United States Court of Appeals

FOR THE DISTRICT OF COLUMBIA CIRCUIT

Argued October 17, 2012 Decided January 4, 2013

No. 08-1250

NATURAL RESOURCES DEFENSE COUNCIL AND SIERRA CLUB,

PETITIONERS

v.

ENVIRONMENTAL PROTECTION AGENCY,

RESPONDENT

FINE PARTICULATE LITIGATION GROUP ET AL.,

INTERVENORS

Consolidated with 09-1102, 11-1430

On Petitions for Review of Final Rules of the 

United States Environmental Protection Agency

Paul Cort argued the cause for the petitioners. Tim D.

Ballo and David S. Baron entered appearances.

Brian H. Lynk, Attorney, United States Department of

Justice, argued the cause for the respondent. Geoffrey L.

Wilcox and Stephanie L. Hogan, Attorneys, United States

Environmental Protection Agency, were on brief.

Charles H. Knauss, Shannon S. Broome, Robert T. Smith,

Denise W. Kennedy, John A. Bryson, Emily C. Schilling,
2

Leslie S. Ritts, Norman W. Fichthorn, Lauren E. Freeman,

Lucinda Minton Langworthy and Lorane F. Hebert were on

brief for the intervenors. Michelle M. Schoeppe entered an

appearance.

Before: HENDERSON and TATEL, Circuit Judges, and

WILLIAMS, Senior Circuit Judge.

Opinion for the Court filed by Circuit Judge HENDERSON.

KAREN LECRAFT HENDERSON, Circuit Judge: The four

petitioners seek review of two final rules, promulgated 1

pursuant to the Clean Air Act (CAA, Act), which govern

implementation of the national ambient air quality standard

(NAAQS) for “fine” particulate matter—that is, particulate

matter (PM) having a diameter equal to or less than 2.5 2

m 2.5 icrometers (PM ). See Final Clean Air Fine Particle

Implementation Rule, 72 Fed. Reg. 20,586 (Apr. 25, 2007)

2.5 (PM Implementation Rule); Implementation of the New

Source Review (NSR) Program for Particulate Matter Less

Than 2.5 Micrometer 2.5 s (PM ), 73 Fed. Reg. 28,321 (May 16,

2008) 2.5 (PM NSR Implementation Rule) (collectively, Final

They include the Natural Resources Defense Council, Sierra

1

Club, American Lung Association and Medical Advocates for Healthy

Air.

“Particulate matter is the generic term for a broad class of 2

chemically and physically diverse substances that exist as discrete

particles (liquid droplets or solids) over a wide range of sizes.” The

particles “originate from a variety of anthropogenic stationary and

mobile sources as well as from natural sources” and “may be emitted

directly or formed in the atmosphere by transformations of gaseous

emissions x xsuch as sulfur oxides (SO ), nitrogen oxides (NO ), and

volatile organic compounds (VOC).” National Ambient Air Quality

Standards for Particulate Matter, 62 Fed. Reg. 38,652, 38,653 (July

18, 1997).
3

PM2.5 Implementation Rules). In particular, the petitioners 3

challenge the decision of the Environmental Protection

Agency 2.5 (EPA) to promulgate the Final PM Implementation

Rules pursuant to the general implementation provisions of

Subpart 1 of Part D of Title I of the Act, 42 U.S.C. §§ 7501-

7509a (Subpart 1), rather than the particulate-matter-specific

provisions of Subpart 4 of Part D of Title I, id. §§ 7513-7513b

(Subpart 4). We agree with the petitioners that EPA erred in

applying the provisions of Subpart 1 rather than Subpart 4.

I.

Section 109 of the Act mandates that EPA establish a

primary NAAQS for each air pollutant for which EPA has

issued “air quality criteria” under CAA section 108. 42

U.S.C. § 7409(a)(1). The Act defines each such NAAQS as 4

that standard “the attainment and maintenance of which in the

judgment of the Administrator, based on such criteria and

allowing an adequate margin of safety, are requisite to protect

the public health.” Id. § 7409(b)(1). EPA is required to

“complete a thorough review” of each pollutant’s standard

and air quality criteria “at five-year intervals” and “make such

revisions in such criteria and standards and promulgate such

new standards as may be appropriate.” Id. § 7409(d)(1). 

