United States Court of Appeals

FOR THE DISTRICT OF COLUMBIA CIRCUIT

Argued February 21, 2012 Decided July 17, 2012

No. 10-1079

AMERICAN PETROLEUM INSTITUTE AND UTILITY AIR 

REGULATORY GROUP,

PETITIONERS

v.

ENVIRONMENTAL PROTECTION AGENCY,

RESPONDENT

NATURAL RESOURCES DEFENSE COUNCIL,

INTERVENOR

Consolidated with 10-1080

On Petitions for Review of Final Action 

of the Environmental Protection Agency

Allison D. Wood argued the cause for petitioner 

American Petroleum Institute. William Pedersen argued the 

cause for petitioner Interstate Natural Gas Association of 

America. With them on the briefs was Lucinda Minton 

Langworthy. Joan Dreskin, Timm L. Abendroth, Daniel J. 

Regan Jr., and Janice K. Raburn entered appearances.
2

Norman L. Rave Jr., U.S. Department of Justice, argued 

the cause for respondent. On the brief was Angeline Purdy, 

Attorney. Michael Augustini, Attorney, entered an 

appearance.

Abigail M. Dillen, Colin O’Brien, John Walke, and 

Adrian Martinez were on the brief for intervenor Natural 

Resources Defense Council in support of respondent.

Before: ROGERS, Circuit Judge, and EDWARDS and 

GINSBURG, Senior Circuit Judges.

Opinion for the Court filed by Senior Circuit Judge 

GINSBURG.

GINSBURG, Senior Circuit Judge: In 2010, the EPA 

promulgated a final rule adopting a new, one-hour primary 

national ambient air quality standard (NAAQS) for nitrogen 

dioxide. The American Petroleum Institute, the Utility Air 

Regulatory Group, and the Interstate Natural Gas Association 

of America (collectively the API) petition for review of that 

rule, claiming the EPA, in adopting the NAAQS, was 

arbitrary and capricious and violated the Clean Air Act. The 

API also challenges a statement in the preamble to the final 

rule regarding the EPA’s intended implementation of the 

NAAQS. We deny the petitions insofar as they challenge the 

EPA’s adoption of the NAAQS, but because the EPA’s 

statement in the preamble was not final, we lack jurisdiction 

to consider those portions of the petitions.

I. Background

The Clean Air Act requires the EPA to establish a 

primary and a secondary NAAQS for any pollutant 

“reasonably ... anticipated to endanger public health or 
3

welfare.” 42 U.S.C. § 7408(a)(1)(A). The EPA must set the

primary NAAQS at a level “requisite to protect the public 

health” with “an adequate margin of safety.” 42 U.S.C. § 

7409(b)(1).

In 1971, in order to control the emission of harmful 

nitrogen oxides,

* the EPA established a primary NAAQS for 

nitrogen dioxide (NO2) of 53 parts per billion (ppb) for the 

annual average in any given area. See National Primary and 

Secondary Ambient Air Quality Standards, 36 Fed. Reg. 

8186, 8187 (April 30, 1971). Then as now the NAAQS 

focused specifically upon NO2 as an indicator for the broader 

category of nitrogen oxides; because those gases are typically

emitted together and in similar proportions, detection of one 

usually indicates the presence of the others. Combustion 

processes, especially those occurring in automobile and truck 

engines and electricity-generating plants, account for most of 

the production of these compounds. Nitrogen oxides have a 

variety of documented adverse effects upon human health, 

including increased airway hyperresponsiveness (contraction 

of the bronchioles) in asthmatics and increased respiratory 

illness in children.

