The San Joaquin region is located within the federally designated San Joaquin Valley Air Basin. The basin is defined by the mountain and foothill ranges to the east and west, the San Joaquin County line to the north, and the Tehachapi and Sierra Nevada Mountains to the south. According to the San Joaquin Valley Air Pollution Control District, this geography creates a giant bowl, which is susceptible to air pollution creation and retention.
Federal air quality regulations require Metropolitan Planning Organizations (MPOs) to monitor air pollutants, including: ozone; particulate matter under 2.5 microns in diameter (PM 2.5); particulate matter under 10 microns in diameter (PM-10); and carbon monoxide (CO).
The San Joaquin Valley is currently designated as nonattainment with respect to Federal air quality standards for ozone and PM 2.5; and has a maintenance plan for PM-10, as well as a maintenance plan for CO for the urbanized/metropolitan areas of Kern, Fresno, Stanislaus, and San Joaquin Counties. As San Joaquin County's transportation planning agency, SJCOG is responsible for demonstrating that transportation plans and programs satisfy the requirements of the Clean Air Act.
The 2018 Air Quality Conformity Document outlines regulations concerning air quality and how those regulations affect the region's ability to deliver transportation projects. The final 2018 Air Quality Conformity Document was adopted by the SJCOG Board on June 28, 2018.