US Supreme Court Briefs

No. 99-1257


In the Supreme Court of the United States

CAROL M. BROWNER, ADMINISTRATOR OF
THE ENVIRONMENTAL PROTECTION AGENCY,
ET AL., PETITIONERS

v.

AMERICAN TRUCKING ASSOCIATIONS, INC., ET AL.

ON A WRIT OF CERTIORARI TO
THE UNITED STATES COURT OF APPEALS
FOR THE DISTRICT OF COLUMBIA CIRCUIT

BRIEF FOR THE PETITIONERS


SETH P. WAXMAN
Solicitor General
Counsel of Record
LOIS J. SCHIFFER
Assistant Attorney General
LAWRENCE G. WALLACE
Deputy Solicitor General
JEFFREY P. MINEAR
Assistant to the Solicitor
General
DAVID J. KAPLAN
MARY F. EDGAR
Attorneys
Department of Justice
Washington, D.C. 20530-0001
(202) 514-2217


GARY S. GUZY
General Counsel
GERALD K. GLEASON
MICHAEL L. GOO
JAN M. TIERNEY
KEVIN W. MCLEAN
Attorneys
Environmental Protection
Agency
Washington, D.C. 20460


QUESTIONS PRESENTED

1. Whether Section 109 of the Clean Air Act (CAA), 42 U.S.C. 7409, as interpretedby the Environmental Protection Agency (EPA) in setting revised NationalAmbient Air Quality Standards (NAAQS) for ozone and particulate matter,effects an unconstitutional delegation of legislative power.

2. Whether the court of appeals exceeded its jurisdiction by reviewing,as a final agency action that is ripe for review, EPA's preliminary preamblestatements on the scope of the agency's authority to implement the revised"eight-hour" ozone NAAQS.

3. Whether provisions of the Clean Air Act Amendments of 1990 specificallyaimed at achieving the long-delayed attainment of the then-existing ozoneNAAQS restrict EPA's general authority under other provisions of the CAAto implement a new and more protective ozone NAAQS until the prior standardis attained.



In the Supreme Court of the United States

No. 99-1257

CAROL M. BROWNER, ADMINISTRATOR OF
THE ENVIRONMENTAL PROTECTION AGENCY,
ET AL., PETITIONERS
v.
AMERICAN TRUCKING ASSOCIATIONS, INC., ET AL.

ON A WRIT OF CERTIORARI TO
THE UNITED STATES COURT OF APPEALS
FOR THE DISTRICT OF COLUMBIA CIRCUIT

BRIEF FOR THE PETITIONERS

OPINIONS BELOW

The opinion of the court of appeals (Pet. App. 1a-69a) is reported at 175F.3d 1027. The opinion on petitions for rehearing and dissenting statementson denial of rehearing en banc (Pet. App. 70a-101a) are reported at 195F.3d 4.

JURISDICTION

The decision of the court of appeals was entered on May 14, 1999. Petitionsfor rehearing were granted in part and denied in part on October 29, 1999.The petition for a writ of certiorari was filed on January 27, 2000, andwas granted on May 22, 2000. The jurisdiction of this Court is invoked underon 28 U.S.C. 1254(1).

CONSTITUTIONAL, STATUTORY, AND REGULATORY PROVISIONS INVOLVED

Article I of the United States Constitution states in pertinent part asfollows:

All legislative Powers herein granted shall be vested in a Congress of theUnited States.

The relevant sections of the Clean Air Act, 42 U.S.C. 7401 et seq., areset forth in the petition appendix at Pet. App. 105a-126a. The EPA rulesat issue in this case are set forth in the petition appendix at Pet. App.102a-104a.

STATEMENT

Section 109 of the Clean Air Act (CAA), 42 U.S.C. 7409, requires the EnvironmentalProtection Agency (EPA) to establish and periodically revise, based on thelatest scientific knowledge, primary National Ambient Air Quality Standards(NAAQS) "requisite to protect" public health with "an adequatemargin of safety," and secondary NAAQS "requisite to protect"other public interests. On July 18, 1997, EPA issued final rules revisingthe NAAQS for two pollutants: particulate matter (PM) and ozone.1 EPA decidedto revise the PM and ozone standards because new scientific evidence showedthat the standards then in effect were not adequately protecting millionsof Americans from adverse health effects. For example, a quantitative riskassessment indicated that PM concentrations below the standards EPA establishedin 1987 may annually subject people in two urban areas alone, representingabout five million people, to hundreds of early deaths, thousands of hospitaladmissions for respiratory illness, and tens of thousands of incidents ofrespiratory symptoms in children. See 61 Fed. Reg. 65,638, 65,650-65,651(1996).

On petitions for review, the court of appeals held that Section 109, asinterpreted by EPA in setting the revised PM and ozone standards, effectedan unconstitutional delegation of legislative authority. The court remandedboth rules for EPA to articulate an "intelligible principle" fordetermining the degree of public health protection to be afforded by theNAAQS. In addition, even though EPA had taken no final agency action toimplement the revised ozone NAAQS, the court issued an opinion, later modified,interpreting the scope of EPA's implementation authority.

I. THE CLEAN AIR ACT'S NAAQS PROVISIONS

The Clean Air Act sets up a comprehensive and extraordinarily detailed programfor control of air pollution through a system of shared federal and stateresponsibility.2 The NAAQS are a central feature of that program. Sections108 and 109 of the Act require EPA to establish, review, and revise nationallyapplicable standards for a small class of common air pollutants. 42 U.S.C.7408-7409. The NAAQS establish permissible concentrations of those pollutantsin the "ambient," or outside, air. Section 110 of the Act thencalls on the States to impose controls on individual sources of air pollutionas necessary to attain and maintain the NAAQS. 42 U.S.C. 7410; see Trainv. NRDC, 421 U.S. 60, 78-79 (1975); Lead Indus. Ass'n v. EPA, 647 F.2d 1130,1137 (D.C. Cir.), cert. denied, 449 U.S. 1042 (1980).

A. Air Quality Criteria And Standards

The NAAQS-setting process begins with identification of air pollutants thatare emitted from "numerous or diverse" sources and that "mayreasonably be anticipated to endanger public health or welfare." 42U.S.C. 7408(a)(1). EPA has identified six such pollutants, commonly referredto as "criteria" pollutants: sulfur oxides; nitrogen oxides; carbonmonoxide; lead; ozone; and particulate matter.

EPA must develop "air quality criteria" reflecting the "latestscientific knowledge" on "all identifiable effects on public healthor welfare" that may result from each criteria pollutant's presencein the ambient air. 42 U.S.C. 7408(a)(2). EPA generally records the scientificassessments constituting air quality criteria in a "Criteria Document,"which provides a rigorous analysis of all pertinent scientific information.EPA also develops a "Staff Paper" to "bridge the gap"between the scientific review and the judgments the Administrator must maketo set standards. See NRDC v. EPA, 902 F.2d 962, 967 (1990), opinion vacatedin part, 921 F.2d 326 (D.C. Cir.), cert. denied, 498 U.S. 1082 (1991). Bothdocuments undergo public notice and comment, as well as extensive scientificpeer-review by the Clean Air Scientific Advisory Committee (CASAC), an independentcommittee established under the Act to advise the EPA Administrator on airquality criteria and NAAQS. 42 U.S.C. 7409(d)(2)(B); see 62 Fed. Reg. 38,654(1997).3

Relying on the "air quality criteria," EPA promulgates "primary"and "secondary" NAAQS to protect against the adverse health andwelfare effects of each criteria pollutant. 42 U.S.C. 7409(a)(1) and (b)(1)-(2).EPA must set "primary" standards at levels that, "in thejudgment of the Administrator," are "requisite to protect thepublic health" with "an adequate margin of safety." 42 U.S.C.7409(b)(1). EPA must set "secondary" standards at levels thatare "requisite to protect the public welfare" from any "knownor anticipated adverse effects." 42 U.S.C. 7409(b)(2).

To ensure that standards keep pace with advances in scientific knowledge,EPA must review the air quality criteria and standards every five yearsand revise them as "appropriate in accordance with [Sections 108 and109(b)]." 42 U.S.C. 7409(d)(1). When setting or revising NAAQS, EPAmust consider and explain any significant departure from CASAC's recommendations.42 U.S.C. 7607(d)(3).

Drawing on legislative guidance, EPA has developed decisional criteria toensure consistency among its NAAQS decisions. EPA considers, among otherpublic health factors, the nature and severity of health effects, the typesof health evidence, the kind and degree of uncertainties involved, and thesize and nature of the sensitive populations at risk. See, e.g., 97-1440C.A. App. (PM App.) 1908. The court of appeals approved EPA's use of thosefactors 20 years ago, Lead Indus., 647 F.2d at 1161, and EPA has since employedthem in numerous NAAQS rulemakings.4 The court reaffirmed its approval ofEPA's use of those factors in this case. Pet. App. 5a, 6a-7a.

B. Implementation Of Air Quality Standards

The CAA sets out a detailed process, resting on principles of federal-statecooperation, to ensure that the air throughout the Nation "attains"the NAAQS. Within three years of promulgating a new or revised NAAQS, EPAmust "designate" areas of the country as either "attainment"(i.e., the area meets that NAAQS), "nonattainment" (i.e., thearea fails to meet that NAAQS), or "unclassifiable" (i.e., adequateinformation is not available). 42 U.S.C. 7407(d)(1). Following designation,EPA must establish the date by which nonattainment areas shall attain thatNAAQS (i.e., the area's attainment date). See 42 U.S.C. 7502(a). The CAAprovides for each State to develop, for EPA's approval, a state implementationplan (SIP) that sets forth pollution control measures necessary to attainall NAAQS by the applicable attainment dates. See 42 U.S.C. 7410(a), 7502(c).See generally Union Elec. Co. v. EPA, 427 U.S. 246 (1976); Train, supra.If a State fails to develop an adequate SIP, then EPA must promulgate measuresto attain the NAAQS in the form of a federal implementation plan (FIP).42 U.S.C. 7410(c).

