they are the most heavily trafficked roads in the country. Again noting
that NO2 concentrations are significantly associated with
traffic counts (Gilbert et al. 2007), these roads segments likely have
the greatest potential for high exposures directly connected to motor
vehicle emissions in the entire country. Typically, these very highly
trafficked roads are in the largest populated CBSAs, such as those with
2,500,000 people or more, and are somewhat atypical for CBSAs with less
than 2,500,000 people. As a result, EPA believes it is appropriate to
require a second monitor in a CBSA that has one or more road segments
with 250,000 AADT counts or more if they do not already have two near-
road monitors required due their population.
    EPA received comments requesting that EPA explain the rationale for
the selection of the population thresholds that trigger minimum
monitoring requirements and also to reconsider the size of the network.
For example, NYDOT suggested that this final rule explain the basis for
the 350,000 and 2,500,000 population thresholds that will establish
near-road monitors. In another comment, the Clean Air Council (CAC)
questioned the selected population thresholds, noting that they believe
that the population thresholds that were proposed were too high.
Specifically, CAC stated that ``at 350,000 persons, numerous metro
areas in the mid-Atlantic and Northeastern States with urban cores and
highways running through will likely be exempted from the new
monitors.'' The Spokane Regional Clean Air Agency stated that they ``do
not believe it is necessary to require air quality monitoring for
NO2 near major roadways in every metropolitan area. It is
our [SRCAA's] view that EPA could establish a statistically significant
number of air quality monitoring stations near roadways and develop a
correlation between traffic density and ambient NO2
levels.'' Further, the EPA received many State comments suggesting
reductions to the overall size of the near-road network; however the
commenters did not provide very specific suggestions on how EPA should
accomplish that reduction in size. For example, the Regional Air
Pollution Control Agency, which represents a portion of Ohio, stated
``given the fairly standard fleet of vehicles on the nation's major
highways, we urge EPA to consider the need for 142 near-roadway
monitors. Perhaps a limited number of monitors across the country would
suffice to sufficiently characterize near-roadway NO2
levels.'' These State commenters provided various reasons which are
discussed throughout this document suggesting that the network be
reduced in size, including funding concerns (section III.B.1.b), the
perceived need to implement a smaller near-road research network in
lieu of a regulatory network (section III.B.1.b), safety issues
(section III.B.7.b), and problems with State implementation plans
(section VI. D) and designation issues (section V).
    EPA notes that the intent of the first tier of the network design
is to support the revised NAAQS in measuring peak NO2
exposures in an area by including a minimum number of monitors
resulting in a sufficiently sized national near-road monitoring network
that will provide data from a geographically and spatially diverse
array of areas, in terms of population, potential fleet mixes,
geographic extent, and geographic setting, from across the country. The
U.S. Department of Transportation (U.S. DOT) Federal Highway
Administration (FHWA) ``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 (U.S.) 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 (U.S.)
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. The basis for the selection of the
proposed CBSA population level of 350,000 to trigger the requirement of
one near-road monitor was chosen in an attempt to provide near-road
monitoring data from a diverse array of areas, as noted above. However,
in response to the significant number of comments discussed above,
which in various ways encouraged at least a reduction of the size of
the required near-road network or the implementation of a relatively
smaller research network, EPA reconsidered the population threshold
that will require one near-road NO2 monitor in a CBSA.
    EPA reviewed the data, such as population, geographic, and spatial
distribution, associated with particular CBSA areas that would and
would not be included in particular CBSA population thresholds.
According to the 2008 U.S. Census Bureau estimates (http://
www.census.gov) there are 143 CBSAs with 350,000 or more persons
(including territories) which contain approximately 71% of the total
population (excluding territories). These

CBSAs collectively represent territory in 44 States, the District of
Columbia, and Puerto Rico. For comparison, there are 391 CBSAs with
100,000 or more persons, which contain approximately 86% of the total
population (excluding territories). These particular CBSAs collectively
represent territory in 49 States, the District of Columbia, and Puerto
Rico. Further, there are 102 CBSAs with 500,000 or more persons, which
contain approximately 66% of the total population (excluding
territories). These 102 CBSAs collectively represent territory in 43
States, the District of Columbia, and Puerto Rico. Finally, there are
22 CBSAs with 2,500,000 or more persons, which contain approximately
39% of the total population, collectively representing territory in 19
States, the District of Columbia, and Puerto Rico. In comparison to the
CBSA population threshold of 350,000, the 500,000 population threshold
has 41 less CBSAs. However, the percentage of the total U.S. population
residing in these two sets of CBSAs differs by only approximately 5
percent of the total population (e.g., 71% in CBSAs of 350,000 or more
versus 66% in CBSAs of 500,000 or more persons). Also, when comparing
the number of States that have some amount of their territory included
in these CBSAs, the difference between the two sets of CBSAs differs by
only 1 State (Alaska).
    Further, EPA notes that the REA Air Quality Analysis, (REA, section
7.3.2) estimated the exceedences of health benchmark levels across the
United States, including explicit consideration of on- or near- roadway
exceedances in 17 urban areas associated with CBSA populations ranging
from approximately 19,000,000 to 540,000. The analysis indicated that
all 17 of the areas under explicit consideration were estimated to
experience NO2 concentrations on or near roads that exceeded
health benchmark levels.
c. Conclusions Regarding the First Tier (Near-Road Monitoring
Component) of the Network Design
    After consideration of public comments, and in light of the
information discussed above, the Administrator has chosen to finalize
the CBSA population threshold for requiring a minimum of one near-road
monitor in CBSAs with a population of 500,000 or more persons. The
Administrator is finalizing the other thresholds that will trigger a
second near-road monitor as proposed. Accordingly, one near-road
NO2 monitor is required in CBSAs with a population greater
than or equal to 500,000 persons and a second near-road monitor is
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 Annual
Average Daily Traffic (AADT) count greater than or equal to 250,000.
    The Administrator has concluded that using a population threshold
of 500,000 to require a minimum of one near-road monitor in a CBSA
provides a sufficiently sized, national network of near-road monitors
that will provide data from a geographically and spatially diverse set
of CBSAs that supports the intent of the revised NAAQS and continues to
meet the monitoring objectives of the network. Combined with the forty
additional monitors that the Regional Administrators are required to
site, discussed below, the monitoring network would cover an additional
percentage of the total population.
    EPA believes that selecting a lower population threshold, such as
100,000 or, to a lesser degree, 350,000, as discussed in the above
examples, would create a much larger network of required near-road
monitors but would provide diminished population coverage per monitor,
compared to that provided by the 500,000 threshold. EPA notes that if a
particular area, such as one with a population less than 500,000
people, might warrant a near-road monitor, the Regional Administrator
has the authority to require additional monitors. The Regional
Administrators' authority is discussed in section III.B.4. Further,
States have the right to conduct additional monitoring above the
minimum requirements on their own initiative. In the Administrator's
judgment, selecting a higher threshold, such as 2,500,000, as was
suggested by some commenters, does not provide a sufficient
geographical and spatially diverse near-road network, compared to that
provided by the 500,000 threshold. The selection of the 2,500,000
population threshold to trigger a second near-road monitor, as noted
earlier in this section, is based on the fact that the larger urban
areas in the country are likely to have a greater number of major roads
across a potentially larger geographic area, and have a corresponding
increase in potential for population exposure to elevated levels in
different settings.
    Changing the CBSA population threshold 350,000 to 500,000 results
in a near-road monitoring network requiring approximately 126 monitors
distributed within 102 CBSAs. Compared to the total number of required
near-road monitors that would have resulted from the proposed CBSA
population threshold of 350,000 (167 monitors), an estimated 41 fewer
monitors are required. EPA has also recognized that susceptible and
vulnerable populations, which include asthmatics and disproportionately
exposed groups, (as discussed in sections II.B.4 and II.F.4.d) are at
particular risk of NO2-related health effects. The
Administrator is therefore requiring the Regional Administrators,
working in collaboration with States, to site forty monitors in
appropriate locations, focusing primarily on protecting such
susceptible and vulnerable communities. This decision is discussed in
detail in section III.B.4.
3. Second Tier (Area-Wide Monitoring Component) of the Network Design
    The following paragraphs provide background, rationale, and details
for the final changes to the second tier of the two-tier NO2
network design. In particular, this section will focus on the threshold
that triggers area-wide monitoring requirements. Area-wide site
selection and siting criteria details will be discussed in a subsequent
section.
a. Proposed Second Tier (Area-Wide Monitoring Component) of the Network
Design
    As the second tier of the proposed two-tier network design, EPA
proposed to require monitors to characterize the expected maximum
NO2 concentrations at the neighborhood and larger (area-
wide) spatial scales in an area. This component of the two-tier network
design provides information on area-wide exposures that may occur due
to an individual or a group of point, area, on-road, and/or non-road
sources. Further, area-wide sites serve multiple monitoring objectives
aside from NAAQS comparison to both the 1-hour and the annual NAAQS,
including photochemical pollutant assessment, aiding in ozone
forecasting, aiding in particulate matter precursor analysis and
particulate matter forecasting. We proposed to require one area-wide
monitoring site in each CBSA with a population greater than or equal to
1,000,000. We proposed that these area-wide sites were to be sited to
represent an area of highest concentration at the neighborhood or
larger spatial scales. Based on 2008 Census Bureau statistics, there
are 52 CBSAs with 1,000,000 people or more, which would result in an
estimated 52 area-wide monitors in as many CBSAs being minimally
required. EPA also proposed to allow any current photochemical
assessment monitoring station (PAMS) sites that are sited where the
highest NO2 concentrations occur in an urban area

