It is useful to consider the implications of our retrospective assessment for California's current policy efforts that focus heavily on eliminating exhaust emissions across the on-road fleet through a combination of electrification and -in the case of HDVs -hydrogen. For every year of the study, approximately 90% or more of the PWM PM2.5 exposure (and absolute exposure disparity) is attributable to exhaust emissions and approximately 80% or more is attributable to secondary formation from precursor exhaust emissions (Fig. ). Because California's policies contemplate eliminating exhaust emissions, this result implies that future vehicle electrification has potential to substantially reduce exposures and absolute disparity.