on the variability in peak NO2 concentrations near important sources of
NO2 such as major roadways, and given the recommendation from CASAC that
the potential for instability in the 99th percentile concentration is
cause for supporting a 98th percentile form, the Administrator judges it
appropriate to set the form based on the 3-year average of the 98th
percentile of the annual distribution of 1-hour daily maximum NO2
concentrations.  This decision is discussed in section II.F.3.c of the
final rule.

(3)	Comment:  Some commenters stated a preference for expressing the
form in terms of the nth highest concentration rather than in terms of a
percentile.  These commenters believe that using the nth highest form
would increase transparency (e.g., Dow, AQRL).  AQRL noted that “it
can provide an unambiguous determination of a ‘design value’ in the
face of missing data if concentrations are high.  The percentile form
does not provide that certainty if data are missing.”

Response:  We disagree that a percentile form does not provide certainty
regarding the determination of the design value.  As discussed above,
and in the final rule (section II.F.3), the Administrator has determined
it appropriate to set a form based on the 3-year average of the 98th
percentile of the annual distribution of 1-hour daily maximum NO2
concentrations.  The interpretation of this standard, including
requirements for when data are missing, is described in Appendix S to 40
CFR part 50 and in section IV of the preamble to the final rule.

Approach and level

Comments on the approach to setting the standard

(1)	Comment:  We received a number of comments on the most appropriate
approach to setting the 1-hour NO2 standard.  In their comments on the
proposal, CASAC was split regarding the most appropriate approach to
setting the 1-hour standard.  In their letter to the Administrator on
the proposal (Samet, 2009b), CASAC stated the following:

There was a split view on the two approaches among both CASAC and CASAC
panel members with a majority of each favoring the Agency's proposed
two-tiered monitoring network because they thought this approach would
be more effective in limiting near-roadway exposures that may reach
levels in the range at which some individuals with asthma may be
adversely affected. Other members acknowledged the need for research and
development of near-road monitoring data for criteria pollutants in
general but favored retention of EPA's current area-wide monitoring for
NO2 regulatory purposes, due to the lack of epidemiological data based
on near-roadway exposure measurements and issues related to implementing
a near-road monitoring system for NO2.

As indicated in their letter, the majority of CASAC Panel members
favored the proposed approach of setting a 1-hour standard that reflects
the maximum allowable NO2 concentration anywhere in an area and linking
such a standard with a 2-tiered monitoring network that would include
both near-road and area-wide monitors.  The recommendation of these
CASAC Panel members was based on their conclusion that the proposed
approach would be more effective than the alternative at limiting
near-roadway exposures to NO2 concentrations that could adversely affect
asthmatics.

In contrast, the minority of CASAC Panel members expressed support for
the alternative approach of setting a 1-hour standard that reflects the
allowable area-wide NO2 concentration.  These CASAC Panel members
concluded that there would be important uncertainties associated with
the proposed approach.  Specifically, they noted that the key U.S. NO2
epidemiologic studies relied upon area-wide NO2 concentrations and that
this introduces uncertainty into the use of these studies to inform a
standard that reflects the maximum allowable NO2 concentration anywhere
in an area.  As a result of this uncertainty, CASAC Panel members who
favored the alternative approach noted that “it would be better to set
the standard on the same area-wide monitoring basis as employed in the
epidemiologic studies upon which it now relies” (Samet, 2009b).  These
CASAC Panel members also noted uncertainties associated with identifying
appropriate monitoring sites near roads (see below and section III.B.2
of the final notice for more discussion of monitoring comments).

Consistent with the views expressed by the majority of CASAC members, a
number of commenters concluded that the most appropriate approach would
be to set a 1-hour standard that reflects the maximum allowable NO2
concentration anywhere in an area and to couple that standard with a
requirement that monitors be placed in locations where maximum
concentrations are expected, including near major roads.  This view was
expressed by some State and local agencies (e.g., in CA, IA, NY, TX, WA,
WI), by the majority of environmental organizations (e.g., CAC, EDF, EJ,
GASP, NRDC), by the ALA, and by a number of individual commenters.
Several additional medical and public health organizations (ACCP, AMA,
ATS, NADRC, NACPR) did not explicitly express a recommendation regarding
the approach though these organizations did recommend that, in setting a
1-hour standard, particular attention should be paid to NOX
concentrations around major roadways.  In support of their
recommendation to adopt the proposed approach and to focus monitoring
around major roads, these commenters generally concluded that a primary
consideration should be the extent to which the NO2 NAAQS protects
at-risk populations that live and/or attend school near important
sources of NO2 such as major roads.  As such, these comments were
typically consistent with the rationale discussed by the Administrator
in the proposal in support of setting a 1-hour standard that reflects
the maximum allowable NO2 concentration anywhere in an area.

Consistent with the view of the minority of CASAC Panel members, several
industry groups and an individual commenter (Roger McClellan) noted
uncertainties associated with using epidemiologic studies to inform
decisions on a standard reflecting the maximum allowable NO2
concentration anywhere in an area.  Specifically, Roger McClellan stated
the following:

In considering the results of the six epidemiological studies that are
at the core of the EPA assessment, it is important to recognize all of
them used NO2 concentration data from central area monitors as a
surrogate for personal exposure. These data are not applicable to
establishing standards for near roadway monitors.

Similar concerns with the proposed approach were expressed by several
industry groups.

Response:  As described in detail in section II.F.4.c of the final
notice, the Administrator agrees with the majority of CASAC Panel
members and other commenters who concluded that the most appropriate
approach to setting the 1-hour NO2 standard is to set a standard
reflecting the maximum allowable NO2 concentration anywhere in an area.
Her consideration of the uncertainties associated with this approach, as
stated by the minority of CASAC Panel members and industry commenters,
is also discussed in the final notice (sections II.F.4.b and II.F.4.c).

(2)	Comment:  Some industry groups concluded that EPA is inappropriately
combining decisions on the standard with decisions on the monitoring
network.  Specifically, AAM states the following with regard to the
proposed approach

[T]he effective stringency of a NAAQS depends on more than simply the
numerical level selected.  It also depends on the sensitivity of the
monitoring system, and the ability of that system to determine
accurately the ambient levels of the pollutant in a consistent manner at
monitoring stations across the country.  By affixing the stringency of a
primary NAAQS to a monitoring system that does not now exist and will be
subject to varying interpretation by regional, state and local
officials, EPA is in effect delegating the final decision on the NAAQS
standard to those officials, contrary to statutory requirements that
judgments concerning such standards reside with the Administrator.

Response:  We disagree with this characterization of the standard.  As
discussed in detail in the final notice (section II.F.4.c), the
Administrator is setting a 1-hour standard reflecting the maximum
allowable NO2 concentration anywhere in an area.  It follows from this
standard that monitors should be placed in locations where maximum NO2
concentrations are expected to occur.  As discussed in the final notice
(section II.A.2 and II.F.4.c), available information supports the
conclusion that these maximum concentrations will occur around major
roads in many areas.  Therefore, the Administrator is requiring monitors
within 50 m of major roads (see section III of the final notice).  In
situations where maximum NO2 concentrations are expected to occur in
locations other than near major roads (e.g., near multiple smaller roads
and/or stationary sources), the Regional Administrator can also require
monitors in these locations.  EPA establishes criteria for the method of
monitoring and for quality assurance/quality control (QA/QC).  Any
hourly data from monitors meeting FRM/FEM and QA/QC requirements will be
considered in making designations.

(3)	Comment:  Several industry and state commenters recommended that EPA
select its alternate monitoring proposal of using area-wide monitors to
be used in conjunction with a new short-term NO2 standard (e.g., EMA,
SCCC, NMED).  In their recommendation of the alternate monitoring
network, NMED noted that the use of area-wide monitors is more
applicable for measuring ambient air concentrations than near-road
monitors since few people live or work as close to major roadways as
near-road monitoring stations would be required to be located.  Other
commenters (e.g., Exxon) also concluded that monitor siting requirements
should allow for consideration of population.

Response:  As noted in the proposal and the final notice (section
II.F.4.c), millions of people in the United States live, work and/or
attend school near important sources of NO2, including major roads.  In
addition, people commuting on major roads can be exposed to elevated NO2
concentrations. As described in the preamble, the Administrator
concludes that short-term elevated NO2 concentrations, including those
occurring on or near roads, pose public health risks.  The Administrator
further concludes it is appropriate to locate monitors where maximum
concentrations are expected to occur, and that generally it is
appropriate to locate monitors near major roads.  States are to consider
population in the site selection process if a state identifies multiple
acceptable candidate sites where maximum hourly NO2 concentrations are
expected to occur.

(4)	Comment:  AQRL commented that EPA’s alternative monitoring
approach should not be chosen and implemented if one of the principal
reasons for the proposed 1-hr NO2 standard is to develop the near-road
monitoring network.

Response:  The rationale supporting a 1-hour standard reflecting the
maximum allowable NO2 concentration anywhere in an area is discussed in
detail in section II.F.4.d.  This rationale does not include the
development of a near-road monitoring network.

(5)	Comment:  Several commenters (e.g., AAM, API) concluded that it is
not appropriate to use the information discussed in the proposal on the
NO2 concentration gradient around roads to inform decisions on the
1-hour standard.  AAM concluded that the focus of the proposed approach
on NO2 concentrations around major roadways is not justified (and would
result in a standard that is more stringent than necessary) because the
REA and the proposal overstate the extent to which NO2 concentrations
near roads are higher than NO2 concentrations farther away from the
road.  AAM used data from the existing NO2 monitoring network as the
basis for their conclusion that “roadside monitors are not measuring
high NO2 concentrations.”  Specifically, they claim that their
analyses suggest the following:

Many of the presently located urban monitoring sites are already located
within 50 meters of a major roadway.

These monitors are not measuring the high concentrations that are of
concern to EPA.

Consequently, there does not appear to be a need to initiate a massive
deployment of new NO2 monitors within 50 m of major roadways.

Other commenters also noted that the highest concentrations of NO2 may
be in urban canyons, near stationary sources, or near airports (e.g.,
NESCAUM).

Response:  With regard to the general point made by several commenters
that maximum NO2 concentrations may not always occur near major roads,
we note that, although the Administrator concluded in the proposal that
maximum NO2 concentrations in many areas are likely to occur around
major roads, she also allowed for situations where this is not the case.
 Specifically, she proposed to set a 1-hour NO2 standard that reflects
the maximum allowable NO2 concentration anywhere in an area, regardless
of where that maximum concentration occurs.  Therefore, the proposed
approach to setting the standard would be expected to limit the maximum
NO2 concentrations anywhere in an area even if in some areas, as is
contended by AAM, those maximum NO2 concentrations do not occur near
roads.

With regard to the analyses submitted by AAM, we agree that there is
uncertainty associated with estimates of roadway-associated NO2
concentrations (see REA, sections 7.4.6 and <IP_ADDRESS> for detailed
discussion of these uncertainties) and in identifying locations where
maximum concentrations are expected to occur.  However, we note that the
Administrator’s conclusions regarding the relationship between NO2
concentrations near roads and those away from roads rely on multiple
lines of scientific evidence and information.  Specifically, the
administrator relied in the proposal on the following in drawing
conclusions regarding the distribution of NO2 concentrations across
areas:

Monitoring studies discussed in the ISA and REA that were designed to
characterize the NO2 concentration gradient around roads, which
indicated that NO2 concentrations near roads are elevated compared to
concentrations in the same area but away from the road

Air quality and exposure analyses presented in the REA which estimate
that NO2 concentrations on roads could be 80% higher than away from the
road, on average across locations, and that roadway-associated exposures
account for the majority of exposures to NO2 concentrations at or above
100 ppb

In contrast, to support their conclusions about the NO2 concentration
gradient, AAM relies largely on an analysis of existing NO2 monitors
that focused on 6 locations with a total of 42 monitors.  While this
analysis does provide information on NO2 concentrations at different
distances from roads, the existing NO2 monitoring network was not
designed to characterize the spatial gradients in NO2 concentrations
surrounding roadways.  Rather, concentrations of NO2 measured by
existing monitors may likely reflect contributions from a combination of
mobile and stationary sources, with one or the other dominating
depending on the proximity of the monitors to these sources.

