on a secondary standard is addressed below. Other more specific public
comments related to consideration of a secondary standard are addressed
in the Response to Comments document.
    One comment (joint submission from Center for Biological Diversity
and others) stated that due to the global influence of CO on climate,
EPA must

establish a secondary NAAQS. The comment provided no information as to
what form, level, or other elements of a secondary standard would be
appropriate in light of the substantial uncertainties and regional
variation in the indirect effects of CO. Rather, the comment asserted
that there is ``a substantial body of knowledge, as reviewed in the
ISA, regarding CO and climate'' and that ``uncertainty does not absolve
the EPA of the obligation to protect public welfare'' (Center for
Biological Diversity comments at p. 9).
    As noted by the commenter, the ISA reviewed the body of knowledge
regarding CO and climate. As discussed above, the ISA concluded that CO
has climate-related effects, that the direct effects of CO are weak,
that there are significant uncertainties concerning the indirect
climate effects of CO, and that these effects appear to be highly
variable and dependent on localized conditions. Further, as noted in
the Policy Assessment, the spatial and temporal variation in emissions
and concentrations of CO and the localized chemical interdependencies
that cause the indirect climate effects of CO make it highly
problematic to evaluate the indirect effects of CO on climate. In light
of the fact that the climate effects of CO are not only uncertain but
highly variable and dependent on local conditions (e.g., concentrations
of other pollutants), EPA believes that there is not adequate
information available to conclude that a secondary standard in the
United States is requisite to protect public welfare. The comment
points to the estimated global effects of CO on climate, but nowhere
does the comment provide evidence that EPA's conclusion regarding
adequacy of the available information is in error.
    EPA fully appreciates that the NAAQS are often established on the
frontiers of scientific knowledge, and EPA continually assesses
scientific uncertainties in judging what NAAQS are requisite to protect
public health and welfare. EPA is not asserting that the fact that
there are some uncertainties prevents EPA from setting a standard.
Rather, EPA has judged that, in light of both the significant
uncertainties and the evidence of the direct effects being weak and the
indirect effects being highly variable and dependent on local
conditions, particularly in light of CO's short lifetime, it is not
possible to anticipate how any secondary standard that would limit
ambient CO concentrations in the United States would in turn affect
climate and thus any associated welfare effects. As additionally
discussed in section III.D below, EPA has reviewed the available
information and judged the absence of a standard as being requisite to
protect public welfare.

D. Conclusions Concerning a Secondary Standard

    The conclusions presented here are based on the assessment and
integrative synthesis of the scientific evidence presented in the ISA,
building on the evidence described in the 2000 AQCD, as well as staff
consideration of this evidence in the Policy Assessment and CASAC
advice, and with consideration of the views of public commenters on the
need for a secondary standard.
    In considering whether the currently available scientific
information supports setting a secondary standard for CO, EPA takes
note of the ISA and Policy Assessment consideration of the body of
available evidence (briefly summarized above in section III.A). First,
EPA concludes that the currently available scientific information with
respect to non-climate welfare effects, including ecological effects
and impacts to vegetation, does not support the need for a CO secondary
standard. Secondly, with respect to climate-related effects, the EPA
takes note of the ISA's conclusions that there are significant
uncertainties concerning the indirect climate effects of CO, and that
these effects appear to be highly variable and dependent on localized
conditions as well as staff considerations in the Policy Assessment and
concurs with staff conclusions that information is insufficient at this
time to support the need for a CO secondary standard. More
specifically, as more fully discussed in consideration of public
comments in section III.C above, EPA has judged that, in light of both
the significant uncertainties and the evidence of the direct effects of
CO on climate being weak and the indirect effects being highly variable
and dependent on local conditions, particularly in light of CO's short
lifetime, it is not possible to anticipate how any secondary standard
that would limit ambient CO concentrations in the United States would
affect climate. Consequently, information that might indicate the need
for additional protection from CO environmental effects and on which
basis EPA might identify a secondary standard for the purposes of
protecting against CO effects on climate processes is not available.
    Thus, in considering the evidence, staff considerations in the
Policy Assessment summarized here, as well as the views of CASAC and
the public, summarized above, the Administrator concludes that no
secondary standards should be set at this time because, as in the past
reviews, having no standard is requisite to protect public welfare from
any known or anticipated adverse effects from ambient CO exposures.

 IV. Amendments to Ambient Monitoring Requirements

    The EPA is finalizing changes to ambient air CO monitoring methods
and the ambient monitoring network design requirements to support the
NAAQS for CO discussed above in Section II. Because ambient CO
monitoring data are essential to the implementation of the NAAQS for
CO, EPA is finalizing minimum monitoring requirements for the ambient
CO monitoring network. State, local, and Tribal monitoring agencies
(``monitoring agencies'') collect ambient CO monitoring data in
accordance with the monitoring requirements contained in 40 CFR parts
50, 53, and 58.

A. Monitoring Methods

    This section provides background and rationale for the amendments
that EPA proposed to the Federal Reference Method (FRM) for CO and to
the associated performance specifications for automated CO analyzers.
It also discusses the public comments on those proposed amendments and
the few minor changes made to them as they are being promulgated today.
    The use of FRMs for the collection of air monitoring data provides
uniform, reproducible measurements of pollutant concentrations in
ambient air. Federal equivalent methods (FEMs) allow for the
introduction of new or alternative technologies for the same purpose,
provided these methods produce measurements directly comparable to the
reference methods. EPA has established procedures for determining and
designating FRMs and FEMs at 40 CFR part 53.
    For ambient air monitoring data for CO to be used for determining
compliance with the CO NAAQS, such data must be obtained using either
an FRM or an FEM, as defined in 40 CFR parts 50 and 53. All CO
monitoring methods in use currently by state and local monitoring
agencies are EPA-designated FRM analyzers. No FEM analyzer, i.e. one
using an alternative measurement principle, has yet been designated by
EPA for CO. These continuous FRM analyzers have been used in monitoring
networks for many years and provide CO monitoring data adequate for
determining CO NAAQS compliance. The current list of all approved FRMs
capable of providing ambient CO data for this purpose may be found on
the EPA Web site, http://www.epa.gov/ttn/amtic/files/ambient/

criteria/reference-equivalent-methods-list.pdf. Although both the
existing CO FRM in 40 CFR part 50 and the FRM and FEM designation
requirements in part 53 remain adequate to support the CO NAAQS, EPA
nevertheless proposed editorial revisions to the CO FRM and both
technical and editorial revisions to part 53, as discussed below.
1. Proposed Changes to Parts 50 and 53
    Reference methods for criteria pollutants are described in several
appendices to 40 CFR part 50; the CO FRM is set forth in appendix C. A
non-dispersive infrared photometry (NDIR) measurement principle is
formally prescribed as the basis for the CO FRM. Appendix C describes
the technical nature of the NDIR measurement principle stipulated for
CO FRM analyzers as well as two acceptable calibration procedures for
CO FRM analyzers. It further requires that an FRM analyzer must meet
specific performance, performance testing, and other requirements set
forth in 40 CFR part 53.
    The CO FRM was first promulgated on April 30, 1971 (36 FR 8186), in
conjunction with EPA's establishment (originally as 42 CFR part 410) of
the first NAAQS for six pollutants (including CO) as now set forth in
40 CFR part 50. The method was amended in 1982 and 1983 (47 FR 54922;
48 FR 17355) to incorporate minor updates, but no substantive changes
in the fundamental NDIR measurement technique have been made since its
original promulgation.
    In connection with the current review of the NAAQS for CO, EPA
reviewed the existing CO FRM to determine if it was still adequate or
if improved or more suitable measurement technology has become
available to better meet current FRM needs as well as potential future
FRM requirements. EPA determined that no new ambient CO measurement
technique has become available that is superior to the NDIR technique
specified for the current FRM, and that the existing FRM continues to
be well suited for both FRM purposes and for use in routine CO
monitoring. No substantive changes were needed to the basic NDIR FRM
measurement principle. Several high quality FRM analyzer models have
been available for many years and continue to be offered and supported
by multiple analyzer manufacturers.
    However, EPA found that the existing CO FRM should be improved and
updated to clarify the language of some provisions, to make the format
match more closely the format of more recently promulgated automated
FRMs, and to better reflect the design and improved performance of
current, commercially available CO FRM analyzers. Accordingly, EPA
proposed appropriate, albeit minor, changes to the FRM. Because these
mostly editorial changes were quite numerous, the entire text of the CO
FRM was revised and re-proposed.
    In close association with the proposed editorial revision to the CO
FRM described above, EPA also proposed to update the performance
requirements for CO FRM analyzers that are contained in 40 CFR part 53.
These requirements were established in the 1970's, based primarily on
the NDIR CO measurement technology available at that time. While the
fundamental NDIR measurement principle, as implemented in commercial
FRM analyzers, has changed little over several decades, FRM analyzer
performance has improved markedly. Contemporary advances in digital
electronics, sensor technology, and manufacturing capabilities have
permitted today's NDIR analyzers to exhibit substantially improved
measurement performance, reliability, and operational convenience at
modest cost. This improved instrument performance was not reflected in
the previous performance requirements for CO FRM analyzers specified in
40 CFR part 53, indicating a need for an update to reflect that
improved performance.
    The updated performance requirements that EPA proposed for CO
analyzers make them more consistent with the typical performance
capability available in contemporary FRM analyzers and will ensure that
newly designated FRM analyzers will have this improved measurement
performance. A review of analyzer manufacturers' specifications has
determined that all existing CO analyzer models currently in use in the
monitoring network already meet the proposed new requirements (for the
standard measurement range). Also in conjunction with this
modernization of the analyzer performance requirements, EPA proposed
new, more stringent performance requirements applicable, on an optional
basis, to analyzers that feature one or more lower, more sensitive
measurement ranges. Such lower ranges will support improved monitoring
data quality in areas of low CO concentrations.
    These updated and new performance requirements are being
promulgated as amendments to subpart B of 40 CFR part 53, which
prescribes the explicit procedures to be used for testing specified
performance aspects of candidate FRM and FEM analyzers, along with the
minimum performance requirements that such analyzers must meet to
qualify for FRM or FEM designation. In particular, the new performance
requirements appear in table B-1 of subpart B of 40 CFR part 53.
Although table B-1 covers candidate methods for sulfur dioxide
(SO2), O3, CO, and NO2, the updates to
table B-1 that EPA is promulgating today affect only candidate methods
for CO.
    The updated performance requirements apply to candidate CO
analyzers that operate on the specified ``standard'' measurement range
(0 to 50 ppm). This measurement range remains unchanged from the
existing requirements as it appropriately addresses the monitoring data
needed for assessing attainment. The measurement noise limit is reduced
from 0.5 to 0.2 ppm, and the lower detectable limit is reduced from 1
to 0.4 ppm. Limits for zero drift and span drift are lowered,
respectively, from 1.0 to 0.5 ppm, and from 2.5% to 2.0%. The
previously existing mid-span drift limit requirement, tested at 20% of
the upper range limit (URL), is withdrawn, as EPA has found that the
mid-span drift requirement was unnecessary for CO instruments because
the upper level span drift (tested at 80% of the URL) completely and
more accurately measures analyzer span drift performance.
    The lag time limit is reduced from 10 to 2 minutes, and the rise
and fall time limits are lowered from 5 to 2 minutes. For precision,
EPA is changing the form of the precision limit specifications from an
absolute measure (ppm) to percent (of the URL) for CO analyzers and
setting the precision limit at 1 percent tested at both 20% and 80% of
the URL. One percent is equivalent to the previous limit value of 0.5
ppm for precision for the standard (0 to 50 ppm) measurement range.
This change in units from ppm to percent makes the requirement
responsive to higher and lower measurement ranges (i.e., more demanding
for lower ranges).
    The interference equivalent limit of 1 ppm for each interferent is
not changed, but EPA is withdrawing the previously existing limit
requirement for the total of all interferents. EPA has found that the
total interferent limit is unnecessary because modern CO analyzers are
subject to only a few interferences, and they tend to be well
controlled.
    The new performance requirements apply only to newly designated CO
FRM or FEM analyzers; however, essentially all existing FRM analyzers
in use today, as noted previously, already meet these requirements, so
existing FRM analyzers are not required to be re-tested and re-

