Abstract. This report provides an overview of the NAAQS implementation process in the context of the 1997standards for fine particulate matter (PM2.5), which consists of particles less than 2.5 micrometers in diameter.The EPA is in the process of implementing the NAAQS for particulates promulgated in 1997, delayed because ofcourt challenges and other factors. The EPA’s 1997 revisions to the particulate matter standards (also referredto as the particulates NAAQS) included separate requirements for PM2.5 for the first time. The PM2.5 NAAQShave been the source of significant concern and national debate. Congress has been particularly interested inEPA’s promulgation and implementation of the CAA standards, and has held numerous hearings on particulatematter (and ozone) NAAQS established in 1997.
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