Based on its review of the air quality criteria and national ambient air quality standards (NAAQS) for particulate matter (PM), EPA is making revisions to the primary and secondary NAAQS for PM to provide increased protection of public health and welfare, respectively. With regard to primary standards for fine particles (generally referring to particles less than or equal to 2.5 micrometers ([micro]m) in diameter, PM<INF>2.5</INF>), EPA is revising the level of the 24-hour PM<INF>2.5</INF> standard to 35 micrograms per cubic meter ([micro]g/m\3\) and retaining the level of the annual PM<INF>2.5</INF> standard at 15[micro]g/m\3\. With regard to primary standards for particles generally less than or equal to 10[mu]m in diameter (PM<INF>10</INF>), EPA is retaining the 24-hour PM<INF>10</INF> and revoking the annual PM<INF>10</INF> standard. With regard to secondary PM standards, EPA is making them identical in all respects to the primary PM standards, as revised.