Once a NAAQS has been established, each state must adopt

Under the Act’s NSR provisions, new or modified pollutant 3

sources must meet “strict standards,” while existing sources are

“ ‘grandfathered.’ ” New York v. U.S. EPA, 413 F.3d 3, 13 (D.C. Cir.

2005).

The Act also requires EPA to promulgate a secondary standard, 4

“the attainment and maintenance of which . . . is requisite to protect

the public welfare from any known or anticipated adverse effects

associated with” the pollutant. 42 U.S.C. § 7409(b)(2). In this case,

EPA promulgated a single NAAQS as both the primary and the

secondary standard. 
4

and submit to EPA for approval a State Implementation Plan

(SIP) that “provides for implementation, maintenance, and

enforcement of [the NAAQS] in each air quality control

region (or portion thereof) within such State.” Id.

§ 7410(a)(1). Each SIP must “include enforceable emission

limitations and other control measures, means, or techniques 

. . . , as well as schedules and timetables for compliance, as

may be necessary or appropriate to meet the [CAA’s]

applicable requirements.” Id. § 7410(a)(2)(A).

Part D of CAA Title I governs “Plan Requirements for

Nonattainment Areas” (that is, areas that have not attained

compliance with the applicable NAAQS) and Subpart 1

thereof, added to the Act in 1977, addresses “Nonattainment

Areas in General.” Subpart 1 provides generally that, once

EPA designates an area as “nonattainment,” it “may classify

the area” so as to establish an attainment deadline and it must

establish a schedule for the state encompassing the

nonattainment area to submit a SIP. Id. § 7502(a)(1)(A). The

SIP, in turn, is required, inter alia, to (1) provide for

implementation of control measures, (2) inventory existing

emissions, (3) identify and quantify pollutant emissions

permissible under the SIP from the construction and operation

of all major new stationary emission sources, (4) require NSR

permits for such construction and operation and (5) establish

compliance schedules and timetables. Id. § 7502(c). Pursuant

to this regime, in 1971, EPA established a particulate matter

NAAQS applicable to “Total Suspended Particles,” i.e.,

particulate matter up to 25-45 micrometers in diameter.

In 1987, EPA revised the NAAQS to apply only to

particle 10s equal to or smaller than 10 micrometers (PM )—a

“size-specific indicator” it determined “represent[ed] those

particles small enough to penetrate to the thoracic region”

because “[t]he risks of adverse health effects associated with

deposition of typical ambient fine and coarse particles in the
5

thorax (tracheobronchial and alveolar regions of the

respiratory tract) are markedly greater than those associated

with deposition in the extrathoracic (head) region.” Revisions

to the National Ambient Air Quality Standards for Particulate

Matter, 52 Fed. Reg. 24,634, 24,639 (July 1, 1987) (footnote

omitted) (1987 PM NAAQS Revisions). 

In 1990, the Congress amended CAA Part D by adding to

it Subparts 2 through 5, each of which contains additional

provisions governing nonattainment plan requirements for a

particular pollutant or group of pollutants. At issue here,

Subpart 4 applies to “Particulate Matter Nonattainment

Areas” and covers such matters as setting attainment dates for

PM nonattainment areas, classifying the nonattainment areas

(as “moderate” or “serious”), reclassifying them (e.g., upon

failure to attain) and extending attainment dates. 42 U.S.C.

§§ 7513-7513b; see also id. §§ 7511-7511f (ozone-specific

requirements); id. §§ 7512-7512a (carbon monoxide-specific

requirements).

In 1997, EPA again revised the particulate matter

NAAQS, 2.5 this time setting separate PM standards for fine

particles (having a diameter of 2.5 micrometers or less), while

10

retaining the existing PM standards. National Ambient Air

Quality Standards for Particulate Matter, 62 Fed. Reg. 38,652,

38,654 nn.5-6 (July 18, 1997) (Final PM NAAQS Rule). We

upheld the new particulate matter standards in 2002 after

remand from the United States Supreme Court. See Am.

Trucking Ass’ns v. EPA, 283 F.3d 355 (D.C. Cir. 2002)

(applying Whitman v. Am. Trucking Ass’ns, 531 U.S. 457

(2001)).