designated under the new requirements. All currently designated FRM
analyzers retain their original FRM designations.
    EPA also recognized that some CO monitoring objectives (e.g., area-
wide monitoring away from major roads and rural area surveillance)
require analyzers with lower, more sensitive measurement ranges than
the standard range used for typical ambient monitoring. To improve data
quality for such lower-range measurements, EPA is adding a separate set
of performance requirements that apply specifically to lower ranges
(i.e., those having a URL of less than 50 ppm) for CO analyzers. These
additional, lower-range requirements are listed in the revised table B-
1. A candidate analyzer that meets the table B-1 requirements for the
standard measurement range (0 to 50 ppm) can optionally have one or
more lower ranges included in its FRM or FEM designation by further
testing to show that it also meets these supplemental, lower-range
requirements.
    Although no substantive changes were determined to be needed to the
test procedures and associated provisions of subpart B for CO, the
detailed language in many of the subpart B sections was in need of
significant updates, clarifications, refinement, and (in a few cases)
correction of minor typographical errors. These changes to the subpart
B text (apart from the changes proposed for table B-1 discussed above)
are very minor and almost entirely editorial in nature, but quite
numerous. Therefore, EPA has revised and is re-promulgating the entire
text of subpart B text.
    As discussed previously, table B-1, which sets forth the pollutant-
specific performance limits, is being amended only as applicable to CO
analyzers. EPA amended table B-1 as applicable to SO2
methods on June 22, 2010 and intends to amend table B-1 for
O3 and NO2 later, if appropriate, when the
associated NAAQS are reviewed.
2. Public Comments
    EPA notes first that CASAC stated that ``more sensitive and precise
monitors need to be deployed to measure levels that are less than or
equal to 1 ppm.'' (Brain and Samet 2010b). Comments from the public on
the proposed revisions to CO monitoring methods are addressed in this
section or in the Response to Comments document. Comments on the
proposed changes to the CO monitoring methodology were received from
only one member of the public, the American Petroleum Institute. The
commenter was generally supportive of EPA's efforts to clarify and
update the regulations for the CO FRM and the CO analyzer performance
requirements. In regard to the CO FRM (40 CFR part 50, appendix C), the
commenter questioned EPA's proposed relaxation in a flow rate control
requirement in the dilution-method calibration procedure, from 1% to
2%. However, EPA believes that the original 1% requirement is
unnecessarily stringent, and that this change is appropriate and
commensurate with the existing 2% flow rate measurement accuracy and
with the overall calibration accuracy needed to obtain adequate data
quality with the method.
    To further improve clarity of the FRM calibration section, the
commenter also suggested a minor change to Equation 1 and the addition
of language indicating that the measurement display or read-out device
connected to the analyzer to monitor its reading during calibration
should be the actual, or at least closely representative of the actual,
data recording system used during field operation of the analyzer. EPA
has accepted both of these suggestions, and appropriate changes have
been incorporated into the changes being made to the CO FRM in this
action.
    Another comment questioned the proposed withdrawal of the previous
total interference limit requirement. In response to this comment, EPA
re-evaluated the efficacy of this limit for CO analyzers and again
determined that the limit was not necessary, because the number of
individual interferences to which FRM (and most potential FEM) CO
analyzers are subject is small (only 2 for FRMs), as listed in table B-
3 of 40 CFR part 53. Also, response to these interferents is typically
well controlled in modern CO analyzers. In addition, the new,
individual interference limit for the lower measurement ranges is one
half the limit for the standard range, which further mitigates any need
for a separate, total interference limit.
    The commenter questioned EPA's proposed withdrawal of the
previously existing limit requirement for span drift measured at 20% of
the upper range limit (URL), contending that this limit was important
because it is closer in concentration to the existing NAAQS than the
span drift measured at 80% of the URL. However, the purpose of the span
drift limit is not to directly assess measurement error at a
particular, mid-scale concentration level. That purpose is served by
the 1-point quality control check for CO monitors described in section
3.2.1 of appendix A of 40 CFR part 58. Rather, for the purpose of
analyzer performance testing, the linear input/output functional
characteristic of the analyzer is best described by its zero point and
its slope, because these parameters are generally subject to change
(drift) independently. Thus, zero drift (change in the zero point) and
span drift (change in the slope) are tested separately. Zero drift is,
of course, measured at zero concentration, and span drift is most
accurately measured at a concentration near the URL. The span drift
test at 80% URL (when the zero drift is within the specified
requirement) more accurately determines any change in the slope
parameter then a test at 20% URL. The previously specified test at 20%
URL thus serves little, if any, purpose in regard to determining change
in the slope. Therefore, EPA has concluded that this requirement can be
withdrawn.
    Finally, the commenter was concerned that existing FRM analyzers
approved under the previously existing performance requirements may
provide data quality inferior to that of analyzers approved under the
proposed new requirements and that older analyzers may be unacceptable
for some applications that demanded higher performance or higher data
quality. A ``tiered'' approach was suggested to handle this situation.
    In proposing more stringent performance requirements for approval
of new FRM and FEM analyzers, EPA noted that the performance of
analyzers approved under the existing performance requirements was
fully adequate for most routine compliance monitoring applications, and
that the proposed new requirements were largely to bring the base FRM
and FEM performance requirements up to date and more commensurate with
the performance of modern commercially available CO analyzers. EPA
further noted that all currently designated FRM analyzers already meet
the proposed new requirements. This means that the quality of routine
CO monitoring data currently being obtained is already of the higher
level portended by the proposed new performance requirements.
    In the proposal, however, EPA did recognize that some special CO
monitoring applications do require a higher level of performance than
that required for routine applications. Therefore, EPA is promulgating
optional, more stringent performance requirements for analyzers having
a more sensitive, ``lower range'' available for such applications. This
is, in fact, a ``tiered'' approach. Applicants would be able to elect
to have such lower ranges approved as part of their FRM or FEM
designation. These new, special performance requirements will alert
monitoring agencies that they should

consider low-range performance of an analyzer for those applications
that may require better low-level performance, and they can select an
analyzer that has such a lower range approved under its FRM (or FEM)
designation.
3. Decisions on Methods
    As discussed above, a few relatively minor changes have been
incorporated into the proposed revised CO FRM in appendix C of part 50,
in response to public comments received by EPA. With these changes, the
revised appendix C is being promulgated as otherwise proposed. Only one
change has been made to the revision proposed for subpart B of part 53,
to fix a typographical error that appeared in proposed table B-1
concerning reversed entries for the span drift limits for the 20% and
80% URL for the CO ``lower range'' column. Aside from this correction,
the revised subpart B is being promulgated exactly as proposed.

B. Network Design

    This section on CO network design provides information on the
proposed network design, the public comments received on the proposed
network design, and the EPA's conclusions, including rationale and
details, on the final changes to the CO network design requirements.
1. Proposed Changes
    The objective of an ambient monitoring network is to (1) provide
air pollution data to the general public in a timely manner, (2)
support compliance with ambient air quality standards and emissions
strategy development, and (3) provide support for air pollution
research (40 CFR part 58, appendix D). The proposed CO network design
was intended to directly support the NAAQS by requiring monitoring that
provides data for use in the designation process and ongoing assessment
of air quality. In particular, the proposed network design was intended
to require a sufficient number of monitors to collect data for
compliance purposes in the near-road environment, where, as noted in
section II.A.1 above, the highest ambient CO concentrations generally
occur, particularly in urban areas (ISA, section <IP_ADDRESS>; REA, section
3.1.3).
    The EPA proposed CO monitors to be required within a subset of
near-road NO2 monitoring stations, which are required in 40
CFR part 58, appendix D, section 4.3. Per the preamble to the final
rule for the NO2 NAAQS promulgated on February 9th, 2010 (75
FR 6474), near-road NO2 monitoring stations are intended to
be placed in the near-road environment at locations of expected maximum
1-hour NO2 concentrations and are triggered for metropolitan
areas based on Core Based Statistical Area (CBSA) population thresholds
and a traffic-related threshold based on annual average daily traffic
(AADT).\29\ The EPA proposed that CO monitors be required to operate in
any CBSA having a population of 1 million or more persons, collocated
with required near-road NO2 monitoring stations. Based upon
2009 Census Bureau estimates and 2008 traffic statistics maintained by
the US Department of Transportation (US DOT) Federal Highways
Administration (FHWA), the CO monitoring proposal was estimated to
require approximately 77 CO monitors to be collocated with near-road
NO2 monitors within 53 CBSAs.\30\
---------------------------------------------------------------------------

    \29\ One near-road NO2 monitor is required in any
CBSA having a population of 500,000 or more persons. Two near-road
NO2 monitors are required in any CBSA having a population
of 2.5 million or more persons, or in any CBSA that has one or more
road segments with an AADT count of 250,000 or more (40 CFR part 58,
appendix D, section 4.3).
    \30\ Since the proposal, EPA has estimated that using 2010
Census Bureau counts the proposed rule would have resulted in
approximately 75 monitors in 52 CBSAs being required.
---------------------------------------------------------------------------

