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 

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 
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 

QUESTIONS PRESENTED 

1. Whether Section 109 of the Clean Air Act (CAA), 42 
U.S.C. 7409, as interpreted by the Environmental Protection 
Agency (EPA) in setting revised National Ambient 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 preamble statements 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 specifically aimed at achieving the long-delayed 
attainment of the then-existing ozone NAAQS restrict 
EPA’s general authority under other provisions of the CAA 
to implement a new and more protective ozone NAAQS until 
the prior standard is attained. 

(I) 

TABLE OF CONTENTS 

Page 

Opinions below ............................................................................... 
1 

Jurisdiction ..................................................................................... 1 

Constitutional, statutory, and regulatory provisions in- 
volved. ........................................................................................ 1 

Statement ....................................................................................... 2 

I. The Clean Air Act’s NAAQS provisions ..................... 

3 

A. Air quality criteria and standards ......................... 
3 

B. Implementation of air quality standards ............. 
5 

II. The particulate matter and ozone rulemaking 

proceedings ................................................................ 8 

A. The particulate matter rule .................................... 
9 

B. The ozone rule ........................................................... 
11 

III. The proceedings below .................................................... 
15 

Summary of argument .................................................................. 
18 

Argument: 

I. The court of appeals erroneously applied the 

nondelegation doctrine .................................................... 

21 

A. Section 109 of the Clean Air Act does not 

constitute an unconstitutional grant of 

legislative power ....................................................... 

22 

B. The court of appeals improperly employed 

the nondelegation doctrine to expand the 

scope of its review .................................................... 

26 

C. EPA has recognized limitations on its 

discretion to revise the particulate matter and 

ozone standards ........................................................ 

31 

II. The court of appeals lacked jurisdiction to review 

EPA’s preamble statements on the scope of its 

authority to implement a revised ozone 

standard ............................................................................... 34 

(III) 

IV 

Table of Contents—Continued: 

Page 

A. EPA’s preamble statements regarding imple- 
mentation authority are not “agency action” 

within the meaing of Section 307(b)(1) of 

the Act ......................................................................... 

36 

B. EPA’s preamble statements do not constitute 

“final” agency action ................................................ 

38 

C. EPA’s preamble statements regarding imple- 
mentation of the eight-hour ozone standard 

are not ripe for review ............................................. 

41 

III. The court of appeals improperly restricted 

EPA’s authority to implement the revised 

ozone standard .................................................................. 

44 

A. The Clean Air Act authorizes EPA to 

implement the revised ozone NAAQS under 

Subpart 1 of Part D .................................................. 

45 

B. Delaying implementation of the revised 

NAAQS until the previous standard is 

attained conflicts with the Clean Air Act’s 

requirement that all NAAQS be attained “as 

expeditiously as practicable” .................................. 

48 

Conclusion ....................................................................................... 50 

Appendix ......................................................................................... 1a 

TABLE OF AUTHORITIES 

Cases: 

Abbott Labs. v. Gardner, 387 U.S. 136 (1967) ......... 

38, 41, 42 

ACLU v. FCC, 823 F.2d 1554 (D.C. Cir. 1987), 

cert. denied, 485 U.S. 959 (1988) ......................................... 

43 

American Power & Light Co. v. SEC, 329 U.S. 90 

(1946) .......................................................................... 

22, 24, 26, 27 

Baltimore Gas & Elec. Co. v. NRDC, 462 U.S. 87 

(1983) ........................................................................................ 27 

V 

Cases—Continued: Page 

Bennett v. Spear, 520 U.S. 154 (1997) ............................ 

38, 41 

Black v. Cutter Labs., 351 U.S. 292 (1956) ........................ 

37 

California v. Rooney, 483 U.S. 307 (1987) ........................ 

37 

Chevron U.S.A. Inc. v. NRDC, 467 U.S. 837 

(1984) .............................................................................. 

43, 48, 50 

Citizens to Preserve Overton Park, Inc. v. Volpe, 

401 U.S. 402 (1971) ............................................................. 

27, 34 

Ethyl Corp. v. EPA, 541 F.2d 1 (D.C. Cir.), cert. 

denied, 426 U.S. 941 (1976) ................................................... 

28 

FPC v. Conway Corp., 426 U.S. 271 (1976) ....................... 

30 

FTC v. Mandel Bros., Inc., 359 U.S. 385 (1959) ............... 

46 

FTC v. Standard Oil Co., 449 U.S. 232 (1980) .............. 

36, 37, 

38, 43 

Federal Energy Admin. v. Algonquin SNG, 

Inc., 426 U.S. 548 (1976) ................................................... 

25, 26 

Harrison v. PPG Indus., Inc., 446 U.S. 578 

(1980) ........................................................................................ 36 

Herb v. Pitcairn, 324 U.S. 117 (1945) ................................ 

37 

INS v. National Ctr. for Immigrants Rights, 

Inc., 502 U.S. 183 (1991) ...................................................... 

46 

International Longshoremen’s & Warehousemen’s 

Union v. Boyd, 347 U.S. 222 (1954) ................................. 

43 

Lead Indus. Ass’n v. EPA, 647 F.2d 1130 (D.C. 

Cir.), cert. denied, 449 U.S. 1042 (1980) .............. 

3, 5, 24, 29 

Loving v. United States, 517 U.S. 748 (1996) .................... 

21 

Lujan v. National Wildlife Fed’n, 497 U.S. 871 

(1990) .................................................................................... 

36, 44 

Mead Corp. v. Tilley, 490 U.S. 714 (1989) ......................... 

46 

Mistretta v. United States, 488 U.S. 361 (1989) ............ 

21, 22, 

23, 24, 25, 44 

Montana-Dakota Util. Co. v. Northwestern Pub. 
Serv. Co., 341 U.S. 246 (1951) ............................................. 30 

VI 

Cases—Continued: Page 

NRDC v. EPA, 902 F.2d 962 (1990), opinion vacated 

in part, 921 F.2d 326 (D.C. Cir.), cert. denied, 498 

U.S. 1082 (1991) .............................................................. 

4, 28, 30 

New York v. EPA, 852 F.2d 574 (D.C. Cir. 1988), 

cert. denied, 489 U.S. 1065 (1989) ....................................... 

28 

Office of Communication of United Church of 

Christ v. FCC, 826 F.2d 101 (D.C. Cir. 1987) ................ 

43 

Ohio Forestry Ass’n v. Sierra Club, 523 U.S. 726 

(1998) ....................................................................... 

41, 42, 43, 44 

Poe v. Ullman, 367 U.S. 497 (1961) .................................... 

42 

Reno v. Catholic Soc. Servs., Inc., 509 U.S. 43 

(1993) .................................................................................... 41-42 

Simon v. Eastern Ky. Welfare Rights Org., 426 

U.S. 26 (1976) .......................................................................... 

42 

Skinner v. Mid-America Pipeline Co., 490 U.S. 

212 (1989) ................................................................................. 

22 

Texas v. United States, 523 U.S. 296 (1998) ...................... 

42 

Toilet Goods Ass’n v. Gardner, 387 U.S. 158 

(1967) .................................................................................... 

43, 44 

Touby v. United States, 500 U.S. 160 (1991) ........... 

21, 24, 25 

Train v. NRDC, 421 U.S. 60 (1975) ..................................... 

3, 6 

Union Elec. Co. v. EPA, 427 U.S. 246 (1976) ................... 

6 

Vermont Yankee Nuclear Power Corp. v. NRDC, 

435 U.S. 519 (1978) ................................................................. 

27 

Yakus v. United States, 321 U.S. 414 (1944) ........... 

21, 22, 26 

Constitution, statutes and regulations: 

U.S. Const. Art. I ...................................................................... 

1 

Administrative Procedure Act: 

5 U.S.C. 551(13) ...................................................................... 

36 

5 U.S.C. 701(b)(2) ................................................................... 

36 

5 U.S.C. 706(2) ........................................................................ 37 

VII 

Statutes and regulations—Continued: 
Page 

Air Pollution Control Act of 1955, ch. 360, 69 

Stat. 322 ................................................................................... 

3 

Air Quality Act of 1967, Pub. L. No. 90-148, § 108(c), 

81 Stat. 492-494 ...................................................................... 

3 

Clean Air Act, 42 U.S.C. 7401 et seq. ..................................... 

2 

§§ 101-193, 42 U.S.C. 7401-7515 (1994 & Supp. III 

1997) ..................................................................................... 45 

§ 107(d), 42 U.S.C. 7407(d) (1982) ....................................... 

6 

§ 107(d), 42 U.S.C. 7407(d) ......................................... 

42, 45, 46 

§ 107(d)(1), 42 U.S.C. 7407(d)(1) .................................. 

5, 40, 48 

§ 107(d)(1)(A), 42 U.S.C. 7407(d)(1)(A) .............................. 

50 

§ 107(d)(1)(C), 42 U.S.C. 7407(d)(1)(C) .............................. 

48 

§ 107(d)(3), 42 U.S.C. 7407(d)(3) .......................................... 

47-48 

§ 107(d)(4), 42 U.S.C. 7404(d)(4) .......................................... 

48 

§ 107(d)(4)(A), 42 U.S.C. 7407(d)(4)(A) .............................. 

48 

§§ 108-109, 42 U.S.C. 7408-7409 .......................................... 

3 

§ 108, 42 U.S.C. 7408 ............................................................. 

5 

§ 108(a), 42 U.S.C. 7408(a) .................................................... 

39 

§ 108(a)(1), 42 U.S.C. 7408(a)(1) .......................................... 

4 

§ 108(a)(1)(A)-(B), 42 U.S.C. 7408(a)(1)(A)-(B) ................ 

23 

§ 108(a)(2), 42 U.S.C. 7408(a)(2) .......................................... 

4, 23 

§ 108(a)(2)(A)-(B), 42 U.S.C. 7408(a)(2)(A)-(B) ................ 

23 

§ 108(b), 42 U.S.C. 7408(b) ................................................... 

28 

§ 109, 42 U.S.C. 7409 ..................... 

2, 18, 22, 24, 26, 28, 29, 31 

§ 109(a)(1), 42 U.S.C. 7409(a)(1) .......................................... 

4 

§ 109(b)(1), 42 U.S.C. 7409(b)(1) .......................................... 

4, 23 

§ 109(b)(1)-(2), 42 U.S.C. 7409(b)(1)-(2) .............................. 

4 

§ 109(b)(2), 42 U.S.C. 7409(b)(2) .......................................... 

4, 5 

§ 109(d), 42 U.S.C. 7409(d) ................................................... 

39 

§ 109(d)(1), 42 U.S.C. 7409(d)(1) ........................................ 

5, 45 

§ 109(d)(2), 42 U.S.C. 7409(d)(2) .......................................... 

23 

§ 109(d)(2)(B), 42 U.S.C. 7409(d)(2)(B) .............................. 

4 

§ 110, 42 U.S.C. 7410 ............................................................. 

3, 6 

§ 110(a), 42 U.S.C. 7410(a) .................................................... 6, 40 

VIII 

Statutes and regulations—Continued: 
Page 

§ 110(a), 42 U.S.C. 7410(a)(1) ............................................... 

6 

§ 110(c), 42 U.S.C. 7410(c) .................................................... 

6 

§ 110(k), 42 U.S.C. 7410(k) ................................................... 

40 

§§ 171-178, 42 U.S.C. 7501-7508 (1982) .............................. 

6 

§§ 171-179, 42 U.S.C. 7501-7509a (1994 & 

Supp. III 1997) ................................................................... 

7 

§§ 171-193, 42 U.S.C. 7501-7515 (1994 & 

Supp. III 1997) ................................................................... 

6 

§ 172, 42 U.S.C. 7502 ......................................................... 
16, 42 

§§ 172(a) and (c), 42 U.S.C. 7502(a) and (c) 
(1982) ................................................................................... 6 

§ 172(a), 42 U.S.C. 7502(a) .................. 

5, 7, 8, 21, 40, 43, 45, 46 

§ 172(a)(1), 42 U.S.C. 7502(a)(1) .......................................... 

45 

§ 172(a)(1)(A), 42 U.S.C. 7502(a)(1)(A) ...................... 

7, 21, 45 

§ 172(a)(1)(C), 42 U.S.C. 7502(a)(1)(C) ........................... 

8, 46 

§ 172(a)(2), 42 U.S.C. 7502(a)(2) .................................... 

45, 49 

§ 172(a)(2)(A), 42 U.S.C. 7502(a)(2)(A) .............................. 

7 

§ 172(a)(2)(C), 42 U.S.C. 7502(a)(2)(C) ............................... 

7 

§ 172(a)(2)(D), 42 U.S.C. 7502(a)(2)(D) .............................. 

8, 46 

§ 172(b), 42 U.S.C. 7502(b) ................................................... 

40 

§ 172(c), 42 U.S.C. 7502(c) .................................................... 

6, 40 

§ 181, 42 U.S.C. 7511 ......................................................... 

16, 42 

§ 181-185B, 42 U.S.C. 7511-7511f (1994 & Supp. III 

1997) ................................................................................... 7 

§§ 181-191, 42 U.S.C. 7511-7514a (1994 & Supp. III 

1997) ................................................................................... 7 

§ 181(a), 42 U.S.C. 7511(a) .................. 

16, 20, 35, 42, 46, 47, 48 

§ 181(a)(1), 42 U.S.C. 7511(a)(1) ................................ 

passim 

§ 181(a)(5), 42 U.S.C. 7511 (a)(5) ......................................... 

49 

§ 181(b), 42 U.S.C. 7511(b) ............................................... 

47, 48 

§§ 182-187, 42 U.S.C. 7512-7512a (1994 & Supp. III 

1997) ................................................................................... 7 

§§ 188-189, 42 U.S.C. 7513-7513b ........................................ 7 

IX 

Statutes and regulations—Continued: 
Page 

§§ 191-192, 42 U.S.C. 7514-7514a ........................................ 

7 

§ 307(b)(1), 42 U.S.C. 7607(b)(1) .............. 

