The EPA is finalizing regulations to implement the New Source Review (NSR) program for fine particulate matter (that is, particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers, generally referred to as "PM<INF>2.5</INF>"). The NSR program was created by the Clean Air Act (Act or CAA) to ensure that stationary sources of air pollution are constructed or modified in a manner that is consistent with air quality goals in the area. The Clean Air Fine Particle Implementation Rule, which was proposed in the Federal Register on November 1, 2005, included requirements and guidance for State and local air pollution agencies to follow in developing State implementation plans (SIPs) and also the NSR provisions. The final implementation rule that was promulgated on April 25, 2007, included all the SIPs related provisions. In this rulemaking, EPA is finalizing the NSR provisions of the November 1, 2005 proposed rule including the major source threshold, significant emissions rate, and offset ratios for PM<INF>2.5</INF>, interpollutant trading for offsets and applicability of NSR to PM<INF>2.5</INF> precursors.