In 1997, the United States Environmental Protection Agency (U.S. EPA) adopted the 24-hour fine particulate matter (PM2.5) standard of 65 micrograms per cubic meter (µg/m3). In 2006, this standard was lowered to a more health-protective level of 35 µg/m3. The South Coast Air Basin (South Coast) is designated nonattainment for both the 65 and 35 µg/m3 24-hour PM2.5 standards (24-hour PM2.5 standards). In 2020, monitored data demonstrated that the South Coast attained both 24-hour PM2.5 standards. The South Coast Air Quality Management District (District) has developed the 2021 Redesignation Request and Maintenance Plan for the 1997 and 2006 24-hour PM2.5 Standards for the South Coast Air Basin (2021 PM2.5 Redesignation Request) demonstrating that the South Coast has met the requirements to be redesignated to attainment for the 24-hour PM2.5 standards. On November 5, 2021, the District will consider approval of the 2021 PM2.5 Redesignation Request. On December 9, 2021, CARB will consider adoption of the 2021 PM2.5 Redesignation Request Plan for inclusion into the California State Implementation Plan.