The EPA began a review of the NAAQS for NO2 in 2005 

and revised the primary NAAQS in 2010. In the time since 

its prior review, accumulated epidemiological and clinical 

evidence suggested adverse health effects occurred at lower 

concentrations of NO2, and for exposures of a much shorter 

duration, than scientists previously had suspected. For that 

reason, the EPA began to consider whether, because the 

 * The EPA defines this class broadly to include “all forms of 

oxidized nitrogen (N) compounds.” ENVIRONMENTAL PROTECTION 

AGENCY, INTEGRATED SCIENCE ASSESSMENT FOR OXIDES OF 

NITROGEN – HEALTH CRITERIA 2:1 (2008).
4

existing NAAQS focused upon the annual average 

concentration in an area, an additional NAAQS was necessary 

to protect against the adverse effects of short-term spikes in

exposure to NO2. In 2005, the EPA made a general call for 

information, 70 Fed. Reg. 73,236 (Dec. 9, 2005), and in 2007, 

after notice and comment, it published the methodology it 

would use to review the NAAQS for NO2, see EPA, 

INTEGRATED REVIEW PLAN FOR THE PRIMARY NATIONAL 

AMBIENT AIR QUALITY STANDARD FOR NITROGEN DIOXIDE

(Aug. 2007). The Review Plan described the EPA’s plans to 

synthesize the results of existing epidemiological and clinical 

research regarding the health effects of exposure to NO2, 

develop forecasts of improved air quality under a hypothetical 

new NAAQS set at various levels then under consideration, 

submit such analyses for external review, and after public 

notice and comment adopt a new NAAQS. Id. at 2–3.

In 2008, pursuant to the Review Plan, the EPA released

its Integrated Science Assessment, in which it undertook “to 

critically evaluate and assess the latest scientific information 

published since [the review it conducted in 1993].” 

ENVIRONMENTAL PROTECTION AGENCY, INTEGRATED 

SCIENCE ASSESSMENT FOR OXIDES OF NITROGEN – HEALTH 

CRITERIA xxvii (2008) (hereinafter ISA). The ISA discussed

epidemiological evidence that showed “positive associations 

of short-term ambient NO2 concentrations below the current 

NAAQS level with increased numbers of [emergency room]

visits and hospital admissions for respiratory causes.” Id. at 

5:11. Many studies observed such effects in areas with 

average daily concentrations of NO2 between 3 and 50 ppb. 

Id. The EPA also presented its updated version of a metaanalysis*

 * A meta-analysis synthesizes the results of multiple studies by 

performing statistical analyses of the results of those studies.

of clinical studies on the health effects of NO2 that 
5

had been done by L.J. Folinsbee in 1992 and that it had 

reviewed in its earlier assessment of the NAAQS. Id. at 3:14–

16. The agency made three changes to the 1992 metaanalysis: It removed one underlying study involving specific 

airway responses to ragweed, added a new study involving 

non-specific airway responses, and measured the effects at 

short-term concentration levels as low as 100 ppb. Id. at 3:16. 

The results of the updated meta-analysis showed a statistically 

significant 66 percent of resting asthmatics experienced an 

increase in hyperresponsiveness in the presence of NO2

concentrations of 100 ppb. Id. The results did not, however, 

reveal a dose-response relationship – one in which the 

measured health effect, here the proportion of asthmatics 

experiencing hyperresponsiveness, increases due to an 

increased concentration or dose of some agent, here NO2 –

which would have provided a stronger indication that shortterm exposure to NO2 causes hyperresponsiveness in 

asthmatics. Indeed, at levels of 200-300 ppb and over 300 

ppb still about 60 percent of asthmatics experienced 

hyperresponsiveness. Id. Considering the various clinical 

and epidemiological studies together, however, the EPA 

concluded the evidence was “sufficient to infer a causal 

relationship” between short-term exposure to NO2 at levels as 

low as 100 ppb and various types of respiratory morbidity; it 

also concluded the data were “suggestive but not sufficient to 

infer a causal relationship” between short-term exposures and 

mortality. Id. at 5:5.

The EPA also assessed risks from NO2 exposure under 

three different assumptions about future air quality: (1) future 

air quality remains at its current level (the “as is” assumption)

(2) future air quality just meets the existing NAAQS of 53 

ppb (the “just meets” assumption), and (3) future air quality 

just meets several different potential hourly NAAQS, to wit,

50, 100, 150, and 200 ppb (the “new NAAQS” assumption). 
6

See EPA, RISK AND EXPOSURE ASSESSMENT TO SUPPORT THE 

REVIEW OF THE NO2 PRIMARY NATIONAL AMBIENT AIR 

QUALITY STANDARD 59, 120 (Nov. 2008) (hereinafter REA). 

The EPA explained that, although it had few actual data 

showing any areas experienced short-term exposures above 

the levels of the NAAQS under consideration in the third 

scenario, REA at 89–95, its simulation procedure showed that 

at the current level of air quality, people near roads are now 

and would be in the future exposed numerous times in a year 

to concentrations above 100 ppb (the short-term exposure 

level at which the ISA concluded adverse health effects were 

likely to occur), REA at 97–99. The number of such 

exposures would rise dramatically under an alternate scenario 

in which each area was forecasted to just meet the existing 

annual standard. Id. at 144. The agency’s projections 

indicated a one-hour standard (defined by the 3-year average 

of the 98th percentile of hourly values) of 100 ppb measured 

area-wide would improve upon the “just meets” but not upon 

the “as is” scenario; a one-hour standard of 50 ppb would 

improve upon the “as is” scenario. Id.