and represent a neighborhood or urban scale to satisfy the area-wide
monitoring requirement.
b. Comments
    Most commenters who commented on area-wide monitoring supported the
adoption of the alternative area-wide network design and did not
specifically comment on the area-wide monitoring component of the
proposed two-tier network design. However, EPA did receive comments
from public health organizations on area-wide monitoring in the context
of the proposed network design. The public health group commenters,
including the ALA, EJ, EDF, and the NRDC, stated they ``oppose the
proposed requirement to retain only 52 air monitors to measure area-
wide concentrations of NO2.''
    EPA understands the perceived concern to be that with this
provision, EPA is actively reducing the number of required area-wide
monitors. Prior to this rulemaking, the Ambient Air Monitoring
Regulations, 71 FR 61236 (Oct. 17, 2006) (2006 monitoring rule) removed
minimum monitoring requirements for NO2, and the rationale
for that action is explained in that rule; however, the 2006 Monitoring
rule has had a limited impact to date, evidenced by the fact that the
size of the NO2 network has remained relatively steady at
around 400 monitors, a majority of which are area-wide monitors, that
were operating in 2008 (Watkins and Thompson, 2008). The stability of
the NO2 network is due in large part to the fact that area-
wide monitors serve multiple monitoring objectives, including
photochemical pollutant assessment, pollutant forecasting, and in some
cases, support to ongoing health research. However, considering the
objective of this two-tier network design, particularly the first tier,
of supporting the revised NAAQS to protect against peak NO2
exposures, some shrinkage in the area-wide network is appropriate and
likely. EPA believes that the actual number of area-wide monitors that
will operate in the NO2 network will be greater than the
minimally required 52 sites, but likely less than the current number.
States and Regional Administrators will work together on which area-
wide sites may warrant retention above the minimum required if States
request existing area-wide sites to be shut down or relocated.
c. Conclusions on the Second Tier (Area-Wide Monitoring Component) of
the Network Design
    Area-wide monitoring sites serve multiple monitoring objectives
aside from NAAQS comparison to both the 1-hour and the annual NAAQS,
including photochemical pollutant assessment, ozone forecasting,
particulate matter precursor analysis and particulate matter
forecasting. EPA recognizes that a significant portion of the existing
NO2 monitoring network can be characterized as area-wide
monitors and that these monitoring sites serve multiple monitoring
objectives, as noted above. In order to ensure that a minimum number of
area-wide monitors continue operating into the future, we are
finalizing the proposed minimum monitoring requirements for area-wide
monitors, where one area-wide monitor is required in any CBSA with
1,000,000 people or more. Since there were no adverse comments received
with regard to allowing PAMS stations that meet siting criteria to
satisfy minimum monitoring requirements for area-wide monitors, we are
finalizing that allowance as proposed. EPA encourages States to use the
upcoming 2010 network assessment process to review existing area-wide
NO2 sites to help determine what monitors might meet minimum
monitoring requirements and whether or not other existing monitors
warrant continued operation.
4. Regional Administrator Authority
    The following paragraphs provide background, rationale, and details
for the final changes to Regional Administrator authority to use
discretion in requiring additional NO2 monitors beyond the
minimum network requirements. The proposed rule estimated that
approximately 167 near-road monitors would be required within CBSAs
having populations of 350,000 or more persons. As discussed above in
section III.B.2, in response to public comments, particularly from
States, EPA is changing the population threshold for siting a minimum
of one near-road NO2 monitor from CBSAs with 350,000 or more
persons to CBSAs with 500,000 or more persons. EPA estimates that this
change in the population threshold will result in a reduction in the
number of minimally required near-road NO2 monitors by
approximately forty monitors. EPA has also recognized that susceptible
and vulnerable populations, which include asthmatics and
disproportionately exposed groups (as discussed in sections II.B.4 and
II.F.4.d) are at particular risk of NO2-related health
effects. The Administrator is therefore requiring the Regional
Administrators, working in collaboration with States, to site these
forty monitors in appropriate locations, focusing primarily on
protecting susceptible and vulnerable communities. In addition, the
Regional Administrators, working with States, may take into account
other considerations described below in using their discretion to
require additional monitors.
a. Proposed Regional Administrator Authority
    EPA proposed that Regional Administrators have the authority to
require monitoring at their discretion in particular instances. First,
EPA proposed that the Regional Administrator 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. Second, EPA proposed to allow Regional
Administrators the discretion to require additional near-road
monitoring sites to address circumstances where minimum monitoring
requirements are not sufficient to meet monitoring objectives, such as
where exposures to NO2 concentrations vary across an area
because of varied fleet mixes, congestion patterns, terrain, or
geographic areas within a CBSA. And third, EPA proposed that Regional
Administrators have the discretion to require additional area-wide
NO2 monitoring sites above the minimum requirements for
area-wide monitors where the minimum requirements are not sufficient to
meet monitoring objectives.
b. Comments
    EPA received comments from the Center on Race, Poverty and
Environment expressing concern that the proposed monitoring provisions
fail to consider ``disproportionately impacted communities'' which
include people of color and of lower socioeconomic status. The
commenter argues that this is ``a gaping hole'' in the proposed
monitoring system and disproportionately impacts minority and low
income populations in rural communities. In addition, the National
Tribal Air Association stated that ``Indian Tribes and Alaska Natives
are highly susceptible to health impacts as a result of NO2
exposure'' and ``the prevalence and severity of asthma is higher among
certain ethnic or racial groups such as Indian Tribes and Alaska
Natives,'' which is also discussed in section II.B.4 and the ISA (ISA,
section 4.4).
    The proposed rule provided the Regional Administrators with the
authority to use their discretion and

