Reflecting the nearly parallel exposure concentration traces over time evident in Fig. , relative disparities in PM2.5 exposure from on-road mobile sources (Fig. ) were strikingly persistent, increasing slightly over this time period. The relative disparity in exposure to on-road mobile sources for Hispanic Californians increased slightly from 12.0% (year-2000) to 13.9% (year-2019) while the relative disparity in exposure for white Californians decreased slightly from -13.5% to -15.5%. Thus, the overall relative difference between the most and least exposed race-ethnicity increased from 30% to 35%. Given expected model uncertainties, these incremental changes may not necessarily represent evidence of a trend that is distinguishable from approximately constant relative disparity. Likewise, relative disparities for Black and Asian Californians also persisted (respectively 10.5-11.5% and 5.4-6.2% over this period). Exposure disparities by race-ethnicity are larger than by income (Fig. ). Notably, we find persistent disparities in exposure to both primary and secondary PM2.5 from vehicle emissions. Relative disparities in exposure to primary PM2.5 components (18.6% for Hispanic Californians) were larger than disparities in exposure to secondary PM2.5 (11.1% for Hispanic Californians).