 United States Court of Appeals
         FOR THE DISTRICT OF COLUMBIA CIRCUIT



Argued February 20, 2014               Decided May 9, 2014

                       No. 13-1069

       NATIONAL ASSOCIATION OF MANUFACTURERS,
                     PETITIONER

                             v.

     ENVIRONMENTAL PROTECTION AGENCY AND GINA
          MCCARTHY, ADMINISTRATOR, EPA,
                   RESPONDENTS

           AMERICAN LUNG ASSOCIATION, ET AL.,
                     INTERVENORS


                Consolidated with 13-1071


       On Petitions for Review of Final Rule of the
      United States Environmental Protection Agency


    William L. Wehrum Jr. argued the cause for petitioner.
With him on the briefs were Andrea Bear Field, Allison D.
Wood, Lucinda Minton Langworthy, Roger R. Martella Jr.,
Timothy K. Webster, Joel F. Visser, Rachel L. Brand, Sheldon
Gilbert, and Quentin Riegel.

    Eric G. Hostetler, Attorney, U.S. Department of Justice,
argued the cause for respondents. With him on the brief were
                               2
Robert G. Dreher, Acting Assistant Attorney General, and
John T. Hannon, Steven E. Silverman, David P.W. Orlin,
Brian L. Doster, Geoffrey L. Wilcox, Attorneys, U.S.
Environmental Protection Agency.

    Peter Zalzal, John D. Walke, Nicholas Morales, and
David S. Baron were on the brief for intervenors
Environmental Defense Fund, et al. in support of respondents.

    Before: TATEL, BROWN, and KAVANAUGH, Circuit
Judges.

    Opinion    for   the   Court   filed   by   Circuit   Judge
KAVANAUGH.

    KAVANAUGH, Circuit Judge: In 2013, EPA tightened the
primary National Ambient Air Quality Standards, or NAAQS,
for fine particulate matter. The National Association of
Manufacturers and other industry groups challenge that
decision. Consistent with the general principle that the Clean
Air Act gives EPA substantial discretion in setting the
NAAQS, we deny the petitions for review.

                               I

      The Clean Air Act requires EPA to establish National
Ambient Air Quality Standards for six common air pollutants.
42 U.S.C. §§ 7408(a)(1), 7409(a)-(b). Each NAAQS consists
of four components: (i) the “indicator,” or regulated pollutant;
(ii) the “level,” or allowable concentration of the pollutant;
(iii) the “averaging time,” which is the time period over which
pollutant concentration measurements are averaged; and (iv)
the “form,” which refers to the way that compliance with the
level will be determined within the averaging time (for
example, that the level not be exceeded more than once per
                               3
year). See American Farm Bureau Federation v. EPA, 559
F.3d 512, 516 (D.C. Cir. 2009). “Primary” NAAQS – the
standards at issue in this case – must be set at a level that EPA
determines is “requisite to protect the public health” with “an
adequate margin of safety.” 42 U.S.C. § 7409(b)(1). The
Supreme Court has interpreted “requisite” to mean “sufficient,
but not more than necessary.” Whitman v. American Trucking
Associations, Inc., 531 U.S. 457, 473 (2001) (internal
quotation mark omitted). After EPA establishes the NAAQS,
the States assume primary responsibility for implementing
and enforcing the standards. See 42 U.S.C. § 7407(a). 1

     To ensure that the NAAQS take account of current
science, the Clean Air Act directs EPA to review the
standards at least once every five years. See id. § 7409(d).

     One pollutant regulated under the NAAQS program is
particulate matter. The term “particulate matter” is a
shorthand for a variety of substances that form particles in the
ambient air. So-called “fine particles” – the kind of
particulate pollution at issue in this case – are produced
mainly by automobiles and power plants. See American Farm
Bureau Federation, 559 F.3d at 515.

