(i.e., overloading of the DNPH cartridge) at high concentrations. While
solutions for these issues have been investigated, these improvements
have not been incorporated into Method TO-11A.
    A recent evaluation of the importance of VOCs and carbonyls to
O3 formation determined that carbonyls, especially
formaldehyde, are very important to O3 formation (Cavender,
2013). CASAC AMMS (U.S. EPA, 2011c) also noted the importance of
carbonyls stating that ``There are many compelling scientific reasons
to measure carbonyls. They are a very important part of O3
chemistry almost everywhere.'' Due to the importance of carbonyls to

understanding O3 chemistry, the EPA believes the need for
carbonyl data outweighs the concerns over the uncertainty in the data.
Therefore, the EPA is proposing to require all required PAMS sites to
measure formaldehyde, acetaldehyde, and acetone. In addition, EPA is
investigating alternatives to further reduce uncertainties in carbonyl
data as described below.
    To improve the carbonyl data that would be collected at required
PAMS sites (and National Air Toxics Trends Station, or NATTS sites
which are also currently measuring carbonyls), the EPA has undertaken
an effort to improve carbonyl sampling and analysis methods to reduce
the uncertainty in carbonyl data. This effort will lead to improvements
to the current Method TO-11A by incorporating solutions to sampling and
analysis issues that have been identified since Method TO-11A was
finalized in 1999, such as the inclusion of an O3 scrubber
in the sampling system to reduce the interference from oxidants such as
O3. Also as part of this effort, the EPA is investigating
alternative cartridge materials that have been identified in the
literature as a replacement for DNPH that may have better collection
efficiency with fewer interferences.
4. Nitrogen Oxides Sampling
    It is well known that NO and NO2 play important roles in
O3 formation (U.S. EPA, 2011a, Section 3.2.2). Under the
current network design, Type 2 PAMS sites are required to measure
NOX (which by definition is the sum of NO and
NO2), and Types 1, 3, and 4 sites are required to measure
NOy which by definition includes NO, NO2, and
other oxidized nitrogen compounds (NOz). NCore sites are
also currently required to measure NOy but are not required
to measure NO2.
    In conventional NOX analyzers, NO2 is
determined as the difference between the measured NO and NOX
concentrations. However, due to the non-selective reduction of oxidized
nitrogen compounds by the molybedenum converter used in conventional
NOX monitors, the NO2 measurement made by
conventional NOX monitors can be biased high due to the
varying presence of NOz compounds that may be reported as
NO2.\244\ The unknown bias from the NOz compounds
is undesirable when attempting to understand O3 chemistry.
---------------------------------------------------------------------------

    \244\ Nitrogen compounds that would likely be reported (along
with NO2) as NO2 with a conventional
NOX monitor include peroxyacetyl nitrate (PAN),
peroxypropionyl nitrate (PPN), peroxymethacryloyl nitrate (MPAN),
and nitric acid (HNO3), and as well as other nitrogen
compounds not listed here.
---------------------------------------------------------------------------

    Improvements in reactive nitrogen measurements have been made since
the original PAMS requirements were promulgated that allow for improved
NO2 measurements. Selective photolytic converters have been
developed that are not significantly biased by NOz compounds
(Ryerson et al., 2000). Monitors using photolytic converters are
commercially available and have been approved as FEMs for the
measurement of NO2. In addition, methods that directly read
NO2 have been developed that allow for very accurate
readings of NO2 without some of the issues inherent to the
``difference method'' used in converter based NOX analyzers.
However, these direct reading NO2 analyzers generally do not
provide an NO estimate, and would need to be paired with a converter-
based NOX monitor or NOy monitor in order to also
measure NO.
    As discussed above, the EPA is proposing to change the PAMS network
design such that PAMS measurements would be required at existing NCore
sites in O3 nonattainment areas. NCore sites currently are
required to measure NO and NOy. NCore sites are not
currently required to measure NO2. Due to the importance of
accurate NO2 data to the understanding of O3
formation, the EPA is proposing to require NO2 measurements
at required PAMS sites. Since existing NCore sites currently measure
NOy, either a direct reading NO2 analyzer or a
photolytic-converter NOX analyzer should be used to meet the
proposed requirement. The EPA believes conventional NOX
analyzers would not be appropriate for making PAMS measurements due to
the uncertainty caused by interferences caused by NOz
compounds.
5. Meteorology Measurements
    Monitoring agencies are currently required to collect surface
meteorology at all PAMS sites. As noted in EPA's TAD (U.S. EPA, 1998)
for the PAMS program, the PAMS requirements do not provide specific
surface meteorological parameters to be monitored. As part of the
implementation efforts for the original PAMS program, a list of
recommended parameters was developed and incorporated into the TAD
which includes wind direction, wind speed, temperature, humidity,
atmospheric pressure, precipitation, solar radiation, and ultraviolet
(UV) radiation. Currently, NCore sites are required to measure the
above parameters with the exceptions of atmospheric pressure,
precipitation, solar radiation, and UV radiation. In recognition of the
importance of these additional measurements for O3, the EPA
is proposing to specify that required PAMS sites are required to
collect wind direction, wind speed, temperature, humidity, atmospheric
pressure, precipitation, solar radiation, and UV radiation. This
proposed revision will provide clarity and consistency to the
collection of surface meteorological parameters important to the
understanding of O3 formation. If PAMS measurements are
moved to NCore sites in O3 nonattainment areas, as is being
proposed, the net impact of this proposed revision to the surface
meteorological requirements for PAMS sites is to add the requirement
for the monitoring of atmospheric pressure, precipitation, solar
radiation, and UV radiation at affected NCore sites.
    The existing PAMS requirements also require the collection of upper
air meteorological measurements at one site in each PAMS area. The term
``upper air meteorological'' is not well defined in the existing PAMS
requirements. As part of the implementation efforts for the original
PAMS program ``mixing height'' was added to the PAMS TAD as a
recommended meteorological parameter to be monitored.
    Most monitoring agencies installed radar profilers to meet the
requirement to collect upper air meteorology. Radar profilers provide
data on wind and speed at multiple heights in the atmosphere. Radio
acoustic sounding system (RASS) profilers are often included with radar
profilers to obtain atmospheric temperature at multiple heights in the
atmosphere and to estimate mixing height. The EPA recognizes that the
upper air data on wind speed and wind direction from radar profilers
can be very useful in O3 modeling. However, many of the
current PAMS radar profilers are old and in need of replacement or
expensive maintenance. In addition, the cost to install and operate
radar profilers at all NCore sites would be prohibitive. Therefore, the
EPA is not proposing to require upper air wind speed and direction as
required meteorological parameters to be monitored at PAMS sites. Where
monitoring agencies find the radar profiler data valuable, continued
operation of existing radar profilers or the installation of new radar
profilers would be appropriate to consider as part of the state's
Enhanced Monitoring Plan.
    As discussed above, mixing height is one upper air meteorological
measurement that has historically been measured at PAMS sites. A number
of methods can be used to measure mixing height in addition to radar
profiler

technology discussed above. Recent developments in ceilometer
technology allow for the measurement of mixing height by changes in
particulate concentrations at the top of the boundary layer (Eresmaa et
al., 2006). Ceilometers provide the potential for continuous mixing
height data at a fraction of the cost of radar profilers. Due to the
importance of mixing height measurements for O3 modeling,
the EPA is proposing to require monitoring agencies to measure mixing
height at PAMS sites. The EPA is aware of a large network of
ceilometers operated by the National Oceanic and Atmospheric
Administration (NOAA) as part of the Automated Surface Observing System
(ASOS). The EPA has been in discussions with NOAA regarding the
potential for these systems to provide the needed mixing height data,
however, the ASOS ceilometers are not currently equipped to provide
mixing height data. Nonetheless, the EPA will continue to work with
NOAA to determine if the ASOS ceilometers can be upgraded to meet the
need for mixing height data, and is including proposed regulatory
language that will allow states a waiver to use nearby mixing height
data from ASOS or other sources to meet the requirement to collect
mixing height data at required PAMS sites.
6. PAMS Season
    Currently, PAMS measurements are required to be taken during the
months of June, July, and August. This 3-month period is referred to as
the ``PAMS Season''. As part of the PAMS re-evaluation, the EPA
considered changes to the PAMS season. The 3-month PAMS season was
originally selected to represent the most active period for
O3 formation. However, the EPA notes that in many areas the
highest O3 concentrations are observed outside of the PAMS
season.\245\ As an example, the highest O3 concentrations in
the Mountain-West often occur during the winter months. Data collected
during the current PAMS season would have limited value in
understanding winter O3 episodes.
---------------------------------------------------------------------------

    \245\ The current O3 monitoring season by state in 40
CFR part 58, appendix D, requires monitoring seasons from 4 to 12
months. As noted in section VI.B. of this preamble, the EPA proposes
to lengthen the seasons further for 33 states.
---------------------------------------------------------------------------

    The CASAC AMMS (U.S. EPA, 2011c) noted in their report to the EPA
that ``it would be desirable to extend the PAMS monitoring season
beyond the current June, July, August sampling period,'' but that ``the
monitoring season should not be mandated and rigid; it should be
flexible and adopted and coordinated on a regional airshed basis (i.e.,
within the same O3 region).'' The EPA agrees with CASAC on
the need for flexibility in determining when PAMS measurements should
be taken to meet local monitoring needs but also agrees with CASAC that
the flexibility ``should not conflict with national goals for the PAMS
program.'' A significant benefit of the standard PAMS season is that it
ensures data availability from all PAMS sites for national- or
regional-scale modeling efforts.
    While the EPA agrees with the potential benefit of extending the
availability of PAMS measurements outside of the current season, we
also considered the burden of requiring monitoring agencies to operate
additional PAMS measurements (e.g., hourly speciated VOC) for periods
that in some cases, might be much longer than the current 3-month
season, for example, if the PAMS season was extended to match each
state's required O3 monitoring season. Being mindful of the
potential burden associated with a lengthening of the PAMS season as
well as the potential benefits of the additional data, the EPA is
proposing to maintain the current 3-month PAMS monitoring season for
required PAMS sites rather than extending the PAMS season to other
periods where elevated O3 may be expected. The EPA believes
that the 3-month PAMS season will provide a consistent data set of
O3 and O3 precursor measurements for addressing
the national PAMS objectives. Monitoring agencies are encouraged to
consider collecting PAMS measurements in additional periods beyond the
required PAMS season as part of the proposed Enhanced Monitoring Plan.
The monitoring agencies should consider factors such as the periods of
expected O3 exceedances and regional consistency when
determining potential expansion of the specific monitoring periods
beyond the required PAMS season.
7. Timing and Other Implementation Issues
    The EPA recognizes that the proposed changes to the PAMS
requirements will require resources and a reasonable implementation
schedule if they are promulgated. The proposed network design changes
would require monitoring agencies to start collection of PAMS
measurements at many NCore sites that are not currently collecting PAMS
measurements. These affected monitoring agencies would need to make
capital investments (primarily for the installation of auto-GCs,
NO2 monitors, and ceilometers). Monitoring agencies will
also need time to develop the expertise, by training existing staff or
otherwise, to successfully collect PAMS measurements. The EPA believes
that the current national funding level of the PAMS program is
sufficient to support these proposed changes, especially in light of
the staggered deployment schedule described below. The current grant
guidance includes the maintenance of a PAMS capital equipment reserve
that could be used to assist monitoring agencies with the purchase of
needed equipment. We also recognize that the proposed revisions would
result in a potential shifting of PAMS resources, and we would work
with the regional offices, affected states, and monitoring
organizations such as the NACAA and the Association of Air Pollution
Control Agencies (AAPCA) to facilitate any shifts in funding during the
implementation phase of the program.
    For these reasons, the EPA is proposing a staggered deployment
schedule for the proposed changes to the PAMS requirements (including
both the monitoring at required PAMS sites and the Enhanced Monitoring
Plans). For areas currently designated as nonattainment for
O3 based on the 2008 NAAQS, the EPA is proposing to require
monitoring agencies to incorporate the proposed PAMS requirements into
their next annual monitoring network plan following promulgation of
these proposed changes (due July 1, 2016, based on current schedules)
and to comply with these proposed PAMS requirements by the following
PAMS season (June 1, 2017, based on current schedules). For new areas
designated as O3 nonattainment based on the initial round of
designations following the promulgation of a revised O3
standard, the EPA is proposing to require monitoring agencies to
incorporate the proposed PAMS requirements into their next annual
monitoring network plan following designations (due July 1, 2018, based
on current schedules) and to comply with new PAMS requirements by the
following PAMS season (June 1, 2019, based on current schedules).
Finally, the EPA is proposing that areas designated as O3
nonattainment following the initial round of designations be allowed 2
years after designation to comply with the proposed PAMS requirements.
The EPA believes that the proposed compliance schedule will allow
monitoring agencies adequate time to implement the proposed PAMS
requirements. The EPA solicits comments on whether the proposed
implementation schedule is practicable, or whether additional time
would be

warranted for installation of new PAMS sites, the development of
Enhanced Monitoring Plans, or other specific new PAMS requirements.