consider certain factors to require monitors above the minimum number
in a CBSA. The proposal described one example where a Regional
Administrator might require an additional near-road monitor where ``a
particular community or neighborhood is significantly or uniquely
affected by road emissions.'' EPA recognizes that susceptible and
vulnerable populations, which include asthmatics and disproportionately
exposed groups, as noted in section II.F.4.d, are at particular risk of
NO2-related health effects, both because of increased
exposure and because these groups have a higher prevalence of asthma
and higher hospitalization rates for asthma. As noted above, in
conjunction with raising the threshold for requiring one near-road
NO2 monitor in CBSAs with 500,000 persons or more, EPA is
requiring the Regional Administrators, under their discretionary
authority, to work with States to site an additional forty monitors,
nationally, focusing primarily on communities where susceptible and
vulnerable populations are located. To address the risks of increased
exposure to these populations, the Administrator has determined that it
is appropriate and necessary, under this provision, to ensure these
additional forty monitors are sited primarily in communities where
susceptible and vulnerable populations are exposed to NO2
concentrations that have the potential to exceed the NAAQS (due to
emissions from motor vehicles, point sources, or area sources). As a
result of this action, the total number of monitors required through
this rulemaking is generally equivalent to the proposed number of
minimally required monitors.
    EPA received comments from public health groups (e.g., ALA, Center
on Race, Poverty, and the Environment, EDF, EJ, NRDC) and the Swinomish
Tribe, who suggested that EPA expand monitoring coverage to address
impacts from stationary sources outside of urban areas. For example,
ALA, EDF, EJ, and NRDC, stated that ``EPA should require States and
local offices to review inventory data to identify any potential
NO2 hotspots outside of those large metropolitan areas. For
instance, if a large power plant or any other source is creating
elevated NO2 levels in proximity to homes, schools or other
sensitive sites, in an area of less than one million people, EPA should
consider requiring a monitor.''
    EPA recognizes that there are major NO2 sources outside
of CBSAs that have the potential to contribute to NO2
concentrations approaching or exceeding the NAAQS. The issue is whether
such monitoring should be addressed through a more extensive set of
minimum requirements that might include monitoring near all large
stationary sources such as airports, seaports, and power plants, which
could lead to deploying a large number of monitors. EPA believes that a
more reasonable approach to address monitoring needs related to the
diverse set of point, area, and non-road mobile NO2 sources,
whether inside or outside of CBSAs, is to provide Regional
Administrators the authority to require additional monitoring in areas
where these impacts could occur. While the proposal did not
specifically state that Regional Administrators could require non-area-
wide monitors outside of CBSAs, EPA believes that it is important that
Regional Administrators have the authority to require NO2
monitoring in locations where NO2 concentrations may be
approaching or exceeding the NAAQS, whether located inside or outside
of CBSAs. Therefore, in the final rule, EPA is not limiting the
Regional Administrators' discretionary authority to require
NO2 monitoring only inside CBSAs; instead, the EPA is
providing Regional Administrators the authority to site monitors in
locations where NO2 concentrations may be approaching or
exceeding the NAAQS, both inside or outside of CBSAs.
    The EPA also received comments from some State groups (e.g. the New
York Department of Environmental Conservation (NYSDEC), New York
Department of Transportation (NYSDOT), and the New York City Law
Department) and an industry group (the Council of Industrial Boiler
Operators) requesting greater clarification on the way in which
Regional Administrators may use their authority to require additional
monitors above the minimum requirements. For example, the Council of
Industrial Boiler Operators stated that ``this [Regional Administrator
authority] unreasonably vests an unbounded amount of discretion in EPA
to determine when ``minimum monitoring requirements are not
sufficient'' and which neighborhoods are ``uniquely affected,'' and
impose additional monitoring requirements where all applicable
monitoring requirements are already met by the State and local
agency.''
    The authority of Regional Administrators to require additional
monitoring above the minimum required is not unique to NO2.
For example, Regional Administrators have or are proposed to have the
authority to use their discretion to require additional Pb monitors (40
CFR Part 58 Appendix D section 4.5), and have the discretion to work
with States or local agencies in designing and/or maintaining an
appropriate ozone network, per 40 CFR Part 58 Appendix D section 4.1.
EPA believes that while the NO2 monitoring network is
sufficiently sized and focused, a nationally applicable network design
may not account for all locations in which potentially high
concentrations approaching or exceeding the NAAQS exist. Therefore, EPA
believes it is important for Regional Administrators to have the
ability to address possible gaps in the minimally required monitoring
network, by granting them authority to require monitoring above the
minimum requirements.
    One case in which the Regional Administrator may exercise
discretion in requiring a monitor might be a location or community
affected by a stationary source where the required near-road
NO2 monitor site is not the location of the maximum hourly
concentration in a CBSA. For any given CBSA, there is the possibility
that the maximum NO2 concentrations could be attributed to
impacts from one, or a combination of, multiple sources that could
include point, area, and non-road source emissions in addition to on-
road mobile source emissions. As a result, the Regional Administrator
may choose to require monitoring in such a location. In addition, there
is the possibility that a single source or group of sources exists
which may contribute to concentrations approaching or exceeding the
NAAQS at locations inside or outside CBSAs, including rural
communities. In such cases, Regional Administrators, working with
States, may require a monitor in these locations. Further, if there are
NO2 sources responsible for producing more widespread
impacts on a community or relatively larger area, Regional
Administrators may require an area-wide monitor to assess wider
population exposures, or to support other monitor objectives served by
area-wide monitors such as photochemical pollutant assessment or
pollutant forecasting.
    Regional Administrators may also require additional monitoring
where a State or local agency is fulfilling its minimum monitoring
requirements with an appropriate number of near-road monitors, but an
additional location is identified where near-road population exposure
exists at concentrations approaching or exceeding the NAAQS. In this
case, the exposure may be due to differences in fleet mix, congestion
patterns, terrain, or geographic area, relative to any minimally
required monitoring site(s) in that area. We note

that such areas might exist in CBSAs with populations less than 500,000
persons.
    EPA recognizes that high concentrations of NO2 that
approach or exceed the NAAQS could potentially occur in a variety of
locations in an area, and we believe that Regional Administrators
should have the discretion to require additional monitoring when a
location is identified based on the factors discussed in the paragraph
above. In such situations, State or EPA Regional staff is likely to
have identified these locations through data analysis, such as the
evaluation of existing ambient data and/or emissions data, or through
air quality modeling. Such information may indicate that an area has
NO2 concentrations that may approach or exceed the NAAQS,
and that there is potential for population exposure to those high
concentrations.
    The Regional Administrator would use this authority in
collaboration with State agencies. We expect Regional Administrators to
work with State and local agencies to design and/or maintain the most
appropriate NO2 network to meet the needs of a given area.
For all the situations where a Regional Administrator may require
additional monitoring, including the forty additional monitors the
Regional Administrators are required to site, EPA expects Regional
Administrators to work on a case-by-case basis with States. Further,
for the forty additional monitors that will focus primarily on
protecting susceptible and vulnerable communities, EPA intends to work
with States to develop criteria to guide site selection for those
monitors.
c. Conclusions on Regional Administrator Authority
    EPA is requiring Regional Administrators to work with States to
site forty NO2 monitors, above the minimum number required
in the two-tier network design, focused primarily in susceptible and
vulnerable communities exposed to NO2 concentrations that
have the potential to approach or exceed NAAQS. In addition,
recognizing that a nationally applicable monitoring network design will
not include all sites with potentially high concentrations due to
variations across locations, and in response to public comments, the
Administrator is providing Regional Administrators with the discretion
to require additional monitors above the minimum requirements.
    Regional Administrators may also use their discretionary authority
to require monitoring above the minimum requirements as necessary to
address situations inside or outside of CBSAs in which (1) The required
near-road monitors do not represent all locations of expected maximum
hourly NO2 concentrations in an area and NO2
concentrations may be approaching or exceeding the NAAQS in that area;
(2) areas that are not required to have a monitor in accordance with
the monitoring requirements and NO2 concentrations may be
approaching or exceeding the NAAQS; or (3) the minimum monitoring
requirements for area-wide monitors are not sufficient to meet
monitoring objectives. In all cases in which a Regional Administrator
may consider the need for additional monitoring, EPA expects that
Regional Administrators will work with the State or local agencies to
evaluate evidence that suggests an area may warrant additional
monitoring. EPA also notes that if additional monitoring should be
required, as negotiated between the Regional Administrator and the
State, the State will modify the information in its Annual Monitoring
Network Plan to include any potential new sites prior to approval by
the EPA Regional Administrator.
5. Monitoring Network Implementation
    The following paragraphs provide background, rationale, and details
for the final changes to the approach for the monitoring network
implementation.
a. Proposed Monitoring Network Implementation Approach
    EPA proposed that State and, when appropriate, local air monitoring
agencies provide a plan for deploying monitors in accordance with the
proposed network design by July 1, 2011. EPA also proposed that the
proposed NO2 network be physically established no later than
January 1, 2013.
b. Comments
    Most environmental and public health group commenters suggested
that EPA change the implementation date from the proposed January 1,
2013 to a date that would require the minimum required NO2
network to be deployed sooner than proposed. Most States and State
group commenters, along with industry group commenters, recommended
that EPA keep the network implementation date as January 1, 2013, or
move it later than proposed. Those commenters who suggested moving it
later noted that issues with monitoring site identification, site
development, and overall lack of experience working in the near-road
environment would make implementation difficult under the proposed
implementation deadline.
    EPA recognizes the challenges involved with deploying the two-tier
network design by the January 1, 2013 date. We recognize the need for
additional information and plan to aid State agencies in the network
implementation process, particularly by developing guidance in
partnership with affected stakeholders, ideally including at a minimum
NACAA and the States. EPA agrees with NACAA's suggestion that the CASAC
Ambient Air Monitoring and Methods subcommittee should be consulted as
part of developing any guidance developed for near-road monitoring, and
has already begun the process by scheduling meetings with them
regarding near-road monitoring. Further, EPA believes that
collaboration with the States and State groups in developing guidance
will be highly beneficial to the implementation process. This would
allow for those States that do have increased experience in near-road
monitoring to support the guidance development process and provide a
conduit for sharing experiences amongst all stakeholders.
    In perspective, EPA believes that the approximate 2 years and 11
months between promulgation of this rulemaking and the mandated January
1, 2013 network implementation date includes extra time relative to
what is traditionally allowed for network implementation following
rulemakings. We are also cognizant of the time needed to collect
complete data that would allow data from the two-tier network to be
considered for designations and for use in the next NO2
NAAQS review data from the 2013, 2014, and 2015 years would provide
critical information in the next NAAQS review, intended to occur on a
5-year cycle, and for use in subsequent designations. Even with
complete data from 2013, 2014, and 2015 years designations would not
occur until 2017, at the earliest.
c. Conclusions on Monitoring Network Implementation
    EPA is finalizing the date by which State and, when appropriate,
local air monitoring agencies shall establish the required
NO2 monitoring network as January 1, 2013, as was proposed.
We believe that the allotted time for implementation will allow for the
development of guidance documentation, particularly allowing for
interactions with CASAC and NACAA/States, and for the processes that
will be involved in deploying this network. However, EPA recognizes
that the network implementation process,

