The EPA is finalizing revisions to the regulations governing the nonattainment new source review (NSR) program mandated by section 110(a)(2)(C) of the Clean Air Act (CAA or Act). These revisions implement changes to the preconstruction review requirements for major stationary sources in nonattainment areas in interim periods between designation of new nonattainment areas and adoption of a revised State Implementation Plan (SIP). The revisions conform the nonattainment permitting rules that apply during the SIP development period following nonattainment designations before SIP approval to the Federal permitting rules applicable to SIP-approved programs. The changes are intended to provide a consistent national program for permitting major stationary sources in nonattainment areas under section 110(a)(2)(C) and part D of title I of the Act. In particular, these changes conform the regulations to the NSR reform provisions that EPA promulgated by notice dated December 31, 2002, except that these changes do not include the NSR reform provisions for "clean units" or "pollution control projects," which the U.S. Court of Appeals for the D.C. Circuit vacated in New York v. EPA, 413 F.3d 3 (DC Cir. 2005). In addition, these changes include an interim interpretation of the NSR reform provision for a "reasonable possibility" standard for recordkeeping and reporting requirements, in accordance with that court decision. This interim interpretation to the "reasonable possibility" standard applies for appendix S purposes, pending the completion of rulemaking to develop a more complete interpretation.