Congress laid the foundation for the CAA's current regulatory scheme throughthe Clean Air Act Amendments of 1970 and the Clean Air Act Amendments of1977. See note 2, supra.5 Congress built further on that foundation throughthe Clean Air Act Amendments of 1990, Pub. L. No. 101-549, 104 Stat. 2399,which address, among other things, the continuing problem of NAAQS nonattainment.Congress retained with limited modifications the basic planning obligationsin Section 110 for States to implement all NAAQS, including "any revisionthereof," in all areas of the Nation, regardless of their designationstatus. 42 U.S.C. 7410(a)(1). Congress, however, adjusted the attainmentobligations for the NAAQS then in existence and revised the attainment obligationsthat would result if EPA promulgated new or revised NAAQS. As a consequence,the 1990 Amendments contain a complicated set of new implementation obligations,set out in the CAA's Title I, Part D, for nonattainment areas. See 42 U.S.C.7501-7515 (1994 & Supp. III 1997).

First, Congress modified the general nonattainment provisions that it hadpreviously set out in Part D, see note 5, supra, and placed them in a newsubpart, titled "Subpart 1 -Nonattainment Areas in General." 42U.S.C. 7501-7509a (1994 & Supp. III 1997). Section 172(a) of that Subpartincludes a new scheme for EPA to classify and establish attainment datesfor nonattainment areas, based upon various factors, including the severityof the area's pollution problem. 42 U.S.C. 7502(a).6 That scheme appliesto all nonattainment areas "with respect to any [NAAQS] (or any revisedstandard, including a revision of any standard in effect on November 15,1990)." 42 U.S.C. 7502(a)(1)(A).

Second, Congress created a series of new subparts in Part D, which addressnonattainment of each of the then-existing NAAQS. See 42 U.S.C. 7511-7514a(1994 & Supp. III 1997) (Subpts. 2-5, Pt. D, Tit. I). Subpart 2 containsspecific implementation provisions for the ozone NAAQS, which apply in additionto the general implementation provisions in Subpart 1. See 42 U.S.C. 7511-7511f(1994 & Supp. III 1997) ("Subpart 2-Additional Provisions for OzoneNonattainment Areas").7 Those provisions address the continued nonattainment,as of 1990, of the primary ozone NAAQS then in existence (i.e., the "one-hour"ozone standard). Section 181(a)(1) of that Subpart sets out specific classificationsand attainment dates that apply "by operation of law" for areasthat, prior to the 1990 Amendments, were designated nonattainment underthe one-hour ozone standard. 42 U.S.C. 7511(a)(1).8

Third, Congress reconciled EPA's general authority under Section 172(a)of Subpart 1 to classify and establish attainment dates for nonattainmentareas with the attainment schedule in Section 181(a)(1) of Subpart 2 (andin other Subparts of Part D). Congress provided that EPA's authority inSection 172(a) shall not apply to "nonattainment areas for which classifications[or "attainment dates"] are specifically provided under otherprovisions of [Part D]." 42 U.S.C. 7502(a)(1)(C) and (a)(2)(D). Thus,to the extent that Section 181(a)(1) specifically provides classificationsand attainment dates for areas designated nonattainment for the one-hourozone standard, EPA may not invoke Section 172(a) to establish classificationsand attainment dates for that ozone NAAQS.

II. THE PARTICULATE MATTER AND OZONE RULEMAKING PROCEEDINGS

On July 18, 1997, EPA promulgated revised primary and secondary air qualitystandards for PM and ozone. In each rulemaking, the Criteria Documents andStaff Papers underwent several rounds of review by CASAC, public comment,and revision by EPA. Ultimately, CASAC notified EPA that the PM and ozoneCriteria Documents provided an adequate scientific basis for regulatorydecisions. PM App. 3151; 97-1441 C.A. App. (Ozone App.) 235. CASAC alsonotified EPA that the PM and ozone Staff Papers, which among other thingsidentified ranges of potential standards for the Administrator's consideration,were likewise scientifically adequate. PM App. 3162; Ozone App. 236-238.As required by Section 109, EPA then set new PM and ozone standards basedon the revised air quality criteria. EPA provided exhaustive explanationsof the basis for the two decisions, which we briefly summarize below.

A. The Particulate Matter Rule

Particulate matter encompasses a broad class of chemically and physicallydiverse liquid and solid particles. 62 Fed. Reg. at 38,653. Scientists generallydistinguish between two categories of PM-fine and coarse. Both were encompassedby the "PM10" standards that EPA set in 1987.9

EPA revised the PM standards based on new scientific studies that had emergedsince EPA's last PM review, including an extensive body of epidemiologicalstudies on exposure to PM pollution.10 More than 60 such studies showedstatistically significant positive associations between exposure to PM airpollution and serious adverse health effects, including premature deathand illness severe enough to require hospital admission. 61 Fed. Reg. at65,641-65,643; PM App. 1375-1778, 1801-1845 (Criteria Document). The sameevidence identified several large "sensitive" populations thatmay experience health effects at lower PM concentrations, or more severely,than the general public. 61 Fed. Reg. at 65,644. Those populations includedthe elderly, children, and people with cardiovascular and respiratory disease,including asthma. Ibid.; PM App. 1991-1993.

The scientific studies indicated that those very serious health effectswere "attributable to PM at levels below the current NAAQS." PMApp. 1870. The Administrator concluded, based on the nature of the healtheffects and the huge size of the affected populations, 62 Fed. Reg. at 38,657,that the studies provided "strong evidence that the current PM10 standardsdo not adequately protect public health, and that revision of the standardsis not only appropriate, but necessary," id. at 38,665.

The Administrator decided she could best protect against the health riskposed by PM by adopting two sets of standards: (1) PM2.5 NAAQS to controlfine particles, which were likely responsible for those health effects associatedwith PM concentrations at or below the 1987 NAAQS; and (2) PM10 NAAQS toprovide continued control of inhalable coarse particles. 62 Fed. Reg. at38,665-38,668. The Administrator selected the annual PM2.5 NAAQS as the"generally controlling" standard to reduce both long-term andpeak PM2.5 concentrations and adopted the 24-hour PM2.5 NAAQS only to addressunusual circumstances. Id. at 38,669.

To select the levels requisite to protect public health, with an adequatemargin of safety, the Administrator relied chiefly on epidemiological studiesthat employed direct measures of fine particles, such as PM2.5. 62 Fed.Reg. at 38,675-38,676 & n.41. "[P]lacing greatest weight on thosestudies that were clearly statistically significant," the Administratorconcluded that an annual PM2.5 standard of 15 micrograms per cubic meterof air (µg/m3) "will provide an adequate margin of safety againstthe effects observed in these epidemiological studies." Id. at 38,676.That level is just below the range of 15.7 to 21 µg/m3 that encompassesthe annual mean PM2.5 levels in locations where epidemiological studieshad shown statistically significant positive associations between fine particlesand adverse health effects. Ibid.; PM App. 3506-3521. The Administratoracknowledged that "the possibility of effects at lower annual concentrationscannot be excluded," but she noted that the evidence supporting thatpossibility-which did not rise to the level of statistical significance-is"highly uncertain," and therefore did not warrant establishmentof a lower annual standard. 62 Fed. Reg. at 38,675-38,676; PM App. 3506-3521.11

B. The Ozone Rule

Ground-level ozone is a ubiquitous pollutant formed in the air from theinteraction in sunlight of nitrogen oxides and volatile organic compoundsemitted from many sources. It is the principal component of smog and a powerfullung irritant. See 62 Fed. Reg. at 38,858.12

EPA's review of the latest scientific knowledge on ozone disclosed a largebody of new research demonstrating associations between adverse health effectsand exposure to ozone over longer periods, at more moderate levels of exertion,and at lower concentrations than had been shown by the studies availablein 1979, when EPA had promulgated an ozone standard of 0.12 parts per million(ppm) averaged over one hour (the one-hour standard). 62 Fed. Reg. at 38,859;61 Fed. Reg. at 65,719-65,720. Some of those new studies showed health effectsassociated with prolonged (six to eight hours) exposure to ozone levelsas low as 0.08 ppm. 62 Fed. Reg. at 38,859. The studies also showed that,in comparison to the general population, active children and workers whoregularly engage in outdoor activities are at greater risk of experiencingadverse health effects from exposure to ozone. Ibid. In addition, peoplewith pre-existing respiratory disease are more susceptible than others tothe effects of ozone. Ibid. See generally Ozone App. 1460-1648, 1740-1780,3770-3786, 3875-3881 (Criteria Document).

The scientific evidence convinced the Administrator that she should reviseboth the averaging time and the concentration level of the 1979 one-hourozone standard. 62 Fed. Reg. at 38,863. She determined, and CASAC concurred,that an eight-hour standard was more consistent than a one-hour standardwith the kind of prolonged exposures at which the scientific evidence showedchildren and others in at-risk populations were experiencing health effectsof concern. Id. at 38,861. In addition, EPA's quantitative exposure andrisk assessments showed that an eight-hour standard would provide significantlygreater nationwide uniformity in health protection than a one-hour standard.Id. at 38,862.

To select a concentration level for the eight-hour averaging period, EPAemployed a weight-of-evidence approach. Using, with CASAC's concurrence,guidelines of the American Thoracic Society, EPA considered the medicalsignificance, or "adversity," of ozone-related health effects,which can vary widely. 62 Fed. Reg. at 38,860.13 EPA also considered thepublic health implications of its conclusions regarding effects on individuals.For that purpose, EPA prepared quantitative exposure and risk assessmentsthat used (among other information) data from human clinical studies toestimate, for various levels of ozone in the ambient air, the number ofpeople within certain sensitive population groups likely to experience effectsthat would interfere with normal activity. Id. at 38,861-38,873.

EPA narrowed its consideration to the range of 0.07 ppm to 0.09 ppm foran eight-hour ozone standard. The upper bound for consideration could beno higher than 0.09 ppm because the exposure and risk assessments showedthat the risks associated with an eight-hour standard of 0.09 ppm were "thesame or only marginally smaller" than those associated with the 1979one-hour standard, which EPA and CASAC agreed provided "little, ifany, margin of safety." 62 Fed. Reg. at 38,863-38,864. The lower boundfor consideration also emerged from the scientific evidence, including inparticular: (1) the absence of any human clinical studies on exposures below0.08 ppm, id. at 38,863; and (2) quantitative exposure assessments showingthat a 0.07 ppm standard would, over the course of an ozone season, limit"exposures of concern" to "essentially zero," ibid.14

The Administrator explained why she found significant differences in thecharacter of the available scientific evidence regarding ozone exposureswithin the range identified. She compared a 0.08 ppm standard to a 0.09ppm standard on the basis of a number of factors, including estimates ofthe relative number of children that would experience adverse health effects,the relative frequency of such effects, and relative increases in hospitaladmissions. Those estimates and estimates of occurrences of "exposuresof concern" under a standard of 0.09 ppm counseled against use of thatconcentration. 62 Fed. Reg. at 38,867-38,868; see note 14, supra. For example,EPA estimated that a 0.09 ppm standard would allow more than three timesas many children to experience exposures of concern than would a standardof 0.08 ppm. 62 Fed. Reg. at 38,868.