In 2005, EPA published its Proposed Rule To Implement

the Fine Particle National Ambient Air Quality Standards, 70

Fed. Reg. 65,984 (Nov. 1, 2005). EPA subsequently issued

the final fine particle implementation rule in two stages. In

2007, 2.5 it published the PM Implementation Rule, setting out
6

2.5 the general SIP requirements for PM . EPA followed up in

2008 with 2.5 the PM NSR Implementation Rule to govern the

NSR permitting proce 2.5 ss. In each of the two Final PM

Implementation Rules, EPA expressly followed the general

implementation provisions in Subpart 1 of Part D rather than

Subpart 4’s particulate-material-specific provisions. See

PM2.5Implementation Rule, 72 Fed. Reg. at 20,589 (“EPA is

2.5 issuing this rule to implement the 1997 PM NAAQS in

accordance with the statutory requirements of the CAA set

forth in Subpart 1 of Part D of Title 1, i.e., sections 171-179B

of the Act. . . . EPA has concluded that Congress did not

intend the Agency to implement particulate matter NAAQS

other 10than those using PM as the indicator in accordance

with Subpart 4 of Part D of T 2.5 itle 1 . . . .”); PM NSR

Implementation Rule, 73 Fed. Reg. at 28,332 (“We do not

ag 2.5 ree that subpart 4 of part D applies to PM nonattainment

areas. Subpart 4 was added to the Act by Congress

10

specifically to address the PM NAAQS. We believe that the

PM2.5standard should be implemented under subpart 1 of part

D, which is the general provision of the Act related to

NAAQS implementation.”). The petitioners filed timely

petitions 2.5 for review of both the PM Implementation Rule

and the PM2.5 NSR Implementation Rule.

II.

We review EPA’s interpretation of the CAA under

Chevron U.S.A. Inc. v. Natural Res. Def. Council, Inc., 467

U.S. 837 (1984). See Natural Res. Def. Council v. EPA, 489

F.3d 1250, 1257 (D.C. Cir. 2007). Under Chevron:

We first ask “whether Congress has directly spoken

to the precise question at issue,” in which case we

“must give effect to the unambiguously expressed

intent of Congress.” If the “statute is silent or

ambiguous with respect to the specific issue,”

however, we move to the second step and defer to
7

the agency’s interpretation as long as it is “based on

a permissible construction of the statute.”

Id. (quoting Chevron, 467 U.S. at 842-43) (other quotation

marks omitted). Before addressing whether EPA correctly

applied Subpart 1 under the Chevron framework, we first

consider the timeliness of the petitioners’ instant challenge.

A.

EPA contends the petitioners’ challenge is untimely

because it should have been raised in 1997 when EPA issued

the Final PM NAAQS Rule, which, EPA maintains, set out its

final decision on Subpart 1’s applicability. Because we

conclude EPA did not take final reviewable action in 1997,

the petitioners’ challenge is timely.

5

In urging that it finalized its decision in 1997, EPA relies

on two excerpts from the preamble to the 1997 Final PM

NAAQS Rule. First, EPA cites its response to comments

challeng 2.5 ing its authority to promulgate a separate PM

standard given that the 1990 amendments referred only to a

PM10 standard. At the conclusion of its response, EPA offered

the following defense of its authority to promulgate the new

PM2.5 standards, rooted in Subpart 1, couched in plainly

tentative language:

EPA’ 2.5 s analysis of its ability to implement a PM

standard under the provisions of subpart 1 of Part D

of Title I does not support the view that Congress

prohibited EPA from promulgating such a standard. 

Congress clearly specified an approach to the

EPA acknow 2.5

5

ledges the instant petitions for review of the PM

2.5

Implementation Rule and the PM NSR Implementation Rule were

timely filed within sixty days after each rule’s publication as required

under 42 U.S.C. § 7607(b)(1). See Br. of Resp’t 1.
8

10

implementation of the PM standard in the

provisions of subpart 4 of Part D of Title I of the Act. 