Specifically, one example used by the commenters to support their
conclusion that NO2 concentrations near roads are not elevated is that
of St. Louis, where the monitors closer to a road measured lower NO2
concentrations than a monitor farther away from the road.  However, a
closer look at the monitor classified as being away from the road
provides a potential explanation for these observations and illustrates
the limitations of relying exclusively on the existing monitoring
network to characterize the NO2 concentration gradient around roads.
The monitor used (ID 295100086) is characterized by EPA’s Air Quality
System (AQS) as having a “high concentration” monitoring objective,
is 133 m from a major road, and is surrounded by 35 NOX emission sources
within 10 km having median emissions of about 17 tons per year (see REA,
Appendix A, Tables A-7 and A-8).  Thus, the single site used in St.
Louis for the ≥ 100 m bin may not necessarily reflect concentrations
at a site distant from a roadway, is likely not exclusively impacted by
roadway emissions, and would likely not be useful in determining the
relationship between near-road NO2 concentrations and those away from
the road.  The REA identified and discussed situations such as this as
an important uncertainty when estimating on-road concentrations (REA,
section 7.4.6, page 135).

Given the considerations above, we conclude that the analysis submitted
by AAM, which does not consider relevant lines of evidence and
information other than their analysis of existing monitors, does not
appropriately characterize the relationship between NO2 concentrations
near roads and those away from roads.

Comments on standard level

Comment:  In commenting on the proposal, CASAC discussed both the
proposed range of standard levels (i.e., 80-100 ppb) and the alternative
range of standard levels (i.e., 50-75 ppb).  Though, as discussed above,
they were split on which approach should be adopted for setting the
1-hour standard, CASAC did express the consensus conclusion that, if the
Agency finalizes a 1-hour standard in accordance with the proposed
approach (i.e., standard level reflects the maximum allowable NO2
concentration anywhere in an area and a monitoring network is
established that includes monitors near major roads), then it is
appropriate to consider the proposed range of standard levels from 80 to
100 ppb.  Specifically, the CASAC letter to the Administrator on the
proposal (Samet, 2009b) stated the following with regard to the proposed
approach:

[T]he level of the one-hour NO2 standard should be within the range of
80-100 ppb and not above 100 ppb. In its letter of December 2, 2008,
CASAC strongly voiced a consensus view that the upper end of the range
should not exceed 100 ppb, based on evidence of risk at that
concentration. The lower limit of 80 ppb was viewed as reasonable by
CASAC; selection of a value lower than 80ppb would represent a policy
judgment based on uncertainty and the degree of public health protection
sought, given the limited health-based evidence at concentrations below
100 ppb.

A number of State and local agencies and organizations also expressed
support for setting the level of the 1-hour NO2 standard within the
proposed range of 80 to 100 ppb, though only a few of these State and
local agencies (e.g., in CA, IA, MI, NY, TX) made this recommendation in
conjunction with a recommendation to focus monitoring near major roads
and other important sources of NO2.

Response:  As is discussed in section II.F.4.d of the final rule, the
Administrator has judged it appropriate to set a standard level of 100
ppb.  Her rationale, which incorporates her consideration of the above
comments, is discussed in detail in this section.

(2)	Comment:  A number of environmental organizations (e.g., CAC, CSE,
EDF, EJ, GASP, NRDC) and medical/public health organizations (e.g.,
ACCP, ALA, AMA, ATS, NACPR, NAMDRC) supported setting a standard level
below 80 ppb for a standard that reflects the maximum allowable NO2
concentration anywhere in an area.  Several of these groups recommended
a standard level of 50 ppb.  This recommendation was typically based on
the commenters’ interpretation of the epidemiologic and controlled
human exposure evidence as well as the NO2 exposure and risk
information.

Some of these commenters noted that the 98th percentile area-wide NO2
concentration was below 80 ppb in the location of a single key U.S.
epidemiologic study (i.e., 50 ppb in study by Delfino).  Given this,
commenters concluded that the standard level should be set at 50 ppb.
Their comments on the monitoring network generally favored a requirement
to place monitors near major roads and, therefore, these commenters
appeared to favor a standard level as low as 50 ppb and to recommend
that such a standard level reflect the maximum allowable NO2
concentration anywhere in an area.  In their comments, the ALA, EDF, EF,
and NRDC stated the following:

Considering the Delfino study alone on EPA’s terms, that is, focusing
on the 98th percentile of the 1-hour daily maximum concentrations, EPA
reports a concentration of 50 ppb where asthma symptoms were observed.
Based primarily on this study, EPA concluded in the REA that it was
appropriate to set the lower end of the range at 50 ppb, which
corresponded to the lowest-observed effects level of airway
hyperresponsiveness in asthmatics. To provide the strongest public
health protection, we therefore urge the level of the standard be set at
50 ppb.

In some cases, the same commenters also appeared to recommend setting a
standard level below 50 ppb because mean area-wide NO2 concentrations
reported in locations of key U.S. epidemiologic studies are below this
concentration.  Specifically, with regard to the key U.S. epidemiologic
studies, these commenters (e.g., ALA, EDF, EJ, NRDC) stated the
following:

These studies clearly identify adverse health effects such as emergency
room visits and hospital admissions for respiratory causes at
concentrations currently occurring in the U.S. Mean concentrations for
all but two of these studies are about or below 50 ppb, suggesting that
the standard must be set below this level to allow for a margin of
safety.

Some of these commenters also concluded that the proposed range of
standard levels fails to provide a margin of safety for effects reported
in controlled human exposure studies.

Response:  The Administrator’s decision to set a standard level of 100
ppb is discussed in detail in section II.F.4.d of the final rule.  The
rationale for this decision includes consideration of the above
comments.  Specific comments on standard level are discussed in section
II.F.4.c of the final rule.

(3)	Comment:  Several environmental and public health groups (e.g., ALA,
EDF, EJ, NRDC) concluded that the REA analyses of NO2 exposures and
risks suggest that “only an hourly standard of no more than 50 ppb
would protect against harm from peak exposures.”

	Response:  We disagree with this characterization.  As discussed in
sections II.C and II.F.4.d of the final rule, the analyses of different
potential alternative standards in the REA are based on the current
monitoring network, which contains primarily area-wide monitors.  The
Administrator concludes that the results of exposure and risk analyses
provide support for limiting area-wide NO2 concentrations to no higher
than 100 ppb.  The Administrator is setting a new 1-hour standard that
reflects the maximum allowable NO2 concentration anywhere in an area.
Therefore, when considering the REA analyses in the context of such a
standard, the Administrator considered available information on the
relationship between the higher NO2 concentrations around roads and
area-wide NO2 concentrations.  Specifically, as described in detail in
section II.F.4.d, she noted that a standard level of 100 ppb reflecting
the maximum allowable NO2 concentration anywhere in an area would be
expected to limit area-wide NO2 concentrations to approximately 50 to 75
ppb.  Therefore, she concluded that a standard level of 100 ppb, for a
standard that reflects the maximum allowable NO2 concentration anywhere
in an area, is consistent with conclusions based on the NO2 exposure and
risk information.

(3)	Comment:  Several industry groups (e.g., AAM, Dow, NAM, NPRA) and
Roger McClellan concluded that, if EPA does choose to set a new 1-hour
standard, the level of that standard should be above 100 ppb.  As a
basis for this recommendation, these groups typically emphasized
uncertainties in the scientific evidence.  Specifically, these
commenters typically concluded that available epidemiologic studies do
not support the conclusion that NO2 causes reported health effects.
This was based on their assertion that the presence of co-pollutants in
the ambient air precludes the identification of a specific NO2
contribution to reported effects.  Some industry groups also concluded
that epidemiologic studies should not be used to inform decisions on the
standard level because these studies were based on area-wide, rather
than near-road, NO2 concentrations.  As a result, these commenters
recommended that a 1-hour standard should be based on the controlled
human exposure evidence and that, in considering that evidence, EPA
should rely on the meta-analysis of NO2 airway responsiveness studies
conducted by Goodman et al., (2009) rather than the meta-analysis
included in the final ISA.  They concluded that in relying on the ISA
meta-analysis, EPA has inappropriately relied on a new unpublished
meta-analysis that has not been peer-reviewed, was not reviewed by
CASAC, and was not conducted in a transparent manner.

Response:  EPA recognizes the uncertainties in the scientific evidence
that are discussed by these industry commenters; however, we strongly
disagree with their conclusions regarding the implications of these
uncertainties for decisions on the NO2 NAAQS.  These comments, and
EPA’s responses, are discussed in detail in section II.E.2 of the
final rule and above (section II) in this Response to Comments Document.
 The Administrator’s conclusions on standard level are described in
section II.F.4.d of the final rule.

(4)	Comment:  Some commenters argued that EPA should not adjust the
standard level to account for postulated near-road concentrations
because, due to differences in concentration gradient, it would
establish a level that is arbitrary and variable across locations (e.g.,
NPRA, NYSDEC, AAM).  AAM further argued that EPA’s  information about
the concentration gradient was not sufficiently precise or “factual”
to inform EPA’s decision making.

Response:  As described in section II.F.4.d of the final rule, EPA has
not adjusted the standard level to account for near-road concentrations.
 Rather, the Administrator has considered the extent to which specific
standard levels would be expected to protect against exposure to the
distribution of NO2 concentrations across an area and, therefore,
against the array of respiratory effects that have been linked to
short-term NO2 exposures.  These considerations are described in detail
in section II.F.4.d of the final rule.  EPA disagrees with AAM’s
suggestion that information about the concentration gradient should be
disregarded in reviewing the standard.

(5)	Comment:  One commenter (NYDOH) concluded that too much weight has
been placed on clinical studies and that more emphasis should be placed
on epidemiologic studies in setting the standard level.

Response:  As discussed in detail in section II.F.4.d of the final rule,
the Administrator has considered both the controlled human exposure and
epidemiologic evidence in setting the standard level.  Both lines of
evidence provide information on the extent to which specific NO2
standards would be expected to protect against the range of respiratory
effects that have been linked to short-term exposures to NO2.

(6)	Comment:  INGAA pointed out that the related health-based standards
(e.g., Short-term Exposure Level (STEL) or ceiling Permissible Exposure
Level (PEL) from Occupational Safety and Health Association (OSHA) or
the National Institute of Occupational Safety and Health (NIOSH)) are
higher than the proposed NO2 NAAQS.  They claimed that personnel have
not been negatively affected by NO2 exposures at their facility.  The
commenter also observed that “when comparing the relative margin of
OSHA or NIOSH standards to the NAAQS for other gases, the proposed NO2
NAAQS is more stringent.  For example, the OSHA NO2 PEL (ceiling) is 5
ppmv [parts per million by volume] (i.e., 5000 ppbv [parts per billion
by volume]) and the NIOSH STEL is 1 ppmv (1000 ppbv).  These levels are
one to two orders of magnitude higher than ranges being considered by
EPA for the 1-hour NO2 NAAQS.  By comparison, the CO [carbon monoxide]
NAAQS 1-hour average standard is 35 ppmv, compared to a NIOSH STEL of
200 ppmv, a factor of 5.7.  This appears to indicate a more conservative
approach for the proposed NO2 NAAQS.”

Response:  The CAA requires that air quality criteria and NAAQS be
reviewed periodically.  After consideration of the latest scientific
knowledge, the NAAQS must be set at levels that are, in the
Administrator’s judgment, requisite to protect public health,
including the health of sensitive subpopulations, with an adequate
margin of safety.  The Administrator has considered this requirement in
setting a new 1-hour NO2 standard as described in section II.F.4.  In
contrast, occupational standards, such as those mentioned by the
commenter, are established based on different legal requirements and may
not be updated in the same manner as the NAAQS.  Therefore, there is no
expectation that the ratio of the NAAQS to an occupational standard
would  be a basis for selecting a NAAQS.

(7)	Comment: NESCAUM argues that “while ozone rapidly oxidizes NO to
NO2, there is usually insufficient ozone to produce substantially
elevated levels of NO2 from this reaction in near-roadway exposure
scenarios during morning rush hours, nighttime, and at least half of the
year (during the non-ozone season).”

Response:  While EPA acknowledges that the extent to which NO2
concentrations near roads are elevated will vary with ozone
concentrations, we disagree with the conclusion that NO2 concentrations
near roads are not usually elevated substantially.  As discussed in the
final rule (sections II.A.2 and II.F.4), elevated NO2 concentrations do
occur on and around roads and people who live, work, and/or attend
school near major roads, or commute in vehicles on major roads, can be
exposed to these elevated concentrations.  For example, based on NO2
monitoring studies the ISA stated that NO2 concentrations in heavy
traffic or on freeways “can be twice the residential outdoor or
residential/arterial road level,” that “exposure in traffic can
dominate personal exposure to NO2,” and that “NO2 levels are
strongly associated with distance from major roads (i.e., the closer to
a major road, the higher the NO2 concentration)” (ISA, sections 2.5.4,
4.3.6).  In addition, a considerable fraction of the population resides,
works, or attends school near major roadways and these populations are
likely to have increased exposure to NO2 (ISA, section 4.4).  Based on
data from the 2003 American Housing Survey, approximately 36 million
individuals live within 300 feet (~90 meters) of a four-lane highway,
railroad, or airport (ISA, section 4.4).  Furthermore, in California,
2.3% of schools with a total enrollment of more than 150,000 students
were located within approximately 500 feet of high-traffic roads (ISA,
section 4.4).

