WHITMAN, ADMINISTRATOR OF ENVIRONMENTAL PROTECTION AGENCY, et al. v. AMERICAN TRUCKING ASSOCIATIONS, INC., et al.

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457 OCTOBER TERM, 2000
Syllabus
WHITMAN, ADMINISTRATOR OF ENVIRONMENTAL
PROTECTION AGENCY, et al. v. AMERICAN
TRUCKING ASSOCIATIONS, INC., et al.
certiorari to the united states court of appeals for
the district of columbia circuit
No. 99–1257. Argued November 7, 2000—Decided February 27, 2001*
Section 109(a) of the Clean Air Act (CAA) requires the Environmental
Protection Agency (EPA) Administrator to promulgate national ambient
air quality standards (NAAQS) for each air pollutant for which “air
quality criteria” have been issued under § 108. Pursuant to § 109(d)(1),
the Administrator in 1997 revised the ozone and particulate matter
NAAQS. Respondents in No. 99–1257, private parties and several
States (hereinafter respondents), challenged the revised NAAQS on
several grounds. The District of Columbia Circuit found that, under
the Administrator’s interpretation, § 109(b)(1)—which instructs the
EPA to set standards “the attainment and maintenance of which . . .
are requisite to protect the public health” with “an adequate margin
of safety”—delegated legislative power to the Administrator in contra-
vention of the Federal Constitution, and it remanded the NAAQS to the
EPA. The Court of Appeals also declined to depart from its rule that
the EPA may not consider implementation costs in setting the NAAQS.
And it held that, although certain implementation provisions for the
ozone NAAQS contained in Part D, Subpart 2, of Title I of the CAA
did not prevent the EPA from revising the ozone standard and desig-
nating certain areas as “nonattainment areas,” those provisions, rather
than more general provisions contained in Subpart 1, constrained the
implementation of the new ozone NAAQS. The court rejected the
EPA’s argument that it lacked jurisdiction to reach the implementation
question because there had been no “final” implementation action.
Held:
1. Section 109(b) does not permit the Administrator to consider im-
plementation costs in setting NAAQS. Because the CAA often ex-
pressly grants the EPA the authority to consider implementation costs,
a provision for costs will not be inferred from its ambiguous provi-
sions. Union Elec. Co. v. EPA, 427 U. S. 246, 257, and n. 5. And since
*Together with No. 99–1426, American Trucking Associations, Inc.,
et al. v. Whitman, Administrator of Environmental Protection Agency,
et al., also on certiorari to the same court.

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458 WHITMAN v. AMERICAN TRUCKING ASSNS., INC.
Syllabus
§ 109(b)(1) is the engine that drives nearly all of Title I of the CAA, the
textual commitment of costs must be clear; Congress does not alter a
regulatory scheme’s fundamental details in vague terms or ancillary
provisions, see MCI Telecommunications Corp. v. American Tele-
phone & Telegraph Co., 512 U. S. 218, 231. Respondents’ arguments
founder upon this principle. It is implausible that § 109(b)(1)’s modest
words “adequate margin” and “requisite” give the EPA the power to
determine whether implementation costs should moderate national air
quality standards. Cf. ibid. And the cost factor is both so indirectly
related to public health and so full of potential for canceling the con-
clusions drawn from direct health effects that it would have been ex-
pressly mentioned in §§ 108 and 109 had Congress meant it to be con-
sidered. Other CAA provisions, which do require cost data, have no
bearing upon whether costs are to be taken into account in setting
the NAAQS. Because the text of § 109(b)(1) in its context is clear, the
canon of construing texts to avoid serious constitutional problems is not
applicable. See, e. g., Miller v. French, 530 U. S. 327, 341. Pp. 464–471.
2. Section 109(b)(1) does not delegate legislative power to the EPA.
When conferring decisionmaking authority upon agencies, Congress
must lay down an intelligible principle to which the person or body
authorized to act is directed to conform. J. W. Hampton, Jr., & Co. v.
United States, 276 U. S. 394, 409. An agency cannot cure an unlawful
delegation of legislative power by adopting in its discretion a limiting
construction of the statute. The limits that § 109(b)(1) imposes on
the EPA’s discretion are strikingly similar to the ones approved in,
e. g., Touby v. United States, 500 U. S. 160, and the scope of discretion
that § 109(b)(1) allows is well within the outer limits of the Court’s non-
delegation precedents, see, e. g., Panama Refining Co. v. Ryan, 293 U. S.
388. Statutes need not provide a determinate criterion for saying how
much of a regulated harm is too much to avoid delegating legislative
power. Pp. 472–476.
3. The Court of Appeals had jurisdiction to consider the implemen-
tation issue under § 307 of the CAA. The implementation policy
constitutes final agency action under § 307 because it marked the con-
summation of the EPA’s decisionmaking process, see Bennett v. Spear,
520 U. S. 154. The decision is also ripe for review. The question is
purely one of statutory interpretation that would not benefit from
further factual development, see Ohio Forestry Assn., Inc. v. Sierra
Club, 523 U. S. 726, 733; review will not interfere with further admin-
istrative development; and the hardship on respondent States in de-
veloping state implementation plans satisfies the CAA’s special judicial-
review provision permitting preenforcement review, see id., at 737.

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459 Cite as: 531 U. S. 457 (2001)
Syllabus
The implementation issue was also fairly included within the challenges
to the final ozone rule that were before the Court of Appeals, which all
parties agree is final agency action ripe for review. Pp. 476–480.
4. The implementation policy is unlawful. Under Chevron U. S. A.
Inc. v. Natural Resources Defense Council, Inc., 467 U. S. 837, if the
statute resolves the question whether Subpart 1 or Subpart 2 applies
to revised ozone NAAQS, that ends the matter; but if the statute is
ambiguous, the Court must defer to a reasonable agency interpretation.
Here, the statute is ambiguous concerning the interaction between
Subpart 1 and Subpart 2, but the Court cannot defer to the EPA’s in-
terpretation, which would render Subpart 2’s carefully designed re-
strictions on EPA discretion nugatory once a new ozone NAAQS has
been promulgated. The principal distinction between the subparts is
that Subpart 2 eliminates regulatory discretion allowed by Subpart 1.
The EPA may not construe the statute in a way that completely nullifies
textually applicable provisions meant to limit its discretion. In addi-
tion, although Subpart 2 was obviously written to govern implemen-
tation for some time into the future, nothing in the EPA’s interpreta-
tion would have prevented the agency from aborting the subpart the
day after it was enacted. It is left to the EPA to develop a reasonable
interpretation of the nonattainment implementation provisions insofar
as they apply to revised ozone NAAQS. Pp. 481–486.
175 F. 3d 1027 and 195 F. 3d 4, affirmed in part, reversed in part, and
remanded.
Scalia, J., delivered the opinion of the Court, Parts I and IV of which
were unanimous, Part II of which was joined by Rehnquist, C. J., and
Stevens, O’Connor, Kennedy, Souter, Thomas, and Ginsburg, JJ.,
and Part III of which was joined by Rehnquist, C. J., and O’Connor,
Kennedy, Thomas, Ginsburg, and Breyer, JJ. Thomas, J., filed a con-
curring opinion, post, p. 486. Stevens, J., filed an opinion concurring in
part and concurring in the judgment, in which Souter, J., joined, post,
p. 487. Breyer, J., filed an opinion concurring in part and concurring in
the judgment, post, p. 490.
Solicitor General Waxman argued the cause for petition-
ers in No. 99–1257 and federal respondents in No. 99–1426.
With him on the briefs were Assistant Attorney General
Schiffer, Deputy Solicitor General Wallace, Jeffrey P.
Minear, Christopher S. Vaden, David J. Kaplan, Mary
F. Edgar, Gary S. Guzy, Gerald K. Gleason, and Michael
L. Goo.

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460 WHITMAN v. AMERICAN TRUCKING ASSNS., INC.
Counsel
Edward W. Warren argued the cause for American Truck-
ing Associations et al., respondents in No. 99–1257 and
cross-petitioners in No. 99–1426. With him on the briefs
were Robert R. Gasaway, Jeffrey B. Clark, Daryl Joseffer,
Charles Fried, Robin S. Conrad, Beth L. Law, Robert S.
Digges, Gary H. Baise, David M. Friedland, Erika Z. Jones,
Timothy S. Bishop, Jan S. Amundson, Dimetria G. (Jim)
Daskal, Douglas I. Greenhaus, and Chet M. Thompson. Ju-
dith L. French, Assistant Attorney General of Ohio, argued
the cause for respondents State of Ohio et al. in No. 99–1257.
With her on the brief in No. 99–1257 and on the briefs
for State of Ohio et al., respondents in support of cross-
petitioners in No. 99–1426, were Betty D. Montgomery, At-
torney General, Edward B. Foley, State Solicitor, Elise W.
Porter, Frank J. Reed, Jr., and James G. Tassie, Assistant
Attorneys General, Mark J. Rudolph, Jennifer M. Gran-
holm, Attorney General of Michigan, Thomas Casey, Solici-
tor General, and Alan F. Hoffman and Pamela J. Stevenson,
Assistant Attorneys General. Thomas F. Reilly, Attorney
General of Massachusetts, Edward G. Bohlen, Assistant At-
torney General, Lisa Heinzerling, John J. Farmer, Attorney
General of New Jersey, and Howard L. Geduldig and John
R. Renella, Deputy Attorneys General, filed briefs for
the Commonwealth of Massachusetts et al., respondents in
support of petitioners in No. 99–1257 and respondents in
No. 99–1426. Howard I. Fox filed briefs for the American
Lung Association, respondent in support of petitioners
in No. 99–1257 and respondent in No. 99–1426. Henry V.
Nickel, F. William Brownell, Lucinda Minton Langworthy,
David E. Menotti, William F. Pedersen, Jeffrey A. Knight,
G. William Frick, M. Elizabeth Cox, Russel S. Frye, Rich-
ard Wasserstrom, Grant Crandall, David F. Zoll, Alexandra
Dapolito Dunn, Julie Becker, Harold P. Quinn, Jr., New-
man R. Porter, David M. Flannery, and Kurt E. Blase filed
briefs for Appalachian Power Co. et al., respondents in