The EPA believes that the clear and express linkage

of 10that approach to the PM standard indicates that a

different PM standard should be implemented under

the general principles of subpart 1 of Part D of Title I

of the Act. That Congress directed specifically how

EPA and 10the States should implement the PM

standard does not carry with it the implication that

Congress intended to prohibit EPA from exercising

its otherwise clear and express authority to adopt a

PM standard based on a different metric . . . .

Final PM NAAQS Rule, 62 Fed. Reg. at 38,695 (emphases

added). Some pages later, in a footnote, EPA more

affirmatively, albeit summarily, stated its position that

implementation of the new standard need not and would not

be governed by Subpart 4: “The SIP requirements of subpart 4

of Part D of Title I of the Act apply to SIPs for areas

designated as not attaining NAAQS 10for PM . Those

2.5 requirements will not apply to SIPs to implement the PM

NAAQS.” Id. at 38,704 n.96. We conclude these two

unembellished snippets, buried in the preamble to the 1997

Final PM NAAQS Rule, did not constitute final agency action

so as to be reviewable in 1997.

“A final agency action is one that marks the

consummation of the agency’s decisionmaking process and

that establishes rights and obligations or creates binding legal

consequences.” Natural Res. Def. Council v. EPA, 559 F.3d

561, 564 (D.C. Cir. 2009) (citing Bennett v. Spear, 520 U.S.

154, 177-78 (1997)). We have observed that “[w]hile

preamble statements,” such as those just quoted, “may in

some unique cases constitute binding, final agency action

susceptible to judicial review, this is not the norm.” Id. at
9

564-65 (citations omitted). As this case is not a “unique” one,

we adhere to the norm.

The above quoted excerpts appear in a document

expressly intended to “describe[] EPA’s decision to revise the

national ambient air quality standards (NAAQS) for

particulate matter (PM),” Final PM NAAQS Rule, 62 Fed.

Reg. at 38,652 (emphasis added)—it did not purport to detail

how the revised standards should be implemented. Indeed,

EPA had earlier addressed the issue of implementation in a

separate Interim Implementation Policy on New or Revised

Ozone and Particulate Matter (PM) National Ambient Air

Quality Standards (NAAQS), 61 Fed. Reg. 65,752 (Dec. 13,

1996) (Interim Implementation Policy). Although the Interim

Implementation Policy likewise expressed an intent to apply

Subpart 1 2.5 to implement the PM standard, 61 Fed. Reg. at

65,753, it made clear that, as its name suggests, it was only a

temporary policy, which “would represent EPA’s preliminary

views” and “while it m[ight] include various statements that

States must take certain actions, these statements [we]re made

pursuant to EPA’s preliminary interpretations, and thus d[id]

not bind the States and public as a matter of law.” Id. at

65,752 (emphases added). Accordingly, “[o]nly after EPA

ha[d] made its interpretations final through rulemaking”—

“follow[ing] the requirements of the Administrative

Procedure Act, 5 U.S.C. section 553(b) and (c)”—“will they

be binding on the States and public as a matter of law.” Id. 

Given EPA’s expressed intent to issue a final, binding noticeand-comment rule on the issue—to supplant its “preliminary”

policies—we do not see how the quoted lines from the

preamble to the 1997 rule revising the standard itself “mark

the consummation of the agency’s decisionmaking process”

on how to implement the standard so as to constitute final

agency action. Bennett v. Spear, 520 U.S. at 177-78 (internal

quotation marks omitted). Instead, we conclude EPA

consummated the decisionmaking process to implement the
10

PM2.5 standard only when it published its final views in the

2.5 two Final PM Implementation Rules now under review. 

Notwithstanding its express and indefinite deferral of a final

implementation policy in 1997, EPA argues the Supreme

Court’s decision in Whitman v. American Trucking

Associations, 531 U.S. 457 (2001), requires us to hold

otherwise. We are not so persuaded. 