(8)	Comment:  Harris County Public Health and Environmental Services
(HCPHES) noted that EPA’s REA “concludes that it is appropriate to
focus on studies that evaluated NO2 health effect associations using
both single- and multi-pollutant models.  However, HCPHES believes that
insufficient study and attention has been given to such synergistic
effects.  Because of this insufficiency, HCPHES believes that EPA should
include an adequate margin of safety and set the one-hour standard
sufficiently below the upper limit of 100 ppb leaning more towards the
bottom end of the proposed range.”

Response:  The Administrator’s decision on standard level, including
her consideration of the requirement to provide an adequate margin of
safety, is discussed in detail in section II.F.4.d of the final rule.

(9)	Comment:  AASHTO recommended that EPA should not set its NO2
standard below background concentrations of NO2 in order to avoid making
the standard unattainable.

	Response:  As described in detail in section II.F.4.d of the final
rule, the Administrator has set an NO2 NAAQS that, in her judgment, is
requisite to protect public health, including the health of sensitive
subpopulations, with an adequate margin of safety.  In setting such a
standard, the Administrator is prohibited from considering such factors
as projections of areas that will or will not attain the standard.
However, EPA notes that we are unaware of any locations with
nonanthropogenic background concentrations that would exceed the
standard.

Comments on the annual standard

(1)	Comment:  With regard to an annual standard, CASAC and a number of
public commenters (e.g., NACAA, NESCAUM; agencies from States including
CA, IN, MO, NC, NY, SC, TX, VA; tribal organizations including Fon du
Lac and NTAO; environmental/medical/public health groups including ACCP,
ALA, AMA, ATS, CAC, EDF, EJ, GASP, NACPR, NAMDRC, NRDC; and industry
groups including AAM, API, Dow, INGAA, UARG) agreed with the proposed
decision to maintain an annual standard, though their recommendations
with regard to the level of that annual standard differed (see below).

In their comments on the final REA, CASAC recommended “retaining the
current standard based on the annual average” based on the “limited
evidence related to potential long-term effects of NO2 exposure and the
lack of strong evidence of no effect” and that “the findings of the
REA do not provide assurance that a short-term standard based on the
one-hour maximum will necessarily protect the population from long-term
exposures at levels potentially leading to adverse health effects”
(Samet, 2008).  A number of State agencies and organizations and
industry groups also recommended maintaining the current level of the
annual standard (i.e., 53 ppb).  This recommendation was based on the
conclusion that, while some evidence supports a link between long-term
NO2 exposures and adverse respiratory effects, that evidence is not
sufficient to support a standard level either higher or lower than the
current level.

In contrast, some environmental organizations and medical/public health
organizations as well as a small number of States (e.g., ALA, EDF, EJ,
NRDC, and organizations in CA) recommended setting a lower level for the
annual standard.  These commenters generally supported their
recommendation by pointing to the State of California’s annual
standard of 30 ppb and to studies where long-term ambient NO2
concentrations have been associated with adverse respiratory effects
such as impairments in lung function growth.

Response:  EPA’s response to these comments, and the Administrator’s
conclusions on the annual standard, are discussed in section II.G of the
final rule.

(2)	Comment: Several petroleum industry commenters (API, UPA, IPAMS,
PAW, UARG) claimed that EPA did not provide a rationale for changing the
units of the annual standard.  These commenters assert that the proposal
to express the level as 53 ppb is different from the current standard
which also expresses the level in terms of micrograms/m3 (100
micrograms/m3).  These commenters claim that by shifting to ppb, the
stringency of the standard is increased for higher elevations (i.e., at
sea level 53 ppb = 100 microgram/m3, but at 5,000 ft, 53 ppb = 84
micrograms/m3).  PAW specifically stated that “the change in the
annual standard from the current mass and volume concentration to a
strictly volume concentration represents a significant and unjustified
tightening of the standard for high altitude areas, which includes many
of the areas in which the oil & gas industry operates in the western
states.”

Response:  The issue raised in the comments is attributed to the
mathematical conversion between ppb (a mixing ratio, by volume) and
micrograms per cubic meter (µg/m3), which is a mass-based metric.
According to the ideal gas law (PV=nRT) the number of molecules (n) are
proportional to their volumes (V) which in turn is proportional to their
pressures (P).  Since the total air pressure, and hence the
concentration of air, decreases with altitude, a constant mixing ratio
will not translate into a constant concentration.  Typically, when
converting from ppb to µg/m3, scientists standardize the process by
using a standard pressure and temperature, e.g., 1 atm and 25 C,
respectively, in the conversion calculations.  This standardization
results in the apparent difference in mass concentration provided as an
example by the commenter.

EPA notes that “parts per” concentration, such as parts per billion
(ppb) or parts per million (ppm), etc., are mixing ratios, and are very
common units for measuring gas phase species.  Further, the use of
mixing ratios is widespread for expressing the relative amounts of
species at various altitudes.  The chemiluminescence FRM for the NO2
NAAQS provides in-situ concentration information, in a mixing ratio by
volume (e.g., ppb), that is compensated for both temperature and
pressure.  As a result, chemiluminescence FRM-produced data, which
measures concentrations from a known volume of air, is not subject to
variation due to ambient temperature or pressure (e.g., altitude).

The parenthetical in the existing standard was intended to be
informative, indicating the mass-based measurement corresponding to the
level of the standard at standard temperature and pressure.  The
parenthetical did not create a second standard, allowing compliance with
either measurement depending on ambient temperature or pressure, and
therefore deletion of the parenthetical is not a change to the standard.
 Since the FRM is not subject to variation due to ambient temperature or
pressure, the ppb level is the only measurement relevant to attainment.
However, EPA recognized that the presence of the parenthetical in the
standard could be confusing, and determined it was appropriate to delete
it to clarify the standard.

Technical Issues with Monitoring Requirements

Comments on near-road monitor siting requirements

(1)	Comment:  Some state agencies (e.g., AASHTO, NYSDOT, and WIDNR)
recommended that the maximum horizontal distance be increased from the
proposed 50 meters to as much as 200 meters, noting that a 50 meter
limit would be infeasible for many locations and could create a serious
safety hazard for monitoring staff and the general public.  In contrast,
several environmental, and industry groups (e.g., GASP and AQRL)
supported the proposed range, and in GASP’s case, supported reducing
the maximum distance to 30 meters or less in order to reduce the
potential variation in roadway distance between monitoring sites and
subsequent measurements of near-road NO2 concentrations.

Response:  EPA’s decision on the siting criteria for NO2 monitors
requires, among others, that the near-road NO2 monitors be sited within
50 meters from the roadway.  EPA discusses the basis for this decision
in detail in section III.B.7 of the preamble to the final rule.

(2)	Comment:  A limited number of comments were received recommending
changes to the requirements for the vertical height of the NO2 monitor
inlet manifold.  Two state organizations (NESCAUM and NYSDEC) noted that
the proposed 2-7 meter vertical range could generate significant
variation in the concentrations reported from monitors located at
different heights.  NESCAUM recommended that the height range be reduced
to 2.5-3.5 meters.  NYSDEC commented that the proposed vertical height
range may not be practical for many sites, especially those located in
urban areas.  In addition, the ALA, EJ, EDF, and NRDC noted that:

[T]he 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.  Additional monitors at other
relationships to these sources may be needed for research purposes, but
they should be in addition to those designed to establish the peak
exposures for NAAQS compliance purposes.

Response:  EPA’s decision on the siting criteria for NO2 monitors
requires, among others, that the near-road NO2 monitors inlet manifolds
be placed between 2 to 7 meters above the ground.  EPA discusses the
basis for this decision in detail in section III.B.7 of the preamble to
the final rule. With regard to the ALA, EJ, EDF, and NRDC comment on
needing additional monitors for research, EPA does not believe that this
particular research issue is appropriate to address through this
rulemaking, but rather through ongoing and future research that further
characterizes the near-road environment.  For the purposes of supporting
the revised 1-hour NAAQS, EPA believes that the siting criteria are
sufficient and appropriate.

(3)	Comment:  Several groups that support the proposed two-tiered
monitoring network requested modifications to the proposed criteria for
determining where a near-road monitor should be located.   Some
environmental/public health organizations (ALA, EJ, NRDC, EDF) commented
that “Near-road monitor placement should be determined not only by the
highest AADT [annual average daily traffic] volumes in a given
[core-based statistical area] CBSA, but also by the highest heavy-duty
truck volumes.”  The NYDOH, IADNR, and some industry groups (e.g., EEI
and SRNS) recommend making population a prominent consideration when
deciding where to locate monitors.  HCPHES recommended that near-road
monitoring stations should take into consideration the location of other
major mobile and point sources for NO2 emissions, such as airports,
seaports, and power plants, or vulnerable population groups like
children, when determining the appropriate locations for near-road
monitors.

Response:  EPA has clarified that the selection criteria should include
the consideration of localized factors when identifying locations of
expected maximum concentrations.  Near-road sites 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 be
highest and the siting criteria can be met in accordance with 40 CFR
Part 58 Appendix E.  EPA discusses the basis for this decision in detail
in section III.B.6 of the preamble to the final rule.

(4)	Comment:  Many state agencies commented that EPA needed to provide
greater guidance to state and municipal agencies about where to site
near-road monitors.  The CAC recommended that state discretion over the
location of near-road monitors be limited “such that gaming is not
tolerated.”

Response:  EPA agrees that guidance will be useful in aiding the
implementation of a near-road network.  As noted in the section III.B.5
of the preamble to the final rule, EPA plans to assist state agencies in
the network implementation process, particularly through guidance
documentation that the Agency intends to prepare and share with state
and local agencies early enough in the overall implementation process to
be useful to states in developing their NO2 monitoring network.
Further, EPA encourages state and local monitoring agencies to include
or cooperate with transportation officials in the development of the
near-road network. EPA believes that state and local monitoring agencies
may benefit greatly from working with federal, state, and/or local
transportation officials during the development of and long-term
maintenance of a near-road network.

EPA believes that the commenter’s concern that the state discretion
allowed in the placement of near-road monitors may lead to installations
in locations unlikely to violate the NAAQS, will be avoided due to the
process outlined in 40 CFR §58.10 under which a state’s annual
monitoring network plan must be made available for public inspection or
comment and approved by the EPA Regional Administrator.  This process
will permit scrutiny of the monitor siting locations and assist in
identifying and siting monitors in appropriate locations within CBSAs.

(5)	Comment:  CASAC advised that siting monitors based on traffic counts
alone might miss locations where maximum NO2 concentrations would occur.
 CASAC recommends that EPA should use model results from Congestion
Mitigation and Air Quality Land Use Regression modeling as well as
Gaussian plume models and emissions inventories to determine where
roadside monitors should be located.

Response:  EPA does not intend for AADT counts to be the sole basis for
choosing a near-road site.  EPA has clarified rule language to reflect
that 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 the siting criteria can be met in accordance with 40 CFR Part
58 Appendix E. This issue is discussed in section III.B.6 of the
preamble to the final rule.  EPA also 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

(6)	Comment:  EPA received a number of comments recommending using
different population thresholds, or a different approach in requiring
near-road monitors.  Several commenters (e.g., NESCAUM, NYSDOT, NYSDEC)
recommended using a higher population threshold than that proposed, for
example, NYSDEC suggested the population threshold be increased to as
much as 2.5 million.  Conversely, CAC suggested that the proposed
threshold may not be low enough.  Other commenters (e.g., AASHTO and
HCPHES) recommended that EPA use an AADT threshold (ranging from 100,000
to 250,000 AADT), in lieu of a population threshold, to require
near-road monitoring.  Another commenter, San Joaquin Air Pollution
Control District suggested the using a combination of population and
AADT thresholds to require near-road monitors.

Response:  EPA’s decision is to require one near-road NO2 monitor 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.  EPA discusses the basis for this decision in
detail in section III.B.2 of the preamble to the final rule.