particularly for near-road monitors, will include the assessment of
road segments in CBSAs to identify locations of maximum expected hourly
NO2 concentrations, identifying and working with other State
and local agencies, such as transportation officials, as needed on
issues regarding access and safety, and the exchange of information and
feedback on potential sites with EPA, prior to any commitment to
selecting and presenting new sites in an annual monitoring plan. As a
result, based on feedback received through public comments, and to
allow for more time to process guidance information, to carry out the
deployment processes, and to allow for information exchanges to occur,
we are changing the date by which State and, when appropriate, local
air monitoring agencies shall provide a plan for deploying monitors in
accordance with required network design, including the monitors
required under the Regional Administrators' discretional authority
which are to be primarily focused on providing protection to
susceptible and vulnerable populations, as discussed in section
III.B.4, from July 1, 2011 to July 1, 2012. EPA strongly encourages
State and local air agencies to supply as much information as possible
on the NO2 sites they may be considering, including possible
site coordinates if available, or have possibly selected, to satisfy
the minimum NO2 network monitoring requirements in their
Annual Monitoring Network Plan submitted July 1, 2011.
6. Near-Road Site Selection
    The following paragraphs provide background, rationale, and details
for the final changes to the approach and criteria by which required
near-road sites shall be selected.
a. Proposed Near-Road Site Selection Criterion
    EPA proposed that the required near-road NO2 monitoring
stations shall be selected by ranking all road segments within a CBSA
by AADT and then identifying a location or locations adjacent to those
highest ranked road segments where maximum hourly NO2
concentrations are expected to be highest and siting criteria can be
met in accordance with that proposed for 40 CFR Part 58 Appendix E
(discussed in III.B.7). 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.
Where one CBSA is required to have two near-road NO2
monitoring stations, we proposed that the sites shall be differentiated
from each other by one or more of the following factors: Fleet mix;
congestion patterns; terrain; geographic area within the CBSA; or
different route, interstate, or freeway designation.
b. Comments
    EPA received many comments from CASAC, public health groups, States
and State groups, and industry groups on the proposed process by which
States will select near-road sites. CASAC, along with some health group
and State commenters questioned how States should select a site near
the road with the highest ranked AADT possible, noting that EPA did not
appear to require States to account for other factors. For example, one
CASAC panel member noted that siting monitors based on traffic counts
alone might miss locations where maximum NO2 concentrations
would occur. They proceeded to recommend the use of modeling to assist
in the site selection process. In another example, the ALA, EDJ, EJ,
and NRDC, stated that ``Near-road monitor placement should be
determined not only by the highest AADT volumes in a given CBSA, but
also by the highest heavy-duty truck volumes.'' NACAA also expressed
concerns on ``* * * basing monitor locations on the annual average
daily traffic (AADT) without regard to vehicle mix or dispersion
characteristics * * *''.
    EPA does not intend for AADT counts to be the sole basis for
choosing a near-road site. As noted earlier in section III.B.2, there
is a general relationship between AADT and mobile source pollution,
where higher traffic counts correspond to higher mobile source
emissions. The use of AADT counts is intended to be a mechanism for
focusing on identifying the locations of expected maximum
NO2 concentrations due to mobile sources. There are other
factors that can influence which road segment in a CBSA may be the
actual location where the maximum NO2 concentrations could
occur. These factors include vehicle fleet mix, roadway design,
congestion patterns, terrain, and meteorology. When States identify
their top-ranked road segments by AADT, EPA intends for States to
evaluate all of the factors listed above in their site selection
process, due to their influence on where the location of expected
maximum NO2 concentration may occur. As a result of the
comments indicating a need for clarification, EPA will specifically
list the factors that must be considered by States in their site
selection process once a State has identified the most heavily
trafficked roads in a CBSA based on AADT counts. In addition, EPA
proposed that States consider these factors when they are required to
place two near-road monitors in a CBSA, i.e., CBSAs with a population
of 2,500,000 persons or more. EPA notes that these factors will be used
in differentiating the two monitoring sites from each other, providing
further characterization of near-road environments in 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 in different settings. Finally, EPA
notes that air quality models, which were noted by the CASAC panel
member to be considered for use in near-road site selection, are tools
that EPA believes will be useful, and likely used by some States to
inform where near-road sites need to be placed.
    EPA received comments from some State and industry commenters (e.g.
Iowa, NY DEC, Edison Electric Institute, and Savannah River Nuclear
Solutions) who suggested that potential population exposure should be a
first-level metric in the near-road monitoring site selection process,
instead of a second-level metric as EPA had proposed.
    EPA notes that the intent of the revised primary NO2
NAAQS is to protect against the maximum allowable NO2
concentration anywhere in an area, which includes ambient air on and
around roads. This would limit exposures to peak NO2
concentrations, including those due to mobile source emissions, across
locations (including those locations where population exposure near
roads is greatest) in a given CBSA or area, with a relatively high
degree of confidence. We also note the agency's historical practice has
been to site ambient air monitors in locations of maximum
concentration, at the appropriate spatial scale. If EPA were to allow
population, population density, or another population weighted metric
to be a primary factor in the decision on where required near-road
NO2 monitors are to be located, it is possible that the
required near-road monitors in a CBSA would not be located at a site of
expected maximum hourly near-road NO2 concentration. By
monitoring in the location of expected maximum 1-hour concentrations,
near-road monitoring sites will likely represent the highest
NO2 concentrations in an area directly attributable to
mobile sources or a group of sources that includes mobile sources. The
proposed rule did permit, and the final rule states, that States are to

consider population in the site selection process in situations when a
State identifies multiple candidate sites where maximum hourly
NO2 concentrations are expected to occur.
    EPA received a comment from HCPHES suggesting that required
monitoring should take into consideration the location of other major
mobile sources for NO2 emissions such as airports and
seaports. EPA also received a comment from the South Carolina
Department of Health and Environmental Control stating that a near-road
network does not address ``widespread pollutants from numerous and
diverse sources.''
    EPA recognizes that there are major NO2 sources outside
of CBSAs that have the potential to contribute to NO2
concentrations approaching or exceeding the NAAQS. The issue is whether
such monitoring should be addressed through a more extensive set of
minimum requirements that might include monitoring near all large
stationary sources such as airports, seaports, and power plants, which
could lead to deploying a large number of monitors. EPA believes that a
more reasonable approach to address monitoring needs related to the
diverse set of point, area, and non-road mobile NO2 sources,
whether inside or outside of CBSAs, is to provide Regional
Administrators the authority to require additional monitoring in areas
where these impacts could occur. Providing the Regional Administrators
with the discretion to require additional monitors allows them to
effectively address such situations, even if that area is satisfying
minimum monitoring requirements. This Regional Administrator authority
is discussed above in section III.B.4. EPA also notes that State and
local agencies may also monitor such locations on their own initiative.
    One State commenter, the Wisconsin Department of Natural Resources,
requested that the term ``major road'' be defined and also requested
clarification on what ``top-ranked'' means with regard to AADT counts
on road segments. While the term ``major road'' is widely used in
literature and can be found to be defined differently from one
scientific study to another, here, EPA is using it in its commonly
understood meaning as a road that is relatively heavily trafficked. EPA
also does not believe it is appropriate to provide a bright-line
definition for ``top-ranked''. Each CBSA will have a different
distribution of total road segments and corresponding AADT counts on
those segments. Further, since required near-road monitors are to be
sited in locations of expected maximum concentrations, a percentile
restriction on ``top ranked'' roads is unnecessary. The intent of the
requirement to rank all road segments by AADT counts and select a site,
considering the other local factors noted above, near a ``top-ranked''
road segment is to focus attention on the most heavily trafficked
roads, around which there is higher potential for maximum
NO2 concentrations to occur.
c. Conclusions on Near-Road Site Selection
    We are finalizing the near-road site selection criteria as
proposed, and are clarifying that the proposal intended the selection
criteria to include consideration of localized factors when identifying
locations of expected maximum concentrations. As a result, required
near-road NO2 monitoring stations shall be selected by
ranking all road segments within a CBSA by AADT and then identifying a
location or locations adjacent to those highest ranked road segments,
considering fleet mix, roadway design, congestion patterns, terrain,
and meteorology, where maximum hourly NO2 concentrations are
expected to occur and siting criteria can be met in accordance with 40
CFR Part 58 Appendix E. As was noted in section III.B.5 above, EPA will
work with States to assist with the near-road site selection process
through the development of guidance material and through information
exchanges amongst the air monitoring community.
    We are also finalizing the requirement, as proposed, that when one
CBSA is required to have two near-road NO2 monitoring
stations, the sites shall be differentiated from each other by one or
more of the following factors: fleet mix; congestion patterns; terrain;
geographic area within the CBSA; or different route, interstate, or
freeway designation, as was proposed.
7. Near-Road Siting Criteria
    The following paragraphs provide background, rationale, and details
for the final changes to the siting criteria for required near-road
monitoring sites.
a. Proposed Near-Road Siting Criteria
    EPA proposed 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. We
solicited comment on, but did not propose, having near-road sites
located on the predominantly downwind side of the target roadways. EPA
proposed that the monitor probe shall be located within 2 to 7 meters
above the ground, as is required for microscale PM2.5 and
PM10 sites. We also proposed 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.
b. Comments
    EPA received comments from a number of States (e.g. Michigan,
Mississippi, and Tennessee) indicating that the near-road network poses
significant safety issues and a related need for increased logistical
flexibility for installing a monitoring site. For example, the
Mississippi Department of Environmental Quality states that ``Given the
fact that these NO2 sites will be required to be housed in
shelters that are within 50 meters of the road, we believe that these
buildings could be large and pose a serious risk to drivers on the
road.''
    EPA notes that in all instances of field work, safety is a top
priority. In this instance of near-road monitoring, we are dealing with
the safety of the public driving on roads and the monitoring staff who
may operate the near-road monitoring station as well. There are various
ways to install near-road sites while ensuring worker and traffic
safety, and safety is an important part of the logistical
considerations that States should consider when selecting and
installing near-road sites. In many cases, State and local monitoring
agencies may be able to work with their State or local transportation
officials during the site selection process to deal with access and
safety issues. In public comments, AASHTO recommended that ``* * *
State and local air monitoring agencies be required to coordinate with
State and local DOTs for near-road monitoring during the establishment
of the monitoring plan.'' Although EPA cannot require States to
coordinate with other State or local entities, EPA believes that
transportation officials would likely be able to assist in finding
solutions to ensure safety while working with monitoring agencies in
accommodating a new near-road monitoring station. An

