Neighborhood-Level Nitrogen Dioxide Inequalities Contribute to Surface Ozone Variability in Houston, Texas.

In Houston, Texas, nitrogen dioxide (NO) air pollution disproportionately affects Black, Latinx, and Asian communities, and high ozone (O) days are frequent. There is limited knowledge of how NO inequalities vary in urban air quality contexts, in part from the lack of time-varying neighborhood-level NO measurements. First, we demonstrate that daily TROPOspheric Monitoring Instrument (TROPOMI) NO tropospheric vertical column densities (TVCDs) resolve a major portion of census tract-scale NO inequalities in Houston, comparing NO inequalities based on TROPOMI TVCDs and spatiotemporally coincident airborne remote sensing (250 m × 560 m) from the NASA TRacking Aerosol Convection ExpeRiment-Air Quality (TRACER-AQ). We further evaluate the application of daily TROPOMI TVCDs to census tract-scale NO inequalities (May 2018-November 2022). This includes explaining differences between mean daily NO inequalities and those based on TVCDs oversampled to 0.01° × 0.01° and showing daily NO column-surface relationships weaken as a function of observation separation distance. Second, census tract-scale NO inequalities, city-wide high O, and mesoscale airflows are found to covary using principal component and cluster analysis. A generalized additive model of O mixing ratios versus NO inequalities reproduces established nonlinear relationships between O production and NO concentrations, providing observational evidence that neighborhood-level NO inequalities and O are coupled. Consequently, emissions controls specifically in Black, Latinx, and Asian communities will have co-benefits, reducing both NO disparities and high O days city wide.