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461 Cite as: 531 U. S. 457 (2001)
Counsel
No. 99–1257 and respondents in support of cross-petitioners
in No. 99–1426. Robert E. Yuhnke filed a brief for Citi-
zens for Balanced Transportation et al., respondents in
No. 99–1426.†
†Briefs of amici curiae urging reversal were filed for the State of New
York et al. by Eliot Spitzer, Attorney General of New York, Preeta D.
Bansal, Solicitor General, Daniel X. Smirlock, Deputy Solicitor General,
and Lisa Feiner and J. Jared Snyder, Assistant Attorneys General, and
by the Attorneys General for their respective States as follows: Bill Lock-
yer of California, Richard Blumenthal of Connecticut, Andrew Ketterer of
Maine, J. Joseph Curran, Jr., of Maryland, Philip McLaughlin of New
Hampshire, D. Michael Fisher of Pennsylvania, Sheldon Whitehouse of
Rhode Island, and William H. Sorrell of Vermont; for the State of North
Carolina by Michael F. Easley, Attorney General, Daniel C. Oakley, Se-
nior Deputy Attorney General, and Marc D. Bernstein, Assistant Attorney
General; for the American Boiler Manufacturers Association by Gene E.
Godley and Shannon H. Ratliff II; and for the American Crop Protection
Association et al. by Herbert L. Fenster and Lawrence S. Ebner.
Briefs of amici curiae urging affirmance were filed for the State of
California et al. by Bill Lockyer, Attorney General of California, Richard
M. Frank, Chief Assistant Attorney General, Theodora P. Berger, Senior
Assistant Attorney General, and Susan L. Durbin and Sean B. Hecht,
Deputy Attorneys General, Richard Blumenthal, Attorney General of
Connecticut, Thomas J. Miller, Attorney General of Iowa, Andrew Ket-
terer, Attorney General of Maine, J. Joseph Curran, Jr., Attorney General
of Maryland, Patricia Madrid, Attorney General of New Mexico, Eliot
Spitzer, Attorney General of New York, Preeta D. Bansal, Solicitor
General, and Daniel X. Smirlock, Deputy Solicitor General, William H.
Sorrell, Attorney General of Vermont, and Christine O. Gregoire, Attor-
ney General of Washington; for the Commonwealth of Virginia by Mark
L. Earley, Attorney General, William Hurd, Solicitor General, Roger L.
Chaffe, Senior Assistant Attorney General, and Stewart T. Leeth, Assist-
ant Attorney General; for the American Institute of Certified Public
Accountants et al. by Theodore B. Olson, Douglas R. Cox, and Mark A.
Perry; for the Association of American Physicians & Surgeons et al. by
Erik S. Jaffe; for the Clean Air Trust et al. by Christopher H. Schroeder;
for the Lincoln Institute for Research and Education et al. by William J.
Olson, John S. Miles, Herbert W. Titus, and Lawrence J. Straw, Jr.; for
the Manufacturers Alliance/MAPI Inc. et al. by David Schoenbrod and
Marci A. Hamilton; for the United States Public Interest Research Group

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462 WHITMAN v. AMERICAN TRUCKING ASSNS., INC.
Opinion of the Court
Justice Scalia delivered the opinion of the Court.
These cases present the following questions: (1) Whether
§ 109(b)(1) of the Clean Air Act (CAA) delegates legisla-
tive power to the Administrator of the Environmental Pro-
tection Agency (EPA). (2) Whether the Administrator may
consider the costs of implementation in setting national
ambient air quality standards (NAAQS) under § 109(b)(1).
(3) Whether the Court of Appeals had jurisdiction to review
the EPA’s interpretation of Part D of Title I of the CAA,
42 U. S. C. §§ 7501–7515, with respect to implementing the
revised ozone NAAQS. (4) If so, whether the EPA’s inter-
pretation of that part was permissible.
I
Section 109(a) of the CAA, as added, 84 Stat. 1679, and
amended, 42 U. S. C. § 7409(a), requires the Administrator
of the EPA to promulgate NAAQS for each air pollutant
for which “air quality criteria” have been issued under § 108,
42 U. S. C. § 7408. Once a NAAQS has been promulgated,
the Administrator must review the standard (and the criteria
Education Fund by James Keith Weeks and David M. Driesen; and for
Senator James H. Inhofe et al. by Paul Rosenzweig.
Briefs of amici curiae were filed for the AEI-Brookings Joint Center
for Regulatory Studies et al. by Robert E. Litan; for Alcan Aluminum
Corp. by Lawrence A. Salibra II; for Environmental Defense et al. by
Richard L. Revesz and Ann Brewster Weeks; for General Electric Co. by
Laurence H. Tribe, Jonathan S. Massey, Thomas C. Goldstein, Benjamin
W. Heineman, Jr., Brackett B. Denniston III, and Matthew Tanzer; for
the Institute for Justice et al. by William H. Mellor, Clint Bolick, Deb-
orah Simpson, Timothy Lynch, and Ronald D. Rotunda; for Intel Corp.
et al. by Richard P. Bress, Claudia M. O’Brien, and Gregory S. Slater;
for the Mercatus Center by Ernest Gelhorn and Ann G. Weymouth; for
the Pacific Legal Foundation et al. by M. Reed Hopper; for People for
the U. S. A. et al. by Christopher C. Horner; for the Washington Legal
Foundation et al. by Paul D. Clement, Jeffrey S. Bucholtz, Daniel J.
Popeo, and Paul D. Kamenar; for Senator Orrin Hatch et al. by Carter G.
Phillips, Alan Charles Raul, Stephen B. Kinnaird, Lloyd N. Cutler, and
C. Boyden Gray; and for Gary E. Marchant et al. by Cary Coglianese.

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Opinion of the Court
on which it is based) “at five-year intervals” and make “such
revisions . . . as may be appropriate.” CAA § 109(d)(1), 42
U. S. C. § 7409(d)(1). These cases arose when, on July 18,
1997, the Administrator revised the NAAQS for particulate
matter and ozone. See NAAQS for Particulate Matter, 62
Fed. Reg. 38652 (codified in 40 CFR § 50.7 (1999)); NAAQS
for Ozone, id., at 38856 (codified in 40 CFR §§ 50.9, 50.10
(1999)). American Trucking Associations, Inc., and its co-
respondents in No. 99–1257—which include, in addition to
other private companies, the States of Michigan, Ohio, and
West Virginia—challenged the new standards in the Court
of Appeals for the District of Columbia Circuit, pursuant to
42 U. S. C. § 7607(b)(1).
The District of Columbia Circuit accepted some of the
challenges and rejected others. It agreed with the No. 99–
1257 respondents (hereinafter respondents) that § 109(b)(1)
delegated legislative power to the Administrator in contra-
vention of the United States Constitution, Art. I, § 1, because
it found that the EPA had interpreted the statute to pro-
vide no “intelligible principle” to guide the agency’s exer-
cise of authority. American Trucking Assns., Inc. v. EPA,
175 F. 3d 1027, 1034 (1999). The court thought, however,
that the EPA could perhaps avoid the unconstitutional dele-
gation by adopting a restrictive construction of § 109(b)(1),
so instead of declaring the section unconstitutional the court
remanded the NAAQS to the agency. Id., at 1038. (On this
delegation point, Judge Tatel dissented, finding the stat-
ute constitutional as written. Id., at 1057.) On the second
issue that the Court of Appeals addressed, it unanimously
rejected respondents’ argument that the court should depart
from the rule of Lead Industries Assn., Inc. v. EPA, 647 F.
2d 1130, 1148 (CADC 1980), that the EPA may not consider
the cost of implementing a NAAQS in setting the initial
standard. It also rejected respondents’ argument that the
implementation provisions for ozone found in Part D, Sub-
part 2, of Title I of the CAA, 42 U. S. C. §§ 7511–7511f, were

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464 WHITMAN v. AMERICAN TRUCKING ASSNS., INC.
Opinion of the Court
so tied to the existing ozone standard that the EPA lacked
the power to revise the standard. The court held that al-
though Subpart 2 constrained the agency’s method of imple-
menting the new standard, 175 F. 3d, at 1050, it did not pre-
vent the EPA from revising the standard and designating
areas of the country as “nonattainment areas,” see 42 U. S. C.
§ 7407(d)(1), by reference to it, 175 F. 3d, at 1047–1048. On
the EPA’s petition for rehearing, the panel adhered to its
position on these points, and unanimously rejected the EPA’s
new argument that the court lacked jurisdiction to reach the
implementation question because there had been no “final”
implementation action. American Trucking Assns., Inc. v.
EPA, 195 F. 3d 4 (CADC 1999). The Court of Appeals de-
nied the EPA’s suggestion for rehearing en banc, with five
judges dissenting. Id., at 13.
The Administrator and the EPA petitioned this Court for
review of the first, third, and fourth questions described in
the first paragraph of this opinion. Respondents condition-
ally cross-petitioned for review of the second question. We
granted certiorari on both petitions, 529 U. S. 1129 (2000);
530 U. S. 1202 (2000), and scheduled the cases for argument
in tandem. We have now consolidated the cases for pur-
poses of decision.
II
In Lead Industries Assn., Inc. v. EPA, supra, at 1148, the
District of Columbia Circuit held that “economic considera-
tions [may] play no part in the promulgation of ambient air
quality standards under Section 109” of the CAA. In the
present cases, the court adhered to that holding, 175 F. 3d,
at 1040–1041, as it had done on many other occasions. See,
e. g., American Lung Assn. v. EPA, 134 F. 3d 388, 389 (1998);
NRDC v. Administrator, EPA, 902 F. 2d 962, 973 (1990),
vacated in part on other grounds, NRDC v. EPA, 921 F. 2d
326 (CADC 1991); American Petroleum Institute v. Costle,
665 F. 2d 1176, 1185 (1981). Respondents argue that these