24, 34, 35, 36, 39, 50 

§ 307(d), 42 U.S.C. 7607(d) ................................................... 

23 

§ 307(d)(2)-(6), 42 U.S.C. 7607(d)(2)-(6) .............................. 

32 

§ 307(d)(3), 42 U.S.C. 7607(d)(3) ...................................... 

5, 24 

§ 307(d)(6), 42 U.S.C. 7607(d)(6) ...................................... 

34, 37 

§ 307(d)(6)(A), 42 U.S.C. 7607(d)(6)(A) .............................. 

24 

§ 307(d)(6)(b), 42 U.S.C. 7607(d)(6)(B) ........................... 

15, 24 

§ 307(d)(7)(B), 42 U.S.C. 7607(d)(7)(B) .............................. 

35 

§ 307(d)(9), 42 U.S.C. 7607(d)(9) ................... 

23, 24, 27, 30, 37 

§ 1, 77 Stat. 395 .................................................................. 

3 

Clean Air Act of 1963, Pub. L. No. 88-206, 77 Stat. 

392 ............................................................................................. 3 

Clean Air Act Amendments of 1970, Pub. L. No. 
91-604, 84 Stat. 1676 .............................................................. 

3 

§ 107(a), 84 Stat. 1679-1683 .............................................. 

3 

Clean Air Act Amendments of 1977, Pub. L. No. 95- 

95, 91 Stat. 685 ........................................................................ 

3 

Clean Air Act Amendments of 1990, Pub. L. No. 
101-549, 104 Stat. 2399 .......................................................... 
3, 6 

Pub. L. No. 105-178, 112 Stat. 107: 

§ 6101(b), 112 Stat. 463 ....................................................... 

40 

§ 6102(c), 112 Stat. 464 ....................................................... 

40 

§ 6103(a)-(b), 112 Stat. 465 ................................................ 

40 

42 U.S.C. 1857c-5(a)(2)(A)(i)(1970) ........................................ 
6 

40 C.F.R.: 

Section 50.4(a)-(b) .................................................................. 

49 

Section 50.8(a)(1)-(2) .............................................................. 

49 

Section 50.9 (1990) ................................................................. 

45 

Section 50.9(b) .................................................................... 

15, 39 

Section 50.10 ........................................................................... 

47 

Pt. 50 App. I ............................................................................ 

47 

Miscellaneous: 

50 Fed. Reg. 25,532 (1985) ....................................................... 

5 

52 Fed. Reg. 24,634-24,635 (1987) .......................................... 
5 

59 Fed. Reg. 38,906-38,907 (1994) .......................................... 5 

X 

Miscellaneous—Continued: Page 

61 Fed. (1996): 
pp. 65,641-65,643 .................................................................... 
9 

p. 65,642 ................................................................................. 32 

p. 65,644 ................................................................................. 10 

pp. 65,650-65,651 .................................................................... 

2 

pp. 65,719-65,720 .................................................................... 
11 

pp. 65,719-65,721 .................................................................... 
31 

p. 65,723 ................................................................................. 12 

p. 65,725-65,726 .................................................................... 14 

p. 65,727 ................................................................................. 33 

p. 65,728 ................................................................................. 32 

p. 65,730 ............................................................................. 

32, 33 

62 Fed. Reg. (1997): 

p. 38,652 ................................................................................. 

2 

p. 38,653 ................................................................................. 
9 

p. 38,654 ................................................................................. 
4, 9 

pp. 38,656-38,657 .................................................................... 
31 

p. 38, 657 ................................................................................ 
10 

p. 38,665 ............................................................................. 
10, 31 

pp. 36,665-38,668 .................................................................... 
10 

p. 38,666-38,667 .................................................................... 
9 

p. 38,669 ................................................................................. 10 

p. 38,675-38,676 .......................................................... 

10, 11, 32 

pp. 38,675-38,677 .................................................................... 
32 

p. 38,676 ............................................................................. 
10, 33 

pp. 38,676-38,677 .................................................................... 

p. 38,677 ................................................................................. 11 

p. 38,683 ................................................................................. 11 

p. 38,688 ................................................................................. 29 

p. 38,856 ................................................................................. 

2 

p. 38,858 ................................................................................. 11 

p. 38,859 ....................................................................... 

11, 12, 31 

p. 38,860 ................................................................................. 12 

p. 38,861 ................................................................................. 12 

pp. 38,861-38,873 .................................................................... 

13 

p. 38,862 ................................................................................. 12 

p. 38,863 ....................................................................... 

12, 13, 33 

pp. 38,863-38,864 ................................................................ 
13, 14 

pp. 38,863-38,868 .................................................................... 14 

XI 

Miscellaneous—Continued: Page 

p. 38, 864 ................................................................................ 

14 

pp. 38,864-38,865 .................................................................... 
14 

pp. 38,864-38,868 .................................................................... 
33 

p. 38,865 ............................................................................. 
13, 33 

pp. 38,867-38,868 .................................................................... 
14 

p. 38,868 ................................................................................. 14 

p. 38,868-38,869 .................................................................... 15 

p. 38,873 ................................................................................. 39 

p. 38,878 ................................................................................. 15 

p. 38,883 ................................................................................. 29 

pp. 38,884-38,885 ................................................... 

15, 17, 35, 36 

H.R. Rep. No. 294, 95th Cong., 1st Sess. (1977) .................. 
24 

H.R. Rep. No. 490, 101st Cong., 2d Sess. Pt. 1 (1990) .... 
47, 49 

Modern Epidemiology (K.J. Rothman & S. Greenland 
eds., 2d ed. 1998) .................................................................... 
9 

S. Rep. No. 1196, 91st Cong., 2d Sess. (1970) ................... 
24, 28 

S. Rep. No. 228, 101st Cong., 1st Sess. (1989) ...................... 
49 

1 Staff of the Senate Comm. on Pub. Works, 93d Cong., 
2d Sess., A Legislative History of the Clean Air Act 
Amendments of 1970 (Comm. Print 1974) .................... 24-25 

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 175 F.3d 1027. The opinion on petitions for 
rehearing and dissenting statements on denial of rehearing 
en banc (Pet. App. 70a-101a) are reported at 195 F.3d 4. 

JURISDICTION 

The decision of the court of appeals was entered on May 
14, 1999. Petitions for 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, and was granted on 
May 22, 2000. The jurisdiction of this Court is invoked under 
on 28 U.S.C. 1254(1). 

CONSTITUTIONAL, STATUTORY, AND REGULATORY 
PROVISIONS INVOLVED 

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

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

(1) 

2 

The relevant sections of the Clean Air Act, 42 U.S.C. 7401 
et seq., are set forth in the petition appendix at Pet. App. 
105a-126a. The EPA rules at 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 Environmental Protection Agency (EPA) to 
establish and periodically revise, based on the latest 
scientific knowledge, primary National Ambient Air Quality 
Standards (NAAQS) “requisite to protect” public health 
with “an adequate margin of safety,” and secondary NAAQS 
“requisite to protect” other public interests. On July 18, 
1997, EPA issued final rules revising the NAAQS for two 
pollutants: particulate matter (PM) and ozone.1 

EPA 
decided to revise the PM and ozone standards because new 
scientific evidence showed that the standards then in effect 
were not adequately protecting millions of Americans from 
adverse health effects. For example, a quantitative risk 
assessment indicated that PM concentrations below the 
standards EPA established in 1987 may annually subject 
people in two urban areas alone, representing about five 
million people, to hundreds of early deaths, thousands of 
hospital admissions for respiratory illness, and tens of 
thousands of incidents of respiratory 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, as interpreted by EPA in setting the revised 
PM and ozone standards, effected an unconstitutional dele- 
gation of legislative authority. The court remanded both 
rules for EPA to articulate an “intelligible principle” for 
determining the degree of public health protection to be 
afforded by the NAAQS. In addition, even though EPA had 

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

3 

taken no final agency action to implement 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 extra- 
ordinarily detailed program for control of air pollution 
through a system of shared federal and state responsibility.2 
The NAAQS are a central feature of that program. Sections 
108 and 109 of the Act require EPA to establish, review, and 
revise nationally applicable standards for a small class of 
common air pollutants. 42 U.S.C. 7408-7409. The NAAQS 
establish permissible concentrations of those pollutants in 
the “ambient,” or outside, air. Section 110 of the Act then 
calls on the States to impose controls on individual sources of 
air pollution as necessary to attain and maintain the 
NAAQS. 42 U.S.C. 7410; see Train v. 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 that are emitted from “numerous or diverse” 

2 Congress first addressed the problem of air pollution through the 
Air Pollution Control Act of 1955, ch. 360, 69 Stat. 322, which authorized 
the Secretary of Health, Education, and Welfare (HEW) to conduct re- 
search 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. Congress later directed States to develop regionally based 
ambient air quality standards and provided mechanisms for enforcement, 
Air Quality Act of 1967, Pub. L. No. 90-148, § 108(c), 81 Stat. 492-494. 
Congress substantially revised that program through the Clean Air Act 
Amendments of 1970, Pub. L. No. 91-604, 84 Stat. 1679, which provided for 
national ambient air quality standards and for state implementation. See 
§ 107(a), 84 Stat. 1679-1683. Congress continued to build on that program 
through the Clean Air Act Amendments of 1977, Pub. L. No. 95-95, 91 
Stat. 685, and the Clean Air Act Amendments of 1990, Pub. L. No. 101- 
549, 104 Stat. 2399. See text at p. 6, infra, and note 5, infra. 

4 

sources and that “may reasonably be anticipated to endanger 
public health or welfare.” 42 U.S.C. 7408(a)(1). EPA has 
identified six such pollutants, commonly referred to as “cri- 
teria” pollutants: sulfur oxides; nitrogen oxides; carbon mon- 
oxide; lead; ozone; and particulate matter. 

EPA must develop “air quality criteria” reflecting the 
“latest scientific knowledge” on “all identifiable effects on 
public health or welfare” that may result from each criteria 
pollutant’s presence in the ambient air. 42 U.S.C. 7408(a)(2). 
EPA generally records the scientific assessments constitut- 
ing air quality criteria in a “Criteria Document,” which pro- 
vides a rigorous analysis of all pertinent scientific informa- 
tion. EPA also develops a “Staff Paper” to “bridge the gap” 
between the scientific review and the judgments the Admin- 
istrator must make to set standards. See NRDC v. EPA, 
902 F.2d 962, 967 (1990), opinion vacated in part, 921 F.2d 
326 (D.C. Cir.), cert. denied, 498 U.S. 1082 (1991). Both docu- 
ments undergo public notice and comment, as well as exten- 
sive scientific peer-review by the Clean Air Scientific Advi- 
sory Committee (CASAC), an independent committee 
established under the Act to advise the EPA Administrator 
on air quality 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 and welfare 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 the judgment of the Administra- 
tor,” are “requisite to protect the public health” with “an 
adequate margin of safety.” 42 U.S.C. 7409(b)(1). EPA must 
set “secondary” standards at levels that are “requisite to 
protect the public welfare” from any “known or anticipated 
adverse effects.” 42 U.S.C. 7409(b)(2). 

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

5 

To ensure that standards keep pace with advances in 
scientific knowledge, EPA must review the air quality 
criteria and standards every five years and revise them as 
“appropriate in accordance with [Sections 108 and 109(b)].” 
42 U.S.C. 7409(d)(1). When setting or revising NAAQS, 
EPA must 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 to ensure consistency among its NAAQS 
decisions. EPA considers, among other public health factors, 
the nature and severity of health effects, the types of health 
evidence, the kind and degree of uncertainties involved, and 
the size and nature of the sensitive populations at risk. See, 

e.g., 97-1440 C.A. App. (PM App.) 1908. The court of appeals 
approved EPA’s use of those factors 20 years ago, Lead 
Indus., 647 F.2d at 1161, and EPA has since employed them 
in numerous NAAQS rulemakings.4 The court reaffirmed its 
approval of EPA’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-state cooperation, to ensure that the air through- 
out the Nation “attains” the NAAQS. Within three years of 
promulgating a new or revised NAAQS, EPA must “desig- 
nate” areas of the country as either “attainment” (i.e., the 
area meets that NAAQS), “nonattainment” (i.e., the area 
fails to meet that NAAQS), or “unclassifiable” (i.e., adequate 
information is not available). 42 U.S.C. 7407(d)(1). Follow- 
ing designation, EPA must establish the date by which 
nonattainment areas shall attain that NAAQS (i.e., the area’s 
attainment date). See 42 U.S.C. 7502(a). The CAA provides 
for each State to develop, for EPA’s approval, a state imple- 

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). 

6 

mentation plan (SIP) that sets forth pollution control mea- 
sures necessary to attain all 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 measures to 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 regu- 
latory scheme through the Clean Air Act Amendments of 
1970 and the Clean Air Act Amendments of 1977. See note 
2, supra.5 Congress built further on that foundation through 
the 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 obliga- 
tions in Section 110 for States to implement all NAAQS, 
including “any revision thereof,” in all areas of the Nation, 
regardless of their designation status. 42 U.S.C. 7410(a)(1). 
Congress, however, adjusted the attainment obligations for 
the NAAQS then in existence and revised the attainment 
obligations that 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). 

5 The Clean Air Amendments of 1970 introduced the NAAQS concept 
and required States to attain each NAAQS “as expeditiously as practica- 
ble but * * * in no case later than three years” after EPA approves a 
SIP. 42 U.S.C. 1857c-5(a)(2)(A)(i) (1970). The Clean Air Act Amend- 
ments of 1977 added 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). The 1977 Amendments also introduced a new “Part D,” which 
contained additional attainment provisions for all NAAQS that apply to all 
nonattainment areas. See 42 U.S.C. 7501-7508 (1982) (Pt. D, Tit. I). 

