area of the city that has relatively uniform land use with dimensions
in the 0.5 to 4.0 kilometers range.
    4. Urban scale--Defines concentrations within an area of city-like
dimensions, on the order of 4 to 50 kilometers. Within a city, the
geographic placement of sources may result in there being no single
site that can be said to represent air quality on an urban scale. The
neighborhood and urban scales have the potential to overlap in
applications that concern secondarily formed or homogeneously
distributed air pollutants.
    5. Regional scale--Defines usually a rural area of reasonably
homogeneous geography without large sources, and extends from tens to
hundreds of kilometers.
    The ISA and REA indicate that one of the largest factors affecting
ambient exposures to NO2 above health benchmark
concentrations are mobile source emissions, particularly at locations
near major roads. Information in the ISA and the REA shows that
concentrations of mobile source pollutants, including NO2,
typically display peak concentrations on or immediately adjacent to
roads, producing a gradient in pollutant concentrations where
concentrations decrease with increasing distance from roads (Section
II.A.2 above, ISA sections 2.5.4 and 4.3.6 and Table 2.2-1; REA section
7.3.2 and Figures 8-17 and 8-18). In the ambient environment,
NO2 is largely a secondary pollutant resulting from the
reaction of NO with available ozone (O3), the concentrations
of which depend on photochemical reactions of ambient hydrocarbons and
prior (pre-cursory) NOX emissions. The ISA notes that the
direct emission of NO2 from mobile sources is estimated to
be only a few percent of the total NOX emissions for light-
duty gasoline vehicles, and anywhere from less than 10 percent up to 70
percent of the total NOX emission from heavy-duty diesel
vehicles, depending on the engine, the use of emission control
technologies such as catalyzed diesel particulate filters (CDPFs), and
mode of vehicle operation.\20\ However, since the rate of conversion of
mobile source NO to NO2 as described above is a generally
rapid process, (i.e., on the order of a minute (ISA Section 2.2.2)),
NO2 behaves like a primary pollutant in the near-road
environment, exhibiting peak concentrations on or closely adjacent to
roads. However, due to the secondary formation characteristic of
NO2, its rate of decay with increasing distance from a road
can be slower than that of the other pollutants directly emitted from
mobile sources including carbon monoxide (CO), ultrafine particulates,
air toxics, and black carbon. Literature values indicate that the
distance required for NO2 concentrations to return to near
area-wide or background concentrations away from major roadways can
range up to 500 meters. The actual distance is variable, and highly
dependent on topography, roadside features, meteorology, and the
related photochemical reactivity conditions (Baldauf et al., 2008;
Beckerman et al., 2007; Clements et al., 2008; Gilbert et al. 2003;
Hagler et al., 2009; Rodes and Holland, 1980; Singer et al., 2003; Zhou
and Levy, 2007). Nonetheless, any efforts to measure peak ambient
NO2 concentrations from on-road mobile sources, or other
mobile source pollutant of interest noted above, would be best served
by monitoring as near as practicable to roadways of interest.
---------------------------------------------------------------------------

    \20\ The ISA references studies of heavy-duty diesel vehicles
retrofitted with a CDPF in describing the range of NO2 to
NOX ratios from diesel vehicles. These studies are based
on vehicles equipped with CDPFs prior to 2009. However, as of
January 1, 2009, EPA's National Clean Diesel Campaign requires that
emission control devices included on its Verified Technologies List
raise the fraction of NO2 in exhaust NOX from
an engine no more than 20% above the baseline engine NO2
to NOX ratio. Retrofit technologies sold after January 1,
2009 that do not meet the NO2 emission limit may not be
installed or sold as EPA verified technologies.
---------------------------------------------------------------------------

2. Proposed Changes
    In conjunction with the proposed 1-hour NAAQS and the proposed
retention of the current annual NAAQS, we propose a number of changes
to the NO2 monitoring network. As described above in Section
II.F.4, we are proposing a 1-hour NO2 NAAQS that reflects
the maximum allowable NO2 concentration in an area. However,
the current network is not oriented to address peak concentrations,
such as the on-road and near-road environment, but many sites may be
situated to assess high concentrations at the neighborhood or larger
spatial scales. The EPA is proposing a two-tier network design to
monitor ambient concentrations of NO2 and assess compliance
with the NO2 NAAQS. The two tiers would provide data for
comparison with both the 1-hour and annual standards, and would be
comprised of (1) monitoring in areas of expected maximum 1-hour
concentrations and (2) monitoring to characterize areas with the
highest expected NO2 concentrations at the neighborhood and
larger spatial scales, or ``area-wide'' scales. Because the maximum
hourly NO2 concentrations in many areas are expected to be
due to on-road mobile emissions, the EPA believes that the first tier
of the monitoring network should include a component requiring
monitoring near major roads, where higher NO2 concentrations
have been identified and there are no significant monitoring efforts to
address roadway exposures. The EPA recognizes that requiring a
component of the ambient NO2 monitoring network to
characterize the peak NO2 concentrations derived from on-
road mobile sources, using monitors placed near major roadways (``near-
road monitors''), will introduce new requirements for monitoring sites
that, for a majority of the state and local monitoring networks,
currently do not exist.\21\ However, the monitoring of maximum hourly
concentrations of NO2, particularly in the near-road
environment, is an essential component

of an ambient monitoring network designed to determine compliance with
the proposed 1-hour NAAQS. In addition, the EPA recognizes that the
establishment of near-road monitoring sites will produce certain other
advantages, by providing a new data source for public health studies
that will support future NAAQS reviews, allowing for the tracking of
mobile source emission reductions progress, providing monitoring
infrastructure that may be of use for mixtures of pollutants in a
multi-pollutant paradigm, and supporting scientific studies of other
mobile source pollutants like CO, ultrafine particulate matter, black
carbon, and air toxics.
---------------------------------------------------------------------------

    \21\For purposes of the discussion, near-road NO2
monitors are defined to be no greater than 50 meters from the
nearest traffic lane of target road segments. The details of
appropriately placing NO2 monitors near roads are
explained in Section III.2.a of this document.
---------------------------------------------------------------------------

    The second tier of the proposed network design, the area-wide
monitoring component, is intended to characterize the highest
concentrations of NO2 typical or representative of
neighborhood and larger spatial scales, to address the wider area
impact of NO2 sources on urban populations. Further, a
requirement for the continuation of area-wide monitoring of
NO2 serves to maintain continuity in collecting area-wide
data that have served to inform long-term pollutant concentration
trends analysis and health and scientific research for more than thirty
years.
    We propose that state and, when appropriate, local air monitoring
agencies provide a plan for deploying monitors in accordance with the
following proposed network design by July 1, 2011. We also propose that
the NO2 network being proposed be physically established no
later than January 1, 2013. Considering the proposed timeline and
criteria presented in the network design, we solicit comment on whether
state and local monitoring agencies should be required to deploy
monitors sooner than January 1, 2013.
a. Monitoring in Areas of Expected Maximum Concentrations Near Major
Roads
    We are proposing to require monitoring in locations of expected
maximum concentrations near major roads in larger urban areas, with
minimum monitoring requirements triggered for metropolitan areas based
on Core Based Statistical Area (CBSA) population thresholds and the
traffic related metric annual average daily traffic (AADT). The U.S.
Department of Transportation (U.S. DOT) Federal Highway
Administration's Status of the Nation's Highways, Bridges, and Transit:
2006 Conditions and Performance document (http://www.fhwa.dot.gov/
policy/2006cpr/es02h.htm) states that ``while urban mileage constitutes
only 24.9 percent of total (US) mileage, these roads carried 64.1
percent of the 3 trillion vehicles miles (VMT) travelled in the United
States in 2004.'' The document also states that ``urban interstate
highways made up only 0.4 percent of total (US) mileage but carried
15.5 percent of total VMT.'' These statements indicate how much more
traffic volume exists on roads in urban areas versus the more rural
areas that have significant amounts mileage of the total public road
inventory. Because the combination of increased mobile source emissions
and increased urban population densities can lead to increased
exposures and associated risks, urban areas are the appropriate areas
to concentrate required near-road monitoring efforts. Therefore, we
propose that one near-road NO2 monitor be required in CBSAs
with a population greater than or equal to 350,000 persons. This
population threshold is proposed to provide the near-road monitoring
component of the network an appropriate spatial extent across the
country, given the limited availability of routine measurements in
these environments. Based on 2007 Census Bureau statistics, this will
result in approximately 142 sites in as many CBSAs.\22\
---------------------------------------------------------------------------

    \22\ We also note that this population threshold corresponds to
the minimum population level in which Air Quality Index (AQI) levels
are required to be reported, as noted in 40 CFR Part 58 Subpart F.
---------------------------------------------------------------------------

    We also propose that a second near-road monitor be required in
CBSAs with a population greater than or equal to 2,500,000 persons, or
in any CBSAs with one or more road segments with an AADT count greater
than or equal to 250,000. Based on 2007 Census Bureau statistics and
data from the 2007 Highway Performance Monitoring System (HPMS)
maintained by the U.S. DOT Federal Highway Administration (FHWA), this
particular element of the minimum monitoring requirements will add
approximately 23 sites to the approximate 142 near-road sites in CBSAs
that already will have one near-road monitor required due to the
350,000 population threshold. Of the 23 additional sites, two sites are
due to the 250,000 AADT threshold and are attributed to the Las Vegas,
Nevada and Sacramento, California CBSAs. The 2,500,000 population
threshold is proposed as a second threshold to allow for further
characterization of larger urban areas that are more likely to have a
greater number of major roads across a potentially larger geographic
area, and a corresponding increase in potential for exposure. Of the
approximate 1.66 million public road segments tracked in the HPMS, road
segments of 250,000 AADT or greater make up the top 0.03 percent of the
most traveled public road segments. The FHWA has also used this
threshold on its Web site to give an indication of the most travelled
urban highways in the country (http://www.fhwa.dot.gov/
policyinformation/tables/02.cfm). We proposed to use HPMS-reported AADT
as the traffic volume metric because AADT appears to be the most widely
used traffic volume metric in the scientific literature, is widely
available, and offers the most objective and consistent metric
available to indicate traffic volumes across the country. These AADT
data are typically available from local Metropolitan Planning
Organizations (MPOs), state departments of transportation, and from the
FHWA's HPMS. The FHWA also provides national guidance on the
appropriate measurement and estimation of AADT for different road types
in their HPMS Field Manual (http://www.fhwa.dot.gov/ohim/hpmsmanl/
hpms.cfm). We are therefore proposing the 250,000 AADT threshold for
requiring a near-road monitor because that threshold represents the
highest traffic volume road segments in the country, which may
correspond to the greatest potential for high exposures directly
connected to motor vehicle emissions.
    In summary, the combination of the above proposed minimum
monitoring requirement thresholds for the near-road monitors as part of
the ambient NO2 monitoring network are anticipated to
require approximately 165 near-road sites in 142 CBSAs. We solicit
comment on the proposed CBSA population threshold values (i.e., 350,000
and 2,500,000) and on the use of population thresholds both lower and
higher than those proposed, the use of the traffic volume metric AADT,
and the 250,000 AADT threshold in establishing the minimum number of
required near-road sites for urban areas.
    In choosing these population and traffic related thresholds for the
minimum monitoring requirements, it should be noted that, based on 2007
Census Bureau statistics, the U.S. Virgin Islands and seven states
(Delaware, Montana, North Dakota, South Dakota, Vermont, West Virginia,
and Wyoming) currently would not have required near-road monitoring
sites under this current proposal. Considering the relative lack of
near-road monitoring data nationwide, the new level and averaging time
of the NAAQS being proposed, and the desire to establish a spatially
representative and protective network, we solicit comment on the
inclusion or