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Opinion of the Court
decisions are incorrect. We disagree; and since the first step
in assessing whether a statute delegates legislative power
is to determine what authority the statute confers, we ad-
dress that issue of interpretation first and reach respondents’
constitutional arguments in Part III, infra.
Section 109(b)(1) instructs the EPA to set primary ambi-
ent air quality standards “the attainment and maintenance of
which . . . are requisite to protect the public health” with “an
adequate margin of safety.” 42 U. S. C. § 7409(b)(1). Were
it not for the hundreds of pages of briefing respondents
have submitted on the issue, one would have thought it
fairly clear that this text does not permit the EPA to con-
sider costs in setting the standards. The language, as one
scholar has noted, “is absolute.” D. Currie, Air Pollution:
Federal Law and Analysis 4–15 (1981). The EPA, “based
on” the information about health effects contained in the
technical “criteria” documents compiled under § 108(a)(2),
42 U. S. C. § 7408(a)(2), is to identify the maximum airborne
concentration of a pollutant that the public health can toler-
ate, decrease the concentration to provide an “adequate”
margin of safety, and set the standard at that level. No-
where are the costs of achieving such a standard made part
of that initial calculation.
Against this most natural of readings, respondents make
a lengthy, spirited, but ultimately unsuccessful attack.
They begin with the object of § 109(b)(1)’s focus, the “public
health.” When the term first appeared in federal clean
air legislation—in the Act of July 14, 1955 (1955 Act), 69
Stat. 322, which expressed “recognition of the dangers to
the public health” from air pollution—its ordinary meaning
was “[t]he health of the community.” Webster’s New Inter-
national Dictionary 2005 (2d ed. 1950). Respondents argue,
however, that § 109(b)(1), as added by the Clean Air Amend-
ments of 1970, 84 Stat. 1676, meant to use the term’s second-
ary meaning: “[t]he ways and means of conserving the health

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466 WHITMAN v. AMERICAN TRUCKING ASSNS., INC.
Opinion of the Court
of the members of a community, as by preventive medicine,
organized care of the sick, etc.” Ibid. Words that can have
more than one meaning are given content, however, by their
surroundings, FDA v. Brown & Williamson Tobacco Corp.,
529 U. S. 120, 132–133 (2000); Jones v. United States, 527
U. S. 373, 389 (1999), and in the context of § 109(b)(1) this
second definition makes no sense. Congress could not have
meant to instruct the Administrator to set NAAQS at a level
“requisite to protect” “the art and science dealing with the
protection and improvement of community health.” Web-
ster’s Third New International Dictionary 1836 (1981). We
therefore revert to the primary definition of the term: the
health of the public.
Even so, respondents argue, many more factors than air
pollution affect public health. In particular, the economic
cost of implementing a very stringent standard might pro-
duce health losses sufficient to offset the health gains
achieved in cleaning the air—for example, by closing down
whole industries and thereby impoverishing the workers
and consumers dependent upon those industries. That is
unquestionably true, and Congress was unquestionably
aware of it. Thus, Congress had commissioned in the Air
Quality Act of 1967 (1967 Act) “a detailed estimate of the
cost of carrying out the provisions of this Act; a compre-
hensive study of the cost of program implementation by
affected units of government; and a comprehensive study of
the economic impact of air quality standards on the Nation’s
industries, communities, and other contributing sources of
pollution.” § 2, 81 Stat. 505. The 1970 Congress, armed
with the results of this study, see The Cost of Clean Air,
S. Doc. No. 91–40 (1969) (publishing the results of the study),
not only anticipated that compliance costs could injure the
public health, but provided for that precise exigency. Sec-
tion 110(f)(1) of the CAA permitted the Administrator to
waive the compliance deadline for stationary sources if, inter

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Opinion of the Court
alia, sufficient control measures were simply unavailable
and “the continued operation of such sources is essential . . .
to the public health or welfare.” 84 Stat. 1683 (emphasis
added). Other provisions explicitly permitted or required
economic costs to be taken into account in implementing
the air quality standards. Section 111(b)(1)(B), for example,
commanded the Administrator to set “standards of perform-
ance” for certain new sources of emissions that as specified
in § 111(a)(1) were to “reflec[t] the degree of emission limi-
tation achievable through the application of the best system
of emission reduction which (taking into account the cost
of achieving such reduction) the Administrator determines
has been adequately demonstrated.” Section 202(a)(2) pre-
scribed that emissions standards for automobiles could take
effect only “after such period as the Administrator finds
necessary to permit the development and application of
the requisite technology, giving appropriate consideration
to the cost of compliance within such period.” 84 Stat.
1690. See also § 202(b)(5)(C) (similar limitation for interim
standards); § 211(c)(2) (similar limitation for fuel additives);
§ 231(b) (similar limitation for implementation of aircraft
emission standards). Subsequent amendments to the CAA
have added many more provisions directing, in explicit
language, that the Administrator consider costs in per-
forming various duties. See, e. g., 42 U. S. C. § 7545(k)(1)
(reformulate gasoline to “require the greatest reduction in
emissions . . . taking into consideration the cost of achieving
such emissions reductions”); § 7547(a)(3) (emission reduction
for nonroad vehicles to be set “giving appropriate consid-
eration to the cost” of the standards). We have therefore
refused to find implicit in ambiguous sections of the CAA
an authorization to consider costs that has elsewhere, and
so often, been expressly granted. See Union Elec. Co. v.
EPA, 427 U. S. 246, 257, and n. 5 (1976). Cf. General Mo-
tors Corp. v. United States, 496 U. S. 530, 538, 541 (1990)

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468 WHITMAN v. AMERICAN TRUCKING ASSNS., INC.
Opinion of the Court
(refusing to infer in certain provisions of the CAA dead-
lines and enforcement limitations that had been expressly
imposed elsewhere).
Accordingly, to prevail in their present challenge, respond-
ents must show a textual commitment of authority to the
EPA to consider costs in setting NAAQS under § 109(b)(1).
And because § 109(b)(1) and the NAAQS for which it pro-
vides are the engine that drives nearly all of Title I of the
CAA, 42 U. S. C. §§ 7401–7515, that textual commitment
must be a clear one. Congress, we have held, does not alter
the fundamental details of a regulatory scheme in vague
terms or ancillary provisions—it does not, one might say,
hide elephants in mouseholes. See MCI Telecommunica-
tions Corp. v. American Telephone & Telegraph Co., 512
U. S. 218, 231 (1994); FDA v. Brown & Williamson Tobacco
Corp., supra, at 159–160. Respondents’ textual arguments
ultimately founder upon this principle.
Their first claim is that § 109(b)(1)’s terms “adequate
margin” and “requisite” leave room to pad health effects
with cost concerns. Just as we found it “highly unlikely
that Congress would leave the determination of whether
an industry will be entirely, or even substantially, rate-
regulated to agency discretion—and even more unlikely
that it would achieve that through such a subtle device as
permission to ‘modify’ rate-filing requirements,” MCI Tele-
communications Corp. v. American Telephone & Telegraph
Co., supra, at 231, so also we find it implausible that Con-
gress would give to the EPA through these modest words
the power to determine whether implementation costs
should moderate national air quality standards. Accord,
Christensen v. Harris County, 529 U. S. 576, 590, n. (2000)
(Scalia, J., concurring in part and concurring in judgment)
(“The implausibility of Congress’s leaving a highly significant
issue unaddressed (and thus ‘delegating’ its resolution to
the administering agency) is assuredly one of the factors

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Opinion of the Court
to be considered in determining whether there is ambiguity”
(emphasis deleted)).1
The same defect inheres in respondents’ next two argu-
ments: that while the Administrator’s judgment about what
is requisite to protect the public health must be “based on
[the] criteria” documents developed under § 108(a)(2), see
§ 109(b)(1), it need not be based solely on those criteria; and
that those criteria themselves, while they must include
“effects on public health or welfare which may be expected
from the presence of such pollutant in the ambient air,” are
not necessarily limited to those effects. Even if we were
to concede those premises, we still would not conclude that
one of the unenumerated factors that the agency can con-
sider in developing and applying the criteria is cost of im-
plementation. That factor is both so indirectly related to
public health and so full of potential for canceling the conclu-
sions drawn from direct health effects that it would surely
have been expressly mentioned in §§ 108 and 109 had Con-
gress meant it to be considered. Yet while those provi-
sions describe in detail how the health effects of pollutants
in the ambient air are to be calculated and given effect, see
§ 108(a)(2), they say not a word about costs.
Respondents point, finally, to a number of provisions in the
CAA that do require attainment cost data to be generated.
Section 108(b)(1), for example, instructs the Administrator
to “issue to the States,” simultaneously with the criteria
documents, “information on air pollution control techniques,
which information shall include data relating to the cost
of installation and operation.” 42 U. S. C. § 7408(b)(l). And
1 None of the sections of the CAA in which the District of Columbia Cir-
cuit has found authority for the EPA to consider costs shares § 109(b)(1)’s
prominence in the overall statutory scheme. See, e. g., Michigan v. EPA,
213 F. 3d 663, 678–679 (CADC 2000); George E. Warren Corp. v. EPA, 159
F. 3d 616, 623–624 (CADC 1998); Natural Resources Defense Council, Inc.
v. EPA, 824 F. 2d 1146, 1154–1163 (CADC 1987) (en banc).