(7)	Comment:  EPA received comments suggesting that EPA require
monitoring at sites non- near-road locations.  One commenter (Center on
Race, Poverty, and the Environment) recommended that EPA account for
populations in rural areas, such as those impacted by agricultural
emissions.  The Fond du Lac Band of Lake Superior Chippewa and the NTAA
suggested that EPA expand monitoring coverage into rural areas and
tribal lands.  Other commenters (ATS, AMA, NAMDRC, NACPR, ACCP, and the
Swinomish Tribe) also recommended that EPA consider sources other than
mobile sources, such as large stationary sources.

Response:  As discussed in section II.F.4.d of the final rule, the
Administrator has set a new 1-hour NO2 standard that reflects the
maximum allowable NO2 concentration anywhere in an area.  In her
judgment, this new standard will protect public health, including the
health of sensitive populations such as asthmatics, with an adequate
margin of safety.  It follows from this standard that monitors should be
placed in locations where maximum NO2 concentrations are expected.  The
Administrator has judged that, in many areas, these maximum
concentrations are likely to occur around major roads (final rule,
sections II.A.2 and II.F.4.d).  Therefore, she is requiring NO2 monitors
within 50 meters of major roads.  In situations where maximum NO2
concentrations are likely to occur in locations other than near a major
road (e.g., near stationary point or area sources, whether agricultural
or industrial (such as those noted by the commenters), the Regional
Administrator has the authority to require additional monitors in these
locations.  Further, the Administrator 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 of the preamble to the final rule) 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.

(8)	Comment:  Two tribal commenters ( Fond Du Lac Band of Lake Superior
Chippewa and the National Tribal Association) recommended that more
monitoring stations be required for rural or tribal roadways since EPA
recognized Native Americans as an at-risk population group.

Response:  As discussed in section II.F.4.d of the final rule, the
Administrator has set a new 1-hour NO2 standard that reflects the
maximum allowable NO2 concentration anywhere in an area.  In her
judgment, this new standard will protect public health, including the
health of sensitive populations such as asthmatics, with an adequate
margin of safety.  It follows from this standard that monitors should be
placed in locations where maximum NO2 concentrations are expected.  The
Administrator has judged that, in many areas, these maximum
concentrations are likely to occur around major roads (final rule,
sections II.A.2 and II.F.4.d).  Therefore, she is requiring NO2 monitors
within 50 meters of major roads.  In situations where maximum NO2
concentrations are likely to occur in locations other than near a major
road (e.g., near multiple smaller roads and/or stationary sources), the
Regional Administrator will have the authority to require additional
monitors in these locations.  EPA notes that it is not in a position to
require monitoring by tribes or on tribal land.  However, EPA has and
will continue to work with tribes in conducting ambient monitoring on
tribal lands.

(9)	Comment:  One state agency, NYSDEC requested that CBSAs with
populations larger than 2.5 million be allowed to have more than two
near-road monitors.

Response:  EPA’s decision is to require, at a minimum, one near-road
NO2 monitor in CBSAs with a population greater than or equal to 500,000
persons and a second near-road monitor 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.  EPA discusses the basis for this
decision in detail in section III.B.2 of the preamble to the final rule.
EPA also notes that states always have the ability to conduct additional
monitoring above the minimum monitoring requirements at their
discretion.

(10)	Comment:  Some public health and environmental groups (e.g., ALA,
CAC, and NRDC) suggested that near-road monitors should be required to
be located on the downwind side of the target road.  Conversely, several
commenters (AQRL and NYSDEC) suggested that such a requirement may be
over restrictive and not necessary.  AQRL commented that siting monitors
in downwind locations would not be feasible for all locations and EPA
should allow upwind monitoring locations so long as upwind monitors are
used in conjunction with air dispersion modeling.

Response:  EPA is not going to finalize 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.  EPA discusses
the basis for this decision in detail in section III.B.7 of the preamble
to the final rule.

(11)	Comment:  Several commenters (e.g., CASAC, ACCP, ALA, AMS ATS, EDF,
NACPR, NAMDRC, NRDC) made comments that the proposed network should form
the basis for a broader near-road monitoring network that would
encompass other pollutants as well, i.e., be a multi-pollutant near-road
monitoring network.  These organizations’ recommendations were based
on the argument that it makes little sense to only monitor NO2
concentrations near roads when it is well-understood that many other
pollutants, hazardous to the public’s health, are emitted by on-road
vehicles along with NO2.

Response:  The scope of this rulemaking pertains to the NO2 NAAQS and
the monitoring associated with it.  However, EPA agrees that
multi-pollutant monitoring is desirable, and believes that the sites
required in the near-road component of the NO2 network design could also
be suitable for monitoring other pollutants including carbon monoxide,
particulate matter (especially ultra-fine particulate matter), air
toxics, and black carbon.

(12)	Comment:  Comments were submitted, particularly from state agencies
(e.g., Michigan, Mississippi, and Tennessee), noting that one of  the
challenges to developing a near-road monitoring network was the
potential safety hazard of having a monitoring station located within 50
meters of busy roadways.

Response:  EPA notes that in all instances of field work, safety is a
top priority.  EPA believes that the safety issue raised in public
comments is something that is an important component of near-road siting
logistics, and that the near-road network can be safely implemented
while still serving its intended purpose of providing data on the
expected maximum NO2 concentrations that occur within 50 meters of
heavily trafficked roads. EPA discusses this issue in further detail in
section III.B.7 of the preamble to the final rule.

(13)	Comment:  The Clean Air Council (CAC) recommended the “EPA not
permit alternative monitoring systems on a state-by-state basis if they
would hinder uniformity to the extent that public understanding and
accountability of government would be degraded.”  In contrast, the
Southeast Michigan Council of Governments (SEMCOG) suggested that,
rather than requiring a near-road monitoring network, EPA should enable
states to select monitoring locations based on each state’s specific
needs and issues as part of the state implementation plan (SIP) process.

Response:  EPA believes that it must use, and has chosen, a balanced
approach in setting monitoring requirements that recognizes the need to
have as nationally consistent monitoring network as possible, while
allowing an appropriate amount of flexibility so that states are able to
comply with monitoring requirements. EPA believes that the near-road
site selection process must include certain considerations such as AADT,
fleet mix, roadway design, congestion patterns, terrain, and meteorology
to identify where maximum hourly NO2 concentrations are expected occur.
While states have flexibility in evaluating what specific thresholds or
criteria are appropriate for their particular situations with respect to
the metrics listed above, they are to make all effort to meet the
primary objective of locating the site in a location of expected
concentration.  This flexibility is necessary when considering the
reality of, for example, safety or site access, and other logistical
issues that are inherent to installing a monitoring network that can
differ on a case-by-case basis. EPA discusses issues of site selection
and siting criteria in further detail in sections III.B.6 and III.B.7 of
the preamble to the final rule.

(14)	Comment:  The Spokane Regional Clean Air Authority (SRCAA) noted
that it might not be necessary for EPA to require an extensive near-road
monitoring network if a smaller network can develop a strong statistical
correlation between particular variables (i.e. traffic density, vehicle
mix) and above-standard NO2 concentrations.

Response:  EPA believes that the currently available data, and the
number of variables that influence the concentration and behavior of NO2
in the near-road environment, including fleet mix, roadway design,
congestion patterns, terrain, and meteorology, do not allow the
development of a “strong,” and nationally applicable, statistical
correlation that would allow the avoidance of what the commenter states
is an “extensive” near-road network. (EPA estimates that
approximately 126 near road monitors will be needed.) The reasoning
behind the size and extent of the near-road monitors required in the
two-tier network design, with respect to SRCAA’s comments, are
discussed in detail in sections III.B.1 and III.B.2 of the preamble to
the final rule..

(15)	Comment:  Several environmental and public health groups (e.g.,
ALA, EDF, EJ, NRDC) pointed out that “only 58 of 489 total NO2
monitors are sited in areas of expected peak concentrations.”

Response: The relative current state of the NO2 network is detailed in
the NOx Network Review and Background document (Watkins and Thompson,
2009), which is posted in the docket.  This document provides
information and summaries on what EPA believes the current monitoring
network, according to state provided meta-data, is addressing.

Comments on area-wide monitor requirements

A number of comments were received, particularly from state agencies, in
support of maintaining the existing area-wide monitoring network.
Comments specific to the siting or area-wide monitors tended to focus on
either (1) the need for more area-wide monitors than the proposed 52 or
(2) the need to make sure that all area-wide monitors were measuring
ambient NO2 concentrations rather than NO2 concentrations near major NO2
emissions sources.

Comment:  Several industry groups and state agencies (e.g., AAM, EMA,
INDEM, and NYSDOT) provided specific comments that they preferred the
alternative monitoring approach of using area-wide monitors to measure
1-hour NO2 concentrations due to the high cost of implementing,
operating, and maintaining a near-road monitoring network and the
uncertain benefits such a network would provide.  In addition, one
commenter recommended the area-wide approach because it provided greater
flexibility for monitors to be located in places where more people are
likely to be exposed to high concentrations of NO2.

Response:  The Administrator has set a new 1-hour NO2 standard that
reflects the maximum allowable NO2 concentration anywhere in an area.
In her judgment, this new standard will protect public health, including
the health of sensitive populations such as asthmatics, with an adequate
margin of safety.  It follows from this standard that monitors should be
placed in locations where maximum NO2 concentrations are expected.  The
Administrator has judged that, in many areas, these maximum
concentrations are likely to occur around major roads (final rule,
sections II.A.2 and II.F.4.d).  Therefore, the Administrator has
concluded that a two-tier network design composed of (1) near-road
monitors which would be placed in locations of expected maximum 1-hour
NO2 concentrations near heavily trafficked roads in urban areas and (2)
monitors located to characterize areas with the highest expected NO2
concentrations at the neighborhood and larger spatial scales (also
referred to as “area-wide” monitors) are needed to implement the
1-hour NO2 NAAQS.  The rationale for this decision is discussed in
section III.B.1 of the preamble to the final rule.

Comment:  Several environmental, public health, and tribal organizations
(ALA, EDF, EJ, NRDC, NTAA) commented that EPA should require more
monitors than currently proposed.  Specifically, the ALA, EJ, NRDC, and
EDF stated that they “oppose the proposed requirement to retain only
52 air monitors to measure area wide concentrations NO2” In addition,
they commented:

“[The] 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.  In particular, certain large
agricultural facilities may emanate high concentrations of NO2 under
certain conditions, such as wet weather.  Many of these facilities are
directly upwind of rural communities, meriting an NO2 monitor.”

Response:  EPA recognizes a variety of exposure scenarios can occur in
an area such as the ones described by the commenters above.  Therefore,
the final rule authorizes Regional Administrators to require additional
monitors above the minimum required number of monitors in circumstances
such as those described by the commenter above where there is a
likelihood of high concentrations of NO2 that approach or exceed the
NAAQS.  The size and extent of the required area-wide monitors in the
network design are discussed in section III.B.3 of the preamble to the
final rule.  A more detailed discussion of the Regional Administrator
authority and some examples where such authority may be exercised is in
section III.B.4 in the preamble to the final rule.

Comment:  One state agency provided comments opposing using only an
area-wide network for monitoring NO2 on the grounds that the network
represents an inadequate alternative to the creation of a near-road
monitoring network.  The commenter was critical of how useful dispersion
modeling would be at identifying NO2 concentrations beyond a monitor’s
immediate area.  The commenter claimed there were too many confounding
factors to accurately estimate the NO2 concentrations near roadways and
other NO2 emissions sources from an area-wide monitor.

Response: The Administrator has set a new 1-hour NO2 standard that
reflects the maximum allowable NO2 concentration anywhere in an area.
In her judgment, using only an area-wide network of NO2 monitors would
not adequately support this new standard because maximum concentrations
of NO2 are likely to occur around major roads (final rule, sections
II.A.2 and II.F.4.d)]. The Administrator has concluded that a two-tier
network design composed of (1) near-road monitors which would be placed
in locations of expected maximum 1-hour NO2 concentrations near heavily
trafficked roads in urban areas and (2) monitors located to characterize
areas with the highest expected NO2 concentrations at the neighborhood
and larger spatial scales (also referred to as “area-wide” monitors)
are needed to implement the 1-hour NO2 NAAQS.  The rationale for this
decision is discussed in section III.B.1 of the preamble to the final
rule.

Comment:  One commenter, Dow, recommended that area-wide monitors should
be located at least 1,000 meters 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.

Response:  EPA believes that Table E-1 of 40 CFR Part 58 Appendix E,
which provides roadway set-back distances for neighborhood and larger
scale sites is appropriate to use to ensure that any NO2 site that is
intended as an area-wide site will be located at a sufficient distance
from any major road.  This issue is discussed section III.B.8.of the
preamble to the final rule.