example of a step that could be taken to alleviate safety concerns
might be purposefully placing a monitoring site behind existing
barriers like guardrails and fencing, or possibly by installing a short
distance of such barriers to protect the site workers, site
infrastructure, and nearby traffic. In addition, EPA notes that the 50m
distance proposed is wide enough to accommodate a site that would
satisfy many setback provisions that exist for private or commercial
building permits near roads, and may be viewed as a confirmation that
our proposed siting criteria are safely attainable.
    Some State commenters (e.g. AASHTO, NYSDOT, and Wisconsin)
suggested that the allowable maximum distance a near-road monitoring
probe can be from the target road be increased from 50 meters to
something wider, such as 200 meters. Conversely, there were some State,
environmental, and industry commenters (e.g. NESCAUM,\24\ Group Against
Smog and Pollution, and Air Quality Research and Logistics) who
suggested that the proposed range was appropriate, or, as suggested by
both NESCAUM and the Group Against Smog and Pollution, the allowable
distance should be reduced to as close as 30 or 20 meters to the
nearest edge of the traffic lanes of the target road segment,
respectively.
---------------------------------------------------------------------------

    \24\ NESCAUM officially supported the alternative network
design; however, they made suggestions regarding the near-road
network in the event EPA finalized the proposed two-tier network
design.
---------------------------------------------------------------------------

    EPA believes that increasing the allowable distance above 50 meters
would compromise the intent of near-road monitoring. As was noted in
the proposal and this document, the ISA (2.5.4 and 4.3.6) and REA
(7.3.2) indicate that on-road, mobile source derived NO2
exhibits a peak concentration on or very near the source road, and
those concentrations decay over a variable but relatively short
distance back to near area-wide or background (upwind of the target
road) concentrations. 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, but the peak concentrations are occurring on or very near
the source roadway. The behavior of NO2 concentrations and
the actual distance over which concentrations return to near area-wide
or background levels 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).
Therefore, monitor probe placement at increasing distances from a road,
such as 200 meters, will correspondingly decrease the potential for
sampling maximum concentrations of NO2 due to the traffic on
the target road. Baldauf et al. (2009) indicate that monitoring probes
would ideally be situated between 10 and 20 meters from the nearest
traffic lane for near-road pollutant monitoring.
    Regarding the comments suggesting required monitor probes be closer
than 50 meters, EPA believes the allowable distance of 50 meters that a
near-road NO2 probe can be from the target road provides
enough flexibility for the logistical issues that can occur on a case-
by-case basis, which is inherent in monitoring site placement, while
not sacrificing the potential to monitor the peak NO2
concentrations. However, in light of the information provided here on
how NO2 peak concentrations can decay over relatively short
distances away from roads, EPA strongly encourages States to place
near-road sites, or at least monitor probes, as close as safely
possible to target roads to increase the probability of measuring the
peak NO2 concentrations that occur in the near-road
environment, again noting that Baldauf et al. (2009) indicate that
monitor probes would ideally be situated between 10 and 20 meters from
the nearest traffic lane for near-road pollutant monitoring.
    EPA also proposed that required near-road NO2 monitor
probes 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. EPA expects that when a State makes a
measurement in determining whether an NO2 inlet probe is no
greater than 50 meters away, horizontally, from the outside nearest
edge of the traffic lanes of the target road segment, that the
measurement would likely represent a path to the monitor probe that is
normal to the target road. However, EPA notes that the monitor probe
will likely be influenced by various parts of the target road segment
that are at a relative angle compared to the normal transect between
the road and the monitor probe. EPA is not adjusting the wording of
this requirement, but does intend for States to consider more than one
linear pathway between the target road and the monitor probe being
clear of obstructions when considering candidate site locations.
    EPA received comments on the solicitation for comment on requiring
near-road monitoring sites to be placed on the downwind side of the
target road where the commenters (e.g. NACAA,\25\ NESCAUM, and the
Clean Air Council) encouraged such a requirement. Conversely, other
commenters (e.g., Air Quality and Logistics and NYSDEC suggested that
such a requirement may be overly restrictive and not necessary. For
example, NYSDEC stated that ``It is important to avoid making the
monitor siting criteria too restrictive. It is very likely that in some
CBSAs, finding suitable locations near the busiest road segments will
not be possible. It is also important to remember that the
NO2 monitoring instrumentation provides data continuously.
Sites located downwind of sources will likely be impacted more
frequently than the sites located upwind particularly when the sites
are more than 50 meters from the source, and are preferred, but either
side of the road will be downwind some of the time. Many of the highest
NO2 concentrations are also likely to occur during inversion
periods and during calm meteorological conditions when the upwind-
downwind designations have little meaning.''
---------------------------------------------------------------------------

    \25\ NACAA made a statement containing many concerns about the
near-road monitoring component proposal which included a passage
regarding the lack of requiring sites to be downwind. They expressed
concern in ``* * * allowing upwind siting of monitors over a wide
range of horizontal and vertical distances from the road * * *''.
---------------------------------------------------------------------------

    EPA noted in its proposal that 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. Further, 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, at least in part, to 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, but also reduces
the absolute need to be downwind of the road. EPA believes that very
few, if any, near-road sites would be able to be situated in a location
that was always downwind. For example, a hypothetical

site may have winds routinely out of several different cardinal
directions throughout the year, without one being a dominant direction.
As a result, given variable meteorology, for some period of a year, a
given near-road site may not be downwind of the target road, no matter
which side of the road it is on. Therefore, EPA is not finalizing a
requirement that near-road sites must be climatologically downwind of
the target road segment because of the additional limitations this
introduces to finding potential site candidates in exchange for what
may be a small increase in the opportunity to monitor peak
NO2 concentrations. However, EPA encourages States to place
monitors in the climatologically downwind direction whenever possible,
in an attempt to measure the peak NO2 concentrations more
often than not. One way States may identify where the predominantly
downwind location might be for candidate sites could be to use portable
meteorological devices to characterize meteorological tendencies, in
addition to evaluating other available meteorological data sources.
    EPA proposed that required near-road NO2 monitor probes
be located within 2 to 7 meters above the ground, as is required for
microscale PM2.5 and PM10 sites. EPA also
proposed 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.
NESCAUM commented that ``EPA needs to reconcile near-roadway
NO2 probe height requirements with the existing micro-scale
near-roadway CO probe height requirement of 2.5 to 3.5 meters above
prevailing terrain. NESCAUM supports using this existing height for all
near-roadway pollution monitors, as it minimizes probe height effects
on measurements, and allows for proper measurement of collocated
particle number concentration (which requires a very short inlet, i.e.,
on the order of inches) and CO.'' NYSDEC commented that ``The height
requirement may not be practical for road segments in dense urban areas
where existing buildings heights may exceed 7 meters. The requirement
to maintain a 1 meter clearance from a supporting wall or structure may
not be adequate for taller walls often found in urban areas. These
walls can create down washing and street canyon effects which will make
the resulting data less representative of nearby areas and will make
interpretation of the resulting data difficult. However, there will
need to be consistency between similar site settings.'' Finally, EPA
received comments from some health groups (e.g., ALA, EJ, EDF, and
NRDC) who commented that ``the lower end of the proposed height of 2 to
7 meters appears to capture the highest NO2 concentrations,
and more accurately represents human exposure at the breathing zone.''
    In the proposal, EPA noted that 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). EPA recognizes that consistency across sites with regard to
probe height is desirable, and consistency with microscale, urban
canyon CO sites might also be desirable. However, as was noted in the
earlier discussion on ``downwind'' site placements, it is important to
avoid making the monitor siting criteria too restrictive. An allowable
range between 2 and 7 meters provides more flexibility in site
installation, which EPA considers important because of the variety of
siting situations each State may have to deal with for each individual
site. While EPA agrees that a tighter allowable range such as 2.5 to
3.5 meters would reduce site to site variability and keep probes nearer
the microscale siting requirements of CO, the wider range of 2 to 7
meters still provides an adequate amount of site to site consistency.
EPA may also address this issue through forthcoming guidance, where an
increased consistency for probe heights in similar situations such as
urban canyons may be a site implementation goal, within the required 2
to 7 meter probe height range. Further, EPA believes that although
certain situations, as noted by NYSDEC, may exist where the 1 meter
clearance from walls or structures may be problematic near taller
buildings or walls, this requirement is consistent with similar such
clearance requirements for microscale CO sites in similar such
situations that exist in urban canyons.
    In the proposed rule, EPA proposed in the siting criteria language
that the subsequent residence time of the pollutant in the sample line
between the inlet probe and the analyzer cannot exceed 20 seconds. EPA
received comments from Air Quality Research and Logistics regarding
guidelines for maximum allowable inlet length and sample residence
time, where they stated that ``* * * the fast photodynamic
O3-NOX equilibrium may occur in darkened sample
lines at residence times of 10-20 seconds (Butcher et al. 1971; Ridley
et al. 1988; Parrish et al. 1990). EPA should correct this apparent
error by specifying much lower maximum residence times (e.g., 1-2
seconds) or accounting for this effect by reporting `corrected' values
in error by no more than the allowed rounding convention (e.g., 1 ppb).''
    EPA notes that in 40 CFR Part 58 Appendix E, paragraph (9)(c),
states that sample probes for reactive gas analyzers, particularly
NOY monitors, at NCore monitoring sites must have a sample
residence time less than 20 seconds. EPA believes this rule is also
appropriate for NO2 monitors, particularly if a monitor
inlet manifold is extended away from the main monitoring shelter. EPA
does agree that shorter sample residence time in the inlet manifold is
desirable. Although we do not believe it appropriate to require
residence times on the order of 1 to 2 seconds, and do not believe
correcting values is appropriate (which was not a concept which was
proposed), we do encourage States to use best practices in selecting
non-reactive manifold materials, and to install sampling manifolds in
an efficient manner that minimizes sample residence time. While EPA
proposed this concept in the preamble to the proposed rule, we did not
include it in the proposed regulatory text. The final rule includes
regulatory text on this subject at 40 CFR Part 58 Appendix E, paragraph
(9)(c).
c. Conclusions on Near-Road Siting Criteria
    We are finalizing the near-road NO2 monitor siting
criteria, as proposed, where (1) required near-road NO2
monitor probes shall be as near as practicable to the outside nearest
edge of the traffic lanes of the target road segment; but shall not be
located at a distance greater than 50 meters, in the horizontal, from
the outside nearest edge of the traffic lanes of the target road
segment, (2) required near-road NO2 monitor probes shall
have an unobstructed air flow, where no obstacles exist at or above the
height of the monitor probe, between the monitor probe and the outside
nearest edge of the traffic lanes of the target road segment, (3)
required near-road NO2 monitors are required to have sampler
inlets between 2 and 7 meters above ground level, and (4) residence
time of NO2 in the sample line between the