The Administrator also explained why she concluded that a standard set below0.08 ppm would be more stringent than requisite to protect against adverseeffects of public health significance. See 62 Fed. Reg. at 38,863-38,868.With CASAC's concurrence, EPA had reasonably assumed, for purposes of thequantitative risk assessment, that there is no "effects threshold"for the categories of health effects measured in human clinical studies-lungfunction decreases and respiratory symptoms. EPA therefore assumed thatthose effects may occur at ozone levels below 0.08 ppm. See 61 Fed. Reg.at 65,725-65,726. As to those effects, the record showed that average responsescaused by exposures even at 0.08 ppm were "typically small or mildin nature." 62 Fed. Reg. at 38,864. The Administrator recognized thatrepeated exposures at the 0.08 ppm level could potentially produce adverseeffects for some unusually sensitive individuals, ibid., but the recordindicated that the "most certain" ozone-related effects at andbelow that level, even when adverse, are "transient and reversible,"id. at 38,868. Moreover, the quantitative exposure and risk assessmentsshowed that a standard set at 0.08 ppm would significantly reduce the numberof such exposures. See ibid. As for more serious health effects, EPA lackedclinical data indicating the existence of an exposure-response relationshipat ozone levels below 0.08 ppm. See id. at 38,863-38,864, 38,868; OzoneApp. 1962. Furthermore, none of the CASAC advisors recommended setting therevised NAAQS at a level below 0.08 ppm. 62 Fed. Reg. at 38,864-38,865,38,868. Accordingly, the Administrator reasonably concluded, based on theavailable evidence, that an eight-hour ozone standard of 0.08 ppm wouldbe sufficient to protect public health with an adequate margin of safety.Id. at 38,868-38,869.15

In addition to explaining the basis for its decisions, EPA responded, asrequired by the Act, 42 U.S.C. 7607(d)(6)(B), to all significant publiccomments. Various commenters had argued that, by enacting in 1990 specificprovisions regarding implementation of the one-hour ozone standard thenin effect, e.g., 42 U.S.C. 7511(a)(1), Congress had effectively codifiedthat standard and precluded EPA from revising it. In response, EPA explainedthat its authority to revise the one-hour ozone standard was clear on theface of the Act and then briefly and generally discussed how some of theAct's provisions would apply to implementation of a revised ozone standard.The sole purpose of that discussion was to respond fully to the commentsarguing that the 1990 Amendments curtailed EPA's authority to revise theozone standard. 62 Fed. Reg. at 38,884-38,885; see App., infra, 1a-6a (reproducingthe preamble discussion).

III. THE PROCEEDINGS BELOW

Numerous industry groups, a public interest group, and several States andindividuals challenged the revised PM and ozone NAAQS. The court of appealsrejected many of the challenges, but nevertheless remanded both final rulesto EPA with instructions "to develop a construction of the act"that would satisfy this Court's "nondelegation doctrine." Pet.App. 4a, 5a. Relying on a theory that the parties had not extensively briefed,the court concluded that EPA's interpretation of Section 109 of the CAA"effects an unconstitutional delegation of legislative power."Id. at 4a. According to the majority, EPA's interpretation of the Act leavesit "free to pick any point between zero and a hair below * * * London'sKiller Fog," a notorious 1952 incident in which air pollution may havecaused approximately 4000 deaths over four days. Id. at 13a. Judge Tateldissented from that portion of the opinion, emphasizing that the majority"ignore[d] the last half-century of Supreme Court nondelegation jurisprudence"upholding numerous statutes containing fewer guiding principles than Section109. Id. at 59a.

In the ozone case (No. 97-1441), the court of appeals rejected the industrypetitioners' argument that the 1990 Amendments, which established mandatoryclassifications and attainment dates for the primary one-hour ozone standardthen in effect, see CAA § 181, 42 U.S.C. 7511, precluded EPA from revisingthe ozone NAAQS. Pet. App. 34a-37a. That ruling resolved the issue beforethe court. The court of appeals nevertheless went on to direct what EPAmay and may not do when it proceeds-in the future-to implement the ozoneNAAQS. The court ruled that EPA cannot implement the revised ozone NAAQSthrough Section 172 (42 U.S.C. 7502), but must instead employ Section 181(a)(42 U.S.C. 7511(a)). Pet. App. 34a, 37a-44a. Because the requirements ofSection 181(a) are tied to the one-hour standard, the court's ruling effectivelymeant, as the court itself recognized, that EPA could promulgate, but couldnot enforce, the revised ozone NAAQS. Id. at 57a.16

EPA and other parties filed petitions for rehearing and suggestions forrehearing en banc. The panel granted rehearing, in part, to modify its opinionregarding EPA's authority to implement the revised ozone standard. Pet.App. 71a-72a. The panel rejected EPA's argument that, because EPA had yetto take final action implementing the revised ozone NAAQS, the court lackedjurisdiction to consider which provisions of the Act would govern implementation,including the specification of classifications and attainment dates. Id.at 78a-80a. The court found that EPA's statements on that issue in the preambleaccompanying the revised ozone standard, made in response to industry commentschallenging EPA's authority to promulgate that standard, see 62 Fed. Reg.at 38,884-38,885, constituted final agency action on the question of implementationthat was ripe for judicial review. Pet. App. 78a-80a.

On the merits, the panel modified its opinion to state that "EPA canenforce a revised primary ozone NAAQS only in conformity with Subpart 2."Pet. App. 81a. Judge Tatel wrote separately because he disagreed with thepanel majority's reasoning. Pet. App. 83a-89a. He found the statute ambiguousand would have deferred to EPA's interpretation. Id. at 84a. Judge Tatelnevertheless concurred in the judgment because, in his view, the modifieddecision would allow EPA to implement the revised ozone standard under Subpart1 once an area has attained the one-hour standard in accordance with Subpart2. Id. at 89a. As to the nondelegation issue, the panel denied EPA's petitionfor rehearing. It expressly rejected EPA's view that the relevant provisionsof the Act set out intelligible principles that limit the agency's discretion.Id. at 72a-76a. Judge Tatel again dissented. Id. at 89a, 97a-99a.

The court also denied EPA's suggestion for rehearing en banc, with fiveof the court's eleven active judges voting in favor of rehearing en banc,and four voting against it. Pet. App. 90a-92a. Judge Silberman and JudgeTatel each wrote statements dissenting from the denial of rehearing en bancon the nondelegation issue. Id. at 92a-96a, 97a-99a. Chief Judge Edwardsand Judge Garland joined in Judge Tatel's statement. Id. at 97a.

SUMMARY OF ARGUMENT

1. The court of appeals incorrectly concluded that Section 109 of the CAA,as interpreted by EPA, violates the nondelegation doctrine. Section 109'srequirement that NAAQS must be set at a level "requisite to protect"public health with "an adequate margin of safety" does not constitutean unconstitutional grant of legislative power. Furthermore, the nondelegationdoctrine does not impose a constitutional obligation on EPA to go beyondwhat Congress has directed and announce a "determinate criterion fordrawing lines." Pet. App. 5a-6a. The court's novel view that the Constitutiondemands such a precise criterion-and that the agency must supply it-is fundamentallyunsound.

Congress has directed EPA to establish NAAQS by reference to the CAA's detailedrequirements, which set out intelligible principles to guide EPA's actions.The CAA's directives, which are more specific than many statutory directivesthat this Court has upheld, amply ensure that Congress has not abdicatedits power to make the laws. The CAA prescribes the legal standards governingEPA's decisions, factors that EPA must consider in making its decisionsunder Section 109, a body of experts that EPA must consult on those decisions,and a rigorous set of procedures that EPA must follow. In short, the Actestablishes multiple specific restrictions that cabin EPA's discretion insetting NAAQS. The nondelegation doctrine does not require more.

The court of appeals' direction that EPA must narrow the scope of Congress'sdirection is not only unprecedented, it also is contrary to the purposeof the nondelegation doctrine. The Court has developed that doctrine toenforce the Constitution's requirement that Congress alone shall exerciselegislative power. The court of appeals has improperly employed the doctrineto expand the scope of its judicial review authority beyond the limits thatCongress has set through the CAA's statutory standards for review of agencyaction. The court of appeals' conclusion that EPA must provide a "determinate,binding standard" for setting NAAQS is not only inconsistent with theCAA's recognition that NAAQS must be set in the face of scientific uncertainties,but it is also likely impracticable. An Executive Branch agency, actingpursuant to congressional direction, is entitled to assess the availableevidence and make a reasoned judgment on the proper regulatory standard.Contrary to the court of appeals' characterization, EPA's interpretationof its authority did not leave it free to set a NAAQS at any point betweenzero and "a hair below" an air pollution level that killed 4000people in four days. To the contrary, the rulemaking records reveal thatEPA properly construed and applied limitations on its discretion. It providedreasoned explanations, supported by the record evidence, for why it chosethe challenged PM and ozone standards in light of continuously evolvingscientific knowledge.

2. The court of appeals also erred in prematurely deciding the scope ofEPA's authority to implement and enforce the revised standard. The courtdid so by subjecting EPA's preamble statements on how it may implement therevised ozone standard to judicial review. Those preamble statements donot constitute judicially reviewable agency action. EPA made those statementsto respond to comments that the implementation scheme in Section 181(a)(1)negates EPA's authority to promulgate a revised ozone standard. Once thecourt of appeals rejected that challenge to EPA's NAAQS revision authority,its task was done. It should not have treated EPA's preamble statementsthat explain the basis for EPA's ozone NAAQS as separate agency action thatis independently subject to judicial review.

Even if EPA's preamble remarks about what future steps it intends to taketo implement the ozone NAAQS constituted "agency action," theyare certainly not "final" agency action. Those statements arenot the consummation of the agency's decisionmaking process and they donot create any rights or obligations. They simply express EPA's currentviews on some aspects of the complicated implementation process that EPAand the States will undertake through future rulemakings. The CAA sets outa detailed procedure for conducting those rulemakings. Under the statutoryprocess, EPA will issue final rules on specific subjects in an orderly fashion,and each final rule will be subject to judicial review when the rule isripe for the court's review.