(5)	Comment:  NYSDEC encourages EPA to develop a table for defining the
minimum distance to the nearest major roadway that can be used to
calculate the area-wide NO2 concentrations, since specific distances are
unlikely to be appropriate for all core based statistical areas (CBSAs).

	Response:  EPA believes that existing data in 40 CFR Part 58 Appendix
E, Table E-1, are  appropriate for use in determining the minimum
distance a monitoring site must be from a road with a given annual
average daily traffic count to be considered a neighborhood or larger
spatially representative site.  If a state feels that an increased
minimum distance compared to Table E-1 is appropriate for an area-wide
site in one or more of their particular CBSAs, or on a case-by-case
basis, the state can elect to site their area-wide monitors accordingly,
so long as they continue to meet siting and network design requirements
specified in 40 CFR Part 58.

(6)	Comment:  Several environmental and public health groups (e.g., ALA,
EDF, EJ, NRDC) opposed the proposed requirement to retain only 52 air
monitors to measure area wide concentrations NO2.

	Response:  EPA is not requiring that the current NO2 network be
reduced; rather, EPA has introduced minimum monitoring requirements
where there was previously no minimum NO2 monitoring requirement.  This
issue is discussed in section III.B.8 of the preamble to the final rule.
Further, the relative current state of the NO2 network is detailed in
the NOx Network Review and Background document (Watkins and Thompson,
2009), which is posted in the docket.  This document provides
information and summaries on what EPA believes the current monitoring
network, according to state provided meta-data, is addressing.

Comments on the need for a research monitoring network

A number of commenters, primarily from industry groups and state
agencies recommended that some form of near-road research monitoring
network be utilized before a full-scale near-road monitoring network is
implemented.

Comment:  A subset of CASAC panel members recommended establishing a
limited roadside monitoring network (20 to 50 monitors in different
cities) for the purpose of informing the development of a national
network.  Specifically, these CASAC member recommended the following:

A small roadside network could provide more information than a national
network of NOx monitors if the smaller network also monitored other
roadway-associated pollutants, including CO and continuous particulate
matter (PM) with speciation, and if the network also included detailed
meteorological measurements and automatic traffic counters.  They note
that measuring only NO2 could lead to the mistaken impression that air
quality is deteriorating as diesel particulate filters, which can
increase the fraction of NOx that is emitted as NO2, become more common.

If EPA undertakes near-road monitoring, the Agency should seek the
advice of technical experts, such as those in the CASAC Ambient Air
Monitoring and Methods (AAMM) subcommittee.

Siting criteria should include consideration of such factors as vehicle
mix, location of susceptible or vulnerable populations (e.g., schools,
hospitals), local physical features such as urban street canyons.

Such a network should be established quickly to capture ongoing changes
in mobile source emissions and should be funded primarily by EPA.

Response:  The Administrator has judged that a regulatory, two-tier
network design, which includes near-road monitors in urban areas (not a
research network), is necessary to support the intent of the revised
NAAQS to protect against risks associated with exposures to peak
concentrations of NO2 anywhere in an area. This rationale is discussed
in section III.B.1 of the preamble to the final rule. EPA believes that
it will be useful to provide guidance to ensure consistent
implementation of the monitoring network and has committed to engage the
CASAC AAMM subcommittee on this effort, and discusses this issue in
section III.B.5 of the preamble to the final rule.  In regard to
measuring other roadway-associated pollutants, the scope of this
rulemaking pertains to the NO2 NAAQS and the monitoring associated with
it. However, EPA agrees that multi-pollutant monitoring is desirable,
and believes that the sites required in the near-road network design
could be suitable for other pollutants including carbon monoxide,
particulate matter (especially ultra-fine particulate matter), air
toxics, and black carbon.

Comment:  Some industry commenters (e.g., CE, EEI, NAM, NPRA, NMC, OIPA,
POH, SRNS, SCCC, and SCMA) provided support for a research monitoring
network due to perceived weaknesses in the scientific basis for
implementing an extensive near-road monitoring network.  Generally
indicating that a research network would allow EPA to gain a better
understanding of near-road peak NO2 concentrations and their impact on
public health before requiring the development of a large and expensive
monitoring network.  For example, NAM commented:

If EPA concludes that NO2 near roadway monitoring is required, the NAM
recommends at a minimum, EPA should consider conducting a near roadway
"special purpose" monitoring network program.  Conducting such a near
road monitoring program would allow EPA to collect necessary data that
can be used to better understand the health impacts associated with
short term NO2 exposures.

Response:  The administrator has judged that a regulatory, two-tier
network design, which includes near-road monitors in urban areas (not a
research network), is necessary to support the intent of the revised
NAAQS to protect against risks associated with exposures to peak
concentrations of NO2 anywhere in an area.  EPA believes that the
existing near-road research provides a sufficient base of information to
implement an appropriately designed near-road monitoring network, and
the collective experience that exists in the ambient monitoring
community will allow for successful implementation of that network. EPA
discusses the basis and rationale for the two-tier network design, which
include near-road monitors for regulatory purposes in section III.B.2 of
the preamble to the final rule.

Comment:  Some state groups (e.g., AASHTO, ILEPA, MIDEQ, MSDEQ, NACAA,
NCDENR, NESCAUM, NMED, SCDHEC, SJAQMD, and VDOT) focused their support
for a research monitoring program by identifying a need to develop more
experience siting near-road monitors.  Creating greater certainty about
where and how near-road monitors ought to be used could reduce
variations in measurement results driven solely by differences in
monitor siting.  These comments are exemplified by NACAA’s comment:

…a major new network – particularly one that is inherently
complicated and untried – should not be rolled out without the benefit
of an effective near-road monitoring research program that can address
many of the relevant data questions, and inform the specific siting
requirements of the rule.

Response:  The Administrator has judged that a regulatory, two-tier
network design, which includes near-road monitors in urban areas (not a
research network), is necessary to support the intent of the revised
NAAQS to protect against risks associated with exposures to peak
concentrations of NO2 anywhere in an area.  EPA believes that the
existing near-road research provides a sufficient base of information to
implement a appropriately designed near-road monitoring network, and the
collective experience that exists in the ambient monitoring community
will allow for successful implementation of that network. EPA discusses
the basis and rationale for the two-tier network design, which include
near-road monitors for regulatory purposes in section III.B.2 of the
preamble to the final rule.

(4)	Comment:  The CASAC panel members who support the alternative
approach, which is coupled to a monitoring network that includes only
area-wide monitors, stated that roadside monitors will likely detect
extreme concentrations of NO2 at certain times (e.g., heavy traffic,
idling truck near monitor) and more effort is needed to characterize
these measurements and their relationship to traditional area-wide
measurements.

Response: EPA believes that some urban areas that will have both
area-wide monitors (whether required or not) and near-road monitors may
be able to provide data to increase the understanding or possibly
quantify the relationship (at least for that particular area) between
near-road and area-wide concentrations.  Intense investigation of the
roadway gradient has been, and will continue to be best served by
research studies that utilize transect monitoring and/or saturation
monitoring around target road segments.

(5)	Comment: The CASAC panel members who support the alternative
approach, which is coupled to a monitoring network that includes only
area-wide monitors, stated that the siting of the near-road monitors
will require consideration of many factors as the monitors will be
sensitive to the microscale environment of the location.  Because the
monitors will capture concentrations at the extreme end of the range,
the data from any two given monitors may not be directly comparable if
the characteristics of their sites vary greatly.

Response: EPA understands that near-road sites will be microscale in
nature, and concentrations at the site will be subject to factors
including AADT, fleet mix, roadway design, congestion patterns, terrain,
and meteorology.  As a result, EPA would expect site to site differences
corresponding to variability in the above factors.  However, 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.  The required near-road monitoring sites are
intended to measure the maximum expected concentrations, considering the
above factors.

(6)	Comment:  The CASAC panel members who support the alternative
approach, which is coupled to a monitoring network that includes only
area-wide monitors, stated that siting monitors based on traffic count
alone may miss locations where maximum concentrations of NO2 occur.  EPA
should investigate model results from Congestion Mitigation and Air
Quality (CMAQ) Land Use Regression modeling as well as Gaussian plume
models and emissions inventories to determine where roadside monitors
should be located.

Response: As noted in section III.B.6 of the preamble to the final rule,
EPA does not intend for AADT counts to be the sole basis for choosing a
near-road site.  EPA understands that 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, which influence where the location of expected maximum NO2
concentration may occur, when evaluating a pool of candidate near-road
monitoring sites.  Further, EPA expects that modeling will be a tool
used by states to assist in informing where near-road monitoring sites
should go.

(7)	Comment:  The CASAC panel members who support the alternative
approach, which is coupled to a monitoring network that includes only
area-wide monitors, commented that diesel particle filters increase the
fraction of NO2 in NOx and may lead to higher measured concentrations of
NO2 in places where vehicles are actually cleaner.

Response:  EPA notes that the required near-road NO2 monitors are to be
sited  in locations that are expected to measure maximum NO2
concentrations.  The issue of whether the fleet, or a component of the
fleet, travelling on the target road is relatively dirty or clean is
part of consideration of fleet mix that states are to consider when
identifying near-road site locations.

(8)	Comment:  Many state and industry commenters (e.g., NACAA, NESCAUM,
many states, Consumers Energy, EA, EEI, NAM) recommended that a
near-road research monitoring program be implemented before a full-scale
near-road monitoring network is required.  Specifically, EA recommended
that a near-road monitoring network not be required until enough
near-road monitoring data was available to ensure that EPA’s proposed
NO2 level is not set below background NO2 levels.

Response:  The EPA believes that is has sufficient understanding of the
near-road environment from existing research to propose a near-road
network that is appropriate for regulatory use.  This issue is discussed
in issue in section III.B.2 of the preamble to the final rule.  In
addition, as discussed in section II.F.4.d of the preamble to the final
rule, the Administrator has set the level of the 1-hour standard at 100
ppb to protect public health with an adequate margin of safety.  Her
decision is based on consideration of available health evidence,
exposure/risk information, the advice of CASAC, and input from the
public.

Justification of meteorological measurements

Most commenters did not mention the issue of meteorological measurements
but the comments received on the subject were unanimously against
requiring monitoring stations to include three-dimensional anemometry
equipment.

Comment:  CASAC Panel members and a number of state commenters (e.g.,
AKDEC, NCDENR, SCDHEC, and WIDNR) questioned the need for meteorological
measurements at the NO2 monitoring sites.  These commenters called into
question the ability of three-dimensional anemometry to provide the
microscale meteorological information EPA desires if the monitors are to
be located close to the ground and other structures, and if they are
averaging measurements over hour long periods of time. SCDHEC commented
that the recording of air turbulence data at monitor stations ought to
be encouraged but not required unless EPA were willing to fully fund the
purchase, installation, and operation of the necessary equipment.  These
commenters concluded that the requirement to include equipment for
measuring meteorological characteristics would be an unnecessary
expense.

Response:  EPA has chosen not to finalize a requirement for
meteorological measurements, including three-dimensional anemometry, at
near-road NO2 monitoring stations, but does encourage states to perform
meteorological monitoring to better characterize the behavior of NO2
cocentrations in the near-road environment.  EPA discusses its rationale
for this decision in section III.B.9 of the preamble to the final rule.

Monitoring technology

Commenters (CASAC Panel members, some state agencies, and some industry
groups) who expressed an opinion regarding monitoring techniques
generally agreed that the proposed chemiluminescence approach is
appropriate.  However, some groups (e.g., CASAC and industry)
recommended that EPA promote the development of additional methods for
measuring true NO2 that would not be subject to positive interference.

(1)	Comment:  Several commenters (e.g., MODNR, SRNS, Teledyne API, and
UARG) recommended that EPA encourage the development of alternative
monitoring technologies, which includes the photolytic-chemiluminescence
method or cavity ring-down spectroscopy, and to permit the use of these
technologies for monitoring if the new technologies provide comparable
or better monitoring results than existing FRM/FEM [Federal Reference
Method/Federal Equivalent Method].  NCDENR urged EPA to maximize the
flexibility in the choice of FRM and FEM technology available to
demonstrate compliance so long as the technology provides comparable
results.

Response:  The FRM/FEM program ensures that only evaluated and approved
methods may be used for comparison to the NAAQS (see 40 CFR  Part 53).
EPA only approves a particular method for use in measuring oxides of
nitrogen once it has been shown to meet requirement set forth in 40 CFR
Part 50 Appendix F, with testing and data provided usually provided by
instrument vendors. The use of FRM/FEMs and furthering method
technologies is discussed in section III.A.1 of the preamble to the
final rule.