In Whitman, the Supreme Court reviewed EPA’s decision

to implement its “8-hour” 0.08 ppm NAAQS for ozone—

which replaced the previous 1-hour ozone standard of 0.12

ppm—under Subpart 1’s general nonattainment area

provisions rather than under Subpart 2’s ozone-specific

provisions added in 1990. See National Ambient Air Quality

Standards for Ozone, 62 Fed. Reg. 38,856, 38,873 (July 18,

1997) (Final Ozone NAAQS Rule) (“[T]he provisions of

subpart 1 of part D of Title I of the Act would apply to the

3

implementation of the new 8-hour O standards.”). The Court

concluded that, in the main, the new ozone NAAQS should be

implemented pursuant to Subpart 2 notwithstanding Subpart 2

was enacted to address the former 1-hour standard and some

provisions might therefore be “ill fitted to implementation of

the revised standard” and thus leave “gaps” for EPA to fill

under Chevron step 2. Whitman, 531 U.S. at 483-84. The

Whitman Court first addressed the threshold question whether

Subpart 1 constituted final agency action subject to review

and concluded that it did. See id. at 477-78. 

Addressing the Interim Implementation Policy, which

covered both the ozone and the particulate matter standards,

the Whitman Court acknowledged: “If the EPA had done no

more, we perhaps could accept its current claim that its action

was not final.” Id. at 477. The Court explained, however,

that, vis-à-vis the ozone standard, EPA had done “more.” 

After the White House issued a “ ‘Memorandum for the

Administrator of the Environmental Protection Agency’ that
11

prescribed implementation procedures for the EPA to follow,”

EPA “supplemented this memorandum with an explanation of

the implementation procedures.” Id.; see Implementation of

Revised Air Quality Standards for Ozone and Particulate

Matter, 62 Fed. Reg. 38,421, 38,422 (July 18, 1997)

(Memorandum of July 16, 1997); Implementation Plan for

Revised Air Quality Standards, 62 Fed. Reg. 38,423

(Implementation Memorandum Supplement). In a section of

the Implementation Memorandum Supplement titled

“Implementation of Ozone Standard,” EPA explained that,

after receiving comments on the proposed Interim

Implementation Policy, it had “reconsidered” its interpretation

in part and determined that “Subpart 2 should continue to

apply as a matter of law for the purpose of achieving

attainment of the current 1-hour standard.” Id. at 38,424. But

EPA made clear it adhered to its previously expressed view

that “[o]nce an area attains the 1-hour standard, those

provisions will no longer apply and the area’s implementation

of the new 8-hour standard would be governed only by the

provisions of Subpart 1 of Part D of Title I.” Id. EPA

subsequently “published [this interpretation] in the

explanatory preamble to its final ozone NAAQS under the

heading, ‘Final decision on the primary standard.’ ” 

Whitman, 531 U.S. at 477-78 (citing Final Ozone NAAQS

Rule, 62 Fed. Reg. at 38,873). Based on this chronology, the

Supreme Court found EPA’s ozone implementation policy

was final and reviewable, explaining:

The EPA’s “decisionmaking process,” which began

with the 1996 proposal and continued with the

reception of public comments, concluded when the

agency, “in light of [these comments],” and in

conjunction with a corresponding directive from the

White House, adopted the interpretation of Part D at

issue here. Since that interpretation issued, the EPA

has refused in subsequent rulemakings to reconsider
12

it, explaining to disappointed commenters that its

earlier decision was conclusive. 

Whitman, 531 U.S. at 478-79 (citing 63 Fed. Reg. 31,014,

31,018-19 2.5 (1998)). The history of the PM standard reveals

no comparable decisionmaking process regarding

implementation. The Implementation Memorandum

Supplement did not even mention Subpart 1 or Subpart 4 in its

d 2.5iscussion of the PM implementation—much less

distinguish between them or discuss their applicability vel non

2.5 to implementation of the PM standard. See 62 Fed. Reg. at

38 2.5,427-29 (section titled “Implementation of New PM

NAAQS”). Nor did EPA thereafter overtly treat its “interim”

PM2.5 implementation policy as final when it promulgated the

2007 and 2008 Final PM2.5 Implementation Rules challenged

here. Accordingly, we conclude the petitioners’ challenge is

timely and proceed to EPA’s substantive decision to

implement the NAAQS under Subpart 1.

B.

EPA contends that because Subpart 4 repeatedly refers to

PM10— 2.5rather than to PM or “particulate matter”

generally—the statutory language limits Subpart 4’s

applicability 10to implementation of the current PM standard. 