7 

First, Congress modified the general nonattainment pro- 
visions that it had previously set out in Part D, see note 5, 
supra, and placed them in a new subpart, titled “Subpart 1 
—Nonattainment Areas in General.” 42 U.S.C. 7501-7509a 
(1994 & Supp. III 1997). Section 172(a) of that Subpart in- 
cludes a new scheme for EPA to classify and establish at- 
tainment dates for nonattainment areas, based upon various 
factors, including the severity of the area’s pollution prob- 
lem. 42 U.S.C. 7502(a).6 That scheme applies to all non- 
attainment areas “with respect to any [NAAQS] (or any 
revised standard, 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 address nonattainment 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 contains specific 
implementation provisions for the ozone NAAQS, which 
apply in addition to the general implementation provisions in 
Subpart 1. 

See 42 U.S.C. 7511-7511f (1994 & Supp. III 1997) 

(“Subpart 2—Additional Provisions for Ozone Nonattain- 
ment 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). Sec- 
tion 181(a)(1) of that Subpart sets out specific classifications 
and attainment dates that apply “by operation of law” for 
areas that, prior to the 1990 Amendments, were designated 

6 The dates must be set so that attainment is achieved as “as expedi- 
tiously as practicable,” with outside dates that may range up to 10 years 
from the date an area is designated nonattainment, with two one-year 
extensions possible. 42 U.S.C. 7502(a)(2)(A) and (C). 

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

8 

nonattainment under the 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 nonattainment areas with the attain- 
ment schedule in Section 181(a)(1) of Subpart 2 (and in other 
Subparts of Part D). Congress provided that EPA’s author- 
ity in Section 172(a) shall not apply to “nonattainment areas 
for which classifications [or “attainment dates”] are specifi- 
cally provided under other provisions 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 classifications and attainment 
dates for areas designated nonattainment for the one-hour 
ozone standard, EPA may not invoke Section 172(a) to 
establish classifications and attainment dates for that ozone 
NAAQS. 

II. THE PARTICULATE MATTER AND OZONE RULE- 
MAKING PROCEEDINGS 

On July 18, 1997, EPA promulgated revised primary and 
secondary air quality standards for PM and ozone. In each 
rulemaking, the Criteria Documents and Staff Papers 
underwent several rounds of review by CASAC, public 
comment, and revision by EPA. Ultimately, CASAC 
notified EPA that the PM and ozone Criteria Documents 
provided an adequate scientific basis for regulatory 
decisions. PM App. 3151; 97-1441 C.A. App. (Ozone App.) 
235. CASAC also notified EPA that the PM and ozone Staff 
Papers, which among other things identified ranges of 

8 Table 1 of Section 181(a)(1) establishes specific classifications for 
nonattainment areas under the one-hour ozone standard based upon the 
area’s “design value,” which refers to the measurement methodology then 
in use. See note 29, infra. Table 1 also sets a corresponding attainment 
date 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 

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 based on the revised air 
quality criteria. EPA provided exhaustive explanations of 
the basis for the two decisions, which we briefly summarize 
below. 

A. The Particulate Matter Rule 

Particulate matter encompasses a broad class of chemi- 
cally and physically diverse liquid and solid particles. 62 
Fed. Reg. at 38,653. Scientists generally distinguish be- 
tween two categories of PM—fine and coarse. Both were en- 
compassed by the “PM10” standards that EPA set in 1987.9 

EPA revised the PM standards based on new scientific 
studies that had emerged since EPA’s last PM review, 
including an extensive body of epidemiological studies on 
exposure to PM pollution. 

10 More than 60 such studies 
showed statistically significant positive associations between 
exposure to PM air pollution and serious adverse health 
effects, including premature death and illness severe enough 
to require hospital admission. 61 Fed. Reg. at 65,641-65,643; 
PM App. 1375-1778, 1801-1845 (Criteria Document). The 
same evidence identified several large “sensitive” popula- 

9 Generally, fine particles are by-products of combustion or the 
reaction and transformation of gases. PM App. 519, 1786. Coarse parti- 
cles generally are the result of abrasion of material into smaller pieces, 
which are then suspended in the air by wind or human activity. Id. at 519, 
1787. PM10 denotes particulate matter up to about 10 micrometers (µm) in 
diameter, which is 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 2.5 µm in diameter. Id. at 38,654 n.5. 

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

10 

tions that may experience health effects at lower PM con- 
centrations, or more severely, than the general public. 61 
Fed. Reg. at 65,644. Those populations included the 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 effects were “attributable to PM at levels below the 
current NAAQS.” PM App. 1870. The Administrator con- 
cluded, based on the nature of the health effects and the 
huge size of the affected populations, 62 Fed. Reg. at 38,657, 
that the studies provided “strong evidence that the current 
PM10 standards do not adequately protect public health, and 
that revision of the standards is not only appropriate, but 
necessary,” id. at 38,665. 

The Administrator decided she could best protect against 
the health risk posed by PM by adopting two sets of stan- 
dards: (1) PM2.5 NAAQS to control fine particles, which were 
likely responsible for those health effects associated with PM 
concentrations at or below the 1987 NAAQS; and (2) PM10 
NAAQS to provide continued control of inhalable coarse 
particles. 62 Fed. Reg. at 38,665-38,668. The Administrator 
selected the annual PM2.5 NAAQS as the “generally control- 
ling” standard to reduce both long-term and peak PM2.5 con- 
centrations and adopted the 24-hour PM2.5 NAAQS only to 
address unusual circumstances. Id. at 38,669. 

To select the levels requisite to protect public health, with 
an adequate margin of safety, the Administrator relied 
chiefly on epidemiological studies that employed direct mea- 
sures of fine particles, such as PM2.5. 62 Fed. Reg. at 38,675- 
38,676 & n.41. “[P]lacing greatest weight on those studies 
that were clearly statistically significant,” the Administrator 
concluded that an annual PM2.5 standard of 15 micrograms 
per cubic meter of air (µg/m3) “will provide an adequate 
margin of safety against the 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 encompasses the 

11 

annual mean PM2.5 levels in locations where epidemiological 
studies had shown statistically significant positive associa- 
tions between fine particles and adverse health effects. 
Ibid.; PM App. 3506-3521. The Administrator acknowledged 
that “the possibility of effects at lower annual concentrations 
cannot be excluded,” but she noted that the evidence 
supporting that possibility—which did not rise to the level of 
statistical significance—is “highly uncertain,” and therefore 
did not warrant establishment of 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 the interaction in sunlight of nitrogen oxides and 
volatile organic compounds emitted from many sources. It is 
the principal component of smog and a powerful lung 
irritant. See 62 Fed. Reg. at 38,858. 

12 

EPA’s review of the latest scientific knowledge on ozone 
disclosed a large body of new research demonstrating asso- 
ciations between adverse health effects and exposure to 
ozone over longer periods, at more moderate levels of exer- 
tion, and at lower concentrations than had been shown by 
the studies available in 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 effects associated with prolonged (six to eight 
hours) exposure to ozone levels as low as 0.08 ppm. 62 Fed. 

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 stan- 
dards identical to the primary PM2.5 standards were appropriate to protect 
public welfare from, among other things, adverse effects on visibility. Id. 
at 38,683. 

12 The ozone NAAQS regulates harmful ground-level or “tropospheric” 
ozone, and not stratospheric ozone, which “provides a protective shield 
from excess ultraviolet radiation.” 62 Fed. Reg. at 38,858. 

12 

Reg. at 38,859. The studies also showed that, in comparison 
to the general population, active children and workers who 
regularly engage in outdoor activities are at greater risk of 
experiencing adverse health effects from exposure to ozone. 
Ibid. In addition, people with pre-existing respiratory 
disease are more susceptible than others to the 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 revise both the averaging time and the con- 
centration level of the 1979 one-hour ozone standard. 62 
Fed. Reg. at 38,863. She determined, and CASAC con- 
curred, that an eight-hour standard was more consistent 
than a one-hour standard with the kind of prolonged expo- 
sures at which the scientific evidence showed children and 
others in at-risk populations were experiencing health 
effects of concern. Id. at 38,861. In addition, EPA’s quan- 
titative exposure and risk assessments showed that an eight- 
hour standard would provide significantly greater nation- 
wide uniformity in health protection than a one-hour 
standard. Id. at 38,862. 

To select a concentration level for the eight-hour averag- 
ing period, EPA employed a weight-of-evidence approach. 
Using, with CASAC’s concurrence, guidelines of the Ameri- 
can Thoracic Society, EPA considered the medical signifi- 
cance, or “adversity,” of ozone-related health effects, which 
can vary widely. 62 Fed. Reg. at 38,860. 

13 EPA also 
considered the public health implications of its conclusions 
regarding effects on individuals. For that purpose, EPA 
prepared quantitative exposure and risk assessments that 
used (among other information) data from human clinical 

13 For example, effects that may be mere nuisances to many healthy 
people may have serious consequences for asthmatics. EPA and CASAC 
also recognized that an effect that may be medically insignificant if experi- 
enced only once may, with repetition, become adverse by setting the stage 
for more serious illness. 61 Fed. Reg. at 65,723; Ozone App. 1881-1882. 

13 

studies to estimate, for various levels of ozone in the ambient 
air, the number of people within certain sensitive population 
groups likely to experience effects that 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 for an eight-hour ozone standard. The upper 
bound for consideration could be no higher than 0.09 ppm 
because the exposure and risk assessments showed that the 
risks associated with an eight-hour standard of 0.09 ppm 
were “the same or only marginally smaller” than those asso- 
ciated with the 1979 one-hour standard, which EPA and 
CASAC agreed provided “little, if any, margin of safety.” 62 
Fed. Reg. at 38,863-38,864. The lower bound for consi- 
deration also emerged from the scientific evidence, including 
in particular: (1) the absence of any human clinical studies 
on exposures below 0.08 ppm, id. at 38,863; and (2) quanti- 
tative exposure assessments showing that 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 the character of the available scientific evi- 
dence regarding ozone exposures within the range identified. 
She compared a 0.08 ppm standard to a 0.09 ppm standard on 
the basis of a number of factors, including estimates of the 
relative number of children that would experience adverse 
health effects, the relative frequency of such effects, and 
relative increases in hospital admissions. Those estimates 
and estimates of occurrences of “exposures of concern” 

14 With CASAC’s concurrence, EPA deemed eight-hour exposures, 
during moderate exertion, to ozone concentrations of 0.08 ppm or above to 
be “exposures of concern” for purposes of the quantitative exposure and 
risk assessments. 62 Fed. Reg. at 38,865. In those analyses, EPA used 
data from human clinical studies, which necessarily related to only the 
mildest health effects. A single “exposure of concern” would not 
necessarily cause adverse effects, but is an indicator of the public health 
impacts of more serious effects. 

14 

under a standard of 0.09 ppm counseled against use of that 
concentration. 62 Fed. Reg. at 38,867-38,868; see note 14, 
supra. For example, EPA estimated that a 0.09 ppm stan- 
dard would allow more than three times as many children to 
experience exposures of concern than would a standard of 

0.08 ppm. 62 Fed. Reg. at 38,868. 
The Administrator also explained why she concluded that 
a standard set below 0.08 ppm would be more stringent than 
requisite to protect against adverse effects of public health 
significance. See 62 Fed. Reg. at 38,863-38,868. With 
CASAC’s concurrence, EPA had reasonably assumed, for 
purposes of the quantitative risk assessment, that there is no 
“effects threshold” for the categories of health effects mea- 
sured in human clinical studies—lung function decreases and 
respiratory symptoms. EPA therefore assumed that those 
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 responses caused by exposures even at 

0.08 ppm were “typically small or mild in nature.” 62 Fed. 
Reg. at 38,864. The Administrator recognized that repeated 
exposures at the 0.08 ppm level could potentially produce 
adverse effects for some unusually sensitive individuals, 
ibid., but the record indicated that the “most certain” ozone- 
related effects at and below that level, even when adverse, 
are “transient and reversible,” id. at 38,868. Moreover, the 
quantitative exposure and risk assessments showed that a 
standard set at 0.08 ppm would significantly reduce the 
number of such exposures. See ibid. As for more serious 
health effects, EPA lacked clinical data indicating the 
existence of an exposure-response relationship at ozone 
levels below 0.08 ppm. See id. at 38,863-38,864, 38,868; 
Ozone App. 1962. Furthermore, none of the CASAC 
advisors recommended setting the revised 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 the available evidence, that an eight-hour ozone standard 

15 

of 0.08 ppm would be 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, as required by the Act, 42 U.S.C. 7607(d)(6)(B), 
to all significant public comments. Various commenters had 
argued that, by enacting in 1990 specific provisions 
regarding implementation of the one-hour ozone standard 
then in effect, e.g., 42 U.S.C. 7511(a)(1), Congress had 
effectively codified that standard and precluded EPA from 
revising it. In response, EPA explained that its authority to 
revise the one-hour ozone standard was clear on the face of 
the Act and then briefly and generally discussed how some 
of the Act’s provisions would apply to implementation of a 
revised ozone standard. The sole purpose of that discussion 
was to respond fully to the comments arguing that the 1990 
Amendments curtailed EPA’s authority to revise the ozone 
standard. 62 Fed. Reg. at 38,884-38,885; see App., infra, 1a- 
6a (reproducing the preamble discussion). 

III. THE PROCEEDINGS BELOW 

Numerous industry groups, a public interest group, and 
several States and individuals challenged the revised PM 
and ozone NAAQS. The court of appeals rejected many of 
the challenges, but nevertheless remanded both final rules to 
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 uncon- 
stitutional delegation of legislative power.” Id. at 4a. 
According to the majority, EPA’s interpretation of the Act 

15 EPA set a revised secondary ozone standard identical to the revised 
primary standard. 62 Fed. Reg. at 38,878. In addition, EPA issued a 
separate rule, 40 C.F.R. 50.9(b), respecting future enforcement of the one- 
hour ozone standard, which the revised eight-hour ozone standard would 
replace. See note 26, infra. 

16 

leaves it “free to pick any point between zero and a hair 
below * * * London’s Killer Fog,” a notorious 1952 incident 
in which air pollution may have caused approximately 4000 
deaths over four days. Id. at 13a. Judge Tatel dissented 
from that portion of the opinion, emphasizing that the major- 
ity “ignore[d] the last half-century of Supreme Court non- 
delegation jurisprudence” upholding numerous statutes con- 
taining fewer guiding principles than Section 109. Id. at 59a. 