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§ 109(d)(2)(C)(iv) requires the Clean Air Scientific Advisory
Committee to “advise the Administrator of any adverse
public health, welfare, social, economic, or energy effects
which may result from various strategies for attainment and
maintenance” of NAAQS.2 42 U. S. C. § 7409(d)(2)(C)(iv).
Respondents argue that these provisions make no sense
unless costs are to be considered in setting the NAAQS.
That is not so. These provisions enable the Administrator
to assist the States in carrying out their statutory role as
primary implementers of the NAAQS. It is to the States
that the CAA assigns initial and primary responsibility for
deciding what emissions reductions will be required from
which sources. See 42 U. S. C. §§ 7407(a), 7410 (giving
States the duty of developing implementation plans). It
would be impossible to perform that task intelligently
without considering which abatement technologies are most
efficient, and most economically feasible—which is why we
have said that “the most important forum for considera-
tion of claims of economic and technological infeasibility
is before the state agency formulating the implementation
plan,” Union Elec. Co. v. EPA, 427 U. S., at 266. Thus, fed-
eral clean air legislation has, from the very beginning, di-
rected federal agencies to develop and transmit implementa-
tion data, including cost data, to the States. See 1955 Act,
2 Respondents contend that this advice is required to be included in
the NAAQS rulemaking record—which, if true, would suggest that it
was relevant to the standard-setting process. But the provision re-
spondents cite for their contention, 42 U. S. C. § 7607(d)(3), requires only
that “pertinent findings, recommendations, and comments by the Scien-
tific Review Committee” be included. The Committee’s advice concerning
certain aspects of “adverse public health . . . effects” from various attain-
ment strategies is unquestionably pertinent; but to say that Committee-
generated cost data are pertinent is to beg the question. Likewise, while
“all written comments” must be placed in the docket, § 7607(d)(4)(B)(i), the
EPA need respond only to the “significant” ones, § 7407(d)(6)(B); comments
regarding cost data are not significant if cost data are irrelevant.

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§ 2(b), 69 Stat. 322; Clean Air Act of 1963, amending §§ 3(a),
(b) of the CAA, 77 Stat. 394; 1967 Act, §§ 103(a)–(d), 104,
107(c), 81 Stat. 486–488. That Congress chose to carry for-
ward this research program to assist States in choosing the
means through which they would implement the standards
is perfectly sensible, and has no bearing upon whether cost
considerations are to be taken into account in formulating
the standards.3
It should be clear from what we have said that the canon
requiring texts to be so construed as to avoid serious con-
stitutional problems has no application here. No matter
how severe the constitutional doubt, courts may choose
only between reasonably available interpretations of a text.
See, e. g., Miller v. French, 530 U. S. 327, 341 (2000); Penn-
sylvania Dept. of Corrections v. Yeskey, 524 U. S. 206, 212
(1998). The text of § 109(b), interpreted in its statutory and
historical context and with appreciation for its importance
to the CAA as a whole, unambiguously bars cost considera-
tions from the NAAQS-setting process, and thus ends the
matter for us as well as the EPA.4 We therefore affirm the
judgment of the Court of Appeals on this point.
3 Respondents scarcely mention in their arguments the secondary
NAAQS required by § 109(b)(2), 42 U. S. C. § 7409(b)(2). For many of the
same reasons described in the body of the opinion, as well as the text of
§ 109(b)(2), which instructs the EPA to set the standards at a level “requi-
site to protect the public welfare from any known or anticipated adverse
effects associated with the presence of such air pollutant in the ambient
air” (emphasis added), we conclude that the EPA may not consider imple-
mentation costs in setting the secondary NAAQS.
4 Respondents’ speculation that the EPA is secretly considering the
costs of attainment without telling anyone is irrelevant to our interpretive
inquiry. If such an allegation could be proved, it would be grounds for
vacating the NAAQS, because the Administrator had not followed the law.
See, e. g., Chevron U. S. A. Inc. v. Natural Resources Defense Council,
Inc., 467 U. S. 837, 842–843 (1984); Atlantic Mut. Ins. Co. v. Commissioner,
523 U. S. 382, 387 (1998). It would not, however, be grounds for this
Court’s changing the law.

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III
Section 109(b)(1) of the CAA instructs the EPA to set
“ambient air quality standards the attainment and main-
tenance of which in the judgment of the Administrator, based
on [the] criteria [documents of § 108] and allowing an ade-
quate margin of safety, are requisite to protect the public
health.” 42 U. S. C. § 7409(b)(1). The Court of Appeals
held that this section as interpreted by the Administrator
did not provide an “intelligible principle” to guide the EPA’s
exercise of authority in setting NAAQS. “[The] EPA,” it
said, “lack[ed] any determinate criteria for drawing lines.
It has failed to state intelligibly how much is too much.”
175 F. 3d, at 1034. The court hence found that the EPA’s
interpretation (but not the statute itself) violated the non-
delegation doctrine. Id., at 1038. We disagree.
In a delegation challenge, the constitutional question is
whether the statute has delegated legislative power to the
agency. Article I, § 1, of the Constitution vests “[a]ll legisla-
tive Powers herein granted . . . in a Congress of the United
States.” This text permits no delegation of those powers,
Loving v. United States, 517 U. S. 748, 771 (1996); see id., at
776–777 (Scalia, J., concurring in part and concurring
in judgment), and so we repeatedly have said that when
Congress confers decisionmaking authority upon agencies
Congress must “lay down by legislative act an intelligible
principle to which the person or body authorized to [act] is
directed to conform.” J. W. Hampton, Jr., & Co. v. United
States, 276 U. S. 394, 409 (1928). We have never suggested
that an agency can cure an unlawful delegation of legislative
power by adopting in its discretion a limiting construction of
the statute. Both Fahey v. Mallonee, 332 U. S. 245, 252–253
(1947), and Lichter v. United States, 334 U. S. 742, 783 (1948),
mention agency regulations in the course of their nondelega-
tion discussions, but Lichter did so because a subsequent
Congress had incorporated the regulations into a revised
version of the statute, ibid., and Fahey because the custom-

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ary practices in the area, implicitly incorporated into the
statute, were reflected in the regulations, 332 U. S., at 250.
The idea that an agency can cure an unconstitutionally stand-
ardless delegation of power by declining to exercise some of
that power seems to us internally contradictory. The very
choice of which portion of the power to exercise—that is to
say, the prescription of the standard that Congress had omit-
ted—would itself be an exercise of the forbidden legislative
authority. Whether the statute delegates legislative power
is a question for the courts, and an agency’s voluntary self-
denial has no bearing upon the answer.
We agree with the Solicitor General that the text of
§ 109(b)(1) of the CAA at a minimum requires that “[f]or a
discrete set of pollutants and based on published air quality
criteria that reflect the latest scientific knowledge, [the] EPA
must establish uniform national standards at a level that
is requisite to protect public health from the adverse effects
of the pollutant in the ambient air.” Tr. of Oral Arg. in
No. 99–1257, p. 5. Requisite, in turn, “mean[s] sufficient,
but not more than necessary.” Id., at 7. These limits on
the EPA’s discretion are strikingly similar to the ones we
approved in Touby v. United States, 500 U. S. 160 (1991),
which permitted the Attorney General to designate a drug
as a controlled substance for purposes of criminal drug en-
forcement if doing so was “ ‘necessary to avoid an imminent
hazard to the public safety.’ ” Id., at 163. They also re-
semble the Occupational Safety and Health Act of 1970 provi-
sion requiring the agency to “ ‘set the standard which most
adequately assures, to the extent feasible, on the basis of
the best available evidence, that no employee will suffer any
impairment of health’ ”—which the Court upheld in Indus-
trial Union Dept., AFL–CIO v. American Petroleum Insti-
tute, 448 U. S. 607, 646 (1980), and which even then-Justice
Rehnquist, who alone in that case thought the statute vio-
lated the nondelegation doctrine, see id., at 671 (opinion con-
curring in judgment), would have upheld if, like the statute

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here, it did not permit economic costs to be considered. See
American Textile Mfrs. Institute, Inc. v. Donovan, 452 U. S.
490, 545 (1981) (Rehnquist, J., dissenting).
The scope of discretion § 109(b)(1) allows is in fact well
within the outer limits of our nondelegation precedents.
In the history of the Court we have found the requisite
“intelligible principle” lacking in only two statutes, one of
which provided literally no guidance for the exercise of dis-
cretion, and the other of which conferred authority to regu-
late the entire economy on the basis of no more precise a
standard than stimulating the economy by assuring “fair
competition.” See Panama Refining Co. v. Ryan, 293 U. S.
388 (1935); A. L. A. Schechter Poultry Corp. v. United States,
295 U. S. 495 (1935). We have, on the other hand, upheld
the validity of § 11(b)(2) of the Public Utility Holding Com-
pany Act of 1935, 49 Stat. 821, which gave the Securities
and Exchange Commission authority to modify the structure
of holding company systems so as to ensure that they are
not “unduly or unnecessarily complicate[d]” and do not
“unfairly or inequitably distribute voting power among se-
curity holders.” American Power & Light Co. v. SEC, 329
U. S. 90, 104 (1946). We have approved the wartime confer-
ral of agency power to fix the prices of commodities at a level
that “ ‘will be generally fair and equitable and will effectuate
the [in some respects conflicting] purposes of th[e] Act.’ ”
Yakus v. United States, 321 U. S. 414, 420, 423–426 (1944).
And we have found an “intelligible principle” in various stat-
utes authorizing regulation in the “public interest.” See,
e. g., National Broadcasting Co. v. United States, 319 U. S.
190, 225–226 (1943) (Federal Communications Commission’s
power to regulate airwaves); New York Central Securities
Corp. v. United States, 287 U. S. 12, 24–25 (1932) (Interstate
Commerce Commission’s power to approve railroad consoli-
dations). In short, we have “almost never felt qualified to
second-guess Congress regarding the permissible degree of
policy judgment that can be left to those executing or apply-