inlet probe and the analyzer does not exceed 20 seconds.
8. Area-Wide Monitor Site Selection and Siting Criteria
    The following paragraphs provide background, rationale, and details
for the final changes to the site selection and monitor siting criteria
for required area-wide monitoring sites.
a. Proposed Area-Wide Monitor Site Selection and Siting Criteria
    EPA proposed that sites required as part of the second tier of the
NO2 monitoring network design, known as the area-wide
monitoring component, be sited to characterize the highest expected
NO2 concentrations at the neighborhood and larger (area-
wide) spatial scales in a CBSA.
b. Comments
    While most commenters who supported area-wide monitoring did so
with regard to the adoption of the alternative area-wide network design
rather than as part of the proposed approach, only a few commented on
the actual sites and siting criteria. The Dow Chemical Company
suggested that area-wide sites should be located at least 1,000 meters
away from any major roads or intersections to ensure that the
concentration of NO2 measured is representative of an area-
wide concentration instead of peak near-road concentrations.
    EPA notes that in order for an NO2 monitoring site to be
classified as a neighborhood (or larger) spatial scale site, it must
meet the roadway set-back requirements in Table E-1 of 40 CFR Part 58
Appendix E. EPA believes that this existing set-back table is
appropriate to use to ensure that any NO2 site that may be
intended as an area-wide site will be sufficiently distanced from any
major road. For example, an NO2 monitoring site may be
considered neighborhood scale if it is 10 or more meters from the edge
of the nearest traffic lane of a road with 10,000 or less AADT counts.
c. Conclusions on Area-Wide Monitor Site Selection and Siting Criteria
    We are finalizing the requirement that any sites required as part
of the second tier of the NO2 monitoring network design,
known as the area-wide monitoring component, be sited to characterize
the highest expected NO2 concentrations at the neighborhood
and larger (area-wide) spatial scales in a CBSA.
9. Meteorological Measurements
    The following paragraphs provide background, rationale, and details
for the final changes to the requirement of meteorological monitoring
at near-road monitoring sites.
a. Proposed Meteorological Measurements
    In further support of characterizing the peak NO2
concentrations occurring in the near-road environment, EPA proposed 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.
b. Comments
    EPA received comments from the South Carolina Department of Health
and Environmental Control commented that the recording of air
turbulence data at near-road monitoring stations should be encouraged
but not required. Other States (e.g., Alaska, North Carolina, and
Wisconsin) provided comments that did not support the proposed
meteorological measurement requirements, noting issues with costs,
problems siting the probe nearer to structures and to the ground than
is typically done, and that the averaging period required to better
understand turbulence (through anemometry data) in the near-road
environment requires a much higher frequency than what is typically
reported.
    EPA is removing the proposed requirements that would have required
meteorological monitoring at near-road NO2 monitoring
stations. However, EPA strongly encourages States to do some
meteorological monitoring to better characterize the conditions under
which they are acquiring NO2 data. The near-road microscale
environment is complex, and understanding the turbulent dispersion that
may be affecting NO2 measurements, along with having a basic
understanding of from which direction the measured NO2
concentrations are coming from, which are very informative in the
effort to fully understand the data being collected. At a minimum,
basic anemometry data would be useful in identifying whether the site
is upwind, downwind, or otherwise oriented, relative to the target
road.
c. Conclusions on Meteorological Measurements
    We are not finalizing the proposal 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.

C. Data Reporting

    The following paragraphs provide background, rationale, and details
for the final changes to the data reporting requirements, data quality
objectives, and measurement uncertainty.
1. Proposed Data Quality Objectives and Measurement Uncertainty
    In the proposal, EPA noted that 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. We also
noted that many 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. We believe these data reporting procedures are appropriate
to support the revised primary NO2 NAAQS.
    EPA proposed to develop data quality objectives (DQOs) for the
proposed NO2 network. We proposed 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.
2. Comments
    EPA received comments from the State of Missouri, supporting the
proposed DQOs and goals for measurement uncertainty, and from North
Carolina, suggesting that measurement uncertainty goals match those of
the NCore multi-pollutant network.
    EPA agrees that it is desirable to have measurement uncertainty
goals that match that of other pollutants. EPA originally proposed the
goals for precision and bias under consideration that there may be a
need to account for potential increased uncertainty in 1-hour near-road
NO2 data. However, we agree with the suggestion from the
State of North Carolina, and are changing the goals 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 10 percent and for bias as an upper 95 percent
confidence limit for the absolute bias of 15 percent. These goals match
the existing goals for NO2 and are consistent with
historical measurement uncertainty goals.

3. Conclusions on Data Quality Objectives and Measurement Uncertainty
    We are finalizing the approach to develop data quality objectives,
and are changing the proposed goal for measurement uncertainty, where
the goals 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 10 percent and for bias
as an upper 95 percent confidence limit for the absolute bias of 15
percent.

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

    The EPA proposed 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
detailed the computations necessary for determining when the proposed
1-hour and existing annual primary NO2 NAAQS are met. The
proposed Appendix S also addressed data reporting, data completeness
considerations, and rounding conventions.
    Two versions of Appendix S were proposed. The first applied to a 1-
hour primary standard based on the annual 4th high value form, while
the second applied to a 1-hour primary standard based on the 99th
percentile daily value form.
    The final version of Appendix S is printed at the end of this
notice and applies to an annual primary standard and a 1-hour primary
standard based on the 98th percentile daily value form. Appendix S is
based on the 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 1-hour standard when making
nonattainment determinations and other findings related to attainment
or violation of the standard.
    The EPA is amending and moving the provisions of 40 CFR 50.11
related to data completeness for the existing annual primary standard
to the new Appendix S, and adding provisions for the proposed 1-hour
primary standard. Substantively, the 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 an addition of
a cross-reference to the Exceptional Events Rule, the addition of
Administrator discretion to consider otherwise incomplete data
complete, and the addition of a provision addressing the possibility of
there being multiple NO2 monitors at one site. The
procedures for the 1-hour primary standard are entirely new.
    The EPA is also making 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 final NO2
NAAQS.
    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 pre-existing annual NO2 NAAQS, originally adopted in
1977, contained 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.

