Based on the Environmental Protection Agency's (EPA's) reconsideration of the air quality criteria and the national ambient air quality standards (NAAQS) for particulate matter (PM), the EPA proposes to revise the primary annual PM<INF>2.5</INF> standard by lowering the level. The Agency proposes to retain the current primary 24-hour PM<INF>2.5</INF> standard and the primary 24-hour PM<INF>10</INF> standard. The Agency also proposes not to change the secondary 24-hour PM<INF>2.5</INF> standard, secondary annual PM<INF>2.5</INF> standard, and secondary 24-hour PM<INF>10</INF> standard at this time. The EPA also proposes revisions to other key aspects related to the PM NAAQS, including revisions to the Air Quality Index (AQI) and monitoring requirements for the PM NAAQS.