exclusion of an additional or alternative monitoring requirement such
that each state and territory would have at least one near-road
monitoring site.
    The EPA recognizes that in certain cases, there can be an area or
areas of expected maximum hourly concentration in a CBSA due to a major
stationary source or to the combination of multiple sources that could
include point, area, and non-road source emissions in addition to on-
road mobile source emissions. Such locations might be identified
through data analysis, such as the evaluation of existing ambient data
and/or emissions data, or through air quality modeling. An example of
such a location might be away from roads and downwind of a stationary
source or sources in situations where the required near-road monitors
do not represent a location or locations of expected maximum hourly
NO2 concentrations in a CBSA. In these situations, where
such locations are known, we propose that the Regional Administrator
will have discretion to require monitoring above the minimum
requirements as necessary to address situations where the required
near-road monitors do not represent a location or locations where the
expected maximum hourly NO2 concentrations exist in a CBSA.
The EPA also proposes to allow Regional Administrators the ability to
require additional near-road monitoring sites to address situations
where minimum monitoring requirements are not sufficient to meet
monitoring objectives, such as a situation where there is a variety of
exposure potential in an area due to variety in the amount or types of
fleet mix, congestion patterns, terrain, or geographic areas within a
CBSA. An example of requiring an additional near-road monitor might be
a case where a particular community or neighborhood is significantly or
uniquely affected by road emissions, but the site or area is not
monitored even though the responsible State or local monitoring agency
is fulfilling the minimum monitoring requirements.
    In all cases, the Regional Administrator and the responsible State
or local air monitoring agency should work together to design and/or
maintain the most appropriate NO2 network to service the
variety of data needs for an area. We solicit comment on the proposal
to allow Regional Administrators the discretion to require monitoring
above the minimum requirements for any CBSA where required near-road
monitors do not represent a location or locations where the expected
maximum hourly NO2 concentrations exist in a CBSA. We also
solicit comment on the proposal to allow Regional Administrators to
require additional near-road NO2 monitoring stations above
the minimum required in situations where the minimum monitoring
requirements are not sufficient to meet monitoring objectives as noted
above.
    The new near-road monitoring sites that are to be part of the
NO2 ambient monitoring network will require specific site
selection criteria to focus monitoring efforts on one or a few major
roads in a given CBSA. The EPA anticipates that these near-road
monitoring sites will likely be best characterized as microscale,
mobile source oriented sites. We propose that monitoring agencies be
required to select their near-road monitoring site location(s) to
characterize the largest traffic volume segment(s) in the CBSA,
determined by ranking all road segments by AADT, and identifying a
location or locations adjacent to those top ranked AADT segments where
motor vehicle emission-derived NO2 concentrations are
expected to be at a maximum. Where a state or local air monitoring
agency identifies multiple acceptable candidate sites where maximum
hourly NO2 concentrations are expected to occur, the
monitoring agency should consider taking into account the potential for
population exposure in the criteria utilized to select the final site
location.
    We propose that near-road NO2 monitoring stations must
be sited so that the NO2 monitor probe is no greater than 50
meters away, horizontally, from the outside nearest edge of the traffic
lanes of the target road segment, and shall have no obstructions in the
fetch between the monitor probe and roadway traffic such as noise
barriers or vegetation higher than the monitor probe height. Baldauf et
al. (2009) indicate that the NO2 probe would ideally be
situated between 10 and 20 meters from the nearest traffic lane. We are
not proposing that the near-road NO2 monitor be on the
predominantly downwind side of the target roadway, however, we solicit
comment on whether this requirement is necessary to ensure near-road
NO2 sites capture maximum expected hourly concentrations.
    We propose that the monitor probe be located within 2 to 7 meters
above the ground, as is required for microscale PM2.5 sites.
EPA recognizes that these near-road monitoring sites will be adjacent
to a variety of road types, where some target roads will be on an even
plane with the monitoring station, while others may be cut roads,
(i.e., below the plane of the monitoring station), or fill and open
elevated roads, (i.e., where the road plane is above the monitoring
station). In any given case, it is most appropriate to place the
NO2 monitor probe as close to the plane of the target road
segment as possible, while staying between 2 to 7 meters above the
ground. In addition, we propose that monitor probe placement on noise
barriers or buildings, where the inlet probe height is no less than 2
meters and no more than 7 meters above the target road, will be
acceptable, so long as the inlet probe is at least 1 meter vertically
or horizontally away (in the direction of the target road) from any
supporting wall or structure, and the subsequent residence time of the
pollutant in the sample line between the inlet probe and the analyzer
does not exceed 20 seconds. Although a wall-mounted or noise barrier-
mounted near-road monitor set-up is not ideal, it may allow for
existing sites to be utilized as near-road monitoring stations if they
also meet the site selection criterion described below.
    As noted above, we are proposing a siting criterion for
NO2 monitor probe placement to be no greater than 50 meters
away from the outside nearest edge of the traffic lanes of the target
road segment. Based on a review of the scientific literature, as
discussed in Section II.A and the background portion of this section,
locations on or immediately adjacent to roads typically exhibit the
peak concentrations for mobile source pollutants, therefore monitor
probe placement at increasing distances from a road will
correspondingly decrease the potential for sampling maximum
concentrations of NO2. In addition, monitor probe placement
within 50 meters of a target road allows for increased probability of
reading elevated concentrations from the mobile source emissions even
when wind conditions cause the near-road monitoring site to be upwind
of the target road. Research literature indicates that in certain
cases, mobile source derived pollutant concentrations, including
NO2, can be detected upwind of roads, above background
levels, due to a phenomenon called upwind meandering. Kalthoff et al.
(2007) indicates that mobile source derived pollutants can meander
upwind on the order of tens of meters, mainly due to vehicle induced
turbulence, while Beckerman et al. (2008) note that near-road pollutant
concentrations on the predominantly upwind side of their study sites
dropped off to near background levels within the first 50 meters, but
were above background in this short and variable upwind range, which
could be due to, at least in part,

vehicle induced turbulence. This upwind meandering characteristic of
pollutants in the near-road environment provides an additional basis
for locating near-road sites within 50 meters of target road segments
because of the increased opportunity to monitor mobile source derived
NO2 concentrations that, although not peak concentrations,
are still elevated above background levels, in meteorological
conditions where the site is upwind of the target road.
    We solicit comment on the proposed near-road NO2 monitor
siting criteria presented here, particularly: (1) The requirement for
monitoring agencies to select near-road NO2 monitor sites by
ranking all road segments in a given CBSA by AADT, (2) selecting a site
adjacent to a top ranked AADT road segment where motor vehicle
emission-derived NO2 concentrations are expected to be at a
maximum, (3) the consideration of population exposure as a selection
criterion in situations where a state or local air monitoring agency
identifies multiple acceptable candidate sites where maximum hourly
NO2 concentrations are expected to occur, (4) the
requirement for near-road NO2 monitor probes to be no
greater than 50 meters in the horizontal from the outside nearest edge
of the traffic lanes of the target road segment, and (5) the
requirement for monitor probes to be between 2 to 7 meters above the
ground, and when located on a wall or supporting structure, that the
inlet probe be at least 1 meter vertically or horizontally away from
any supporting wall or structure.
    We also solicit comment on an alternative approach that would allow
state and local agencies greater discretion in selecting monitoring
locations to fulfill minimum monitoring requirements for measurements
of expected maximum NO2 concentrations in each CBSA. In this
alternative approach, an NO2 monitor would still be required
in locations of expected maximum NO2 concentrations in CBSAs
with a population greater than or equal to 350,000 persons. An
additional monitor would be required in CBSAs with a population greater
than or equal to 2,500,000, or in any CBSAs with one or more road
segments with an AADT count greater than or equal to 250,000. Under
this approach, states would not be specifically required to place
monitors near roads, but would have flexibility to place monitors at
locations of expected maximum concentrations. However, if a location or
locations of expected maximum concentration were near roads in a CBSA,
we would expect the NO2 monitor to be placed near those
roads. Further, we solicit comment on alternative ways of considering
population exposure, in concert with the identification of locations of
maximum expected NO2 concentrations, in determining where to
place near-road NO2 monitors. In suggesting an appropriate
role for population exposure, we invite comment on how the suggested
role would take into account the fact that NAAQS are designed to
protect all of the public, including at-risk or sensitive sub-
populations, which can include smaller sub-populations that may be
exposed to higher concentrations. We also invite comment on how any
suggested role would compare with EPA's historic practice of placing
monitors at locations of maximum concentration at the appropriate
spatial scale, reflecting consideration of the averaging time of the
NAAQS.
    In situations where open-path monitors are used at near-road
NO2 sites, we have not identified an appropriate path length
for this microscale monitoring site. For the purpose of this proposal,
we propose a path length range of 50 to 300 meters as an appropriate
path length range for open-path near-road NO2 monitors. The
high end of this proposed range coincides with path lengths identified
for other pollutants at the micro and middle-scales. We solicit comment
on the appropriate path length for a near-road NO2 open-path
monitor.
    During the near-road monitor site selection process, monitoring
agencies may utilize forms of quantitative analysis, such as emissions
and/or air quality modeling, data analysis, or saturation studies, to
better evaluate which of their top ranked AADT road segments may
exhibit the potential for creating the highest NO2
concentrations that might be monitored in the CBSA. As an example, such
an analysis might indicate that of the top ranked AADT road segments in
a given area, those segments that are part of or adjacent to
interchanges and toll plazas, that have higher ratios of heavy duty
diesel traffic to light duty traffic, have a high fraction of rapidly
accelerating or grade-climbing vehicles, or that are located in or near
particular terrain or land features, may exhibit higher potential
maximum NO2 concentrations. In addition, top ranked AADT
road segment analysis may allow the monitoring agencies to select a
near-road monitoring site located in a more densely populated area or a
location representing more vulnerable populations from a pool of
otherwise similarly categorized site candidates. In CBSAs required to
have two near-road monitoring sites, we propose that the second site be
selected based on AADT ranking and expected maximum concentration, but
differentiated from the first site by factors such as: Fleet mix,
congestion patterns, terrain, or geographic area within the CBSA, or at
minimum, selecting a site along a different road with a different
route, interstate, or freeway designation. This differentiation is to
avoid having the two sites characterize the same traffic when there are
potentially other road segments with different traffic characteristics
available that meet siting criteria for the second near-road monitor.
We solicit comment on the factors and methods to be used to
differentiate a second required near-road NO2 monitoring
site from the first such site in a given CBSA.
    In further support of characterizing the peak NO2
concentrations occurring in the near-road environment, the EPA proposes
to require three-dimensional anemometry, providing wind vector data in
the horizontal and vertical planes, along with temperature and relative
humidity measurements, at all required near-road monitoring sites. Due
to the near-road NO2 site being a somewhat specialized
microscale site, we propose that the meteorological measurement
hardware would be required to be situated at the same height as the
NO2 monitor probe, as opposed to a standardized height, to
aid in characterizing what NO2 analyzers are measuring from
the target road segments. The requirement of three-dimensional
anemometry is to allow for the determination of the standard deviation
of vertical wind velocities ([sigma]w). Venkatram et al.
(2007) notes that [sigma]w is a key meteorological factor in
governing the dispersion of on road pollutant emissions. Therefore, the
measurement of three dimensional wind would serve to inform when the
near-road site is relatively upwind or downwind of the target road,
provide a method to potentially identify the magnitude of vehicle
induced turbulence, permit calculation of [sigma]w in the
near-road environment to provide a better understanding of the mixing
of mobile source pollutants at the monitoring site and how site
characteristics influence mixing, and, with the inclusion of
temperature and relative humidity, provide basic meteorological data.
We solicit comment on the proposed requirement for three-dimensional
anemometry, the placement of the meteorological equipment at the same
height of the NO2 monitor probe height, and the requirement
for meteorological