Even if EPA's preamble statements constituted final agency action, theywould not be ripe for review. The issue of how to reconcile the numerousprovisions governing implementation is, at this stage, too abstract. Thecourts do not have the benefit of EPA's explanation of how and why it hasimplemented a NAAQS in a particular way, which would be available only afterEPA has completed the relevant rulemakings, including any required publicnotice and response to comments, and taken final action that actually implementsthe standard. The courts should not review those complex implementationissues until EPA has had the opportunity to work through the various implementationprovisions, reconcile any conflicts, make any policy judgments, and applyits expertise to resolve any ambiguities in the statute.

3. If the Court decides to reach the merits, it should rule that the courtof appeals' modified decision is incorrect, even as interpreted by JudgeTatel in his partial concurrence. The CAA authorizes EPA to implement therevised national ozone standard contemporaneously throughout the country,regardless of whether an area is violating the one-hour ozone standard.The court of appeals' decision would inappropriately force EPA to delayprotecting the public from the very health consequences that warrant a NAAQSrevision in the first place, until the area attains an air quality standardthat EPA has concluded is inadequate to protect public health. Congresscould not have intended that implausible result.

The statutory provision on which the court of appeals primarily relied-Section181(a) of Subpart 2-implements only the one-hour ozone standard. It doesnot apply to the revised eight-hour ozone NAAQS or otherwise curtail EPA'sauthority to implement that standard under Section 172(a) and any otherapplicable provision of Subpart 1. Moreover, because the Act requires theattainment of all NAAQS "as expeditiously as practicable," 42U.S.C. 7502(a)(1)(A), 7511(a)(1), the court of appeals erred in concludingthat EPA must delay implementation of the eight-hour NAAQS in any area untilit attains the one-hour ozone standard.

ARGUMENT

I. THE COURT OF APPEALS ERRONEOUSLY APPLIED THE NONDELEGATION DOCTRINE

The nondelegation doctrine is "rooted in the principle of separationof powers." Mistretta v. United States, 488 U.S. 361, 371 (1989). "Thefundamental precept of the delegation doctrine is that the lawmaking functionbelongs to Congress, U.S. Const., Art. I, § 1, and may not be conveyedto another branch or entity." Loving v. United States, 517 U.S. 748,758 (1996). The nondelegation doctrine does not require, however, that Congressdictate every detail of a regulatory program. Congress may rely on the otherbranches to make rules that carry out its will. See Loving, 517 U.S. at758; Mistretta, 488 U.S. at 372.

This Court's application of the nondelegation doctrine has been "drivenby a practical understanding that in our increasingly complex society, repletewith ever changing and more technical problems, Congress simply cannot doits job absent an ability to delegate power under broad general directives."Mistretta, 488 U.S. at 372. The Court has accordingly recognized that Congressdoes not violate the Constitution "merely because it legislates inbroad terms, leaving a certain degree of discretion to executive or judicialactors." Touby v. United States, 500 U.S. 160, 165 (1991); see Yakusv. United States, 321 U.S. 414, 425 (1944) (Congress may "call forthe exercise of judgment, and for the formulation of subsidiary administrativepolicy within the prescribed framework").

The Court has specifically emphasized that Congress does not violate thenondelegation doctrine if "Congress clearly delineates the generalpolicy, the public agency which is to apply it, and the boundaries of thisdelegated authority." Mistretta, 488 U.S. at 372-373 (quoting AmericanPower & Light Co. v. SEC, 329 U.S. 90, 105 (1946)); Skinner v. Mid-AmericaPipeline Co., 490 U.S. 212, 218-219 (1989). "Only if we could say thatthere is an absence of standards for the guidance of the [agency's] action,so that it would be impossible in a proper proceeding to ascertain whetherthe will of Congress has been obeyed, would we be justified in overridingits choice of means for effecting its declared purpose." Mistretta,488 U.S. at 379 (emphasis added) (quoting Yakus, 321 U.S. at 425-426).

A. Section 109 Of The Clean Air Act Does Not Constitute An UnconstitutionalGrant Of Legislative Power

Contrary to the court of appeals' conclusion, Section 109 easily satisfiesthis Court's "intelligible principle" standard. This Court's decisionsleave no doubt that Section 109 does not amount to an invalid delegationof legislative power and that EPA can properly fulfill the responsibilitiesthat Section 109 assigns. Section 109's directives "are far more specificthan the sweeping statutory delegations consistently upheld by [this] Courtfor more than sixty years." Pet. App. 97a (Tatel, J., dissenting fromdenial of rehearing en banc); see also id. at 93a (Silberman, J., dissentingfrom denial of rehearing en banc); id. at 59a-60a (Tatel, J., dissenting)(collecting cases).

The starting point for nondelegation analysis is the CAA's language, whichmust be read in context with due regard to the Act's purpose and history.See American Power & Light, 329 U.S. at 104. A perusal of this comprehensivelegislation, which Congress has repeatedly amended in light of new knowledgeand developments (see note 2, supra), reveals that Congress has exercisedits lawmaking function with exacting care. The Act, which now occupies morethan 280 pages in the United States Code, is extraordinarily detailed andprescriptive. As the Act has evolved, Congress has consistently recognizedthe need to rely on an Executive Branch agency's scientific resources andexpertise in executing the legislative purposes. At the same time, Congresshas carefully channeled EPA's discretion through increasingly detailed substantiveand procedural requirements.

Section 109(b)(1) of the Act requires that primary NAAQS be set at levels"requisite to protect the public health" with an "adequatemargin of safety" and that secondary standards be set at levels "requisiteto protect the public welfare." 42 U.S.C. 7409(b)(1). To warrant thesetting of a NAAQS, a pollutant must "reasonably be anticipated toendanger public health or welfare" and be emitted from "numerousor diverse * * * sources." 42 U.S.C. 7408(a)(1)(A)-(B). Each standardmust be based on "air quality criteria" that reflect "thelatest scientific knowledge," 42 U.S.C. 7408(a)(2), including informationon "variable factors" that "may alter the effects on publichealth," as well as interactions with other pollutants "to producean adverse effect on public health or welfare." 42 U.S.C. 7408(a)(2)(A)-(B).Further, the Act establishes and prescribes the composition of CASAC (seep. 4, supra) and requires EPA to consider, and explain any significant departurefrom, CASAC's advice on revision of the air quality criteria and standards.42 U.S.C. 7409(d)(2), 7607(d)(9).17

Section 307(d) of the Act, 42 U.S.C. 7607(d), which sets out the proceduresfor rulemaking and judicial review, further ensures that EPA adheres toa "disciplined decisionmaking process" in setting NAAQS. See Pet.App. 63a (Tatel, J., dissenting). Congress has prescribed a rulemaking processthat ensures extensive public participation. EPA must discuss the data,methodology, and major legal and policy interpretations underlying proposedNAAQS, 42 U.S.C. 7607(d)(3); provide a reasoned explanation for its decision,42 U.S.C. 7607(d)(6)(A); and respond to significant comments, 42 U.S.C.7607(d)(6)(B). EPA's rule is then subject to judicial review. 42 U.S.C.7607(b)(1) and (d)(9).18

The Act's legislative history "provides additional guidance for [EPA's]consideration of the statutory factors" that is relevant for assessingthe constitutionality of Section 109. Mistretta, 488 U.S. at 376 n.10. Thatlegislative history, which the court below failed to consider, indicatesthat the health effects justifying a NAAQS must be "adverse,"Lead Indus., 647 F.2d at 1152 (citing S. Rep. No. 1196, 91st Cong., 2d Sess.10 (1970) (S. Rep. 1196)), in the sense that they are medically significantand not merely detectable, id. at 1155 n.51. To provide an "adequatemargin of safety," standards must be "preventative or precautionary,"reflecting an emphasis on the "predominant value of protection of publichealth." Ibid. (quoting H.R. Rep. No. 294, 95th Cong., 1st Sess. 49(1977) (H.R. Rep. 294)); id. at 1155 (EPA must "err on the side ofcaution"). Furthermore, public health is distinct from individual health;the standards must protect sensitive populations, such as asthmatics, id.at 1152, but not the most sensitive individuals within those populations.See S. Rep. 1196, at 10 (EPA must consider effects on "a representativesample of persons comprising the sensitive group rather than to a singleperson in such a group."), in 1 Staff of the Senate Comm. on Pub. Works,93d Cong., 2d Sess., A Legislative History of the Clean Air Act Amendmentsof 1970, at 410 (Comm. Print 1974).

In short, Congress has placed "multiple specific restrictions"on EPA's discretion in setting and revising NAAQS that satisfy the constitutionalrequirements of the nondelegation doctrine. Touby, 500 U.S. at 167. Thoserestrictions are at least as rigorous as those in Touby and other nondelegationcases, many of which in fact involved far less prescriptive legislation.See id. at 165.19 The Act prescribes the legal standard EPA is to apply,factors that EPA is to consider, a body of experts that EPA is to consult,and procedures that EPA must follow in making its highly technical scientificjudgments about the health and welfare effects of particular pollutants.As in American Power & Light Co., the Act provides "a veritablecode of rules" for EPA to follow in fulfilling Congress's will. 329U.S. at 105; see Yakus, 321 U.S. at 426.20

B. The Court Of Appeals Improperly Employed The Nondelegation Doctrine ToExpand The Scope Of Its Review

This Court's nondelegation doctrine preserves the Constitution's separationof powers by ensuring that Congress does not abdicate its power to makelaws. The court of appeals transformed that doctrine, however, into a judicialcheck on executive power. The court of appeals employed the nondelegationdoctrine as an additional means, beyond the explicit judicial review provisionsof the CAA, to supervise the exercise of administrative discretion. SeePet. App. 14a. The court directed EPA to "develop[] determinate, bindingstandards for itself" to reduce the likelihood that EPA would "exercisethe delegated authority arbitrarily" and to "enhance the likelihoodthat meaningful judicial review will prove feasible." Ibid. That noveluse of the nondelegation doctrine departs from the doctrine's purpose, ithas no basis in this Court's precedents, and it trenches on Congress's powerto specify appropriate standards for judicial review of executive action.See id. at 93a (Silberman, J., dissenting from the denial of rehearing enbanc).