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ing the law.” Mistretta v. United States, 488 U. S. 361, 416
(1989) (Scalia, J., dissenting); see id., at 373 (majority
opinion).
It is true enough that the degree of agency discretion that
is acceptable varies according to the scope of the power con-
gressionally conferred. See Loving v. United States, 517
U. S., at 772–773; United States v. Mazurie, 419 U. S. 544,
556–557 (1975). While Congress need not provide any direc-
tion to the EPA regarding the manner in which it is to define
“country elevators,” which are to be exempt from new-
stationary-source regulations governing grain elevators, see
42 U. S. C. § 7411(i), it must provide substantial guidance on
setting air standards that affect the entire national economy.
But even in sweeping regulatory schemes we have never
demanded, as the Court of Appeals did here, that statutes
provide a “determinate criterion” for saying “how much [of
the regulated harm] is too much.” 175 F. 3d, at 1034. In
Touby, for example, we did not require the statute to decree
how “imminent” was too imminent, or how “necessary” was
necessary enough, or even—most relevant here—how “haz-
ardous” was too hazardous. 500 U. S., at 165–167. Simi-
larly, the statute at issue in Lichter authorized agencies to
recoup “excess profits” paid under wartime Government con-
tracts, yet we did not insist that Congress specify how much
profit was too much. 334 U. S., at 783–786. It is therefore
not conclusive for delegation purposes that, as respondents
argue, ozone and particulate matter are “nonthreshold” pol-
lutants that inflict a continuum of adverse health effects at
any airborne concentration greater than zero, and hence re-
quire the EPA to make judgments of degree. “[A] certain
degree of discretion, and thus of lawmaking, inheres in most
executive or judicial action.” Mistretta v. United States,
supra, at 417 (Scalia, J., dissenting) (emphasis deleted); see
488 U. S., at 378–379 (majority opinion). Section 109(b)(1)
of the CAA, which to repeat we interpret as requiring the
EPA to set air quality standards at the level that is “requi-

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site”—that is, not lower or higher than is necessary—to pro-
tect the public health with an adequate margin of safety, fits
comfortably within the scope of discretion permitted by our
precedent.
We therefore reverse the judgment of the Court of Ap-
peals remanding for reinterpretation that would avoid a
supposed delegation of legislative power. It will remain for
the Court of Appeals—on the remand that we direct for
other reasons—to dispose of any other preserved challenge
to the NAAQS under the judicial-review provisions con-
tained in 42 U. S. C. § 7607(d)(9).
IV
The final two issues on which we granted certiorari con-
cern the EPA’s authority to implement the revised ozone
NAAQS in areas whose ozone levels currently exceed the
maximum level permitted by that standard. The CAA des-
ignates such areas “nonattainment,” § 107(d)(1), 42 U. S. C.
§ 7407(d)(1); see also Pub. L. 105–178, § 6103, 112 Stat. 465
(setting timeline for new ozone designations), and it ex-
poses them to additional restrictions over and above the
implementation requirements imposed generally by § 110
of the CAA. These additional restrictions are found in the
five substantive subparts of Part D of Title I, 42 U. S. C.
§§ 7501–7515. Subpart 1, §§ 7501–7509a, contains general
nonattainment regulations that pertain to every pollutant
for which a NAAQS exists. Subparts 2 through 5, §§ 7511–
7514a, contain rules tailored to specific individual pollutants.
Subpart 2, added by the Clean Air Act Amendments of 1990,
§ 103, 104 Stat. 2423, addresses ozone. 42 U. S. C. §§ 7511–
7511f. The dispute before us here, in a nutshell, is whether
Subpart 1 alone (as the agency determined), or rather Sub-
part 2 or some combination of Subparts 1 and 2, controls
the implementation of the revised ozone NAAQS in non-
attainment areas.

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A
The Administrator first urges, however, that we vacate
the judgment of the Court of Appeals on this issue because
it lacked jurisdiction to review the EPA’s implementation
policy. Section 307(b)(1) of the CAA, 42 U. S. C. § 7607(b)(1),
gives the court jurisdiction over “any . . . nationally ap-
plicable regulations promulgated, or final action taken, by
the Administrator,” but the EPA argues that its implementa-
tion policy was not agency “action,” was not “final” action,
and is not ripe for review. We reject each of these three
contentions.
At the same time the EPA proposed the revised ozone
NAAQS in 1996, it also proposed an “interim implementation
policy” for the NAAQS, see 61 Fed. Reg. 65752 (1996), that
was to govern until the details of implementation could be
put in final form through specific “rulemaking actions.” The
preamble to this proposed policy declared that “the interim
implementation policy . . . represent[s] EPA’s preliminary
views on these issues and, while it may include various state-
ments that States must take certain actions, these state-
ments are made pursuant to EPA’s preliminary interpreta-
tions, and thus do not bind the States and public as a matter
of law.” Ibid. If the EPA had done no more, we perhaps
could accept its current claim that its action was not final.
However, after the agency had accepted comments on its
proposed policy, and on the same day that the final ozone
NAAQS was promulgated, the White House published in the
Federal Register what it titled a “Memorandum for the Ad-
ministrator of the Environmental Protection Agency” that
prescribed implementation procedures for the EPA to follow.
62 Fed. Reg. 38421 (1997). (For purposes of our analysis
we shall assume that this memorandum was not itself action
by the EPA.) The EPA supplemented this memorandum
with an explanation of the implementation procedures, which
it published in the explanatory preamble to its final ozone

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NAAQS under the heading, “Final decision on the primary
standard.” Id., at 38873. “In light of comments received
regarding the interpretation proposed in the Interim Im-
plementation Policy,” the EPA announced, it had “reconsid-
ered that interpretation” and settled on a new one. Ibid.
The provisions of “subpart 1 of part D of Title I of the Act”
will immediately “apply to the implementation of the new
8-hour [ozone] standards.” Ibid.; see also id., at 38885
(new standard to be implemented “simultaneously [with the
old standard] . . . under the provisions of . . . subpart 1”).
Moreover, the provisions of subpart 2 “will [also] continue
to apply as a matter of law for so long as an area is not
attaining the [old] 1-hour standard.” Id., at 38873. Once
the area reaches attainment for the old standard, however,
“the provisions of subpart 2 will have been achieved and
those provisions will no longer apply.” Ibid.; see also id.,
at 38884–38885.
We have little trouble concluding that this constitutes final
agency action subject to review under § 307. The bite in
the phrase “final action” (which bears the same meaning in
§ 307(b)(1) that it does under the Administrative Procedure
Act (APA), 5 U. S. C. § 704, see Harrison v. PPG Industries,
Inc., 446 U. S. 578, 586 (1980)), is not in the word “action,”
which is meant to cover comprehensively every manner in
which an agency may exercise its power. See FTC v. Stand-
ard Oil Co. of Cal., 449 U. S. 232, 238, n. 7 (1980). It is
rather in the word “final,” which requires that the action
under review “mark the consummation of the agency’s de-
cisionmaking process.” Bennett v. Spear, 520 U. S. 154,
177–178 (1997). Only if the “EPA has rendered its last
word on the matter” in question, Harrison v. PPG Indus-
tries, Inc., supra, at 586, is its action “final” and thus review-
able. That standard is satisfied here. The EPA’s “decision-
making process,” which began with the 1996 proposal and
continued with the reception of public comments, concluded

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when the agency, “in light of [these comments],” and in con-
junction 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 it, explaining to disap-
pointed commenters that its earlier decision was conclusive.
See 63 Fed. Reg. 31014, 31018–31019 (1998). Though the
agency has not dressed its decision with the conventional
procedural accoutrements of finality, its own behavior thus
belies the claim that its interpretation is not final.
The decision is also ripe for our review. “Ripeness ‘re-
quir[es] us to evaluate both the fitness of the issues for judi-
cial decision and the hardship to the parties of withholding
court consideration.’ ” Texas v. United States, 523 U. S. 296,
300–301 (1998) (quoting Abbott Laboratories v. Gardner, 387
U. S. 136, 149 (1967)). The question before us here is purely
one of statutory interpretation that would not “benefit from
further factual development of the issues presented.” Ohio
Forestry Assn., Inc. v. Sierra Club, 523 U. S. 726, 733 (1998).
Nor will our review “inappropriately interfere with further
administrative action,” ibid., since the EPA has concluded
its consideration of the implementation issue. Finally, as for
hardship to the parties: The respondent States must—on
pain of forfeiting to the EPA control over implementation
of the NAAQS—promptly undertake the lengthy and expen-
sive task of developing state implementation plans (SIP’s)
that will attain the new, more stringent standard within five
years. See 42 U. S. C. §§ 7410, 7502. Whether or not this
would suffice in an ordinary case brought under the review
provisions of the APA, see 5 U. S. C. § 704, we have charac-
terized the special judicial-review provision of the CAA, 42
U. S. C. § 7607(b), as one of those statutes that specifically
provides for “preenforcement” review, see Ohio Forestry
Assn., Inc. v. Sierra Club, supra, at 737. Such statutes, we
have said, permit “judicial review directly, even before the

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concrete effects normally required for APA review are felt.”
Lujan v. National Wildlife Federation, 497 U. S. 871, 891
(1990). The effects at issue here surely meet that lower
standard.
Beyond all this, the implementation issue was fairly in-
cluded within the challenges to the final ozone rule that were
properly before the Court of Appeals. Respondents argued
below that the EPA could not revise the ozone standard, be-
cause to do so would trigger the use of Subpart 1, which
had been supplanted (for ozone) by the specific rules of Sub-
part 2. Brief for Industry Petitioners and Intervenors in
No. 97–1441 (and consolidated cases) (CADC), pp. 32–34.
The EPA responded that Subpart 2 did not supplant but
simply supplemented Subpart 1, so that the latter section
still “applies to all nonattainment areas for all NAAQS,
. . . including nonattainment areas for any revised ozone
standard.” Final Brief for EPA in No. 97–1441 (and con-
solidated cases) (CADC), pp. 67–68. The agency later re-
iterated that Subpart 2 “does not supplant implementation
provisions for revised ozone standards. This interpretation
fully harmonizes Subpart 2 with EPA’s clear authority to re-
vise any NAAQS.” Id., at 71. In other words, the EPA
was arguing that the revised standard could be issued, de-
spite its apparent incompatibility with portions of Subpart 2,
because it would be implemented under Subpart 1 rather
than Subpart 2. The District of Columbia Circuit ultimately
agreed that Subpart 2 could be harmonized with the EPA’s
authority to promulgate revised NAAQS, but not because
Subpart 2 is entirely inapplicable—which is one of EPA’s
assignments of error. It is unreasonable to contend, as the
EPA now does, that the Court of Appeals was obligated to
reach the agency’s preferred result, but forbidden to assess
the reasons the EPA had given for reaching that result.
The implementation issue was fairly included within re-
spondents’ challenge to the ozone rule, which all parties
agree is final agency action ripe for review.