A. Interpretation of the Primary NAAQS for Oxides of Nitrogen for the
Annual Primary Standard

    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 regulatory text at 40 CFR 50.11,
anticipating and resolving in advance various future situations that
could occur. 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 addressed several issues in ways which
are specific to the individual primary NO2 standards, as
described below.
1. Proposed Interpretation of the Annual Standard
    The proposed data interpretation provisions for the annual standard
are consistent with the pre-existing instructions included along with
the statement of the level and form of the standard in 40 CFR 50.11.
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).
    In the proposal, EPA noted that 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 also incorporated some such
features.
2. Comments on Interpretation of the Annual Standard
    We received four comments, all from State agencies, on data
interpretation for the annual NO2 standard. Of the four
commenters, two recommended the use of a weighted annual mean to
appropriately implement the annual primary standard. Two other
commenters asserted that there is no strong seasonality in
NO2 concentrations, and that therefore there is no need to
use a weighted annual mean or to require data completeness quarter-by-
quarter.

3. Conclusions on Interpretation of the Annual Standard
    Upon investigating the issue of NO2 seasonality using
data from AQS as part of considering the comments, we have found that
there are notable variations in quarterly mean NO2
concentrations. It is therefore quite possible that an unweighted
annual mean calculated without a quarter-by-quarter data completeness
requirement might not represent the true annual mean as well as a
weighted annual mean calculated with a quarter-by-quarter completeness
requirement. However, the current practice of requiring 75%
completeness of all of the hours in the year and calculating the annual
mean without weighting has been retained in the final rule, because of
its simplicity and because we believe it will not interfere with
effective implementation of the annual NAAQS. No area presently is
nonattainment for or comes close to violating the annual standard.
Therefore, the choice between the two approaches can only have a
practical effect, if any, on whether at some time in the future an area
is determined to be newly violating the annual standard. If a monitor
has a complete and valid design value below the standard using the
unweighted mean approach (with only an annual data completeness
requirement) but the design value would be considered incomplete and
invalid under a hypothetical weighted mean approach (with a quarterly
completeness requirement), the monitor would in either case be
considered not to be violating and its data would not be the basis for
a nonattainment designation. If a monitor has a design value above the
standard using the unweighted annual mean approach but is incomplete
with respect to a hypothetical quarterly completeness requirement, then
the two approaches would have different implications for the
determination of a violation. A quarterly completeness requirement
would make a finding of violation impossible, unless the Administrator
chose to treat the data as if complete under another provision of the
final rule. The unweighted annual mean approach would allow but not
force a finding of violation, because the Administrator will have
discretion to make any such findings because there will be no mandatory
round of designations for the annual standard given that the annual
standard has not been revised in this review. The Administrator will be
able to consider the representativeness of the unweighted annual mean
when deciding whether to make a discretionary nonattainment
redesignation. Given that the annual standard requires only one year of
monitoring data for the calculation of a design value, little time will
be lost if the Administrator chooses to work with a State to obtain a
new design value based on more complete and/or seasonally balanced
monitoring data.

B. Interpretation of the Primary NAAQS for Oxides of Nitrogen 1-Hour
Primary Standard

1. Proposed Interpretation of the 1-Hour Standard
    With regard to data completeness for the 1-hour primary standard
with a 4th highest daily value form, the proposed Appendix followed
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 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 was proposed to be applied at the daily and quarterly
levels.
    Recognizing that there may be years with incomplete data, the
proposed text provided that a design value derived from incomplete data
would 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
high values to exceed the standard. In this situation, more complete
monitoring could not possibly have indicated that the standard was
actually met.
    Second, we proposed a diagnostic data substitution test which was
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.
    It should be noted that one possible outcome of applying the
proposed substitution test is that a year with incomplete data may
nevertheless be determined to not have a valid design value and thus to
be unusable in making 1-hour primary NAAQS compliance determinations
for that 3-year period.
    Also, we proposed 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.
    The second version of the proposed Appendix S contained 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 had somewhat different
provisions for dealing with data incompleteness. One difference was 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 provided 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 provided instructions for rounding (not
truncating) the average of three annual 99th percentile hourly
concentrations before comparison to the level of the primary NAAQS.
2. Comments on Interpretation of the 1-Hour Standard
    Three commenters expressed the view that the 75% completion per
quarter requirement should apply with respect to the 1-hour standard. A
fourth commenter recommended that the requirement be increased to 82%.
Another person commented that the requirement of 75% of the hours in a
day is too stringent. The commenter noted that it would be
inappropriate not to count the day if the maximum concentration
observed in the hours measured is sufficiently high to make a
difference with regard to compliance with the NAAQS. A comment was
received that the substitution test should not be included, on the
grounds that nonattainment should not be declared without irrefutable
proof. This commenter also said that the same completeness requirement
as used for nonattainment should be used for attainment. We received
one comment that the computation of design values where multiple
monitors are present at a site should be averaged and not taken from a
designated primary monitor.
3. Conclusions on Interpretation of the 1-Hour Standard
    Consistent with the Administrator's decision to adopt a 98th
percentile form for the 1-hour NAAQS, the final version of Appendix S
is based on that form. Table 1 has been revised from the version that
was proposed, so that it results in the selection of the 98th
percentile value rather than the 99th percentile value.
    We agree with the three comments expressing the view that the
requirement for 75% data completeness per quarter should apply with
respect to the 1-hour standard. A fourth comment recommended that the
requirement be increased to 82%. We believe 82% is too stringent
because of the number of monitors that would not achieve such a
requirement and we believe that 75% captures the season. We agree that
an incomplete day should be counted if the maximum concentration
observed in the hours measured is sufficiently high to make a
difference with regard to compliance with the NAAQS, and we have
accounted for that in section 3.2.c.i by validating the design value if
it is above the level of the primary 1-hour standard when at least 75
percent of the days in each quarter have at least one reported hourly
value. We agree that substitution should not be used for the
establishment of attainment/nonattainment. The commenter who remarked
on this issue appears not to have understood that the specific proposed
substitution tests have essentially zero probability of making a clean
area fail the NAAQS, or vice versa, because the substituted values are
chosen to be conservative against such an outcome. As noted in section
3.2(c)(i), when substitution is used, the 3-year design value based on
the data actually reported, not the ``test design value'', shall be
used as the valid design value.
    In the course of considering the above comment regarding data
substitution tests to be used in cases of data incompleteness, EPA has
realized that there could be some cases of data incompleteness in which
the proposed procedure for calculating the 1-hour design value might
result in an in appropriately low design value. As proposed, only days
with measurements for at least 75% of the hours in the day would be
considered in any way when identifying the 99th percentile value (99th
for purposes of the adopted NAAQS). However, there could be individual
hours in other, incompletely monitored days that had measured
concentrations higher than the identified 98th percentile value from
the complete days. It would be inappropriate not to consider those
hours and days in some way. However, if all days with at least one
hourly concentration were used to identify the 99th percentile value
without any regard to their incompleteness, this could also result in a
design value that is biased low because the extra days could increase
the number of ``annual number of days with valid data'' enough to
affect which row of Table 1 of Appendix S is used. It could, for
example, result in the 8th highest ranked daily maximum concentration
being identified as the 98th percentile value (based on Table 1 of
Appendix S) rather than a higher ranked concentration; this would also
be inappropriate because days which were not monitored intensively
enough to give a reasonable likelihood of catching the maximum hourly
concentration would in effect be treated as if they had such a
likelihood. For example, 50 days with only one hourly measurement
during a time of day with lower concentrations would ``earn'' the State
the right to drop one notch lower in the ranking of days when
identifying the 98th percentile day, inappropriately. The final version
of Appendix S solves this problem by providing that two procedures be
used to identifying the 98th percentile value, the first based only on
days with 75% data completeness and the second based on all days with
at least one hourly measurement. The final design value is the higher
of the two values that result from these two procedures.
    With regard to situations with multiple monitors operating at one
site, we think as discussed in the proposal, that designation of a
primary monitor is preferable to averaging the data from multiple
monitors based on administrative simplicity and transparency for the
public, and is unbiased with respect to compliance outcome provided the
State is able to make the designation only before any data has been
collected.
    Finally, as proposed, the final version of Appendix S has a cross
reference to the Exceptional Events Rule (40 CFR 50.14) with regard to
the exclusion of data affected by exceptional events. In addition, the
specific steps for including such data in completeness calculations
while excluding such data from actual design value calculations is
clarified in Appendix S.

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.''
    EPA proposed revised exceptional event data flagging and
documentation deadlines in FR 34404 [Federal Register/Vol. 74, No. 134/
Wednesday, July 15, 2009/Proposed Rules] and invited comments from the
public. The Agency received no comments related to the revised proposed
schedule for NO2 exceptional event data flagging and
documentation deadlines.
    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.
    The final rule text at the end of this notice shows the changes
that will 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.
    Table 1 below summarizes the data flagging and documentation
deadlines corresponding to the two year designation schedule discussed
in this section. If the promulgation date for a revised NO2
NAAQS occurs on a different date than January 22, 2010, EPA will revise
the final NO2 exceptional event flagging and documentation
submission deadlines accordingly to provide States with reasonably
adequate opportunity to review, identify, and document exceptional
events that may affect an area designation under a revised NAAQS.