The court of appeals viewed the nondelegation doctrine as requiring Congress,or agencies interpreting the intent of Congress, to delineate a "determinatecriterion for drawing lines." Pet. App. 6a. In the court's view, theConstitution requires that EPA supply a single principle that would enablethe court to conclude that EPA's NAAQS are set at what the court deems exactlythe "right" level. See id. at 10a-11a, 73a. That approach, however,is inconsistent with the court's limited role in reviewing NAAQS. The CAAmakes clear that EPA's actions in setting NAAQS are subject to review underthe arbitrary or capricious standard of judicial review. See 42 U.S.C. 7607(d)(9).Under that standard, the court is limited to examining whether EPA's action"was based on consideration of the relevant factors and whether therehas been a clear error of judgment." Citizens to Preserve Overton Park,Inc. v. Volpe, 401 U.S. 402, 416 (1971) (Overton). "The court is notempowered to substitute its judgment for that of the agency." Ibid.As Judge Silberman recognized, the court of appeals' approach would "implicitlyassert[] a greater role for a reviewing court than is justified." Pet.App. 96a. See Baltimore Gas & Elec. Co. v. NRDC, 462 U.S. 87, 103 (1983)("When examining this kind of scientific determination, as opposedto simple findings of fact, a reviewing court must generally be at its mostdeferential.").21

Moreover, the court of appeals' demand for a determinate criterion to governEPA's NAAQS decisions is difficult to reconcile in practice with the Act'scommand that EPA set NAAQS-and revise them, as appropriate, every five years-basedon the "latest scientific knowledge." 42 U.S.C. 7408(b). As theD.C. Circuit has recognized in the past, Congress has directed EPA to make"predictions * * * at the frontiers of science." NRDC, 902 F.2dat 968 (quoting New York v. EPA, 852 F.2d 574, 580 (D.C. Cir. 1988), cert.denied, 489 U.S. 1065 (1989)); accord Lead Indus., 647 F.2d at 1147. Because"the statute is 'precautionary' in nature, the evidence 'uncertainor conflicting' and the 'regulations designed to protect the public health,'"the court of appeals has recognized that Congress did "not demand rigorousstep-by-step proof of cause and effect." NRDC, 902 F.2d at 968 (citationsomitted).

The purpose of Section 109's requirement that NAAQS provide an "adequatemargin of safety" is to ensure "a reasonable degree of protection* * * against hazards which research has not yet identified." LeadIndus., 647 F.2d at 1150 (quoting S. Rep. 1196, at 10). EPA must thereforebe able to draw conclusions from "suspected, but not completely substantiated,relationships between facts, from trends among facts, from theoretical projectionsfrom imperfect data, from probative preliminary data not yet certifiableas 'fact,' and the like." NRDC, 902 F.2d at 968 (quoting Ethyl Corp.v. EPA, 541 F.2d 1, 28 (D.C. Cir.) (en banc), cert. denied, 426 U.S. 941(1976)); H.R. Rep. 294, at 43-51, 110-112. To hold EPA to the court's noveldemand for precision would restrict the agency's ability to act on a precautionarybasis in the face of scientific uncertainties, thereby potentially erodingthe public health protection Congress intended NAAQS to afford.

The court of appeals' requirement that EPA develop a "determinate criterionfor drawing lines" (Pet. App. 6a), which EPA would presumably be requiredto apply in every NAAQS proceeding (see id. at 73a), is also inconsistentwith EPA's own expert assessment of the flexibility necessary to apply Section109's mandate to all the pollutants for which EPA must develop standards.In the PM and ozone rulemaking proceedings, EPA received comments arguingthat the Act required the agency to adopt various specific approaches todecisions under Section 109, such as, for example, first determining a "safelevel" and then applying a margin of safety. 62 Fed. Reg. at 38,688,38,883. In its response to those comments, EPA noted that the D.C. Circuithad specifically rejected claims that any of the approaches suggested bythe commenters were required by the Act and instead had ruled that "[t]hiscourt must allow [the Administrator] the discretion to determine which approachwill best fulfill the goals of the Act." Ibid. (quoting Lead Indus.,647 F.2d at 1161-1162).

The criteria pollutants that are subject to the NAAQS process vary widelyin relation to key factors, including their health effects, the types ofavailable scientific evidence, the kind and degree of scientific uncertainties,and the size of sensitive populations. Because of that wide variation:

[T]he most appropriate approach to establishing a NAAQS with an adequatemargin of safety may be different for each standard under review. Thus,no generalized paradigm * * * can substitute for the Administrator's carefuland reasoned assessment of all relevant health factors in reaching sucha judgment.

62 Fed. Reg. at 38,688; see id. at 38,883.22

At bottom, the court's rationale for its approach-to prevent arbitrary agencyaction and to enhance judicial review (Pet. App. 14a)-overlooks that Congressis entitled to set the parameters for judicial oversight of EPA's scientificjudgments. Congress has concluded that EPA's actions in setting NAAQS aresubject to the arbitrary or capricious test. See 42 U.S.C. 7607(d)(9). EPAmust consider the factors that the Act prescribes and provide a reasonedexplanation, based on scientific evidence, for its decision. When reviewingthat decision, a court is not entitled to demand that EPA demonstrate thatthe numerical standard the agency selected was the sole possible choice.To the contrary, as this Court explained in reviewing rates set by the FederalPower Commission under a statute requiring rates to be "just and reasonable":

[T]here is no single cost-recovering rate, but a zone of reasonableness:"Statutory reasonableness is an abstract quality represented by anarea rather than a pinpoint. It allows a substantial spread between whatis unreasonable because too low and what is unreasonable because too high."

FPC v. Conway Corp., 426 U.S. 271, 278 (1976) (quoting Montana-Dakota Util.Co. v. Northwestern Pub. Serv. Co., 341 U.S. 246, 251 (1951)).

This Court's decisions in Conway and similar cases do not announce novelconcepts. The D.C. Circuit has itself acknowledged, when it reviewed the1987 PM standard, that a reviewing court should not ask if EPA has identified"the clear and sole appropriate standard," but rather whetherEPA has selected a standard that is reasonable in light of the record evidence.NRDC, 902 F.2d at 972. The court of appeals here relied on the nondelegationdoctrine as its sole justification for departing from that established standardof review. Pet. App. 12a-13a. Under this Court's precedents, Section 109does not violate the nondelegation doctrine. The court of appeals improperlyrelied on that doctrine to depart from traditional principles governingthe scope of judicial review of agency action.

C. EPA Has Recognized Limitations On Its Discretion To Revise The ParticulateMatter And Ozone Standards

The court of appeals' nondelegation holding rests on the erroneous conceptionthat EPA interprets Section 109 to set no limits on its discretion. Thecourt characterized EPA as claiming discretion so broad as to leave it freeto "pick any point between zero and a hair below * * * London's KillerFog." Pet. App. 13a. To the contrary, EPA has recognized and appliedprinciples that channel its discretion far more narrowly than the courtacknowledged.

The CAA's directive that EPA must base the revised NAAQS on "air qualitycriteria" reflecting the "latest scientific knowledge" limits,at the outset, the alternatives that EPA can consider. EPA found that awide range of adverse health effects were occurring at concentrations belowthe pre-existing PM and ozone NAAQS, which effectively dictated an upperbound for any revised NAAQS. The revised PM and ozone NAAQS had to be atleast as protective as those pre-existing standards. See, e.g., 62 Fed.Reg. at 38,656-38,657, 38,665; id. at 38,859; 61 Fed. Reg. at 65,719-65,721;pp. 10-13, supra. In each case, EPA also identified a lower bound for considerationat the most protective levels the scientific evidence reasonably supported.For PM, the lower bound was the lowest level at which long-term epidemiologicaldata indicated there might be an "effects threshold" below whichthere is no risk of health effects. See PM App. 2145, 2147. For ozone, whichappears to have no effects threshold (see note 23, infra), the lower bound-0.07ppm-was the level at which EPA's exposure assessment showed that exposuresof public health concern were "essentially zero." 61 Fed. Reg.at 65,728, 65,730.

EPA's review of the latest scientific knowledge on the health effects ofPM confined the agency to considering a quite limited range of 12.5 to 20µg/m3 for the annual PM2.5 standard (and 20 to 65 µg/m3 forthe daily PM2.5 standard). See 62 Fed. Reg. at 38,675-38,677; PM App. 2158(Staff Paper). That range is obviously far more narrow than a range fromzero to a "hair below" 2,500 µg/m3 (the level the courtof appeals assumed for the "Killer Fog"). Similarly, EPA's reviewof the latest scientific knowledge on the health effects of ozone confinedthe agency to considering an eight-hour ozone standard between 0.07 ppmand 0.09 ppm. See p. 13, supra. EPA had identified those ranges in its StaffPapers, and CASAC had agreed that EPA's identification of those ranges hadsound scientific support. See PM App. 3162; Ozone App. 238; pp. 8-9, supra.

Furthermore, although EPA may exercise discretion in selecting a standard,EPA is constrained in doing so by the CAA's explicit requirement that theagency consider relevant factors, apply them to relevant facts, respondto criticisms, and adequately explain its rationale. 42 U.S.C. 7607(d)(2)-(6).In fulfilling those obligations, EPA employed the decisional criteria thatthe agency has long used to ensure consistency in its NAAQS decisions. Seep. 5, supra.

For example, in setting the annual PM2.5 standards, EPA took account ofthe "types of health evidence" and the "kind and degree ofuncertainties." EPA identified a scientific criterion applicable toepidemiological studies-statistical significance to the 95% confidence level-todetermine "how much uncertainty [was] too much" within the narrowrange under consideration. See Pet. App. 10a; 62 Fed. Reg. at 38,675-38,676;61 Fed. Reg. at 65,642 n.8; see note 10, supra. The scientific evidenceshowed statistically significant positive associations between PM2.5 andadverse health effects in locations where PM2.5 ranged from 15.7 to 21 µg/m3.See pp. 10-11, supra. But no study showed a statistically significant associationbetween adverse health effects and PM2.5 in any area with an annual PM2.5level below 15.7 µg/m3. See 62 Fed. Reg. at 38,676; PM App. 3506-3521.EPA therefore set the annual PM2.5 standard at 15 µg/m3, which EPAdetermined would be requisite to protect public health with an adequatemargin of safety.