The EPA submitted both the ISA and the REA to the 

Clean Air Scientific Advisory Committee (CASAC) for 

review, as required by the Clean Air Act, 42 U.S.C. 

7409(d)(2)(A). The CASAC agreed with the EPA’s 

assessment that the current annual NAAQS was not adequate 

to protect human health, and it suggested the agency adopt a 

one-hour standard for NO2 of no greater than 100 ppb.

In 2009 the EPA proposed to set a new hourly NAAQS 

with allowable maximum concentration levels between 80 

and 100 ppb. 74 Fed. Reg. 34,404 (July 15, 2009). The 

petitioners each submitted comments criticizing the EPA for 

proposing a revision to the NAAQS based upon an 

unpublished study, i.e., the updated meta-analysis, and for 
7

discounting a published and peer-reviewed study that did not 

conclude exposures to NO2 at 100 ppb caused a measureable

adverse health effect. They also expressed skepticism about

the EPA’s interpretation of the epidemiological evidence, 

questioned the assumptions built into the forecasts in the 

REA, and pointed out the proposed rule provided no guidance 

as to how a permit applicant for a new or modified source of 

NO2 pollution should demonstrate compliance with the new 

NAAQS.

In its Final Rule, the EPA adopted a new one-hour 

primary NAAQS, requiring in effect that “the three-year 

average of the annual 98th percentile of the daily maximum 1-

hour average concentration [be] less than or equal to 100 

ppb.” Primary National Ambient Air Quality Standards for 

Nitrogen Dioxide, 75 Fed. Reg. 6474, 6531 (Feb. 9, 2010)

(codified at 40 C.F.R. § 50.11(f)). The EPA concluded this 

standard was needed “to provide protection for asthmatics and 

other at-risk populations against an array of adverse 

respiratory health effects related to short-term NO2 exposure.” 

Id. at 6502.

II. Analysis

The API petitioned for review of the Final Rule under 42 

U.S.C. § 7607(b), which gives this court exclusive jurisdiction 

to hear a challenge to a NAAQS. We review the EPA’s 

setting of a NAAQS to determine whether it was “arbitrary, 

capricious, an abuse of discretion, or otherwise not in 

accordance with law.” 42 U.S.C. § 7607(d)(9)(A); see also 5 

U.S.C. § 706(2)(A). According to the API, the EPA was 

arbitrary and capricious in how it dealt with the record 

evidence and the NAAQS it adopted is unlawful because 

more stringent than “requisite to protect the public health” 

with “an adequate margin of safety,” 42 U.S.C. § 7409(b)(1). 
8

In addition, the API argues the EPA’s implementation of the 

NAAQS was arbitrary and capricious because, when the EPA 

stated a permit applicant for a new or modified source of 

pollution must demonstrate compliance with the new 

NAAQS, the agency – or so the API asserts – did not consider 

whether it would be able to resolve applications within the 

statutorily required time period or what effect such a 

requirement might have upon economic growth.

 

A. The EPA’s Adoption of the One Hour NAAQS

The API claims the process by which the EPA adopted 

the new NAAQS was flawed and the standard must therefore 

be vacated. More specifically, it faults the EPA for (1) 

relying upon an unpublished, non-peer-reviewed metaanalysis of clinical studies, (2) discounting a published metaanalysis that called into question the EPA’s conclusions, (3)

treating the same epidemiological study differently in reviews 

of the NAAQS for NO2 and for ozone, and (4) projecting the 

benefits to air quality from the new NAAQS based upon

faulty assumptions.

1. Peer Review of the Meta-Analysis

The API first contends the EPA, by relying upon an 

internal meta-analysis that was not published, “did not follow 

its own requirements ... that it rely only on peer-reviewed and

published studies in reviewing NAAQS.” Pet. Br. at 26. 

Perhaps the API should have had its brief peer-reviewed. In 

quoting the EPA’s Review Plan, see Pet. Br. at 28, the API

omits the first and most relevant word of the following 

sentence: “Generally, only information that has undergone 

scientific peer review and that has been published (or 

accepted for publication) in the open literature will be 

considered,” Review Plan at 11; see also ISA Annexes at 1:1. 
9

Of course, “generally” here indicates the practice in question

will not invariably be followed, see Kurke v. Oscar Gruss and 

Son, Inc., 454 F.3d 350, 355–56 (D.C. Cir. 2006) (“as ... the 

word ‘generally’ suggests, there are exceptions to the rule”); 

Bernhardt v. City & Suburban Ry. Co., 263 F. 1009, 1015 

(D.C. Cir. 1920) (“the word ‘generally’ ... indicates that there 

may be [exceptions to the stated rule]”). A bad start for the 

petitioners.