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B
Our approach to the merits of the parties’ dispute is the
familiar one of Chevron U. S. A. Inc. v. Natural Resources
Defense Council, Inc., 467 U. S. 837 (1984). If the stat-
ute resolves the question whether Subpart 1 or Subpart 2
(or some combination of the two) shall apply to revised ozone
NAAQS, then “that is the end of the matter.” Id., at 842–
843. But if the statute is “silent or ambiguous” with re-
spect to the issue, then we must defer to a “reasonable inter-
pretation made by the administrator of an agency.” Id., at
844. We cannot agree with the Court of Appeals that Sub-
part 2 clearly controls the implementation of revised ozone
NAAQS, see 175 F. 3d, at 1048–1050, because we find the
statute to some extent ambiguous. We conclude, however,
that the agency’s interpretation goes beyond the limits of
what is ambiguous and contradicts what in our view is
quite clear. We therefore hold the implementation policy
unlawful. See AT&T Corp. v. Iowa Utilities Bd., 525 U. S.
366, 392 (1999).
The text of Subpart 1 at first seems to point the way to
a clear answer to the question, which Subpart controls?
Two sections of Subpart 1, 7502(a)(1)(C) and 7502(a)(2)(D),
contain switching provisions stating that if the classification
of ozone nonattainment areas is “specifically provided [for]
under other provisions of [Part D],” then those provisions
will control instead of Subpart 1’s. Thus, it is true but in-
complete to note, as the Administrator does, that the sub-
stantive language of Subpart 1 is broad enough to apply to
revised ozone standards. See, e. g., § 7502(a)(1)(A) (instruct-
ing the Administrator to classify nonattainment areas ac-
cording to “any revised standard, including a revision of any
standard in effect on November 15, 1990”); § 7502(a)(2)(A)
(setting attainment deadlines). To determine whether that
language does apply one must resolve the further textual
issue whether some other provision, namely Subpart 2, pro-
vides for the classification of ozone nonattainment areas. If

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it does, then according to the switching provisions of Sub-
part 1 it will control.
So, does Subpart 2 provide for classifying nonattainment
ozone areas under the revised standard? It unquestionably
does. The backbone of the subpart is Table 1, printed in
§ 7511(a)(1) and reproduced in the margin here,5 which de-
fines five categories of ozone nonattainment areas and pre-
scribes attainment deadlines for each. Section 7511(a)(1)
funnels all nonattainment areas into the table for classifica-
tion, declaring that “[e]ach area designated nonattainment
for ozone . . . shall be classified at the time of such desig-
nation, under table 1, by operation of law.” And once an
area has been classified, “the primary standard attainment
date for ozone shall be as expeditiously as practicable but
not later than the date provided in table 1.” The EPA
argues that this text is not as clear or comprehensive as
it seems, because the title of § 7511(a) reads “Classification
and attainment dates for 1989 nonattainment areas,” which
suggests that Subpart 2 applies only to areas that were in
nonattainment in 1989, and not to areas later designated non-
5 TABLE 1
Primary standard
Area class Design value* attainment date**
Marginal . . . . . . . . . . . . . . 0.121 up to 0.138 . . . . . . . . . . . . . . 3 years after
November 15, 1990
Moderate . . . . . . . . . . . . . . 0.138 up to 0.160 . . . . . . . . . . . . . . 6 years after
November 15, 1990
Serious . . . . . . . . . . . . . . . . 0.160 up to 0.180 . . . . . . . . . . . . . . 9 years after
November 15, 1990
Severe . . . . . . . . . . . . . . . . . 0.180 up to 0.280 . . . . . . . . . . . . . . 15 years after
November 15, 1990
Extreme. . . . . . . . . . . . . . . 0.280 and above . . . . . . . . . . . . . . . 20 years after
November 15, 1990
*The design value is measured in parts per million (ppm).
**The primary standard attainment date is measured from November
15, 1990.

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attainment under a revised ozone standard. The suggestion
must be rejected, however, because § 7511(b)(1) specifically
provides for the classification of areas that were in attain-
ment in 1989 but have subsequently slipped into nonattain-
ment. It thus makes clear that Subpart 2 is not limited
solely to 1989 nonattainment areas. This eliminates the in-
terpretive role of the title, which may only “she[d] light on
some ambiguous word or phrase in the statute itself,” Carter
v. United States, 530 U. S. 255, 267 (2000) (internal quotation
marks omitted) (quoting Pennsylvania Dept. of Corrections
v. Yeskey, 524 U. S., at 212, in turn quoting Trainmen v. Bal-
timore & Ohio R. Co., 331 U. S. 519, 528–529 (1947)).
It may well be, as the EPA argues—and as the concurring
opinion below on denial of rehearing pointed out, see 195
F. 3d, at 11–12—that some provisions of Subpart 2 are ill
fitted to implementation of the revised standard. Using the
old 1-hour averages of ozone levels, for example, as Sub-
part 2 requires, see § 7511(a)(1); 44 Fed. Reg. 8202 (1979),
would produce at best an inexact estimate of the new 8-hour
averages, see 40 CFR § 50.10, and App. I (1999). Also, to
the extent that the new ozone standard is stricter than the
old one, see Reply Brief for Petitioners in No. 99–1257, p. 17
(“the stricter 8-hour NAAQS”); 62 Fed. Reg. 38856, 38858
(1997) (8-hour standard of 0.09 ppm rather than 0.08 ppm
would have “generally represent[ed] the continuation of
the [old] level of protection”), the classification system of
Subpart 2 contains a gap, because it fails to classify areas
whose ozone levels are greater than the new standard (and
thus nonattaining) but less than the approximation of the
old standard codified by Table 1. And finally, Subpart 2’s
method for calculating attainment dates—which is simply
to count forward a certain number of years from Novem-
ber 15, 1990 (the date the 1990 CAA Amendments took
force), depending on how far out of attainment the area
started—seems to make no sense for areas that are first
classified under a new standard after November 15, 1990.

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Opinion of the Court
If, for example, areas were classified in the year 2000, many
of the deadlines would already have expired at the time of
classification.
These gaps in Subpart 2’s scheme prevent us from con-
cluding that Congress clearly intended Subpart 2 to be the
exclusive, permanent means of enforcing a revised ozone
standard in nonattainment areas. The statute is in our view
ambiguous concerning the manner in which Subpart 1 and
Subpart 2 interact with regard to revised ozone standards,
and we would defer to the EPA’s reasonable resolution of
that ambiguity. See FDA v. Brown & Williamson Tobacco
Corp., 529 U. S., at 132; INS v. Aguirre-Aguirre, 526 U. S.
415, 424 (1999). We cannot defer, however, to the interpre-
tation the EPA has given.
Whatever effect may be accorded the gaps in Subpart 2
as implying some limited applicability of Subpart 1, they
cannot be thought to render Subpart 2’s carefully designed
restrictions on EPA discretion utterly nugatory once a new
standard has been promulgated, as the EPA has concluded.
The principal distinction between Subpart 1 and Subpart 2
is that the latter eliminates regulatory discretion that the
former allowed. While Subpart 1 permits the EPA to es-
tablish classifications for nonattainment areas, Subpart 2
classifies areas as a matter of law based on a table. Com-
pare § 7502(a)(1) with § 7511(a)(1) (Table 1). Whereas the
EPA has discretion under Subpart 1 to extend attainment
dates for as long as 12 years, under Subpart 2 it may grant
no more than 2 years’ extension. Compare §§ 7502(a)(2)(A)
and (C) with § 7511(a)(5). Whereas Subpart 1 gives the
EPA considerable discretion to shape nonattainment pro-
grams, Subpart 2 prescribes large parts of them by law.
Compare §§ 7502(c) and (d) with § 7511a. Yet according to
the EPA, Subpart 2 was simply Congress’s “approach to the
implementation of the [old] 1-hour” standard, and so there
was no reason that “the new standard could not simultane-
ously be implemented under . . . subpart 1.” 62 Fed. Reg.

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Opinion of the Court
38856, 38885 (1997); see also id., at 38873 (“[T]he provisions
of subpart 1 . . . would apply to the implementation of the
new 8-hour ozone standards”). To use a few apparent gaps
in Subpart 2 to render its textually explicit applicability to
nonattainment areas under the new standard utterly inoper-
ative is to go over the edge of reasonable interpretation.
The EPA may not construe the statute in a way that com-
pletely nullifies textually applicable provisions meant to limit
its discretion.
The EPA’s interpretation making Subpart 2 abruptly ob-
solete is all the more astonishing because Subpart 2 was
obviously written to govern implementation for some time.
Some of the elements required to be included in SIP’s under
Subpart 2 were not to take effect until many years after
the passage of the CAA. See § 7511a(e)(3) (restrictions on
“electric utility and industrial and commercial boiler[s]” to be
“effective 8 years after November 15, 1990”); § 7511a(c)(5)(A)
(vehicle monitoring program to “[b]egi[n] 6 years after No-
vember 15, 1990”); § 7511a(g)(1) (emissions milestone re-
quirements to be applied “6 years after November 15, 1990,
and at intervals of every 3 years thereafter”). A plan reach-
ing so far into the future was not enacted to be abandoned
the next time the EPA reviewed the ozone standard—which
Congress knew could happen at any time, since the tech-
nical staff papers had already been completed in late 1989.
See 58 Fed. Reg. 13008, 13010 (1993); see also 42 U. S. C.
§ 7409(d)(1) (NAAQS must be reviewed and, if appropriate,
revised at least once every five years). Yet nothing in the
EPA’s interpretation would have prevented the agency from
aborting Subpart 2 the day after it was enacted. Even
now, if the EPA’s interpretation were correct, some areas
of the country could be required to meet the new, more strin-
gent ozone standard in at most the same time that Sub-
part 2 had allowed them to meet the old standard. Compare
§ 7502(a)(2) (Subpart 1 attainment dates) with § 7511(a) (Sub-
part 2 attainment dates). Los Angeles, for instance, “would

