United States Court of Appeals

FOR THE DISTRICT OF COLUMBIA CIRCUIT

Filed June 8, 2007

No. 04-1200

SOUTH COAST AIR QUALITY MANAGEMENT DISTRICT,

PETITIONER

v.

ENVIRONMENTAL PROTECTION AGENCY,

RESPONDENT

NATIONAL ENVIRONMENTAL DEVELOPMENT ASSOCIATION'S

CLEAN AIR REGULATORY PROJECT, ET AL.,

INTERVENORS

Consolidated with

No. 04-1201, et al.

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.
2

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 IntervenorRespondents American Chemistry Council, et al. 
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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.

Before: HENDERSON, ROGERS and BROWN, Circuit Judges.

ROGERS, Circuit Judge: 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 (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.

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 fourth-highest annual eight-hour
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average concentration. 531 U.S. at 482. 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. 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:

[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.

531 U.S. at 483 (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. 

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
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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. 

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 eight-hour

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.

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. 
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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). 

II.

Four petitioners seek rehearing on which aspects of EPA’s

regulation of one-hour ozone must be retained under the eighthour 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 (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
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Petitioners present nothing to suggest that Congress intended

such a glaring loophole and, accordingly, the court properly

deferred to EPA’s reasonable interpretation.

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.

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. 

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
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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.