Statewide Trends in Overall Exposure and Relative Exposure Disparity California's mobile-source policy has succeeded in its overall goal of reducing PM2.5 exposures (Fig. ). We find that the modeled statewide population-weighted mean (PWM) PM2.5 exposure concentration attributable to on-road vehicles decreased from approximately 3.2 to 1.1 μg/m 3 from 2000 to 2019, a ~65% (i.e., nearly a factor-of-3) decrease in exposure on average for all Californians. This reduction in PM2.5 exposure from on-road vehicles outpaced the overall statewide improvement in ambient air quality (Fig. ). For context, multiple independent estimates of total PWM PM2.5 from all sources in California show an approximate ~40% decrease from 15 to 9 µg/m 3 from 2000 to 2019 .