    The EPA proposed that any required near-road CO monitors shall be
reflected in State annual monitoring network plans due in July 2012.
Further, the Agency proposed that required near-road CO monitors be
operational by January 1, 2013. Due to the proposed collocation of
required CO monitors with required near-road NO2 monitors,
these implementation dates were proposed in order to match those of the
forthcoming near-road NO2 monitoring network.
    In light of the proposal to require near-road CO monitors be
collocated with required near-road NO2 monitors, the EPA
proposed that siting criteria for microscale CO monitors be revised to
match those of microscale near-road NO2 monitors (and also
microscale PM2.5 monitors). In particular, the EPA proposed
that microscale CO siting criteria for probe height and horizontal
spacing be changed to match those of near-road NO2 monitors
as prescribed in 40 CFR part 58 appendix E, sections 2, 4(d), 6.4(a),
and table E-4. Specifically, EPA proposed the following: (1) To allow
microscale CO monitor inlet probes to be between 2 and 7 meters above
the ground; (2) that microscale near-road CO monitor inlet probes be
placed so they have an unobstructed air flow, where no obstacles exist
at or above the height of the monitor probe, between the monitor probe
and the outside nearest edge of the traffic lanes of the target road
segment; and (3) that required near-road CO monitor inlet probes shall
be as near as practicable to the outside nearest edge of the traffic
lanes of the target road segment, but shall not be located at a
distance greater than 50 meters in the horizontal from the outside
nearest edge of the traffic lanes of the target road segment.
    Finally, the EPA recognized that a single monitoring network design
may not always be sufficient for fulfilling specific or otherwise
unique data needs or monitoring objectives for every area across the
nation. As such, the EPA proposed to provide the Regional
Administrators with the discretion to require monitoring above the
minimum requirements as necessary to address situations where minimum
monitoring requirements are not sufficient to meet monitoring
objectives.
2. Public Comments
    EPA first notes that CASAC expressed concern over the current
monitoring network, stating ``[m]ore extensive coverage may be
warranted for areas where concentrations may be more elevated, such as
near roadway locations. The Panel found that in some instances current
networks underestimated carbon monoxide levels near roadways.'' (Brain
and Samet 2010b). General comments from the public based on relevant
factors that either support or oppose the proposed changes to the CO
network design are addressed in this section. Specific public comments
related to the network design, but with regard to material which was
not specifically proposed by the EPA or posed for solicitation of
comment, are addressed in the Response to Comments document.
a. Near-Road Monitoring and Collocation With Near-Road Nitrogen Dioxide
Monitors
    The EPA received multiple public comments on the overall merit of
monitoring for CO in the near-road environment, the proposal that
required CO monitors be collocated with required near-road
NO2 monitors, and the number of required CO monitors that
might be appropriate. In general, public health and environmental
groups (e.g., American Lung Association [ALA], American Thoracic
Society [ATS], Environmental Defense Fund [EDF]), some states or state
environmental agencies or organizations (e.g. National Association of
Clean Air Agencies [NACAA], Northeast States for Coordinated Air Use
Management [NESCAUM], New York State Department of Environment
Conservation [NYSDEC], and State of Wisconsin Department of Natural

Resources [WIDNR]), and some private citizen commenters provided
support for a requirement for CO monitors in the near-road environment.
For example, ALA, ATS, and EDF state that they ``* * * are pleased to
see EPA take seriously the public health threats that are posed to
millions of residents and other sensitive receptors who live near or
work on or near highways as well as other high exposure areas.'' They
go on to note that ``[near-road ambient monitoring] data have been
sorely lacking from the national monitoring network and are long
overdue.'' Further, many of the commenters who were supportive of near-
road monitoring were supportive of collocating CO monitors with near-
road NO2 monitors as it establishes multipollutant
monitoring within the ambient air monitoring network. For example,
NACAA stated the following in their comments: ``* * * NACAA supports
EPA's proposal to collocate CO near roadway monitors at a subset of
NO2 near-roadway sites. This is consistent with the
recommendations of EPA's Clean Air Scientific Advisory Committee
(CASAC), which urged the agency to develop the near roadway monitoring
network with a multipollutant focus and included CO in its list of
pollutants that should be measured.''
    Some industry commenters (e.g., Association of Automobile
Manufacturers [AAM] and American Electric Power Service Corporation
[AEPSC]) and a number of other states or state groups (e.g., Indiana
Department of Environmental Management [IDEM], North Carolina
Department of Air Quality [NCDAQ], New Mexico Air Quality Bureau
[NMAQB], South Carolina Department of Health and Environmental Control
[SCDHEC], Southeast Michigan Council of Governments [SEMCOG], and Texas
Commission on Environmental Quality [TCEQ]) generally did not support
the proposed near-road CO monitoring requirements. For example, IDEM
stated that ``CO measured by roadside monitors is not representative of
ambient air quality everywhere in a city or county containing the
roadway'' and that ``* * * roadside monitoring measurements represent
source-specific data. Therefore, Indiana does not believe that roadside
monitoring should apply to an ambient air quality standard.'' SCDHEC
stated it ``* * * does not believe that the use of a near-road
monitoring network in a state-wide ambient air monitoring network is
the appropriate choice to protect our community's public health'' and
that ``this monitoring method biases the monitoring effort into areas
of little or no population while monitoring for the community
population exposure is neglected.'' Similarly, industry commenter AAM
stated that ``the current proposal does not include a requirement that
the near-roadway monitors be sited in locations where there is actual
human exposure to the ambient air for time periods corresponding to the
1-hour or 8-hour CO NAAQS.''
    The EPA stated in the CO proposal (76 FR 8158) that the proposed
near-road CO monitoring requirements were intended to ensure a network
of adequate size and focus to provide data for comparison to the NAAQS,
support health studies and model verification, and to fulfill Agency
multipollutant monitoring objectives. In response to the comment that
near-road monitoring data would be ``source-specific'' and may not be
appropriately applicable to an ambient air standard, the Agency notes
that monitoring for CO in the near-road environment (as a mobile source
oriented measurement) is a longstanding agency practice, as evidenced
by the first monitoring rule promulgated in 1979 (44 FR 27558, May 10,
1979). That 1979 monitoring rule included the requirement to monitor
for ``peak'' CO concentrations in urban areas having populations of
500,000 people or more in locations ``* * * around major traffic
arteries and near heavily traveled streets in downtown areas.'' The
Agency believes that the use of near-road CO monitors as proposed is
not a departure from the Agency's longstanding intent to measure peak
concentrations of CO in the near-road environment. Rather, the proposal
was consistent with the Agency's approach to require monitors for CO,
and other criteria pollutants, in locations that likely experience peak
ambient concentrations. The Agency also notes that source-oriented
monitoring is and has long been a common practice in ambient monitoring
networks, although more often associated with stationary sources, where
the ambient data collected are used for comparison to the NAAQS. Data
on ambient air concentrations, including near-road data, which may be
most appropriately classified as on-road mobile source oriented, are
appropriate to compare to the NAAQS.
    With regard to the comments asserting that near-road monitoring
would result in monitoring areas of ``little or no population'' and
thus population exposure is not represented, the EPA notes that on-road
mobile sources are ubiquitous in urban areas and are a dominant
component of the national CO emissions inventory, at nearly 60% of the
total inventory, based on the 2008 NEI. As such, microenvironments
influenced by on-road mobile sources are important contributors to
ambient CO exposures, particularly in urban areas (REA, section 2.7).
Further, the ambient CO exposures of most concern are short-term.
Accordingly, near-road monitoring is focused on characterizing peak or
elevated ambient concentrations. The relevance of this focus for the
purposes of both ensuring compliance with the NAAQS and gathering data
to inform our consideration of ambient CO exposures is demonstrated by
the ubiquity of on-road mobile sources throughout urban areas, the time
spent by people on or near roadways and the large number of American
citizens living in urban areas and near roadways. As was noted in the
ISA, the 2007 American Housing Survey (http://www.census.gov/hhes/www/housing/ahs/ahs07/ahs07.html) estimates that 17.9 million housing units
are within 300 feet (~91 meters) of a 4-lane highway, airport, or
railroad. Using the same survey, and considering that the average
number of residential occupants in a housing unit is approximately
2.25, an estimate can be made that at least 40 million American
citizens live near 4-lane highways, airports, or railroads. Among these
three transportation facilities, roads are the most pervasive of the
three, suggesting that a significant number of people may live near
major roads. Furthermore, the 2008 American Time Use Survey (http://www.bls.gov/tus/) reported that the average U.S. civilian spent over 70
minutes traveling per day. Based on these considerations, the Agency
has concluded that monitoring in the near-road environment would
characterize the ambient concentrations that contribute to ambient CO
exposure for a significant portion of the population that would
otherwise not be captured.
    The AAM also commented that the EPA ``* * * proposal to locate more
near roadway monitors appears to be an attempt to find problems where
none are likely to exist.'' The Agency proposal for near-road monitors
is in line with longstanding monitoring objectives to monitor for peak
or elevated ambient pollutant concentrations where they may occur. The
Agency agrees that CO is no longer as pervasive a problem as it was in
the past; however, there is still a responsibility to appropriately
characterize and assess ambient concentrations to ensure that they do
not exceed the NAAQS. In comments on the first draft of the ISA, CASAC
advised that ``* * * relying only on

EPA's [current] fixed monitoring network, CO measurements may
underestimate CO exposures for specific vulnerable populations such as
individuals residing near heavily trafficked roads and who commute to
work on a daily basis.'' In comments on the second draft of the ISA,
CASAC commented that ``the panel expresses concern about the existing
CO monitoring network, both for its [spatial] coverage and for its
utility in estimating human exposure'' and that ``CO exposures may not
be adequately characterized for populations that may be exposed to
higher CO levels because of where they live and work,'' such as the
near-road environment. Finally, in comments on the second draft of the
REA, CASAC stated that ``the approach for siting monitors needs greater
consideration. More extensive coverage may be warranted for areas where
concentrations may be more elevated, such as near-roadway locations.''
In light of these comments and upon a review of the existing CO
network, the Administrator concluded that the current CO monitoring
network (circa 2010) lacked a necessary focus. While some currently
existing sites that were established in the 1970s and 1980s continue to
monitor near-road locations in downtown areas or within urban street
canyons, and a minimum number of area-wide monitors are currently
required at National Core (NCore) multipollutant stations, few monitors
exist that characterize the more heavily trafficked roads that are
prevalent in the modern roadway network, particularly in our larger
urban areas. The Agency's proposal was intended to require a modest but
appropriate number of CO monitors to characterize the near-road
environment where peak or elevated ambient CO concentrations are
expected to occur near heavily trafficked roads, as compared with
neighborhood or urban background concentrations. If CO levels turn out
to be low in these near-road locations, so much the better for public
health, and monitoring networks can be adjusted in the future, as they
have over time in response to an increased understanding of where
levels of concern to public health are likely to occur.
    Although the EPA received a number of comments that were largely
supportive for the proposed requirement of collocating CO monitors
within the forthcoming near-road NO2 monitoring stations,
several commenters encouraged the Agency to provide flexibility to
allow for the separation of the newly required CO monitors from the
near-road NO2 sites, if necessary, to better monitor peak
near-road CO concentrations. In their comments supporting the
collocation concept, NACAA also stated that their organization ``* * *
also encourages EPA to allow flexibility for state and local agencies
to use alternative siting of near-roadway CO monitors on a case-by-case
basis, where there is a scientific justification for siting the CO
monitor in a different location from the NO2 monitor, to
ensure the best possible measurement of near roadway CO
concentrations.'' Similarly, NCDAQ recognized that ``* * * light duty
vehicles tend to have more impact on CO concentrations than do heavy
[duty] vehicles'' and went on to surmise that ``* * * not all near-road
NO2 monitoring stations will be well situated to measure
maximum CO concentrations.''
    The Agency has expressed its intent to pursue the integration of
monitoring networks and programs through the encouragement of
multipollutant monitoring wherever possible, as evidenced by actions
taken in the 2006 monitoring rule that created the NCore network, the
expression of the multipollutant paradigm in the 2008 Ambient Air
Monitoring Strategy for State, Local, and Tribal Air Agencies, and
within this rulemaking process as part of the rationale in proposing
the collocation of required near-road CO monitors with near-road
NO2 monitors. Multipollutant monitoring is viewed as a means
to broaden the understanding of air quality conditions and pollutant
interactions, furthering the capability to evaluate air quality models,
develop emission control strategies, and support research, including
health studies. However, the Agency also recognizes that the
measurement objectives of individual pollutants may not always
correspond in a way that would support multipollutant monitoring as the
most appropriate option in a network design. On the issue raised by
NACAA and NCDAQ concerning the potential difference in locations of
peak CO and NO2 concentrations in the near-road environment,
the EPA recognizes the primary influence to be the different emission
characteristics between light duty (LD) and heavy duty (HD) vehicles
and vehicle operating conditions, which were discussed in section
III.B.2 of the CO proposal. The public comments suggesting the need for
flexibility in siting near-road CO monitors derives from the fact that
near-road NO2 sites will be sited at locations where peak
NO2 are expected to occur. Since NO2 is more
heavily influenced by HD vehicles and CO is more heavily influenced by
LD vehicles on a per vehicle basis, respectively, there may be cases
where the peak CO and NO2 concentrations could occur along
different road segments within the same CBSA. As a general observation,
the EPA believes that this situation may have more likelihood of
occurring in the relatively larger (by population) CBSAs where a higher
number of heavily trafficked roads with a wider variety of fleet mix
(e.g. HD to LD vehicle ratios) tend to exist versus relatively smaller
CBSAs. In recognition of these considerations, the final regulation
allows for flexibility in CO monitor placement in the near-road
environment when justified, as discussed below in section IV.B.3.
b. Population Thresholds for Requiring Near-Road Carbon Monoxide
Monitors
    The EPA proposed that required CO monitors be collocated with every
required near-road NO2 monitor in a CBSA with a population
of 1 million or more persons. Due to the requirement to locate one CO
monitor at each required near-road NO2 site, the proposal
would have required two monitors in each CBSA having 2.5 million or
more persons or having one or more road segments with Annual Average
Daily Traffic (AADT) counts of 250,000 or more. The proposal would have
also required one monitor within those CBSAs having 1 million or more
persons (but fewer than 2.5 million persons).\31\ Based upon 2009
Census Bureau estimates and US DOT maintained traffic summary data, the
proposal was estimated to require 77 monitors within 53 CBSAs. Using
recent 2010 Census data, and US DOT maintained traffic summary data,
the proposal would have required approximately 75 monitors within 52
CBSAs.
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    \31\ One near-road NO2 monitor is required in any
CBSA having a population of 500,000 or more persons. Two near-road
NO2 monitors are required in CBSAs with population of
greater than 2.5 million, or in any CBSA with a population of
500,000 or more persons that has one or more roadway segments with
annual average daily traffic (AADT) counts of 250,000 or more. (40
CFR part 58, Appendix D, Section 4.3).
---------------------------------------------------------------------------