measurements in general at all required near-road monitoring sites.
b. Area-Wide Monitoring at Neighborhood and Larger Spatial Scales
    As the second tier of the NO2 ambient monitoring
network, we are proposing a minimum number of monitors to characterize
that area with highest expected NO2 concentrations at the
neighborhood and larger (area-wide) spatial scales. We are proposing to
require one area-wide monitoring site in each CBSA with a population
greater than or equal to 1,000,000, to be sited to represent an area of
maximum concentration at the neighborhood or larger spatial scales.
This minimum monitoring requirement is expected to trigger 52
monitoring sites in as many CBSAs. Many of these monitors are likely
already in place as part of the approximately 400 NO2
monitoring sites that are currently operating across the country.
Further, the EPA proposes to allow any current photochemical assessment
monitoring station (PAMS) sites that are situated to address the
highest NO2 concentrations in an urban area and sited at
neighborhood or urban scales to satisfy this proposed area-wide
monitoring requirement. While in many cases it may be found that these
area-wide monitors may show lower concentrations than the maximum
concentration near-road NO2 monitors, data from these larger
spatially representative sites would provide information on area-wide
exposures from an individual or a group of point, area, on-road and/or
non-road mobile sources. These area-wide monitoring data may also, when
coupled with the near-road monitoring data, assist in the determination
of spatial variation of NO2 concentrations across a given
area, and assist in providing insight to the gradients that exist
between local near-road or stationary source derived concentration
maxima and the area-wide concentration levels.
    The EPA recognizes that the minimum number of area-wide monitors
required in this proposal may be less than the total number of
NO2 monitoring sites needed to satisfy the multiple
monitoring objectives that neighborhood and larger scale sites can
serve. These additional monitoring objectives include ambient
photochemical pollutant assessment, aiding in ozone forecasting, aiding
in PM precursor analysis and PM forecasting, and characterization of
point and area sources that may be impacting certain communities. We
propose that EPA Regional Administrators have the discretion to require
additional area-wide NO2 monitoring sites above the minimum
monitoring requirements where the minimum monitoring requirements for
area-wide monitors are not sufficient to meet monitoring objectives.
For example, the Regional Administrator may require additional
NO2 monitors in certain communities, both inside and outside
of CBSAs, which are affected by an individual or group of sources but
are not required to have an NO2 monitor as part of the
minimum monitoring requirements. The Regional Administrator and the
responsible State or local air monitoring agency should work together
to design and/or maintain the most appropriate NO2 network
to service the variety of data needs for an area.
    We solicit comment on the proposed minimum monitoring requirement
of approximately 52 monitors to characterize areas with highest
expected NO2 concentrations at the area-wide (neighborhood
and larger) spatial scales in CBSAs with populations of 1,000,000 or
more persons. We also solicit comment on the proposal that the Regional
Administrator can require additional monitoring sites on a case-by-case
basis, to address situations where the minimum monitoring requirements
for area-wide monitoring sites are not sufficient for an area.
3. Solicitation for Comment on an Alternative Network Design
    In conjunction with the solicitation of comment on an alternative
NAAQS that is discussed in Section II.F.4, the complementary network
design would not reflect peak NO2 concentrations anywhere in
an area. Instead, the alternative network design would rely on monitors
sited at the neighborhood and larger spatially representative scales,
which is identical to the second component of the two-tiered network
design being proposed except for having different population thresholds
for minimum required monitoring. The currently operating NO2
network would likely satisfy a portion of this alternative network
design, however the entire network would need to be assessed before
state or local agencies could make such determinations. State and local
agencies would have to determine what each currently operating site is
actually assessing to identify if any given site represents the highest
concentrations for a given CBSA at the neighborhood and larger spatial
scales. We solicit comment on an alternative network design where near-
road monitors are not specifically included in the minimum monitoring
requirements, and only monitors sited at the neighborhood and larger
spatial scales are required. In this alternative network design,
minimum monitoring requirements would apply to CBSAs based on
population thresholds, where one monitor would be required in CBSAs
with populations of 350,000 or more persons and a second monitor would
be required for CBSAs with populations of 1,000,000 or more persons.
Based on 2007 U.S. Census Bureau statistics, we estimate that these
population thresholds would require approximately 194 monitoring sites
in 142 CBSAs. The first monitor required in any CBSA would be expected
to be sited at the neighborhood or larger scale to characterize that
area with highest expected NO2 concentrations. Any second
monitor required in a CBSA would be expected to characterize a separate
area within the same CBSA, also with expected high NO2
concentrations. All such monitor site locations are anticipated to be
in areas of higher population densities of CBSAs and in, or adjacent
to, urban cores. The alternative network design would allow the
Regional Administrators to use their discretion to require monitoring
above the minimum requirements to address community impacts from the
variety of NO2 emission sources. EPA expects that this
network design will result in little or no progress being made in the
development of long-term near-road monitoring capabilities due to the
lack of specific network design requirements. EPA seeks comment on this
alternative network design.
    In addition to soliciting comment generally on this alternative
area-wide monitoring approach, the Administrator specifically requests
comment on the appropriate definition of area-wide NO2
concentrations and how best to use data representing these
concentrations to determine compliance with a 1-hour standard
reflecting the alternative approach of selecting a level for maximum
area-wide concentrations on which EPA is soliciting comment. Comparing
NO2 concentrations measured near major roadways to a level
meant to reflect the maximum allowable NO2 concentrations at
neighborhood and larger spatially representative scales would have the
effect of increasing the stringency of the standard beyond that
intended. With regard to this specific request for comment, the
Administrator notes that the definition of area-wide concentrations
could include a provision requiring that they be monitored at a
distance greater than or equal to some prescribed distance from the
nearest roadway. The Administrator notes that, while it is clear that
peak

roadway-associated NO2 concentrations occur on or very near
major roads, the point at which these concentrations return to area-
wide concentrations comparable to the area-wide standard is less
certain and may vary considerable by location. As discussed above
(section II.A.2), the scientific literature suggests that
concentrations can return to typical urban background concentrations
within distances of up to 500 meters from roads, though the actual
distance will vary with topography, roadside features, meteorology, and
photochemical reactivity conditions. The REA notes that studies suggest
the return to background concentrations can occur from within distances
of up to 200 to 500 m from the roads. Therefore, the Administrator
requests comment on the degree to which these distances (up to 200 m,
and up to 500m) serve to further define the distance from major roads
that would represent concentrations comparable to the alternative
standard. Further, since roadways of various sizes and traffic volumes
can affect nearby NO2 concentrations and roadways are
ubiquitous in urban areas, the Administrator notes that defining
representative area-wide concentrations could require more than a
uniform assumption of a single specific distance from a class of
roadway. The Administrator notes that the approach to defining
representative area-wide distances could include consideration of
location-specific roadway traffic volume and location-specific roadway
characteristics such as topography, presence of sound walls, vehicle
mix, and traffic patterns, to adequately address the variability. Given
these considerations, the Administrator solicits comment on how to
define the minimum distance to the nearest major roadway such that
measured concentrations at this distance (or farther) would represent
area-wide NO2 concentrations for comparison to the
alternative standard.

C. Data Reporting

    NO2 chemiluminescence FRMs are continuous gas analyzers,
producing updated data values on the order of every 20 seconds. Data
values are typically aggregated into minute averages and then compiled
into hourly averages for reporting purposes. State and local monitoring
agencies are required to report hourly NO, NO2, and
NOX data to AQS within 90 days of the end of each calendar
quarter. Some agencies also voluntarily report their pre-validated data
on an hourly basis to EPA's real time AIRNow data system, where the
data may be used by air quality forecasters to assist in ozone
forecasting. The EPA believes these data reporting procedures are
appropriate to support the current NO2 NAAQS and any options
being considered for a revised primary NO2 NAAQS.
    As a part of the larger data quality performance requirements of
the ambient monitoring program, we are proposing to develop data
quality objectives (DQOs) for the proposed NO2 network. The
DQOs are meant to identify measurement uncertainty for a given
pollutant method. We propose a goal for acceptable measurement
uncertainty for NO2 methods to be defined for precision as
an upper 90 percent confidence limit for the coefficient of variation
(CV) of 15 percent and for bias as an upper 95 percent confidence limit
for the absolute bias of 15 percent. We solicit comment on the proposed
goals for acceptable measurement uncertainty.

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

    The EPA is proposing to add Appendix S, Interpretation of the
Primary National Ambient Air Quality Standards for Oxides of Nitrogen,
to 40 CFR part 50 in order to provide data handling procedures for the
proposed NO2 1-hour primary standard and for the existing
NO2 annual primary standard. The proposed Appendix S would
detail the computations necessary for determining when the proposed 1-
hour and existing annual primary NO2 NAAQS are met. The
proposed Appendix S also would address data reporting, data
completeness considerations, and rounding conventions.
    Two versions of the proposed Appendix S are printed at the end of
this notice. The first applies to an annual primary standard and a 1-
hour primary standard based on the annual 4th high value form, while
the second applies to an annual primary standard and a 1-hour primary
standard based on the 99th percentile daily value form. The discussion
here addresses the first of these versions, followed by a brief
description of the differences found in the second version.
    Both versions of the proposed Appendix S are based on a near-
roadway approach to the setting the level of the 1-hour standard and to
siting monitors. As such, these versions place no geographical
restrictions on which monitoring sites' concentration data can and will
be compared to the standard when making nonattainment determinations
and other findings related to attainment or violation of the standard.
If the final rule adopts the area-wide approach on which section
II.F.4.e of this notice invites comment, provisions would be added to
section 2 of Appendix S to specify geographical criteria for
determining which monitoring sites' data can and will be compared to
the standard consistent with the area-wide approach as described in
that section.
    The EPA is proposing to amend and move the provisions of 40 CFR
50.11 related to data completeness for the existing annual primary
standard to the new Appendix S, and to add provisions for the proposed
1-hour primary standard. Substantively, the proposed data handling
procedures for the annual primary standard in Appendix S are the same
as the existing provisions in 40 CFR 50.11 for that standard, except
for a proposed addition of a cross-reference to the Exceptional Events
Rule, a proposed addition of Administrator discretion to consider
otherwise incomplete data complete, and a proposed provision addressing
the possibility of there being multiple NO2 monitors at one
site. The proposed procedures for the 1-hour primary standard are
entirely new.
    The EPA is also proposing NO2-specific changes to the
deadlines, in 40 CFR 50.14, by which States must flag ambient air data
that they believe have been affected by exceptional events and submit
initial descriptions of those events, and the deadlines by which States
must submit detailed justifications to support the exclusion of that
data from EPA determinations of attainment or nonattainment with the
NAAQS. The deadlines now contained in 40 CFR 50.14 are generic, and are
not always appropriate for NO2 given the anticipated
schedule for the designations of areas under the proposed
NO2 NAAQS.