In the ozone case (No. 97-1441), the court of appeals 
rejected the industry petitioners’ argument that the 1990 
Amendments, which established mandatory classifications 
and attainment dates for the primary one-hour ozone 
standard then in effect, see CAA § 181, 42 U.S.C. 7511, 
precluded EPA from revising the ozone NAAQS. Pet. App. 
34a-37a. That ruling resolved the issue before the court. 
The court of appeals nevertheless went on to direct what 
EPA may and may not do when it proceeds—in the 
future—to implement the ozone NAAQS. The court ruled 
that EPA cannot implement the revised ozone NAAQS 
through 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 of Section 181(a) are tied 
to the one-hour standard, the court’s ruling effectively 
meant, as the court itself recognized, that EPA could pro- 
mulgate, but could not enforce, the revised ozone NAAQS. 
Id. at 57a. 

16 

EPA and other parties filed petitions for rehearing and 
suggestions for rehearing en banc. The panel granted re- 
hearing, in part, to modify its opinion regarding EPA’s 
authority to implement the revised ozone standard. Pet. 
App. 71a-72a. The panel rejected EPA’s argument that, 

16 The court of appeals resolved some, but not all, of the other chal- 
lenges to the PM and ozone rules. See Pet. App. 4a-5a. The court con- 
cluded that some of the issues could not be resolved “until such time as 
EPA may develop a constitutional construction of the act.” Id. at 5a. 

17 

because EPA had yet to take final action implementing the 
revised ozone NAAQS, the court lacked jurisdiction to con- 
sider which provisions of the Act would govern implemen- 
tation, including the specification of classifications and 
attainment dates. Id. at 78a-80a. The court found that 
EPA’s statements on that issue in the preamble accom- 
panying the revised ozone standard, made in response to 
industry comments challenging EPA’s authority to pro- 
mulgate that standard, see 62 Fed. Reg. at 38,884-38,885, 
constituted final agency action on the question of imple- 
mentation that was ripe for judicial review. Pet. App. 78a- 
80a. 

On the merits, the panel modified its opinion to state that 
“EPA can enforce a revised primary ozone NAAQS only in 
conformity with Subpart 2.” Pet. App. 81a. Judge Tatel 
wrote separately because he disagreed with the panel ma- 
jority’s reasoning. Pet. App. 83a-89a. He found the statute 
ambiguous and would have deferred to EPA’s interpreta- 
tion. Id. at 84a. Judge Tatel nevertheless concurred in the 
judgment because, in his view, the modified decision would 
allow EPA to implement the revised ozone standard under 
Subpart 1 once an area has attained the one-hour standard in 
accordance with Subpart 2. Id. at 89a. As to the non- 
delegation issue, the panel denied EPA’s petition for re- 
hearing. It expressly rejected EPA’s view that the relevant 
provisions of 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 five of 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 Judge Tatel each wrote 
statements dissenting from the denial of rehearing en banc 
on the nondelegation issue. Id. at 92a-96a, 97a-99a. Chief 
Judge Edwards and Judge Garland joined in Judge Tatel’s 
statement. Id. at 97a. 

18 

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’s requirement that 
NAAQS must be set at a level “requisite to protect” public 
health with “an adequate margin of safety” does not con- 
stitute an unconstitutional grant of legislative power. Fur- 
thermore, the nondelegation doctrine does not impose a con- 
stitutional obligation on EPA to go beyond what Congress 
has directed and announce a “determinate criterion for 
drawing lines.” Pet. App. 5a-6a. The court’s novel view that 
the Constitution demands such a precise criterion—and that 
the agency must supply it—is fundamentally unsound. 
Congress has directed EPA to establish NAAQS by refer- 
ence to the CAA’s detailed requirements, which set out 
intelligible principles to guide EPA’s actions. The CAA’s 
directives, which are more specific than many statutory 
directives that this Court has upheld, amply ensure that 
Congress has not abdicated its power to make the laws. The 
CAA prescribes the legal standards governing EPA’s 
decisions, factors that EPA must consider in making its de- 
cisions under 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 Act establishes multiple 
specific restrictions that cabin EPA’s discretion in setting 
NAAQS. The nondelegation doctrine does not require more. 
The court of appeals’ direction that EPA must narrow the 
scope of Congress’s direction is not only unprecedented, it 
also is contrary to the purpose of the nondelegation doctrine. 
The Court has developed that doctrine to enforce the Con- 
stitution’s requirement that Congress alone shall exercise 
legislative power. The court of appeals has improperly 
employed the doctrine to expand the scope of its judicial 
review authority beyond the limits that Congress has set 
through the CAA’s statutory standards for review of agency 

19 

action. The court of appeals’ conclusion that EPA must 
provide a “determinate, binding standard” for setting 
NAAQS is not only inconsistent with the CAA’s recognition 
that NAAQS must be set in the face of scientific uncer- 
tainties, but it is also likely impracticable. An Executive 
Branch agency, acting pursuant to congressional direction, is 
entitled to assess the available evidence and make a rea- 
soned judgment on the proper regulatory standard. Con- 
trary to the court of appeals’ characterization, EPA’s inter- 
pretation of its authority did not leave it free to set a 
NAAQS at any point between zero and “a hair below” an air 
pollution level that killed 4000 people in four days. To the 
contrary, the rulemaking records reveal that EPA properly 
construed and applied limitations on its discretion. It pro- 
vided reasoned explanations, supported by the record evi- 
dence, for why it chose the challenged PM and ozone stan- 
dards in light of continuously evolving scientific knowledge. 

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

Even if EPA’s preamble remarks about what future steps 
it intends to take to implement the ozone NAAQS consti- 
tuted “agency action,” they are certainly not “final” agency 
action. Those statements are not the consummation of the 
agency’s decisionmaking process and they do not create any 

20 

rights or obligations. They simply express EPA’s current 
views on some aspects of the complicated implementation 
process that EPA and the States will undertake through 
future rulemakings. The CAA sets out a detailed procedure 
for conducting those rulemakings. Under the statutory pro- 
cess, 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 is ripe for the court’s review. 

Even if EPA’s preamble statements constituted final 
agency action, they would not be ripe for review. The issue 
of how to reconcile the numerous provisions governing 
implementation is, at this stage, too abstract. The courts do 
not have the benefit of EPA’s explanation of how and why it 
has implemented a NAAQS in a particular way, which would 
be available only after EPA has completed the relevant rule- 
makings, including any required public notice and response 
to comments, and taken final action that actually implements 
the standard. The courts should not review those complex 
implementation issues until EPA has had the opportunity to 
work through the various implementation provisions, 
reconcile any conflicts, make any policy judgments, and 
apply its expertise to resolve any ambiguities in the statute. 

3. If the Court decides to reach the merits, it should rule 
that the court of appeals’ modified decision is incorrect, even 
as interpreted by Judge Tatel in his partial concurrence. 
The CAA authorizes EPA to implement the revised 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 inappropri- 
ately force EPA to delay protecting the public from the very 
health consequences that warrant a NAAQS revision in the 
first place, until the area attains an air quality standard that 
EPA has concluded is inadequate to protect public health. 
Congress could not have intended that implausible result. 
The statutory provision on which the court of appeals 
primarily relied—Section 181(a) of Subpart 2—implements 

21 

only the one-hour ozone standard. It does not apply to the 
revised eight-hour ozone NAAQS or otherwise curtail EPA’s 
authority to implement that standard under Section 172(a) 
and any other applicable provision of Subpart 1. Moreover, 
because the Act requires the attainment of all NAAQS “as 
expeditiously as practicable,” 42 U.S.C. 7502(a)(1)(A), 
7511(a)(1), the court of appeals erred in concluding that EPA 
must delay implementation of the eight-hour NAAQS in any 
area until it attains the one-hour ozone standard. 

ARGUMENT 

I. THE COURT OF APPEALS ERRONEOUSLY AP- 
PLIED THE NONDELEGATION DOCTRINE 

The nondelegation doctrine is “rooted in the principle of 
separation of powers.” Mistretta v. United States, 488 U.S. 
361, 371 (1989). “The fundamental precept of the delegation 
doctrine is that the lawmaking function belongs to Congress, 
U.S. Const., Art. I, § 1, and may not be conveyed to another 
branch or entity.” Loving v. United States, 517 U.S. 748, 758 
(1996). The nondelegation doctrine does not require, how- 
ever, that Congress dictate every detail of a regulatory pro- 
gram. Congress may rely on the other branches to make 
rules that carry out its will. See Loving, 517 U.S. at 758; 
Mistretta, 488 U.S. at 372. 

This Court’s application of the nondelegation doctrine has 
been “driven by a practical understanding that in our 
increasingly complex society, replete with ever changing and 
more technical problems, Congress simply cannot do its job 
absent an ability to delegate power under broad general 
directives.” Mistretta, 488 U.S. at 372. The Court has 
accordingly recognized that Congress does not violate the 
Constitution “merely because it legislates in broad terms, 
leaving a certain degree of discretion to executive or judicial 
actors.” Touby v. United States, 500 U.S. 160, 165 (1991); see 
Yakus v. United States, 321 U.S. 414, 425 (1944) (Congress 

22 

may “call for the exercise of judgment, and for the formu- 
lation of subsidiary administrative policy within the pre- 
scribed framework”). 

The Court has specifically emphasized that Congress does 
not violate the nondelegation doctrine if “Congress clearly 
delineates the general policy, the public agency which is to 
apply it, and the boundaries of this delegated authority.” 
Mistretta, 488 U.S. at 372-373 (quoting American Power & 
Light Co. v. SEC, 329 U.S. 90, 105 (1946)); Skinner v. Mid- 
America Pipeline Co., 490 U.S. 212, 218-219 (1989). “Only if 
we could say that there is an absence of standards for the 
guidance of the [agency’s] action, so that it would be impossi- 
ble in a proper proceeding to ascertain whether the will of 
Congress has been obeyed, would we be justified in over- 
riding its 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 Unconstitutional Grant Of Legislative Power 

Contrary to the court of appeals’ conclusion, Section 109 
easily satisfies this Court’s “intelligible principle” standard. 
This Court’s decisions leave no doubt that Section 109 does 
not amount to an invalid delegation of legislative power and 
that EPA can properly fulfill the responsibilities that Section 
109 assigns. Section 109’s directives “are far more specific 
than the sweeping statutory delegations consistently upheld 
by [this] Court for more than sixty years.” Pet. App. 97a 
(Tatel, J., dissenting from denial of rehearing en banc); see 
also id. at 93a (Silberman, J., dissenting from denial of re- 
hearing en banc); id. at 59a-60a (Tatel, J., dissenting) (collect- 
ing cases). 

The starting point for nondelegation analysis is the CAA’s 
language, which must 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 comprehensive 

23 

legislation, which Congress has repeatedly amended in light 
of new knowledge and developments (see note 2, supra), re- 
veals that Congress has exercised its lawmaking function 
with exacting care. The Act, which now occupies more than 
280 pages in the United States Code, is extraordinarily 
detailed and prescriptive. As the Act has evolved, Congress 
has consistently recognized the need to rely on an Executive 
Branch agency’s scientific resources and expertise in execut- 
ing the legislative purposes. At the same time, Congress has 
carefully channeled EPA’s discretion through increasingly 
detailed substantive and 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 “adequate margin of safety” and that secon- 
dary standards be set at levels “requisite to protect the 
public welfare.” 42 U.S.C. 7409(b)(1). To warrant the 
setting of a NAAQS, a pollutant must “reasonably be anti- 
cipated to endanger public health or welfare” and be emitted 
from “numerous or diverse * * * sources.” 42 U.S.C. 
7408(a)(1)(A)-(B). Each standard must be based on “air 
quality criteria” that reflect “the latest scientific knowl- 
edge,” 42 U.S.C. 7408(a)(2), including information on “vari- 
able factors” that “may alter the effects on public health,” as 
well as interactions with other pollutants “to produce an 
adverse effect on public health or welfare.” 42 U.S.C. 
7408(a)(2)(A)-(B). Further, the Act establishes and pre- 
scribes the composition of CASAC (see p. 4, supra) and 
requires EPA to consider, and explain any significant de- 
parture from, 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 procedures for rulemaking and judicial review, further 

17 See Mistretta, 488 U.S. at 376 n.10 (“Congress’ explicit requirement 
that the Commission consult with authorities in the field,” among other 
things, gives content to the statutory mandate.). 

24 

ensures that EPA adheres to a “disciplined decisionmaking 
process” in setting NAAQS. See Pet. App. 63a (Tatel, J., 
dissenting). Congress has prescribed a rulemaking process 
that ensures extensive public participation. EPA must dis- 
cuss the data, methodology, and major legal and policy 
interpretations underlying proposed NAAQS, 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 assessing the constitutionality of Section 109. 
Mistretta, 488 U.S. at 376 n.10. That legislative history, 
which the court below failed to consider, indicates that 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 significant and not merely detectable, id. at 1155 

n.51. To provide an “adequate margin of safety,” standards 
must be “preventative or precautionary,” reflecting an 
emphasis on the “predominant value of protection of public 
health.” 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 of caution”). Furthermore, public health is dis- 
tinct 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 repre- 
sentative sample of persons comprising the sensitive group 
rather than to a single person in such a group.”), in 1 Staff of 

18 The availability of such review weighs strongly in favor of the 
constitutionality of Section 109’s grant of agency authority. See American 
Power & Light, 329 U.S. at 105 (“[p]rivate rights are protected by access 
to the courts to test the application of the policy in the light of the[] 
legislative declarations”); Touby, 500 U.S. at 170 (Marshall, J., concurring). 

25 

the Senate Comm. on Pub. Works, 93d Cong., 2d Sess., A 
Legislative History of the Clean Air Act Amendments of 
1970, at 410 (Comm. Print 1974). 