In the ozone rule, EPA selected the standard based primarily on considerationof "the nature and severity of the health effects," "thesize of the sensitive population at risk," and, again, the "typesof health evidence." EPA recognized that a standard of 0.09 ppm wouldnot protect public health with an adequate margin of safety. See pp. 13-14,supra. EPA also recognized that its mandate is not to set standards morestringent than requisite to protect against health effects of public healthsignificance. EPA identified important and meaningful differences in thecharacter of the scientific evidence regarding risks-including the estimatedfrequency and duration of adverse health effects-associated with levelsabove and below 0.08 ppm. Those differences amply justified the Administrator'sselection of the 0.08 ppm level as requisite to protect public health withan adequate margin of safety. E.g., 62 Fed. Reg. at 38,864-38,868; 61 Fed.Reg. at 65,727, 65,730; see also pp. 13-15, supra.23

The record accordingly demonstrates that EPA did not exercise unfettereddiscretion in promulgating the revised PM and ozone standards. To the contrary,EPA explained in detail, with reference to the scientific evidence in therecord, why it selected the challenged PM and ozone standards. The courtof appeals thus failed to appreciate the record before it in erroneouslyconcluding that EPA claimed such wide discretion that it could have setthe new standards at virtually any level. Cf. Overton, 401 U.S. at 416.

II. THE COURT OF APPEALS LACKED JURISDICTION TO REVIEW EPA'S PREAMBLE STATEMENTSON THE SCOPE OF ITS AUTHORITY TO IMPLEMENT A REVISED OZONE STANDARD

Section 307(b)(1) of the CAA authorizes the D.C. Circuit to review "actionof the Administrator in promulgating any [NAAQS]" and other "nationallyapplicable regulations promulgated, or final action taken, by the Administrator."42 U.S.C. 7607(b)(1). In this case, the court of appeals plainly had jurisdictionto review EPA's promulgation of the ozone NAAQS. The NAAQS, which consistsof a specific, two-paragraph rule, Pet. App. 104a, is final agency action.The court of appeals erred, however, in concluding that it also had authorityto critique portions of EPA's explanatory preamble and thereby dictate thecourse of the agency's future implementation actions. The court of appeals'broad pronouncement that "EPA can enforce a revised primary ozone NAAQSonly in conformity with Subpart 2," Pet. App. 81a, results from thatcourt's premature and unfocused exploration of issues that were not properlybefore that court.

EPA's rulemaking addressed promulgation of a revised ozone NAAQS. The issueof implementation arose in the ozone case because participants in the rulemakingproceeding argued that, when Congress enacted the 1990 Amendments and included-inSection 181(a)(1) of Subpart 2-a scheme for implementing the then-currentone-hour ozone standard, Congress thereby implicitly prohibited EPA fromever promulgating a revised ozone standard. See p. 15, supra. Section 307(d)(6)of the CAA requires EPA to respond to "significant comments."42 U.S.C. 7607(d)(6). EPA accordingly addressed those arguments in the rulemakingpreamble and, later, in its brief in the court of appeals. EPA explainedgenerally, as part of its demonstration why the Section 181(a) scheme doesnot prevent EPA from promulgating a revised NAAQS, that the revised standardcould be implemented through Subpart 1. See App., infra, 1a-6a; 62 Fed.Reg. at 38,884-38,885.24

The court of appeals was obligated to address the specific arguments thatthe rulemaking participants had raised in their judicial challenge to EPA'spromulgation of a revised ozone NAAQS. See 42 U.S.C. 7607(d)(7)(B). Theonly issue involving "implementation" before the court of appeals,however, was whether the participants were correct that the Section 181(a)scheme precluded EPA from promulgating the revised standard. Once the courtanswered that question in the negative, Pet. App. 34a-37a, its task wasdone. It should not have gone on to consider prematurely whether and howEPA could implement the revised NAAQS.

The government objected, through petitions for rehearing and rehearing enbanc, to the court of appeals' decision to address an issue that was notproperly before it. The court responded by asserting that it had jurisdictionto address the views that EPA expressed in the preamble because those explanatorystatements about the agency's future intentions independently satisfiedthe final agency action requirement of Section 307(b) of the CAA. Pet. App.77a-78a. That conclusion is wrong.

A. EPA's Preamble Statements Regarding Implementation Authority Are Not"Agency Action" Within The Meaning Of Section 307(b)(1) Of TheAct

The court of appeals has undertaken to address prospectively how to reconciletwo complex portions of the CAA- Subparts 1 and 2 of Part D-even thoughEPA has not yet undertaken that task through rulemaking. The court justifiedits review on the basis that EPA stated, in an explanatory preamble, howit intends to reconcile those provisions. See 62 Fed. Reg. at 38,884-38,885(App., infra, 1a-6a). Section 307(b)(1), however, limits the court of appealsto review of particular agency actions, such as "promulgating any ** * [NAAQS]" and other "final action * * * taken[] by the Administrator."42 U.S.C. 7607(b)(1).

The CAA does not define the phrase "action * * * taken[] by the Administrator,"but its meaning can be discerned from conventional principles of administrativelaw. Cf. Harrison v. PPG Indus., Inc., 446 U.S. 578, 586 (1980). The AdministrativeProcedure Act (APA) defines the term "agency action" as "thewhole or a part of an agency rule, order, license, sanction, relief, orthe equivalent or denial thereof, or failure to act." 5 U.S.C. 551(13);see 5 U.S.C. 701(b)(2). As this Court has indicated, the phrase "agencyaction" is limited to discrete acts that affect legal rights. See Lujanv. National Wildlife Fed'n, 497 U.S. 871, 891 (1990) ("Under the termsof the APA, respondent must direct its attack against some particular 'agencyaction' that causes it harm."); FTC v. Standard Oil Co., 449 U.S. 232,247 (1980) ("In general, the term encompasses formal orders, rules,and interpretive decisions that crystallize or modify private rights.")(Stevens, J., concurring).

The CAA also draws a clear distinction between agency action and the agency'sexplanation of its action. For example, a promulgated rule-a familiar formof agency action-must be "accompanied" by "a statement ofbasis and purpose" and "a response to each of the significant[public] comments [on the proposed rule]." 42 U.S.C. 7607(d)(6). Thatrequirement facilitates judicial review of whether the agency's rule is"arbitrary, capricious, or an abuse of discretion," 42 U.S.C.7607(d)(9). A court is entitled to set aside the rule if it concludes thatthe agency's rationale for the rule is inadequate. But in that situation,the court invalidates the rule itself -viz., the agency's action-and notthe agency's explanation for its action. See ibid.; see also 5 U.S.C. 706(2).The agency's explanation is not itself "agency action" that isindependently subject to review. Cf. California v. Rooney, 483 U.S. 307,311 (1987) (per curiam) ("This Court 'reviews judgments, not statementsin opinions.'") (quoting Black v. Cutter Labs., 351 U.S 292, 297 (1956));Herb v. Pitcairn, 324 U.S. 117, 126 (1945) ("our power is to correctwrong judgments, not to revise opinions").

In this case, EPA's "action" is promulgation of the revised ozoneNAAQS, which consists of a discrete rule. See Pet. App. 104a. The rule itselfmakes clear that the preamble sets out the "reasons" for the rule.Ibid. The related preamble statements at issue here (see App., infra, 1a-6a)could properly be considered by the court of appeals only as they relateto the agency action in question-promulgation of the revised ozone NAAQS.Those statements do not themselves constitute "agency action."If they did, then virtually any regulatory preamble that endeavors to explainthe basis for an agency's action would arguably spawn additional agencyactions that are each potentially subject to judicial review and revision.Congress surely did not authorize courts to engage in that sort of broadand limitless anticipatory oversight of CAA programs. See Standard Oil,449 U.S. at 247-249 (Stevens, J., concurring).

B. EPA's Preamble Statements Do Not Constitute "Final" AgencyAction

Even if EPA's preamble statements constituted "agency action,"they do not constitute "final" agency action. In Bennett v. Spear,520 U.S. 154 (1997), this Court identified two conditions that must be satisfiedfor agency action to be "final": (1) it "must mark the 'consummation'of the agency's decisionmaking process"; and (2) it "must be oneby which 'rights or obligations have been determined,' or from which 'legalconsequences will flow.'" Id. at 177-178. EPA's discussion of the Act'simplementation provisions in the preamble does not satisfy either of thoserequirements.

The court of appeals improperly reconfigured the "consummation"prong by focusing solely on whether the plans that EPA described in thepreamble appeared tentative or likely to change. See Pet. App. 77a-78a.Under Bennett, however, the proper inquiry is not merely whether the agencyhas any present intention to alter its position. Rather, the question iswhether the agency has consummated its decisionmaking process. The answernecessarily depends upon what steps the governing statute requires.25

When EPA's preamble statements are considered in light of the CAA's implementationprogram, it is clear that they do not constitute final agency action. EPAcompleted the statutory process for reviewing the existing ozone standard,42 U.S.C. 7408(a), 7409(d), and reached a final decision promulgating theeight-hour ozone standard. EPA thus consummated its decisionmaking processand took final agency action in promulgating the NAAQS. 42 U.S.C. 7607(b)(1).EPA, however, has hardly begun and has not yet completed any step in theCAA's distinct process for implementing the revised ozone NAAQS, which requiresadditional rulemaking procedures.26

The CAA provides EPA up to three years after promulgating a revised NAAQSto designate all areas within the Nation as attainment, nonattainment, orunclassifiable for that standard. 42 U.S.C. 7407(d)(1).27 At the same time,for nonattainment areas, EPA must establish schedules for States to submitstate implementation plans. 42 U.S.C. 7502(b). EPA may establish classificationsfor nonattainment areas and must establish their attainment dates. 42 U.S.C.7502(a); see also 42 U.S.C. 7511(a)(1). States develop, for EPA approvalor disapproval, their SIPs to implement the NAAQS by the applicable attainmentdates. See 42 U.S.C. 7410(a) and (k), 7502(c). Under that statutory structure,NAAQS implementation proceeds through a careful decisionmaking process thatincludes designation, setting dates for SIP submissions, classifying nonattainmentareas, developing SIPs, setting attainment dates, and obtaining EPA's approvalof the SIPs. EPA's expression of its views, in a regulatory preamble, onsome aspects of that future process cannot reasonably be viewed as completingany of the discrete steps that make up that process.

EPA did not take action in the rule under review to designate, classify,or set attainment dates for any areas, to set schedules for SIP submissions,or to approve or disapprove any SIP. Thus, EPA's preamble statements donot mark the consummation of any part of the agency's implementation process.They do not conclude the agency's thinking on how it may implement the revisedozone standard, or precisely whether or how implementation of the revisedeight-hour standard may be affected by any Subpart 2 provisions. EPA's deliberationson those matters are ongoing and have not yet resulted in final agency actionthat is ripe for judicial review.