A. Background

    The purpose of a data interpretation appendix in general is to
provide the practical details on how to make a comparison between
multi-day and possibly multi-monitor ambient air concentration data and
the level of the NAAQS, so that determinations of compliance and
violation are as objective as possible. Data interpretation guidelines
also provide criteria for determining whether there are sufficient data
to make a NAAQS level comparison at all.
    The regulatory language for the current NO2 NAAQS,
originally adopted in 1977, contains data interpretation instructions
only for the issue of data completeness. This situation contrasts

with the situations for ozone, PM2.5, PM10, and
most recently Pb for which there are detailed data interpretation
appendices in 40 CFR part 50 addressing more issues that can arise in
comparing monitoring data to the NAAQS. EPA has used its experience
drafting and applying these other data interpretation appendices to
develop the proposed text for Appendix S.
    An exceptional event is defined in 40 CFR 50.1 as an event that
affects air quality, is not reasonably controllable or preventable, is
an event caused by human activity that is unlikely to recur at a
particular location or a natural event, and is determined by the
Administrator in accordance with 40 CFR 50.14 to be an exceptional
event. Air quality data that is determined to have been affected by an
exceptional event under the procedural steps and substantive criteria
specified in section 50.14 may be excluded from consideration when EPA
makes a determination that an area is meeting or violating the
associated NAAQS. The key procedural deadlines in section 50.14 are
that a State must notify EPA that data have been affected by an event,
i.e., ``flag'' the data in the Air Quality Systems (AQS) database, and
provide an initial description of the event by July 1 of the year after
the data are collected, and that the State must submit the full
justification for exclusion within 3 years after the quarter in which
the data were collected. However, if a regulatory decision based on the
data, for example a designation action, is anticipated, the schedule is
foreshortened and all information must be submitted to EPA no later
than a year before the decision is to be made. This generic schedule
presents problems when a NAAQS has been recently revised, as discussed
below.
    The REA did not address data interpretation details. However, the
approach to data interpretation used in the REA, for example to report
the number of cities which would violate possible 1-hour primary NAAQS,
was generally consistent with the proposed data interpretation
procedures.

B. Interpretation of the Primary NAAQS for Oxides of Nitrogen

    The purpose of a data interpretation rule for the NO2
NAAQS is to give effect to the form, level, averaging time, and
indicator specified in the proposed regulatory text at 40 CFR 50.11,
anticipating and resolving in advance various future situations that
could occur. The proposed Appendix S provides common definitions and
requirements that apply to both the annual and the 1-hour primary
standards for NO2. The common requirements concern how
ambient data are to be reported, what ambient data are to be considered
(including the issue of which of multiple monitors' data sets will be
used when more than one monitor has operated at a site), and the
applicability of the Exceptional Events Rule to the primary
NO2 NAAQS.
    The proposed Appendix S also addresses several issues in ways which
are specific to the individual primary NO2 standards, as
described below.
1. Annual Primary Standard
    The proposed data interpretation provisions for the annual standard
are consistent with the current instructions included along with the
statement of the level and form of the standard in 40 CFR 53.11. These
are the following: (1) At least 75% of the hours in the year must have
reported concentration data. (2) The available hourly data are
arithmetically averaged, and then rounded (not truncated) to whole
parts per billion. (3) The design value is this rounded annual average
concentration. (4) The design value is compared with the level of the
annual primary standard (expressed in parts per billion).
    It would be possible to introduce additional steps for the annual
primary standard which in principle could make the design value a more
reliable indicator of actual annual average concentration in cases
where some monitoring data have been lost. For example, averaging
within a calendar quarter first and then averaging across quarters
could help compensate for uneven data capture across the year. For some
aspects of the data interpretation procedures for some other
pollutants, the current data interpretation appendices do contain such
additional steps. The proposed provisions for the proposed 1-hour
NO2 standard (described immediately below) also incorporate
some such features. However, we believe that such complexity is not
needed to appropriately implement the annual primary standard,
especially since no area presently comes close to violating the
standard. EPA invites comment on whether the annual primary standard
design value should be a weighted annual mean (e.g. averaging within
calendar quarters before averaging across quarters), rather than the
mean of all available hourly values.
2. 1-Hour Primary Standard Based on the Annual 4th High Value Form
    With regard to data completeness for the proposed 1-hour primary
standard, the proposed Appendix follows past EPA practice for other
NAAQS pollutants by requiring that in general at least 75% of the
monitoring data that should have resulted from following the planned
monitoring schedule in a period must be available for the key air
quality statistic from that period to be considered valid. For the
proposed 1-hour primary NO2 NAAQS, the key air quality
statistics are the daily maximum 1-hour concentrations in three
successive years. It is important that sampling within a day encompass
the period when concentrations are likely to be highest and that all
seasons of the year are well represented. Hence, the 75% requirement is
proposed to be applied at the daily and quarterly levels. EPA invites
comment on the proposed completeness requirements.
    Recognizing that there may be years with incomplete data, the
proposed text provides that a design value derived from incomplete data
will nevertheless be considered valid in either of two situations.
    First, if the design value calculated from at least four days of
monitoring observations in each of these years exceeds the level of the
1-hour primary standard, it would be valid. This situation could arise
if monitoring was intermittent but high NO2 levels were
measured on enough hours and days for the mean of the three annual 4th
values to exceed the standard. In this situation, more complete
monitoring could not possibly have indicated that the standard was
actually met.
    Second, we are proposing a diagnostic data substitution test which
is intended to identify those cases with incomplete data in which it
nevertheless is very likely, if not virtually certain, that the daily
1-hour design value would have been observed to be below the level of
the NAAQS if monitoring data had been minimally complete.
    The diagnostic test would be applied only if there is at least 50%
data capture in each quarter of each year and if the 3-year mean of the
observed annual 4th highest maximum hourly values in the incomplete
data is below the NAAQS level. The test would substitute a high
hypothetical concentration for as much of the missing data as needed to
meet the 100% requirement in each quarter. The value that is
substituted for the missing values is the highest daily maximum 1-hour
observed in the same quarter, looking across all three years under
evaluation. If the resulting 3-year design value is below the NAAQS, it
is highly likely that the design value calculated from complete data
would also have been below the NAAQS, so the original design value
indicating compliance would be considered valid.

    It should be noted that one outcome of applying the proposed
substitution test is that a year with incomplete data may nevertheless
be determined to not have a valid design value and thus to be unusable
in making 1-hour primary NAAQS compliance determinations for that 3-
year period. EPA invites comment on incorporating into the final rule
the proposed substitution test.
    Also, we are proposing that the Administrator have general
discretion to use incomplete data based on case-specific factors,
either at the request of a state or at her own initiative. Similar
provisions exist already for some other NAAQS.
3. 1-Hour Primary Standard Based on the Annual 99th Percentile Daily
Value Form
    The second version of the proposed Appendix S appearing at the end
of this notice contains proposed interpretation procedures for a 1-hour
primary standard based on the 99th percentile daily value form. The 4th
high daily value form and the 99th percentile daily value form would
yield the same design value in a situation in which every hour and day
of the year has reported monitoring data, since the 99th percentile of
365 daily values is the 4th highest value. However, the two forms
diverge if data completeness is 82% or less, because in that case the
99th percentile value is the 3rd highest (or higher) value, to
compensate for the lack of monitoring data on days when concentrations
could also have been high.
    Logically, provisions to address possible data incompleteness under
the 99th percentile daily value form should be somewhat different from
those for the 4th highest form. With a 4th highest form, incompleteness
should not invalidate a design value that exceeds the standard, for
reasons explained above. With the 99th percentile form, however, a
design value exceeding the standard stemming from incomplete data
should not automatically be considered valid, because concentrations on
the unmonitored days could have been relatively low, such that the
actual 99th percentile value for the year could have been lower, and
the design value could have been below the standard. The second
proposed version of Appendix S accordingly has somewhat different
provisions for dealing with data incompleteness. One difference is the
addition of another diagnostic test based on data substitution, which
in some cases can validate a design value based on incomplete data that
exceeds the standard.
    The second version of the proposed Appendix S provides a table for
determining which day's maximum 1-hour concentration will be used as
the 99th percentile concentration for the year. The proposed table is
similar to one used now for the 24-hour PM2.5 NAAQS, which is based on
a 98th percentile form, but adjusted to reflect a 99th percentile form
for the 1-hour primary NO2 standard. The proposed Appendix S
also provides instructions for rounding (not truncating) the average of
three annual 99th percentile hourly concentrations before comparison to
the level of the primary NAAQS.

C. Exceptional Events Information Submission Schedule

    The Exceptional Events Rule at 40 CFR 50.14 contains generic
deadlines for a state to submit to EPA specified information about
exceptional events and associated air pollutant concentration data. A
state must initially notify EPA that data has been affected by an event
by July 1 of the year after the data are collected; this is done by
flagging the data in AQS and providing an initial event description.
The state must also, after notice and opportunity for public comment,
submit a demonstration to justify any claim within 3 years after the
quarter in which the data were collected. However, if a regulatory
decision based on the data (for example, a designation action) is
anticipated, the schedule to flag data in AQS and submit complete
documentation to EPA for review is foreshortened, and all information
must be submitted to EPA no later than one year before the decision is
to be made.
    These generic deadlines are suitable for the period after initial
designations have been made under a NAAQS, when the decision that may
depend on data exclusion is a redesignation from attainment to
nonattainment or from nonattainment to attainment. However, these
deadlines present problems with respect to initial designations under a
newly revised NAAQS. One problem is that some of the deadlines,
especially the deadlines for flagging some relevant data, may have
already passed by the time the revised NAAQS is promulgated. Until the
level and form of the NAAQS have been promulgated a state does not know
whether the criteria for excluding data (which are tied to the level
and form of the NAAQS) were met on a given day. The only way a state
could guard against this possibility is to flag all data that could
possibly be eligible for exclusion under a future NAAQS. This could
result in flagging far more data than will eventually be eligible for
exclusion. EPA believes this is an inefficient use of state and EPA
resources, and is potentially confusing and misleading to the public
and regulated entities. Another problem is that it may not be feasible
for information on some exceptional events that may affect final
designations to be collected and submitted to EPA at least one year in
advance of the final designation decision. This could have the
unintended consequence of EPA designating an area nonattainment as a
result of uncontrollable natural or other qualified exceptional events.
    When Section 50.14 was revised in March 2007, EPA was mindful that
designations were needed under the recently revised PM2.5
NAAQS, so exceptions to the generic deadline were included for
PM2.5. The EPA was also mindful that similar issues would
arise for subsequent new or revised NAAQS. The Exceptional Events Rule
at section 50.14(c)(2)(v) indicates ``when EPA sets a NAAQS for a new
pollutant, or revises the NAAQS for an existing pollutant, it may
revise or set a new schedule for flagging data for initial designation
of areas for those NAAQS.''
    For the specific case of NO2, EPA anticipates that
initial designations under the revised NAAQS may be made by January 22,
2012 based on air quality data from the years 2008-2010. (See Section
VI below for more detailed discussion of the designation schedule and
what data EPA intends to use.) If final designations are made by
January 22, 2012, all events to be considered during the designations
process must be flagged and fully documented by states one year prior
to designations, by January 22, 2011. This date also coincides with the
Clean Air Act deadline for Governors to submit to EPA their
recommendations for designating all areas of their states.
    EPA is proposing revisions to 40 CFR 50.14 to change submission
dates for information supporting claimed exceptional events affecting
NO2 data. The proposed rule text at the end of this notice
shows the changes that would apply if a revised NO2 NAAQS is
promulgated by January 22, 2010, and designations are made two years
after promulgation of a NO2 NAAQS revision. For air quality
data collected in 2008, we propose to extend the generic July 1, 2009
deadline for flagging data (and providing a brief initial description
of the event) to July 1, 2010. EPA believes this extension provides
adequate time for states to review the impact of exceptional events
from 2008 on the revised standard and notify EPA by flagging the
relevant data in AQS. EPA is not proposing to change the generic
deadline of January 22, 2011 for