In short, Congress has placed “multiple specific restric- 
tions” on EPA’s discretion in setting and revising NAAQS 
that satisfy the constitutional requirements of the nondele- 
gation doctrine. Touby, 500 U.S. at 167. Those restrictions 
are at least as rigorous as those in Touby and other non- 
delegation cases, 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 pro- 
cedures that EPA must follow in making its highly technical 
scientific judgments about the health and welfare effects of 
particular pollutants. As in American Power & Light Co., 
the Act provides “a veritable code of rules” for EPA to fol- 

19 For example, in Touby, the Court held that the challenged statute, 
which authorizes the Attorney General to regulate new “designer” drugs, 
“meaningfully constrains” the Attorney General’s discretion by requiring 
her to find that action is “necessary to avoid an imminent hazard to the 
public safety”; to “consider” three factors and statutorily prescribed 
criteria; to publish notice in the Federal Register; and to consider com- 
ments from an agency head. 500 U.S. at 166. In Mistretta, the Court held 
that the statutory authorization for sentencing guidelines is “sufficiently 
specific and detailed to meet constitutional requirements,” noting that 
Congress specified three “goals” and four “purposes”; “prescribed the 
specific tool” for regulating sentencing; directed the Commission to con- 
sider seven “factors,” and prohibited it from considering other factors; and 
explicitly required the Commission to consult authorities in the field of 
criminal sentencing. 488 U.S. at 374-375 & 376 n.10. In Federal Energy 
Administration v. Algonquin SNG, Inc., 426 U.S. 548 (1976), the Court 
held the challenged statute constitutional because it established precon- 
ditions to presidential action; allowed the President to act only to the 
extent “necessary” to achieve the statutory objective; and articulated a 
series of specific factors that he was to consider in exercising his author- 
ity. Id. at 559. 

26 

low in fulfilling Congress’s will. 329 U.S. at 105; see Yakus, 
321 U.S. at 426. 

20 

B. The Court Of Appeals Improperly Employed The 

Nondelegation Doctrine To Expand The Scope Of Its 

Review 

This Court’s nondelegation doctrine preserves the Consti- 
tution’s separation of powers by ensuring that Congress 
does not abdicate its power to make laws. The court of 
appeals transformed that doctrine, however, into a judicial 
check on executive power. The court of appeals employed 
the nondelegation doctrine as an additional means, beyond 
the explicit judicial review provisions of the CAA, to super- 
vise the exercise of administrative discretion. See Pet. App. 
14a. The court directed EPA to “develop[] determinate, 
binding standards for itself ” to reduce the likelihood that 
EPA would “exercise the delegated authority arbitrarily” 
and to “enhance the likelihood that meaningful judicial 
review will prove feasible.” Ibid. 

That novel use of the 

nondelegation doctrine departs from the doctrine’s purpose, 
it has no basis in this Court’s precedents, and it trenches on 
Congress’s power to specify appropriate standards for 
judicial review of executive action. See id. at 93a (Silber- 
man, J., dissenting from the denial of rehearing en banc). 

20 Because Section 109 so plainly satisfies the nondelegation doctrine, 
there is no need to consider, as some of the industry respondents have 
urged, whether EPA should have read Section 109 more narrowly to avoid 
a constitutional issue. This Court rejected a similar argument in 
Algonquin SNG, Inc., 426 U.S. at 558-559. In that case, the Court held 
that because the standards provided by the challenged statute were 
“clearly sufficient to meet any delegation doctrine attack,” there was no 
need to give the statute a narrow construction to avoid an alleged “serious 
question of unconstitutional delegation of legislative power.” Id. at 559. 
So too, in this case, “the terminology” of the Act “does not come so close 
to” the “boundaries limiting the scope of congressional delegation to the 
executive branch” as “to raise a serious constitutional problem.” Pet. App. 
93a (Silberman, J., dissenting from denial of rehearing en banc). 

27 

The court of appeals viewed the nondelegation doctrine as 
requiring Congress, or agencies interpreting the intent of 
Congress, to delineate a “determinate criterion for drawing 
lines.” Pet. App. 6a. In the court’s view, the Constitution 
requires that EPA supply a single principle that would 
enable the court to conclude that EPA’s NAAQS are set at 
what the court deems exactly the “right” level. See id. at 
10a-11a, 73a. That approach, however, is inconsistent with 
the court’s limited role in reviewing NAAQS. The CAA 
makes clear that EPA’s actions in setting NAAQS are 
subject to review under the 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 there has been a clear error of judgment.” 
Citizens to Preserve Overton Park, Inc. v. Volpe, 401 U.S. 
402, 416 (1971) (Overton). “The court is not empowered to 
substitute its judgment for that of the agency.” Ibid. As 
Judge Silberman recognized, the court of appeals’ approach 
would “implicitly assert[] 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 opposed to simple find- 
ings of fact, a reviewing court must generally be at its most 
deferential.”). 

21 

Moreover, the court of appeals’ demand for a determinate 
criterion to govern EPA’s NAAQS decisions is difficult to 

21 The court’s direction to EPA to develop “determinate, binding stan- 
dards” to govern the agency’s NAAQS decisions (Pet. App. 14a, 73a) is 
also inconsistent with this Court’s decision in American Power & Light 
Co., which rejected the notion that there is “any constitutional require- 
ment” obligating an agency to translate legislative standards into “formal 
and detailed rules of thumb” before applying them. 329 U.S. at 106. Cf. 
Vermont Yankee Nuclear Power Corp. v. NRDC, 435 U.S. 519, 543-545 
(1978) (courts may not impose on agencies procedures that are not 
imposed by statute). 

28 

reconcile in practice with the Act’s command that EPA set 
NAAQS—and revise them, as appropriate, every five 
years—based on the “latest scientific knowledge.” 42 U.S.C. 
7408(b). As the D.C. Circuit has recognized in the past, 
Congress has directed EPA to make “predictions * * * at 
the frontiers of science.” NRDC, 902 F.2d at 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 ‘uncertain or conflicting’ and the ‘regulations 
designed to protect the public health,’ ” the court of appeals 
has recognized that Congress did “not demand rigorous step- 
by-step proof of cause and effect.” NRDC, 902 F.2d at 968 
(citations omitted). 

The purpose of Section 109’s requirement that NAAQS 
provide an “adequate margin of safety” is to ensure “a rea- 
sonable degree of protection * * * against hazards which 
research has not yet identified.” Lead Indus., 647 F.2d at 
1150 (quoting S. Rep. 1196, at 10). EPA must therefore be 
able to draw conclusions from “suspected, but not completely 
substantiated, relationships between facts, from trends 
among facts, from theoretical projections from imperfect 
data, from probative preliminary data not yet certifiable as 
‘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 novel demand for precision would 
restrict the agency’s ability to act on a precautionary basis in 
the face of scientific uncertainties, thereby potentially erod- 
ing the public health protection Congress intended NAAQS 
to afford. 

The court of appeals’ requirement that EPA develop a 
“determinate criterion for drawing lines” (Pet. App. 6a), 
which EPA would presumably be required to apply in every 
NAAQS proceeding (see id. at 73a), is also inconsistent with 
EPA’s own expert assessment of the flexibility necessary to 

29 

apply Section 109’s mandate to all the pollutants for which 
EPA must develop standards. In the PM and ozone rule- 
making proceedings, EPA received comments arguing that 
the Act required the agency to adopt various specific ap- 
proaches to decisions under Section 109, such as, for exam- 
ple, first determining a “safe level” and then applying a mar- 
gin of safety. 62 Fed. Reg. at 38,688, 38,883. In its response 
to those comments, EPA noted that the D.C. Circuit had 
specifically rejected claims that any of the approaches sug- 
gested by the commenters were required by the Act and in- 
stead had ruled that “[t]his court must allow [the Adminis- 
trator] the discretion to determine which approach will 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 widely in relation to key factors, including their 
health effects, the types of available 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 adequate margin of safety may be dif- 
ferent for each standard under review. Thus, no general- 
ized paradigm * * * can substitute for the Administra- 
tor’s careful and reasoned assessment of all relevant 
health factors in reaching such a judgment. 

62 Fed. Reg. at 38,688; see id. at 38,883. 

22 

22 The two pollutants at issue here illustrate this fact. In assessing the 
health effects of PM and ozone, EPA determined that the most useful 
scientific information currently consists primarily of epidemiological 
studies in the case of PM, but currently consists primarily of human 
clinical studies in the case of ozone. The PM epidemiological studies pro- 
vide evidence of very serious health effects associated with ambient 
pollution concentrations, but that evidence must be evaluated in light of 
potentially confounding variables that cannot be directly controlled when 
studying “real world” populations. The human clinical studies on ozone 
provide strong evidence of specific effects triggered by controlled 

30 

At bottom, the court’s rationale for its approach—to pre- 
vent arbitrary agency action and to enhance judicial review 
(Pet. App. 14a)—overlooks that Congress is entitled to set 
the parameters for judicial oversight of EPA’s scientific 
judgments. Congress has concluded that EPA’s actions in 
setting NAAQS are subject to the arbitrary or capricious 
test. See 42 U.S.C. 7607(d)(9). EPA must consider the fac- 
tors that the Act prescribes and provide a reasoned explana- 
tion, based on scientific evidence, for its decision. When re- 
viewing that decision, a court is not entitled to demand that 
EPA demonstrate that the numerical standard the agency 
selected was the sole possible choice. To the contrary, as 
this Court explained in reviewing rates set by the Federal 
Power 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 ab- 
stract quality represented by an area rather than a 
pinpoint. It allows a substantial spread between what is 
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 novel concepts. The D.C. Circuit has itself ac- 
knowledged, when it reviewed the 1987 PM standard, that a 
reviewing court should not ask if EPA has identified “the 
clear and sole appropriate standard,” but rather whether 
EPA 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 nondelegation doctrine as its sole 

pollutant concentrations, but—for ethical and other reasons—cannot be 
used to measure directly very serious health effects or effects in highly 
susceptible individuals. 

31 

justification for departing from that established standard of 
review. Pet. App. 12a-13a. Under this Court’s precedents, 
Section 109 does not violate the nondelegation doctrine. The 
court of appeals improperly relied on that doctrine to depart 
from traditional principles governing the scope of judicial 
review of agency action. 

C. EPA Has Recognized Limitations On Its Discretion To 

Revise The Particulate Matter And Ozone Standards 

The court of appeals’ nondelegation holding rests on the 
erroneous conception that EPA interprets Section 109 to set 
no limits on its discretion. The court characterized EPA as 
claiming discretion so broad as to leave it free to “pick any 
point between zero and a hair below * * * London’s Killer 
Fog.” Pet. App. 13a. To the contrary, EPA has recognized 
and applied principles that channel its discretion far more 
narrowly than the court acknowledged. 

The CAA’s directive that EPA must base the revised 
NAAQS on “air quality criteria” reflecting the “latest 
scientific knowledge” limits, at the outset, the alternatives 
that EPA can consider. EPA found that a wide range of 
adverse health effects were occurring at concentrations 
below the pre-existing PM and ozone NAAQS, which 
effectively dictated an upper bound for any revised NAAQS. 
The revised PM and ozone NAAQS had to be at least 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 consideration at the most pro- 
tective levels the scientific evidence reasonably supported. 
For PM, the lower bound was the lowest level at which long- 
term epidemiological data indicated there might be an 
“effects threshold” below which there is no risk of health 
effects. See PM App. 2145, 2147. For ozone, which appears 
to have no effects threshold (see note 23, infra), the lower 
bound—0.07 ppm—was the level at which EPA’s exposure 

32 

assessment showed that exposures of 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 of PM confined the agency to considering a 
quite limited range of 12.5 to 20 µg/m3 for the annual PM2.5 
standard (and 20 to 65 µg/m3 for the 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 from zero to a “hair below” 2,500 µg/m3 (the level the 
court of appeals assumed for the “Killer Fog”). Similarly, 
EPA’s review of the latest scientific knowledge on the health 
effects of ozone confined the agency to considering an eight- 
hour ozone standard between 0.07 ppm and 0.09 ppm. See p. 
13, supra. EPA had identified those ranges in its Staff 
Papers, and CASAC had agreed that EPA’s identification of 
those ranges had sound 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 the agency consider 
relevant factors, apply them to relevant facts, respond to 
criticisms, and adequately explain its rationale. 42 U.S.C. 
7607(d)(2)-(6). In fulfilling those obligations, EPA employed 
the decisional criteria that the agency has long used to 
ensure consistency in its NAAQS decisions. See p. 5, supra. 

For example, in setting the annual PM2.5 standards, EPA 
took account of the “types of health evidence” and the “kind 
and degree of uncertainties.” EPA identified a scientific 
criterion applicable to epidemiological studies—statistical 
significance to the 95% confidence level—to determine “how 
much uncertainty [was] too much” within the narrow range 
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 evidence showed statistically significant 
positive associations between PM2.5 and adverse health 
effects in locations where PM2.5 ranged from 15.7 to 21 µg/m3. 

33 

See pp. 10-11, supra. But no study showed a statistically 
significant association between adverse health effects and 
PM2.5 in any area with an annual PM2.5 level 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 
EPA determined would be requisite to protect public health 
with an adequate margin of safety. 

In the ozone rule, EPA selected the standard based pri- 
marily on consideration of “the nature and severity of the 
health effects,” “the size of the sensitive population at risk,” 
and, again, the “types of health evidence.” EPA recognized 
that a standard of 0.09 ppm would not 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 
more stringent than requisite to protect against health 
effects of public health significance. EPA identified impor- 
tant and meaningful differences in the character of the 
scientific evidence regarding risks—including the estimated 
frequency and duration of adverse health effects—associated 
with levels above and below 0.08 ppm. Those differences 
amply justified the Administrator’s selection of the 0.08 ppm 
level as requisite to protect public health with an 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 unfettered discretion in promulgating the revised 
PM and ozone standards. To the contrary, EPA explained in 
detail, with reference to the scientific evidence in the record, 
why it selected the challenged PM and ozone standards. The 
court of appeals thus failed to appreciate the record before it 

23 EPA and CASAC recognized that ozone has no apparent effects 
threshold. See, e.g., 62 Fed. Reg. at 38,863. CASAC acknowledged that 
fact when it commented that no “bright line” differentiated ozone levels 
within the range of 0.07 ppm to 0.09 ppm. Ozone App. 238. CASAC’s com- 
ment did not mean, however, that the public health effects were the same 
at any level within the range. See 62 Fed. Reg. at 38,865. 