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486 WHITMAN v. AMERICAN TRUCKING ASSNS., INC.
Thomas, J., concurring
be required to attain the revised NAAQS under Subpart 1
no later than the same year that marks the outer time limit
for attaining Subpart 2’s one-hour ozone standard.” Brief
for Petitioners in No. 99–1257, p. 49. An interpretation of
Subpart 2 so at odds with its structure and manifest purpose
cannot be sustained.
We therefore find the EPA’s implementation policy to be
unlawful, though not in the precise respect determined by
the Court of Appeals. After our remand, and the Court of
Appeals’ final disposition of these cases, it is left to the EPA
to develop a reasonable interpretation of the nonattainment
implementation provisions insofar as they apply to revised
ozone NAAQS.
* * *
To summarize our holdings in these unusually complex
cases: (1) The EPA may not consider implementation costs
in setting primary and secondary NAAQS under § 109(b)
of the CAA. (2) Section 109(b)(1) does not delegate legis-
lative power to the EPA in contravention of Art. I, § 1, of
the Constitution. (3) The Court of Appeals had jurisdic-
tion to review the EPA’s interpretation of Part D of Title I
of the CAA, relating to the implementation of the revised
ozone NAAQS. (4) The EPA’s interpretation of that Part
is unreasonable.
The judgment of the Court of Appeals is affirmed in part
and reversed in part, and the cases are remanded for pro-
ceedings consistent with this opinion.
It is so ordered.
Justice Thomas, concurring.
I agree with the majority that § 109’s directive to the
agency is no less an “intelligible principle” than a host of
other directives that we have approved. Ante, at 474–476.
I also agree that the Court of Appeals’ remand to the agency
to make its own corrective interpretation does not accord
with our understanding of the delegation issue. Ante, at
472–473. I write separately, however, to express my con-

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487 Cite as: 531 U. S. 457 (2001)
Opinion of Stevens, J.
cern that there may nevertheless be a genuine constitu-
tional problem with § 109, a problem which the parties did
not address.
The parties to these cases who briefed the constitutional
issue wrangled over constitutional doctrine with barely a nod
to the text of the Constitution. Although this Court since
1928 has treated the “intelligible principle” requirement as
the only constitutional limit on congressional grants of power
to administrative agencies, see J. W. Hampton, Jr., & Co. v.
United States, 276 U. S. 394, 409 (1928), the Constitution does
not speak of “intelligible principles.” Rather, it speaks in
much simpler terms: “All legislative Powers herein granted
shall be vested in a Congress.” U. S. Const., Art. 1, § 1 (em-
phasis added). I am not convinced that the intelligible prin-
ciple doctrine serves to prevent all cessions of legislative
power. I believe that there are cases in which the principle
is intelligible and yet the significance of the delegated deci-
sion is simply too great for the decision to be called anything
other than “legislative.”
As it is, none of the parties to these cases has examined
the text of the Constitution or asked us to reconsider our
precedents on cessions of legislative power. On a future
day, however, I would be willing to address the question
whether our delegation jurisprudence has strayed too far
from our Founders’ understanding of separation of powers.
Justice Stevens, with whom Justice Souter joins,
concurring in part and concurring in the judgment.
Section 109(b)(1) delegates to the Administrator of the En-
vironmental Protection Agency (EPA) the authority to pro-
mulgate national ambient air quality standards (NAAQS).
In Part III of its opinion, ante, at 472–476, the Court con-
vincingly explains why the Court of Appeals erred when
it concluded that § 109 effected “an unconstitutional delega-
tion of legislative power.” American Trucking Assns., Inc.
v. EPA, 175 F. 3d 1027, 1033 (CADC 1999) (per curiam).

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488 WHITMAN v. AMERICAN TRUCKING ASSNS., INC.
Opinion of Stevens, J.
I wholeheartedly endorse the Court’s result and endorse its
explanation of its reasons, albeit with the following caveat.
The Court has two choices. We could choose to articulate
our ultimate disposition of this issue by frankly acknowledg-
ing that the power delegated to the EPA is “legislative” but
nevertheless conclude that the delegation is constitutional
because adequately limited by the terms of the authorizing
statute. Alternatively, we could pretend, as the Court does,
that the authority delegated to the EPA is somehow not
“legislative power.” Despite the fact that there is language
in our opinions that supports the Court’s articulation of our
holding,1 I am persuaded that it would be both wiser and
more faithful to what we have actually done in delegation
cases to admit that agency rulemaking authority is “legisla-
tive power.” 2
The proper characterization of governmental power should
generally depend on the nature of the power, not on the iden-
tity of the person exercising it. See Black’s Law Dictionary
899 (6th ed. 1990) (defining “legislation” as, inter alia, “[f]or-
mulation of rule[s] for the future”); 1 K. Davis & R. Pierce,
Administrative Law Treatise § 2.3, p. 37 (3d ed. 1994) (“If
legislative power means the power to make rules of conduct
that bind everyone based on resolution of major policy issues,
scores of agencies exercise legislative power routinely by
1 See, e. g., Touby v. United States, 500 U. S. 160, 165 (1991); United
States v. Shreveport Grain & Elevator Co., 287 U. S. 77, 85 (1932); J. W.
Hampton, Jr., & Co. v. United States, 276 U. S. 394, 407 (1928); Field v.
Clark, 143 U. S. 649, 692 (1892).
2 See Mistretta v. United States, 488 U. S. 361, 372 (1989) (“[O]ur juris-
prudence has been driven by a practical understanding that in our increas-
ingly complex society . . . Congress simply cannot do its job absent an
ability to delegate power . . .”). See also Loving v. United States, 517
U. S. 748, 758 (1996) (“[The nondelegation] principle does not mean . . .
that only Congress can make a rule of prospective force”); 1 K. Davis &
R. Pierce, Administrative Law Treatise § 2.6, p. 66 (3d ed. 1994) (“Except
for two 1935 cases, the Court has never enforced its frequently announced
prohibition on congressional delegation of legislative power”).

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Opinion of Stevens, J.
promulgating what are candidly called ‘legislative rules’ ”).
If the NAAQS that the EPA promulgated had been pre-
scribed by Congress, everyone would agree that those rules
would be the product of an exercise of “legislative power.”
The same characterization is appropriate when an agency
exercises rulemaking authority pursuant to a permissible
delegation from Congress.
My view is not only more faithful to normal English usage,
but is also fully consistent with the text of the Constitution.
In Article I, the Framers vested “All legislative Powers” in
the Congress, Art. I, § 1, just as in Article II they vested
the “executive Power” in the President, Art. II, § 1. Those
provisions do not purport to limit the authority of either
recipient of power to delegate authority to others. See
Bowsher v. Synar, 478 U. S. 714, 752 (1986) (Stevens, J.,
concurring in judgment) (“Despite the statement in Article
I of the Constitution that ‘All legislative powers herein
granted shall be vested in a Congress of the United States,’
it is far from novel to acknowledge that independent agencies
do indeed exercise legislative powers”); INS v. Chadha, 462
U. S. 919, 985–986 (1983) (White, J., dissenting) (“[L]egisla-
tive power can be exercised by independent agencies and
Executive departments . . .”); 1 Davis & Pierce, Administra-
tive Law Treatise § 2.6, at 66 (“The Court was probably mis-
taken from the outset in interpreting Article I’s grant of
power to Congress as an implicit limit on Congress’ author-
ity to delegate legislative power”). Surely the authority
granted to members of the Cabinet and federal law enforce-
ment agents is properly characterized as “Executive” even
though not exercised by the President. Cf. Morrison v.
Olson, 487 U. S. 654, 705–706 (1988) (Scalia, J., dissenting)
(arguing that the independent counsel exercised “executive
power” unconstrained by the President).
It seems clear that an executive agency’s exercise of rule-
making authority pursuant to a valid delegation from Con-
gress is “legislative.” As long as the delegation provides a

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490 WHITMAN v. AMERICAN TRUCKING ASSNS., INC.
Opinion of Breyer, J.
sufficiently intelligible principle, there is nothing inherently
unconstitutional about it. Accordingly, while I join Parts I,
II, and IV of the Court’s opinion, and agree with almost ev-
erything said in Part III, I would hold that when Congress
enacted § 109, it effected a constitutional delegation of legis-
lative power to the EPA.
Justice Breyer, concurring in part and concurring in
the judgment.
I join Parts I, III, and IV of the Court’s opinion. I also
agree with the Court’s determination in Part II that the
Clean Air Act does not permit the Environmental Protec-
tion Agency to consider the economic costs of implemen-
tation when setting national ambient air quality standards
under § 109(b)(1) of the Act. But I would not rest this con-
clusion solely upon § 109’s language or upon a presumption,
such as the Court’s presumption that any authority the Act
grants the EPA to consider costs must flow from a “textual
commitment” that is “clear.” Ante, at 468. In order better
to achieve regulatory goals—for example, to allocate re-
sources so that they save more lives or produce a cleaner
environment—regulators must often take account of all of a
proposed regulation’s adverse effects, at least where those
adverse effects clearly threaten serious and disproportion-
ate public harm. Hence, I believe that, other things being
equal, we should read silences or ambiguities in the language
of regulatory statutes as permitting, not forbidding, this
type of rational regulation.
In these cases, however, other things are not equal. Here,
legislative history, along with the statute’s structure, indi-
cates that § 109’s language reflects a congressional decision
not to delegate to the agency the legal authority to consider
economic costs of compliance.
For one thing, the legislative history shows that Congress
intended the statute to be “technology forcing.” Senator
Edmund Muskie, the primary sponsor of the 1970 amend-