     In 1971, EPA first set NAAQS for particulate matter.
Several times since then, the agency has considered whether
to revise those standards. See id. at 516-17. The most recent
revision process began in 2007. By 2013, both EPA and the
Clean Air Scientific Advisory Committee ultimately
determined that the then-existing standards for particulate
matter were not sufficiently protective of public health, based

    1
        Under the NAAQS program, EPA also establishes a
“secondary” set of standards “requisite to protect the public
welfare.” 42 U.S.C. § 7409(b)(2). The secondary NAAQS are not
at issue in this case.
                               4
on an “increased confidence in the association between
exposure” to particulate matter and “serious public health
effects.” National Ambient Air Quality Standards for
Particulate Matter, 78 Fed. Reg. 3086, 3120 (Jan. 15, 2013).
In reaching that conclusion, EPA explained that several key
epidemiological studies had reported statistically significant
associations between adverse health effects and particulate
matter exposure at concentrations between 12.8 and 14.8
μg/m3. See id. at 3106-08, 3135 Fig. 4. In 2013, EPA
therefore issued a Final Rule revising the level of the annual
standard for particulate matter emissions from 15.0 μg/m3 to
12.0 μg/m3, a level slightly lower than the lowest
concentrations reported as causing adverse health effects in
the epidemiological studies analyzed by EPA. See id. at
3162-64.

    EPA’s Final Rule also revised the form of the standard to
eliminate a provision that had allowed certain areas to
demonstrate compliance based on the averaged results from
multiple monitoring sites. EPA reasoned that the averaging
provision, called “spatial averaging,” could result in a
standard that was not sufficiently protective of sensitive
individuals living in areas with high particulate matter
concentrations. See id. at 3124-26.

    Finally, EPA amended regulations regarding the monitors
used to measure concentrations of particulate matter in the air.
The amended regulations require the installation of additional
monitors near heavily trafficked roads in urban areas where
more than 1 million people live. See id. at 3238-41.

    Petitioners here challenge EPA’s Final Rule pursuant to
Section 307(b)(1) of the Clean Air Act. See 42 U.S.C.
§ 7607(b)(1), 7607(d)(9). Citing the arbitrary and capricious
standard of review, petitioners argue that EPA’s revisions to
                              5
the level and form of the particulate matter NAAQS were
unreasonable. Petitioners also contend that EPA acted
unreasonably by amending the monitoring network
provisions.    Petitioners further assert that EPA acted
unreasonably by promulgating the Final Rule without first
issuing certain implementation documents that petitioners
contend are necessary to enable compliance with the Rule.
We address those arguments in turn.

                              II

     In the 2013 Rule, EPA lowered the level of the
particulate matter NAAQS from 15.0 μg/m3 to 12.0 μg/m3.
EPA did so after it considered a broad array of scientific
sources, as well as the views of EPA staff and the Clean Air
Scientific Advisory Committee. See 78 Fed. Reg. at 3106-21;
Letter from Dr. Jonathan M. Samet, Chair, Clean Air
Scientific Advisory Committee, to Lisa P. Jackson, EPA
Administrator i-ii (Sept. 10, 2010). EPA selected the 12.0
μg/m3 level because it was somewhat below the lowest long-
term mean concentration shown by certain key epidemiologic
studies to cause adverse health effects. See 78 Fed. Reg. at
3158-59, 3161. EPA followed a similar approach in earlier
particulate matter NAAQS revisions, and we upheld those
EPA decisions. See American Farm Bureau Federation v.
EPA, 559 F.3d 512, 526-27 (D.C. Cir. 2009) (EPA
“reasonably decided to address long-term exposure with an
annual standard somewhat below the long-term mean
concentrations in the ACS and Six Cities studies”); American
Trucking Associations, Inc. v. EPA, 283 F.3d 355, 372 (D.C.
Cir. 2002) (upholding particulate matter NAAQS where “EPA
ultimately set the standard just below the range of mean
annual [particulate matter] concentrations observed in studies
showing a statistically significant association between fine
particulate matter and health effects”).
                               6
    Petitioners raise several arguments about EPA’s decision.

     First, petitioners assert that EPA “prejudged” the
outcome of the review process by failing to request comment
on whether to revise the NAAQS at all. Although it is true
that EPA did not specifically ask for comments on whether
revision was necessary, the preamble to EPA’s Notice of
Proposed Rulemaking requested comments on “all issues”
related to the agency’s proposal to lower the level of the
particulate matter NAAQS. See National Ambient Air
Quality Standards for Particulate Matter, 77 Fed. Reg. 38,890,
38,899 (June 29, 2012). That broad request necessarily
encompassed the question of whether any revision of the
particulate matter NAAQS was warranted. Moreover, when
EPA requested comments on how to revise the NAAQS,
regulated entities could have responded by disputing the
premise that revisions were required in the first place. Indeed,
some petitioners did just that by submitting comments
advocating retention of the 2006 NAAQS. See Comments of
Utility Air Regulatory Group at 7-8 (Aug. 31, 2012). EPA’s
notice sufficed.