D. Addition of a New Federal Reference Method (FRM) for O3

    To be used in a determination of compliance with the O3
NAAQS, O3 monitoring data must be obtained using either a
FRM or a FEM, as defined in 40 CFR parts 50 and 53. Nearly all the
monitoring methods for O3 currently used by state and local
monitoring agencies are FEM continuous analyzers utilizing a
measurement principle based on quantitative measurement of the
absorption of UV light by O3. This type of O3
analyzer was introduced into the monitoring networks in the 1980s and
has since become the most predominant type of method used because of
its all-optoelectronic design and ease of installation and use. The
existing O3 FRM utilizes a measurement principle based on
quantitative measurement of the chemiluminescence from the reaction of
O3 with ethylene. Ozone analyzers based on this FRM
principle are no longer used for routine O3 field monitoring
and are no longer commercially available. The current list of all
approved FRMs and FEMs capable of providing ambient O3 data
for use in NAAQS attainment decisions may be found on the EPA's Web
site and in the docket for this action (U.S. EPA, 2014g).
    The EPA proposes to revise the FRM to establish a new technique for
measuring O3 in the ambient air. This new technique would be
a new type of analyzer based on Nitric Oxide-chemiluminescence (NO-CL)
methodology. Because of the similarity of this new chemiluminescence
technique to the existing ethylene-chemiluminescence (ET-CL)
methodology, the EPA proposes that it be incorporated into the existing
O3 FRM, using the same calibration procedure. Appendix D of
40 CFR part 50 would be revised to include both the original ET-CL as
well as the new NO-CL methodology. A minor change is proposed to the
existing O3 FRM calibration procedure, which would be
applicable to both chemiluminescence FRM methodologies. The proposed
change in section <IP_ADDRESS> of the calibration procedure in Part 50
provides for more flexibility in the range of the linearity test.
    FRMs, as set forth in several appendices to 40 CFR part 50, serve
two primary purposes. The first is to provide a specified, definitive
methodology for routinely measuring concentrations of various ambient
air pollutants for comparison to the NAAQS in Part 50, for quality
assurance assessment of monitoring data, and for other air monitoring
objectives. The second is to provide a standard of comparison for
determining equivalence to the specified reference method of
alternative and perhaps more practical pollutant measurement methods
(equivalent methods, or FEMs) that can be used in lieu of the FRM for
routine monitoring.
    Some of the FRMs contained in appendices to Part 50 (such as the
original SO2 FRM and the lead FRM) are manual methods that
are completely specified in a step-by-step manner. Others (such as the
O3 FRM) are in the form of a measurement principle along
with an associated calibration procedure that must be implemented in a
commercially-produced FRM analyzer model. Such FRM-type analyzers must
be tested and shown to meet explicit performance and other
qualification requirements that are set forth in 40 CFR part 53
(Ambient Air Monitoring Reference and Equivalent Methods). Each
analyzer model is then considered to be an FRM only upon specific
designation as an FRM by the EPA under the provisions of 40 CFR 53.2
(General requirements for a reference method determination).
    As pollutant measurement technology advances and changes, the
reference methods in part 50 are assessed by the EPA to determine if
improved or more suitable measurement technology is available to better
meet current FRM needs as well as potential future FRM requirements.
New technology can either be presented to the EPA for evaluation by an
FEM applicant under 40 CFR 53.16 (Supersession of reference methods),
or (as in this case) the EPA can originate the process as provided in
40 CFR 53.7 (Testing of methods at the initiative of the
Administrator).
    The current FRM for measuring O3 in the ambient air was
promulgated on April 30, 1971 (36 FR 8186), in conjunction with the
EPA's establishment (originally as 42 CFR part 410) of the first
national ambient air quality standards for six criteria pollutants
(including O3), as now set forth in 40 CFR part 50. On
February 8, 1979 (44 FR 8224), the original O3 FRM
calibration procedure was changed from a wet-chemical standard to a UV
photometric calibration procedure. Minor updates to technical
references were made on July 18, 1997 (62 FR 38895). This FRM is
specified as a measurement principle and calibration procedure in
Appendix D of Part 50. The measurement principle of the FRM is based on
the quantitative measurement of chemiluminescent light intensity
emitted by the chemical reaction of O3 in an air sample with
ethylene gas mixed in a measurement cell. This ET-CL measurement is
calibrated by the specified calibration procedure, which is based on
photometric assay of O3 calibration concentrations in a
dynamic flowing system, using measurement of the absorption of UV light
by the O3 calibration concentrations at a nominal wavelength
of 254 nm.
    At the time of the FRM's original promulgation, analyzers based on
the ET-CL FRM were widely used for field monitoring of O3.
Laboratory testing prior to, during, and following analyzer development
indicated that interferences to which the method was susceptible were
few and relatively minor in magnitude. Further, subsequent field
experience with the FRM analyzers showed them to be stable, accurate,
and reliable. Operation of these FRM analyzers requires a supply of
ethylene gas, provided by an attendant high-pressure compressed gas
cylinder. Installation of this high-pressure cylinder of flammable and
potentially explosive gas proved problematic at many field-monitoring
sites due to fire codes or other safety restrictions. Further, the
ethylene gas cylinder required periodic replacement--a considerable
cost and operational inconvenience.
    Following the development of FEM O3 analyzers based on
UV absorption, use of these newer UV FEM analyzers eventually
supplanted the ET-CL FRM analyzers because the UV analyzers required no
gas supply or other reagents and were much easier to install and
operate. Currently, nearly all compliance monitoring in the U.S. is
carried out with UV absorption type FEM analyzers (Long, 2014). This
transition from ET-CL FRM analyzers to UV absorption analyzers in U.S.
(as well as world-wide) monitoring networks has become so extensive
that analyzer manufacturers no longer manufacture the ET-CL FRM
analyzers. The last new O3 FRM analyzer was designated by
EPA in 1979. As a result, no FRM O3 analyzers are
commercially available to serve as reference standards for testing and
designation of new O3 FEM analyzers, for O3
compliance monitoring, and for quality assurance of field monitors. FRM
units manufactured years ago are becoming increasingly difficult to
maintain in operational condition due to aging of components and lack
of replacement parts (several of the original FRM analyzer
manufacturers no longer exist).
    Until the last few years, relatively few measurement techniques
have been

successfully implemented in a continuous ambient O3 analyzer
model that has achieved designation by the EPA as either an FRM or FEM
(U.S. EPA, 2014g). These include the ET-CL technique, the UV absorption
technique and differential optical absorption spectroscopy (DOAS, an
open-path method represented by two FEM instrument models from
different manufacturers). A relatively new technology is nitric oxide
(NO)-O3 chemiluminescence, which is represented by two FEM
instrument models from a single manufacturer. An even newer technology
is a ``scrubberless'' UV absorption technique that is represented by a
single analyzer model for which FEM designation was recently achieved.
    As noted above, the ET-CL technique is technically advantageous as
an FRM, but its ethylene supply requirement and the lack of
commercially available analyzers severely limit its ability to fulfill
the needs for an O3 FRM. DOAS analyzers are not suitable for
some FRM purposes because of their open-path nature.
    Commercial availability of conventional UV-absorption O3
analyzers is excellent, and their widespread use makes the measurement
technique desirable for consideration as an FRM. However, the technique
is susceptible to potential measurement interference from mercury, some
volatile aromatic hydrocarbons, water, and other compounds that
sometimes occur in ambient air (Spicer et al., 2010). These
interferences are substantially reduced by the use of scrubbers (as
discussed below) in UV FEM analyzers, such that the technique can be
used extensively for compliance monitoring. Although the interferences
are substantially reduced by the use of scrubbers, the potential for
interferences prevents the technique from consideration as an FRM.
    It is important to make a distinction between use of the UV-
absorption measurement technique for assay of O3
concentrations, as described in the FRM calibration procedure of Part
50, Appendix D, and use of the UV absorption technique for measurement
of O3 in ambient air. For assay of calibration
concentrations, the technique is used in a system with clean, zero air
(air that must be free of contaminants which would cause a detectable
response from the O3 analyzer) such that potential ambient-
air-borne interferences are not an issue. Under these clean-air
conditions, the UV assay technique is very accurate and highly
reproducible, so much so that the National Institute of Standards and
Technology (NIST) utilizes it for its O3 Standard Reference
Photometer.
    In contrast, use of the UV-absorption technique to measure
O3 in ambient air is much more difficult because of the need
to deal with UV-absorbing (and hence potential interfering) species
present in ambient air. Ambient UV O3 monitors typically
suppress interferences by using an ``O3 scrubber'' that
attempts to remove O3 from ambient air without removing
potentially interfering species, to create a zero-O3
reference air that still contains any potentially interfering species.
In a differential measurement process that compares the UV absorption
measurement of O3 in the ambient air sample with that in
this zero-O3 reference air, the net effect of interferences
is minimized by cancellation. FEM analyzers using such O3
scrubbers are able to meet the FEM interference test requirements of 40
CFR part 53 and provide adequate O3 monitoring data at most
typical O3 monitoring sites.
    On October 7, 2011, the EPA designated two NO-CL O3
analyzers as FEMs (76 FR 62402). These analyzers use a variation of the
current FRM measurement principle, based on measurement of the
chemiluminescence produced by the chemical reaction of O3
with NO rather than with ethylene. As explained below, the EPA believes
that this variation has performance suitable for an O3 FRM
and offers a substantial implementation advantage over the existing
FRM.
    The NO-CL measurement technique for O3 is quite similar
to the existing ET-CL FRM technique, in that both are based on the
measurement of the intensity of the chemiluminescence resulting from a
chemical reaction of a reactant with the O3 in the ambient
air sample. The principle difference is that the reactant is NO rather
than ethylene. As a potential variation of the FRM measurement
principle, the measurement would be calibrated with the same
calibration procedure specified in the FRM.
    The performance of NO-CL analyzers has been shown to be very
similar to the performance of ET-CL FRM analyzers, providing stable,
accurate, highly reproducible measurements of ambient O3
with minimal potential interferences (U.S. EPA, 2014h). As with ET-CL,
some minor interference from variable humidity in ambient air can be
minimized with a sample air dryer. The analyzers require a supply of NO
gas, typically from a high-pressure compressed gas cylinder. However,
unlike ethylene, NO is neither flammable nor explosive, so use of the
method in field applications is eased considerably relative to use of
ET-CL analyzers. Nitric oxide gas is toxic, but it is possible to use a
cylinder of much less toxic, non-combustible nitrous oxide
(N2O) gas with a photolytic N2O-to-NO converter
to supply NO gas for the instrument as needed. There will be no
requirement for states to switch to NO-CL analyzers; therefore, UV-
absorption FEM analyzers can still be used for routine O3
monitoring. As noted previously, the EPA has designated two NO-CL FEM
analyzers (from the same manufacturer), both of which would qualify for
re-designation as FRMs if the NO-CL technique is finalized as an FRM.
NO-CL analyzers would then be available for those applications where an
FRM analyzer is needed.
    Because of the similarity of the NO-CL technique to the existing
ET-CL technique, the EPA is proposing to amend the ET-CL FRM by adding
the NO-CL technique as a variation to the existing FRM measurement
principle specified in Appendix D of Part 50. The specified calibration
procedure would be applicable to both FRM ET-CL and NO-CL measurement
techniques. Since the existing ET-CL FRM measurement principle remains
a technically adequate FRM, and the proposed new NO-CL FRM is
technically adequate, it is prudent to retain the existing FRM
measurement principle. The designation of all currently designated
O3 FEMs is based on comparison to the ET-CL FRM, so
retention of the ET-CL FRM allows those FEM designations to be
retained.
    Adding the proposed NO-CL measurement technique to the current
O3 FRM would allow at least two commercially available FRM
analyzer models (currently FEMs) to be re-designated as FRMs to fulfill
FRM analyzer needs. Some older FRM analyzers based on the existing ET-
CL measurement principle may still be in operable condition, and there
is no technical reason to cancel their designation by withdrawing the
original ET-CL FRM technique. Additionally, retaining the existing ET-
CL FRM technique allows for the possibility of an instrument
manufacturer offering an ET-CL FRM analyzer in the future.
    The second of the newly introduced O3 measurement
techniques is known as the scrubberless UV absorption (UV-SL)
technique. It utilizes the UV-absorption measurement technique that is
widely used in O3 monitoring networks. The new UV-SL
technique specifies removal of O3 from the sample air for
the zero reference by a gas-phase reaction with NO rather than via a
conventional chemical scrubber. The NO reacts with

the O3 much faster than with other potential interfering
compounds and is very effective at removing the O3 without
affecting other compounds that may be present in the ambient air
sample. The differential UV measurement can effectively eliminate
interferences to an insignificant level. Other potential interference
arising from changes in water vapor concentration can be minimized with
a sample air dryer.
    The UV-SL technique appears to have characteristics that are
advantageous for meeting the requirements of a new O3 FRM.
Analyzers implementing this technique require a supply of NO (such as a
high-pressure gas cylinder). As noted previously in connection with the
NO-CL technique, NO is neither flammable nor explosive, so use of the
method in field applications is eased considerably relative to use of
ET-CL analyzers. Use of N2O gas, also supplied in compressed
gas cylinders but less toxic than NO, is also possible with a
photolytic N2O to NO converter. One commercially available
UV-SL analyzer was approved as an FEM on June 18, 2014 (79 FR 34734).
The performance of the analyzer, as reported by the manufacturer \246\
and some initial field and laboratory studies performed by the EPA
(U.S. EPA, 2014h), suggests that the analyzer may meet existing, as
well as the proposed, requirements for an O3 FRM.
---------------------------------------------------------------------------