Thus, by default, EPA contends, PM2.5 must be implemented

pursuant to the general (and less stringent ) implementation 6

For example, (1) Subpart 4 requires a nonattainment area to be 6

classified as “moderate” and upon failure to attain to be reclassified as

“serious,” 42 U.S.C. § 7513(a)-(c), while under Subpart 1, EPA “may”

but is not required to classify a nonattainment area, id.

§ 7502(a)(1)(A); (2) under Subpart 4, a “serious” attainment date may

be extended only once (for a maximum of 5 years) and only if the SIP

includes the “most stringent measures” included in any state’s SIP or

achieved in any State and feasible for the area, id. § 7513(e), while

Subpart 1 allows attainment date extensions of up to 10 years with no
13

procedure in Subpart 1. This argument ignores the plain

meaning of the statute and the lesson of Whitman.

Before the Congress enacted Subpart 4, EPA had

promulgated a 10single particulate matter standard—the PM

standard—which encompassed all particulate matter with a

diameter of 10 micrometers or less—including both coarse

and fine particulate matter, that is, particulate matter now

governed by both 10 2.5 the PM and PM standards—and the

1990 CAA amendments adopted this broad meaning in

defining “PM10.” 1987 PM NAAQS Revisions, 52 Fed. Reg.

at 24,639 (“The Administrator . . . has decided to replace

[Total Suspended Particles] as the particle indicator for the

primary standards with a new indicator that includes only

those particles less than a nominal 10 [micrometers] in

diameter. . . . In defining the standards for particulate matter,

10

this new indicator is termed PM .”); 42 U.S.C. § 7602(t)

(“The term ‘PM-10’ means particulate matter with an

aerodynamic diameter less than or equal to a nominal ten

micrometers . . . .”). Thus, by its express terms, Subpart 4,

when enac 10ted, governed all PM particles, including those

now denominated PM2.5. The scope of the statutory

definition—and consequently of Subpart 4’s application—did

not change when EPA 10subdivided PM by regulation. As the

“stringent measures” requirement therefor, id. § 7502(a)(2)(A); (3)

Subpart 4 subjects a “serious” nonattainment area that fails to timely

attain to a mandatory annual 5% pollutant reduction, id. § 7513a(d),

while Subpart 1 includes no such requirement; (4) Subpart 4 requires

that “reasonable available control measures” must be implemented

within 4 years after designation, id. § 7513a(a)(1)(C), while Subpart

1 requires such measures be implemented “as expeditiously as

practicable,” id. § 7502(c)(1); and (5) Subpart 4 requires that best

available control measures be implemented no later than 4 years after

an area is classified or reclassified as “serious,” id. § 7513a(b)(1)(B),

while Subpart 1 has no best available control measures requirement.
14

Whitman Court made clear, the intent of the 1990

amendments was to limit the broad implementation discretion

Subpart 1 had previously granted EPA. Cf. Whitman, 531

U.S. at 484 (“The principal distinction between Subpart 1 and

Subpart 2 is that the latter eliminates regulatory discretion

that the former allowed.”). It makes no sense then that the

Congress would have wanted EPA to relax Subpart 4’s more

stringent, nondiscretionary requirements for implementing

2.5 the PM standard at the same time EPA decided to

2.5 strengthen the PM standard itself based on “evidence from

numerous health studies demonstrating that serious health

effects are associated with exposures to elevated levels of

PM2.5 2.5 .” PM Implementation Rule, 72 Fed. Reg. at 20,586;

see also id. at 20,586-87 (“Epidemiological studies have

shown statistically significant correlations between elevated

PM2.5 levels and premature mortality. Other important effects

associated with PM2.5 exposure include aggravation of

respiratory and cardiovascular disease (as indicated by

increased hospital admissions, emergency room visits,

absences from school or work, and restricted activity days),

changes in lung function and increased respiratory symptoms,

as well as new evidence for more subtle indicators of

cardiovascular health. Individuals particularly sensitive to

PM2.5 exposure include older adults, people with heart and

lung disease, and children.”). Notwithstanding the plain 7

The regulations’ treatment of precursors provides a useful 7

example of how the Agency has used Subpart 1 to establish a less

stringent implementation regime than envisioned by Subpart 4. 