     Second, petitioners challenge EPA’s weighing of the
scientific evidence. Among other things, petitioners argue
that EPA applied inconsistent peer-review standards and
afforded disproportionate weight to certain studies finding
statistically significant associations between particulate matter
exposure and adverse health effects. Under the arbitrary and
capricious standard, we exercise great deference when we
evaluate claims about competing bodies of scientific research.
See City of Waukesha v. EPA, 320 F.3d 228, 247 (D.C. Cir.
2003). Here, we can be brief: Petitioners simply have not
identified any way in which EPA jumped the rails of
reasonableness in examining the science. EPA offered
reasoned explanations for how it approached and weighed the
                               7
evidence, and why the scientific evidence supported revision
of the NAAQS.

    Third, according to petitioners, EPA did not respond when
petitioners’ comments cited certain studies that supported
retention of the existing particulate matter NAAQS. EPA
admittedly did not directly address every study that petitioners
cited to the agency. But our precedents do not require as
much, and EPA acted within its discretion in this case in
addressing the more significant comments. See Northside
Sanitary Landfill, Inc. v. Thomas, 849 F.2d 1516, 1519 (D.C.
Cir. 1988) (“Comments must be significant enough to step
over a threshold requirement of materiality before any lack of
agency response or consideration becomes of concern.”)
(alteration omitted); see also City of Waukesha, 320 F.3d at
257 (an agency “need not address every comment”) (internal
quotation mark omitted).

                              III

    In the Final Rule, EPA also amended the form of the
particulate matter standard by eliminating “spatial averaging.”
Citing the arbitrary and capricious standard, petitioners
challenge EPA’s decision as unreasonable.

    With spatial averaging, certain areas can demonstrate
compliance with emission standards by averaging results from
multiple monitoring sites within that area. In 1997, EPA first
adopted spatial averaging in the particulate matter NAAQS.
See National Ambient Air Quality Standards for Particulate
Matter, 62 Fed. Reg. 38,652, 38,671-72 (July 18, 1997). In
the 2006 NAAQS, EPA retained spatial averaging, but the
agency restricted the circumstances under which spatial
averaging could be used due to concerns that spatial
averaging might allow greater exposures for sensitive
populations. See National Ambient Air Quality Standards for
                              8
Particulate Matter, 71 Fed. Reg. 61,144, 61,165-67 (Oct. 17,
2006). In the 2013 NAAQS, EPA eliminated spatial
averaging altogether. See 78 Fed. Reg. at 3124-27.

    Petitioners contend that EPA acted unreasonably by
eliminating spatial averaging. Their claim rests on EPA’s
supposed failure to explain empirically why the constraints
imposed on spatial averaging in the 2006 NAAQS no longer
sufficed to protect against exposure hazards. That argument
misunderstands the nature of our review. For example, when
EPA revises the level of the NAAQS, this Court does “not ask
why the prior NAAQS once was ‘requisite’ but is no longer
up to the task.” Mississippi v. EPA, 744 F.3d 1334, 1343
(D.C. Cir. 2013). Rather, the only inquiry is “whether EPA’s
proposed NAAQS is ‘requisite.’” Id. In other words, we do
not assign “presumptive validity” to the prior NAAQS; the
question is whether EPA reasonably explains the current
standards. Id. So it is with the form of the standards as well.

    EPA here fulfilled its obligation to reasonably explain its
decision not to employ spatial averaging. As the agency
stated, spatial averaging would enable some portions of a
compliance area – particularly those areas where sensitive
individuals are likely to live – to exceed the NAAQS for
periods of time. See 78 Fed. Reg. at 3124-27. EPA
reasonably concluded that allowing those excess emissions
under all the circumstances here was inconsistent with EPA’s
goal of ensuring that the NAAQS provide requisite protection
for all individuals. Id.; see also id. at 3168.