    \246\ 2B FEM test data via http://www.twobtech.com/model_211.htm.
---------------------------------------------------------------------------

    The CASAC AMMS provided a peer review of the proposed FRM and
changes to the Part 53 requirements on April 3, 2014. The CASAC AMMS
recommended that the EPA consider the UV-SL as a FRM. The EPA is
independently conducting further laboratory and field tests of the UV-
SL analyzer to verify its performance. Although this new UV-SL
methodology shows substantial promise for future consideration as a new
O3 FRM, there is currently insufficient documented test and
performance information available on the method to propose it as a new
FRM at this time. The EPA is continuing to study the method and assess
its potential suitability as a new O3 FRM, and the EPA
solicits comment on its potential and suitability as an FRM.
    The EPA is not proposing to supersede (replace) the existing
O3 FRM measurement principle under the provisions of 40 CFR
53.16. Rather, for the reasons in the preamble and having conducted the
necessary tests, the EPA is proposing, consistent with 40 CFR 53.7, to
revise the existing O3 FRM to widen the scope of its ET-CL
measurement principle to include the NO-CL measurement technique as
well.
    Following promulgation of the proposed revised O3 FRM
measurement principle, any new candidate O3 FRM analyzers
would be required to use either the ET-CL or NO-CL measurement
principle, and would also be subject to the O3 FRM
performance requirements proposed in 40 CFR part 53. The FRM
calibration procedure specified in Appendix D would apply to both
O3 FRM measurement techniques.
    A substantial number of laboratory tests have confirmed the
excellent performance of the NO-CL analyzers as well as very close
agreement with both ET-CL and UV analyzers in collocated field tests.
Therefore, the EPA believes the proposed FRM measurement principle that
incorporates the NO-CL methodology is the best approach to improve the
availability of FRM analyzers for O3. No other currently
known approach or alternative methodology appears to be more
appropriate for a new FRM. Adding the NO-CL technology to the existing
O3 FRM is also endorsed by the EPA's CASAC AMMS. The EPA
solicits comment on the proposal to retain the existing O3
FRM measurement principle and amend it to include the NO-CL variation
as well. Comments are also solicited on the nature and adequacy of the
proposed revised FRM.
    The generic description of the FRM measurement principle for the
existing ET-CL FRM in Appendix D would be amended to include the NO-CL
variation (see the proposed rule text for Appendix D). As noted
previously, the new NO-CL technique would also use the same calibration
procedure in Appendix D and would be similarly coupled with the
explicit O3 FRM analyzer performance requirements specified
in subpart B of 40 CFR part 53. In addition to the incorporation of the
NO-CL methodology, numerous minor clarifications, wording changes,
additional details, and a more refined numbering system are being
proposed for Appendix D. Accordingly, the entire Appendix D is proposed
to be revised as identified in the proposed regulatory text.
    Because the new NO-CL technique is proposed to be added to the
existing FRM measurement principle, while the existing ET-CL FRM
principle would be retained and remain in effect, all existing
designated FEM analyzer models will continue their designated status.
Thus, this action would cause no negative consequences on monitoring
agencies, and no disruption of, or required change to, their
O3 monitoring programs. Comparative testing has been carried
out at several field monitoring sites under a variety of ambient
conditions, and the results confirm that the proposed new NO-CL FRM
measurement technique provides ambient O3 measurements that
compare and correlate excellently with measurements using the existing
ET-CL measurement principle, with no significant bias, offset, or
discrepancy (U.S. EPA, 2014h).

E. Revisions to the Procedures for Testing Performance Characteristics
and Determining Comparability Between Candidate Methods and Reference
Methods

    The only substantial changes proposed to the requirements of Part
53 are in Tables B-1 and B-3 of Subpart B. Table B-1 has been updated
in recent years with regard to FRM and FEM methods for SO2
(74 FR 64877, December 8, 2009) and CO (76 FR 54294, August 31, 2011).
Similar update changes to Table B-1 are proposed here for
O3. Modest changes proposed for Table B-3 would add new
interferent test concentrations specifically for NO-CL analyzers,
adding a test for NO2. The table would also clarify that the
existing test concentrations apply to ET-CL O3 analyzers.
Figure B-5 is revised to correct a minor inconsistency in the
``Calculations'' column for the two ``Precision'' rows to change ``%
URL'' to ``% Standard Deviation.''
    Several changes to the performance requirements given in Table B-1
are proposed for O3. The performance requirements for
``standard range'' instruments would be updated to be more consistent
with current O3 analyzer performance capabilities. The noise
requirement limit would be reduced from 0.005 to 0.001 ppm for
O3 analyzers, the lower detectable limit would be reduced
from 0.010 to 0.003 ppm, and the maximum interference equivalent limits
would be reduced from 0.02 to 0.005 ppm for each potential interfering
agent (interferent). The performance limit requirement for the total of
all interferents is proposed to be withdrawn for O3 methods.
This withdrawal is appropriate because O3 analyzer test
performance, as reported in recent FEM applications, has shown that the
limits established for individual interferents are sufficiently
effective to define adequate analyzer performance, and the separate
limit for the total of all interferences is unnecessary.
    Maximum zero drift for O3 analyzers would be reduced
from 0.02 to 0.004 ppm. The existing limit for span drift at 20% of the
upper range limit (URL) is proposed to be withdrawn. Analyzer
performance test results have clearly

shown that the existing 80% URL limits are fully adequate and better
specify span drift performance and that the 20% URL span drift limits
are ineffective and unnecessary. The span drift limit applicable to
O3 analyzers is proposed to be reduced from 5.0%
to 3.0%. Lag time limits would be reduced from 20 to 2
minutes, and rise and fall time limits would be similarly reduced from
15 to 2 minutes.
    For precision, the EPA proposes to change the form of the precision
limit specifications (at both 20% and 80% of URL) for O3
analyzers from ppm to percent (of the URL). This change would make the
limits responsive to higher and lower measurement ranges, as
appropriate, and is consistent with the same change previously made in
the corresponding precision requirements for SO2 and CO
analyzers. Both limits would be set at 2% for O3 analyzers,
which is equivalent to, and, therefore effectively unchanged, from the
existing limits of 0.01 ppm (for a URL of 0.5 ppm). Although the
changes to Part 53 proposed here are generally restricted to methods
for O3, this change in form for the precision limits is
proposed to be extended to methods for NO2 as well, to
simplify Table B-1 and make it consistent for all pollutants covered by
the Table. The precision limits that would be applicable to methods for
NO2 are proposed to be changed to 4% and 6% of the URL (for
20% and 80% of the URL, respectively). These values are exactly
equivalent to the existing limits of 0.020 ppm and 0.030 ppm,
respectively, for the specified URL of 0.5 ppm. Therefore, these
precision limits for NO2 remain effectively unchanged, but
specified as a percent rather than an absolute concentration. A new
footnote is proposed for Table B-1 to clarify that these revised
precision limits are given as ``standard deviation expressed as percent
of the URL.'' Therefore, Figure B-5 will be revised to correct a minor
inconsistency in the ``Calculation'' column for the two ``Precision''
rows to change the ``% URL'' to ``% Standard Deviation.''
    The EPA has reviewed the documented performance of currently
designated FRM and FEM methods for O3 (that are still in
commercial production or in service in monitoring networks) and has
verified that all would meet the proposed new performance requirements
for O3 methods (Long, 2014). Therefore, adoption of the
proposed new performance requirements in Table B-1 would not require
the withdrawal or cancelation of the FRM or FEM designation of any such
O3 analyzers.
    Finally, to meet a need for analyzers with more sensitive
measurement ranges for monitoring in relatively clean areas, new,
``lower range'' performance limit requirements are proposed for
O3 analyzers. These lower range limits are set forth in a
new ``lower range'' column in Table B-1 and would be optional. But
where a lower measurement range is included in the FRM or FEM
designation, these proposed new requirements would provide more
stringent performance for analyzers commensurate with greater accuracy
for low-level measurements in lower-level concentration ranges.
    The EPA believes that these proposed changes in the performance
requirements of Tables B-1 and B-3 are appropriate, based on analyzer
performance data available from analyzer manuals and recent FRM and FEM
applications. The EPA solicits comment as to whether the proposed
changes are reasonable, appropriate, beneficial, and achievable without
undue burden.
    The EPA is proposing minor changes to the general provisions in
subpart A of Part 53 to ease the administrative burden associated with
processing and reviewing modification requests to existing FRMs and
FEMs. This change in 40 CFR 53.14(c) will extend the length of time for
the Administrator to take action on a request for modification of a
reference or equivalent method from 30 days to 90 days. Section
53.14(c) would read: ``Within 90 calendar days after receiving a report
under paragraph (a) of this section, the Administrator will take one or
more of the following actions:'' The EPA is also proposing to remove
the obsolete provision that manufacturers who offered PM2.5
or PM10-2.5 samplers or analyzers for sale as part of a FRM
or FEM may continue to do so only so long as updates of the Product
Manufacturing Checklist are submitted annually. This change is
accomplished through the removal of section (i) from 40 CFR 53.9 and
Figure E-2 from subpart E of Part 53.

VII. Implementation of Proposed O3 Standards

    The proposed revisions to the primary and secondary O3
NAAQS discussed in sections II.E and IV.G of this preamble, if
finalized, would trigger a process under which states \247\ make
recommendations to the Administrator regarding area designations, and
the EPA promulgates the final area designations. States would also be
required to review, modify, and supplement their existing SIPs. The
proposed O3 NAAQS revisions would also affect the
transportation conformity and general conformity processes. The revised
O3 NAAQS and the subsequent designations process could
affect which preconstruction permitting requirements apply to
O3 in some areas and the nature of those requirements in
others.
---------------------------------------------------------------------------

    \247\ This and all subsequent references to ``state'' are meant
to include state, local, and tribal agencies responsible for the
implementation of an O3 control program.
---------------------------------------------------------------------------

    The EPA has regulations in place addressing the requirements for
SIPs and several provisions in these existing rules cover O3
(40 CFR part 51). States likewise have provisions in their SIPs to
address air quality for O3 and to implement the existing
O3 NAAQS. The EPA has also provided general guidance on the
development of SIPs for all pollutants and administration of
construction permitting programs, as well as specific guidance on
implementing the O3 NAAQS in some contexts under the CAA and
the EPA regulations.
    When the EPA proposes to revise a NAAQS for a particular criteria
pollutant, it considers the extent to which existing EPA regulations
and guidance are sufficient to implement the standard and whether any
revisions or updates to those regulation and guidance would be helpful
or appropriate in facilitating the implementation of the revised
standard by states. The CAA does not require that the EPA promulgate
new implementing regulations every time that a NAAQS is revised.
Likewise, the CAA does not require the issuance of additional
implementing regulations or guidance by the EPA before a revised NAAQS
becomes effective. Existing EPA regulations may be sufficient in many
cases to enable the EPA and the states to begin the process of
implementing a revised NAAQS. However, where the nature of revisions to
a NAAQS indicate that additional EPA regulations or guidance (or
revisions to existing regulations or guidance) may be helpful to
implement unique aspects of the revised standard, the EPA endeavors to
provide those regulations and guidance in a timely way to facilitate
preparation of SIPs plans. It is important to note, however, that the
existing EPA regulations in 40 CFR part 51 applicable to SIPs generally
and to particular pollutants continue to apply even without such
updates. Accordingly, the discussion below provides the EPA's current
thoughts about the extent to which revisions to existing regulations
and additional guidance might be helpful or appropriate to aid in the

implementation of a revised O3 NAAQS, should one be
finalized through this rulemaking.
    This section provides background information for understanding the
possible implications of the proposed NAAQS changes in some areas, and
describes the EPA's plans for providing revised rules or additional
guidance on some subjects in a timely manner to assist states with
their implementation efforts under the requirements of the CAA. This
section also describes existing EPA interpretations of CAA requirements
and other EPA guidance relevant to implementation of revised
O3 NAAQS. Relevant CAA provisions that provide potential
flexibility with regard to meeting implementation timelines are also
discussed.
    This section contains a discussion of how existing requirements to
reduce the impact on O3 concentrations from the stationary
source construction in permit programs under the CAA may be affected by
the proposed revisions of the O3 NAAQS. These are the PSD
and Nonattainment New Source Review (NNSR) programs. To facilitate the
timely implementation of the PSD requirements, the EPA proposes as part
of this rulemaking to add a grandfathering provision to its regulations
that would apply to certain PSD permit applications that are pending on
the effective date of the revised O3 NAAQS. If the proposed
NAAQS revisions are finalized, this grandfathering provision could be
finalized at the same time as the revised NAAQS (see section VII.D of
this preamble).
    The EPA intends to propose additional regulations and issue
additional guidance, as necessary, related to the implementation
requirements for any revised O3 NAAQS resulting from this
proposal. The EPA intends to take these actions on a schedule that
provides timely assistance to air agencies. Accordingly, in this
section, the EPA solicits comment on several issues that the agency
anticipates addressing in future guidance or regulatory actions to
assist with implementation of the revised O3 NAAQS. Because
these issues are not relevant to the establishment of the NAAQS, and
the CAA does not require that the EPA provide implementation rules or
guidance for each revised NAAQS, the EPA does not expect to respond,
nor is the agency required to respond, to these comments in the final
action on this proposal. However the EPA expects these comments will be
helpful as future guidance and regulations are developed.