Ammonia is a precursor to fine particulate matter, making it a

precur 2.5 10 10sor to both PM and PM . For a PM nonattainment area

governed by Subpart 4, a precursor is presumptively regulated. See 42

U.S.C. § 7513a(e) 2.5. But under the PM rules challenged here, the

EPA established a rebuttable presumption against regulating ammonia

unless a State or the EPA “provides an appropriate technical

demonstration” that shows emissions from ammonia “significantly
15

meaning of the statutory language and the force of Whitman,

8

EPA offers several unconvincing arguments to support

2.5 implementing the new PM standard pursuant to Subpart 1

rather than Subpart 4.

First, EPA claims Subpart 4 “contains requirements that

are exp 10ressly based upon the form of the PM NAAQS.” Br.

of Resp’t 31. This may be true but Subpart 4 also expressly

governs implementation of the “PM-10” standard, see 42

U.S.C. §§ 7513-7513b, and the Act defines “PM-10” as

“particulate matter with an aerodynamic diameter less than or

contr 2.5ibute to PM concentration in the nonattainment area.” 40

C.F.R. § 51.1002(c)(4)(i). When Congress enacted Subpart 4, it

sought to end this administrative gamesmanship.

EPA offers several grounds to distinguish Whitman—none of 8

them persuasive. First EPA notes that the text of Subpart 2 refers

generically to “ozone” while Subpart 4’s text refers specifically to

PM10, EPA Br. 36—but Subpart 4’s title refers generically to

“Particulate Matter” and, as we have noted, when the 1990

amendments 10 2.5to the CAA were enacted, PM included PM under

both the new statutory definition and the existing EPA definition. 

Second, EPA argues that Subpart 4’s provisions do not

“comprehensively prescribe[] classifications and attainment dates for

all particulate matter nonattainment areas.” Br. of Resp’t 37

(emphasis in original). Subpart 4 may not be as comprehensive as

Subpart 2 but its requirements are specific, more stringent and far less

discretionary than Subpart 1. See supra note 6. Third, EPA contends

2.5

that in contrast to Whitman, EPA’s application of Subpart 1 to PM

does not render Subpart 4 “utterly nugatory” because Subpart 4 still

applies 10to the remaining PM standard. Br. of Resp’t 37 (quoting

Whitman, 531 U.S. at 484). But if EPA’s interpretation stands,

Subpart 4 will be “utterly nugatory” with respect to implementation of

2.5

the PM standard—notwithstanding the Congress expressly directed

10 25

the standard applicable to all PM particles, including PM , be

regulated under Subpart 4.
16

equal to a nominal ten micrometers,” 42 U.S.C. § 7602(t). 

Thus, under Chevron step 1, EPA must implement all

10 2.5

standards applicable to PM —including its PM

standards—pursuant to Subpart 4.

Second, EPA urges that because in the 1987 PM NAAQS

Revisions, it “had considered whether to establish a separate

NAAQS 2.5 for fine particles, using PM as the indicator,” the

Congress should have foreseen that it might do so later. Br.

of Resp’t 32. It is not at all clear that the Congress should

have so foreseen—EPA cites a single, vague footnote to

support its claim the Congress was on notice such a change

was likely. Id. at 32 (citing 52 Fed. Reg. at 24,639 n.2

(“Particles in ambient air usually occur in two somewhat

overlapping size distributions, fine (diameter less than 2.5

[micrometers]) and coarse (diameter larger than 2.5

[micrometers]. The two size fractions tend to have different

origins and composition.” (staff document citation omitted)). 

But even were such notice clear, it does not follow that the

Congress 2.5 therefore intended that a separate PM standard (if

promulgated) be exempt from Subpart 4’s requirements. As

in Whitman, the possibility of such a change suggests only

that gaps resulting therefrom might “prevent us from

concluding that Congress clearly intended [the specific

pollutant subpart] to be the exclusive, permanent means of

enforcing a revised ozone standard in nonattainment areas.” 

