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 longterm 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, “nearroad” 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, nearroad 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 nearroad 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.