A. NAAQS Implementation Plans

1. Background
    As directed by the CAA, reducing pollution to meet national air
quality standards always has been a shared task, one involving the
federal government, states, tribes and local air quality management
agencies. The EPA develops regulations and strategies to reduce
pollution on a broad scale, while states and tribes are responsible for
implementation planning and any additional emission reduction measures
necessary to bring areas into attainment. The agency supports
implementation planning with technical resources and guidance, while
states and local agencies use their knowledge of local needs and
opportunities in designing emission reduction strategies that will work
best for their industries and communities.
    This partnership has proved effective since the EPA first issued
O3 standards more than three decades ago. For example, 101
areas were designated as nonattainment for the 1-hour O3
standards issued in 1979. As of the end of 2013, air quality in 98 of
those areas meets the 1-hour standards. The EPA strengthened the
O3 standards in 1997, shifting to an 8-hour standard to
improve public health protection, particularly for children, the
elderly, and other sensitive individuals, against effects such as
reduced lung function and respiratory symptoms, hospital and emergency
room visits for asthma, and possible irreversible damage to the lungs.
The 1997 standards drew significant public attention when they were
proposed, with numerous parties voicing concerns about states' ability
to comply. However, after close collaboration between the EPA, states,
tribes and local governments to reduce O3-forming
pollutants, significant progress has been made. Air quality in 90% of
the original 113 areas designated as nonattainment for the 1997
O3 NAAQS now meets the 1997 standards. The EPA designated 46
areas as nonattainment for the 2008 O3 NAAQS in 2012. We
expect these areas to make similar progress in achieving clean air.
    The majority of man-made NOX and VOC emissions that
contribute to O3 formation in the U.S. come from the
following sectors: On-road and nonroad mobile sources, industrial
processes (including solvents), consumer and commercial products, and
the electric power industry. In 2011, the most recent year for which
the National Emissions Inventory (NEI) is available, onroad and nonroad
mobile sources accounted for about 60% of annual NOX
emissions; and the electric power industry accounted for about nearly
15%. With respect to VOC, industrial processes (including solvents)
accounted for about 57% of manmade VOC emissions; and mobile sources
accounted for about 39%. Emissions from natural sources, such as trees,
also comprise around 70% of total VOC emissions nationally, with a
higher proportion during the O3 season and in areas with
more vegetative cover. See section VII.F of this preamble for more
detail on background O3.
    Since 2000, the EPA has issued numerous emissions and fuels
standards for on-road and nonroad mobile sources, as well as emissions
standards for many types of stationary sources. Benefits from new
engine standards increase each year as older, more-polluting vehicles
and engines are replaced with newer, cleaner models. Benefits from fuel
programs generally begin as soon as a new fuel is available. The
ongoing emission reductions from federal programs such as these will
provide for substantial emissions reductions well into the future, and
will complement state and local efforts to attain any revised
O3 NAAQS.
    Over the past 15 years, the EPA has established new emissions
standards under title II of the CAA, 42 U.S.C. 7521-7574, for numerous
classes of automobile, truck, bus, motorcycle, earth mover, aircraft,
and locomotive engines, and for the fuels used to power these engines.
The EPA also established new standards for the smaller engines used in
small watercraft, and lawn and garden equipment. In March 2008, the EPA
promulgated new standards for locomotive and for marine diesel engines
and in April 2010 the EPA promulgated new standards for Category 3 (C3)
engines installed on U.S. ocean-going vessels and to marine diesel
fuels produced and distributed in the U.S. In September 2011, the EPA
and the National Highway Transportation Safety Administration
established greenhouse gas and fuel efficiency standards for new 2014-
2018 model year medium and heavy-duty engines and vehicles. In addition
to improving fuel efficiency and reducing greenhouse gas emissions this
rule reduces emissions of NOX from the subject vehicles. In
March 2014, the EPA promulgated Tier 3 standards for tailpipe and
evaporative emissions from passenger cars, light-duty trucks, medium-
duty passenger vehicles, and some heavy-duty vehicles. The associated
gasoline sulfur standard will enable more stringent vehicle emissions
standards and will make existing emissions control systems more
effective. Compared to current standards, the VOC and NOX
tailpipe

standards for light-duty vehicles represent approximately an 80%
reduction from today's fleet average, and the heavy-duty tailpipe
standards represent about a 60% reduction in VOC and NOX.
    The emission reductions from all of these mobile source programs
are significant and will continue to be realized throughout the
implementation period for any revised O3 NAAQS. The EPA
projects that between 2011 and 2025, onroad and nonroad mobile
NOX will decline by more than 60% and onroad and nonroad
mobile VOC will decline by more than 50%.\248\
---------------------------------------------------------------------------

    \248\ ``Regulatory Impact Analysis for the Proposed Revisions to
the National Ambient Air Quality Standards for Ground-Level Ozone,''
(December 2014) at http://www.epa.gov/ttnecas1/ria.html.
---------------------------------------------------------------------------

    The reduction of VOC emissions from industrial processes has been
achieved either directly or indirectly through implementation of
control technology standards, including maximum achievable control
technology (MACT), reasonably available control technology (RACT), and
best available control technology (BACT) standards; or is anticipated
due to proposed or upcoming proposals based on generally available
control technology or best available controls under provisions related
to consumer and commercial products. These standards have resulted in
VOC emission reductions of almost a million tons per year accumulated
starting in 1997 from a variety of sources including combustion
sources, coating categories, and chemical manufacturing. The EPA also
finalized emission standards and fuel requirements for new stationary
engines. In the area of consumer and commercial products, the EPA
finalized new national VOC emission standards for aerosol coatings in
2008 and will review and revise, as necessary, existing rules for
household and institutional consumer products, architectural and
industrial maintenance coatings, and automobile refinish coatings.
Additionally, in O3 nonattainment areas, we anticipate
reductions of an additional 10,000 tons per year as states adopt rules
implementing control techniques recommendations issued in 2008 for four
additional categories of consumer and commercial products, such as
surface coatings and adhesives used in industrial manufacturing
operations. These emission reductions primarily result from solvent
controls and typically occur where and when the solvent is used, such
as during manufacturing processes.
    As noted above, the power industry is responsible for a nearly 15%
of NOX emissions across the U.S. Power industry emission
sources include large electric generating units (EGU) and some large
industrial boilers and turbines. The EPA's Clean Air Interstate Rule
(CAIR), issued on March 10, 2005 (70 FR 25612; May 12, 2005), was
designed to permanently reduce power industry emissions of
NOX in the eastern U.S. The first phase of the cap was to
begin in 2009, and a lower second phase cap was to begin in 2015. The
EPA had projected that by 2015, the CAIR and other programs would
reduce NOX emissions during the O3 season by
about 50% and annual NOX emissions by about 60% from 2003
levels in the Eastern U.S. However, on July 11, 2008, and December 23,
2008, the U.S. Court of Appeals for the DC Circuit (DC Circuit) issued
decisions on petitions for review of the CAIR. In its July 11 opinion,
the court found CAIR unlawful and decided to vacate CAIR and its
associated Federal implementation plans (FIPs) in their entirety. State
of North Carolina v. EPA, 531 F. 3d 896. On December 23, 2008, however,
the court granted EPA's petition for rehearing to the extent that it
remanded without vacatur for EPA to conduct further proceedings
consistent with the Court's prior opinion. Under this decision, CAIR
will remain in place only until replaced by EPA with a rule that is
consistent with the Court's July 11 opinion.
    The EPA issued the final CSAPR on July 6, 2011 (76 FR 48208; August
8, 2011), to replace CAIR. CSAPR requires states to significantly
improve air quality by reducing power plant emissions that contribute
to O3 and/or fine particle pollution in other states. CSAPR
requires a total of 28 states to reduce annual SO2
emissions, annual NOX emissions and/or O3 season
NOX emissions to assist downwind states in attaining the
1997 O3 and fine particle and 2006 PM2.5 NAAQS.
On December 30, 2011, the D.C. Circuit issued an order staying CSAPR
and ordering the EPA to continue implementing CAIR. Subsequently, on
August 21, 2012, the D.C. Circuit issued an opinion vacating CSAPR. EME
Homer City Generation LP v. EPA, 696 F. 3d 7. In its decision the Court
again instructed the EPA to continue administering CAIR. The U.S. and
other parties appealed the D.C. Circuit decision to the U.S. Supreme
Court and on April 29, 2014, the U.S. Supreme Court issued an opinion
reversing the judgment of the D.C. Circuit, upholding the EPA's
interpretation of the CAA ``good neighbor'' provision (CAA section 110
(a)(2)(d)(ii)), and remanding the case back to the D.C. Circuit for
further proceedings consistent with the Supreme Court opinion. EME
Homer City Generation LP v. EPA, 134 S. Ct. 1584. On June 26, 2014, the
U.S. Government filed a motion with the D.C. Circuit to lift the stay
of the CSAPR. The D.C. Circuit has since lifted the stay of the rule.
Order, Document #1518738, EME Homer City Generation, L.P. v. EPA, Case
#11-1302 (D.C. Cir. Oct. 23, 2014).
    The EPA proposed the Clean Power Plan for existing power plants on
June 2, 2014 (79 FR 34830; June 18, 2014). In this action the EPA
proposed state-specific rate-based goals for CO2 emissions
from the power sector, as well as guidelines for states to follow in
developing plans to achieve the state-specific goals. This rule, as
proposed, would continue progress already underway to reduce
CO2 emissions from existing fossil fuel-fired power plants
in the U.S. Actions taken to comply with the proposed guidelines would
reduce emissions of CO2 and other air pollutants, including
SO2, NOX and directly emitted PM2.5,
from the electric power industry. The EPA estimates that the Clean
Power Plan, as proposed, would reduce precursors for both O3
and particulate matter leading to decreases in the concentrations of
those pollutants of approximately 25% in 2030.
    It should also be noted, in general, that new EGUs are subject to
NOX limits under New Source Performance Standards (NSPS)
under CAA section 111, as well as either PSD or NNSR requirements. The
EPA's regulations for commercial, industrial and solid waste
incinerators set standards for NOX and several air toxics
for all commercial incinerators, as required under Section 129 of the
Act. Air toxics rules for industrial boilers will yield co-benefit
NOX reductions as a result of tune-ups and energy efficiency
measures, especially from boilers that burn coal. And several new
source performance standards and air toxics standards are expected to
make further cuts to NOX and VOC emissions from new and
existing sources of pollution. These include upcoming review and
revisions for gas turbines and municipal waste combustors, along with
proposed requirements for the petroleum refining industry. The NSPS and
air toxics standards that have recently taken effect for stationary
engines will also make cuts to NOX and VOC emissions. The
EPA also anticipates reductions in O3 precursors to result
from implementation of the Mercury and Air Toxics Standard rule, as
well as from measures to address Regional Haze best

available retrofit technology (BART) determinations.
    While the EPA uses its regulatory opportunities to reduce
NOX and VOCs, the agency also is pursuing non-regulatory
efforts as we strive toward cleaner air. Energy Star, a joint program
of the EPA and the U.S. Department of Energy, protects the environment
and saves money through energy efficient products and practices.
Improving energy efficiency in homes, buildings and industry helps
reduce all emissions from the power sector--including NOX--
while reducing compliance costs for electricity providers. As part of
its new Advance Program, the EPA is working collaboratively with state,
local, and tribal governments that want to take steps to reduce air
pollution in O3 and particulate matter attainment areas.
Although these areas are not currently subject to nonattainment
planning requirements, Advance Program participants are interested in
undertaking their own planning efforts with the goal of keeping their
air healthy and creating an improved buffer against future air quality
violations. Participating areas are implementing a mix of voluntary and
mandatory measures relating to mobile, area, and point sources as well
as energy efficiency measures, and they are also pursuing education and
awareness programs to improve their communities' understanding of air
quality issues.
    The EPA recognizes that a number of areas of the country have been
working to reduce O3 precursors for many years and now may
need to turn to newer, more innovative approaches for reducing
emissions as they develop their implementation plans. These approaches,
such as smart growth policies and renewable energy portfolios, hold
great promise for improved air quality and health, and the EPA is
working with air quality agencies and stakeholders to identify ways to
include these types of programs in implementation plans. For example,
the EPA developed a roadmap for giving SIP credit to energy efficiency/
renewable energy projects.\249\ Recognition of innovative programs will
allow states and tribes to pursue effective strategies that address
some of the more challenging issues affecting air quality, such as land
use planning, ever increasing motor vehicle use, and planning for long-
term energy needs.
---------------------------------------------------------------------------

