A stratification of pollutant exposure by study area and US Census-reported race and ethnicity (Fig ) reveals both a wide range in the measures of air pollution within each racial/ethnic group and systematic differences in exposure among groups. Figure highlights the role of regional demographic patterns in shaping the distribution of exposure across members of each racial/ethnic group. Study areas with a greater share of a given race-ethnicity are represented by larger areas within the shape of the distribution. For example, exposure for the Asian community within our study areas is dominated by neighborhoods in San Francisco (shades of pink), while exposure for Black residents is almost entirely determined by concentrations in Oakland neighborhoods (shades of blue). These aggregate exposure profiles reveal an overall pattern of racial/ethnic disparities: higher concentration ranges in predominantly Black and Hispanic/Latino neighborhoods result in higher mean exposure for those groups. Notably, many of the neighborhoods with the highest average pollution exposures in our measurement dataset were subjected to overtly racially discriminatory housing policies (i.e., redlining) during the 20 th century (SI Appendix, Figure ). At the local level, there is wide overlap among the exposure distributions of each racial/ethnic group (SI Appendix Fig ). While study areas do show weak patterns of local disparity-census blocks with majority white residents showed modestly lower concentrations than blocks with majority Black and Hispanic residents within the same study area-there are not universal trends.