The API also points to guidelines the EPA promulgated 

pursuant to the Information Quality Act (IQA), Pub. L. 106-

554, § 515(b)(2)(A) (requiring each federal agency to issue 

guidelines “for ensuring and maximizing the quality, 

objectivity, utility, and integrity of information disseminated 

by the agency”), which it contends also require peer review. 

See EPA, GUIDELINES FOR ENSURING AND MAXIMIZING THE 

QUALITY, OBJECTIVITY, UTILITY, AND INTEGRITY OF 

INFORMATION DISSEMINATED BY THE ENVIRONMENTAL 

PROTECTION AGENCY (Oct. 2002). By their terms, however, 

the Guidelines provide only “non-binding policy and 

procedural guidance.” Id. at 4. Such a statement would not 

override a specific commitment made elsewhere in the 

document, see Appalachian Power Co. v. EPA, 208 F.3d 

1015, 1022–23 (D.C. Cir. 2000), but the petitioners point to 

none. In keeping with the Review Plan and the ISA, the

Guidelines also state that “major scientifically and technically 

based work products ... related to Agency decisions should be 

peer-reviewed.” Guidelines at 11. The use of the phrase

“should be” rather than “shall” suggests but does not 

necessarily mean the Guidelines are not binding. Compare 

Doe v. Hampton, 566 F.2d 265, 281 (D.C. Cir. 1977) (“that 

the provision in question employs the directory ‘should be’ 

rather than the mandatory ‘shall’ or ‘must’ ... should not be 

automatically determinative of the issue”), with Jolly v. 

Listerman, 672 F.2d 935, 945 (D.C. Cir. 1982) (“use of the 
10

word ‘should’ ... detracts significantly from any claim that 

this guideline is more than merely precatory”), and Military 

Toxics Project v. EPA, 146 F.3d 948, 958 (D.C. Cir. 1998) 

(accepting as permissible EPA’s interpretation of “word 

‘should’ ... as calling for an exercise of judgment and hence 

conferring discretion upon the Administrator”). More 

important, the Guidelines themselves expressly commit “the 

decision whether to employ peer review” to the discretion of 

agency management. Guidelines at 11. Finally, the 

Guidelines note the EPA’s Peer Review Handbook “provides 

detailed guidance for implementing” the agency’s peer review 

policy, id., and the Handbook in turn states specifically the 

relevant decision-makers “need[] to make a judgment” 

whether peer review is appropriate in a specific case because 

“[t]here is no easy single yes/no test,” EPA, PEER REVIEW 

HANDBOOK § 2.2.3 (2000). No doubt the EPA believes peer 

review is important and it intended to impress that value upon 

its staff, but the agency did not bind itself to a judicially 

enforceable norm.

We need not decide the extent, if any, to which an 

agency must account for any departure from a non-binding 

guideline, compare Sitka Sound Seafoods, Inc. v. NLRB, 206 

F.3d 1175, 1182 (D.C. Cir. 2000) (because manual was nonbinding, question was whether, apart from requirements of 

manual, agency acted reasonably), with Edison Elec. Inst. v. 

EPA, 391 F.3d 1267, 1269 & n.3 (D.C. Cir. 2004) (agency 

must account for departure from non-binding plan), because 

the EPA, contrary to the API’s claim, did not depart from its 

non-binding peer review policy. The EPA merely updated the 

Folinsbee meta-analysis, which was originally peer-reviewed 

and published; the only data it added to the meta-analysis 

were the results of a study that was itself peer-reviewed and 

published; and the CASAC peer-reviewed the results of the 

updated meta-analysis. See Peer Review Handbook § 2.4.3(d) 
11

(listing the CASAC among acceptable sources of external 

peer review); cf. City of Portland, Or. v. EPA, 507 F.3d 706, 

716 (D.C. Cir. 2007) (holding “advice from [EPA’s] Science 

Advisory Board [a group of outside scientists, similar to the 

CASAC, organized by the EPA to review its scientific 

analyses] ... [was an] acceptable form of peer review”). The 

EPA also relied upon epidemiological studies, as well as 

individual clinical studies underlying the meta-analysis that

had been published and peer-reviewed. The EPA’s staff 

conducting the review of the proposed NAAQS judged the 

CASAC’s review of the meta-analysis was sufficient, and the 

API has presented no reason for us to disturb that judgment.