submitting documentation to justify an NO2-related
exceptional event from 2008. We believe the generic deadline provides
adequate time for states to develop and submit proper documentation.
    For data collected in 2009, EPA does not believe it is necessary to
change the generic deadline of July 1, 2010 for flagging data and
providing initial event descriptions. Similarly, EPA does not believe
it is necessary to change the generic deadline of January 22, 2011 for
states to submit documentation to justify an NO2-related
exceptional event from 2009.
    For data collected in 2010, EPA believes the designations deadline
of January 22, 2011 for flagging data and providing initial event
descriptions does not provide states with adequate time to review and
identify potential exceptional events that occur in calendar year 2010,
especially events that might occur late in the year. Therefore, EPA is
proposing that states may flag and provide initial event descriptions
for 2010 data no later than April 1, 2011. This affords states more
than 2 additional months than would be provided under the generic
schedule to review and identify exceptional events affecting 2010
NO2 data. Similarly, EPA believes the designations schedule
that would require states to submit detailed documentation to justify
2010 events claims by January 22, 2011 is not reasonable, because it
would potentially preclude states from completing the required public
review of the documentation prior to submitting to EPA. Therefore, EPA
is proposing to extend this deadline to July 1, 2011. This would afford
states more than 5 additional months than provided by the generic
schedule to complete the required public review and submit full
supporting documentation, yet would still allow EPA adequate time to
review the documentation and develop its final plans for designations
by January 22, 2012.
    Table 2 below summarizes the proposed two year designation
deadlines discussed in this section. If the promulgation date for a
revised NO2 NAAQS will occur on a different date than
January 22, 2010, EPA will revise the final NO2 exceptional
event flagging and documentation submission deadlines accordingly,
consistent with this proposal, to provide states with reasonably
adequate opportunity to review, identify, and document exceptional
events that may affect an area designation under a revised NAAQS. EPA
invites comment on these proposed changes in the exceptional event
flagging and documentation submission deadlines.

      Table 2--Schedule for Exceptional Event Flagging and Documentation Submission for Data To Be Used in
                                 Designations Decisions for New or Revised NAAQS
----------------------------------------------------------------------------------------------------------------
                                       Air quality data
NAAQS pollutant/standard/(level)/   collected for calendar    Event flagging & initial   Detailed documentation
        promulgation date                    year               description deadline       submission deadline
----------------------------------------------------------------------------------------------------------------
PM2.5/24-Hr Standard (35 [mu]g/    2004-2006...............  October 1, 2007 \a\......  April 15, 2008.\a\
 m3) Promulgated October 17, 2006.
Ozone/8-Hr.......................  2005-2007...............  June 18, 2009 \b\........  June 18, 2009.\b\
Standard (0.075 ppm) Promulgated   2008....................  June 18, 2009\b\.........  June 18, 2009.\b\
 March 12, 2008.
                                   2009....................  60 Days after the end of   60 Days after the end of
                                                              the calendar quarter in    the calendar quarter in
                                                              which the event occurred   which the event
                                                              or February 5, 2010,       occurred or February 5,
                                                              whichever date occurs      2010, whichever date
                                                              first \b\.                 occurs first.\b\
NO2/1-Hour Standard (80-100 PPB,   2008....................  July 1, 2010 \b\.........  January 22, 2011.
 final level TBD).
                                   2009....................  July 1, 2010.............  January 22, 2011.
                                   2010....................  April 1, 2011 \b\........  July 1, 2011.\b\
----------------------------------------------------------------------------------------------------------------
\a\ These dates are unchanged from those published in the original rulemaking, and are shown in this table for
  informational purposes.
\b\ Indicates change from general schedule in 40 CFR 50.14.
Note: EPA notes that the table of revised deadlines only applies to data EPA will use to establish the final
  initial designations for new or revised NAAQS. The general schedule applies for all other purposes, most
  notably, for data used by EPA for redesignations to attainment.

V. Clean Air Act Implementation Requirements

    This section of the preamble discusses the Clean Air Act (CAA)
requirements that states and emissions sources must address when
implementing new or revised NO2 NAAQS based on the structure
outlined in the CAA and existing rules.\23\ EPA may provide additional
guidance in the future, as necessary, to assist states and emissions
sources to comply with the CAA requirements for implementing new or
revised NO2 NAAQS.
---------------------------------------------------------------------------

    \23\ Since EPA is proposing to retain the annual standard
without revision, the discussion in this section relates to
implementation of the proposed 1-hour standard, rather than the
annual standard.
---------------------------------------------------------------------------

    The CAA assigns important roles to EPA, states, and, in specified
circumstances, Tribal governments to achieve the NAAQS. States have the
primary responsibility for developing and implementing State
Implementation Plans (SIPs) that contain state measures necessary to
achieve the air quality standards in each area. EPA provides assistance
to states by providing technical tools, assistance, and guidance,
including information on the potential control measures that may assist
in helping areas attain the standards.
    States are primarily responsible for ensuring attainment and
maintenance of ambient air quality standards once they have been
established by EPA. Under section 110 of the CAA, 42 U.S.C. 7410, and
related provisions, states are required to submit, for EPA approval,
SIPs that provide for the attainment and maintenance of such standards
through control programs directed at sources of NO2
emissions. If a state fails to adopt and implement the required SIPs by
the time periods provided in the CAA, the EPA has responsibility under
the CAA to adopt a Federal Implementation Plan (FIP) to assure that
areas attain the NAAQS in an expeditious manner.
    The states, in conjunction with EPA, also administer the prevention
of significant deterioration (PSD) program for NO2. See
sections 160-169 of the CAA. In addition, Federal programs provide for
nationwide reductions in emissions of NO2 and other air
pollutants under Title II of the Act, 42

U.S.C. 7521-7574, which involves controls for automobiles, trucks,
buses, motorcycles, nonroad engines, and aircraft emissions; the new
source performance standards (NSPS) for stationary sources under
section 111 of the CAA, 42 U.S.C. 7411; and the national emission
standards for hazardous air pollutants for stationary sources under
section 112 of the CAA, 42 U.S.C. 7412.
    CAA Section 301(d) authorizes EPA to treat eligible Indian Tribes
in the same manner as states (TAS) under the CAA and requires EPA to
promulgate regulations specifying the provisions of the statute for
which such treatment is appropriate. EPA has promulgated these
regulations--known as the Tribal Authority Rule or TAR--at 40 CFR Part
49. See 63 FR 7254 (February 12, 1998). The TAR establishes the process
for Indian Tribes to seek TAS eligibility and sets forth the CAA
functions for which TAS will be available. Under the TAR, eligible
Tribes may seek approval for all CAA and regulatory purposes other than
a small number of functions enumerated at section 49.4. Implementation
plans under section 110 are included within the scope of CAA functions
for which eligible Tribes may obtain approval. Section 110(o) also
specifically describes Tribal roles in submitting implementation plans.
Eligible Indian Tribes may thus submit implementation plans covering
their reservations and other areas under their jurisdiction.
    Under the CAA and TAR, Tribes are not, however, required to apply
for TAS or implement any CAA program. In promulgating the TAR EPA
explicitly determined that it was not appropriate to treat Tribes
similarly to states for purposes of, among other things, specific plan
submittal and implementation deadlines for NAAQS-related requirements.
40 CFR 49.4(a). In addition, where Tribes do seek approval of CAA
programs, including section 110 implementation plans, the TAR provides
flexibility and allows them to submit partial program elements, so long
as such elements are reasonably severable--i.e., ``not integrally
related to program elements that are not included in the plan
submittal, and are consistent with applicable statutory and regulatory
requirements''. 40 CFR 49.7.
    To date, very few Tribes have sought TAS for purposes of section
110 implementation plans. However, some Tribes may be interested in
pursuing such plans to implement today's proposed standard. As noted
above, such Tribes may seek approval of partial, reasonably severable
plan elements, or they may seek to implement all relevant components of
an air quality program for purposes of meeting the requirements of the
Act. In several sections of this preamble, EPA describes the various
roles and requirements states will address in implementing today's
proposed standard. Such references to states are generally intended to
include eligible Indian Tribes to the extent consistent with the
flexibility provided to Tribes under the TAR. Where Tribes do not seek
TAS for section 110 implementation plans, EPA will promulgate Federal
implementation plans as ``necessary or appropriate to protect air
quality.'' 40 CFR 49.11(a)
    EPA also notes that some Tribes operate air quality monitoring
networks in their areas. For such monitors to be used to measure
attainment with this primary NAAQS for NO2, the criteria and
procedures identified in this rule would apply.

A. Designations

    After EPA establishes or revises a NAAQS, the CAA requires EPA and
the states to begin taking steps to ensure that the new or revised
NAAQS are met. The first step is to identify areas of the country that
do not meet the new or revised NAAQS. The CAA defines EPA's authority
to designate areas that do not meet a new or revised NAAQS. Section
107(d)(1) provides that, ``By such date as the Administrator may
reasonably require, but not later than 1 year after promulgation of a
new or revised NAAQS for any pollutant under section 109, the Governor
of each state shall * * * submit to the Administrator a list of all
areas (or portions thereof) in the state'' that designates those areas
as nonattainment, attainment, or unclassifiable. Section
107(d)(1)(B)(i) further provides, ``Upon promulgation or revision of a
NAAQS, the Administrator shall promulgate the designations of all areas
(or portions thereof) * * * as expeditiously as practicable, but in no
case later than 2 years from the date of promulgation. Such period may
be extended for up to one year in the event the Administrator has
insufficient information to promulgate the designations. ``The term
``promulgation'' has been interpreted by the courts to be signature and
dissemination of a rule. By no later than 120 days prior to
promulgating designations, EPA is required to notify states of any
intended modifications to their boundaries as EPA may deem necessary.
States then have an opportunity to comment on EPA's tentative decision.
Whether or not a state provides a recommendation, EPA must promulgate
the designation that it deems appropriate.
    Thus, following promulgation of the revised NO2 NAAQS in
January 2010, EPA must promulgate initial designations by January 2012
(2 years after promulgation of the revised NAAQS), or, by January 2013
in the event that the Administrator has insufficient information to
promulgate initial designations within 2 years. In the case of the
NO2 NAAQS, in today's action EPA is proposing new
NO2 monitor siting rules that focus on roadways. EPA
anticipates that it will require up to 3 years to get a new monitoring
network in place, plus an additional 3 years of monitoring thereafter
in order to determine compliance with the revised standard. This means
that a full set of air quality data from the new network will not be
available until approximately 2016. Since data from the new network
will not be available prior to the CAA designation deadlines even if
EPA takes an additional year, EPA intends to complete initial
designations in 2012 using air quality data from the current
NO2 monitoring network in place, using NO2
monitoring data from the years 2008-2010.
    Accordingly, Governors will be required to submit their initial
designation recommendations to EPA no later than January 2011. If the
Administrator intends to modify any state area recommendation, EPA will
notify the Governor no later than 120 days prior to initial
designations in January 2012. States that believe the Administrator's
modification is inappropriate will have an opportunity to demonstrate
why they believe their recommendation is more appropriate before
designations are promulgated in January 2012. As explained below in
more detail, we intend to designate areas under the current
NO2 monitoring network as ``unclassifiable'' or
``nonattainment'' based on the data set for 2008-2010.
    We intend to designate areas that do not show violations of the
revised NO2 NAAQS as ``unclassifiable'' since the existing
area-wide monitoring network does not fully satisfy the near roadway-
oriented NO2 monitoring requirements proposed in this
notice. Because there are no monitors in the current NO2
network that meet the proposed definition of ``near-roadway,''
monitoring data that does not indicate a violation of the NAAQS would
not provide a sufficient basis for concluding that an area is meeting
the revised NO2 NAAQS. Rather, an area-wide monitor may
record concentrations that are below the revised NO2 NAAQS
because it is not sited where concentrations in the area are highest.
Thus, we do not