34 

in erroneously concluding that EPA claimed such wide 
discretion that it could have set the new standards at 
virtually any level. Cf. Overton, 401 U.S. at 416. 

II. THE COURT OF APPEALS LACKED JURIS- 
DICTION TO REVIEW EPA’S PREAMBLE STATE- 
MENTS ON 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 “action of the Administrator in promulgating any 
[NAAQS]” and other “nationally applicable 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 jurisdiction to review EPA’s promulgation of the 
ozone NAAQS. The NAAQS, which consists of a specific, 
two-paragraph rule, Pet. App. 104a, is final agency action. 
The court of appeals erred, however, in concluding that it 
also had authority to critique portions of EPA’s explanatory 
preamble and thereby dictate the course of the agency’s 
future implementation actions. The court of appeals’ broad 
pronouncement that “EPA can enforce a revised primary 
ozone NAAQS only in conformity with Subpart 2,” Pet. App. 
81a, results from that court’s premature and unfocused 
exploration of issues that were not properly before that 
court. 

EPA’s rulemaking addressed promulgation of a revised 
ozone NAAQS. The issue of implementation arose in the 
ozone case because participants in the rulemaking pro- 
ceeding argued that, when Congress enacted the 1990 
Amendments and included—in Section 181(a)(1) of Subpart 
2—a scheme for implementing the then-current one-hour 
ozone standard, Congress thereby implicitly prohibited EPA 
from ever 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 rule- 

35 

making preamble and, later, in its brief in the court of 
appeals. EPA explained generally, as part of its demonstra- 
tion why the Section 181(a) scheme does not prevent EPA 
from promulgating a revised NAAQS, that the revised 
standard could 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 that the rulemaking participants had raised in 
their judicial challenge to EPA’s promulgation of a revised 
ozone NAAQS. See 42 U.S.C. 7607(d)(7)(B). The only 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 court answered that 
question in the negative, Pet. App. 34a-37a, its task was 
done. It should not have gone on to consider prematurely 
whether and how EPA could implement the revised 
NAAQS. 

The government objected, through petitions for rehearing 
and rehearing en banc, to the court of appeals’ decision to 
address an issue that was not properly before it. The court 
responded by asserting that it had jurisdiction to address the 
views that EPA expressed in the preamble because those 
explanatory statements about the agency’s future intentions 
independently satisfied the final agency action requirement 
of Section 307(b) of the CAA. Pet. App. 77a-78a. That con- 
clusion is wrong. 

24 Consistent with its position here, EPA explained in the rulemaking 
that “[a] number of commentors submitted comments * * * regarding 
implementation issues that are not relevant to the Ozone NAAQS review. 
Therefore, they are not being responded to in this document.” Ozone App. 
223. EPA clearly recognized that such comments were premature and 
would be addressed, if necessary, in later rulemakings. 

36 

A. EPA’s Preamble Statements Regarding Implementation 

Authority Are Not “Agency Action” Within The 

Meaning Of Section 307(b)(1) Of The Act 

The court of appeals has undertaken to address prospec- 
tively how to reconcile two complex portions of the CAA— 
Subparts 1 and 2 of Part D—even though EPA has not yet 
undertaken that task through rulemaking. The court justi- 
fied its review on the basis that EPA stated, in an 
explanatory preamble, how it 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 
appeals to 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 administrative law. 
Cf. Harrison v. PPG Indus., Inc., 446 U.S. 578, 586 (1980). 
The Administrative Procedure Act (APA) defines the term 
“agency action” as “the whole or a part of an agency rule, 
order, license, sanction, relief, or the 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 “agency 
action” is limited to discrete acts that affect legal rights. See 
Lujan v. National Wildlife Fed’n, 497 U.S. 871, 891 (1990) 
(“Under the terms of the APA, respondent must direct its 
attack against some particular ‘agency action’ 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’s explanation of its action. For exam- 
ple, a promulgated rule—a familiar form of agency ac- 
tion—must be “accompanied” by “a statement of basis and 

37 

purpose” and “a response to each of the significant [public] 
comments [on the proposed rule] . ” 
42 U.S.C. 7607(d)(6). 

That requirement facilitates judicial review of whether the 
agency’s rule is “arbitrary, capricious, or an abuse of dis- 
cretion,” 42 U.S.C. 7607(d)(9). A court is entitled to set aside 
the rule if it concludes that the agency’s rationale for the 
rule is inadequate. But in that situation, the court invali- 
dates the rule itself —viz., the agency’s action—and not the 
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 is independently subject to review. Cf. Califor- 
nia v. Rooney, 483 U.S. 307, 311 (1987) (per curiam) (“This 
Court ‘reviews judgments, not statements in 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 
correct wrong judgments, not to revise opinions”). 

In this case, EPA’s “action” is promulgation of the revised 
ozone NAAQS, which consists of a discrete rule. See Pet. 
App. 104a. The rule itself makes 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 relate to 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 explain 
the basis for an agency’s action would arguably spawn 
additional agency actions that are each potentially subject to 
judicial review and revision. Congress surely did not 
authorize courts to engage in that sort of broad and limitless 
anticipatory oversight of CAA programs. See Standard Oil, 
449 U.S. at 247-249 (Stevens, J., concurring). 

38 

B. EPA’s Preamble Statements Do Not Constitute “Final” 

Agency Action 

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 satisfied for agency action to be 
“final”: (1) it “must mark the ‘consummation’ of the agency’s 
decisionmaking process”; and (2) it “must be one by which 
‘rights or obligations have been determined,’ or from which 
‘legal consequences will flow.’ ” Id. at 177-178. EPA’s dis- 
cussion of the Act’s implementation provisions in the 
preamble does not satisfy either of those requirements. 

The court of appeals improperly reconfigured the “con- 
summation” prong by focusing solely on whether the plans 
that EPA described in the preamble appeared tentative or 
likely to change. See Pet. App. 77a-78a. Under Bennett, 
however, the proper inquiry is not merely whether the 
agency has any present intention to alter its position. 
Rather, the question is whether the agency has consum- 
mated its decisionmaking process. The answer necessarily 
depends upon what steps the governing statute requires. 

25 

When EPA’s preamble statements are considered in light 
of the CAA’s implementation program, it is clear that they 
do not constitute final agency action. EPA completed the 

25 For example, the Court concluded in Standard Oil Co., supra, that 
the action at issue—filing an administrative complaint—was not final 
agency action under the relevant statutory process. The Court explained 
that the action “is a prerequisite to a definitive agency position on the 
question whether Socal violated the Act, but itself is a determination only 
that adjudicatory proceedings will commence.” 449 U.S. at 241-242. Like- 
wise, in cases involving rulemakings, the Court has concluded that agency 
regulations are final if the agency has completed the applicable rule- 
making procedures and promulgated a legally binding rule that completed 
action within the context of the substantive regulatory program. See, e.g., 
Abbott Labs. v. Gardner, 387 U.S. 136, 149-152 (1967) (discussing cases). 
Thus, the certitude of an agency’s statements, standing alone, does not 
satisfy the consummation prong. 

39 

statutory process for reviewing the existing ozone standard, 
42 U.S.C. 7408(a), 7409(d), and reached a final decision prom- 
ulgating the eight-hour ozone standard. EPA thus consum- 
mated its decisionmaking process and 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 the CAA’s distinct process for implementing the 
revised ozone NAAQS, which requires additional rulemaking 
procedures. 

26 

The CAA provides EPA up to three years after prom- 
ulgating a revised NAAQS to designate all areas within the 
Nation as attainment, nonattainment, or unclassifiable for 

26 As part of the ozone NAAQS rulemaking, EPA issued a separate 
rule, 40 C.F.R. 50.9(b), respecting future enforcement of the one-hour 
ozone standard, which the eight-hour ozone NAAQS will replace. That 
rule states that 

The 1-hour standards set forth in this section will no longer apply to 
an area once EPA determines that the area has air quality meeting 
the 1-hour standard. Area designations are codified in 40 CFR part 

81. 

Ibid. EPA issued that rule as a transition measure to relieve areas that 
are in compliance with the one-hour ozone standard from the obligation to 
comply with both the old one-hour standard and the new eight-hour 
standard. See 62 Fed. Reg. at 38,873. In the course of explaining that 
rule, EPA stated in the preamble that Subpart 1 would apply to imple- 
mentation of the new eight-hour ozone standard. Ibid. See App., infra, 
6a-8a. 

Neither 40 C.F.R. 50.9(b) nor EPA’s related preamble statement 
provides a jurisdictional basis for the court of appeals’ decision limiting 
EPA’s authority to implement the eight-hour standard under Subpart 1. 
As an initial matter, no party in this case challenged 40 C.F.R. 50.9(b), the 
court of appeals accordingly did not review it, and thus it clearly was not 
the predicate for the court of appeals’ ruling. In any event, 40 C.F.R. 

50.9(b) merely addresses interim enforcement of the pre-existing one-hour 
standard. Neither 40 C.F.R. 50.9(b) nor EPA’s preamble statements de- 
scribing it resolve whether or how Subparts 1 and 2, and other provisions 
of the Act, may interact to limit EPA’s authority to implement the eight- 
hour standard. 

40 

that standard. 42 U.S.C. 7407(d)(1). 

27 At the same time, for 
nonattainment areas, EPA must establish schedules for 
States to submit state implementation plans. 42 U.S.C. 
7502(b). EPA may establish classifications for nonattain- 
ment 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 approval or disapproval, their SIPs to implement 
the NAAQS by the applicable attainment dates. See 42 
U.S.C. 7410(a) and (k), 7502(c). Under that statutory 
structure, NAAQS implementation proceeds through a care- 
ful decisionmaking process that includes designation, setting 
dates for SIP submissions, classifying nonattainment areas, 
developing SIPs, setting attainment dates, and obtaining 
EPA’s approval of the SIPs. EPA’s expression of its views, 
in a regulatory preamble, on some aspects of that future pro- 
cess cannot reasonably be viewed as completing any 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 dis- 
approve any SIP. Thus, EPA’s preamble statements do not 
mark the consummation of any part of the agency’s imple- 
mentation process. They do not conclude the agency’s 
thinking on how it may implement the revised ozone stan- 
dard, or precisely whether or how implementation of the 
revised eight-hour standard may be affected by any Subpart 
2 provisions. EPA’s deliberations on those matters are 
ongoing and have not yet resulted in final agency action that 
is ripe for judicial review. 

The preamble statements also do not satisfy the second 
Bennett requirement that “the action must be one by which 
‘rights or obligations have been determined,’ or from which 

27 Congress slightly modified this schedule in 1998 with respect to the 
revised standards at issue here. Pub. L. No. 105-178, §§ 6101(b), 6102(c), 
6103(a)-(b), 112 Stat. 463-465. 

41 

‘legal consequences will flow.’ ” 520 U.S. at 178. The court of 
appeals concluded that EPA’s preamble statements respect- 
ing future implementation were final action because by “pro- 
mulgating a revised 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 to do 
so.” Pet. App. 78a. Any obligations triggered by pro- 
mulgation of the NAAQS arise, however, regardless of what 
EPA said, or did not say, in the preamble about imple- 
mentation. No legal consequences flow from the preamble 
statements themselves. EPA’s views on implementation will 
produce tangible legal consequences only when EPA takes 
actual steps to implement the NAAQS through the 
prescribed rulemaking processes. Affected parties will be 
able to obtain judicial review of EPA’s judgments on 
implementation once EPA takes final action that actually 
creates new legal obligations. 

C. EPA’s Preamble Statements Regarding Implementation 

Of The Eight-Hour Ozone Standard Are Not Ripe For 

Review 

Even if EPA’s preamble statements were final agency 
action, that purported agency action would not be ripe for 
judicial review. The ripeness doctrine serves “to prevent 
the courts, through avoidance of premature adjudication, 
from entangling themselves in abstract disagreements over 
administrative policies, and also to protect the agencies from 
judicial interference until an administrative decision has 
been formalized and its effects felt in a concrete way by the 
challenging parties.” Ohio Forestry Ass’n v. Sierra Club, 
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 on judicial power and from prudential reasons for 
refusing to exercise jurisdiction.” Reno v. Catholic Soc. 

42 

Servs., Inc., 509 U.S. 43, 57 n.18 (1993). To determine 
whether a controversy is ripe a court must “evaluate both 
the fitness of the issues for judicial decision and the hardship 
to the parties of withholding court consideration.” Texas v. 
United States, 523 U.S. 296, 301 (1998). “A claim is not ripe 
for adjudication if it rests upon ‘contingent future events 
that may not occur as anticipated, or indeed may not occur at 
all.’ ” Id. at 300. 

The court of appeals’ concerns regarding how to reconcile 
Subparts 1 and 2 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 
exercise its authority to implement the eight-hour ozone 
standard. See, e.g., Ohio Forestry, 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 provisions of the Act, is complex. As we have 
explained, EPA expressed views on selected implementation 
provisions of the Act to respond to comments in the ozone 
rulemaking that those provisions negate EPA’s NAAQS 
revision authority. A court’s consideration of whether and 
how Section 181(a) and other sections of Subpart 2 may 
affect EPA’s authority under the various provisions of 
Subpart 1 would be on much surer footing if the reviewing 
court had the benefit of EPA’s full explanation of how and 
why it has implemented the revised ozone standard in a 
particular way, after the completion of a relevant decisional 
process (including any required public notice and comment) 
that actually implements the standard. 