    \249\ ``The Roadmap for Incorporating Energy Efficiency/
Renewable Energy Policies and Programs into State and Tribal
Implementation Plans,'' (July 2012) at http://epa.gov/airquality/eere/.
---------------------------------------------------------------------------

    With respect to agricultural sources, the U.S. Department of
Agriculture (USDA) has approved conservation systems and activities
that reduce agricultural emissions of NOX and VOC. The EPA
recognizes that USDA has been working with the agricultural community
to develop site-specific conservation systems and activities to control
emissions of O3 precursors. The EPA will continue to work
with USDA on these activities with efforts to identify and/or improve
the control efficiencies, prioritize the adoption of these conservation
systems and activities, and ensure that appropriate criteria are used
for identifying the most effective application of conservation systems
and activities.
    The EPA will work together with USDA and with states to identify
appropriate measures to meet the primary and secondary standards,
including site-specific conservation systems and activities. Based on
prior experience identifying conservation measures and practices to
meet the PM NAAQS requirements, the EPA will use a similar process to
identify measures that could meet the O3 requirements. The
EPA anticipates that certain USDA approved conservation systems and
activities that reduce agricultural emissions of NOX and VOC
may be able to satisfy the requirements for applicable sources to
implement reasonably available control measures for purposes of
attaining the primary and secondary O3 NAAQS.
    The agency also is active in work to reduce the international
transport of O3 and other pollutants that can contribute to
``background'' O3 levels in the U.S. Under the Convention on
Long-Range Transboundary Air Pollution (LRTAP) of the United Nations
Economic Commission for Europe, the U.S. has been a party to the
Protocol to Abate Acidification, Eutrophication, and Ground-level Ozone
(known as the Gothenburg Protocol) since 2005. The U.S. is also active
in the LRTAP Task Force for Hemispheric Transport of Air Pollution,
which in 2010 produced a comprehensive assessment of the
intercontinental transport of air pollution (including O3)
in the northern hemisphere.
    The U.S. has worked bilaterally with Canada under the US-Canada Air
Quality Agreement to adopt an Ozone Annex to address transboundary
O3 impacts. The EPA also continues to work with rapidly
growing countries such as China on air quality management activities
and the development of analytical tools to help these countries address
significant air quality problems, including the emissions of
O3-forming pollutants. This work includes supporting China's
efforts to rapidly deploy power plant pollution controls that can
achieve NOX reductions of at least 80 to 90%.
    We know that developing the implementation plans that outline the
steps a nonattainment area will take to meet an air quality standard
requires a significant amount of work on the part of state, tribal or
local air agencies. The EPA routinely looks for ways to reduce this
workload, including assisting with air quality modeling by providing
inputs such as emissions, meteorological and boundary conditions; and
sharing national-scale model results that states can leverage in their
development of their attainment demonstrations. At the same time, we
work with air agencies to provide implementation flexibility to the
extent allowed by law.
2. Timing of Rules and Guidance
    In public comment periods associated with several recent
rulemakings, the EPA received comments from a variety of states and
organizations asking for rules and guidance associated with a revised
NAAQS to be issued in a timely manner. Although issuance of such rules
and guidance is not a part of the NAAQS review process, National Ass'n
of Manufacturers v. EPA, 750 F. 3d 921, 926-27 (D.C. Cir. 2014), toward
that end the EPA intends to produce appropriate revisions to necessary
implementation rules and provided additional guidance in time frames
that would be more useful to states when developing their
implementation plans than has been the case with some previous rules
and guidance.
    Certain requirements under the PSD preconstruction permit review
program apply immediately to a revised NAAQS upon the effective date of
that NAAQS, unless the EPA has established a grandfathering provision
through rulemaking. To ensure a smooth transition to a revised
O3 NAAQS, the EPA is proposing a grandfathering provision
similar to the one finalized in the 2012 PM2.5 NAAQS Rule.
See section VII.D of this preamble for more details on the PSD program.
    Promulgation of the NAAQS starts a clock for the EPA to designate
areas as either attainment or nonattainment. State recommendations for
area designations are due to the EPA within 12 months of promulgation
of the NAAQS. In an effort to allow states to make more informed
recommendations, the EPA intends to issue guidance concerning the
designations process within 4 months of promulgation of the NAAQS, or
approximately 8 months before state recommendations are due. The EPA
has issued designation

guidance for several NAAQS in recent years. While generally the EPA
considers information related to the same factors in making designation
decisions, the guidance is tailored to the particular NAAQS. The EPA
anticipates that the guidance for a revised NAAQS resulting from this
proposal would be similar to the designation guidance for the 2008
O3 NAAQS. The EPA generally completes area designations 2
years after promulgation of a NAAQS. See section VII.C of this preamble
for additional details on designations.
    Clean Air Act section 110 requires SIPs to be submitted within 3
years of promulgation of a revised NAAQS. These SIPs are referred to as
``infrastructure SIPs.'' The EPA issued general guidance on submitting
infrastructure SIPs on September 13, 2013.\250\ It should be noted that
this guidance did not address certain state planning and emissions
control requirements related to interstate pollution transport. Should
this guidance need to be modified for this prospective O3
NAAQS, the EPA intends to issue that updated guidance no later than 1
year after promulgation of a revised O3 NAAQS. See section
VII.B.3 of this preamble for additional information on infrastructure
SIPs.
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    \250\ See memorandum from Stephen D. Page to Regional Air
Directors, ``Guidance on Infrastructure State Implementation Plan
(SIP) Elements under Clean Air Act Sections 110(a)(1) and
110(a)(2)'' September 13, 2013.
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    The EPA intends to propose any appropriate rules for assisting with
implementing any revised O3 NAAQS resulting from this
proposal within 1 year after a revised NAAQS is established. The rules
that EPA is considering, as with implementation of previous NAAQS,
would address nonattainment area classification methodologies, SIP due
dates, attainment dates, and required implementation programs such as
NNSR and conformity. At that same time the EPA intends to address any
modifications needed as a result of this revised NAAQS to guidance
pertaining to developing nonattainment area emissions inventories and
attainment demonstrations, and demonstrating conformity. The EPA
anticipates finalizing these items by the time areas are designated
nonattainment. Finalizing rules and guidance by this time would provide
air agencies with the information to develop any CAA-required SIPs
associated with nonattainment designations. In an area designated as
nonattainment, new major sources and major modifications at existing
sources are required to comply with NNSR requirements including the
application of ``lowest achievable emission rate'' (LAER) and emissions
offsets at ratios prescribed by the CAA. See section VII.B.4 of this
preamble for additional information on nonattainment SIPs.
3. Section 110 State Implementation Plans
    The CAA section 110 specifies the general requirements for SIPs.
Within 3 years after the promulgation of revised NAAQS (or such shorter
period as the Administrator may prescribe \251\) each state must adopt
and submit ``infrastructure'' SIPs to the EPA to address the
requirements of section 110(a)(1) and (2), as applicable. These
``infrastructure SIPs'' establish the basic state programs to
implement, maintain, and enforce revised NAAQS and provide assurances
of state resources and authorities. States are to develop and maintain
an air quality management infrastructure that includes enforceable
emission limitations, a permitting program, an ambient monitoring
program, an enforcement program, air quality modeling capabilities, and
adequate personnel, resources, and legal authority. Section 110(b) of
the CAA provides that the EPA may extend the deadline for the
``infrastructure'' SIP submission for a revised secondary standard by
up to 18 months beyond the initial 3 years. If both the primary NAAQS
and a distinct secondary NAAQS are finalized, the EPA currently
believes it would be more efficient for states and the EPA if each
affected state submits a single section 110 infrastructure SIP that
addresses both standards at the same time (i.e., within 3 years of
promulgation of the O3 NAAQS), because the EPA does not at
present discern any need for there to be any significant substantive
difference in the infrastructure SIPs for the two standards. However,
the EPA also recognizes that states may prefer the flexibility to
submit the secondary NAAQS infrastructure SIP at a later date. The EPA
solicits comment on these infrastructure SIP submittal timing
considerations, and specifically on challenges that would justify
needing 18 additional months to complete the submission of an
infrastructure SIP for the secondary standard.
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    \251\ While the CAA allows the EPA to set a shorter time for
submission of these SIPs, the EPA does not currently intend to do
so.
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    It is the responsibility of each state to review its air quality
management program's infrastructure SIP provisions in light of each
revised NAAQS. Most states have revised and updated their
infrastructure SIPs in recent years to address requirements associated
with recently revised NAAQS. It may be the case that for a number of
infrastructure elements, the state may believe it has adequate state
regulations already adopted and approved into the SIP to address a
particular requirement with respect to the revised O3 NAAQS.
For such portions of the state's infrastructure SIP submittal, the
state may provide a ``certification'' specifying that certain existing
provisions in the SIP are adequate. Although the term ``certification''
does not appear in the CAA as a type of infrastructure SIP submittal,
the EPA sometimes uses the term in the context of infrastructure SIPs,
by policy and convention, to refer to a state's SIP submission. If a
state determines that its existing EPA-approved SIP provisions are
adequate in light of the revised O3 NAAQS with respect to a
given infrastructure SIP element (or sub-element), then the state may
make a ``certification'' that the existing SIP contains provisions that
address those requirements of the specific CAA section 110(a)(2)
infrastructure elements. In the case of a certification, the submittal
does not have to include another copy of the relevant provision (e.g.,
rule or statute) itself. Rather, the submittal may provide citations to
the already SIP-approved state statutes, regulations, or non-regulatory
measures, as appropriate, which meet the relevant CAA requirement. Like
any other SIP submittal, such certification can be made only after the
state has provided reasonable notice and opportunity for public
hearing. This ``reasonable notice and opportunity for public hearing''
requirement for infrastructure SIP submittals appears at section
110(a), and it comports with the more general SIP requirement at
section 110(l) of the CAA. Under the EPA's regulations at 40 CFR part
51, if a public hearing is held, an infrastructure SIP submittal must
include documentation by the state that the public hearing was held in
accordance with the EPA's procedural requirements for public hearings.
See 40 CFR part 51, Appendix V, paragraph 2.1(g), and 40 CFR 51.102.
4. Nonattainment Area Requirements
    Part D of the CAA describes the various program requirements that
apply to states with nonattainment areas for different NAAQS. Section
182 (found in subpart 2 of Part D) includes the SIP requirements that
govern the O3 program, and supplements the more general
nonattainment area requirements in sections 172 and 173. Under CAA
section 182, states generally are required to submit attainment