    The EPA received a number of comments supporting different
population thresholds by which to require near-road CO monitors. Those
state agencies or state agency groups who generally supported required
CO monitoring in the near-road environment (e.g., NACAA, NESCAUM,
NYSDEC, and WIDNR) suggested a population threshold of 2.5 million by
which near-road CO monitors should be required. In addition, NCDAQ, who
did not support near-road CO monitoring,

suggested that if it is required, it be required only within CBSAs of
2.5 million or more. The use of a population threshold of 2.5 million
persons, versus 1 million as proposed, would require approximately 42
near-road CO monitors within 21 CBSAs, based on 2010 Census data.
Industry commenter American Petroleum Institute (API) stated that the
proposed population threshold of 1 million persons ``* * * appears
appropriate, but EPA should not require that both [near-road
NO2] sites in the largest CBSAs host CO monitors.'' API's
suggestion would require approximately 52 near-road CO monitors within
52 CBSAs. Finally, the public health and environmental groups ALA, ATS,
and EDF suggested the EPA promulgate minimum monitoring requirements
``* * * to encompass cities in smaller metro areas, including cities
with populations of 500,000 or more, similar to the requirements for
NO2 roadside monitoring.'' ALA, ATS, and EDF's suggestion
would result in the requirement of approximately 126 monitors within
103 CBSAs.
    As was noted in the proposal, the Agency believes that with the
continuing decline of ambient CO levels, as summarized in the EPA's
most recent trends report Our Nation's Air: Status and Trends Through
2008 (http://www.epa.gov/airtrends/2010/), there is less likelihood for
high CO concentrations in relatively smaller CBSAs (by population).
Accordingly, the Agency proposed the requirement for what it believed
would be a sufficient number of CO monitors, which would be collocated
with required near-road NO2 monitors in CBSAs having
populations of 1 million or more persons. The Administrator considered
alternative population thresholds, including the 2.5 million and
500,000 person thresholds, but concluded that those thresholds would
require too few or too many monitors, respectively, in light of
existing information on CO emissions data, ambient data, and the lack
of data for locations near highly trafficked roads. The rationale for
the proposed 1 million person threshold was to require a modest but
sufficiently sized network that would effectively assess near-road CO
concentrations for comparison to the NAAQS and could also provide data
from within a multipollutant framework to support research (which
includes health studies), facilitate model verification, and assess and
evaluate emissions control strategies. However, after considering
public comments, the EPA has concluded that one monitor in each CBSA of
1 million or more persons will provide for monitoring of a wide range
of diverse situations with regard to traffic volume, traffic patterns,
roadway designs, terrain/topography, meteorology, climate, as well as
surrounding land use and population characteristics. Accordingly, in
the final rule EPA has modified the proposed requirements for CO
monitors so that only one CO monitor is required in CBSAs of 1 million
or more persons, as discussed in Section IV.B.3 below.
c. Implementation Schedule
    The EPA received a number of comments on the timeline for
implementation of any required CO monitoring promulgated as part of
this rulemaking. ALA, ATS, and EDF stated that they ``* * * support
EPA's requirement that CO monitors be installed in near-highway
locations by July 1, 2013.'' In light of the support these commenters
expressed for rapid deployment of near road CO monitors, these
commenters may have intended to support the proposed implementation
date of January 1, 2013 instead of July 1, 2013 as quoted. The Agency
received a number of comments from state agencies, state agency
organizations, and industry encouraging the Agency to extend the time
by which any required monitoring must be implemented. For example, API
suggested that the proposed date by which required near-road CO
monitors be established be extended to July 1, 2013, while NACAA and
WIDNR suggested January 1, 2014. Several commenters suggested that
required near-road monitors should be phased in over a period of time.
For example, NACAA, stated ``[i]t may be necessary to develop a program
for phasing in new monitoring sites and reevaluate network
implementation.'' NACAA also pointed to comments from CASAC that it
would be advisable to phase in near-road monitoring for NO2,
because ``[t]he first round of sites could be used to gather
information on appropriate siting in the near roadway environment, near
roadway gradient, and spatial relationships.''
    The EPA recognizes that states are already implementing newly
required monitoring related to lead and NO2, and that the
current financial and logistical burdens may make the implementation of
new monitoring requirements difficult. A number of state and industry
commenters noted the need for funding to accommodate a new monitoring
requirement, and some also noted the financial and logistical hardships
that many states are currently experiencing (e.g., IDEM, NACAA, NCDAQ,
SCDHEC, and WIDNR). The EPA recognizes the significance of the
financial and logistical burden that new monitoring requirements pose
and the impact of multiple new monitoring requirements stemming from
other recent rulemakings. As such, the Agency has taken these comments
into consideration in the final rule with regard to when required CO
monitors are to be operational, as discussed in Section IV.B.3 below.
d. Siting Criteria
    The EPA received comments regarding the proposed revisions to
microscale CO siting criteria. Those who commented (AAM, API, and
NCDAQ) all supported having two sets of siting criteria that would
apply to near-road CO monitors such as those that might be collocated
with near-road NO2 monitors and to those CO monitors
operating in downtown areas and urban street canyon locations,
respectively. AAM stated that ``* * * there should be two separate
criteria for siting microscale CO monitors. The earlier height and
distance guidelines are still appropriate for downtown areas and
arterial highways with sidewalks, but a separate set of guidelines
should be established for limited access, heavily-travelled
expressways.'' API commented that ``* * * the proposed CO [near-road]
criteria are acceptable. EPA should create two-tiered siting criteria
for microscale CO monitoring * * *'' and that ``there will be an
ongoing need for CO monitoring in downtown, urban and/or street
canyon[s] for health-related concerns as well as SIP-related issues.''
Finally, NCDAQ stated that ``* * * the US EPA should maintain separate
siting criteria for the two types of micro-scale CO monitoring sites *
* *'' noting that the current siting criteria intended for downtown
areas and urban street canyon sites ``* * * are still valid for that
purpose and CO monitoring stations being placed for this purpose should
still be required to meet these siting criteria.''
    The EPA agrees with the commenters that the existing siting
criteria are still appropriate for any existing or future downtown area
or urban street canyon CO monitoring site, and that new siting criteria
are appropriate for CO monitors being collocated with near road
NO2 monitors. As such, the Agency is finalizing siting
criteria for microscale CO sites that include criteria for both
downtown area/urban street canyon microscale sites and other near-road
microscale CO sites, as presented below in Section IV.B.3.
e. Area-Wide Monitoring
    The EPA received a number of comments from transportation groups,

public health and environmental groups, and an industry commenter
(e.g., AAM, ALA/ATS/EDF, American Association of State Highway and
Transportation Officials [AASHTO], New York State Department of
Transportation [NYSDOT], Texas Department of Transportation [TXDOT],
and Virginia Department of Transportation [VDOT]) regarding the fate of
many of the CO monitors in the current network that characterize
concentrations representative of neighborhood or larger spatial
scales,\32\ known as area-wide monitors. For example, AASHTO commented
that ``EPA appears to be proposing that CO monitoring sites to
characterize area-wide CO concentration levels at the neighborhood and
larger spatial scales is no longer required. AASHTO is concerned that
this proposal will de-emphasize the need for neighborhood scale CO
monitors.'' AASHTO and some state DOTs expressed that the data for
neighborhood scale monitors are used for other purposes, such as
National Environmental Policy Act (NEPA) and transportation conformity,
and that they are concerned about the potential loss of these types of
data in the future. In another example, ALA/ATS/EDF stated that they
call upon EPA to ``establish a comprehensive roadside air pollution
network, while retaining the current area-wide CO network.''
---------------------------------------------------------------------------