28 

28 The Court has recognized that deferring review is appropriate 
where “the need for some further procedure, some further contingency of 
application or interpretation . . . serve[s] to make remote the issue 
which was sought to be presented to the Court.” Simon v. Eastern Ky. 
Welfare Rights Org., 426 U.S. 26, 51-52 (1976) (Brennan, J., concurring) 
(quoting Poe v. Ullman, 367 U.S. 497, 528 (1961) (Harlan, J., dissenting)); 

43 

The case for deferring review is especially strong here 
because the resolution of any tension between the various 
provisions in Subparts 1 and 2 may depend upon the cir- 
cumstances of the particular nonattainment area at issue. 
See, e.g., Pet. App. 40a-41a (expressing concern regarding 
the interplay and future application of Sections 172(a) and 
181(a)(1) on Los Angeles). Deferring review of those imple- 
mentation issues would allow EPA the opportunity to work 
through the various implementation provisions in concrete 
settings, reconcile conflicts, make policy judgments, and 
apply its expertise as necessary to 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 an opportunity to correct its own mistakes and to 
apply its expertise.” Standard Oil, 449 U.S. at 242. Defer- 
ring review would facilitate future judicial review by reduc- 
ing the issues to manageable proportions. The importance of 
a concrete setting for judicial review is underscored by the 
court’s own confusion regarding EPA’s interpretation, com- 
pare Pet. App. 43a-44a, with id. at 80a-81a and id. at 87a-88a, 
its reliance upon predicted future outcomes in particular 
areas, id. at 40a-41a, and the extreme breadth and lack of 
clarity of the court’s ultimate conclusion that “EPA can 
enforce a revised primary ozone NAAQS only in conformity 
with Subpart 2,” id. at 81a. 

Finally, deferring review will not work substantial hard- 
ship. EPA’s expression of its views in the preamble created 

see, e.g., Toilet Goods Ass’n v. Gardner, 387 U.S. 158, 163-164 (1967) 
(interpretive rule not ripe for review). In this case, “[d]etermination of 
the scope * * * of legislation in advance of its immediate adverse effect 
in the context of a concrete case involves too remote and abstract an in- 
quiry for the proper exercise of the judicial function.” International 
Longshoremen’s & Warehousemen’s Union v. Boyd, 347 U.S. 222, 224 
(1954). See ACLU v. FCC, 823 F.2d 1554, 1577 (D.C. Cir. 1987), cert. 
denied, 485 U.S. 959 (1988); Office of Communication of United Church of 

Christ v. FCC, 826 F.2d 101, 106 (D.C. Cir. 1987). 

44 

no obligations that adversely affect any parties’ day-to-day 
operations, and the parties will have ample opportunity to 
bring their legal challenge when any harm is more imme- 
diate and certain. See Lujan, 497 U.S. at 891; Ohio Forestry, 
523 U.S. at 733-734; Toilet Goods Ass’n v. Gardner, 387 U.S. 
158, 164 (1967). 

III. THE COURT OF APPEALS IMPROPERLY RE- 
STRICTED EPA’S AUTHORITY TO IMPLEMENT 
THE REVISED OZONE STANDARD 

If this Court were to reach the merits of the court of 
appeals’ decision respecting implementation, it should re- 
verse that decision. The court of appeals correctly upheld 
EPA’s authority to revise the ozone NAAQS, and it cor- 
rectly concluded that the CAA requires EPA to designate all 
areas of the Nation as attainment, nonattainment, or unclas- 
sifiable areas for the revised standard. Pet. App. 34a-37a. 
The court erred, however, in concluding that EPA could not 
enforce a more protective ozone standard in those desig- 
nated areas. See id. at 37a-44a. On rehearing, the court 
modified its views and concluded that “EPA can enforce a 
revised primary ozone NAAQS only in conformity with 
Subpart 2.” Id. at 81a. Judge Tatel explained in his partial 
concurrence that the panel’s revised decision allows EPA to 
enforce its revised ozone standard under Subpart 1 in an 
area only after that area attains the one-hour standard under 
Subpart 2. Id. at 89a (Tatel, J., concurring). But even under 
that view, the court of appeals’ decision is incorrect. 

As we explain below, EPA reasonably interprets the CAA 
to require that EPA implement a revised ozone standard 
under Subpart 1. The revised NAAQS is a National 
Ambient Air Quality Standard that should apply throughout 
the entire Nation, for all members of the public, including 
those that reside in areas that do not currently attain the 
one-hour standard. There is no warrant for categorically 

45 

requiring that EPA ensure compliance with the very one- 
hour ozone standard that it found inadequate to protect 
public health before it can require efforts to attain the more 
protective revised ozone NAAQS. 

A. The Clean Air Act Authorizes EPA To Implement The 

Revised Ozone NAAQS Under Subpart 1 Of Part D 

Title I of the CAA, 42 U.S.C. 7401-7515 (1994 & Supp. III 
1997), governs the 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, revise the NAAQS—including the pre- 
existing one-hour ozone standard—every five years. 42 
U.S.C. 7409(d)(1); Pet. App. 34a. Subpart 1 of Part D, which 
governs implementation for “Nonattainment Areas in Gen- 
eral,” sets out specific provisions for implementing revised 
NAAQS. 42 U.S.C. 7502(a)(1). It follows that EPA’s revised 
ozone NAAQS would be subject to implementation under 
Subpart 1. The court of appeals’ counter-intuitive conclusion 
—that the revised ozone NAAQS must be implemented in 
conformity with Subpart 2, which addresses the former 
ozone NAAQS—conflicts at the outset with the basic 
framework of the Act. 

Subpart 1’s specific language reveals that the court’s 
construction is wrong. Section 172(a) establishes classifi- 
cations and attainment dates for all areas designated non- 
attainment “pursuant to section [107(d)] with respect to any 

* * * revised standard, including a revision of any standard 
in effect on November 15, 1990.” 42 U.S.C. 7502(a)(1)(A). 
Section 172(a)(1)(A)’s reference to “any” revised standard 
includes a revision of the one-hour ozone standard, because 
that standard was “in effect on November 15, 1990.” See 40 
C.F.R. 50.9 (1990). Thus, Section 172(a), on its face, makes 
clear that Subpart 1 governs the selection of classifications 
and attainment dates for a revised ozone NAAQS. 

46 

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-setting authority 
under Section 172(a) does not apply to “nonattainment areas 
for which classifications [or “attainment dates”] are specifi- 
cally provided 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 Section 181(a)(1), in Subpart 2 of Part D, 
provides that “each area designated nonattainment for ozone 
pursuant to [Section 107(d)]” is to be classified and given an 
attainment date under its Table 1. 42 U.S.C. 7511(a)(1). See 
Pet. App. 38a. In the court’s view, Section 181(a)(1) dictates 
that all areas that are designated as nonattainment for ozone 
under Section 107(d), including areas designated under the 
revised ozone NAAQS, are subject to Subpart 2’s provisions. 
Id. at 38a-39a. Congress, however, adequately answered the 
court’s concern over those seemingly competing references. 

Section 181(a)—which is contained in Subpart 2 of Part 
D—“specifically provide[s]” classifications and attainment 
dates for only a particular subset of ozone “nonattainment 
areas.” Section 181(a)’s caption states that the Section 
provides “Classification and attainment dates for 1989 
nonattainment areas.” 42 U.S.C. 7511(a) (emphasis added). 
The 1989 nonattainment areas are, of course, the areas that 
were subject to the one-hour ozone standard then in force. 
Congress enacted Subpart 2 out of concern over the con- 
tinuing nonattainment of the one-hour ozone standard that 
existed when it enacted the 1990 Amendments. It plainly 
crafted Section 181(a)(1) to address that specific problem. 
The title of Section 181(a) clarifies that Section’s reach and 
resolves any confusion about whether Subpart 2 governs 
implementation of the revised ozone NAAQS. See INS v. 
National Ctr. for Immigrants’ Rights, Inc., 502 U.S. 183, 189 
(1991); Mead Corp. v. Tilley, 490 U.S. 714, 723 (1989); FTC v. 
Mandel Bros., 359 U.S. 385, 388-389 (1959). 

47 

The court of appeals’ contrary conclusion would lead to 
unworkable and absurd results. For example, Section 
181(a)(1) sets attainment dates and classifications based on 
an area’s “design value,” which is an air quality measure that 
specifically applies to the one-hour ozone standard that was 
in existence in 1990. See 42 U.S.C. 7511(a)(1). 

29 It would 
make no sense—and, indeed, would be impossible—to clas- 
sify areas and set their attainment dates for the revised 
NAAQS’s eight-hour standard using an air quality measure- 
ment based upon one-hour averaging. The eight-hour 
NAAQS rests on an entirely different averaging meth- 
odology, statistical form, and concentration. See 40 C.F.R. 

50.10 & Pt. 50 App. I, ¶¶ 2-3. 
In addition, Section 181(a) calculates attainment dates for 
areas based upon a fixed number of years from 1990. See 42 
U.S.C. 7511(a)(1) (Table 1). Section 181(a)(1) makes refer- 
ence to 1990 because it establishes attainment dates for the 
“1989 nonattainment areas,” which had not attained the one- 
hour ozone standard at the time of enactment of the 1990 
Amendments. That timetable makes no sense in calculating 
attainment dates for a revised NAAQS. Indeed, many of 
Section 181(a)(1)’s attainment dates, including those for 
“marginal,” “moderate,” and “serious” nonattainment areas, 
have already passed. See 42 U.S.C. 7511(a) (Table 1). 

30 

29 See H.R. Rep. No. 490, 101st Cong., 2d Sess. Pt. 1, at 197 (1990). 
(“The primary ozone standard, established to protect human health, is a 
daily maximum hourly concentration of 0.12 parts per million (ppm) [i.e., 
the one-hour ozone standard]. Compliance with the ozone standard is 
evaluated on the basis of a ‘design value,’ which is the fourth highest one- 
hour ozone reading over three years.”). The court of appeals correctly 
noted this fact. See Pet. App. 32a n.6. 

30 The text of Section 181(b), 42 U.S.C. 7511(b), provides further 
evidence that Section 181 applies only to the implementation of the one- 
hour standard. Section 181(b) recognizes that areas initially designated 
shortly after enactment of the 1990 Amendments as “attainment” areas 
for the one-hour ozone standard may be redesignated as “nonattainment” 
if, for example, air quality in the area deteriorates. See 42 U.S.C. 

48 

In light of those considerations, Section 181(a)(1) cannot 
reasonably be construed to have “specifically provided” clas- 
sifications and attainment dates for the eight-hour ozone 
standard. Rather, the text and context of Section 181(a) 
indicate that Congress intended Section 181(a)(1) to provide 
classifications and attainment dates only for “1989 non- 
attainment areas” that had been designated under the then- 
current one-hour ozone standard. See 42 U.S.C. 
7407(d)(1)(C) and (4)(A). EPA’s view that Congress in- 
tended EPA to implement the revised NAAQS under Sub- 
part 1 and to implement the former NAAQS under Subpart 
2 represents, at a minimum, a permissible and reasonable 
accommodation of the provisions entrusted to the agency’s 
care. See, e.g., Chevron, 467 U.S. at 842-845. 

B. Delaying Implementation Of The Revised NAAQS Until 

The Previous Standard Is Attained Conflicts With The 

Clean Air Act’s Requirement That All NAAQS Be 

Attained “As Expeditiously As Practicable” 

The court of appeals also erred in its apparent conclusion 
that EPA cannot implement the revised ozone NAAQS in an 
area until that area has had an opportunity to meet the 
attainment dates for the one-hour ozone standard. See Pet. 
App. 89a. The court overlooked that the attainment dates 
set out in Section 181(a)(1) establish the maximum period of 
time allowed for attainment. See 42 U.S.C. 7511(a)(1). Both 

7407(d)(3). Section 181(b) allows for adjustment of the attainment date set 
out in Section 181(a)(1)’s “Table 1” in that circumstance. See 42 U.S.C. 
7511(b). Section 181(b) makes no provision, however, for using Table 1 if 
EPA promulgates a revised ozone standard and designates an area as 
“nonattainment” under the revised standard. Section 181(b) expressly 
applies only to areas that were initially designated as “attainment” for the 
one-hour ozone standard pursuant to 42 U.S.C. 7407(d)(4) and are later 
redesignated as “nonattainment” for that standard under 42 U.S.C. 
7407(d)(3). See 42 U.S.C. 7511(b). Section 181(b) does not apply to de- 
signations for revised NAAQS, which are made under 42 U.S.C. 
7407(d)(1). 

49 

Subpart 1 and Subpart 2 require that all areas attain the 
NAAQS “as expeditiously as practicable.” CAA §§ 172(a)(2), 
181(a)(1), 42 U.S.C. 7502(a)(2), 7511(a)(1); see H.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 concluding that it should implement the revised ozone 
standard without delay throughout the 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 conceivably arise for the Los Angeles area 
between Subpart 1’s deadline to attain the revised ozone 
standard and Subpart 2’s attainment date for the one-hour 
ozone standard. See Pet. App. 41a. It is entirely reasonable, 
however, for Congress to require that, once EPA determines 
that a revised NAAQS is necessary to protect public health, 
the revised NAAQS should be attained without avoidable 
delay notwithstanding the timetable that Congress en- 
visioned for the standard then in effect. 

31 

Moreover, the court of appeals has overstated the 
practical problem that the revised NAAQS would pose. As 
we have noted, the deadlines for attainment in Section 
181(a)(1) are only outer time limits for attaining the one-hour 
standard. See 42 U.S.C. 7511(a)(1). Los Angeles would 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. 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, how- 
ever, does not necessarily pose any practical problems. For 

31 The court of appeals’ concerns may have arisen from a mistaken 
belief that it is unusual for areas to be subject to more than one NAAQS at 
any given time. To the contrary, it is common for an area to be subject to 
simultaneous implementation of two or more NAAQS, including two 
NAAQS governing the same pollutant. See, e.g., 40 C.F.R. 50.4(a)-(b), 

50.8(a)(1)-(2). 

50 

example, it may be “practicable”—and preferable from an 
implementing State’s perspective—to achieve both the one- 
hour ozone standard and the revised ozone standard at 
approximately the same time. There is no reason to believe 
that Congress intended to preclude that approach. 