demonstration SIPs within 3 or 4 years of the effective date of area
designations by the EPA, depending on the classification of the area.
These plans need to show how the nonattainment area will attain the
primary O3 standard ``as expeditiously as practicable,'' but
no later than within the relevant time frame from the effective date of
designations associated with the classification of the area.
    Section 181(a)(1) of the CAA establishes classification categories
for areas designated nonattainment for the primary O3 NAAQS.
These categories range from ``Marginal,'' the lowest O3
classification with the fewest requirements associated with it, to
``Extreme,'' the highest classification with the most required
programs. Areas with worse O3 problems are given more time
to attain the NAAQS and more associated emission control requirements.
Pursuant to previous O3 NAAQS reviews, the EPA set the
secondary NAAQS equal to the primary NAAQS. Thus, previous
implementation programs for O3 standards did not include a
separate classification threshold methodology for the secondary NAAQS.
For this NAAQS review, which may result in a secondary standard
different in form and level compared to the primary standard, the EPA
is considering methodologies for establishing the air-quality based
thresholds for assigning the section 181 classifications to areas out
of attainment with a secondary O3 NAAQS. Any such methods
would be proposed for comment if the EPA finalizes a distinct secondary
NAAQS.
    There are two main EPA rulemakings relating to implementation of
the 2008 O3 NAAQS. In May 2012, the EPA issued the final
Classifications Rule (77 FR 30160; May 21, 2012). The Classifications
Rule detailed the classifications approach, established attainment
deadlines and revoked the 1997 O3 NAAQS for purposes of
transportation conformity. In June 2013, the EPA proposed a SIP
Requirements Rule (78 FR 34178; June 6, 2013) to provide rules and
guidance to states regarding development of SIPs to attain the 2008
O3 NAAQS. The EPA believes that the overall framework and
policy approach of the proposed SIP Requirements Rule for the 2008
O3 NAAQS provides an effective and appropriate template for
the general approach states would follow in planning for attainment of
a revised primary O3 standard. The EPA intends to develop
and propose a new SIP Requirements Rule that will address, to the
extent necessary, any new implementation requirements that would result
from any revised O3 NAAQS. The EPA intends to propose this
implementation rule within 1 year after the revised O3 NAAQS
are promulgated, and finalize the implementation rule by no later than
the time the area designations process is finalized (approximately 2
years after promulgation of the O3 NAAQS).
    In general, when developing an attainment plan, the state begins
with the evaluation of the air quality improvements the nonattainment
area can expect in the future due to ``on the books'' existing federal,
state, and local emission reduction measures. The state then must
conduct a further assessment of relevant NOX and VOC
emission sources in the nonattainment area, and the additional
reasonably available control measures (RACM) and reasonably available
control technology (RACT) that can be implemented by these sources, in
determining how soon the area can attain the standard. Under section
172(c)(1) of the CAA as interpreted by the EPA, attainment
demonstrations must include a RACM analysis showing that no additional
reasonably available measures could be adopted and implemented such
that the SIP could specify an attainment date that is 1 or more years
earlier.
    The evaluation of these potential emissions reductions and
associated air quality improvement is commonly performed with
sophisticated air quality modeling tools. Given that O3
concentrations are affected both by regionally-transported
O3 and O3 precursor emissions and emissions of
precursors from local sources in the nonattainment area (e.g.,
industrial sources, EGUs, and on-road mobile sources), the EPA
recommends the use of regional grid-based models (such as CMAQ and
CAMx) to develop O3 attainment strategies. Although, as
described above, the EPA projects significant improvements in
O3 concentrations regionally resulting from a number of
ongoing emission reduction programs already in place (e.g., mobile
source engine and fuel standards and regulations for power plants) and
from a number of recently promulgated rules such as the Cross State Air
Pollution Rule (76 FR 48208; August 8, 2011), the Mercury and Air
Toxics Standards rule (77 FR 9304; February 16, 2012) and the Tier 3
rule (79 FR 23414; April 28, 2014) that will result in VOC and
NOX reductions from many geographically dispersed sources,
local reductions of direct O3 precursors can also result in
important health benefits.
    States must also ensure that a nonattainment area will make
``reasonable further progress'' (RFP) in accordance with subpart 2 of
the CAA from the time of the nonattainment designation to its
attainment date. The amount of RFP required is based on the
classification of the nonattainment area. Under the approach outlined
in the proposed SIP Requirements Rule for the 2008 O3 NAAQS,
areas designated nonattainment and classified as Moderate would
generally be required to reduce emissions by 15% over the first six
years after the effective date of designations. Areas classified higher
than Moderate would be required to produce additional emission
reductions after this 6-year period for an area that average 3%
reductions per year. All RFP and attainment plans must also include
contingency measures which would apply without significant delay in the
event the area fails to attain by its attainment date or meet RFP
milestones.
    The EPA expects that the same general approach for determining
attainment of the previous 1997 and 2008 8-hour O3 primary
standards by the attainment deadline would be followed for determining
attainment with any revised primary O3 standard. Attainment
would be evaluated based on the 3 most recent years of certified,
complete, and quality-assured air quality data in the nonattainment
area. Areas are able to obtain up to two 1-year attainment date
extensions provided under CAA section 181 under certain circumstances.
Under previous 8-hour O3 NAAQS rules, an area whose design
value based on the most recent 3 years of data exceeds the standard
could receive a 1-year attainment date extension if the air quality
concentration for the third year alone does not exceed the level of the
standard. Similarly, an area that has received a 1-year extension could
receive a second 1-year extension if the average of the area's air
quality concentration in the ``extension year'' and the previous year
does not exceed the level of the standard.

B. Implementing a Distinct Secondary O3 NAAQS, if One Is Established

    In each of the previous O3 NAAQS reviews the secondary
standard was set equal to the primary standard. As discussed in section
IV of this preamble, the EPA is proposing to retain the current
averaging time and form of the secondary standard and to revise the
level. The EPA is also soliciting comment on the alternative approach
of revising the secondary standard to a cumulative, seasonal,
concentration-weighted form based on the W126 index.
    If the EPA were to establish a distinct secondary standard, there
would be

unique implementation issues to consider. These could include issues
related to, but not limited to, PSD implementation, nonattainment area
classification thresholds, attainment planning, and conformity
demonstrations. These issues would be addressed in future
implementation rules and guidance, as necessary. The EPA solicits
comments on the specific kinds of implementation-related issues (with
examples, where possible) that air agencies and affected sources would
face if a separate and distinct secondary standard is established.

C. Designation of Areas

    After the EPA establishes or revises a NAAQS, the CAA directs the
EPA and the states to take steps to ensure that the new or revised
NAAQS is met. One of the first steps, known as the initial area
designations, involves identifying areas of the country that either do
not meet the new or revised NAAQS along with the nearby areas that
contribute to the violations.
    Section 107(d)(1) 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 national ambient air quality standard
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 EPA must then promulgate the area
designations according to a specified process, including procedures to
be followed if the EPA intends to modify a recommendation. The CAA
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 national ambient air quality standard, 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 of the new or revised national ambient
air quality standard. Such period may be extended for up to one year in
the event the Administrator has insufficient information to promulgate
the designations.'' In certain contexts, with respect to the NAAQS, the
term ``promulgation'' has been interpreted by the courts to be
signature and widespread dissemination of a final NAAQS rule.\252\ By
no later than 120 days prior to promulgating area designations, the EPA
is required to notify states of any intended modifications to their
recommendations that the EPA may deem necessary. States then have an
opportunity to demonstrate why any proposed modification is
inappropriate. Whether or not a state provides a recommendation, the
EPA must timely promulgate the designation that the agency deems
appropriate.
---------------------------------------------------------------------------

    \252\ American Petroleum Institute v. Costle, 609 F.2d 20 (D.C.
Cir. 1979).
---------------------------------------------------------------------------

    While section 107 of the CAA specifically addresses states, the EPA
intends to follow the same process for tribes to the extent
practicable, pursuant to CAA section 301(d) regarding tribal authority
and the Tribal Authority Rule (63 FR 7254, February 12, 1998). To
provide clarity and consistency in doing so, the EPA issued a 2011
guidance memorandum on working with tribes during the designation
process.\253\
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    \253\ Page, S. (2011). Guidance to Regions for Working with
Tribes during the National Ambient Air Quality Standards (NAAQS)
Designations Process, Memorandum from Stephen D. Page, Director, EPA
Office of Air Quality Planning and Standards to Regional Air
Directors, Regions I-X, December 20, 2011. Available: http://www.epa.gov/ttn/oarpg/t1/memoranda/20120117naaqsguidance.pdf.
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    As discussed in sections II and IV of this preamble, the EPA is
proposing to revise both the primary and secondary O3 NAAQS,
which currently are identical 8-hour standards that were set at 0.075
ppm in the 2008 NAAQS rule (73 FR 16436; March 27, 2008). If the EPA
revises the primary and secondary O3 NAAQS based on this
proposal, the EPA intends to complete designations for both NAAQS
following the standard 2-year process discussed above. The EPA is
required to sign the final rule for this O3 NAAQS review no
later than October 1, 2015, under a court-ordered deadline. In
accordance with section 107(d)(4) of the CAA, state Governors (and
tribes, if they choose) should submit their initial designation
recommendations for a revised primary and secondary NAAQS no later than
1 year after promulgation of any revised O3 NAAQS (for
example, by October 1, 2016, if the EPA promulgates such NAAQS on
October 1, 2015.) If the EPA intends to modify any state
recommendation, the EPA would notify the appropriate state Governor (or
tribal leader) no later than 120 days prior to making final designation
decisions. A state or tribe that believes the modification is
inappropriate would then have the opportunity to demonstrate to EPA why
it believes its original recommendation (or a revised recommendation)
is more appropriate. The EPA would take any additional input into
account in making the final designation decisions.
    Consistent with previous designations, the EPA intends to use area-
specific multi-factor analyses to support area boundary decisions for
any revised primary or secondary O3 standards. Historically,
the EPA has evaluated information related to the following factors for
designations: air quality data, emissions-related data, meteorology,
geography/topography, and jurisdictional boundaries. The EPA solicits
comment related to establishing area designation boundaries for the
proposed revised primary and secondary NAAQS, including any relevant
technical information that should be considered by the EPA and the
extent to which different considerations may be relevant to
establishing boundaries for a distinct secondary NAAQS. As noted
earlier, the EPA intends to issue designation guidance to the states
shortly after the promulgation of any revised O3 NAAQS to
provide information on the designation process and to assist states in
developing their recommendations. The EPA invites preliminary comment
on all aspects of the designation process at this time, which the EPA
will consider in developing that guidance.

D. Prevention of Significant Deterioration and Nonattainment New Source
Review Programs for the Proposed Revised Primary and Secondary O3 NAAQS

    The CAA, at parts C and D of title I, contains NSR requirements
that constitute preconstruction review and permitting programs
applicable to new major stationary sources and major modifications of
existing major sources. The preconstruction review of each new major
source and major modification generally applies on a pollutant-specific
basis, and the requirements that apply for each pollutant generally
depend on whether the area is designated as attainment (or
unclassifiable) or nonattainment for that pollutant. For the
O3 NAAQS, in areas designated attainment and unclassifiable,
the PSD requirements under part C apply. In nonattainment areas for
O3, the NNSR requirements under part D apply. Collectively,
those two sets of permit requirements are commonly referred to as the
``major NSR programs.''
    Until areas are designated for the proposed revised O3
NAAQS, the NSR provisions applicable under an area's designation for
the 2008 NAAQS (including any applicable anti-backsliding requirements)
would continue to apply. See 40 CFR 51.166(i)(2) and 52.21(i)(2). When
the

