Cite as: 531 U. S. 457 (2001)
Opinion of the Court
B
Our approach to the merits of the parties' dispute is the familiar one of Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc., 467 U. S. 837 (1984). If the statute resolves the question whether Subpart 1 or Subpart 2 (or some combination of the two) shall apply to revised ozone NAAQS, then "that is the end of the matter." Id., at 842- 843. But if the statute is "silent or ambiguous" with respect to the issue, then we must defer to a "reasonable interpretation made by the administrator of an agency." Id., at 844. We cannot agree with the Court of Appeals that Subpart 2 clearly controls the implementation of revised ozone NAAQS, see 175 F. 3d, at 1048-1050, because we find the statute to some extent ambiguous. We conclude, however, that the agency's interpretation goes beyond the limits of what is ambiguous and contradicts what in our view is quite clear. We therefore hold the implementation policy unlawful. See AT&T Corp. v. Iowa Utilities Bd., 525 U. S. 366, 392 (1999).
The text of Subpart 1 at first seems to point the way to a clear answer to the question, which Subpart controls? Two sections of Subpart 1, 7502(a)(1)(C) and 7502(a)(2)(D), contain switching provisions stating that if the classification of ozone nonattainment areas is "specifically provided [for] under other provisions of [Part D]," then those provisions will control instead of Subpart 1's. Thus, it is true but incomplete to note, as the Administrator does, that the substantive language of Subpart 1 is broad enough to apply to revised ozone standards. See, e. g., § 7502(a)(1)(A) (instructing the Administrator to classify nonattainment areas according to "any revised standard, including a revision of any standard in effect on November 15, 1990"); § 7502(a)(2)(A) (setting attainment deadlines). To determine whether that language does apply one must resolve the further textual issue whether some other provision, namely Subpart 2, provides for the classification of ozone nonattainment areas. If
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