    \32\ Spatial scales are defined in 40 CFR Part 58 Appendix D,
Section 1.2, where the scales of representativeness of most interest
for the monitoring site types include:
    1. Microscale--Defines the concentration in air volumes
associated with area dimensions ranging from several meters up to
about 100 meters.
    2. Middle scale--Defines the concentration typical of areas up
to several city blocks in size, with dimensions ranging from about
100 meters to 0.5 kilometers.
    3. Neighborhood scale--Defines concentrations within some
extended area of the city that has relatively uniform land use with
dimensions in the 0.5 to 4.0 kilometers range.
    4. Urban scale--Defines concentrations within an area of city-
like dimensions, on the order of 4 to 50 kilometers. Within a city,
the geographic placement of sources may result in there being no
single site that can be said to represent air quality on an urban
scale. The neighborhood and urban scales have the potential to
overlap in applications that concern secondarily formed or
homogeneously distributed air pollutants.
    5. Regional scale--Defines usually a rural area of reasonably
homogeneous geography without large sources, and extends from tens
to hundreds of kilometers.
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    The EPA notes that prior to this final rulemaking, the only
required CO monitoring within 40 CFR part 58, appendix D was for the
operation of a CO monitor within all NCore multipollutant monitoring
stations. There are approximately 80 NCore stations nationwide, and by
design, they are area-wide monitoring sites. In the proposal, the
Agency estimated that 345 CO monitors were operational at some point
during 2009. A more recent examination of AQS data (utilizing EPA's Air
Explorer Web tools located at http://www.epa.gov/airexplorer) indicate
that approximately 328 CO monitors were operational as of May 20, 2011.
These 328 active CO monitors include the 80 NCore monitors now in
operation nationwide. This means that a significant portion of the
current network is composed of monitors that are additional to those
required by EPA as part of a national network design. It is critical to
note that in this rulemaking the EPA is actually increasing the total
number of required sites in the national CO monitoring network design
and is not removing any area-wide monitoring requirements as AASHTO and
other commenters suggested. Some of the potential for misperception on
this issue may have arisen from the Agency's stated expectation that
state and local air monitoring agencies will likely move existing CO
monitors into near-road locations to satisfy the minimum monitoring
requirements promulgated in this rulemaking. Based on this final rule,
state and local agencies would only move, at most, approximately 52
monitors out of the 328 in operation (circa May 2011). Therefore a
majority of CO monitors would likely continue operating in their
existing locations. However, it should be noted that with ambient CO
concentrations well below the NAAQS, particularly at area-wide sites,
states may identify some area-wide CO monitors to be no longer
necessary. As such, the retirement of these sites may be justified, and
their removal would save state and local resources. The EPA does
recognize the value of maintaining some level of area-wide CO
monitoring to meet the overarching monitoring objectives, which
includes tracking long-term trends and to support research. In the
proposal, the Agency did not propose establishing requirements for
additional area-wide monitoring sites because: (1) There is the
existing NCore requirement, and (2) there is an expectation based on
experience that some number of non-required area-wide sites will
continue to operate in the future without minimum monitoring
requirements. Regarding the removal or shutdown of any individual
ambient air pollutant monitor, the Agency notes that there is a
publicly transparent process by which any existing CO monitor would be
shut-down. The shut-down of any State and Local Air Monitoring Station
(SLAMS) monitor is allowable under certain conditions specified in 40
CFR 58.14 System Modification. These conditions provide state and local
air agencies multiple options by which they may propose, with
justification, for a monitor to be shut down. Whatever the
justification may be, each monitor proposed to be shut-down must go
through an established process to receive EPA Regional Administrator
approval for shut-down. As part of that process, the EPA Regional
Administrator provides opportunity for public comment before making a
decision to approve or disapprove the request. In conclusion, the EPA
believes that even without requirements for area-wide CO monitors
additional to the NCore sites, some number of area-wide monitors will
continue to operate into the future. EPA anticipates that monitors that
states find useful for other regulatory purposes, such as NEPA, would
be among the monitors that may continue to operate. The NCore sites,
along with monitors currently operating in the absence of other area-
wide monitoring requirements, will likely provide a sufficient set of
area-wide monitors to meet monitoring objectives.
    The EPA also received a number of comments from transportation
groups, state and local groups, and an industry commenter (e.g., AAM,
AASHTO, NESCAUM, NYSDEC, NYSDOT, TXDOT, and VDOT) suggesting that
required near-road CO monitors should be paired with an area-wide CO
monitor within the same CBSA. For example, AASHTO recommended that ``*
* * EPA ensure that adequate coverage continues from neighborhood-scale
monitors to estimate background concentration levels, and that there is
at least one neighborhood scale monitor in every urbanized area that is
required to have a near-road monitor.'' NESCAUM recommended ``* * *
that EPA locate near-road CO monitors near urban NCore CO sites'' (as
noted above, NCore sites are area-wide sites by design).
    The EPA recognizes that a pairing of near-road CO monitors with
area-wide CO monitors will provide information by which an estimate of
the difference between near-road concentrations to relative background
concentrations might be determined. As noted earlier, the Agency
believes that the combination of required NCore sites and those area-
wide monitors currently operating in the absence of minimum monitoring
requirements (of which many will likely continue operating in the
future) will largely fulfill the area-wide component of any near-road
site/area-wide site pairing in an urban area. An analysis of NCore site
locations (site data available from http://www.epa.gov/ttn/amtic/ncore/index.html), along with

all those area-wide CO monitors believed to be operating as of May 20,
2011 (utilizing EPA's Air Explorer Web tools located at http://www.epa.gov/airexplorer) indicated that of the 52 CBSAs with a
population of 1 million persons or more, based on 2010 Census data,,
only 4 are believed to be without an area-wide CO monitor.\33\ The EPA
believes that, based on the considerations discussed above, the
existing network will likely provide sufficient area-wide CO
concentration information on which a near-road to area-wide data
comparison could be based.
---------------------------------------------------------------------------

    \33\ The EPA notes that of the 52 CBSAs that have 1 million or
more persons, 39 CBSAs contain an NCore monitoring station, which
includes a CO monitor.
---------------------------------------------------------------------------

f. Regional Administrator Authority
    The EPA received a number of comments from states and
transportation groups (e.g., AASHTO, NYSDOT, TCEQ, TXDOT, and VDOT) on
the proposal for Regional Administrators to have the discretion to
require monitoring above the minimum requirements as necessary to
address situations where minimum monitoring requirements are not
sufficient to meet monitoring objectives. For example, AASHTO commented
that ``the proposed rule includes some examples of where additional
monitors may be necessary. AASHTO is concerned that these brief
examples may not be sufficient to ensure uniform application of this
additional authority among the EPA Regions,'' and that EPA should
provide guidance on this so that there is ``reasonable uniformity
between EPA Regions in the implementation of these provisions.'' TCEQ
commented that it ``does not agree that this discretion is appropriate,
particularly where EPA has not proposed a process by which Regional
Administrators must consult with states and the public regarding these
decisions.'' Further TCEQ stated that ``* * * the potential requirement
for additional monitors when `minimum monitoring requirements are not
sufficient to meet monitoring objectives' is overly broad and should be
refined to include objective criteria that will consistently applied
across all EPA Regions.''
    The EPA notes that the authority of Regional Administrators to
require additional monitoring above the minimum required is not unique
to the CO NAAQS. For example, Regional Administrators have the
authority to use their discretion to require additional NO2,
lead, and sulfur dioxide monitors (40 CFR part 58 appendix D sections
4.3.4, 4.4.3, and 4.5, respectively) and to work with state and local
air agencies in designing and/or maintaining an appropriate ozone
monitoring network (40 CFR part 58 appendix D section 4.1). The EPA
believes that a nationally applicable network design may not always
account for all locations in every area where monitors may be
warranted. Example situations where the Regional Administrator
authority could be utilized, which were provided in the proposal, could
be for unmonitored locations where data or other information suggest
that CO concentrations may be approaching or exceeding the NAAQS due to
stationary CO sources, in downtown areas or urban street canyons, or in
areas that are subject to high ground-level CO concentrations
particularly due to or enhanced by topographical and meteorological
impacts. The Agency cannot anticipate every example that may exist
where the Regional Administrator authority might be used for inclusion
in this preamble text. However, the Agency believes it is important for
Regional Administrators to have the authority to address possible gaps
in the minimally required monitoring network in situations such as
those examples provided here. In response to public comments, the EPA
notes that Regional Administrators would use their authority in
collaboration with state agencies, working with stakeholders to design
and/or maintain the most appropriate CO monitoring network to meet the
needs of a given area. Finally, the Agency notes that any monitor
required by the Regional Administrator (or any new monitor proposed by
the state itself) is not done so with unfettered discretion. Any such
action would be included in the Annual Monitoring Network Plan per 40
CFR 58.10, and this plan must be made available for public inspection
and comment before any decisions are made by the EPA Regional
Administrator.
3. Conclusions on the Network Design
    This section provides the rationale and details for the final
decision on changes to the CO monitoring network design and siting
criteria. As discussed above in section IV.B.2.a, motor vehicle
emissions are important contributors to ambient CO concentrations (REA,
section 2.2), contributing nearly 60% of the total CO emitted
nationally (per the 2008 NEI). As a result, microenvironments
influenced by on-road mobile sources are important contributors to
ambient CO exposures, particularly in urban areas (REA, section 2.7).
Therefore, the Administrator has concluded that monitoring in the near-
road environment to characterize and assess ambient CO concentrations
continues to be an appropriate objective for the CO monitoring network.
The EPA believes that the promulgation of minimum requirements for CO
monitors in the near-road environment is necessary to ensure a network
of adequate size and focus to provide data for comparison to the NAAQS,
support research which includes health studies, allow for model
verification, and fulfill multipollutant monitoring objectives.
Further, considering the lack of CO monitors assessing higher
trafficked roads in urban areas and CASAC's advice that the Agency
develop greater monitoring capacity for CO in near-road environments
(Brain and Samet, 2010b), the Agency believes that a number of CO
monitors should be focused in such locations. Highly trafficked roads
are expected to show elevated CO concentrations relative to area-wide
concentrations and to represent the locations where ambient CO
concentrations may be highest in an area. Regarding the locations where
required near-road CO monitors might be placed, the EPA proposed that
they be collocated with a subset of near-road NO2 monitors.
The EPA expects required near-road NO2 monitors (as
prescribed in 40 CFR part 58, appendix D, Section 4.3) to be adjacent
to highly trafficked roads within the CBSAs where they are required.
Recognizing this and also recognizing the benefits associated with
collocating monitors at the same site, the Agency is finalizing
requirements for CO monitors that will leverage required near-road
NO2 monitoring sites to house collocated near-road CO
monitors to create data for comparison to the NAAQS, support research
which includes health studies, provide data for model evaluation, and
foster the fulfillment of multipollutant objectives.
    As noted in section IV.B.2.b above, after considering public
comments, EPA has modified the requirements for CO monitors from that
which was proposed so that only one CO monitor is required in each CBSA
in which near-road CO monitoring is required.\34\ This approach reduces
the total number of monitors that would have been required under the
proposal from 75 monitors within 52 CBSAs to 52 monitors within 52
CBSAs (based on 2010 Census data). The EPA believes this network design
addresses public comments while maintaining monitoring in a
sufficiently diverse set

of locations throughout 52 different urban areas around the country. By
having monitors within 52 different CBSAs, this network design is
expected to provide for monitoring in a wide range of diverse
situations with regard to traffic volumes, traffic patterns, roadway
designs, terrain/topography, meteorology, climate, as well as
surrounding land use and population characteristics.
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    \34\ This approach only requires one CO monitor to be installed
in those CBSAs that have two required near-road NO2
monitors.
---------------------------------------------------------------------------