new designations for any revised O3 NAAQS are effective,
they generally will serve to determine whether the PSD or nonattainment
NSR program applies.
1. Prevention of Significant Deterioration (PSD)
    The statutory requirements for a PSD permit program set forth under
part C (sections 160 through 169 of the CAA) are addressed by the EPA's
PSD regulations found at 40 CFR 51.166 (minimum requirements for an
approvable SIP) and 40 CFR 52.21 (federal PSD permit program for areas
lacking an EPA-approved PSD program in the applicable SIP and for lands
owned by the federal government and tribal lands). Both sets of
regulations already apply to O3. See 40 CFR 51.166(b)(23),
(49); 40 CFR 52.21(b)(23), (50).. Among other things, in
attainment and unclassifiable areas, the PSD program requires a new
major stationary source or a major modification to an existing major
source to apply BACT for each applicable pollutant and to conduct an
air quality impact analysis to demonstrate that the proposed source or
project will not cause or contribute to a violation of any NAAQS or PSD
increment (see CAA section 165(a)(3)-(4), 40 CFR 51.166(j)-(k), 40 CFR
52.21(j)-(k)). PSD requirements may also include, in appropriate cases,
an analysis of potential adverse impacts on Class I areas (see CAA
sections 162 and 165).\254\ These existing requirements of the PSD
program will remain applicable to O3 and the demonstration
required under 40 CFR 51.166(k) and 52.21(k) will apply to any revised
O3 NAAQS when such NAAQS become effective, except to the
extent that a pending permit application is subject to a grandfathering
provision that the EPA establishes through rulemaking.
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    \254\ Congress established certain Class I areas in section
162(a) of the CAA, including international parks, national
wilderness areas, and national parks that meet certain criteria.
Such Class I areas, known as mandatory federal Class I areas, are
afforded special protection under the CAA. In addition, states and
tribal governments may establish Class I areas within their own
political jurisdictions to provide similar special air quality
protection.
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    To address ambient O3 impacts of VOC and NOX
precursor emissions from individual stationary sources, Appendix W to
40 CFR part 51 currently directs states to consult with the applicable
EPA Regional Office to determine the appropriate techniques on a case-
by-case basis, which may or may not involve the use of air quality
models, for evaluating whether a PSD source causes or contributes to a
violation of the O3 NAAQS (40 CFR part 51, Appendix W,
section 5.2.1.c). At present, the EPA is evaluating the models and
techniques available to address atmospheric chemistry of O3
formation in assessing such single source impacts, and as part of that
evaluation has conducted discussions of such tools with the regulatory
modeling community. Consistent with its commitment to engage in a
rulemaking process to determine whether updates to Appendix W in 40 CFR
part 51 are warranted,\255\ the EPA is planning to propose a rulemaking
in the spring of 2015 to consider whether to update Appendix W. If the
EPA concludes that it is technically and scientifically appropriate, it
will propose appropriate regulatory updates to Appendix W as part of
that rulemaking and may also make related updates to technical
guidance, as appropriate. In the meantime, in order to demonstrate that
a proposed source or modification does not cause or contribute to a
violation of the applicable O3 NAAQS, PSD permit applicants
would follow the current provisions in Appendix W until any revisions
to them are in effect.
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    \255\ See Letter from Gina McCarthy, Assistant Administrator, to
Robert Ukeiley, at 1 (Jan. 4, 2012), available at http://www.epa.gov/scram001/10thmodconf/review_material/Sierra_Club_Petition_OAR-11-002-1093.pdf.
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    For PSD, a ``major stationary source'' is one with the potential to
emit 250 tons per year (TPY) or more of any regulated NSR pollutant,
unless the new or modified source is classified under a list of 28
source categories contained in the statutory definition of ``major
emitting facility'' in section 169(1) of the CAA. For those 28 source
categories, a ``major stationary source'' is one with the potential to
emit 100 TPY or more of any regulated NSR pollutant. A ``major
modification'' is a physical change or a change in the method of
operation of an existing major stationary source that results first, in
a significant emissions increase of a regulated NSR pollutant at a
project, and second, in a significant net emissions increase of that
pollutant at the source.\256\ See 40 CFR 51.166(b)(2)(i), 40 CFR
52.21(b)(2)(i).
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    \256\ As explained in 40 CFR 52.21(a)(2)(iv)(a) and
51.166(a)(7)(iv)(a), ``[t]he project is not a major modification if
it does not cause a significant emissions increase. If the project
causes a significant emissions increase, then the project is a major
modification only if it also results in a significant net emissions
increase.'' The PSD regulations at 40 CFR 51.166(a)(7) and
52.21(a)(2) also explain in more detail the two-pronged test for
determining whether a proposed project at a facility is a major
modification.
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    The EPA's regulations define the term ``regulated NSR pollutant''
to include ``[a]ny pollutant for which a [NAAQS] has been promulgated
and any pollutant identified [in EPA regulations] as a constituent or
precursor to such pollutant'' (40 CFR 51.166(b)(49); 40 CFR
52.21(b)(50)). These regulations identify VOC and NOX as
precursors to O3 in all attainment and unclassifiable areas
(40 CFR 51.166(b)(49)(i)(a); 40 CFR 52.21(b)(50)(i)(a)). Thus, for
O3, the PSD program currently requires the review and
control of emissions of VOC and NOX, as applicable, as
precursors of O3.
    As noted above, section 165(a)(3) of the CAA and the implementing
PSD regulations require the owner or operator of a proposed facility
to, among other things, demonstrate that ``emissions from construction
or operation of such facility will not cause, or contribute to, air
pollution in excess of any . . . national ambient air quality standard
in any air control region.'' See also 40 CFR 51.166(k), 40 CFR
52.21(k). The EPA has interpreted this requirement to include any NAAQS
that is in effect as of the date a permit is issued, unless it has
grandfathered permit applications from the requirement to demonstrate
that the proposed facility does not cause or contribute to a violation
of the new or revised NAAQS.\257\ See, e.g., 73 FR 28321, 28324, 28340
(May 16, 2008); 78 FR 3253 (Jan. 15, 2013); Memorandum from Stephen D.
Page, Director, Office of Air Quality Planning & Standards,
``Applicability of the Federal Prevention of Significant Deterioration
Permit Requirements to New and Revised National Ambient Air Quality
Standards'' (April 1, 2010). Consistent with this interpretation, any
revised O3 NAAQS finalized through this rulemaking will need
to be addressed by PSD permit applicants and permitting authorities, in
permits issued on or after the date when the revised NAAQS become
effective, unless the permit application has been grandfathered through
rulemaking, as described below in this proposal.
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    \257\ In the past the EPA has asserted the discretion to take
such grandfathering action, under appropriate circumstances, either
by rulemaking or through a case-by-case determination for a specific
permit application. The United States Court of Appeals for the Ninth
Circuit recently vacated a decision by the EPA to issue an
individual PSD permit grandfathering a permit applicant from certain
requirements. See Sierra Club v. EPA, 762 F.3d 971 (9th Cir. 2014).
In light of that decision, the EPA is no longer asserting authority
to grandfather permit applications on a case-by-case basis. However,
in the same opinion the court also stated that it did ``not doubt,
or express any opinion on, the EPA's traditional authority to employ
formal rulemaking to implement grandfathering'' and distinguished
that authority from the permit-specific grandfathering at issue in
the case before it. Id., at 982, n. 7 & 982-983. Thus, the EPA does
not interpret this opinion to limit its authority to grandfather
through rulemaking, but rather believes that the decision offers
support for such authority.
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    Because the complex chemistry of O3 formation poses
significant challenges

for the assessing the impacts of individual stationary sources on
O3 formation, the EPA's judgment has been that it was not
technically sound to designate a specific air quality model that must
be used in the PSD permitting process to make this demonstration for
O3.\258\ The EPA has explained that sources must make the
demonstration required under CAA section 165(a)(3) and the implementing
regulations, that this demonstration necessarily involves an analysis,
and has established a process to determine on a case-by-case basis, in
consultation with the appropriate EPA Regional Office, what analytical
techniques should be used to assess the impact of an individual source
\259\ (40 CFR part 51, Appendix W, Section 5.2.1.c). The EPA has,
however, granted a petition from Sierra Club requesting, among other
things, that it initiate rulemaking to designate air quality models for
O3, and consistent with that petition grant, has been going
through a process to evaluate potential updates to Appendix W.\260\
While that process is underway, individual sources should continue to
follow the existing procedures to determine what method is appropriate
to use to evaluate their impacts on O3 formation.
---------------------------------------------------------------------------

    \258\ Letter from Gina McCarthy, Assistant Administrator, to
Robert Ukeiley, at 2 (Jan. 4, 2012), available at http://www.epa.gov/scram001/10thmodconf/review_material/Sierra_Club_Petition_OAR-11-002-1093.pdf.
    \259\ See, e.g., id.
    \260\ See id. at 1 and 3.
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    The PSD rules in 40 CFR 51.166(i)(2) and 52.21(i)(2) contain an
exemption for particular pollutants from the PSD requirements if the
owner or operator of the source demonstrates that the area in which the
facility is located is designated as nonattainment for that pollutant
under CAA section 107. Thus, new major sources and modifications will
generally be subject to the PSD program requirements for O3
if they are locating in an area that does not have a current
nonattainment designation under CAA section 107 for O3. As
explained in the recent proposal for the implementation rule for the
2008 O3 NAAQS, references to historical nonattainment
designations for a revoked standard should not be viewed as current
``nonattainment designation[s] under CAA section 107'' within the
meaning of 40 CFR 51.166(i)(2) and 52.21(i)(2) and, therefore, do not
trigger the exemption from PSD requirements that would otherwise result
from those provisions (78 FR 34216, June 6, 2013).
a. PSD Grandfathering Provision
    Recognizing that some PSD applications may have already been
submitted and could be in the review process when a revised
O3 NAAQS becomes effective, the EPA is proposing a
transition plan that would enable certain PSD applications to make the
demonstration that the proposed project will not cause or contribute to
a violation of any NAAQS with respect to the O3 NAAQS that
were in effect on the date the reviewing authority determines the
permit application complete or the date the public notice on the draft
permit or preliminary determination is first published (depending on
which grandfathering provision applies), rather than the revised
O3 NAAQS.\261\
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    \261\ The proposed grandfathering provision is intended to apply
to pending PSD permit applications that meet one or both of the
specified criteria and that are for sources locating in areas where
PSD continues to apply with respect to O3 at the time the
permit is issued. The proposed grandfathering provision is not
intended to apply to sources locating in areas where NNSR applies at
the time of permit issuance (for example, if the area had been
designated as attainment for O3 when the permit
application was submitted but was subsequently designated as
nonattainment for O3 and that nonattainment designation
would be in effect when the permit would be issued). For such
sources, the permit application must be resubmitted in accordance
with the applicable NNSR requirements.
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    The EPA is proposing and taking comment on adding a grandfathering
provision to EPA's regulations at 40 CFR 51.166 and 52.21 that would
apply specifically to two categories of PSD permit applications that
are pending when the EPA issues the revised O3 NAAQS: (1)
Applications for which the reviewing authority has formally determined
that the application is complete on or before the signature date of the
revised NAAQS; and (2) applications for which the reviewing authority
has first published a public notice of a draft permit or preliminary
determination before the effective date of the revised NAAQS. These two
categories are proposed because some states do not do completeness
determinations as part of their permit process.
    As explained above, the EPA interprets the CAA and implementing PSD
regulations at 40 CFR 52.21(k)(1) and 51.166(k)(1) to require that PSD
permit applications must include a demonstration that new major sources
and major modifications will not cause or contribute to a violation of
any NAAQS that is in effect as of the date the PSD permit is issued.
Thus, if the EPA revises the O3 NAAQS, any proposed new
source or modification with a PSD permit application pending at the
time the revised O3 NAAQS takes effect would be expected to
conduct an analysis to demonstrate that it does not cause or contribute
to a violation of that NAAQS, absent some type of transition provision
exempting the application from that requirement. This demonstration, as
noted above, should be completed in consultation with the applicable
EPA Regional Office.
    Nevertheless, the agency has previously recognized that the CAA
provides discretion for the EPA to grandfather PSD permit applications
from requirements that become applicable while the applications are
pending (45 FR 52683, August 7, 1980; 52 FR 24672, July 1, 1987; 78 FR
3086, January 15, 2013). As discussed in more detail in these
referenced actions, section 165(a)(3) of the CAA requires that a permit
applicant demonstrate that its proposed project will not cause or
contribute to a violation of any NAAQS. At the same time, section
165(c) of the CAA requires that a PSD permit be granted or denied
within 1 year after the permitting authority determines the application
for such permit to be complete. In addition, section 301 of the CAA
authorizes the Administrator ``to prescribe such regulations as are
necessary to carry out his functions under this chapter.'' When read in
combination, these three provisions of the CAA provide the EPA with the
discretion to issue regulations to grandfather pending permit
applications from having to address a revised NAAQS where necessary to
achieve both CAA objectives to protect the NAAQS and to avoid delays in
processing PSD permit applications. Moreover, in a recent opinion the
U.S. Court of Appeals for the Ninth Circuit recognized the EPA's
traditional exercise of grandfathering authority through rulemaking and
indicated that this approach was consistent with statutory requirement
to ``enforce whatever regulations are in effect at the time the agency
makes a final decision'' because it involved identifying ``an operative
date, incident to setting the new substantive standard, and the
grandfathering of pending permit applications was explicitly built into
the new regulations.'' Sierra Club v. EPA, 762 F.3d 971, 983 (9th Cir.
2014).
    In the EPA's most recent adoption of a grandfathering provision for
PSD, it adopted a provision for PM2.5 that provides a
reasonable transition for implementing certain new PSD requirements
related to the 2012 PM2.5 NAAQS for pending permit
applications that have met certain criteria. As finalized, the
PM2.5 grandfathering provision included the same two
categories of permit applications that

