in two northern New
England cities: An ecological time-series study.  Environ Res.
97:312-321.

Winterton DL, Kaufman J, Keener CV, Quigley S, Farin FM, Williams PV,
Koenig JQ.  (2001). Genetic polymorphisms as biomarkers of sensitivity
to inhaled sulfur dioxide in subjects with asthma.  Ann Allergy Asthma
Immunol.  86:232-238.

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 AMBIENT AIR QUALITY STANDARDS

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

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

Subpart A—General Provisions

2.  Section 50.14 is amended by revising paragraph (c)(2)(vi) to read as
follows:

§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

NAAQS Pollutant/

Standard/(Level)/

Promulgation Date	Air Quality Data Collected for Calendar Year	Event
Flagging & Initial Description Deadline	Detailed Documentation
Submission Deadline

PM2.5/24-Hr Standard (35 µg/m3)  Promulgated October 17, 2006	2004-2006
October 1, 2007a	April 15, 2008a

Ozone/8-Hr Standard (0.075 ppm)Promulgated March 12, 2008	2005-2007	June
18, 2009a	June 18, 2009a

	2008	June 18, 2009a	June 18, 2009a

	2009	60 Days after the end of the calendar quarter in which the event
occurred or February 5, 2010, whichever date occurs firstb	60 Days after
the end of the calendar quarter in which the event occurred or February
5, 2010, whichever date occurs firstb

NO2/1-Hour Standard(80-100 PPB, final level TBD)	2008	July 1, 2010a
January 22, 2011a

	2009	July 1, 2010a 	January 22, 2011a

	2010	 April 1, 2011a	July 1, 2011 a

SO2/1-Hour Standard (50-100 PPB, final level TBD)	2008	October 1, 2010b
June 1, 2011b

	2009	October 1, 2010b	June 1, 2011 b

	2010	June 1, 2011 b	June 1, 2011 b

	2011	60 Days after the end of the calendar quarter in which the event
occurred or March 31, 2011, whichever date occurs firstb	60 Days after
the end of the calendar quarter in which the event occurred or March 31,
2011, whichever date occurs firstb

aThese 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.

bIndicates 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.

*****

3.  A new Section 50.16 is added to read as follows:

§ 50.16   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

*****

4. EPA proposes to add Appendix A-1 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 §50.4 and
§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.

oroethylene (PTFE Teflon™), 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 µmole/mole) or SRM 1694a (100 µmole/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

with the pollutant are of glass, Teflon™, 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:

where:

Fc = corrected flow rate (L/min at 25° 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:

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 SO 2 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 www.epa.gov/ttn/amtic/qabook.html.)

Figure 1.  UVF SO2 analyzer schematic diagram.

Figure 2. Calibration system using a compressed gas standard.

5. EPA proposes to recode Appendix A to read as follows:

Appendix A-2 to Part 50—Reference Method for the Determination of
Sulfur Dioxide in the Atmosphere (Pararosaniline Method)

6. If EPA finalizes the 4th highest daily maximum form, an Appendix T
would be added as follows:

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 § 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 §§
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 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”).

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.

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 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 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.

If EPA finalizes the 99th percentile form, an Appendix T would be added
as follows:

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 § 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 §§
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