For each demographic group, we compute exposure disparity as the absolute (µg/m 3 ) and relative (percent) difference between the average modeled concentration experienced by a group versus the overall state population (Fig. , see also Methods and Table ). In this work, we discuss exposure disparities in both absolute and relative terms. Both metrics provide useful insights into exposure inequality. Because increases in PM2.5 concentration have a causal relationship with increases in adverse health outcomes, it is critical that absolute differences between groups of people are minimized to the extent possible. However, systemic inequality in terms of relative exposure disparity can persist even if the most overburdened areas receive the largest reductions in exposure in absolute terms, if those reductions are not also the largest in percentage terms. Crucially, our analyses focus exclusively on PM2.5 exposure disparities attributable to on-road vehicles. Most other major emitting sectors in California also disparately expose residents of overburdened communities and people of color to PM2.5 . Likewise, exposures to other air pollutants are also unequally distributed . Accordingly, when we find that disparities persist, they persist in a larger story of environmental inequity in California.