 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
petitioners1 seek review of two final rules, promulgated
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)2 having a diameter equal to or less than 2.5
micrometers (PM2.5). See Final Clean Air Fine Particle
Implementation Rule, 72 Fed. Reg. 20,586 (Apr. 25, 2007)
(PM2.5 Implementation Rule); Implementation of the New
Source Review (NSR) Program for Particulate Matter Less
Than 2.5 Micrometers (PM2.5), 73 Fed. Reg. 28,321 (May 16,
2008) (PM2.5 NSR Implementation Rule) (collectively, Final


    1
     They include the Natural Resources Defense Council, Sierra
Club, American Lung Association and Medical Advocates for Healthy
Air.
    2
      “Particulate matter is the generic term for a broad class of
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 such as sulfur oxides (SOx), nitrogen oxides (NOx), 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).3 In particular, the petitioners
challenge the decision of the Environmental Protection
Agency (EPA) to promulgate the Final PM2.5 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).4 The Act defines each such NAAQS as
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

    3
      Under the Act’s NSR provisions, new or modified pollutant
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).
    4
      The Act also requires EPA to promulgate a secondary standard,
“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
particles equal to or smaller than 10 micrometers (PM10)—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, this time setting separate PM2.5 standards for fine
particles (having a diameter of 2.5 micrometers or less), while
retaining the existing PM10 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, it published the PM2.5 Implementation Rule, setting out
                               6

the general SIP requirements for PM2.5. EPA followed up in
2008 with the PM2.5 NSR Implementation Rule to govern the
NSR permitting process. In each of the two Final PM2.5
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
PM2.5 Implementation Rule, 72 Fed. Reg. at 20,589 (“EPA is
issuing this rule to implement the 1997 PM2.5 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 than those using PM10 as the indicator in accordance
with Subpart 4 of Part D of Title 1 . . . .”); PM2.5 NSR
Implementation Rule, 73 Fed. Reg. at 28,332 (“We do not
agree that subpart 4 of part D applies to PM2.5 nonattainment
areas. Subpart 4 was added to the Act by Congress
specifically to address the PM10 NAAQS. We believe that the
PM2.5 standard 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 for review of both the PM2.5 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
challenging its authority to promulgate a separate PM2.5
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’s analysis of its ability to implement a PM2.5
     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


     5
     EPA acknowledges the instant petitions for review of the PM2.5
Implementation Rule and the PM2.5 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

    implementation of the PM10 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 that approach to the PM10 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 the States should implement the PM10
    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 for PM10. Those
requirements will not apply to SIPs to implement the PM2.5
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 to implement the PM2.5 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 notice-
and-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
two Final PM2.5 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
implementation of the new 8-hour O3 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 (1998)). The history of the PM2.5 standard reveals
no comparable decisionmaking process regarding
implementation.       The Implementation Memorandum
Supplement did not even mention Subpart 1 or Subpart 4 in its
discussion of the PM2.5 implementation—much less
distinguish between them or discuss their applicability vel non
to implementation of the PM2.5 standard. See 62 Fed. Reg. at
38,427-29 (section titled “Implementation of New PM2.5
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—rather than to PM2.5 or “particulate matter”
generally—the statutory language limits Subpart 4’s
applicability to implementation of the current PM10 standard.
Thus, by default, EPA contends, PM2.5 must be implemented
pursuant to the general (and less stringent6) implementation


     6
      For example, (1) Subpart 4 requires a nonattainment area to be
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 single particulate matter standard—the PM10
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 the PM10 and PM2.5 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,
this new indicator is termed PM10.”); 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 enacted, governed all PM10 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 subdivided PM10 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
the PM2.5 standard at the same time EPA decided to
strengthen the PM2.5 standard itself based on “evidence from
numerous health studies demonstrating that serious health
effects are associated with exposures to elevated levels of
PM2.5.” PM2.5 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.”).7 Notwithstanding the plain

    7
      The regulations’ treatment of precursors provides a useful
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
precursor to both PM2.5 and PM10. For a PM10 nonattainment area
governed by Subpart 4, a precursor is presumptively regulated. See 42
U.S.C. § 7513a(e). But under the PM2.5 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
implementing the new PM2.5 standard pursuant to Subpart 1
rather than Subpart 4.
     First, EPA claims Subpart 4 “contains requirements that
are expressly based upon the form of the PM10 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


contribute to PM2.5 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.
     8
      EPA offers several grounds to distinguish Whitman—none of
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 to the CAA were enacted, PM10 included PM2.5 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
that in contrast to Whitman, EPA’s application of Subpart 1 to PM 2.5
does not render Subpart 4 “utterly nugatory” because Subpart 4 still
applies to the remaining PM10 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
the PM2.5 standard—notwithstanding the Congress expressly directed
the standard applicable to all PM10 particles, including PM25, 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
standards applicable to PM 10—including its PM 2.5
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 for fine particles, using PM2.5 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 therefore intended that a separate PM2.5 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 reality that the “PM10”
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 to apply to PM2.5 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
micrometers—including what is now denominated PM2.5.9

     9
      Moreover, “judges must exercise extreme caution before
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
for Particulate Matter Less Than 2.5 Micrometers (PM2.5), 73
Fed. Reg. 28,321 (May 16, 2008). We remand to EPA to re-
promulgate 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).
     10
       In light of our disposition, we need not address the petitioners’
challenge to the presumptions in 40 C.F.R. § 51.1002(c)(3)-(4) that
volatile organic compounds and ammonia are not PM2.5 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).