2. Treatment of the Goodman Study

Next, the API argues the EPA inappropriately discounted 

the results of a published meta-analysis by Dr. Julie E. 

Goodman et al., Meta-Analysis of Nitrogen Dioxide Exposure 

and Airway Hyper-Responsiveness in Asthmatics, 39 CRIT.

REV. TOXICOLOGY 719 (2009). According to the API, the 

study suggests, contrary to the EPA’s findings, there is no 

causal relationship between an increase in ambient 

concentrations of NO2 and an increase in health effects, such 

as airway hyperresponsiveness in asthmatics. The EPA 

defends its treatment of the study as follows: The agency did 

not receive the study until after it had conducted the analyses 

described in the ISA and the REA and submitted them to the 

CASAC for review; it nevertheless considered the study but 

found its methodology wanting and therefore not a reason for 

reopening its review process.

An agency’s action is arbitrary and capricious if it 

“entirely failed to consider an important aspect of the problem 

[or] offered an explanation for its decision that runs counter to 

the evidence before the agency.” North Carolina v. EPA, 531 
12

F.3d 896, 906 (D.C. Cir. 2008) (quoting Motor Vehicle Mfrs. 

Ass’n v. State Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43 

(1983)). The API has not shown the EPA’s treatment of the 

Goodman study fell below these standards. 

First, the results of the Goodman study did not “run[] 

counter to the evidence before the agency,” North Carolina, 

531 F.3d at 906. Contrary to the API’s description, the study 

did not establish there was “no dose-response relationship”; it 

simply failed to reject the null hypothesis to that effect. That 

is, the authors could not tell whether there is no such 

relationship or their test merely lacked sufficient power to 

detect the relationship. See David H. Kaye & David A. 

Freedman, Reference Guide on Statistics, in REFERENCE 

MANUAL ON SCIENTIFIC EVIDENCE 211, 253–54 (Fed. Judicial 

Ctr. 3d ed. 2011), available at

http://www.fjc.gov/public/pdf.nsf/lookup/SciMan3D01.pdf/$f

ile/SciMan3D01.pdf. The Goodman study, moreover, did not 

test for the possibility of a non-linear dose-response 

relationship.

*

 See Goodman at 733. 

 * See Daniel L. Rubinfeld, Reference Guide on Multiple Regression, 

in REFERENCE MANUAL ON SCIENTIFIC EVIDENCE at 303, 316

(explaining "[f]ailure to account for nonlinearities [in the estimated 

equation] can lead to either overstatement or understatement of the 

effect of a change in the value of an explanatory variable on the 

dependent variable"). The underlying data in the EPA’s metaanalysis indeed suggest that roughly the same proportion of 

asthmatics, 58 to 66 percent, experience airway 

hyperresponsiveness whether exposed to levels of 100 ppb, 200 

ppb, or even 300 or more ppb. See ISA at 3:14–16. These results 

are consistent with a non-linear dose-response relationship that 

increases sharply at a low concentration of ambient NO2 and then 

flattens out as the dose nears a concentration of 100 ppb.
13

Second, because the EPA gave the specific reasons for 

which it disagreed with Goodman’s methodology, it did not 

“fail[] to consider” the study, nor did it fail to “offer[] an 

explanation” for not relying upon that study. North Carolina,

531 F.3d at 906. The EPA explained that it had decided not 

to focus upon detecting a dose-response relationship in its 

meta-analysis because differences in the assumptions made 

and in the methodologies used in the underlying studies 

would likely make it impossible to derive a reliable estimate. 

See Final Rule, 75 Fed. Reg. at 6487, 6498. The EPA did 

acknowledge the limitations inherent in its own study, noting 

“uncertainty with regard to the magnitude and [to] the 

clinical-significance of NO2-induced increases in airway 

responsiveness,” id. at 6488, but it explained the Clean Air 

Act requires the agency to promulgate a primary NAAQS to 

protect the public health even where, as here, the risks from 

the pollutant could not be quantified or “precisely identified 

as to nature or degree,” Am. Trucking Ass’ns v. EPA, 283 F.3d 

355, 369 (D.C. Cir. 2002) (internal quotation marks and 

citation omitted). The EPA was therefore justified in revising 

the NAAQS considering the evidence of a statistically 

significant relationship between relevant health conditions 

and NO2 exposure at various concentrations, even if the 

agency did not know the precise dose-response relationship 

between NO2 and airway responsiveness, among other health 

effects.