believe the current monitoring network provides information that
supports designating an area as ``attainment'' with today's proposed
standards.
    The EPA anticipates that areas designated as ``unclassifiable'' in
January 2012 will remain so until a new NO2 monitoring
network is deployed and 3 years of monitoring data have been collected.
Once the NO2 monitors are placed in locations meeting the
proposed near-roadway siting requirements and monitoring data become
available, the Agency could subsequently redesignate areas as
``nonattainment'' or ``attainment'' under section 107(d)(3).
    In January 2012 we intend to designate as ``nonattainment'' areas
that show violations of the revised standard under the current
monitoring network. As discussed above, the current monitoring network
may not record NO2 concentrations near roadways where
NO2 concentrations are highest. We thus anticipate that any
area showing violations of the revised NO2 standard based on
the current monitoring network will continue to show violations when
monitors are placed in near-roadway locations.
    In summary, as required by section 107(d)(1)(A)(i) of the CAA, in
January 2012 the EPA must designate as ``nonattainment'' any areas with
monitors within the existing network that report violations of the
revised NO2 NAAQS. All other areas not indicating a
violation of the revised NO2 NAAQS will be designated as
``unclassifiable.'' While the CAA provides the Agency an additional
third year from promulgation of a NAAQS to complete designations in the
event that there is insufficient information to make NAAQS compliance
determinations, we anticipate that delaying designations for this
additional year would not result in significant additional data that
would allow EPA to designate areas that would otherwise be designated
``unclassifiable.'' Once a near-roadway network has been deployed and 3
years of air quality data has been collected, we anticipate
redesignating unclassifiable areas as ``attainment'' or
``nonattainment'' where additional data from the new network provides a
basis for such a designation.
    EPA is also taking comment on the area-wide approach discussed in
section II.F.4.e above. If this approach is finalized, we anticipate
designating areas as either ``attainment,'' ``nonattainment'' or
``unclassifiable'' in 2012, based on air quality data for years 2008-
2010. Unlike the near-roadway approach, we would expect to have
sufficient data to designate some areas showing no violations of the
revised NAAQS as ``attainment'' rather than ``unclassifiable.'' As
required by CAA section 107(d), we would expect to designate areas with
violating monitors and nearby areas, including those with major
roadways that contribute to such violations, as ``nonattainment.'' Any
areas which EPA cannot classify on the basis of available information
as meeting or not meeting the revised NAAQS would be designated as
``unclassifiable.''

B. Classifications

    Section 172(a)(1)(A) of the CAA authorizes EPA to classify areas
designated as nonattainment for the purpose of applying an attainment
date pursuant to section 172(a)(2), or for other reasons. In
determining the appropriate classification, EPA may consider such
factors as the severity of the nonattainment problem and the
availability and feasibility of pollution control measures (see section
172(a)(1)(A) of the CAA). The EPA may classify NO2
nonattainment areas, but is not required to do so. The primary reason
to establish classifications is to set different deadlines for each
class of nonattainment area to complete the planning process and to
provide for different attainment dates based upon the severity of the
nonattainment problem for the affected area. However, the CAA
separately establishes specific planning and attainment deadlines in
sections 191 and 192: 18 months for the submittal of an attainment plan
and as expeditiously as possible but no later than 5 years for areas to
attain standard. EPA believes that classifications are unnecessary in
light of these relatively short deadlines. Therefore, EPA is not
proposing to establish classifications for a revised NO2
NAAQS.

C. Attainment Dates

    The maximum deadline date by which an area is required to attain
the NO2 NAAQS is determined from the effective date of the
nonattainment designation for the affected area. For areas designated
nonattainment for the revised NO2 NAAQS, SIPs must provide
for attainment of the NAAQS as expeditiously as practicable, but no
later than 5 years from the date of the nonattainment designation for
the area (see section 192(a) of the CAA). The EPA will determine
whether an area has demonstrated attainment of the NO2 NAAQS
by evaluating air quality monitoring data consistent with the form of
the NO2 NAAQS if revised, which will be codified at 40 CFR
part 50, Appendix F.
1. Attaining the NAAQS
    In order for an area to be redesignated as attainment, the state
must comply with the five requirements as provided under section
107(d)(3)(E) of the CAA. This section requires that:

--EPA must have determined that the area has met the NO2
NAAQS;
--EPA has fully approved the state's implementation plan;
--the improvement in air quality in the affected area is due to
permanent and enforceable reductions in emissions;
--EPA has fully approved a maintenance plan for the area; and
--The state(s) containing the area have met all applicable requirements
under section 110 and part D.
2. Consequences of Failing To Attain by the Statutory Attainment Date
    Any NO2 nonattainment area that fails to attain by its
statutory attainment date would be subject to the requirements of
sections 179(c) and (d) of the CAA. EPA is required to make a finding
of failure to attain no later than 6 months after the specified
attainment date and publish a notice in the Federal Register. The state
would be required to submit an implementation plan revision, no later
than one year following the effective date of the Federal Register
notice making the determination of the area's failure to attain, which
demonstrates that the standard will be attained as expeditiously as
practicable, but no later than 5 years from the effective date of EPA's
finding that the area failed to attain. In addition, section 179(d)(2)
provides that the SIP revision must include any specific additional
measures as may be reasonably prescribed by EPA, including ``all
measures that can be feasibly implemented in the area in light of
technological achievability, costs, and any nonair quality and other
air quality-related health and environmental impacts.''

D. Section 110(a)(2) NAAQS Infrastructure Requirements

    Section 110(a)(2) of the CAA requires all states to develop and
maintain a solid air quality management infrastructure, including
enforceable emission limitations, an ambient monitoring program, an
enforcement program, air quality modeling, and adequate personnel,
resources, and legal authority. Section 110(a)(2)(D) also requires
state plans to prohibit emissions from within the state which
contribute significantly to nonattainment or maintenance areas in any
other State, or which interfere with programs under part C to prevent

significant deterioration of air quality or to achieve reasonable
progress toward the national visibility goal for Federal class I areas
(national parks and wilderness areas).
    Under section 110(a)(1) and (2) of the CAA, all states are required
to submit SIPs to EPA which demonstrate that basic program elements
have been addressed within 3 years of the promulgation of any new or
revised NAAQS. Subsections (A) through (M) of section 110(a)(2) listed
below, set forth the elements that a State's program must contain in
the SIP.\24\ The list of section 110(a)(2) NAAQS implementation
requirements are the following:
---------------------------------------------------------------------------

    \24\ Two elements identified in section 110(a)(2) are not listed
below because, as EPA interprets the CAA, SIPs incorporating any
necessary local nonattainment area controls would not be due within
3 years, but rather are due at the time the nonattainment area
planning requirements are due. These elements are: (1) Emission
limits and other control measures, section 110(a)(2)(A), and (2)
Provisions for meeting part D, section 110(a)(2)(I), which requires
areas designated as nonattainment to meet the applicable
nonattainment planning requirements of part D, title I of the CAA.
---------------------------------------------------------------------------

     Ambient air quality monitoring/data system: Section
110(a)(2)(B) requires SIPs to provide for setting up and operating
ambient air quality monitors, collecting and analyzing data and making
these data available to EPA upon request.
     Program for enforcement of control measures: Section
110(a)(2)(C) requires SIPs to include a program providing for
enforcement of measures and regulation and permitting of new/modified
sources.
     Interstate transport: Section 110(a)(2)(D) requires SIPs
to include provisions prohibiting any source or other type of emissions
activity in the state from contributing significantly to nonattainment
in another state or from interfering with measures required to prevent
significant deterioration of air quality or to protect visibility.
     Adequate resources: Section 110(a)(2)(E) requires states
to provide assurances of adequate funding, personnel and legal
authority for implementation of their SIPs.
     Stationary source monitoring system: Section 110(a)(2)(F)
requires states to establish a system to monitor emissions from
stationary sources and to submit periodic emissions reports to EPA.
     Emergency power: Section 110(a)(2)(G) requires states to
include contingency plans, and adequate authority to implement them,
for emergency episodes in their SIPs.
     Provisions for SIP revision due to NAAQS changes or
findings of inadequacies: Section 110(a)(2)(H) requires states to
provide for revisions of their SIPs in response to changes in the
NAAQS, availability of improved methods for attaining the NAAQS, or in
response to an EPA finding that the SIP is inadequate.
     Consultation with local and Federal government officials:
Section 110(a)(2)(J) requires states to meet applicable local and
Federal government consultation requirements when developing SIP and
reviewing preconstruction permits.
     Public notification of NAAQS exceedances: Section
110(a)(2)(J) requires states to adopt measures to notify the public of
instances or areas in which a NAAQS is exceeded.
     PSD and visibility protection: Section 110(a)(2)(J) also
requires states to adopt emissions limitations, and such other
measures, as may be necessary to prevent significant deterioration of
air quality in attainment areas and protect visibility in Federal Class
I areas in accordance with the requirements of CAA Title I, part C.
     Air quality modeling/data: Section 110(a)(2)(K) requires
that SIPs provide for performing air quality modeling for predicting
effects on air quality of emissions of any NAAQS pollutant and
submission of data to EPA upon request.
     Permitting fees: Section 110(a)(2)(L) requires the SIP to
include requirements for each major stationary source to pay permitting
fees to cover the cost of reviewing, approving, implementing and
enforcing a permit.
     Consultation/participation by affected local government:
Section 110(a)(2)(M) requires states to provide for consultation and
participation by local political subdivisions affected by the SIP.

