489 F.3d 1245

SOUTH COAST AIR QUALITY MANAGEMENT 

DISTRICT, Petitioner

v.

ENVIRONMENTAL PROTECTION AGENCY, 

Respondent

National Environmental Development Association's 

Clean Air Regulatory Project, et al., Intervenors.

No. 04-1200.

No. 04-1201.

United States Court of Appeals, District of 

Columbia Circuit.

June 8, 2007.

On Petitions for Rehearing.

David S. Baron, Barbara B. Baird, Adam Babich, Ann B. Weeks, and Jonathan F. Lewis were on the petition 

for rehearing filed by the Environmental Petitioners and South Coast Air Quality Management District and 

the response to the petition for rehearing filed by the Environmental Protection Agency.

John C. Cruden, Deputy Assistant Attorney General, U.S. Department of Justice, David J. Kaplan and Natalia 

T. Sorgente, Attorneys, and Jan M. Tierney, Attorney, U.S. Environmental Protection Agency were on the 

petition for rehearing filed by the Environmental Protection Agency.

Martha Coakley, Attorney General, Attorney General's Office of Commonwealth of Massachusetts, William 

L. Pardee, Assistant Attorney General, Richard Blumenthal, Attorney General, Attorney General's Office of 

the State of Connecticut, Kimberly Massicotte and Matthew Levine, Assistant Attorneys General, Joseph R. 

Biden, III, Attorney General, Attorney General's Office of the State of Delaware, Valerie S. Csizmadia, 

Deputy Attorney General, G. Steven Rowe, Attorney General, Attorney General's Office of the State of 

Maine, Gerald D. Reid, Assistant Attorney General, Andrew M. Cuomo, Attorney General, Attorney 

General's Office of the State of New York, Barbara Underwood, Solicitor General, David A. Munro and Lisa 

S. Kwong, Assistant Attorneys General, Robert A. Reiley, Counsel, Commonwealth of Pennsylvania, 

Department of Environmental Protection, Linda Singer, Attorney General, Attorney General's Office of the 

District of Columbia, Todd S. Kim, Solicitor General, Edward S. Schwab, Deputy Solicitor General, and 

Donna M. Murasky, Senior Litigation Counsel, were on the response of petitioner Commonwealth of 

Massachusetts, et al., to the petition for rehearing filed by the Environmental Protection Agency.

Charles H. Knauss, Robert V. Zener, and Robert S. Taylor were on the petition for rehearing filed by the 

Industry Petitioners.

Norman W. Fichthorn and Lucinda Minton Langworthy were on the petition for rehearing filed by 

Intervenor-Respondents American Chemistry Council, et al.

Before: HENDERSON, ROGERS and BROWN, Circuit Judges.

ROGERS, Circuit Judge.
1

Before the court are five petitions for rehearing1 with regard to the vacatur and remand of a 

final rule implementing the eight-hour national ambient air quality standard ("NAAQS") for 

ozone under the Clean Air Act ("the CAA"), 42 U.S.C. § 7401 et seq. See Final Phase 1 Rule To 

Implement the 8-Hour Ozone NAAQS, 69 Fed.Reg. 23,951 (Apr. 30, 2004) (codified at 40 

C.F.R. parts 40, 51, 81) ("2004 Rule"). The petitions overlap in part, challenging principally the 

court's interpretation of the statutory gap, described in Whitman v. American Trucking Ass'ns,

531 U.S. 457, 121 S.Ct. 903, 149 L.Ed.2d 1 (2001), that arises from the decision of the 

Environmental Protection Agency ("EPA") to change from a one-hour to an eight-hour 

measurement system for ozone, and the court's construction of the CAA's anti-backsliding 

provision. See S. Coast Air Quality Mgmt. Dist. v. EPA, 472 F.3d 882 (D.C.Cir.2006). None of 

these challenges has merit and we deny the petitions. However, we grant the joint request of 

EPA and the Environmental Petitioners to clarify the description of the required conformity 

determinations and to modify the scope of the vacatur of the 2004 Rule.