(2)	Comment:  One industry commenter, Aerodyne, expressed concern that
current NO2 monitoring equipment and siting protocols will not be
suitable for use in near-road applications without proper
reconfiguration. The commenter notes that the method by which the
chemiluminescence FRM determines NO2 concentrations, using alternating
measurements of NO and NOX and subsequently using the difference to
indicate NO2, may not be appropriate because this technique does not
possess the time response required to accurately track the plumes of
combustion gas emitted by passing vehicles.  The commenter notes that
these plumes “tend to be short-lived, with durations on the order of 3
to 30 seconds.” As a result, the commenter asserts that the values
reported by chemiluminescence FRMs “…can be quite inaccurate because
of the inability of the alternating channel monitors to properly average
these plumes.” The commenter goes on to note that this issue
“…begs the question of whether any of this affects reported 1 hour
average NO2 concentrations, the subject of the proposed regulations.”

Response:   The “alternating measurement” technique utilized by the
chemiluminescence FRM is asserted by the commenter to cause variability
in measuring short duration plumes or ‘bursts’ of NO2.  EPA believes
this variability would be most apparent when there is only one plume, or
a few individual plumes, that may pass the monitor for a short period of
time, but is unlikely to cause a discernable effect in the 1-hour
average.  EPA believes that this particular characteristic of the
chemiluminescence FRM does not warrant a new measurement approach for
near-road monitors because the averaging time of the NAAQS is 1 hour.
The NAAQS is a 1-hour standard, which EPA believes is a long enough
averaging period where short-term variations, on the order of 3 to 30
seconds will be averaged out, an are not expected to have a discernible
effect.  The commenter states that “It has always been (rightly)
assumed that when reporting 24 hour and /or yearly averages, the short
term upsets observed in the NO2 data have no discernible effect.”  EPA
notes that states calculate 24-hour and annual averages from the 1 hour
averages they acquire each day.

	The commenter suggests several alternatives to relying on a single
chemiluminescence analyzer at near-road sites.  EPA has expressed its
desire to further the development of alternative methods in determining
NO2 concentrations, which is discussed in section III.A.1 of the
preamble to the final rule, and also is open to alternative applications
of existing methods, all of which would need to follow the process for
submission and approval described in 40 CFR part 53.

(3)	Comment:  Some industry commenters expressed concern that open path
monitors might not be appropriate for use in near-road applications.

Response:  EPA notes that path integrated optical remote sensing
techniques, also known as open-path methods, are not typically used by
states at State and Local Ambient Monitoring Station (SLAMS) sites.
However, there are approved open-path methods capable of providing
hourly NO2 concentrations that can be compared to both the annual and
1-hour standard.  EPA believes that an appropriate path length is
between 50 meters to 300 meters, where 50 corresponds to the maximum
distance away from the edge of the nearest traffic lane of a nearby road
segment and 300 meters corresponds to the traditional maximum path
length at micro- or middle scales site.  EPA recognizes that if open
path methods are going to be used in the near-road environment,  issues
regarding path orientation, safety, and optimal path length within the
allowable range will likely be considered in the monitoring guidance
that will need to be developed to assist states in the implementation of
the network design.

(4)	Comment:  One industry commenter, AQRL, requested that EPA set
guidelines for the maximum allowable inlet length and sample residence
time.

Response:  EPA has only chosen to set a maximum residence time of NO2 in
the sample line between the inlet probe and the analyzer of 20 seconds.
EPA discusses this issue in section III.B.7 of the preamble to the final
rule.

(5)	Comment:  API commented that, because state and local air monitoring
agencies have little experience in near-road NO2 monitoring, EPA needs
to be prepared to support significant field validation and statistical
analysis to assess monitor performance and dispersion and photochemical
modeling analyses to assist in siting monitors.

Response:  EPA believes it has systems in place that can provide
“field validation and statistical analysis” of any ambient
monitoring network. Field validation and statistical analysis starts
with the initial testing of instruments to ensure that they are
operating properly and providing precise and unbiased measurements
before monitoring begins. All monitoring organizations are required to
have quality management plans and quality assurance project plans that
provide the necessary elements to help in their achievement of the NO2
data quality goals.  In addition, the quality assurance (QA)
requirements in 40 CFR part 58 Appendix A provide the quality control
samples, the auditing activities and the appropriate statistical
analysis that monitoring organizations and EPA can use to judge whether
the monitoring systems are under control from a data quality standpoint.

(6)	Comment:  Several state commenters (e.g., MODNR and NCDENR) suggest
that the current bias measurement uncertainty criteria used for other
NAAQS will be appropriate and acceptable for use with a 1-hr NO2
standard.

Response: EPA is finalizing the approach to develop data quality
objectives, and is  changing the proposed goal for measurement
uncertainty, to match those criteria of the NCore network and the
historical approach for NO2, where the goals for acceptable measurement
uncertainty for NO2 methods for precision is an upper 90 percent
confidence limit for the coefficient of variation (CV) of 10 percent and
for bias is an upper 95 percent confidence limit for the absolute bias
of 15 percent.

This issue is discussed section III.C of the preamble to the final rule.

(7)	Comment:  A state commenter, IADNR, recommend allowing provisions
for mobile monitoring to determine NO2 exposure to motorists.

Response:  The use of mobile monitoring may be a very beneficial tool to
assist states in locating candidate near-road NO2 sites; however, EPA
does not believe that mobile monitoring is suitable for regulatory
monitoring.  The network design is predicated on placing monitors in the
location of expected maximum concentration, which is inherently in a
generally fixed location.  Further, much consideration would have to be
given to issues regarding the deviation from the standard practice of
using fixed point (or fixed path-integrated) data for comparison to the
NAAQS. Another issue that would arise would be regarding data
completeness and representation, e.g. at what time and where the data
are valid, and whether the data are representative of a given location.
EPA is encouraged by the interest in mobile monitoring, but we believe
that such monitoring is currently best suited for non-regulatory
informational purposes.

Timing of monitor deployment

In general, the majority of comments about the timing of monitor
deployment, State Implementation Plan (SIP) development, and
determination of attainment were received from state agencies and
industry groups recommending that EPA keep the proposed current
implementation deadlines as proposed or extend the deadlines further.  A
few environment and public health groups provided comments urging EPA to
move the implementation deadlines forward. [who were the commenters
among the states, industry and enviros?]

Comment:  A lage majority of state and industry groups who made comments
on network implementation recommended that the deadline for installing
near-road monitors remain January 1, 2013, or that EPA provide the
maximum amount of time possible.  They claimed that the current January
1, 2013 deadline provides insufficient time to plan and implement such a
complicated network of monitors.  SJAQMD went further,  recommending
that EPA allow for schedule relief if a state can demonstrate that
monitor installation delays are the result of delays in obtaining
permits or rights-of-way for the near-road monitors.  Conversely, the
environmental and public health groups who made comments on network
implementation recommended that urged “EPA to seek Congressional
funding for an expanded network and to set a deadline for deployment of
no later than January 1, 2012.”

Response:  EPA recognizes the need to aid state agencies in the network
implementation process, particularly through guidance documentation that
will be developed in partnership between EPA and various stakeholders
including NACAA and the states.  Further, EPA has modified the timelines
for implementation by 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 from July
1, 2011 to July 1, 2012.  However, 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.  The basis and rationale for this decision is discussed in
section III.B.5 of the preamble to the final rule.

Other monitoring issues

Many comments about the monitoring network associated with a one-hour
standard were also submitted, including comments on what should be
considered an exceptional event and the appropriate requirements for
using data from monitors for evaluating attainment.

Comment: Some commenters urged EPA to create criteria for defining
exceptional events for near-road monitors that included events like road
construction.

Response:  The Exceptional Events Rule (EER) and the accompanying
preamble (72 FR 13560, March 22, 2007) set forth and explain the
criteria and procedures that must be used to determine whether an event
qualifies as an exceptional event and the documentation that must be
submitted to support an exceptional events claim.  For an exceptional
event claim to be approved and data affected by such an event to be
excluded from consideration in any NAAQS attainment designations, the
data would need to meet the criteria and procedures established in the
rule.  EPA believes that these criteria and procedures are sufficient to
address any exceptional events claims that may arise for NO2 NAAQS.
Additions or modifications to the EER are not needed for any exceptional
events claims that may arise for NO2.  In addition, the current
exceptional event data flags available in the AQS--unique traffic
disruption and other-- provide sufficient flexibility to address
near-road exceptional events.

Comment:  One state commenter, NYSDOT, recommended (if EPA chose to
finalize the two-tier network design which included near-road
monitoring) that “EPA establish national guidance so there is
reasonable uniformity among EPA regions in the implementation of these
provisions.”

Response:  EPA notes that network consistency, from site to site, is
achieved in ambient monitoring networks by the adherence to monitoring
regulations and through the use of guidance. EPA has detailed siting
criteria  as specific as we believe is necessary and appropriate to
develop a consistent monitoring network , while allowing some necessary
flexibility for logistical considerations that will occur on a
case-by-case basis.  Further, EPA recognizes the need to aid state
agencies in the network implementation process, particularly through
guidance documentation that will be developed in partnership between EPA
and various stakeholders including NACAA and the states.  This issue is
discussed in section III.B.5 of the preamble to the final rule.

Comment:  Some commenters recommended that the annual primary standard
design value be calculated by averaging all 1-hour values for the year,
while a third commenter recommended the design value be calculated by
averaging within calendar quarters before averaging across calendar
quarters.

Response:  This issue is discussed in the final notice (Section IV.A).

Comment:  Several comments were made in regard to EPA’s data
completeness test.  For example, three commenters agreed that the
completeness test ought to stay at 75% for each quarter while a fourth
commenter recommended the percentage be increased to 82%.

	Response:  This issue is discussed in the final notice (Section IV.B).

Comment:  A comment from a State agency noted that the proposed 75%
capture requirement was inappropriate and should not be used for a 1-hr
NO2 standard.

	Response:  This issue is discussed in the final notice (Section IV.B).

Comment:  A commenter requested that EPA truncate NO2 concentration
measurements rather than rounding them.

	Response: EPA agrees with this comment, as reflected in the final
notice.

Comment:  An industry group requested that EPA further clarify the
guidelines for situations where incomplete monitoring data could be
considered valid.

Response:  The rule text identifies factors for the administrator to
consider in determining when to use such data.  No further clarification
is necessary because the variety and uniqueness of such situations
require that they be treated on a case by case basis.

Comment:  One commenter expressed concern that the use of near-road
monitoring would lead to near-source monitoring for other point sources
of NO2 and other pollutant emissions.

Response:  EPA is establishing a two-tier monitoring network, which
includes both near-road and area-wide monitoring, under this rule. EPA
does not believe that near-road monitoring will directly result in
non-near-road monitoring.  However, EPA recognizes that in certain
circumstances, there can be an area or areas of expected maximum
concentrations of NO2 due to non-road, point, or area sources, that may
not be monitored even though a state is fulfilling its minimum
monitoring requirements.  EPA has included a mechanism to deal with such
circumstances by providing the Regional Administrator with the authority
to require additional monitors above those minimally required. This
issue is discussed in section III.B.4 of the preamble to the final rule.

Comment:  A State agency recommended that EPA allow averaging across
monitors for design value calculations and substitution of values from
additional monitors for the primary monitor, for example, if the primary
monitor is taken offline for quality control (QC) during a high
pollutant period.

Response:  This issue is discussed in the final notice (Section IV.B).

Air Quality Index

Comment:  Many State agency commenters discouraged the use of near-road
concentrations in calculating the AQI since near-road NO2 concentrations
do not represent exposure of the general public to ambient NO2.  Several
other commenters, including NACAA, expressed concern that using
near-road monitors for calculating the AQI could diminish the value of
the index as a metric for reporting air quality to the general public by
making it sensitive to NO2 concentrations that are present only in small
areas.  CASAC also raised questions about how the AQI would be affected
by roadside monitors.  An additional commenter noted that it would be
difficult to forecast the AQI for regions where near-road monitoring
stations existed, since near-road NO2 concentrations are likely to be
unpredictable.

	Response:  The response to this comment on the AQI is discussed in
section VII of the final rule.