today are being proposed for O3. See 40 CFR 51.166(i)(10)
and 52.21(i)(11). In the rulemaking, adding the grandfathering
provision for the PM2.5 NAAQS, the EPA also provided a
detailed rationale and legal basis for including the grandfathering
provision in the PSD program. See 78 FR 3087 at 3253-59 (January 15,
2013); see also 77 FR 39023-24 (June 29, 2012).
    When the PM2.5 NAAQS grandfathering provision was
originally proposed, the EPA provided for only one category of pending
PSD applications--applications for which the reviewing authority has
published a public notice on the draft permit prior to the effective
date of the revised PM2.5 NAAQS. A majority of the
commenters supported the adoption of a grandfathering provision but
some responded that a grandfathering milestone based on the submittal
of a complete application would be more appropriate in order to avoid
significant burdens associated with having to withdraw an application.
These commenters pointed out the significant level of effort, resources
and time involved in preparing all of the information necessary for a
complete permit application. They claimed that it would be unfair to
establish grandfathering milestones beyond the complete application
date because the processes and timeframe involved in generating the
draft permit or preliminary determination materials and publishing the
public notice are largely out of the control of the permit applicant
and vary from agency to agency.
    Based on this and other pertinent information provided by the
commenters, the EPA concluded in that rulemaking that it should add an
additional grandfathering milestone to avoid substantial additional
burden and delay for permit applications that have reached a stage in
the review process by which significant resources have been expended to
complete PSD analyses and demonstrations that would have to be redone
to address the revised NAAQS. Accordingly, the EPA adopted a
grandfathering provision for the PM2.5 NAAQS in the final
rule that included two milestones for establishing grandfathering
eligibility. The EPA believes that these considerations and this
rationale also apply to pending PSD permit applications that would be
affected by a revised O3 NAAQS. Accordingly, the EPA is
proposing to apply these same two milestones in this proposed
rulemaking for the revised O3 NAAQS.
    The proposed grandfathering provision does not apply to any
applicable PSD requirements related to O3 other than the
requirement to demonstrate that the proposed source does not cause or
contribute to a violation of any revised O3 NAAQS. Sources
with projects qualifying under the grandfathering provision will be
required to apply BACT to all applicable pollutants, demonstrate that
the project emissions will not cause or contribute to a violation of
the existing O3 NAAQS, and address any Class I area and
additional O3-related impacts in accordance with the PSD
regulatory requirements.
    For the reasons provided both herein and in the prior EPA actions
referenced above, the EPA proposes to amend the federal PSD permitting
regulations at 40 CFR 52.21 to add the described grandfathering
provision for the proposed O3 NAAQS revision. Specifically,
the proposed provision provides that qualifying new sources and
modifications seeking PSD permits under 40 CFR 52.21 shall not be
required to demonstrate that their proposed emissions will not cause or
contribute to a violation of the revised O3 NAAQS, but
instead must demonstrate that their proposed emissions will not cause
or contribute to a violation of the O3 NAAQS in effect on
the date the reviewing authority determines the permit application
complete or the date the public notice on the draft permit or
preliminary determination is first published, depending on which prong
of the grandfathering provision is applicable for that source. See
proposed 40 CFR 52.21(i)(12).
    For sources subject to the PSD program under section 52.21, it
should be noted that the EPA intends for a source that satisfies either
milestone in the proposed revisions to section 52.21(i) to be
grandfathered from this requirement if those revisions are finalized.
Accordingly, if a particular source does not qualify under the first
milestone based on a complete application, it may qualify under the
second milestone based on the issuance of a public notice. Conversely,
a source may qualify for grandfathering under the first milestone, even
if it does not satisfy the second. As explained below, states with EPA-
approved PSD programs in their SIPs would have additional flexibility
for implementing the proposed grandfathering provision to the extent
that any alternative approach is at least as stringent as the federal
provision.
    The EPA also proposes that states that issue PSD permits under a
SIP-approved PSD permit program should have discretion to
``grandfather'' pending PSD permits in the same manner under these same
circumstances. Therefore, the EPA is proposing to revise its rules at
40 CFR 51.166 to provide a comparable exemption applicable to SIP-
approved PSD programs, although such states are under no obligation to
grandfather. See proposed 40 CFR 51.166(i)(11). The EPA recognizes that
such states interested in grandfathering PSD sources for O3
will not have time to revise their rules and submit them to the EPA for
approval into the SIP, since the need to grandfather sources will occur
immediately upon the effective date of the revised O3 NAAQS.
As explained in an earlier rulemaking, the EPA believes that states
implementing a SIP-approved PSD program have the discretion to allow
grandfathering consistent with the grandfathering provision contained
in the federal rule provisions, even in the absence of an express
grandfathering provision in their state rules, if the particular
state's laws and regulations may be interpreted to provide such
discretion. See 78 FR 3086 at 3258.
    Because state SIPs cannot be less stringent than federal
requirements, the states' discretion must be limited to applying
grandfathering consistent with the federal rule provisions for
O3. However, we believe that such consistent application
affords states with ample flexibility for implementing the provision.
Accordingly, a state may elect to apply both milestones or it may elect
to rely solely upon one of the milestones for grandfathering PSD
permits for O3. For example, in states that do not issue a
formal completeness determination, the complete application milestone
would not serve any practical purpose for grandfathering a PSD source,
so the state may choose not to use this milestone. These states may
elect to rely solely upon the public notice milestone, regardless of
whether it issues formal completeness determinations. However, the EPA
anticipates that once a decision is made concerning either the use of
both milestones or only one, states will apply the provision
consistently to all PSD permit applications that would qualify under
the elected milestone(s).
    The EPA seeks comments on all aspects of the proposed
grandfathering provisions under either 40 CFR 52.21 or 51.166 as they
would apply to exempt certain pending PSD permit applications from
having to address the revised O3 NAAQS.
b. PSD Screening Tools
    The EPA has historically allowed the use of screening tools to help
facilitate the implementation of the NSR program

by reducing the source's burden and streamlining the permitting process
for circumstances where pollutant emissions or ambient impacts could be
considered de minimis. For example, the EPA has established significant
emission rates or SERs that are used to determine when the NSR
requirements should be applied to a particular new or modified source
with regard to each regulated NSR pollutant. See 40 CFR 51.166(b)(23)
and 52.21(b)(23). For O3, the EPA established a separate SER
in these regulations of 40 tpy for emissions of each O3
precursor--VOC and NOX. For PSD, these SER values for VOC
and NOX are used to determine when the proposed major source
or major modification must complete PSD review for that precursor,
including complying with BACT for that precursor and completing the
appropriate air quality analyses associated with the proposed emissions
increase of that precursor.
    Another key screening tool commonly used for PSD is the significant
impact level (SIL). This particular tool is used to determine the
extent to which an ambient impact analysis must be completed for the
applicable pollutant. The EPA has not established a SIL for
O3. The PSD regulations currently state that ``[n]o de
minimis air quality level is provided for ozone. However, any net
emissions increase of 100 tons per year or more of [VOC] or
[NOX] subject to PSD would be required to perform an ambient
impact analysis, including the gathering of ambient air quality data.''
\262\ The EPA intends to consider whether it is appropriate to make any
revisions to the PSD regulations related to the screening tools for
O3 in a separate rulemaking that will specifically address
various implementation issues for O3. However, there are no
such revisions being proposed in today's rulemaking. Until any
rulemaking to amend existing regulations is completed, permitting
decisions should continue to be based on the existing 40 TPY SER for
O3 precursors (NOX and VOC) in existing
regulations. Further decisions regarding the need for an analysis to
assess the impact of an individual source on the O3 NAAQS
and the method of analysis depend on the nature of the source and its
emissions, and, as noted above, should be determined in consultation
with the EPA Regional Office on a case-by-case basis in accordance with
section 5.2.1.c. of Appendix W to 40 CFR part 51.
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    \262\ This language is contained in a footnote in the PSD
regulations at 40 CFR 51.166(i)(5)(i) and 52.21(i)(5)(i), and it has
not been revisited by the EPA since the issuance of the 8-hour
O3 NAAQS. These values do not reflect a categorical
conclusion by the EPA that sources emitting less than 100 tpy of
VOCs or NOX will not cause or contribute to a violation
of the current (or any revised) O3 NAAQS, nor does it
reflect a conclusion that such sources should be categorically
excluded from the requirement for an ambient impact analysis.
Instead, the EPA recommends consultation with the appropriate EPA
Regional Office in accordance with section 5.2.1.c of Appendix W
when a review of an application for a new source or modification
involves emissions less than 100 tpy of either O3
precursor. See Letter from Gina McCarthy, Assistant Administrator,
to Robert Ukeiley, at 4 (Jan. 4, 2012), available at http://www.epa.gov/scram001/10thmodconf/review_material/Sierra_Club_Petition_OAR-11-002-1093.pdf.
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c. Other PSD Transition Issues
    As explained earlier in this section, the EPA anticipates that the
existing O3 air quality in some areas will no longer be in
attainment of the primary O3 standard when it is revised,
and that these areas will be designated as ``nonattainment'' at a later
date consistent with the designation process set forth for
O3 under the CAA. However, until such nonattainment
designation occurs, proposed new major sources or major modifications
located in any area designated attainment or unclassifiable for the
2008 O3 NAAQS will continue to be required to obtain a PSD
permit.\263\ This raises the question as to how a source can be issued
a PSD permit in light of known existing ambient violations of the
revised NAAQS.
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    \263\ Any proposed major stationary source or major modification
for O3 that does not receive its PSD permit by the
effective date of a new nonattainment designation for the area where
the source would locate would then be required to satisfy all of the
applicable NNSR preconstruction permit requirements for
O3.
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    Section 165(a)(3)(B) of the CAA requires that a proposed source may
not construct unless it demonstrates that it will not cause or
contribute to a violation of any NAAQS. This statutory requirement is
implemented through a provision contained in the PSD regulations at 40
CFR 51.166(k) and 52.21(k). If a source cannot make this demonstration
or if its initial air quality impact analysis shows that the source's
impact does cause or contribute to a violation, a PSD permit may not be
issued until that adverse impact is mitigated.\264\ The PSD
regulations, however, do not explicitly specify remedial actions that a
prospective source can take to address such a situation. Nevertheless,
the EPA has historically recognized in regulations and through other
actions that sources applying for PSD permits may utilize offsets as
part of the required PSD demonstration under the CAA section
165(a)(3)(B), even though the PSD provisions of the Act do not
expressly reference offsets, in contrast to the NNSR provisions of the
Act.\265\
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    \264\ See, e.g., Stephen D. Page, Director, Office of Air
Quality Planning and Standards, to Regional Air Division Directors,
``Guidance Concerning Implementation of the 1-hour SO2
NAAQS for the Prevention of Significant Deterioration Program,''
(August 23, 2010); 44 FR 3278 (January 16, 1979).
    \265\ See, e.g., In re Interpower of New York, Inc., 5 E.A.D.
130, 141 (EAB 1994) (describing an EPA Region 2 PSD permit that
relied in part on offsets to demonstrate the source would not cause
or contribute to a violation of the NAAQS). 52 FR 24698 (July 1,
1987); 78 FR 3261-62 (Jan. 15, 2013).
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    The EPA has looked to the procedures contained in a separate set of
regulations at 40 CFR 51.165(b) to guide the process by which a source
that is located in an area designated as attainment or unclassifiable
for a NAAQS, but that is determined to cause or contribute to a
violation of that NAAQS in any area, can use offsets to mitigate its
adverse impact on the NAAQS and ultimately meet the PSD demonstration
requirement under CAA section 165(a)(3)(B) and the implementing
regulations.\266\
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    \266\ 78 FR 3261 (January 15, 2013); Stephen D. Page, Director,
Office of Air Quality Planning and Standards, to Regional Air
Division Directors, ``Guidance Concerning Implementation of the 1-
hour SO2 NAAQS for the Prevention of Significant
Deterioration Program,'' (August 23, 2010).
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    Section 51.165(b) states that plans shall include a preconstruction
review permit program (or its equivalent) to satisfy the requirements
of CAA section 110(a)(2)(D)(i) for major sources and major
modifications, and that the program shall apply to any major stationary
source or major modification locating in an area designated attainment
or unclassifiable for any NAAQS, when that source would cause or
contribute to a NAAQS violation.\267\ Paragraph (b)(3) of that
regulation provides that the required permit program may include a
provision allowing a proposed major source or major modification to
reduce the impact of its emissions on air quality by obtaining
sufficient emissions reductions to, at a minimum, compensate for its
adverse ambient impact where the source or modification would otherwise
cause or contribute to a violation of any NAAQS. Although section
51.165(b) refers explicitly to CAA section 110(a)(2)(D)(i), which now
addresses transport issues, but not CAA section 165(a)(3)(B), the EPA
has previously explained that 51.165(b) may also be interpreted to
apply to the section 165(a)(3)(B) demonstration

based on the regulatory history (78 FR 3262, n. 256).\268\
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    \267\ The definition of ``major stationary source'' and ``major
modification'' in this regulation is based on the respective
definitions in the NNSR regulations at 40 CFR 51.165(a), which are
more inclusive than the respective PSD definitions, but clearly
include major sources covered by the PSD requirements.
    \268\ Briefly, in 1980, the EPA had determined that the
statutory requirements under CAA section 165(a)(3)(B), taken
together with the requirements of CAA section 110(a)(2)(D) required
all major sources locating outside a nonattainment area, but causing
or contributing to a NAAQS violation to reduce the impact on air
quality so as to assure attainment and maintenance of the NAAQS. 45
FR 31310 (May 13, 1980). In a footnote, the EPA further indicated
that this offset requirement must apply to sources causing or
contributing to a newly discovered NAAQS violation until the area is
designated nonattainment. See 45 FR 31310 (May 13, 1980). In the
1980 rule, the EPA adopted section 51.18(k), which was later
renumbered section 51.165(b). The EPA revised 51.165(b) to expressly
authorize an offset program to meet the requirements of CAA section
110(a)(2)(D)(i), but this provision may also be interpreted to apply
to section 165(a)(3)(B), consistent with the EPA's reading of
section 51.18(k) in 1980. It is also worth noting that at the time
of these rules, before the 1990 CAA amendments, section 110(a)(2)(D)
required each state to have ``a permit or equivalent program for any
major emitting facility . . . to assure (i) that national air
quality standards are achieved and maintained . . ..''
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    Generally, the offset needed to compensate for a proposed source's
adverse impact would be determined by the ability of any particular
emissions reduction to mitigate the source's adverse impact at the
location of the violation. As long as the emissions reduction or offset