Whitman, 531 U.S. at 484 (emphasis added). It does not

render “utterly nugatory” the restrictions that the 1990

amendments imposed on EPA’s discretion in implementing

the particulate matter standards for all particles 10

micrometers or less in diameter. See id. As the Supreme

Court observed regarding Subpart 2, “[a] plan reaching so far

into the future was not enacted to be abandoned the next time

the EPA reviewed the [pollutant’s] standard—which

Congress knew could happen at any time.” Id. at 485.
17

EPA also argues that the Congress “could have easily

used the general term ‘particulate matter,’ rather than the

specific term ‘PM-10.’ ” Br. of Resp’t 33. That the Congress

could have done so does not negate the 10reality that the “PM ”

standard to which the Congress referred in fact included fine

PM2.5 (both under the 1987 Rule and the 1990 statutory

definition). 

In a final Chevron step 1 effort, EPA asserts that the

legislative history makes the Congress’s intent clear. 

Assuming legislative history could override the plain,

unambiguous directive of Subpart 4, the history cited here is

unconvincing. EPA relies on a single congressman’s

statement: “ ‘The Title I PM-10 provisions of H.R. 3030

somewhat reschedule the attainment dates that would

otherwise apply under the PM-10 standards as promulgated

by EPA.’ ” Br. of Resp’t 39 (quoting A Legislative History of

the Clean Air Act Amendments of 1990, at 2996 (Comm. Print

1993) (statement of Rep. John Murtha)). This statement

avails EPA nought. “[P]utting to one side the fact that this

was the statement of a single [member of Congress], . . . it is

not necessarily inconsistent with” the petitioners’ view that

Subpart 4 continues 2.5 to apply to PM standards. See Grand

Canyon Air Tour Coal. v. FAA, 154 F.3d 455, 474 (D.C. Cir.

1998). At the time the statement was uttered, “the PM-10

standards as promulgated by EPA” applied to all particulate

matter having a diameter equal to or less than 10

micrometer 2.5 s—including what is now denominated PM .

9

Moreover, “judges must exercise extreme caution before

9

concluding that a statement made in floor debate, or at a hearing, or

printed in a committee document may be taken as statutory gospel, in

light of the endemic interplay, in Congress, of political and legislative

considerations likely unrelated to the interpretive tasks of a court.”

Tex. Mun. Power Agency v. EPA, 89 F.3d 858, 875 (D.C. Cir. 1996)

(per curiam) (quotation marks and alterations omitted). Here, it is
18

See 1987 PM NAAQS Revisions, 52 Fed. Reg. at 24,639.

 EPA additionally argues that its “reading of the act is, at

minimum, a ‘permissible’ interpretation entitled to deference

under Chevron step two.” Br. of Resp’t 41 (upper case

lowered). This argument is foreclosed, however, under

Chevron step 1 because the statute is plain on its face. 

For the foregoing reasons, we grant the petitions for

review of the Final Clean Air Fine Particle Implementation

Rule, 72 Fed. Reg. 20,586 (Apr. 25, 2007), and the

Implementation of the New Source Review (NSR) Program

2.5 for Particulate Matter Less Than 2.5 Micrometers (PM ), 73

Fed. Reg. 28,321 (May 16, 2008). We remand to EPA to repromulgate these rules pursuant to Subpart 4 consistent with

this opinion.10

So ordered.

hard to ignore “the irony that [EPA] points to the same floor

statement that the [petitioners] contend[] supports [their] opposite

view.” Grand Canyon Air Tour Coal., 154 F.3d at 474 (emphasis in

original).

In light of our disposition, we need not address the petitioners’

10

challenge to the presumptions in 40 C.F.R. § 51.1002(c)(3)-(4) that

vo 2.5latile organic compounds and ammonia are not PM precursors as

Subpart 4 expressly governs precursor presumptions. See 42 U.S.C.

§ 7513a(e). Moreover, we decline the petitioners’ invitation to set a

deadline for EPA upon remand or to retain jurisdiction pending such

action. See Natural Res. Def. Council v. EPA, 489 F.3d 1364, 1375

(D.C. Cir. 2007) (“We decline to set a two year limit on EPA’s

proceedings on remand as the NRDC requests; mandamus affords a

remedy for undue delay.”); North Carolina v. EPA, 550 F.3d 1176,

1178 (D.C. Cir. 2008) (per curiam) (declining invitation to “impose a

definitive deadline by which EPA must correct [clean air rule’s]

flaws” and reminding petitioners of availability of mandamus).