The API mistakenly places much weight upon our recent 

decision in Business Roundtable v. SEC, 647 F.3d 1144 (D.C. 

Cir. 2011). As the foregoing discussion makes clear, the 

EPA’s analysis of the proposed NAAQS was materially better 

than the analysis for which we faulted the SEC in that case. 

There the agency had ignored “numerous studies submitted by 

commenters that reached the opposite result” and relied 

instead upon “two relatively unpersuasive studies.” 647 F.3d 
14

at 1150–51. Putting aside the analytical incoherence of the 

SEC’s rationale, which would have been fatal by itself, the 

evidentiary problem in Business Roundtable was not limited 

to the agency’s insufficient treatment of any one study, 

though there was that, see id. at 1151; it was the agency’s 

larger failure to deal with the weight of the evidence against 

it. The EPA’s analysis at issue here was in no way 

comparable to the botched job on display in Business 

Roundtable. The EPA, in addition to performing a metaanalysis of 19 underlying clinical studies of the effects NO2

exposure has upon health, relied upon numerous 

epidemiological studies, which evidenced a relationship 

between an increase in local ambient NO2 concentrations and 

an increase in local emergency room visits, see Final Rule, 75 

Fed. Reg. at 6488–89. The API has pointed to nothing 

arbitrary or capricious either in the agency’s handling of the 

Goodman study in particular, or in its treatment of this other 

record evidence supporting the EPA’s conclusion. 

3. Treatment of the Schildcrout Study

The API also argues the EPA acted inconsistently, and 

therefore arbitrarily and capriciously, by relying upon an 

epidemiological study by Jonathan S. Schildcrout et al., 

Ambient Air Pollution and Asthma Exacerbations in 

Children: An Eight City Analysis, 164 AM. J. EPIDEMIOLOGY

505–17 (2006), in its review of the NAAQS for NO2 although 

the agency allegedly had decided in 2006 not to rely upon the 

same study when it was reviewing the NAAQS for ozone. 

According to the EPA, the study came too late in its 2006 

review process for ozone but the agency did consider it in a 

later assessment of recent studies relevant to the NAAQS for 

ozone. See Final Rule, 75 Fed. Reg. at 6486. The agency’s 

explanation is rational, and the API makes no attempt to rebut 

it; enough said about this issue.
15

4. Alternate Scenarios

The API next contends the EPA used faulty assumptions 

in projecting the degree to which air quality would be 

improved under the new NAAQS and therefore exceeded its 

authority under the Clean Air Act by adopting a NAAQS 

more stringent than is “requisite to protect the public health” 

with “an adequate margin of safety,” 42 U.S.C. § 7409(b)(1). 

In particular, the API points to the EPA’s comparison of air 

quality under various potential new NAAQS against several 

different projections of air quality without a new NAAQS, 

including one scenario in which it assumed all areas just meet 

the current air quality standards. The API underscores that 

the EPA acknowledged, contrary to this “just meets” 

assumption, current air quality is significantly better than 

what the existing annual NAAQS for NO2 requires, and the 

EPA has even projected that if it took no action air quality 

would continue to improve in this respect. Therefore, the API 

reasons, the EPA should have measured the likely benefits of 

the new NAAQS relative to a projection of air quality more 

accurate than its “just meets” scenario, which change it claims 

would have shown the one-hour NAAQS was not necessary 

“to protect the public health” with “an adequate margin of 

safety.”

The EPA says the API misunderstands the agency’s 

analysis. In predicting a benefit to air quality from adopting 

the new NAAQS for NO2, it did not rely solely upon the 

assumption that air quality would just meet existing NAAQS 

if a new NAAQS was not in place; it also measured the

improvement in air quality under the “as is” assumption, in 

which the agency assumed air quality would remain at current 

levels.
16

The API is correct to the extent that, as the word 

“requisite” in § 109(b)(1) of the Clean Air Act indicates, the 

EPA is to set a NAAQS that is “not lower or higher than is 

necessary ... to protect the public health,” Whitman v. Am.

Trucking Ass’ns, 531 U.S. 457, 475–76 (2001) (interpreting 

42 U.S.C. § 7409(b)(1)). The same statutory provision, 

however, unhorses the API’s argument because it enjoins the 

EPA to set the standard with “an adequate margin of safety,”

which means the agency is to “err on the side of caution.” 

Am. Farm Bureau Fed’n v. EPA, 559 F.3d 512, 533 (D.C. Cir. 