E. Attainment Planning Requirements

1. Nonattainment Area SIPs
    Any state containing an area designated as nonattainment with
respect to the NO2 NAAQS must develop for submission a SIP
meeting the requirements of part D, Title I, of the CAA, providing for
attainment by the applicable statutory attainment date (see sections
191(a) and 192(a) of the CAA). As indicated in section 191(a) all
components of the NO2 part D SIP must be submitted within 18
months of the effective date of an area's designation as nonattainment.
    Section 172 of the CAA includes general requirements for all
designated nonattainment areas. Section 172(c)(1) requires that each
nonattainment area plan ``provide for the implementation of all
reasonably available control measures (RACM) as expeditiously as
practicable (including such reductions in emissions from existing
sources in the area as may be obtained through the adoption, at a
minimum, of Reasonably Available Control Technology (RACT)), and shall
provide for attainment of the national primary ambient air quality
standards.'' States are required to implement RACM and RACT in order to
attain ``as expeditiously as practicable''.
    Section 172(c) requires states with nonattainment areas to submit a
SIP for these areas which contain an attainment demonstration which
shows that the affected area will attain the standard by the applicable
statutory attainment date. The State must also show that the area will
attain the standards as expeditiously as practicable, and it must
include an analysis of whether implementation of reasonably available
measures will advance the attainment date for the area.
    Part D SIPs must also provide for reasonable further progress (RFP)
(see section 172(c)(2) of the CAA). The CAA defines RFP as ``such
annual incremental reductions in emissions of the relevant air
pollution as are required by part D, or may reasonably be required by
the Administrator for the purpose of ensuring attainment of the
applicable NAAQS by the applicable attainment date.'' (See section 171
of the CAA) Historically, for some pollutants, RFP has been met by
showing annual incremental emission reductions sufficient to maintain
generally linear progress toward attainment by the applicable
attainment date.
    All NO2 nonattainment area SIPs must include contingency
measures which must be implemented in the event that an area fails to
meet RFP or fails to attain the standards by its attainment date. (See
section 172(c)(9)) These contingency measures must be fully adopted
rules or control measures that take effect without further action by
the state or the Administrator. The EPA interprets this requirement to
mean that the contingency measures must be implemented with only
minimal further action by the state or the affected sources with no
additional rulemaking actions such as public hearings or legislative
review.
    Emission inventories are also critical for the efforts of State,
local, and Federal agencies to attain and maintain the NAAQS that EPA
has established for criteria pollutants including NO2.
Section 191(a) in conjunction with section 172(c) requires that areas
designated as nonattainment for NO2 submit an emission
inventory to EPA no later than 18 months after designation as
nonattainment. In the case of NO2, sections 191(a) and
172(c) also require that states submit periodic emission

inventories for nonattainment areas. The periodic inventory must
include emissions of NO2 for point, nonpoint, mobile (on-
road and non-road), and area sources.
2. New Source Review and Prevention of Significant Deterioration
Requirements
    The Prevention of Significant Deterioration (PSD) and nonattainment
New Source Review (NSR) programs contained in parts C and D of Title I
of the CAA govern preconstruction review of any new or modified major
stationary sources of air pollutants regulated under the CAA as well as
any precursors to the formation of that pollutant when identified for
regulation by the Administrator.\25\ The EPA rules addressing these
programs can be found at 40 CFR 51.165, 51.166, 52.21, 52.24, and part
51, appendix S. States which have areas designated as nonattainment for
the NO2 NAAQS must submit, as a part of the SIP due 18
months after an area is designated as nonattainment, provisions
requiring permits for the construction and operation of new or modified
stationary sources anywhere in the nonattainment area. SIPs that
address the PSD requirements related to attainment areas are due no
later than 3 years after the promulgation of a revised NAAQS for
NO2.
---------------------------------------------------------------------------

    \25\ The terms ``major'' and ``minor'' define the size of a
stationary source, for applicability purposes, in terms of an annual
emissions rate (tons per year, tpy) for a pollutant. Generally, a
minor source is any source that is not ``major.'' ``Major'' is
defined by the applicable regulations--PSD or nonattainment NSR.
---------------------------------------------------------------------------

    The NSR program is composed of three different permit programs:
     Prevention of Significant Deterioration (PSD).
     Nonattainment NSR (NA NSR).
     Minor NSR.
    The PSD program applies when a major source, that is located in an
area that is designated as attainment or unclassifiable for any
criteria pollutant, is constructed, or undergoes a major
modification.\26\ The nonattainment NSR program applies on a pollutant-
specific basis when a major source constructs or modifies in an area
that is designated as nonattainment for that pollutant. The minor NSR
program addresses both major and minor sources that undergo
construction or modification activities that do not qualify as major,
and it applies, as necessary to ensure attainment, regardless of the
designation of the area in which a source is located.
---------------------------------------------------------------------------

    \26\ In addition, the PSD program applies to non-criteria
pollutants subject to regulation under the Act, except those
pollutants regulated under section 112 and pollutants subject to
regulation only under section 211(o).
---------------------------------------------------------------------------

    The PSD requirements include but are not limited to the following:
     Installation of Best Available Control Technology (BACT);
     Air quality monitoring and modeling analyses to ensure
that a project's emissions will not cause or contribute to a violation
of any NAAQS or maximum allowable pollutant increase (PSD increment);
     Notification of Federal Land Manager of nearby Class I
areas; and
     Public comment on permit.
    Nonattainment NSR requirements include but are not limited to:
     Installation of Lowest Achievable Emissions Rate (LAER)
control technology;
     Offsetting new emissions with creditable emissions
reductions;
     A certification that all major sources owned and operated
in the state by the same owner are in compliance with all applicable
requirements under the CAA;
     An alternative siting analysis demonstrating that the
benefits of a proposed source significantly outweigh the environmental
and social costs imposed as a result of its location, construction, or
modification; and
     Public comment on the permit.
    Minor NSR programs must meet the statutory requirements in section
110(a)(2)(C) of the CAA which requires ``* * * regulation of the
modification and construction of any stationary source * * * as
necessary to ensure that the [NAAQS] are achieved.'' Areas which are
newly designated as nonattainment for the NO2 NAAQS as a
result of any changes made to the NAAQS will be required to adopt a
nonattainment NSR program to address major sources of NO2
where the program does not currently exist for the NO2 NAAQS
and may need to amend their minor source program as well. Prior to
adoption of the SIP revision addressing major source nonattainment NSR
for NO2 nonattainment areas, the requirements of 40 CFR part
51, appendix S will apply.
3. General Conformity
    Section 176(c) of the CAA, as amended (42 U.S.C. 7401 et seq.),
requires that all Federal actions conform to an applicable
implementation plan developed pursuant to section 110 and part D of the
CAA. The EPA rules, developed under the authority of section 176(c) of
the CAA, prescribe the criteria and procedures for demonstrating and
assuring conformity of Federal actions to a SIP. Each Federal agency
must determine that any actions covered by the general conformity rule
conform to the applicable SIP before the action is taken. The criteria
and procedures for conformity apply only in nonattainment areas and
those areas redesignated attainment since 1990 (``maintenance areas'')
with respect to the criteria pollutants under the CAA: \27\ Carbon
monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone
(O3), particulate matter (PM2.5 and
PM10), and sulfur dioxide (SO2). The general conformity
rules apply one year following the effective date of designations for
any new or revised NAAQS.
---------------------------------------------------------------------------

    \27\ Criteria pollutants are those pollutants for which EPA has
established a NAAQS under section 109 of the CAA.
---------------------------------------------------------------------------

    The general conformity determination examines the impacts of direct
and indirect emissions related to Federal actions. The general
conformity rule provides several options to satisfy air quality
criteria, such as modeling or offsets, and requires the Federal action
to also meet any applicable SIP requirements and emissions milestones.
The general conformity rule also requires that notices of draft and
final general conformity determinations be provided directly to air
quality regulatory agencies and to the public by publication in a local
newspaper.
4. Transportation Conformity
    Transportation conformity is required under CAA section 176(c) (42
U.S.C. 7506(c)) to ensure that transportation plans, transportation
improvement programs (TIPs) and Federally supported highway and transit
projects will not cause new air quality violations, worsen existing
violations, or delay timely attainment of the relevant NAAQS or interim
reductions and milestones. Transportation conformity applies to areas
that are designated nonattainment and maintenance for transportation-
related criteria pollutants: carbon monoxide (CO), ozone (O3), nitrogen
dioxide (NO2), and particulate matter (PM2.5 and
PM10). Transportation conformity for a revised
NO2 NAAQS does not apply until one year after the effective
date of a nonattainment designation. (See CAA section 176(c)(6) and 40
CFR 93.102(d)).
    EPA's Transportation Conformity Rule (40 CFR Part 51, Subpart T,
and Part 93, Subpart A establishes the criteria and procedures for
determining whether transportation activities conform to the SIP. The
EPA is not proposing changes to the Transportation Conformity rule in
this proposed rulemaking. However, in the future, EPA will review the
need to conduct a

rulemaking to establish any new or revised transportation conformity
tests that would apply under a revision to the NO2 NAAQS for
transportation plans, TIPs, and applicable highway and transit
projects.

VI. Communication of Public Health Information

    Information on the public health implications of ambient
concentrations of criteria pollutants is currently made available
primarily through EPA's Air Quality Index (AQI) program. The current
Air Quality Index has been in use since its inception in 1999 (64 FR
42530). It provides accurate, timely, and easily understandable
information about daily levels of pollution (40 CFR 58.50). The AQI
establishes a nationally uniform system of indexing pollution levels
for NO2, carbon monoxide, ozone, particulate matter and
sulfur dioxide. The AQI converts pollutant concentrations in a
community's air to a number on a scale from 0 to 500. Reported AQI
values enable the public to know whether air pollution levels in a
particular location are characterized as good (0-50), moderate (51-
100), unhealthy for sensitive groups (101-150), unhealthy (151-200),
very unhealthy (201-300), or hazardous (300-500). The AQI index value
of 100 typically corresponds to the level of the short-term NAAQS for
each pollutant. An AQI value greater than 100 means that a pollutant is
in one of the unhealthy categories (i.e., unhealthy for sensitive
groups, unhealthy, very unhealthy, or hazardous) on a given day; an AQI
value at or below 100 means that a pollutant concentration is in one of
the satisfactory categories (i.e., moderate or good). Decisions about
the pollutant concentrations at which to set the various AQI
breakpoints, that delineate the various AQI categories, draw directly
from the underlying health information that supports the NAAQS review.
    The Agency recognizes the importance of revising the AQI in a
timely manner to be consistent with any revisions to the NAAQS.
Therefore EPA proposes to finalize conforming changes to the AQI, in
connection with the Agency's final decision on the NO2 NAAQS
if revisions to the primary standard are promulgated. Currently, no AQI
breakpoints are identified below an AQI value of 200 since there is no
short-term NO2 NAAQS. Therefore, if a short-term
NO2 NAAQS is promulgated, conforming changes would include
setting the 100 level of the AQI at the same level as the revised
primary NO2 NAAQS and also setting the other AQI breakpoints
at the lower end of the AQI scale (i.e., AQI values of 50 and 150). EPA
does not propose to change breakpoints at the higher end of the AQI
scale (from 200 to 500), which would apply to state contingency plans
or the Significant Harm Level (40 CFR 51.16), because the information
from this review does not inform decisions about breakpoints at those
higher levels.
    With regard to an AQI value of 50, the breakpoint between the good
and moderate categories, historically this value is set at the level of
the annual NAAQS, if there is one, or one-half the level of the short-
term NAAQS in the absence of an annual NAAQS (63 FR 67823, Dec. 12,
1998). Taking into consideration this practice, EPA is proposing to set
the AQI value of 50 to be between 0.040 and 0.053 ppm NO2,
1-hour average. EPA anticipates that figures towards the lower end of
this range would be appropriate if the standard is set towards the
lower end of the proposed range for the standard (e.g. 80 ppb), while
figures towards the higher end of the range would be more appropriate
for standards set at the higher end of the range for the standard
(e.g., 100 ppb). EPA solicits comments on this range for an AQI of 50,
and the appropriate basis for selecting an AQI of 50 both within this
range and, in light of EPA's solicitation of comment on standard levels
below 80 ppb and above 100 ppb, above or below this range.
    With regard to an AQI value of 150, the breakpoint between the
unhealthy for sensitive groups and unhealthy categories, historically
values between the short-term standard and an AQI value of 500 are set
at levels that are approximately equidistant between the AQI values of
100 and 500 unless there is health evidence that suggests a specific
level would be appropriate (63 FR 67829, Dec. 12, 1998). For an AQI
value of 150, the range of 0.360 to 0.370 ppm NO2, 1-hour
average, represents the midpoint between the proposed range for the
short-term standard and the level of an AQI value of 200 (0.64 ppm
NO2, 1-hour average). Therefore, EPA is proposing to set the
AQI value of 150 to be between 0.360 and 0.370 ppm NO2, 1-
hour average.

