The South Coast Air Basin (Basin) was designated as a nonattainment area for the 1997 annual and 24-hour PM2.5 National Ambient Air Quality Standards (NAAQS or standards) in 2005, and later reclassified as a “moderate” nonattainment area in 2014. However, stringent rules and regulations have driven emission reductions that successfully brought PM2.5 levels in the Basin below the 1997 standards. Since 2013, the Basin has consistently met these standards. To be redesignated to attainment, South Coast AQMD must submit redesignation requests and maintenance plans demonstrating continued compliance with the standards. Accordingly, this State Implementation Plan (SIP) revision includes the required redesignation requests and maintenance plans for the 1997 PM2.5 standards.
The Basin was designated as a “moderate” nonattainment area for the 1987 24-hour PM10 standard in 1990 and later reclassified as a “serious” nonattainment area in 1993. After exclusion of exceptional events, monitoring data collected from 2004–2008 demonstrated attainment of the 24-hour PM10 standard in the Basin. In 2010, South Coast AQMD submitted a redesignation request and adopted the first PM10 maintenance plan, which were approved by U.S. EPA in 2013. The Basin has since remained below this standard, provided that potential exceptional events like wind-blown dust and wildfires are excluded. Under Section 175A(b) of the Clean Air Act (CAA), a second maintenance plan must be submitted eight years after redesignation to demonstrate continued attainment. To fulfill this requirement, this SIP revision also includes a second PM10 maintenance plan, which extends the demonstration of continued attainment through 2033—20 years after the Basin's redesignation.