2009) (internal quotation marks and citation omitted). In 

other words the Act contemplates the agency “should set 

standards providing ‘a reasonable degree of protection ... 

against hazards which research has not yet identified.’” 

Coalition of Battery Recyclers Ass’n v. EPA, 604 F.3d 613, 

618 (D.C. Cir. 2010) (quoting Natural Res. Def. Council v. 

EPA, 824 F.2d 1146, 1152 (D.C. Cir. 1987) (en banc)). The 

uncertainty inherent in predicting the future is particularly 

vexing when one is making a projection of air quality, the 

actual future of which depends upon regulatory policy, 

technological change, economic performance, and political 

outcomes, among other variables. Although air quality had 

improved and was expected to keep improving, it was 

certainly possible this trend would be reversed. Therefore, it 

was not unreasonable for the EPA to measure expected 

benefits from the new NAAQS in part upon the assumption 

that, if the new NAAQS were not adopted, then each area 

would in the future just meet the existing standard.

Moreover, the EPA maintains its comparison in the REA 

of expected benefits under a new 100 ppb hourly NAAQS 

(the “new NAAQS” scenario) against the more realistic “as 

is” scenario does not, as the API contends, show the new 

NAAQS would provide no benefit. As the agency explains, 

the API disregards a critical difference between the 
17

hypothetical 100 ppb standard in the REA and the 100 ppb 

standard the EPA eventually adopted: The “new NAAQS” 

scenario in the REA assumed the standard would be set at an 

area-wide average, i.e., the average value recorded by the

monitors in an area equaled the level set by the NAAQS, so 

that some monitors would record concentrations of NO2

above and some below that standard. The new NAAQS the 

EPA actually adopted, however, applies to peak rather than to

average concentrations, i.e., it requires that all monitors in an 

area be below the 100 ppb level. Accordingly, the assumption 

in the REA that an area meets a hypothetical new NAAQS of 

100 ppb does not fully capture the expected improvement in 

air quality from the hourly 100 ppb peak concentration 

standard the agency ultimately adopted. 

Because a peak hourly concentration of 100 ppb is 

roughly equivalent to an area-wide hourly average 

concentration of between 50 and 75 ppb, see Final Rule, 75 

Fed. Reg. at 6494, the EPA concluded the standard it adopted 

corresponds more closely to the “new NAAQS” scenario in 

the REA with a standard of 50 ppb than the scenario using the 

100 ppb assumption upon which the API focuses its criticism.

In the REA the agency had projected a new NAAQS of 50 

ppb area-wide would provide a substantial improvement over 

current air quality. See REA at 120. 

Considering its duty to err on the side of caution, we 

conclude the EPA did not act unreasonably by comparing the 

benefits of the one-hour standard against not only a scenario 

based upon existing air quality but also upon an alternate 

scenario in which areas just meet the annual NAAQS set in 

1971. For that reason, and because the record adequately 

supports the EPA’s conclusion that material negative health 

effects result from ambient air concentrations as low as the 

100 ppb level, we cannot conclude the agency was arbitrary 
18

and capricious or violated the Act in adopting that level as the 

new one-hour NAAQS for NO2.

*

B. Statement Regarding Permitting

Finally, the API claims the EPA was arbitrary and 

capricious when it allegedly decided to require applicants for 

new or modified sources of pollution under § 165(a) of the 

Clean Air Act, 42 U.S.C. § 7475(a) (prohibiting construction 

of a “major emitting facility” without a permit), to 

demonstrate their compliance with the new NAAQS despite 

the lack of an adequate technique to model compliance. 

According to the API, the EPA should have considered the 

effect of that decision upon the agency’s ability to resolve

each application within one year of its filing, as required by § 

165(c) of the Act, 42 U.S.C. § 7475(c) (“Any completed 

permit application ... for a major emitting facility ... shall be 

granted or denied not later than one year after the date of 

filing”), and upon its alleged duty under § 160(3) of the Act to 

consider the effect of its permitting decisions upon economic 

growth, see 42 U.S.C. § 7470(3) (“purposes of this part 

[include] ... insur[ing] that economic growth will occur in a 

manner consistent with the preservation of existing clean air 

resources”). The API argues that until such time as methods 

for modeling compliance with the new one-hour NAAQS are

developed and have been approved by the agency, the EPA 

should allow applicants to demonstrate compliance with the 

 * We note the API does not take issue with the EPA’s simulation of 

air quality at and near roadways as routinely exceeding the new 100 

ppb standard. Indeed, counsel for the API confirmed at oral 

argument that, so long as we accept the agency's findings on the 

health effects of NO2 at concentrations as low as 100 ppb and we 

reject the API's criticism of the agency's forecasts, it has raised no 

challenge to the EPA's setting of the new NAAQS at 100 ppb. So 

be it.
19

pre-existing annual NAAQS, as they previously had to do. 