VII. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

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

B. Paperwork Reduction Act

    The information collection requirements in this proposed rule have
been submitted for approval to the Office of Management and Budget
(OMB) under the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. The
Information Collection Request (ICR) document prepared by EPA for these
proposed revisions to part 58 has been assigned EPA ICR number 2358.01.
    The information collected under 40 CFR part 53 (e.g., test results,
monitoring records, instruction manual, and other associated
information) is needed to determine whether a candidate method intended
for use in determining attainment of the National Ambient Air Quality
Standards (NAAQS) in 40 CFR part 50 will meet the design, performance,
and/or comparability requirements for designation as a Federal
reference method (FRM) or Federal equivalent method (FEM). We do not
expect the number of FRM or FEM determinations to increase over the
number that is currently used to estimate burden associated with
NO2 FRM/FEM determinations provided in the current ICR for
40 CFR part 53 (EPA ICR numbers 2358.01). As such, no change in the
burden estimate for 40 CFR part 53 has been made as part of this
rulemaking.
    The information collected and reported under 40 CFR part 58 is
needed to determine compliance with the NAAQS, to characterize air
quality and associated health impacts, to develop emissions control
strategies, and to measure progress for the air pollution program. The
proposed amendments would revise the technical requirements for
NO2 monitoring sites, require the siting and operation of
additional NO2 ambient air monitors, and the reporting of
the collected ambient NO2 monitoring

data to EPA's Air Quality System (AQS). The annual average reporting
burden for the collection under 40 CFR part 58 (averaged over the first
3 years of this ICR) is $3,616,487. Burden is defined at 5 CFR
1320.3(b). State, local, and Tribal entities are eligible for State
assistance grants provided by the Federal government under the CAA
which can be used for monitors and related activities.
    An agency may not conduct or sponsor, and a person is not required
to respond to, a collection of information unless it displays a
currently valid OMB control number. The OMB control numbers for EPA's
regulations in 40 CFR are listed in 40 CFR part 9.
    To comment on the Agency's need for this information, the accuracy
of the provided burden estimates, and any suggested methods for
minimizing respondent burden, EPA has established a public docket for
this rule, which includes this ICR, under Docket ID number EPA-HQ-OAR-
2006-0922. Submit any comments related to the ICR to EPA and OMB. See
ADDRESSES section at the beginning of this notice for where to submit
comments to EPA. Send comments to OMB at the Office of Information and
Regulatory Affairs, Office of Management and Budget, 725 17th Street,
NW., Washington, DC 20503, Attention: Desk Office for EPA. Since OMB is
required to make a decision concerning the ICR between 30 and 60 days
after July 15, 2009, a comment to OMB is best assured of having its
full effect if OMB receives it by August 14, 2009. The final rule will
respond to any OMB or public comments on the information collection
requirements contained in this proposal.

C. Regulatory Flexibility Act

    The Regulatory Flexibility Act (RFA) generally requires an agency
to prepare a regulatory flexibility analysis of any rule subject to
notice and comment rulemaking requirements under the Administrative
Procedure Act or any other statute unless the agency certifies that the
rule will not have a significant economic impact on a substantial
number of small entities. Small entities include small businesses,
small organizations, and small governmental jurisdictions.
    For purposes of assessing the impacts of this rule on small
entities, small entity is defined as: (1) A small business that is a
small industrial entity as defined by the Small Business
Administration's (SBA) regulations at 13 CFR 121.201; (2) a small
governmental jurisdiction that is a government of a city, county, town,
school district or special district with a population of less than
50,000; and (3) a small organization that is any not-for-profit
enterprise which is independently owned and operated and is not
dominant in its field.
    After considering the economic impacts of this proposed rule on
small entities, I certify that this action will not have a significant
economic impact on a substantial number of small entities. This
proposed rule will not impose any requirements on small entities.
Rather, this rule establishes national standards for allowable
concentrations of NO2 in ambient air as required by section
109 of the CAA. American Trucking Assn's v. EPA, 175 F. 3d 1027, 1044-
45 (D.C. cir. 1999) (NAAQS do not have significant impacts upon small
entities because NAAQS themselves impose no regulations upon small
entities). Similarly, the proposed amendments to 40 CFR part 58 address
the requirements for States to collect information and report
compliance with the NAAQS and will not impose any requirements on small
entities. We continue to be interested in the potential impacts of the
proposed rule on small entities and welcome comments on issues related
to such impacts.

D. Unfunded Mandates Reform Act

    Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public
Law 104-4, establishes requirements for Federal agencies to assess the
effects of their regulatory actions on State, local, and Tribal
governments and the private sector. Unless otherwise prohibited by law,
under section 202 of the UMRA, EPA generally must prepare a written
statement, including a cost-benefit analysis, for proposed and final
rules with ``Federal mandates'' that may result in expenditures to
State, local, and Tribal governments, in the aggregate, or to the
private sector, of $100 million or more in any one year. Before
promulgating an EPA rule for which a written statement is required
under section 202, section 205 of the UMRA generally requires EPA to
identify and consider a reasonable number of regulatory alternatives
and to adopt the least costly, most cost-effective or least burdensome
alternative that achieves the objectives of the rule. The provisions of
section 205 do not apply when they are inconsistent with applicable
law. Moreover, section 205 allows EPA to adopt an alternative other
than the least costly, most cost-effective or least burdensome
alternative if the Administrator publishes with the final rule an
explanation why that alternative was not adopted. Before EPA
establishes any regulatory requirements that may significantly or
uniquely affect small governments, including Tribal governments, it
must have developed under section 203 of the UMRA a small government
agency plan. The plan must provide for notifying potentially affected
small governments, enabling officials of affected small governments to
have meaningful and timely input in the development of EPA regulatory
proposals with significant Federal intergovernmental mandates, and
informing, educating, and advising small governments on compliance with
the regulatory requirements.
    This action is not subject to the requirements of sections 202 and
205 of the UMRA. EPA has determined that this proposed rule does not
contain a Federal mandate that may result in expenditures of $100
million or more for State, local, and Tribal governments, in the
aggregate, or the private sector in any one year. The revisions to the
NO2 NAAQS impose no enforceable duty on any State, local or
Tribal governments or the private sector. The expected costs associated
with the monitoring requirements are described in EPA's ICR document,
but those costs are not expected to exceed $100 million in the
aggregate for any year. Furthermore, as indicated previously, in
setting a NAAQS, EPA cannot consider the economic or technological
feasibility of attaining ambient air quality standards. Because the
Clean Air Act prohibits EPA from considering the types of estimates and
assessments described in section 202 when setting the NAAQS, the UMRA
does not require EPA to prepare a written statement under section 202
for the revisions to the NO2 NAAQS.
    With regard to implementation guidance, the CAA imposes the
obligation for States to submit SIPs to implement the NO2
NAAQS. In this proposed rule, EPA is merely providing an interpretation
of those requirements. However, even if this rule did establish an
independent obligation for States to submit SIPs, it is questionable
whether an obligation to submit a SIP revision would constitute a
Federal mandate in any case. The obligation for a State to submit a SIP
that arises out of section 110 and section 191 of the CAA is not
legally enforceable by a court of law, and at most is a condition for
continued receipt of highway funds. Therefore, it is possible to view
an action requiring such a submittal as not creating any enforceable
duty within the meaning of 2 U.S.C. 658 for purposes of the UMRA. Even
if it did, the duty could be viewed as falling within the exception for
a condition of Federal assistance under 2 U.S.C. 658.

    EPA has determined that this proposed rule contains no regulatory
requirements that might significantly or uniquely affect small
governments because it imposes no enforceable duty on any small
governments. Therefore, this rule is not subject to the requirements of
section 203 of the UMRA.

E. Executive Order 13132: Federalism

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

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

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

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

    This action is subject to Executive Order (62 FR 19885, April 23,
1997) because it is an economically significant regulatory action as
defined by Executive Order 12866, and we believe that the environmental
health risk addressed by this action has a disproportionate effect on
children. The proposed rule will establish uniform national ambient air
quality standards for NO2; these standards are designed to
protect public health with an adequate margin of safety, as required by
CAA section 109. The protection offered by these standards may be
especially important for asthmatics, including asthmatic children,
because respiratory effects in asthmatics are among the most sensitive
health endpoints for NO2 exposure. Because asthmatic
children are considered a sensitive population, we have evaluated the
potential health effects of exposure to NO2 pollution among
asthmatic children. These effects and the size of the population
affected are discussed in chapters 3 and 4 of the ISA; chapters 3, 4,
and 8 of the REA, and sections II.A through II.E of this preamble.

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

    This rule is not a ``significant energy action'' as defined in
Executive Order 13211, ``Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use'' (66 FR 28355
(May 22, 2001)) because it is not likely to have a significant adverse
effect on the supply, distribution, or use of energy. The purpose of
this rule is to establish revised NAAQS for NO2. The rule
does not prescribe specific control strategies by which these ambient
standards will be met. Such strategies will be developed by States on a
case-by-case basis, and EPA cannot predict whether the control options
selected by States will include regulations on energy suppliers,
distributors, or users. Thus, EPA concludes that this rule is not
likely to have any adverse energy effects.

I. National Technology Transfer and Advancement Act

    Section 12(d) of the National Technology Transfer and Advancement
Act of 1995 (NTTAA), Public Law 104-113, section 12(d) (15 U.S.C. 272
note) directs EPA to use voluntary consensus standards in its
regulatory activities unless to do so would be inconsistent with
applicable law or otherwise impractical. Voluntary consensus standards
are technical standards (e.g., materials specifications, test methods,
sampling procedures, and business practices) that are developed or
adopted by voluntary consensus standards bodies. The NTTAA directs EPA
to provide Congress, through OMB, explanations when the Agency decides
not to use available and applicable voluntary consensus standards.
    This proposed rulemaking involves technical standards with regard
to ambient monitoring of NO2. The use of this voluntary
consensus standard would be impractical because the

analysis method does not provide for the method detection limits
necessary to adequately characterize ambient NO2
concentrations for the purpose of determining compliance with the
proposed revisions to the NO2 NAAQS.
    EPA welcomes comments on this aspect of the proposed rule, and
specifically invites the public to identify potentially applicable
voluntary consensus standards and to explain why such standards should
be used in the regulation.

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

    Executive Order 12898 (59 FR 7629; Feb. 16, 1994) establishes
Federal executive policy on environmental justice. Its main provision
directs Federal agencies, to the greatest extent practicable and
permitted by law, to make environmental justice part of their mission
by identifying and addressing, as appropriate, disproportionately high
and adverse human health or environmental effects of their programs,
policies, and activities on minority populations and low-income
populations in the United States.
    EPA has determined that this proposed rule will not have
disproportionately high and adverse human health or environmental
effects on minority or low-income populations because it increases the
level of environmental protection for all affected populations without
having any disproportionately high and adverse human health effects on
any population, including any minority or low-income population. The
proposed rule will establish uniform national standards for
NO2 in ambient air. EPA solicits comment on environmental
justice issues related to the proposed revision of the NO2
NAAQS.

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