The preamble statements also do not satisfy the second Bennett requirementthat "the action must be one by which 'rights or obligations have beendetermined,' or from which 'legal consequences will flow.'" 520 U.S.at 178. The court of appeals concluded that EPA's preamble statements respectingfuture implementation were final action because by "promulgating arevised ozone NAAQS the EPA has triggered the provisions of §§107(d)(1) and 172, which impose a number of requirements upon the states* * * [and] those areas that do not comply will ultimately be required todo so." Pet. App. 78a. Any obligations triggered by promulgation ofthe NAAQS arise, however, regardless of what EPA said, or did not say, inthe preamble about implementation. No legal consequences flow from the preamblestatements themselves. EPA's views on implementation will produce tangiblelegal consequences only when EPA takes actual steps to implement the NAAQSthrough the prescribed rulemaking processes. Affected parties will be ableto obtain judicial review of EPA's judgments on implementation once EPAtakes final action that actually creates new legal obligations.

C. EPA's Preamble Statements Regarding Implementation Of The Eight-HourOzone Standard Are Not Ripe For Review

Even if EPA's preamble statements were final agency action, that purportedagency action would not be ripe for judicial review. The ripeness doctrineserves "to prevent the courts, through avoidance of premature adjudication,from entangling themselves in abstract disagreements over administrativepolicies, and also to protect the agencies from judicial interference untilan administrative decision has been formalized and its effects felt in aconcrete way by the challenging parties." Ohio Forestry Ass'n v. SierraClub, 523 U.S. 726, 732-733 (1998) (quoting Abbott Labs., 387 U.S. at 148-149).

The ripeness doctrine "is drawn both from Article III limitations onjudicial power and from prudential reasons for refusing to exercise jurisdiction."Reno v. Catholic Soc. Servs., Inc., 509 U.S. 43, 57 n.18 (1993). To determinewhether a controversy is ripe a court must "evaluate both the fitnessof the issues for judicial decision and the hardship to the parties of withholdingcourt consideration." Texas v. United States, 523 U.S. 296, 301 (1998)."A claim is not ripe for adjudication if it rests upon 'contingentfuture events that may not occur as anticipated, or indeed may not occurat all.'" Id. at 300.

The court of appeals' concerns regarding how to reconcile Subparts 1 and2 are not yet fit for review because, at this stage, the matter is too abstract,as demonstrated by the breadth and generality of the court's conclusion.EPA has neither fully developed its interpretation nor attempted to exerciseits authority to implement the eight-hour ozone standard. See, e.g., OhioForestry, 523 U.S. at 732-738; Abbott Labs., 387 U.S. at 148-149.

The interplay among Sections 107(d), 172, and 181, and other relevant provisionsof the Act, is complex. As we have explained, EPA expressed views on selectedimplementation provisions of the Act to respond to comments in the ozonerulemaking that those provisions negate EPA's NAAQS revision authority.A court's consideration of whether and how Section 181(a) and other sectionsof Subpart 2 may affect EPA's authority under the various provisions ofSubpart 1 would be on much surer footing if the reviewing court had thebenefit of EPA's full explanation of how and why it has implemented therevised ozone standard in a particular way, after the completion of a relevantdecisional process (including any required public notice and comment) thatactually implements the standard.28

The case for deferring review is especially strong here because the resolutionof any tension between the various provisions in Subparts 1 and 2 may dependupon the circumstances of the particular nonattainment area at issue. See,e.g., Pet. App. 40a-41a (expressing concern regarding the interplay andfuture application of Sections 172(a) and 181(a)(1) on Los Angeles). Deferringreview of those implementation issues would allow EPA the opportunity towork through the various implementation provisions in concrete settings,reconcile conflicts, make policy judgments, and apply its expertise as necessaryto resolve ambiguities in the statute. See Ohio Forestry, 523 U.S. at 733-734;Chevron U.S.A. Inc. v. NRDC, 467 U.S. 837, 842-845 (1984).

Judicial intervention at this point would also "den[y] the agency anopportunity to correct its own mistakes and to apply its expertise."Standard Oil, 449 U.S. at 242. Deferring review would facilitate futurejudicial review by reducing the issues to manageable proportions. The importanceof a concrete setting for judicial review is underscored by the court'sown confusion regarding EPA's interpretation, compare Pet. App. 43a-44a,with id. at 80a-81a and id. at 87a-88a, its reliance upon predicted futureoutcomes in particular areas, id. at 40a-41a, and the extreme breadth andlack of clarity of the court's ultimate conclusion that "EPA can enforcea revised primary ozone NAAQS only in conformity with Subpart 2," id.at 81a.

Finally, deferring review will not work substantial hardship. EPA's expressionof its views in the preamble created no obligations that adversely affectany parties' day-to-day operations, and the parties will have ample opportunityto bring their legal challenge when any harm is more immediate and certain.See Lujan, 497 U.S. at 891; Ohio Forestry, 523 U.S. at 733-734; Toilet GoodsAss'n v. Gardner, 387 U.S. 158, 164 (1967).

III. THE COURT OF APPEALS IMPROPERLY RESTRICTED EPA'S AUTHORITY TO IMPLEMENTTHE REVISED OZONE STANDARD

If this Court were to reach the merits of the court of appeals' decisionrespecting implementation, it should reverse that decision. The court ofappeals correctly upheld EPA's authority to revise the ozone NAAQS, andit correctly concluded that the CAA requires EPA to designate all areasof the Nation as attainment, nonattainment, or unclassifiable areas forthe revised standard. Pet. App. 34a-37a. The court erred, however, in concludingthat EPA could not enforce a more protective ozone standard in those designatedareas. See id. at 37a-44a. On rehearing, the court modified its views andconcluded that "EPA can enforce a revised primary ozone NAAQS onlyin conformity with Subpart 2." Id. at 81a. Judge Tatel explained inhis partial concurrence that the panel's revised decision allows EPA toenforce its revised ozone standard under Subpart 1 in an area only afterthat area attains the one-hour standard under Subpart 2. Id. at 89a (Tatel,J., concurring). But even under that view, the court of appeals' decisionis incorrect.

As we explain below, EPA reasonably interprets the CAA to require that EPAimplement a revised ozone standard under Subpart 1. The revised NAAQS isa National Ambient Air Quality Standard that should apply throughout theentire Nation, for all members of the public, including those that residein areas that do not currently attain the one-hour standard. There is nowarrant for categorically requiring that EPA ensure compliance with the very one-hour ozone standardthat it found inadequate to protect public health before it can requireefforts to attain the more protective revised ozone NAAQS.

A. The Clean Air Act Authorizes EPA To Implement The Revised Ozone NAAQSUnder Subpart 1 Of Part D

Title I of the CAA, 42 U.S.C. 7401-7515 (1994 & Supp. III 1997), governsthe promulgation and implementation of all NAAQS, and it directs that the NAAQS be attained "as expeditiously as practicable." 42 U.S.C. 7502(a)(2), 7511(a)(1).Part A expressly requires EPA to reconsider and, if appropriate, revisethe NAAQS-including the pre-existing one-hour ozone standard-every fiveyears. 42 U.S.C. 7409(d)(1); Pet. App. 34a. Subpart 1 of Part D, which governsimplementation for "Nonattainment Areas in General," sets outspecific provisions for implementing revised NAAQS. 42 U.S.C. 7502(a)(1).It follows that EPA's revised ozone NAAQS would be subject to implementationunder Subpart 1. The court of appeals' counter-intuitive conclusion -thatthe revised ozone NAAQS must be implemented in conformity with Subpart 2,which addresses the former ozone NAAQS-conflicts at the outset with thebasic framework of the Act.

Subpart 1's specific language reveals that the court's construction is wrong.Section 172(a) establishes classifications and attainment dates for allareas designated nonattainment "pursuant to section [107(d)] with respectto any * * * revised standard, including a revision of any standard in effecton November 15, 1990." 42 U.S.C. 7502(a)(1)(A). Section 172(a)(1)(A)'sreference to "any" revised standard includes a revision of theone-hour ozone standard, because that standard was "in effect on November15, 1990." See 40 C.F.R. 50.9 (1990). Thus, Section 172(a), on itsface, makes clear that Subpart 1 governs the selection of classificationsand attainment dates for a revised ozone NAAQS.

The court of appeals questioned that interpretation because Sections 172(a)(1)(C)and 172(a)(2)(D) provide that EPA's classification and attainment date-settingauthority under Section 172(a) does not apply to "nonattainment areasfor which classifications [or "attainment dates"] are specificallyprovided under other provisions of [Part D]." 42 U.S.C. 7502(a)(1)(C)and (a)(2)(D). See Pet. App. 37a. The court of appeals noted that Section181(a)(1), in Subpart 2 of Part D, provides that "each area designatednonattainment for ozone pursuant to [Section 107(d)]" is to be classifiedand given an attainment date under its Table 1. 42 U.S.C. 7511(a)(1). SeePet. App. 38a. In the court's view, Section 181(a)(1) dictates that allareas that are designated as nonattainment for ozone under Section 107(d),including areas designated under the revised ozone NAAQS, are subject toSubpart 2's provisions. Id. at 38a-39a. Congress, however, adequately answeredthe court's concern over those seemingly competing references.

Section 181(a)-which is contained in Subpart 2 of Part D-"specificallyprovide[s]" classifications and attainment dates for only a particularsubset of ozone "nonattainment areas." Section 181(a)'s captionstates that the Section provides "Classification and attainment datesfor 1989 nonattainment areas." 42 U.S.C. 7511(a) (emphasis added).The 1989 nonattainment areas are, of course, the areas that were subjectto the one-hour ozone standard then in force. Congress enacted Subpart 2out of concern over the continuing nonattainment of the one-hour ozone standardthat existed when it enacted the 1990 Amendments. It plainly crafted Section181(a)(1) to address that specific problem. The title of Section 181(a)clarifies that Section's reach and resolves any confusion about whetherSubpart 2 governs implementation of the revised ozone NAAQS. See INS v.National Ctr. for Immigrants' Rights, Inc., 502 U.S. 183, 189 (1991); MeadCorp. v. Tilley, 490 U.S. 714, 723 (1989); FTC v. Mandel Bros., 359 U.S.385, 388-389 (1959).

