ELR Citation: 43 ELR 20001
No(s). 08-1250 (D.C. Cir. Jan 4, 2013)

The D.C. Circuit ordered EPA to repromulgate two final rules it issued under the CAA concerning the implementation of the NAAQS for fine particulate matter (PM). Environmental groups challenged EPA's decision to issue the rules pursuant to the general implementation provisions of Subpart 1 of Part D of Title I of the Act rather than the PM-specific provisions of Subpart 4 of Part D. EPA argued that because Subpart 4 repeatedly refers to PM10 (PM having a diameter equal to or less than 10 micrometers) rather than to PM 2.5 (PM having a diameter equal to or less than 2.5 micrometer) or PM generally—the statutory language limits Subpart 4's applicability to implementation of the current PM10 standard. Thus, EPA contends, PM2.5 must be implemented pursuant to the general (and less stringent) implementation procedure in Subpart 1. But the court disagreed, concluding that EPA's argument ignores the plain meaning of the statute and the U.S. Supreme Court's ruling in Whitman v. American Trucking Associations, 531 U.S. 457 (2001). Before Congress enacted Subpart 4, EPA had promulgated a single particulate matter standard—the PM10 standard—which encompassed all particulate matter with a diameter of 10 micrometers or less—including both coarse and fine particulate matter, that is, particulate matter now governed by both the PM10 and PM2.5 standards—and the 1990 CAA amendments adopted this broad meaning in defining "PM10." Thus, by its express terms, Subpart 4, when enacted, governed all PM10 particles, including those now denominated PM2.5. The scope of the statutory definition—and consequently of Subpart 4’s application—did not change when EPA subdivided PM10 by regulation. As the Whitman Court made clear, the intent of the 1990 amendments was to limit the broad implementation discretion Subpart 1 had previously granted EPA. Accordingly, it would make no sense that Congress would have wanted EPA to relax Subpart 4's more stringent, nondiscretionary requirements for implementing the PM2.5 standard at the same time EPA decided to strengthen the PM2.5 standard. On remand, EPA must issue the rules under Subpart 4.