Based on its review of the air quality criteria and the national ambient air quality standards (NAAQS) for particulate matter (PM), the EPA is making revisions to the suite of standards for PM to provide requisite protection of public health and welfare and to make corresponding revisions to the data handling conventions for PM and to the ambient air monitoring, reporting, and network design requirements. The EPA also is making revisions to the prevention of significant deterioration (PSD) permitting program with respect to the NAAQS revisions. With regard to primary (health-based) standards for fine particles (generally referring to particles less than or equal to 2.5 micrometers ([mu]m) in diameter, PM<INF>2.5</INF>), the EPA is revising the annual PM<INF>2.5</INF> standard by lowering the level to 12.0 micrograms per cubic meter ([mu]g/m\3\) so as to provide increased protection against health effects associated with long- and short-term exposures (including premature mortality, increased hospital admissions and emergency department visits, and development of chronic respiratory disease), and to retain the 24-hour PM<INF>2.5</INF> standard at a level of 35 [mu]g/m\3\. The EPA is revising the Air Quality Index (AQI) for PM<INF>2.5</INF> to be consistent with the revised primary PM<INF>2.5</INF> standards. With regard to the primary standard for particles generally less than or equal to 10 [micro]m in diameter (PM<INF>10</INF>), the EPA is retaining the current 24-hour PM<INF>10</INF> standard to continue to provide protection against effects associated with short-term exposure to thoracic coarse particles (i.e., PM<INF>10-2.5</INF>). With regard to the secondary (welfare-based) PM standards, the EPA is generally retaining the current suite of secondary standards (i.e., 24-hour and annual PM<INF>2.5</INF> standards and a 24-hour PM<INF>10</INF> standard). Non-visibility welfare effects are addressed by this suite of secondary standards, and PM-related visibility im