    The EPA is generally requiring CO monitors to be collocated with
near-road NO2 monitors. However, upon consideration of
public comments, the Agency is allowing flexibility for states to use
an alternate near-road location, which includes downtown areas, urban
street canyons, and other near-road locations. This flexibility is
provided for a required CO monitor, on a case-by-case basis, with EPA
Regional Administrator approval, when the state can provide
quantitative justification showing the expectation of higher peak CO
concentrations for that alternate location compared to a near-road
NO2 location. Such requests could be based upon appropriate
modeling, exploratory monitoring, or other methods, comparing the
alternative CO location and the near-road NO2 location.
    In summary, based upon 2010 Census Bureau data this final rule will
require approximately 52 CO monitors to be collocated with near-road
NO2 monitors (or otherwise operated at an alternate, EPA
Regional Administrator approved, near-road location where peak CO
concentrations are expected) within 52 CBSAs that have populations of 1
million or more persons.
    Regarding the deployment and operation of required CO monitors, the
Agency recognizes that many state and local air agencies are under
financial and related resource duress. EPA has concluded that allowing
additional time for installing CO monitors will provide an opportunity
for state and local agencies to work with EPA Regions to identify which
existing CO monitors may be appropriate to relocate to the near-road
locations. In many cases, EPA and the state may believe it is
appropriate to relocate monitors, including some of those that are
currently operated pursuant to existing maintenance plans. In these
cases, additional time may be necessary to allow states to revisit and
possibly revise, in consultation with (and subject to the approval of)
the EPA Regions, existing maintenance plans in a way that may allow
certain CO monitors to be free for relocation, if appropriate. Further,
if a state chooses to investigate whether it will request that a
required near-road CO monitor be sited in a near-road location other
than a required near-road NO2 site, the time allotted by the
final rule is expected to provide states with adequate time to perform
necessary analyses for submission to the Regional Administrator for
approval. Furthermore, EPA has concluded that public comments
suggesting a phased-in implementation, allowing for later stages to
benefit from experience in an initial round of monitor installations,
have merit.
    As a result, the EPA has chosen not to require the implementation
of required CO sites by January 1, 2013 as was proposed. Instead, the
Agency is finalizing a two-phased implementation requirement. Those CO
monitors required within CBSAs having 2.5 million or more persons are
to be operational by January 1, 2015, although the Agency strongly
encourages the implementation of these required monitors as soon as
practicable. Those CO monitors required in CBSAs having 1 million or
more persons (and fewer than 2.5 million persons) are to be operational
by January 1, 2017. EPA intends to review the experience of states with
the first round of near-road CO monitors and the data produced by such
monitors and consider whether adjustments to the network requirements
are warranted. These required CO monitors shall be reflected in a
state's annual monitoring network plans due six months prior to
installation, i.e., on July 1, 2014 or July 1, 2016, respectively.
    Regarding siting criteria, the EPA received public support to
adjust microscale CO siting criteria to match those of near-road
NO2 monitors (and microscale PM2.5 monitors). The
Agency also was urged to retain the existing microscale siting
criteria, for explicit use with microscale CO sites in downtown areas
or urban street canyon settings. As a result, the EPA is retaining the
existing siting criteria for microscale CO monitors in downtown areas
and urban street canyons and is finalizing the additional siting
criteria for those near-road microscale CO monitors outside of downtown
areas and urban street canyons to have probe height and horizontal
spacing to match those of near-road NO2 monitors as
prescribed in 40 CFR part 58 appendix E, sections 2, 4(d), 6.4(a), and
table E-4.
    Specifically, the Agency is finalizing the following: (1) A
microscale near-road CO monitor inlet probe shall be between 2 and 7
meters above the ground; (2) a microscale CO monitor inlet probe in the
near-road environment shall be placed so it has an unobstructed air
flow, where no obstacles exist at or above the height of the monitor
probe, between the monitor probe and the outside nearest edge of the
traffic lanes of the target road segment; and (3) that CO monitors in
the near-road environment shall have inlet probes as near as
practicable to the outside nearest edge of the traffic lanes of the
target road segment, but shall not be located at a distance greater
than 50 meters in the horizontal from the outside nearest edge of the
traffic lanes of the target road segment.
    Further, as suggested through public comments, the EPA is retaining
existing regulatory siting criteria language for microscale CO monitors
in downtown areas or urban street canyon locations, where: (1) The
inlet probe for a near-road microscale CO monitor in a downtown area or
urban street canyon shall be between 2.5 meters and 3.5 meters above
ground level; (2) the inlet probe for a near-road microscale CO monitor
in a downtown area or urban street canyon shall be within 10 meters
from the edge of the nearest traffic lane; and (3) near-road microscale
CO monitors in street canyons are required to be at least 10 meters
from an intersection.
    Finally, the EPA recognizes that a monitoring network design may
not always require monitoring on a national scale that is sufficient in
fulfilling specific or otherwise unique data needs or monitoring
objectives for every area across the nation. Thus, the EPA is
finalizing the provision that EPA Regional Administrators have the
authority to require monitoring above the minimum requirements, as
necessary, in any area, to address situations where the minimally
required monitoring network is not sufficient to meet monitoring
objectives. Example situations where the Regional Administrator
Authority could be utilized include, but are not limited to, those
unmonitored locations where data or other information suggest that CO
concentrations may be approaching or exceeding the NAAQS due to
stationary CO sources, in downtown areas or urban street canyons, or in
areas that are subject to high ground-level CO concentrations
particularly due to or enhanced by topographical and meteorological
impacts. In all cases in which a Regional Administrator may consider
the need for additional monitoring, it is expected that the Regional
Administrators will work with the state or local air agencies to
evaluate evidence or needs to determine whether a particular area may
warrant additional monitoring.

V. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive
Order 13563: Improving Regulation and Regulatory Review

    Under Executive Order 12866 (58 FR 51735, October 4, 1993), this
action is a ``significant regulatory action'' because it was deemed to
``raise novel legal or policy issues.'' Accordingly, EPA submitted this
action to the Office of Management and Budget (OMB) for review under
Executive Orders 12866 and 13563 (76 FR 3821, January 21, 2011) and any
changes made in response to OMB recommendations have been documented in
the docket for this action.

B. Paperwork Reduction Act

    The information collection requirements in this final rule have
been submitted for approval to the Office of Management and Budget
(OMB) under the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. The
information collection requirements are not enforceable until OMB
approves them. The Information Collection Request (ICR) document
prepared by EPA for these revisions to part 58 has been assigned EPA
ICR number 0940.24.
    The information collected under 40 CFR part 53 (e.g., test results,
monitoring records, instruction manual, and other associated
information) is needed to determine whether a candidate method intended
for use in determining attainment of the NAAQS in 40 CFR part 50 will
meet comparability requirements for designation as a FRM or FEM. We do
not expect the number of FRM or FEM determinations to increase over the
number that is currently used to estimate burden associated with CO
FRM/FEM determinations provided in the current ICR for 40 CFR part 53
(EPA ICR numbers 0940.24). As such, no change in the burden estimate
for 40 CFR part 53 has been made as part of this rulemaking.
    The information collected and reported under 40 CFR part 58 is
needed to determine compliance with the NAAQS, to characterize air
quality and associated health impacts, to develop emissions control
strategies, and to measure progress for the air pollution program. The
amendments would revise the technical requirements for CO monitoring
sites, require the relocation or siting of ambient CO air monitors, and
the reporting of the collected ambient CO monitoring data to EPA's Air
Quality System (AQS). The annual average reporting burden for the
collection under 40 CFR part 58 (averaged over the first 3 years of
this ICR) for a network of 311 CO monitors is $7,235,483. Burden is
defined at 5 CFR 1320.3(b). State, local, and Tribal entities are
eligible for State assistance grants provided by the Federal government
under the CAA which can be used for monitors and related activities.
    An agency may not conduct or sponsor, and a person is not required
to respond to, a collection of information unless it displays a
currently valid OMB control number. The OMB control numbers for EPA's
regulations in 40 CFR are listed in 40 CFR part 9. When this ICR is
approved by OMB, the Agency will publish a technical amendment to 40
CFR part 9 in the Federal Register to display the OMB control number
for the approved information collection requirements contained in this
final rule.

C. Regulatory Flexibility Act

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

D. Unfunded Mandates Reform Act

    This rule does not contain a Federal mandate that may result in
expenditures of $100 million or more for State, local, and Tribal
governments, in the aggregate, or the private sector in any one year.
This rule retains the existing national ambient air quality standards
for carbon monoxide. The expected costs associated with the monitoring
requirements are described in EPA's ICR document, but those costs are
expected to be well less than $100 million (adjusted for inflation) in
the aggregate for any year. Furthermore, as indicated previously, in
setting a NAAQS, EPA cannot consider the economic or technological
feasibility of attaining ambient air quality standards. Thus, this rule
is not subject to the requirements of sections 202 or 205 of the UMRA.
    This rule is also not subject to the requirements of section 203 of
the UMRA because it imposes no enforceable duty on any small
governments.

E. Executive Order 13132: Federalism

    This action does not have federalism implications. It will not have
substantial direct effects on the States, on the relationship between
the national government and the States, or on the distribution of power
and responsibilities among the various levels of government, as
specified in Executive Order 13132. The rule does not alter the
relationship between the Federal government and the States regarding
the establishment and implementation of air quality improvement
programs as codified in the CAA. Under section 109 of the CAA, EPA is
mandated to establish and review NAAQS; however, CAA section 116
preserves the rights of States to establish more stringent requirements
if deemed necessary by a State. Furthermore, this rule does not impact
CAA section 107 which establishes that the States have primary
responsibility for implementation of the NAAQS. Finally, as noted in
section D (above) on UMRA, this rule does not impose significant costs
on State, local or Tribal governments or the private sector. Thus,
Executive Order 13132 does not apply to this rule.

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

    This action does not have Tribal implications, as specified in
Executive Order 13175 (65 FR 67249, November 9, 2000). It does not have
a substantial direct effect on one or more Indian Tribes, since Tribes
are not obligated to adopt or implement any NAAQS. Thus, Executive
Order 13175 does not apply to this action.

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

    This action is not subject to EO 13045 (62 FR 19885, April 23,
1997) because it is not economically significant as defined in EO
12866, and because the Agency does not believe the environmental health
or safety risks addressed by this action present a disproportionate
risk to children. This action's health and risk assessments are
described in section II.A.

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

    This action is not a ``significant energy action'' as defined in
Executive Order 13211 (66 FR 28355 (May 22, 2001)) because it is not
likely to have a significant adverse effect on the supply,
distribution, or use of energy. The rule concerns the review of the
NAAQS for CO. The rule does not prescribe specific pollution control
strategies by which these ambient standards will be met. Such
strategies are developed by States on a case-by-case basis, and EPA
cannot predict whether the control options selected by States will
include regulations on energy suppliers, distributors, or users.

I. National Technology Transfer and Advancement Act

    Section 12(d) of the National Technology Transfer and Advancement
Act of 1995 (NTTAA), Public Law 104- 113, section 12(d) (15 U.S.C. 272
note) directs EPA to use voluntary consensus standards in its
regulatory activities unless to do so would be inconsistent with
applicable law or otherwise impractical. Voluntary consensus standards
are technical standards (e.g., materials specifications, test methods,
sampling procedures, and business practices) that are developed or
adopted by voluntary consensus standards bodies. The NTTAA directs EPA
to provide Congress, through OMB, explanations when the Agency decides
not to use available and applicable voluntary consensus standards.
    This rulemaking involves technical standards with regard to ambient
monitoring of CO. We have not identified any potentially applicable
voluntary consensus standards that would adequately characterize
ambient CO concentrations for the purposes of determining compliance
with the CO NAAQS and none have been brought to our attention in
comments. Therefore, EPA has decided to use the method ``Measurement
Principle and Calibration Procedure for the Measurement of Carbon
Monoxide in the Atmosphere (Non-Dispersive Infrared Photometry)'' (40
CFR part 50, appendix C), as revised by this action, for the purposes
of ambient monitoring of CO concentrations.