                              IV

     Petitioners also challenge EPA’s new requirement that
States place monitors near heavily trafficked roads in large
metropolitan areas.
                               9
     Under the NAAQS program, States must develop and
operate (subject to EPA approval) monitoring networks to
measure concentrations of the six NAAQS pollutants in the
air. See 42 U.S.C. §§ 7619, 7410(a)(2)(B); 40 C.F.R. pt. 58.
EPA uses the data from those networks for several purposes,
including for research and for determining compliance with
air quality standards.

     As part of the review process for the 2013 particulate
matter NAAQS revision, EPA proposed adding a new, “near-
road” component to the particulate matter monitoring network
to “better understand the potential health impacts” of
particulate matter exposures around heavily traveled roads.
77 Fed. Reg. at 39,009. In the Final Rule, EPA adopted that
approach, concluding that requiring “a modest network” of
near-road compliance particulate matter monitors “is
necessary . . . including for comparison to the NAAQS.” 78
Fed. Reg. at 3238. The Rule requires approximately 50 new
monitors to be installed near heavily traveled roads in large
metropolitan areas. Id. at 3238-41.

     Petitioners challenge that decision on substantive and
procedural grounds. On the substantive side, petitioners
contend that near-road monitoring will make the NAAQS for
particulate matter overly stringent. As petitioners see it, near-
road monitoring will generate data from areas with
unrepresentatively high particulate matter concentrations.
EPA responds that the goal here was to ensure that the
NAAQS represent real-world conditions. The point of the
NAAQS program is to safeguard the quality of the “ambient
air,” which is defined as the “portion of the atmosphere,
external to buildings, to which the general public has access.”
42 U.S.C. § 7409(a); 40 C.F.R. § 50.1(e). That definition
obviously includes near-road areas.           Therefore, EPA
explained that monitoring near-road areas – and not just non-
                              10
near-road areas – was important in order to obtain an
accurate, area-wide picture of ambient air quality. It stated:
“Ignoring monitoring results from [near-road] areas (or not
monitoring at all) would abdicate this responsibility. Put
another way, monitoring in such areas does not make the
standard more stringent, but rather affords requisite protection
to the populations, among them at-risk populations, exposed
to fine particulate in these areas.” 78 Fed. Reg. at 3240.

     In the context of this statutory scheme that grants EPA
substantial discretion, EPA’s decision and explanation are at
least reasonable.

     On the procedural side, petitioners maintain that EPA did
not afford them an opportunity to comment generally on near-
road monitoring, and specifically on EPA’s decision to use
near-road data for compliance purposes, not simply for
research. But EPA’s proposal mentioned using near-road
monitors for many purposes, including “collection of NAAQS
comparable data” – in other words, to assess compliance. 77
Fed. Reg. at 39,009. That statement sufficed to put regulated
entities on notice regarding the possible uses of near-road
data. Petitioners themselves had no problem understanding
the scope of the issues up for consideration; several
petitioners submitted comments opposing the use of near-road
monitors for compliance purposes. See, e.g., Comments of
Utility Air Regulatory Group at 54-55 (Aug. 31, 2012)
(“[B]ecause reliance on near-road monitors to judge
compliance would be unreasonable, the Agency does not have
an adequate basis to require states to incur the cost to install
and operate them.”).

    Petitioners also suggest that EPA improperly relied on
data from a Census Bureau study without providing
opportunity to comment on the study. Petitioners have filed a
                             11
petition for reconsideration with EPA raising their objections
on that issue. We therefore do not address that challenge at
this time. See Utility Air Regulatory Group v. EPA, 744 F.3d
741, 746-47 (D.C. Cir. 2014).

                              V

     Finally, petitioners argue that EPA should not have
issued, or at least should not require compliance with, the
2013 NAAQS without first providing States and regulated
parties certain implementation guidance. We disagree. The
NAAQS sets a clear numerical target specifying the
maximum levels of emissions in the States. Under the law,
States will devise implementation plans to meet that target.
Nothing in the law dictates additional guidance from EPA at
this point.

                            ***

    We have considered all of petitioners’ arguments. We
deny the petitions for review.

                                                  So ordered.