I.

2

In Whitman, the Supreme Court acknowledged that Subpart 2 of the CAA "unquestionably" 

provides for classifying nonattainment ozone areas even after EPA changed the system for 

measuring ozone levels from the highest annual one-hour average concentration to the fourthhighest annual eight-hour average concentration. 531 U.S. at 482, 121 S.Ct. 903. However, 

because Congress had defined the classification system in 1990 in terms of one-hour ozone, 

there were several limited gaps in the CAA. See id. at 484, 121 S.Ct. 903. This court concluded 

that EPA had misconstrued the extent of the gaps to exercise its interpretative discretion more 

broadly than the Supreme Court had authorized. See S. Coast Air Quality Mgmt. Dist., 472 F.3d 

at 892-94. In its petition for rehearing, EPA disagrees with our interpretation of the following 

passage in Whitman:

3

[T]o the extent that the new ozone standard is stricter than the old one, see 62 Fed.Reg. 

38856, 38858 (1997) (8-hour standard of 0.09 ppm rather than 0.08 ppm would have 

"generally represent[ed] the continuation of the [old] level of protection"), the classification 

system of Subpart 2 contains a gap, because it fails to classify areas whose ozone levels are 

greater than the new standard (and thus nonattaining) but less than the approximation of the 

old standard codified by Table 1.

4

531 U.S. at 483, 121 S.Ct. 903 (citation omitted). EPA maintains that "the approximation of 

the old standard codified by Table 1" does not refer to the previous citation, which repeats EPA's 

assertion in the 1997 Rule that 0.09 ppm under the eight-hour measurement scheme is roughly 

equivalent to the old standard of 0.12 ppm of one-hour ozone. Instead, according to EPA, the 

"approximation" being referenced is 0.121 ppm of one-hour ozone, the lowest nonattaining 

design value in Table 1. See EPA Pet'n at 4.

5
EPA's interpretation is irreconcilable with the CAA and Whitman. First, every other ozone 

level referenced in the sentence is in eight-hour terms and there is no signal that the final ozone 

level (the "approximation") used a different metric. Second, 0.121 is not an "approximation" of 

0.12, because an approximation is typically less precise than the true value. Here, Congress 

started the statutory Table 1 with the value 0.121 because it is the smallest design value that 

qualifies as nonattaining. An area with a design value of precisely 0.12 would "meet[]" the 

NAAQS under section 107 of the CAA, 42 U.S.C. § 7407. Third, nowhere in Whitman does the 

Supreme Court signal that "the approximation of the old standard" is shorthand for 0.121 ppm 

of one-hour ozone.

6

EPA also maintains that there can be no eight-hour approximation of the one-hour ozone 

level because there is no one-to-one correspondence between the two metrics. EPA Pet'n at 5-6. 

But the lack of a precise equivalence is precisely why an approximation is necessary. The 

approximation referenced by the court, 0.09 ppm, is not, as EPA suggests, an arbitrary 

expression of the court's scientific prowess; as acknowledged by the Supreme Court, the 

approximation comes directly from the rulemaking record, which stated that 0.09 ppm of eighthour ozone "generally represent[ed] the continuation of the [old] level of protection." See 1997 

Rule, 62 Fed. Reg. at 38,858. In short, there is every reason to believe that the gap intended by 

Whitman is the gap described by the court in South Coast Air Quality Management District,

472 F.3d at 892-93.

7

EPA next objects to the court's failure to defer, under Chevron Step 2, to EPA's application of 

Subpart 1 to gap areas. The court merely recognized that under Chevron agency action that does 

not constitute a reasonable interpretation of the statute must be vacated. See id. at 894. Because 

Congress sought to reduce EPA discretion by enacting Subpart 2 as part of the 1990 

amendments to the CAA, EPA could not reasonably rely upon its preference for regulatory 

flexibility in setting the boundary between Subpart 1 and Subpart 2. EPA's claim that the court 

nullified the discretion recognized by the Supreme Court in Whitman is meritless. See Whitman,

531 U.S. at 484, 121 S.Ct. 903.

II.