Comment:  The ALA, EJ, EDF, NRDC support setting the 100 level of the
AQI at 50 ppb and the level of the “moderate” category well below 50
ppb (i.e., 25 ppb).  These commenters disagree with EPA’s proposal to
maintain the breakpoints at the higher end of the AQI scale (i.e., 200
to 500).  They note that the 500 level has not been changed in the last
22 years, and EPA cannot claim that it represents the most up-to-date
scientific evidence without more extensive review.  They also note that
the proposed 200 level for NO2 is too high, relative to the 100 level,
given the relationship between these levels for other pollutants.  As a
result, these commenters recommend that EPA “establish a meaningful
and practical scale of levels of concern and graduated cautionary
statements for both sensitive groups as well as the general
population” based on the current scientific evidence.

In addition, NACAA expressed support for the “EPA’s proposed range
of 0.040 to 0.053 ppm for the AQI value of 50 and 0.360 and 0.370 ppm
for the AQI value of 150.”  But NACAA did express some concern that it
might make for a “confusing outreach message if the AQI level of 50 is
set below the annual standard of 0.053 ppm” since this would mean that
state and local air agencies would “be forecasting moderate air
quality even though an area is meeting the annual standard.”

Response:  With respect to an AQI value of 100, EPA has concluded that
it is appropriate in this case to set this value at 100 ppb NO2, 1-hour
average, the level of the short-term standard.  With respect to an AQI
value of 50, EPA agrees with the NACAA comment which noted it might make
for a confusing outreach message if this value is set below the level of
the annual standard.  This method of structuring the index is
appropriate in the case where a short-term standard is set to protect
against the health effects associated with short-term exposures and/or
an annual standard is set to protect against health effects associated
with long-term exposures.  In such cases, the short-term standard in
effect defines a level of health protection provided against short-term
risks and thus can be a useful benchmark against which to compare daily
air quality concentrations.

With respect to the breakpoints at the higher end of the AQI scale
(i.e., 200 to 500), EPA acknowledges that these breakpoints have been in
place for a long period of time, and that an AQI value of 200 is higher
for NO2, relative to the 100 level, than it is for the other pollutants
in the AQI.  EPA does not agree that there is new health evidence that
would provide support for changing these levels.  The levels at the
upper end of the AQI are linked to a related program designed to prevent
air pollution emergencies.  Some state and local air agencies are
required to have plans to take actions at these levels, thus it is
important to have a firm basis for revising these levels.

Significant harm levels (SHL) are those ambient concentrations of air
pollutants that present an imminent and substantial endangerment to
public health or welfare, or to the environment, as established in 40
CFR part 51.151.  The SHL is typically set at the same ambient
concentration of a pollutant as the AQI value of 500.  Appendix L of 40
CFR part 51 includes example emergency episode plans as part of the
Prevention of Air Pollution Emergency Episodes program.  This program
requires specified areas to have contingency plans in place and to
implement these plans during episodes when high levels of air pollution,
approaching the SHL, are in danger of being reached or have been
reached.  The Appendix L example links the AQI with emergency episodes.
 SEQ CHAPTER \h \r 1  AQI values of 200, 300 and 400 are the basis for
the example Alert, Warning and Emergency episode levels included in 40
CFR part 51, Appendix L.  In this guidance, the Alert level corresponds
to the breakpoint between the Unhealthy and Very Unhealthy categories,
and the Warning level corresponds to the breakpoint between the Very
Unhealthy and Hazardous categories.  The Hazardous category ranges up to
the SHL.

Comments on the Process for Reviewing the NO2 Primary NAAQS

A number of comments were received recommending changes to the current
rulemaking process, either for NAAQS in general or the NO2 NAAQS in
particular.

Comment:  A number of industry groups and state agencies recommended
that the proposed near-road monitoring network be considered in a
separate rulemaking from the proposed new 1-hr NO2 standard, because it
represents a dramatic shift in the method of monitoring ambient air
quality from previous NAAQS.

Response: EPA notes that separating the monitoring issues from the NAAQS
revision is not consistent with recently finalized or planned NAAQS
reviews.  EPA has promulgated monitoring rules as part of, or
simultaneously with the PM and Pb rules, and has proceeded to include
the monitoring rule as part of this primary NO2, as well as the primary
SO2, the secondary NOx/SOx, and CO revisions.  Monitoring issues were
handled separately from the 2008 ozone NAAQS revision, however EPA
intends that future ozone NAAQS reviews will integrate monitoring into
the action.

Comment:  Some commenters (e.g., NACAA, NESCAUM, Roger McClellan) noted
that EPA had originally intended to publish an advance notice of
proposed rulemaking (ANPR) and that because no ANPR was published, the
public and CASAC had limited opportunity to comment on the range of
available options.  Other comments expressed disapproval with the
limited amount of time for stakeholders to comment on EPA’s ISA and
REA; the late notifications that EPA provided when comment periods were
extended; and the inclusion of new sections and studies in the final
versions of the ISA and REA, which denied stakeholders the opportunity
to comment on these additions.

Response:  The Clean Air Act requires EPA to review and to revise, as
appropriate, the NAAQS every five years.  As a result of a lawsuit
challenging EPA’s failure to complete its review of the air quality
criteria for NOX and the NAAQS for NO2, inter alia, EPA agreed in a
consent decree to a schedule for this review of the NO2 primary NAAQS.
Pursuant to CAA § 113, EPA provided an opportunity for comment on the
consent decree.  This schedule was approved by the United States
District Court for the District of Columbia.

We disagree that EPA’s decision to not publish an ANPR limited the
opportunity for meaningful comment on the rulemaking.  EPA on occasion
uses an ANPR to seeking input from stakeholders before issuing a
proposed rule, but EPA is not required to publish an ANPR.  Moreover,
EPA provided for stakeholder comment throughout the review process,
including 60 days of comment and held two public hearings on the
proposed rule.  To the extent that “new sections and studies” were
added to the final version of the ISA and REA, stakeholders had the
opportunity to comment on this material following the notice of proposed
rulemaking.

Comment:  API commented that EPA did not not adequately address comments
provided by other government agencies on the draft proposed rule.

Response:  EPA engaged in extensive discussions with other agencies as
part of the interagency review process prior to the publication of the
proposed rule.  Under section 307(d) of the CAA, EPA is under no
obligation to provide written responses to comments provided by other
agencies during the interagency review process.  The scientific
rationale for the standards is clearly provided in the record for the
final rule.

Comment:  AASHTO requested that if EPA creates a 1-hr NO2 standard more
stringent than 80 ppb, an additional public comment period be created to
allow stakeholders to comment directly on the specific standard level
selected.

Response:  As described in section II.F.4.d of the final rule, the
Administrator has set the level of the 1-hour standard at 100 ppb.

Comment:  AGCA commented that EPA’s Regulatory Impact Analysis (RIA)
did not provide enough information to predict which areas of the country
will not be in attainment with a new standard if the proposed near-road
monitoring network is also included.  This lack of information has the
potential to negatively affect AGCA members because it prevents the
organization from assessing the potential impact of a new near-road
monitoring network on the road construction industry.

Response:  We developed the best estimate we were able to develop of
future design values at currently existing monitors, based on emission
inventory projections for 2020, using the best available emission data
and control strategy information.  What we are not able to do is to
credibly estimate specific design values at locations where monitors do
not currently exist, but will in the future.  States will determine
where to place those monitors as they implement the NAAQS.  In addition,
we did not model near-roadway concentrations as a function of traffic
density; this RIA is a national scale analysis.

Interpretation of the Clean Air Act

Comment: Numerous comments were received from industry groups and state
agencies expressing concern with EPA using near-road measurements of NO2
concentrations to evaluate area-wide attainment with an NO2 NAAQS.  Many
of the commenters note that EPA’s proposed near-road monitoring
network focuses on monitoring roadways likely to have high NO2
concentrations without requiring any demonstration that large and
adjacent populations are exposed to similarly high concentrations.
Consequently, the commenters argue that EPA has proposed a monitoring
network using rationale that does not reflect the purpose of the CAA and
NAAQS, which is to protect the public from exposure to unhealthy
concentrations of pollutants found within “ambient air” rather than
just “air”.

Response:  We note that ambient air includes the outdoor air present
around roads as well as the air that intrudes from outdoors into homes,
buildings, or vehicles on/near those roads.  As discussed in the final
rule, people who spend time on or around major roads (e.g., because they
live there, go to school there, or commute in vehicles on major roads)
can be exposed to elevated concentrations of ambient NO2.

Comment:  A number of industry groups provided comments maintaining that
EPA may have overstepped its regulatory authority with its proposed 1-hr
NO2 standard.  Comments included claims that the health effects from
short-term exposure to high concentrations of NO2 fail to constitute the
“adverse health effects” called for in the CAA.  Other comments
noted that EPA is authorized by the CAA to set its NAAQS at levels
intended to protect sensitive subpopulations, not the most sensitive
individual.  In addition, some commenters noted that NAAQS are not
intended to eliminate all risks.

Response:  The issues raised by these commenters are addressed in
sections II.E.2, II.E.3, II.F.4 in the final rule.

Comment:  Roger McClellan provided some general comments on the role of
CASAC and concluded that--

In offering recommendations for a specific upper bound for the Standard,
the Committee moved beyond advising on the science informing the policy
judgments inherent in setting the Standard, to taking on a role reserved
for the Administrator – the setting of the Standard. The Clean Air Act
wisely delegates the setting of the Standard to the Administrator and
calls for a Clean Air Scientific Advisory Committee, not a Clean Air
Standard Setting Committee.

Response:     Section 109(d)(2)(B) of the Clean Air Act, and the charter
of CASAC, provide that CASAC shall review the air quality criteria and
the NAAQS and “recommend to the Administrator any new national ambient
air quality standards and revisions of existing criteria and standards
as may be appropriate.”   EPA believes that CASAC fulfilled this duty
and provided helpful advice as a committee on the science issues raised
by this review.  Of course, the Administrator cannot, and did not,
delegate the setting of the standard to CASAC.

Comment:  NPRA commented that EPA lacks the legal authority to withhold
a designation of “attainment” from districts unless the districts
cannot be classified on the basis of available information as meeting or
not meeting the national air quality standard.  The commenter argued
that, at present, EPA cannot know whether it will lack the necessary
information in 2012.  According to NPRA, “it is clear from the statute
that for NO2 EPA must designate areas as in attainment that have
attaining monitors absent an affirmative showing that such an area is
contributing to downwind nonattainment in another area..”  In
addition, NPRA commented that section 107(d) of the CAA requires that
EPA “consider the recommendations of States with regard to the
designation of areas as attainment, nonattainment and unclassifiable.”

One state agency agreed with EPA’s proposal to designate all areas
currently in attainment with the NO2 standard as “unclassifiable”
until a near-road network has been established and measurements have
been evaluated.

	Response:  (Implementation group)

(5)	Comment:  Several environmental groups (e.g., ALA, EDF, EJ, NRDC)
noted that the CAA requires that NAAQS be set to protect public health
with an adequate margin of safety without consideration of cost and
that, in setting the NAAQS, EPA must err on the side of protecting
public health.  These groups stated that this includes protecting
sensitive subpopulations and guarding against “potential” health
effects.

Response:  EPA agrees that the NAAQS must be requisite (i.e., no less
and no more stringent than necessary) to protect the public health,
including the health of sensitive populations, with an adequate margin
of safety.  The Administrator’s consideration of this issue in the
current review is described in section II.F.4.d of the final rule.

Comments on Implementation

(1)	Comment:  A minority of CASAC Panel members posed the question of
what would be an effective control strategy to reduce NO2 concentrations
around major roads.  A number of public commenters also expressed the
concern that states have little ability to reduce on-road emissions from
motor vehicles.  Several went on to opine that it is the role of the
federal government to reduce emissions from motor vehicles.  One pointed
out that their state has already implemented measures to reduce on-road
emissions of NOX as part of their plan to attain the ozone standard.
One commenter opined that states have few options to reduce on-road
emissions beyond federal requirements.  Another commenter suggested that
one option for states would be to adopt California’s mobile source
regulations including those that apply to non-road equipment.  The
commenter is concerned that adoption of California’s non-road
regulations would place a significant burden on the construction
industry.  The commenter is also concerned that states may attempt to
reduce emissions from non-road equipment by imposing operating
restrictions, requiring older equipment to be replaced or mandating
retrofits for older equipment.