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491 Cite as: 531 U. S. 457 (2001)
Opinion of Breyer, J.
ments to the Act, introduced them by saying that Congress’
primary responsibility in drafting the Act was not “to be
limited by what is or appears to be technologically or eco-
nomically feasible,” but “to establish what the public interest
requires to protect the health of persons,” even if that means
that “industries will be asked to do what seems to be impos-
sible at the present time.” 116 Cong. Rec. 32901–32902
(1970), 1 Legislative History of the Clean Air Amendments
of 1970 (Committee Print compiled for the Senate Committee
on Public Works by the Library of Congress), Ser. No. 93–18,
p. 227 (1974) (hereinafter Leg. Hist.) (emphasis added).
The Senate directly focused upon the technical feasibility
and cost of implementing the Act’s mandates. And it made
clear that it intended the Administrator to develop air qual-
ity standards set independently of either. The Senate Re-
port for the 1970 amendments explains:
“In the Committee discussions, considerable concern
was expressed regarding the use of the concept of tech-
nical feasibility as the basis of ambient air standards.
The Committee determined that 1) the health of people
is more important than the question of whether the
early achievement of ambient air quality standards
protective of health is technically feasible; and, 2) the
growth of pollution load in many areas, even with appli-
cation of available technology, would still be deleterious
to public health. . . .
“Therefore, the Committee determined that existing
sources of pollutants either should meet the standard
of the law or be closed down . . . .” S. Rep. No. 91–1196,
pp. 2–3 (1970), 1 Leg. Hist. 402–403 (emphasis added).
Indeed, this Court, after reviewing the entire legislative
history, concluded that the 1970 amendments were “ex-
pressly designed to force regulated sources to develop pollu-
tion control devices that might at the time appear to be eco-
nomically or technologically infeasible.” Union Elec. Co.

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492 WHITMAN v. AMERICAN TRUCKING ASSNS., INC.
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v. EPA, 427 U. S. 246, 257 (1976) (emphasis added). And the
Court added that the 1970 amendments were intended to be
a “drastic remedy to . . . a serious and otherwise uncheckable
problem.” Id., at 256. Subsequent legislative history con-
firms that the technology-forcing goals of the 1970 amend-
ments are still paramount in today’s Act. See Clean Air
Conference Report (1977): Statement of Intent; Clarification
of Select Provisions, 123 Cong. Rec. 27070 (1977) (stating,
regarding the 1977 amendments to the Act, that “this year’s
legislation retains and even strengthens the technology forc-
ing . . . goals of the 1970 Act”); S. Rep. No. 101–228, p. 5
(1989) (stating that the 1990 amendments to the Act require
ambient air quality standards to be set at “the level that
‘protects the public health’ with an ‘adequate margin of
safety,’ without regard to the economic or technical feasibil-
ity of attainment” (emphasis added)).
To read this legislative history as meaning what it says
does not impute to Congress an irrati ona l intent.
Technology-forcing hopes can prove realistic. Those per-
sons, for example, who opposed the 1970 Act’s insistence on
a 90% reduction in auto emission pollutants, on the ground
of excessive cost, saw the development of catalytic converter
technology that helped achieve substantial reductions with-
out the economic catastrophe that some had feared. See
§ 6(a) of the Clean Air Act Amendments of 1970, amending
§§ 202(b)(1)(A), (B), 84 Stat. 1690 (codified at 42 U. S. C.
§§ 7521(b)(1)(A), (B)) (requiring a 90% reduction in emis-
sions); 1 Leg. Hist. 238, 240 (statement of Sen. Griffin) (ar-
guing that the emissions standards could “force [the automo-
bile] industry out of existence” because costs “would not be
taken into account”); see generally Reitze, Mobile Source Air
Pollution Control, 6 Env. Law. 309, 326–327 (2000) (discussing
the development of the catalytic converter).
At the same time, the statute’s technology-forcing objec-
tive makes regulatory efforts to determine the costs of
implementation both less important and more difficult. It

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means that the relevant economic costs are speculative, for
they include the cost of unknown future technologies. It
also means that efforts to take costs into account can breed
time-consuming and potentially unresolvable arguments
about the accuracy and significance of cost estimates. Con-
gress could have thought such efforts not worth the delays
and uncertainties that would accompany them. In any
event, that is what the statute’s history seems to say. See
Union Elec., supra, at 256–259. And the matter is one for
Congress to decide.
Moreover, the Act does not, on this reading, wholly ignore
cost and feasibility. As the majority points out, ante, at
466–467, the Act allows regulators to take those concerns
into account when they determine how to implement ambient
air quality standards. Thus, States may consider economic
costs when they select the particular control devices used
to meet the standards, and industries experiencing difficulty
in reducing their emissions can seek an exemption or vari-
ance from the state implementation plan. See Union Elec.,
supra, at 266 (“[T]he most important forum for consideration
of claims of economic and technological infeasibility is before
the state agency formulating the implementation plan”).
The Act also permits the EPA, within certain limits,
to consider costs when it sets deadlines by which areas
must attain the ambient air quality standards. 42 U. S. C.
§ 7502(a)(2)(A) (providing that “the Administrator may ex-
tend the attainment date . . . for a period no greater than 10
years from the date of designation as nonattainment, consid-
ering the severity of nonattainment and the availability and
feasibility of pollution control measures”); § 7502(a)(2)(C)
(permitting the Administrator to grant up to two additional
1-year extensions); cf. §§ 7511(a)(1), (5) (setting more rigid
attainment deadlines for areas in nonattainment of the ozone
standard, but permitting the Administrator to grant up to
two 1-year extensions). And Congress can change those
statutory limits if necessary. Given the ambient air quality

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494 WHITMAN v. AMERICAN TRUCKING ASSNS., INC.
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standards’ substantial effects on States, cities, industries,
and their suppliers and customers, Congress will hear from
those whom compliance deadlines affect adversely, and Con-
gress can consider whether legislative change is warranted.
See, e. g., Steel Industry Compliance Extension Act of 1981,
95 Stat. 139 (codified at 42 U. S. C. § 7413(e) (1988 ed.)) (re-
pealed 1990) (granting the Administrator discretion to ex-
tend the ambient air quality standard attainment date set in
the 1977 Act by up to three years for steelmaking facilities).
Finally, contrary to the suggestion of the Court of Appeals
and of some parties, this interpretation of § 109 does not
require the EPA to eliminate every health risk, however
slight, at any economic cost, however great, to the point of
“hurtling” industry over “the brink of ruin,” or even forcing
“deindustrialization.” American Trucking Assns., Inc. v.
EPA, 175 F. 3d 1027, 1037, 1038, n. 4 (CADC 1999); see also
Brief for Cross-Petitioners in No. 99–1426, p. 25. The stat-
ute, by its express terms, does not compel the elimination of
all risk; and it grants the Administrator sufficient flexibility
to avoid setting ambient air quality standards ruinous to
industry.
Section 109(b)(1) directs the Administrator to set stand-
ards that are “requisite to protect the public health” with
“an adequate margin of safety.” But these words do not de-
scribe a world that is free of all risk—an impossible and un-
desirable objective. See Industrial Union Dept., AFL–CIO
v. American Petroleum Institute, 448 U. S. 607, 642 (1980)
(plurality opinion) (the word “safe” does not mean “risk-
free”). Nor are the words “requisite” and “public health” to
be understood independent of context. We consider football
equipment “safe” even if its use entails a level of risk that
would make drinking water “unsafe” for consumption. And
what counts as “requisite” to protecting the public health
will similarly vary with background circumstances, such as
the public’s ordinary tolerance of the particular health risk
in the particular context at issue. The Administrator can

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consider such background circumstances when “decid[ing]
what risks are acceptable in the world in which we live.”
Natural Resources Defense Council, Inc. v. EPA, 824 F. 2d
1146, 1165 (CADC 1987).
The statute also permits the Administrator to take account
of comparative health risks. That is to say, she may con-
sider whether a proposed rule promotes safety overall. A
rule likely to cause more harm to health than it prevents is
not a rule that is “requisite to protect the public health.”
For example, as the Court of Appeals held and the parties
do not contest, the Administrator has the authority to deter-
mine to what extent possible health risks stemming from re-
ductions in tropospheric ozone (which, it is claimed, helps
prevent cataracts and skin cancer) should be taken into ac-
count in setting the ambient air quality standard for ozone.
See 175 F. 3d, at 1050–1053 (remanding for the Administrator
to make that determination).
The statute ultimately specifies that the standard set must
be “requisite to protect the public health” “in the judgment
of the Administrator,” § 109(b)(1), 84 Stat. 1680 (emphasis
added), a phrase that grants the Administrator considerable
discretionary standard-setting authority.
The statute’s words, then, authorize the Administrator
to consider the severity of a pollutant’s potential adverse
health effects, the number of those likely to be affected, the
distribution of the adverse effects, and the uncertainties
surrounding each estimate. Cf. Sunstein, Is the Clean Air
Act Unconstitutional?, 98 Mich. L. Rev. 303, 364 (1999).
They permit the Administrator to take account of compara-
tive health consequences. They allow her to take account
of context when determining the acceptability of small risks
to health. And they give her considerable discretion when
she does so.
This discretion would seem sufficient to avoid the extreme
results that some of the industry parties fear. After all, the
EPA, in setting standards that “protect the public health”

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496 WHITMAN v. AMERICAN TRUCKING ASSNS., INC.
Opinion of Breyer, J.
with “an adequate margin of safety,” retains discretionary
authority to avoid regulating risks that it reasonably con-
cludes are trivial in context. Nor need regulation lead to
deindustrialization. Preindustrial society was not a very
healthy society; hence a standard demanding the return of
the Stone Age would not prove “requisite to protect the pub-
lic health.”
Although I rely more heavily than does the Court upon
legislative history and alternative sources of statutory flexi-
bility, I reach the same ultimate conclusion. Section 109
does not delegate to the EPA authority to base the national
ambient air quality standards, in whole or in part, upon the
economic costs of compliance.