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

    Executive Order 12898 (59 FR 7629 (Feb. 16, 1994)) establishes
Federal executive policy on environmental justice. Its main provision
directs Federal agencies, to the greatest extent practicable and
permitted by law, to make environmental justice part of their mission
by identifying and addressing, as appropriate, disproportionately high
and adverse human health or environmental effects of their programs,
policies, and activities on minority populations and low-income
populations in the United States.
    EPA has determined that this final rule will not have
disproportionately high and adverse human health or environmental
effects on minority or low-income populations because it does not
affect the level of protection provided to human health or the
environment. The action in this notice is to retain without revision
the existing NAAQS for CO. Therefore this action will not cause
increases in source emissions or air concentrations.

K. Congressional Review Act

    The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the
Small Business Regulatory Enforcement Fairness Act of 1996, generally
provides that before a rule may take effect, the agency promulgating
the rule must submit a rule report, which includes a copy of the rule,
to each House of the Congress and to the Comptroller General of the
United States. EPA will submit a report containing this rule and other
required information to the U.S. Senate, the U.S. House of
Representatives, and the Comptroller General of the United States prior
to publication of the rule in the Federal Register. A major rule cannot
take effect until 60 days after it is published in the Federal
Register. This action is not a ``major rule'' as defined by 5 U.S.C.
804(2). This rule will be effective October 31, 2011.

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Wellenius G.A.; Bateson T.F.; Mittleman M.A.; Schwartz J. (2005)
Particulate air pollution and the rate of hospitalization for
congestive heart failure among medicare beneficiaries in Pittsburgh,
Pennsylvania. Am J Epidemiol 161:1030-1036.
Zhu Y.; Hinds W.C.; Kim S.; Shen S.; Sioutas C. (2002) Study of
ultrafine particles near a major highway with heavy-duty diesel
traffic. Atmos Environ, 36:4323-4335.

List of Subjects

40 CFR Part 50

    Environmental protection, Air pollution control, Carbon monoxide,
Lead, Nitrogen dioxide, Ozone, Particulate matter, Sulfur oxides.

40 CFR Part 53

    Environmental protection, Administrative practice and procedure,
Air pollution control, Intergovernmental relations, Reporting and
recordkeeping requirements.

40 CFR Part 58

    Environmental protection, Administrative practice and procedure,
Air pollution control, Intergovernmental relations, Reporting and
recordkeeping requirements.

    Dated: August 12, 2011.
Lisa P. Jackson,
Administrator.

    For the reasons stated in the preamble, title 40, chapter I of the
Code of Federal Regulations is amended as follows:

PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY
STANDARDS

0
1. The authority citation for part 50 continues to read as follows:

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

0
2. Appendix C to part 50 is revised to read as follows:

Appendix C to Part 50--Measurement Principle and Calibration Procedure
for the Measurement of Carbon Monoxide in the Atmosphere (Non-
Dispersive Infrared Photometry)

1.0 Applicability

    1.1 This non-dispersive infrared photometry (NDIR) Federal
Reference Method (FRM) provides measurements of the concentration of
carbon monoxide (CO) in ambient air for determining compliance with
the primary and secondary National Ambient Air Quality Standards
(NAAQS) for CO as specified in Sec.  50.8 of this chapter. The
method is applicable to continuous sampling and measurement of
ambient CO concentrations suitable for determining 1-hour or longer
average measurements. The method may also provide measurements of
shorter averaging times, subject to specific analyzer performance
limitations. Additional CO monitoring quality assurance procedures
and guidance are provided in part 58, appendix A, of this chapter
and in reference 1 of this appendix C.

2.0 Measurement Principle

    2.1 Measurements of CO in ambient air are based on automated
measurement of the absorption of infrared radiation by CO in an
ambient air sample drawn into an analyzer employing non-wavelength-
dispersive, infrared photometry (NDIR method). Infrared energy from
a source in the photometer is passed through a cell containing the
air sample to be analyzed, and the quantitative absorption of energy
by CO in the sample cell is measured by a suitable detector. The
photometer is sensitized specifically to CO by employing CO gas in a
filter cell in the optical path, which, when compared to a
differential optical path without a CO filter cell, limits the
measured absorption to one or more of the characteristic wavelengths
at which CO strongly absorbs. However, to meet measurement
performance requirements, various optical filters, reference cells,
rotating gas filter cells, dual-beam configurations, moisture traps,
or other means may also be used to further enhance sensitivity and
stability of the photometer and to minimize potential measurement
interference from water vapor, carbon dioxide (CO2), or
other species. Also, various schemes may be used to provide a
suitable zero reference for the photometer, and optional automatic
compensation may be provided for the actual pressure and temperature
of the air sample in the measurement cell. The measured infrared
absorption, converted to a digital reading or an electrical output
signal, indicates the measured CO concentration.
    2.2 The measurement system is calibrated by referencing the
analyzer's CO measurements to CO concentration standards traceable
to a National Institute of Standards and Technology (NIST) primary
standard for CO, as described in the associated calibration
procedure specified in section 4 of this reference method.
    2.3 An analyzer implementing this measurement principle will be
considered a reference method only if it has been designated as a
reference method in accordance with part 53 of this chapter.
    2.4 Sampling considerations. The use of a particle filter in the
sample inlet line of a CO FRM analyzer is optional and left to the
discretion of the user unless such a filter is specified or
recommended by the analyzer manufacturer in the analyzer's
associated operation or instruction manual.

3.0 Interferences

    3.1 The NDIR measurement principle is potentially susceptible to
interference from water vapor and CO2, which have some
infrared absorption at wavelengths in common with CO and normally
exist in the atmosphere. Various instrumental techniques can be used
to effectively minimize these interferences.

4.0 Calibration Procedures

    4.1 Principle. Either of two methods may be selected for dynamic
multipoint calibration of FRM CO analyzers, using test gases of
accurately known CO concentrations obtained from one or more
compressed gas cylinders certified as CO transfer standards:
    4.1.1 Dilution method: A single certified standard cylinder of
CO is quantitatively diluted as necessary with zero air to obtain
the various calibration concentration standards needed.
    4.1.2 Multiple-cylinder method: Multiple, individually certified
standard cylinders of CO are used for each of the various
calibration concentration standards needed.
    4.1.3 Additional information on calibration may be found in
Section 12 of reference 1.
    4.2 Apparatus. The major components and typical configurations
of the calibration systems for the two calibration methods are shown
in Figures 1 and 2. Either system may be made up using common
laboratory components, or it may be a commercially manufactured
system. In either case, the principal components are as follows:
    4.2.1 CO standard gas flow control and measurement devices (or a
combined device) capable of regulating and maintaining the standard
gas flow rate constant to within  2 percent and
measuring the gas flow rate accurate to within  2
percent, properly calibrated to a NIST-traceable standard.
    4.2.2 For the dilution method (Figure 1), dilution air flow
control and measurement devices (or a combined device) capable of
regulating and maintaining the air flow rate constant to within
 2 percent and measuring the air flow rate accurate to
within  2 percent, properly calibrated to a NIST-
traceable standard.
    4.2.3 Standard gas pressure regulator(s) for the standard CO
cylinder(s), suitable for use with a high-pressure CO gas cylinder
and having a non-reactive diaphragm and internal parts and a
suitable delivery pressure.
    4.2.4 Mixing chamber for the dilution method of an inert
material and of proper design to provide thorough mixing of CO
standard gas and diluent air streams.
    4.2.5 Output sampling manifold, constructed of an inert material
and of sufficient diameter to ensure an insignificant pressure drop
at the analyzer connection. The system must have a vent designed to
ensure nearly atmospheric pressure at the analyzer connection port
and to prevent ambient air from entering the manifold.

4.3 Reagents

    4.3.1 CO gas concentration transfer standard(s) of CO in air,
containing an appropriate concentration of CO suitable for the
selected operating range of the analyzer under calibration and
traceable to a NIST standard reference material (SRM). If the CO
analyzer has significant sensitivity to CO2, the CO
standard(s) should also contain 350 to 400 ppm CO2 to
replicate the typical CO2 concentration in ambient air.
However, if the zero air dilution ratio used for the dilution method
is not less than 100:1 and the zero air contains ambient levels of
CO2, then the CO standard may be contained in nitrogen
and need not contain CO2.
    4.3.2 For the dilution method, clean zero air, free of
contaminants that could cause a detectable response on or a change
in sensitivity of the CO analyzer. The zero air should contain < 0.1
ppm CO.

4.4 Procedure Using the Dilution Method

    4.4.1 Assemble or obtain a suitable dynamic dilution calibration
system such as the one shown schematically in Figure 1. Generally,
all calibration gases including zero air must be introduced into the
sample inlet of the analyzer. However, if the analyzer has special,
approved zero and span inlets and automatic valves to specifically
allow introduction of calibration standards at near atmospheric
pressure, such inlets may be used for calibration in lieu of the
sample inlet. For specific operating instructions, refer to the
manufacturer's manual.
    4.4.2 Ensure that there are no leaks in the calibration system
and that all flowmeters are properly and accurately calibrated,
under the conditions of use, if appropriate, against a reliable
volume or flow rate standard such as a soap-bubble meter or wet-test
meter traceable to a NIST standard. All volumetric flow rates should
be corrected to the same temperature and pressure such as 298.15 K
(25 [deg]C) and 760 mm Hg (101 kPa), using a correction formula such
as the following:
[GRAPHIC] [TIFF OMITTED] TR31AU11.001

Where:

Fc = corrected flow rate (L/min at 25 [deg]C and 760 mm Hg),
Fm = measured flow rate (at temperature Tm and pressure Pm),
Pm = measured pressure in mm Hg (absolute), and
Tm = measured temperature in degrees Celsius.

    4.4.3 Select the operating range of the CO analyzer to be
calibrated. Connect the measurement signal output of the analyzer to
an appropriate readout instrument to allow the analyzer's
measurement output to be continuously monitored during the
calibration. Where possible, this readout instrument should be the
same one used to record routine monitoring data, or, at least, an
instrument that is as closely representative of that system as
feasible.
    4.4.4 Connect the inlet of the CO analyzer to the output-
sampling manifold of the calibration system.
    4.4.5 Adjust the calibration system to deliver zero air to the
output manifold. The total air flow must exceed the total demand of
the analyzer(s) connected to the output manifold to ensure that no
ambient air is pulled into the manifold vent. Allow the analyzer to
sample zero air until a stable response is obtained. After the
response has stabilized, adjust the analyzer zero reading.
    4.4.6 Adjust the zero air flow rate and the CO gas flow rate
from the standard CO cylinder to provide a diluted CO concentration
of approximately 80 percent of the measurement upper range limit
(URL) of the operating range of the analyzer. The total air flow
rate must exceed the total demand of the analyzer(s) connected to
the output manifold to ensure that no ambient air is pulled into the
manifold vent. The exact CO concentration is calculated from:
[GRAPHIC] [TIFF OMITTED] TR31AU11.002

Where:

[CO]OUT = diluted CO concentration at the output manifold (ppm),
[CO]STD = concentration of the undiluted CO standard (ppm),
FCO = flow rate of the CO standard (L/min), and
FD = flow rate of the dilution air (L/min).

