Our conclusions come with several caveats. First, mobile monitoring was conducted during daytime, weekday hours. Concentrations and spatial gradients may differ during nighttime and weekend hours due to changes in emission patterns and atmospheric dynamics . Second, we assess here the implications of temporally averaged patterns, which are associated with chronic health effects. However, concentrations and spatial patterns show strong diurnal and seasonal variation that may have acute effects. While we believe that we sampled representative conditions (see Methods), temporal pollution dynamics could add another dimension to exposure disparity patterns. For this reason, we recommend that in-depth neighborhood monitoring include continuous fixed-site measurements in addition to mobile measurements . Third, we found that our conclusions are likely sensitive to the choice of neighborhoods, so we cannot assert that the disparity patterns we found are fully representative of conditions throughout the Bay Area (i.e., in unsampled neighborhoods). Finally, disparities in personal exposure to pollutants of outdoor origin depend not only on fine-scale patterns of outdoor air pollution -as measured here -but also personal mobility and the penetration of pollutants into the indoor environment. Future developments in measurement and modeling could usefully refine understanding of these dimensions of disparity. However, this study affirms that assessments of racial/ethnic air pollution disparities in the United States should include a broad range of representative neighborhoods that capture the varied experiences of those within each racial/ethnic group, considering the context of historic and present-day municipal-level segregation.