In any event, the question of how to reconcile any 
competing compliance deadlines is clearly the type of issue 
that should first be addressed by EPA through future final 
action under the implementation process, including any 
required public notice and opportunity for comment. EPA’s 
determinations can 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 Subparts 1 and 2, it 
will be up to EPA to harmonize the applicable provisions, 
and the courts must defer to EPA’s reasonable judgment on 
the matter. Chevron, 467 U.S. at 845. Those issues, 
however, are properly reserved for another day. Regardless 
of how those provisions may ultimately be applied, they 
certainly do not justify the court of appeals’ conclusion that 
Congress prohibited EPA from implementing the revised 
ozone standard in an area until it attains the very standard 
that EPA found was not adequate to protect public health. 

CONCLUSION 

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

Respectfully submitted. 

51 

GARY S. GUZY 

General Counsel 

GERALD K. GLEASON 
MICHAEL L. GOO 
JAN M. TIERNEY 
KEVIN W. MCLEAN 

Attorneys 
Environmental Protection 

Agency 
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 

JULY 2000 

APPENDIX 

Excerpts From Federal Register Notice: 

National Ambient Air Quality Standards For 
Ozone; Final Rule (62 Fed. Reg. 38,856 (1997)) 

1. In discussing its jurisdiction to review EPA’s imple- 
mentation of the eight-hour ozone NAAQS (Pet. App. 77a- 
78a), the court of appeals cited the following passage from 
the preamble of the Federal Register Notice describing 
EPA’s Final Rule: National Ambient Quality Standards For 
Ozone: 

D. 1990 Act Amendments 

Contrary to the view expressed in some public 
comments, EPA maintains that the provisions of subpart 
2 of Part D of Title I of the Clean Air Act, enacted in 1990, 
do not preclude EPA from revising the O3 standard. The 
provisions of subpart 2 simply do not limit EPA’s clear 
authority under section 109 to revise the standard. 

The basic contention of the commenters is that be- 
cause the provisions of subpart 2 are linked to the current 
1-hour, 0.12 ppm O3 standard, they prohibit EPA from 
revising the O3 standard. These provisions, however, do 
not lead to such a conclusion. Moreover, the view ex- 
pressed in these comments ignores provisions indicating 
that Congress believed that EPA could revise the O3 
NAAQS. 

At the outset, it should be noted that Congress ex- 
pressly authorized EPA to revise any ambient air quality 
standard in section 109. That section, which requires 
EPA to review and revise, as appropriate, each NAAQS 
every 5 years, contains no language expressly or im- 
plicitly prohibiting EPA from revising a NAAQS. If 
Congress had intended to preclude EPA from reviewing 
and revising a NAAQS, which is one of EPA’s 

(1a) 

2a 

fundamental functions, Congress would have specifically 
done so. Clearly, Congress knew how to preclude EPA 
from exercising otherwise existing regulatory authority 
and did so in other instances. See section 
202(b)(1)(C)(expressly precluding EPA from modifying 
certain motor vehicle standards prior to model year 2004); 
section 112(b)(2)(preventing EPA from adding to the list 
of hazardous air pollutants any air pollutants that are 
listed under section 108(a) unless they meet the specific 
exceptions of section 112(b)(2)); section 249(e)(3), (f) and 
section 250(b)(limiting EPA’s authority regarding certain 
clean-fuel vehicle programs). No such language was 
included in either section 109 or elsewhere in the Act and 
no such implication may properly be based on the 
provisions of subpart 2 of Part D of Title I. 

Second, other provisions of the Act expressly con- 
template EPA’s ability to revise any NAAQS, and 
provide no indication that such ability is limited to stan- 
dards other than those whose implementation is the 
subject of subparts 2, 3 and 4 of Part D. For example, 
section 110(a)(2)(H)(i) provides that SIPs are to provide 
for revisions “from time to time as may be necessary to 
take account of revisions of such national primary or 
secondary ambient air quality standard * * *.” Section 
107(d)(1)(A) provides a process for designating areas as 
attainment, nonattainment, or unclassifiable “after 
promulgation of a new or revised standard for any 
pollutant under section 109 * * *.” Section 172(e) 
addresses modifications of national primary ambient air 
quality standards. Finally, section 172(a)(1) expressly 
contemplates that EPA may revise a standard in effect at 
the time of enactment of the 1990 Clean Air Act 
Amendments. Section 172(a)(1)(A) provides EPA with 
authority to classify nonattainment areas on or after the 
designation of an area as nonattainment with respect to 
“any revised standard, including a revision of any 

3a 

standard in effect on the date of the enactment of the 
Clean Air Act Amendments of 1990.” Plainly, Congress 
had no intention of prohibiting EPA from revising any of 
the ambient standards in effect at the time of the 
enactment of the 1990 amendments. 

Third, the provisions of subpart 2 of Part D do not 
support the contention that they somehow preclude EPA 
from exercising its authority to revise the NAAQS under 
section 109. The fact that Congress laid out an 
implementation program for the O3 standard existing at 
the time of the 1990 amendments in no way suggests that 
Congress intended to preclude EPA from exercising the 
authority it provided EPA to revise the NAAQS when 
the health data on which EPA bases such decisions war- 
ranted a change in the standard. Contrary to this conten- 
tion, section 181(a) does not preclude the designation of 
areas as nonattainment for O3 that have design values less 
than 0.121 ppm. EPA has designated as nonattainment 
numerous areas whose design value was less than 0.121 
ppm, but which violated the existing 1-hour, 0.12 ppm O3 
standard. These areas, referred to as “nonclassifiable 
nonattainment areas,” include “submarginal” areas (i.e., 
O3 nonattainment areas with design values below 0.121 
ppm), (See 57 FR 13498, 13524-27, April 16, 1992). These 
areas include areas that were designated nonattainment 
prior to the 1990 amendments and whose nonattainment 
designation Congress required to be continued after 1990. 
See section 107(d)(1)(C)(i). Clearly, Congress did not 
prohibit the designation of areas as nonattainment for O3 
with design values below 0.121 ppm; in fact, in some cases, 
Congress required it. Furthermore, the position 
advanced by the commenters would mean that, in effect, 
Congress in the 1990 amendments legislatively revised 
the then-existing 1-hour, 0.12 ppm O3 standard to a 0.121 
ppm standard. There is no indication that Congress in- 
tended to do that. 

4a 

In addition, the fact that Congress directed EPA to use 
“the interpretation methodology issued by the Admini- 
strator most recently” before the date of the enactment of 
the Clean Air Act Amendments of 1990 in the context of 
subpart 2 does not add any support to the commenters’ 
position; it merely shows that Congress intended the 
existing 1-hour, 0.12 ppm standard to be implemented in a 
specified way, not that Congress intended to preclude 
EPA from using its otherwise applicable authority to 
revise the standard. 

The EPA also disagrees with the contention that 
sections 172(a)(1)(C) and (a)(2)(D), which provide that the 
general classification and attainment date provisions of 
section 172 do not apply to areas for which classifications 
or attainment dates “are specifically provided under other 
provisions of this part,” support the conclusion that 
Congress intended to prohibit EPA from revising the O3 
standard. These provisions simply mean that where 
Congress elsewhere provided for specific classifications 
and attainment dates, as in the case of subpart 2 
regarding the 1-hour, 0.12 ppm standard, EPA is not to 
modify those classifications or dates. The EPA is not pur- 
porting to do this. These provisions do not lead to the 
conclusion that because Congress established them for 
the O3 standard in effect at the time of the 1990 
amendments, Congress meant that EPA could not revise 
that standard in order to appropriately protect public 
health. 

EPA does not accept the thesis that revising the O3 
standard forces EPA to violate other provisions of the 
Act and, therefore, is not an “appropriate” revision of the 
standard under section 109. Revising the O3 standard in 
accordance with the language of section 109 does not 
result in EPA violating any provision of the Act. On the 
other hand, a determination by EPA that the O3 standard 
should not be revised, even though EPA concludes that it 

5a 

needs to be revised to protect public health with an 
adequate margin of safety, would violate section 109. 

Also, EPA does not believe that carrying out the 
provisions of section 109 to set a new O3 standard to 
protect public health with an adequate margin of safety 
somehow “risks undermining both perceptions and reality 
of the functioning of our democratic form of government.” 
EPA is merely implementing the words of the Clean Air 
Act, a statute passed by the Congress and signed by the 
President. To refuse to revise the standard 
notwithstanding the need to protect public health as 
enunciated in section 109 would thwart the objectives of 
those who passed and signed the Clean Air Act on behalf 
of the American public. 

Finally, for the reasons stated above, EPA’s analy- 
sis of its ability to implement the revised O3 standard 
under the provisions of subpart 1 of Part D of Title I does 
not support the view that Congress prohibited EPA from 
revising the standard. Congress clearly specified an 
approach to the implementation of the 1-hour, 0.12 ppm O3 
standard in the provisions of subpart 2 of Part D. EPA 
believes that the clear and express linkage of that 
approach to the 1-hour, 0.12 ppm standard indicates that 
it may implement a revised O3 standard in accord with the 
general principles of subpart 1 of Part D, as informed by 
the no-backsliding principle embodied in section 172(e). 
That Congress directed specifically how EPA and the 
States should implement the 1-hour, 0.12 ppm O3 standard 
does not carry with it the implication that Congress 
intended to prohibit EPA from exercising its otherwise 
clear and express authority to revise that standard in 
order to carry out one of its fundamental missions, the 
establishment of ambient air quality standards to protect 
public health with an ample margin of safety. If Congress 
had intended to prohibit EPA from exercising such a 

6a 

fundamental authority it would have clearly specified (as 
it did in other instances) that EPA could not do so. 

The EPA also disagrees with the contention that a 
revised O3 standard may not be implemented for so long 
as the current 1-hour, 0.12 ppm O3 standard remains in 
effect. The fact that the provisions of subpart 2 of Part D 
are focused on the implementation of the current standard 
does not mean that, if a new or revised O3 standard is 
promulgated pursuant to section 109, the new standard 
could not simultaneously be implemented under the 
provisions of section 110 and subpart 1 of Part D, which 
apply regardless of the criteria pollutant of concern. 
There is no language in sections 181 or 182 that precludes 
the implementation of a different standard under other 
authority; those provisions simply govern the implemen- 
tation of the 1-hour, 0.12 ppm O3 standard. EPA further 
notes that it has historically had more than one primary 
standard for criteria pollutants (e.g., annual and 24-hour 
PM10 and sulfur dioxide standards, and 8-hour and 1-hour 
CO standards) and believes that had Congress wanted to 
preclude EPA from implementing two primary O3 stan- 
dards simultaneously it would have expressly precluded 
EPA from doing so. Thus, EPA does not believe that it 
must repeal the 1-hour, 0.12 ppm O3 standard before it can 
promulgate and implement a new primary O3 standard. 

62 Fed. Reg. 38,884-38,885 (1997). 

2. The preamble of the Federal Register Notice also 
describes EPA’s separate final rule, 40 C.F.R. 50.9(b), re- 
specting future enforcement of the one-hour ozone NAAQS. 
The preamble contains the following passage, which provides 
an additional discussion of implementation of the ozone 
NAAQS: 

4. Final decision on the primary standard. After 
carefully considering the information presented in the 
Criteria Document and the Staff Paper, the advice and 

7a 

recommendations of CASAC, public comments received 
on the proposal, and for the reasons discussed above, the 
Administrator is replacing the existing 1-hour, 0.12 ppm 
primary standard with a new 8-hour, 0.08 ppm primary 
standard. The new 8-hour standard will become effective 
September 16, 1997. 

The 8-hour, 0.08 ppm primary standard will be met 
at an ambient air quality monitoring site when the 3-year 
average of the annual fourth-highest daily maximum 8- 
hour average O3 concentration is less than or equal to 0.08 
ppm. Data handling conventions are specified in a new 
Appendix I to 40 CFR part 50 as discussed in Unit VI 
below. 

In the proposal, EPA proposed that the revocation 
of the existing 1-hour O3 standard be delayed for certain 
purposes until EPA had approved State Implementation 
Plans to implement the new 8-hour O3 standard. EPA had 
proposed continuing the applicability of the 1-hour 
standard in this way in order to facilitate continuity in 
public health protection during the transition to a new 
standard. (See Memorandum from John S. Seitz to Mary 
D. Nichols, November 20, 1996; Docket No. A-95-58, item 
II-B-3.) Also, at the time of the proposal of the new O3 
standard, EPA had proposed an interpretation of the Act 
in the proposed Interim Implementation Policy (61 FR 
65764, December 13, 1996) under which the provisions of 
subpart 2 of part D of Title I of the Act would not apply to 
existing O3 nonattainment areas once a new O3 standard 
becomes effective. 

In light of comments received regarding the 
interpretation proposed in the Interim Implementation 
Policy, EPA has reconsidered that interpretation and now 
believes that the Act should be interpreted such that the 
provisions of subpart 2 continue to apply to O3 
nonattainment areas for purposes of achieving attainment 
of the current 1-hour standard. As a consequence, the 

8a 

provisions of subpart 2, which govern implementation of 
the 1-hour O3 standard in O3 nonattainment areas, will 
continue to apply as a matter of law for so long as an area 
is not attaining the 1-hour standard. Once an area attains 
that standard, however, the purpose of the provisions of 
subpart 2 will have been achieved and those provisions 
will no longer apply. However, the provisions of subpart 
1 of part D of Title I of the Act would apply to the 
implementation of the new 8-hour O3 standards. 

To facilitate the implementation of those provisions 
and to ensure a smooth transition to the implementation 
of the new 8-hour standard, the 1-hour standard should 
remain applicable to areas that are not attaining the 1- 
hour standard. Therefore, the 1-hour standard will 
remain applicable to an area until EPA determines that it 
has attained the 1-hour standard, at which point the 1- 
hour standard will no longer apply to that area. 

62 Fed. Reg. 38,873 (1997).