The EPA maintains the Final Rule does not constitute a final 

decision concerning the permitting of new or modified 

sources under the new NAAQS, and is therefore not subject to 

judicial review, see Portland Cement Ass’n v. EPA, 665 F.3d 

177, 193 (D.C. Cir. 2011) (“The Clean Air Act gives [the 

court] jurisdiction to review only ‘final’ agency actions” 

(citing 42 U.S.C. § 7607(b))). 

The only reason the API has for suggesting the EPA has 

taken any final action regarding the permitting of a new or 

modified source is the statement in the preamble to the Final 

Rule that “major new and modified sources applying for 

[permits under § 165 of the Act] will initially be required to 

demonstrate that their proposed emissions increases of NOx

will not cause or contribute to a violation of ... the [new] 1-

hour NO2 NAAQS.” 75 Fed. Reg. at 6525. Although “there 

is [no] categorical bar to judicial review of a preamble,” 

Kennecott Utah Copper Corp. v. U.S. Dep’t of Interior, 88 

F.3d 1191, 1222 (D.C. Cir. 1996) (citation omitted), it “is not 

the norm,” Natural Res. Def. Council v. EPA, 559 F.3d 561, 

565 (D.C. Cir. 2009). The operative question when faced 

with such a challenge is “whether the [preambular statement] 

has independent legal effect, which in turn is a function of the 

agency’s intention to bind either itself or regulated parties.” 

Kennecott, 88 F.3d at 1223. 

Any action of an agency, including a statement in a 

preamble, is “final” only if it (1) “mark[s] the consummation 

of the agency’s decisionmaking process” and (2) is “one by 

which rights or obligations have been determined, or from 

which legal consequences will flow[.]” Bennett v. Spear, 520 

U.S. 154, 178 (1997) (internal quotation marks and citations 

omitted). The preambular statement challenged here has 

neither effect, as indicated both on its face and, more clearly,
20

by the context in which it was made. To be sure, one could 

reasonably read as mandatory the isolated statement that 

permit applicants “will initially be required” to meet the new 

NAAQS. At the same time, the statement could reasonably 

be read to mean the EPA intends in the future to establish 

such a requirement, in which case the statement falls short of 

being the consummation of the agency’s decisionmaking 

process. The Supreme Court similarly has said “a statement 

in [an agency’s land management] plan that [it] ‘will’ [rather 

than “shall”] take this, that, or the other action ... is not [a 

binding commitment] ... absent clear indication” to the 

contrary, Norton v. S. Utah Wilderness Alliance, 542 U.S. 55, 

69 (2004), which suggests the statement that applicants “will 

initially be required” is predictive of the agency’s future 

actions, not one from which “legal consequences w[ould] 

flow.”

Read in context, the lack of finality in the statement is 

more obvious:

The EPA acknowledges that a decision to promulgate 

a new short-term NO2 NAAQS will clearly have 

implications for the air permitting process. The full 

extent of how a new short-term NO2 NAAQS will 

affect the [new source review] process will need to be 

carefully evaluated. First, major new and modified 

sources applying for [new source review or prevention 

of significant deterioration] permits will initially be 

required to demonstrate that their proposed emissions 

increases of NOX will not cause or contribute to a 

violation of ... the annual or 1-hour NO2 NAAQS ....

Final Rule, 75 Fed. Reg. at 6525. By acknowledging it had 

not yet, but “w[ould] need to[,] ... carefully evaluate[]” the 

effect of the new NAAQS on the permitting process, the EPA 
21

made clear it was not making a final decision. The subject 

statement does not express a final agency action, and so we 

lack jurisdiction under the Clean Air Act, 42 U.S.C. § 

7607(b), to consider the API’s challenge to it.

III. Conclusion

Because the API has not shown the EPA’s adoption of 

the one-hour NAAQS for NO2 was either arbitrary and 

capricious or in violation of the Clean Air Act, we shall deny 

the petitions in that respect. The portions of the petitions

challenging the EPA’s non-final statement regarding 

permitting in the preamble to the Final Rule we shall dismiss 

for lack of jurisdiction.

So ordered.