      Table 1--Schedule for Exceptional Event Flagging and Documentation Submission for Data To Be Used in
                                 Designations Decisions for New or Revised NAAQS
----------------------------------------------------------------------------------------------------------------
                                         Air quality
  NAAQS pollutant/standard/(level)/    data collected  Event flagging & initial       Detailed documentation
          promulgation date             for calendar     description deadline          submission deadline
                                            year
----------------------------------------------------------------------------------------------------------------
NO2/1-Hour Standard (100 PPB)........            2008  July 1, 2010 \a\........  January 22, 2011.
                                                 2009  July 1, 2010............  January 22, 2011.
                                                 2010  April 1, 2011\a\........  July 1, 2011.\a\
----------------------------------------------------------------------------------------------------------------
\a\ 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. Designation of Areas

A. Proposed Process

    The CAA requires EPA and the States to take steps to ensure that
the new or revised NAAQS are met following promulgation. The first step
is to identify areas of the country that do not meet the 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 should be
designated as nonattainment, attainment, or unclassifiable for the new
NAAQS. 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.''
    No later than 120 days prior to promulgating designations, EPA is
required to notify States of any intended modifications to their
designations 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, the EPA must promulgate the designation that it deems
appropriate.
    Accordingly, Governors must submit their initial NO2
designation recommendations to EPA no later than January 2011. If the
Administrator intends to modify any State's recommendation, the EPA
will notify the Governor no later than 120 days prior to 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 finalized.

B. Public Comments

    Several industry commenters requested that EPA slow the timeline
for implementing a near-roadway monitoring network and designating
roadway areas because they believe EPA lacks significant information
about the implementation and performance of a national, near-roadway
monitoring network. Two commenters also requested that if a near-
roadway monitoring network is deployed, that 1-hour NO2
standards be made more

lenient until the next review period so that more information will be
available about near-roadway NO2 concentrations before a
stringent standard is selected.
    A response to commenters' requests that EPA slow the monitoring
implementation schedule and the request that EPA make the 1-hour
NO2 standard more lenient until the next review period are
addressed in sections III.B.5 and II.F.4.D, respectively.
    Section 110(d)(1)(B) requires the EPA to designate areas no later
than 2 years following promulgation of a new or revised NAAQS (i.e., by
January 2012). 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 an
additional year would not result in significant new data to inform the
initial designations. A near-roadway monitoring network is not expected
to be fully deployed until January 2013 therefore, EPA must proceed
with initial designations using air quality data from the existing
NO2 monitoring network. Because none of the current
NO2 monitors are sited to measure near-roadway ambient air,
we expect that most areas in the country with current NO2
monitors will not violate the new NO2 NAAQS. In the event
that a current NO2 monitor indicates a violation of the
revised standards, EPA intends to designate such areas
``nonattainment'' no later than 2 years following promulgation of the
revised standards. We intend to designate the rest of the country as
``unclassifiable'' for the revised NO2 NAAQS until
sufficient air quality data is collected from a near-roadway monitoring
network. Once the near-roadway network is fully deployed and 3 years of
air quality data are available, the EPA has authority under the CAA to
redesignate areas as appropriate from ``unclassifiable'' to
``attainment'' or ``nonattainment.'' We anticipate that sufficient data
to conduct designations would be available after 2015.
    A number of commenters, largely from industry groups, focused on
the concern that a near-roadway monitoring network would lead to
regional nonattainment on the basis of high NO2
concentrations found near roadways. These commenters requested that any
future nonattainment areas be limited to the area directly surrounding
roadways found to have above-standard NO2 concentrations.
    The CAA requires that any area that does not meet a NAAQS or that
contributes to a violation in a nearby area that does not meet the
NAAQS be designated ``nonattainment.'' States and EPA will need to
determine which sources and activities contribute to a NAAQS violation
in each area. Depending on the circumstances in each area this may
include sources and activities in areas beyond the area directly
surrounding a major roadway. EPA intends to issue nonattainment area
boundary guidance after additional information is gathered on the
probable contributors to violating near-roadway NO2
monitors.

C. Final Designations Process

    The EPA intends to promulgate initial NO2 designations
by January 2012 (2 years after promulgation of the revised NAAQS).
Along with today's action EPA is also promulgating new monitoring rules
that focus on roadways. As noted in section III, States must site
required NO2 near-roadway monitors and have them operational
by January 1, 2013. States will need an additional 3 years thereafter
to collect air quality data in order to determine compliance with the
revised NAAQS. This means that a full set of air quality data from the
new network will not be available until after 2015. Since we anticipate
that data from the new network will not be available prior to the CAA
designation deadlines discussed above, the EPA intends to complete
initial NO2 designations by January 2012 using the 3 most
recent years of quality-assured air quality data from the current
monitoring network, which would be for the years 2008-2010. The EPA
will designate as ``nonattainment'' any areas with NO2
monitors recording violations of the revised NO2 NAAQS. We
intend to designate all other areas of the country as
``unclassifiable'' to indicate that there is insufficient data to
determine whether or not they are attaining the revised NO2
NAAQS.
    Once the NO2 monitors are positioned in locations
meeting the near-roadway siting requirements and monitoring data become
available, the Agency has authority under section 107(d)(3) of the CAA
to redesignate areas as appropriate from ``unclassifiable'' to
``attainment'' or ``nonattainment.'' The EPA intends to issue guidance
on the factors that States should consider when determining
nonattainment boundaries after additional information is gathered on
the probable contributors to violating near-roadway NO2
monitors.

VI. 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.\26\ 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.
---------------------------------------------------------------------------

    \26\ Since EPA is retaining 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 help
areas meet 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 and
nonattainment new source review (NSR). 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.
    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. Classifications

1. Proposal
    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 for
certain pollutants including NO2 in sections 191 and 192: 18
months from nonattainment designation for the submittal of an
attainment plan, and as expeditiously as possible, but no later than 5
years from nonattainment designation for areas to attain the standard.
In the proposal, EPA stated its belief that classifications are
unnecessary in light of these relatively short deadlines.
2. Public Comments
    One commenter stated that they disagree with EPA's decision not to
impose non-attainment classifications on areas with measured near-road
NO2 concentrations in excess of the new NO2
standard, and urged EPA to provide a graduated non-attainment
classification system for the new standard. According to the commenter,
``a classification system defining higher levels of non-attainment with
increasingly stringent requirements at those levels is one that allows
for finer calibration of air quality regulatory response defined at the
Federal level.''
    As stated in the proposed rule, Section 192(a), of part D, of the
CAA specifically provides an attainment date for areas designated as
nonattainment for the NO2 NAAQS. Therefore, EPA has legal
authority to classify NO2 nonattainment areas, but the 5-
year attainment date addressed under section 192(a) cannot be extended
pursuant to section 172(a)(2)(D). Based on this limitation, EPA
proposed not to establish classifications within the 5- year interval
for attaining any new or revised NO2 NAAQS. It is also EPA's
belief that given the short deadlines that States have to develop and
submit SIP's and for areas to achieve emissions reductions in order to
attain the standard within the 5 year attainment period, a graduated
classifications system would not be appropriate. Therefore, EPA is
using it's discretion under the CAA not to establish classifications.
3. Final
    EPA is not making any changes to the discussion on classifications
in the proposed rule. Therefore, there will be no classifications for
the revised NO2 NAAQS.

B. Attainment Dates

    The maximum deadline 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 NAAQS for NO2 if revised, which will be codified at 40
CFR part 50, Appendix F.
1. Attaining the NAAQS
a. Proposal
    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.
b. Final
    EPA did not receive any comments on this aspect of the proposed
rule and is not making any changes to the

discussion on attaining the NAAQS in the proposed rule.
2. Consequences of Failing To Attain by the Statutory Attainment Date
a. Proposal
    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.''
b. Final
    EPA did not receive any comments on this aspect of the proposed
rule and is not making any changes to the discussion on consequences of
failing to attain by the statutory attainment date in the proposed
rule.

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

1. Proposal
    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.\27\ The list of section 110(a)(2) NAAQS implementation
requirements are the following:
---------------------------------------------------------------------------

    \27\ 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 and 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.
2. Final
    EPA did not receive any comments on this aspect of the proposed
rule and is not making any changes to the discussion on section
110(a)(2) NAAQS infrastructure requirements in the proposed rule.

D. Attainment Planning Requirements

1. Nonattainment Area SIPs
a. Proposal
    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 contains an attainment demonstration that
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.
b. Public Comments
    Several commenters indicated that EPA should take steps to ensure
that States actually require mobile source emissions reductions in
order to attain the NO2 NAAQS as opposed to controlling
point sources. Another commenter went further and stated that States be
required to control on-road emissions as opposed to emissions from
stationary sources and in particular EGUs. This commenter also
indicated that EPA should delay nonattainment designations until States
had a cost effective means of reducing on-road emissions of
NO2.
    EPA cannot require States to develop a SIP that only addresses one
type of source, in this case on-road mobile sources. States may select
appropriate control measures to attain the NAAQS and EPA must approve
them if they otherwise meet all applicable requirements of the Act. See
CAA 116. EPA expects that States will evaluate a range of control
measures that will reduce NO2 emissions within the time
allowed to attain the standard. This would include the emissions
reductions attributable to Federal controls on on-road and non-road
mobile sources, and controls that they have put in place to reduce
NOX emissions in order to attain the 8-hour ozone NAAQS and/