Response:  EPA agrees that it is a federal responsibility to implement
regulations that reduce emissions from new light- and heavy-duty
vehicles.  However, states have authority that can be used to reduce
emissions from in-use light- and heavy-duty vehicles.  For example,
states can implement programs to retrofit heavy-duty diesel vehicles to
reduce their NOX emissions.  States can implement regulations to reduce
or eliminate long-duration idling of heavy-duty diesel vehicles.  They
can implement an inspection and maintenance program for light-duty
vehicles.  Additionally, states can implement a wide range of programs
to improve travel efficiency.  States can implement strategies such as
congestion pricing, programs to reduce trips for commuting purposes, and
measures to improve the operational efficiency of the transportation
network.  States can also work with freight shippers to improve the
efficiency of goods movement in an area.

EPA agrees that a number of states have already implemented controls on
on-road sources.  The emissions reductions attributable to those
measures will help such areas to attain the NO2 NAAQS and can be
included in a SIP for NO2.   If such an area was designated
nonattainment for NO2, EPA would expect the state to evaluate mobile
source controls that it had not yet implemented and to evaluate the
potential for controlling emissions from other sources that are
contributing to the nonattainment problem.

With regard to the comments related to the adoption of California’s
on-road and non-road regulations by other states and the possibility
that some states may choose to reduce NOX emissions by requiring older
non-road equipment to be replaced or equipped with retrofits or impose
operating restrictions on non-road equipment, EPA expects each state
with a designated NO2 nonattainment area to develop a SIP that brings
the area into attainment by the applicable deadline and that each state
would evaluate the potential for controlling emissions from all sources
that are contributing to the nonattainment problem.  CAA section 177
allows states to adopt California’s standards that apply to new motor
vehicles or new motor vehicle engines and CAA section 209(e)(2)(B)
allows states to adopt California’s standards that apply to new or
used non-road engines and equipment.  California, and therefore other
states, are prohibited by CAA section 209(e)(1) from promulgating
standards for new construction and farm equipment with engines smaller
than 175 hp and from new locomotives and locomotive engines.  It is
possible that a state could choose to adopt California’s standards
that apply to new on-road and/or other non-road equipment in order to
attain the NO2 NAAQS.  States may also choose to reduce emissions from
non-road equipment through operating restrictions, or requiring older
equipment to be replaced to the extent that such measures are not
federally pre-empted.  EPA would expect that before any state included
any of these types of measures in a SIP for NO2 the state would have
evaluated a wide range of potential control measures and concluded that
such measures are necessary to bring the area into attainment by the
applicable deadline.

(2)	Comment:  Some commenters stated that modeling for permitting of the
short term 1-hr NO2 standard could likely show that stationary sources
violate the standard as opposed to near-road mobile sources.  Others
requested that if EPA requires near-roadway monitoring for NO2, it
should provide clarifying guidance stating that near-road monitors would
not be applicable for NSR or other point source permit applications.

Response:  The permitting regulations for Prevention of Significant
Deterioration of Air Quality (PSD) require applicants to provide 1 year
of air quality data representative of the air quality in the area that
the proposed new or modified source will impact.  Typically, such
monitoring data is used to represent background air quality levels that
are considered along with modeled concentrations of a pollutant to show
that the source’s predicted impact will not cause or contribute to a
violation of any NAAQS.  We agree that the ambient data collected from
near-road monitoring sites for NO2 may not be representative of
background air quality levels throughout the area of concern.  However,
if used correctly, such data could be useful in assessing the source’s
contribution in specific areas of potentially high ambient NO2
concentrations largely attributable to near-road mobile source
emissions.  EPA will give further consideration to this comment as we
evaluate any NSR guidance and regulations that may be needed to
implement a 1-hour NO2 NAAQS.

(3)	Comment:  API recommends that EPA update the Guidelines on Air
Quality Models to address screening and refined models for modeling peak
short-term concentrations in order to accurately predict short-term NO2
concentrations in diverse environmental settings.

Response:   The EPA agrees with this comment and intends to review the
need to revise the Guideline on Air Quality Models to address issues
associated with the promulgation of a short-term NO2 NAAQS.

(4)	Comment:  API also recommends that EPA develop a database of NO2 to
NOX emissions ratios for the variety of sources that would be affected
by any new NO2 standards.  The database could also include methods to
make use of data from existing ambient monitoring networks to provide
realistic background ozone and NO2 concentrations required for the
short-term NO2 modeling framework.

Response: The EPA will review the need for the development of a database
of NO2 to NOX emissions ratios sources following the promulgation of the
NO2 NAAQS.

(5)	Comment:  CAC disagrees 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 urges EPA to
provide a graduated non-attainment classification system for the new
standard.  According to the Council, “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.”

Response:  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. See the preamble to the final rule for consequences
for areas failing to meet the attainment date.  Once EPA makes a
determination that an area has failed to meet its attainment date, the
State will be requested to submit a SIP revision which must show that it
can attain the standard as expeditiously as practicable, but no later
than 5 years from the determination of failure to attain.

(6)	Comment:  One commenter opined that states that fail to develop SIPs
or meet EPA’s CAA deadlines would be subject to “numerous federal
sanctions” including emissions caps, limiting economic development and
the loss of federal highway transportation dollars.  The commenter
specifically states that a construction ban would impede projects that
would improve municipal water supplies and wastewater treatment.

Response:  CAA section 179 provides EPA with only two sanctions.  These
are the 2:1 offset sanction that applies to new or modified major
stationary sources and the highway funding sanction.  These sanctions
are only applied in specific circumstances, such as when a state has
failed to submit a required SIP or when a SIP revision is disapproved.
 The CAA no longer contains a sanction specifically aimed at limiting
development.  The CAA Amendments of 1990 do not include the construction
ban that applied in certain situations under the 1977 CAA.  Therefore,
EPA disagrees that, if the available sanctions are imposed in an NO2
nonattainment area, they would result in a de facto construction ban and
they would not delay municipal water or wastewater projects.  It must be
noted that there is no sanction for failing to reach attainment by the
CAA deadline.  For areas that fail to attain by the applicable deadline
CAA section 179(d) requires that such areas submit a revised SIP within
one year after EPA publishes a notice finding that the area failed to
attain.  In the case of NO2, this revised SIP would have to demonstrate
attainment as expeditiously as practicable, but no later than 5 years
after the date of the Federal Register notice in which EPA made the
finding that the area had failed to attain.

(7)	Comment: One commenter pointed out that a new 1-hr standard for NO2
will complicate permitting of small sources that may contribute to local
NO2 emissions.

Response: Section 110(a)(2)(C) of the CAA requires states to regulate
the construction and modification of any stationary source as necessary
to assure that NAAQS are achieved.  Consequently, the addition of a
1-hour NO2 NAAQS would require that the necessary consideration be given
to preventing sources from violating a 1-hour NO2 NAAQS.  We do not,
however, view this as a complication of the permitting process.  In some
instances, a modeling analysis may be required to make the necessary
compliance demonstration, while in other cases modeling may not be
required.  Such decisions as to the level of analysis needed to make the
necessary compliance demonstration must be made by the applicable state
or local agency permitting authority.

(8)	Comment:  Several industry commenters requested that EPA slow the
timeline for implementing a near-road monitoring network and designating
roadway areas, because they believe EPA lacks significant information
about the implementation and performance of a national, near-road
monitoring network.

Response:  EPA believes that there is sufficient information to
implement a near-road NO2 network and that the timeline for
implementation will allow EPA to consult CASAC and collaborate with
states in the development of guidance that will assist in the
implementation of a network that is as consistent as possible.  This
issue is discussed in section III.B.5 of the preamble to the final rule.

(9)	Comment:  Numerous comments were received, primarily from state
agencies, noting the significant cost of a near-road monitoring networks
and requesting that the federal government pay for a large percentage of
the network’s cost by funding the monitors through Section 103 of the
CAA, rather than section 105.  Many commenters claimed that without
federal funds, and because of the tight budgets faced by state
governments presently, the funding of a near-road monitoring network
would result in less spending on other valuable environmental programs.

Response:  EPA understands the resource concerns of the states and
intends to work with states in identifying available funds and assess
the increased resource needs that may be needed for network
implementation.  This issue is discussed in section III.B.1 of the
preamble to the final rule.

(10)	Comment:  Several commenters claim that EPA significantly
underestimates the cost of near-road monitors for many locations where
monitors are likely to be installed.

Response:  EPA used direct quotes or its best estimate for the variety
of capital and logistical costs that will be associated with
implementing the network design.  EPA must make its estimates as
nationally applicable as possible, and cannot anticipate the individual
variations in resource needs, or in the actual costs themselves, that
may occur from one location of the country to the next.  EPA intends to
work with states in identifying available funds and consider the
increased resource needs that may be needed for network implementation.

(11)	Comment:  State agencies requested that EPA provide additional
guidelines for the criteria that would be used by Regional
Administrators in determining when additional near-road monitors would
be required or when requests for additional monitors will be granted.
An additional comment requested that EPA provide further guidance and
oversight of Regional Administrators to ensure the consistent
implementation of any near-road monitoring network across the country.
State agencies also requested that the Regional Administrator be
required to coordinate with the state government in deciding where
near-road monitors would be placed.

Response:  EPA has provided multiple examples of situations where
Regional Administrator may use their discretion to require additional
monitors above the minimum required in section III.B.4 of the preamble
to the final rule.  In particular, EPA notes that in situations where a
Regional Administrator may consider the need for additional monitoring,
EPA expects that the state and the Regional Administrator would work
together to evaluate quantitative evidence that suggests an area may
warrant additional monitoring.

(12)	Comment:  AASHTO recommended that state and local air monitoring
agencies be required to coordinate with their respective DOTs when
developing a near-road monitoring plan.

Response:  Although can not require state and local air agencies to work
with another state or local entity, EPA believes that state and local
air monitoring agencies can greatly benefit from collaboration with
their counterparts in state or local transportation authorities.  Such
collaboration may help in site identification, site access, and ensuring
public and worker safety at near-road sites.

(13)	Comment:  Several State Agencies commented on the interaction
between NOX and O3.  For example, AASHTO requested that EPA clarify how
areas can overcome potential negative impacts on ambient O3 of increased
control of NOX emissions.  In contrast, one State Agency (HCPHES)
commented that a more stringent NO2 standard will help them attain the
O3 NAAQS because NO2 is a precursor to O3.

Response:  It has long been recognized that reducing NOX emissions will
result in lower concentrations of regional O3 (National Research
Council, 1991).  This has been confirmed in numerous photochemical model
simulations and assorted ambient data analyses over the past two decades
(EPA 2005b; EPA, 2008d).  As a result, efforts to reduce NOX emissions
are the foundation of Federal and State actions to attain the ozone
NAAQS.  However, because of the complex chemistry of ozone formation,
there are some specific instances in which certain NOX reductions can
lead to localized ozone increases.  In these areas, the local planning
process will need to consider the multipollutant aspects of air quality
management and derive the most appropriate set of local control measures
needed to attain multiple NAAQS simultaneously.

(15)	Comment: One state agency recommended that state and local DOTs
should be required to perform air quality impact analyses for NO2 prior
to road construction projects as well as conduct regular mobile monitor
testing to demonstrate that the construction projects are not causing
violations of the 1-hr NO2 standard.

Response:  Any such requirement for state and local DOT’s to perform
air quality impact analysis prior to road construction or to conduct any
testing would have to be established and carried out under state or
local authority.

(16)	Comment:  One commenter encouraged EPA to develop a 1-hr NO2
significant impact level (SIL) without which, “any increase in NO2 in
a nonattainment area (or a near non-attainment area) could result in
denial of the proposed permit, even if the increase is not significant
or offset with offsite emission reduction credits” (CAAPCOA).

	Response:  This issue is discussed in section VI.D.2 of the preamble to
the final rule.

(17)	Comment:  The North Carolina Department of Environment and Natural
Resources (NCDENR) supports the use of a weighted annual mean (quarterly
average) for the annual primary standard.

Response:  This issue is discussed in the final notice (Section IV.A).

(18)	Comment:  SJVAPCD recommended that EPA include guidelines for
near-road monitoring that allows for monitoring to stop at locations
where sufficient data has been collected to conclude that measured
concentrations of NO2 are less than 85% of the standard level.

Response: 40 CFR § 58.14(c),  explains the process by which states may
request approval for discontinuing monitoring at an individual site.
The discontinuation is subject to Regional Administrator approval, and
requires the satisfaction of multiple requirements which are spelled out
in the regulation text.

(19)	Comment:  CASAC Panel members who supported the alternative
approach, as well as some public commenters (e.g., States) also raised
questions related to how non-attainment areas would be designated if
roadside monitors measure violations.  For example, some commenters
questioned whether an entire county could be out of attainment based on
a roadside monitor.

	Response:  This comment is addressed in sections V.B and V.C of the
final notice.