Sample this CO concentration until a stable response is obtained.
Adjust the analyzer span control to obtain the desired analyzer
response reading equivalent to the calculated standard
concentration. If substantial adjustment of the analyzer span
control is required, it may be necessary to recheck the zero and
span adjustments by repeating steps 4.4.5 and 4.4.6. Record the CO
concentration and the analyzer's final response.
    4.4.7 Generate several additional concentrations (at least three
evenly spaced points across the remaining scale are suggested to
verify linearity) by decreasing FCO or increasing FD. Be sure the
total flow exceeds the analyzer's total flow demand. For each
concentration generated, calculate the exact CO concentration using
equation (2). Record the concentration and the analyzer's stable
response for each concentration. Plot the analyzer responses
(vertical or y-axis) versus the corresponding CO concentrations
(horizontal or x-axis). Calculate the linear regression slope and
intercept of the calibration curve and verify that no point deviates
from this line by more than 2 percent of the highest concentration
tested.
    4.5 Procedure Using the Multiple-Cylinder Method. Use the
procedure for the dilution method with the following changes:
    4.5.1 Use a multi-cylinder, dynamic calibration system such as
the typical one shown in Figure 2.
    4.5.2 The flowmeter need not be accurately calibrated, provided
the flow in the output manifold can be verified to exceed the
analyzer's flow demand.
    4.5.3 The various CO calibration concentrations required in
Steps 4.4.5, 4.4.6, and 4.4.7 are obtained without dilution by
selecting zero air or the appropriate certified standard cylinder.
    4.6 Frequency of Calibration. The frequency of calibration, as
well as the number of points necessary to establish the calibration
curve and the frequency of other performance checking, will vary by
analyzer. However, the minimum frequency, acceptance criteria, and
subsequent actions are specified in reference 1, appendix D,
``Measurement Quality Objectives and Validation Template for CO''
(page 5 of 30). The user's quality control program should provide
guidelines for initial establishment of these variables and for
subsequent alteration as operational experience is accumulated.
Manufacturers of CO analyzers should include in their instruction/
operation manuals information and guidance as to these variables and
on other matters of operation, calibration, routine maintenance, and
quality control.

5.0 Reference

    1. QA Handbook for Air Pollution Measurement Systems--Volume II.
Ambient Air Quality Monitoring Program. U.S. EPA. EPA-454/B-08-003
(2008).
BILLING CODE 6560-50-P
[GRAPHIC] [TIFF OMITTED] TR31AU11.003

[GRAPHIC] [TIFF OMITTED] TR31AU11.004

BILLING CODE 6560-50-C

PART 53--AMBIENT AIR QUALITY REFERENCE AND EQUIVALENT METHODS

0
3. The authority citation for part 53 continues to read as follows:

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

0
4. Subpart B of part 53 is revised to read as follows:
Subpart B--Procedures for Testing Performance Characteristics of
Automated Methods for SO2, CO, O3, and NO2
Sec.
53.20 General provisions.
53.21 Test conditions.
53.22 Generation of test atmospheres.
53.23 Test procedure.
Figure B-1 to Subpart B of Part 53--Example
Table B-1 to Subpart B of Part 53--Performance Limit Specifications
for Automated Methods
Table B-2 to Subpart B of Part 53--Test Atmospheres
Table B-3 to Subpart B of Part 53--Interferent Test Concentration, 1
Parts Per Million
Table B-4 to Subpart B of Part 53-- Line Voltage and Room
Temperature Test Conditions
Table B-5 to Subpart B of Part 53--Symbols and Abbreviations
Appendix A to Subpart B--Optional Forms for Reporting Test Results

Subpart B--Procedures for Testing Performance Characteristics of
Automated Methods for SO2, CO, O3, and NO2

Sec.  53.20  General provisions.

    (a) The test procedures given in this subpart shall be used to test
the performance of candidate automated methods against the performance
requirement specifications given in table B-1 to subpart B of part 53.
A test analyzer representative of the candidate automated method must
exhibit performance better than, or not outside, the specified limit or
limits for each such performance parameter specified (except range) to
satisfy the requirements of this subpart. Except as provided in
paragraph (b) of this section, the measurement range of the candidate
method must be the standard range specified in table B-1 to subpart B
of part 53 to satisfy the requirements of this subpart.
    (b) Measurement ranges. For a candidate method having more than one
selectable measurement range, one range must be the standard range
specified in table B-1 to subpart B of part 53, and a test analyzer
representative of the method must pass the tests required by this
subpart while operated in that range.
    (i) Higher ranges. The tests may be repeated for one or more higher
(broader) ranges (i.e., ranges extending to higher concentrations) than
the standard range specified in table B-1 to subpart B of part 53,
provided that the range does not extend to concentrations more than
four times the upper range limit of the standard range specified in
table B-1 to subpart B of part 53. For such higher ranges, only the
tests for range (calibration), noise at 80% of the upper range limit,
and lag, rise and fall time are required to be repeated. For the
purpose of testing a higher range, the test procedure of Sec.  53.23(e)
may be abridged to include only those components needed to test lag,
rise and fall time.
    (ii) Lower ranges. The tests may be repeated for one or more lower
(narrower) ranges (i.e., ones extending to lower concentrations) than
the standard range specified in table B-1 to subpart B of part 53. For
methods for some pollutants, table B-1 to subpart B of part 53
specifies special performance limit requirements for lower ranges. If
special low-range performance limit requirements are not specified in
table B-1 to subpart B of part 53, then the performance limit
requirements for the standard range apply. For lower ranges for any
method, only the tests for range (calibration), noise at 0% of the

measurement range, lower detectable limit, (and nitric oxide
interference for SO2 UVF methods) are required to be
repeated, provided the tests for the standard range shows the
applicable limit specifications are met for the other test parameters.
    (iii) If the tests are conducted and passed only for the specified
standard range, any FRM or FEM determination with respect to the method
will be limited to that range. If the tests are passed for both the
specified range and one or more higher or lower ranges, any such
determination will include the additional higher or lower range(s) as
well as the specified standard range. Appropriate test data shall be
submitted for each range sought to be included in a FRM or FEM method
determination under this paragraph (b).
    (c) For each performance parameter (except range), the test
procedure shall be initially repeated seven (7) times to yield 7 test
results. Each result shall be compared with the corresponding
performance limit specification in table B-1 to subpart B of part 53; a
value higher than or outside the specified limit or limits constitutes
a failure. These 7 results for each parameter shall be interpreted as
follows:
    (1) Zero (0) failures: The candidate method passes the test for the
performance parameter.
    (2) Three (3) or more failures: The candidate method fails the test
for the performance parameter.
    (3) One (1) or two (2) failures: Repeat the test procedures for the
performance parameter eight (8) additional times yielding a total of
fifteen (15) test results. The combined total of 15 test results shall
then be interpreted as follows:
    (i) One (1) or two (2) failures: The candidate method passes the
test for the performance parameter.
    (ii) Three (3) or more failures: The candidate method fails the
test for the performance parameter.
    (d) The tests for zero drift, span drift, lag time, rise time, fall
time, and precision shall be carried out in a single integrated
procedure conducted at various line voltages and ambient temperatures
specified in Sec.  53.23(e). A temperature-controlled environmental
test chamber large enough to contain the test analyzer is recommended
for this test. The tests for noise, lower detectable limit, and
interference equivalent shall be conducted at any ambient temperature
between 20 [deg]C and 30 [deg]C, at any normal line voltage between 105
and 125 volts, and shall be conducted such that not more than three (3)
test results for each parameter are obtained in any 24-hour period.
    (e) If necessary, all measurement response readings to be recorded
shall be converted to concentration units or adjusted according to the
calibration curve constructed in accordance with Sec.  53.21(b).
    (f) All recorder chart tracings (or equivalent data plots),
records, test data and other documentation obtained from or pertinent
to these tests shall be identified, dated, signed by the analyst
performing the test, and submitted.

    Note to Sec.  53.20: Suggested formats for reporting the test
results and calculations are provided in Figures B-2, B-3, B-4, B-5,
and B-6 in appendix A to this subpart. Symbols and abbreviations
used in this subpart are listed in table B-5 of appendix A to this
subpart.

Sec.  53.21  Test conditions.

    (a) Set-up and start-up of the test analyzer shall be in strict
accordance with the operating instructions specified in the manual
referred to in Sec.  53.4(b)(3). Allow adequate warm-up or
stabilization time as indicated in the operating instructions before
beginning the tests. The test procedures assume that the test analyzer
has a conventional analog measurement signal output that is connected
to a suitable strip chart recorder of the servo, null-balance type.
This recorder shall have a chart width of at least 25 centimeters,
chart speeds up to 10 cm per hour, a response time of 1 second or less,
a deadband of not more than 0.25 percent of full scale, and capability
either of reading measurements at least 5 percent below zero or of
offsetting the zero by at least 5 percent. If the test analyzer does
not have an analog signal output, or if a digital or other type of
measurement data output is used for the tests, an alternative
measurement data recording device (or devices) may be used for
recording the test data, provided that the device is reasonably suited
to the nature and purposes of the tests, and an analog representation
of the analyzer measurements for each test can be plotted or otherwise
generated that is reasonably similar to the analog measurement
recordings that would be produced by a conventional chart recorder
connected to a conventional analog signal output.
    (b) Calibration of the test analyzer shall be carried out prior to
conducting the tests described in this subpart. The calibration shall
be as indicated in the manual referred to in Sec.  53.4(b)(3) and as
follows: If the chart recorder or alternative data recorder does not
have below zero capability, adjust either the controls of the test
analyzer or the chart or data recorder to obtain a +5% offset zero
reading on the recorder chart to facilitate observing negative response
or drift. If the candidate method is not capable of negative response,
the test analyzer (not the data recorder) shall be operated with a
similar offset zero. Construct and submit a calibration curve showing a
plot of recorder scale readings or other measurement output readings
(vertical or y-axis) against pollutant concentrations presented to the
analyzer for measurement (horizontal or x-axis). If applicable, a plot
of base analog output units (volts, millivolts, milliamps, etc.)
against pollutant concentrations shall also be obtained and submitted.
All such calibration plots shall consist of at least seven (7)
approximately equally spaced, identifiable points, including 0 and 90
 5 percent of the upper range limit (URL).
    (c) Once the test analyzer has been set up and calibrated and the
tests started, manual adjustment or normal periodic maintenance is
permitted only every 3 days. Automatic adjustments which the test
analyzer performs by itself are permitted at any time. The submitted
records shall show clearly when any manual adjustment or periodic
maintenance was made during the tests and describe the specific
operations performed.
    (d) If the test analyzer should malfunction during any of the
performance tests, the tests for that parameter shall be repeated. A
detailed explanation of the malfunction, remedial action taken, and
whether recalibration was necessary (along with all pertinent records
and charts) shall be submitted. If more than one malfunction occurs,
all performance test procedures for all parameters shall be repeated.
    (e) Tests for all performance parameters shall be completed on the
same test analyzer; however, use of multiple test analyzers to
accelerate testing is permissible for testing additional ranges of a
multi-range candidate method.

Sec.  53.22  Generation of test atmospheres.

    (a) Table B-2 to subpart B of part 53 specifies preferred methods
for generating test atmospheres and suggested methods of verifying
their concentrations. Only one means of establishing the concentration
of a test atmosphere is normally required, provided that that means is
adequately accurate and credible. If the method of generation can
produce accurate, reproducible concentrations, verification is
optional. If the method of generation is not reproducible or reasonably