The federal Clean Air Act (Act) establishes planning requirements for areas that exceed the health-based National Ambient Air Quality Standards. Areas are designated as nonattainment based on monitored exceedances of these standards.
In 2015, the United States Environmental Protection Agency (U.S. EPA) strengthened the ambient air quality standard for 8-hour ozone from 75 to 70 parts per billion (ppb). Effective August 3, 2018, U.S. EPA designated 19 areas in California as nonattainment for the 2015 70 ppb 8-hour ozone standard and classified them as marginal, moderate, serious, severe or extreme. For ozone, the Act requires states to prepare baseline emission inventories for all areas exceeding the standard within two years of designation. Per U.S. EPA guidance, CARB has prepared the 2017 baseline emissions inventory for oxides of nitrogen and reactive organic gases for all ozone nonattainment areas, except San Diego, which will be included in their SIP later this summer.
Also within two years of designations, the Act requires states to submit enforceable transportation control strategies and transportation control measures to offset any growth in emissions from growth in VMT or numbers of vehicle trips (VMT emissions offset demonstration) for severe and extreme ozone nonattainment areas. The VMT offset demonstration for South Coast, Coachella Valley, and San Joaquin Valley were submitted as a part of the “70 ppb Ozone SIP Submittal.” The analysis for Western Mojave Desert was submitted as part of the proposed “West Mojave Desert VMT Offset Demonstration.”
The Board approved the 70 ppb Ozone SIP Submittal consisting of the baseline emissions inventory and VMT emissions offset demonstration (for South Coast, Coachella Valley, and San Joaquin Valley) required for the 2015 70 ppb 8-hour ozone standard on June 25, 2020. It was subsequently submitted to U.S. EPA on July 27, 2020. The Board approved the West Mojave Desert VMT Offset Demonstration on October 22, 2020, and it was submitted to U.S. EPA on December 29, 2020.