The court of appeals' contrary conclusion would lead to unworkable and absurdresults. For example, Section 181(a)(1) sets attainment dates and classificationsbased on an area's "design value," which is an air quality measurethat specifically applies to the one-hour ozone standard that was in existencein 1990. See 42 U.S.C. 7511(a)(1).29 It would make no sense-and, indeed,would be impossible-to classify areas and set their attainment dates forthe revised NAAQS's eight-hour standard using an air quality measurementbased upon one-hour averaging. The eight-hour NAAQS rests on an entirelydifferent averaging methodology, statistical form, and concentration. See40 C.F.R. 50.10 & Pt. 50 App. I, ¶¶ 2-3.

In addition, Section 181(a) calculates attainment dates for areas basedupon a fixed number of years from 1990. See 42 U.S.C. 7511(a)(1) (Table1). Section 181(a)(1) makes reference to 1990 because it establishes attainmentdates for the "1989 nonattainment areas," which had not attainedthe one-hour ozone standard at the time of enactment of the 1990 Amendments.That timetable makes no sense in calculating attainment dates for a revisedNAAQS. Indeed, many of Section 181(a)(1)'s attainment dates, including thosefor "marginal," "moderate," and "serious"nonattainment areas, have already passed. See 42 U.S.C. 7511(a) (Table 1).30

In light of those considerations, Section 181(a)(1) cannot reasonably beconstrued to have "specifically provided" classifications andattainment dates for the eight-hour ozone standard. Rather, the text andcontext of Section 181(a) indicate that Congress intended Section 181(a)(1)to provide classifications and attainment dates only for "1989 nonattainmentareas" that had been designated under the then-current one-hour ozonestandard. See 42 U.S.C. 7407(d)(1)(C) and (4)(A). EPA's view that Congressintended EPA to implement the revised NAAQS under Subpart 1 and to implementthe former NAAQS under Subpart 2 represents, at a minimum, a permissibleand reasonable accommodation of the provisions entrusted to the agency'scare. See, e.g., Chevron, 467 U.S. at 842-845.

B. Delaying Implementation Of The Revised NAAQS Until The Previous StandardIs Attained Conflicts With The Clean Air Act's Requirement That All NAAQSBe Attained "As Expeditiously As Practicable"

The court of appeals also erred in its apparent conclusion that EPA cannotimplement the revised ozone NAAQS in an area until that area has had anopportunity to meet the attainment dates for the one-hour ozone standard.See Pet. App. 89a. The court overlooked that the attainment dates set outin Section 181(a)(1) establish the maximum period of time allowed for attainment.See 42 U.S.C. 7511(a)(1). Both Subpart 1 and Subpart 2 require that allareas attain the NAAQS "as expeditiously as practicable." CAA§§ 172(a)(2), 181(a)(1), 42 U.S.C. 7502(a)(2), 7511(a)(1); seeH.R. Rep. No. 490, 101st Cong., 2d Sess. Pt. at 1, at 229; S. Rep. No. 228,101st Cong., 1st Sess. 37 (1989). EPA accordingly is justified in concludingthat it should implement the revised ozone standard without delay throughoutthe Nation in accordance with the timing provisions set out in Subpart 1.42 U.S.C. 7502(a)(2).

The court of appeals expressed concern that a practical conflict could conceivablyarise for the Los Angeles area between Subpart 1's deadline to attain therevised ozone standard and Subpart 2's attainment date for the one-hourozone standard. See Pet. App. 41a. It is entirely reasonable, however, forCongress to require that, once EPA determines that a revised NAAQS is necessaryto protect public health, the revised NAAQS should be attained without avoidabledelay notwithstanding the timetable that Congress envisioned for the standardthen in effect.31

Moreover, the court of appeals has overstated the practical problem thatthe revised NAAQS would pose. As we have noted, the deadlines for attainmentin Section 181(a)(1) are only outer time limits for attaining the one-hourstandard. See 42 U.S.C. 7511(a)(1). Los Angeles would be required to attainthe revised NAAQS under Subpart 1 no later than the same year that marksthe outer time limit for attaining Subpart 2's one-hour ozone standard.Compare CAA § 172(a)(2), 42 U.S.C. 7502(a)(2), with CAA § 181(a)(1)and (5), 42 U.S.C. 7511(a)(1) and (5). That situation, however, does notnecessarily pose any practical problems. For example, it may be "practicable"-andpreferable from an implementing State's perspective-to achieve both theone-hour ozone standard and the revised ozone standard at approximatelythe same time. There is no reason to believe that Congress intended to precludethat approach.

In any event, the question of how to reconcile any competing compliancedeadlines is clearly the type of issue that should first be addressed byEPA through future final action under the implementation process, includingany required public notice and opportunity for comment. EPA's determinationscan then be subject to judicial review in the appropriate court of appeals.See 42 U.S.C. 7607(b)(1). To the extent that there is tension between Subparts1 and 2, it will be up to EPA to harmonize the applicable provisions, andthe courts must defer to EPA's reasonable judgment on the matter. Chevron,467 U.S. at 845. Those issues, however, are properly reserved for anotherday. Regardless of how those provisions may ultimately be applied, theycertainly do not justify the court of appeals' conclusion that Congressprohibited EPA from implementing the revised ozone standard in an area untilit attains the very standard that EPA found was not adequate to protectpublic health.

CONCLUSION

The judgment of the court of appeals should be reversed and the case remandedfor further proceedings.

Respectfully submitted.

SETH P. WAXMAN
Solicitor General
LOIS J. SCHIFFER
Assistant Attorney General
LAWRENCE G. WALLACE
Deputy Solicitor General
JEFFREY P. MINEAR
Assistant to the Solicitor
General
DAVID J. KAPLAN
MARY F. EDGAR
Attorneys

GARY S. GUZY
General Counsel
GERALD K. GLEASON
MICHAEL L. GOO
JAN M. TIERNEY
KEVIN W. MCLEAN
Attorneys
Environmental Protection
Agency


JULY 2000

1 See NAAQS for Particulate Matter, 62 Fed.Reg. 38,652 (1997); NAAQS for Ozone, 62 Fed. Reg. 38,856 (1997). Copiesof the Federal Register notices have been lodged with the Clerk of the Court.

2 Congress first addressed the problem of air pollution through the AirPollution Control Act of 1955, ch. 360, 69 Stat. 322, which authorized theSecretary of Health, Education, and Welfare (HEW) to conduct research activities.Congress later expanded HEW's authority to include, among other things,compiling and publishing air quality criteria based on scientific studies,Clean Air Act of 1963, Pub. L. No. 88-206, §1, 77 Stat. 392, 395. Congresslater directed States to develop regionally based ambient air quality standardsand provided mechanisms for enforcement, Air Quality Act of 1967, Pub. L.No. 90-148, § 108(c), 81 Stat. 492-494. Congress substantially revisedthat program through the Clean Air Act Amendments of 1970, Pub. L. No. 91-604,84 Stat. 1679, which provided for national ambient air quality standardsand for state implementation. See § 107(a), 84 Stat. 1679-1683. Congresscontinued to build on that program through the Clean Air Act Amendmentsof 1977, Pub. L. No. 95-95, 91 Stat. 685, and the Clean Air Act Amendmentsof 1990, Pub. L. No. 101-549, 104 Stat. 2399. See text at p. 6, infra, andnote 5, infra.

3 We have provided a set of the Criteria Documents and Staff Papers forPM and ozone to the Clerk of the Court.

4 See, e.g., 59 Fed. Reg. 38,906-38,907 (1994) (carbon monoxide NAAQS);52 Fed. Reg. 24,634-24,635 (1987) (PM NAAQS); 50 Fed. Reg. 25,532 (1985)(nitrogen dioxide NAAQS).

5 The Clean Air Amendments of 1970 introduced the NAAQS concept and requiredStates to attain each NAAQS "as expeditiously as practicable but ** * in no case later than three years" after EPA approves a SIP. 42U.S.C. 1857c-5(a)(2)(A)(i) (1970). The Clean Air Act Amendments of 1977added a new outside attainment date (1982, or 1987 if extended, 42 U.S.C.7502(a) and (c) (1982)), and introduced the concept of designating areas"nonattainment" for each NAAQS. 42 U.S.C. 7407(d) (1982). The1977 Amendments also introduced a new "Part D," which containedadditional attainment provisions for all NAAQS that apply to all nonattainmentareas. See 42 U.S.C. 7501-7508 (1982) (Pt. D, Tit. I).

6 The dates must be set so that attainment is achieved as "as expeditiouslyas practicable," with outside dates that may range up to 10 years fromthe date an area is designated nonattainment, with two one-year extensionspossible. 42 U.S.C. 7502(a)(2)(A) and (C).

7 Subparts 3-5 contain additional provisions that address the continuednonattainment of the other existing standards. 42 U.S.C. 7512-7512a (1994& Supp. III 1997); 42 U.S.C. 7513-7513b, 7514-7514a.

8 Table 1 of Section 181(a)(1) establishes specific classifications fornonattainment areas under the one-hour ozone standard based upon the area's"design value," which refers to the measurement methodology thenin use. See note 29, infra. Table 1 also sets a corresponding attainmentdate for each classification, expressed as either 3, 6, 9, 15, or 20 years"after November 15, 1990," when the 1990 Amendments were enacted.42 U.S.C. 7511(a)(1).

9 Generally, fine particles are by-products of combustion or the reactionand transformation of gases. PM App. 519, 1786. Coarse particles generallyare the result of abrasion of material into smaller pieces, which are thensuspended in the air by wind or human activity. Id. at 519, 1787. PM10 denotesparticulate matter up to about 10 micrometers (µm) in diameter, whichis the fraction of PM that can be inhaled into the human lungs. 62 Fed.Reg. at 38,654 n.1, 38,666-38,667. PM2.5 denotes particles up to about 2.5µm in diameter. Id. at 38,654 n.5.

10 Epidemiological studies examine patterns of disease in real-world humanpopulations. Epidemiologists look for statistical associations that mayreflect cause-and-effect relationships, using the concept of statisticalsignificance to separate those associations from results that may be theproduct of chance. See Modern Epidemiology 184 (K.J. Rothman & S. Greenlandeds., 2d ed. 1998).

11 EPA adopted a 24-hour PM2.5 NAAQS of 65 µg/m3 to "supplement"the protection afforded by the annual PM2.5 standard. 62 Fed. Reg. at 38,677.The Administrator also determined that secondary PM2.5 standards identical

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