8

Four petitioners seek rehearing on which aspects of EPA's regulation of one-hour ozone must 

be retained under the eight-hour ozone NAAQS. See 42 U.S.C. § 7502(e).2 EPA determined that 

"if Congress intended areas to remain subject to the same level of control where a NAAQS was 

relaxed, [Congress] also intended that such controls not be weakened where the NAAQS is made 

more stringent." 2004 Rule, 69 Fed.Reg. at 23,972. Contrary to the rehearing petitions of the 

Industry Petitioners (NPRA, Baton Rouge, and ACC), EPA's determination that section 172(e) 

supports the introduction of anti-backsliding measures is reasonable. EPA's interpretation does 

not violate the plain text of section 172(e), which does not specify how to proceed when the 

NAAQS is strengthened but the related reclassification would result in weakened controls. The 

Industry Petitioners would require a negative inference, but their interpretation would have an 

absurd result, cf. Hartford Underwriters Ins. Co. v. Union Planters Bank, N.A., 530 U.S. 1, 5, 

120 S.Ct. 1942, 147 L.Ed.2d 1 (2000), because then EPA could continually "strengthen" a 

NAAQS by the smallest margin and avoid ever implementing the time-delayed controls 

mandated by the CAA. See S. Coast Air Quality Mgmt. Dist., 472 F.3d at 902-03. The Industry 
Petitioners present nothing to suggest that Congress intended such a glaring loophole and, 

accordingly, the court properly deferred to EPA's reasonable interpretation.

9

EPA and the Industry Petitioners claim, however, that in applying EPA's interpretation of 

section 172(e), the court treated the provision as legally binding and usurped EPA's discretion. 

Not so. In the rulemaking, EPA concluded that "Congress would have intended that control 

obligations that applied for purposes of the 1-hour NAAQS should remain in place." Phase 1 

Implementation of the 8-Hour Ozone NAAQS: Reconsideration, 70 Fed. Reg. 30,592, 30,593 

(May 26, 2005). While the Industry Petitioners renew their arguments that the term "controls" 

in section 172(e) is ambiguous and that EPA's interpretation eliminating certain controls is 

entitled to Chevron deference, they provide no basis to doubt the court's conclusion that the 

"controls" at issue had a settled meaning. See S. Coast Air Quality Mgmt. Dist., 472 F.3d at 900-

05.

III.

10

We grant the joint request by EPA and the Environmental Petitioners to make explicit that 

the court's reference to conformity determinations speaks only to the use of one-hour motor 

vehicle emissions budgets as part of eight-hour conformity determinations until eight-hour 

motor vehicle emissions budgets are available. See id. at 904-05.

11

We also grant their request that the 2004 Rule be vacated only to the extent that the court has 

sustained challenges to it. Although certain states and the District of Columbia object to partial 

vacatur on the ground that this will inequitably exempt Subpart 1 areas from regulation while 

the remand is pending, complete vacatur of a partially valid rule would only serve to stall 

progress where it is most needed. EPA is urged to act promptly in promulgating a revised rule 

that effectuates the statutory mandate by implementing the eight-hour standard, which was 

deemed necessary to protect the public health a decade ago.

Notes:

1

Separate petitions for rehearing were filed by a group of Environmental Petitioners, the Chamber of 

Greater Baton Rouge et al. ("Baton Rouge"), National Petrochemical & Refiners Association ("NPRA"), 

American Chemistry Council et al. ("ACC"), and EPA

2

Section 172(e) of the CAA provides that

[i]f the Administrator relaxes a national primary ambient air quality standard . . . the Administrator shall .

. . promulgate requirements applicable to all areas which have not attained that standard as of the date of 

such relaxation. Such requirements shall provide for controls which are not less stringent than the 

controls applicable to areas designated nonattainment before such relaxation.

42 U.S.C. § 7502(e).

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