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

In Houston, Texas, nitrogen dioxide (NO 2 ) air pollution disproportionately affects Black, Latinx, and Asian communities, and high ozone (O 3 ) days are frequent. There is limited knowledge of how NO 2 inequalities vary in urban air quality contexts, in part from the lack of time-varying neighborhood-level NO 2 measurements. First, we demonstrate that daily TROPOspheric Monitoring Instrument (TROPOMI) NO 2 tropospheric vertical column densities (TVCDs) resolve a major portion of census tract-scale NO 2 inequalities in Houston, comparing NO 2 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 2 inequalities (May 2018-November 2022). This includes explaining differences between mean daily NO 2 inequalities and those based on TVCDs oversampled to 0.01° × 0.01° and showing daily NO 2 column-surface relationships weaken as a function of observation separation distance. Second, census tract-scale NO 2 inequalities, city-wide high O 3 , and mesoscale airflows are found to covary using principal component and cluster analysis. A generalized additive model of O 3 mixing ratios versus NO 2 inequalities reproduces established nonlinear relationships between O 3 production and NO 2 concentrations, providing observational evidence that neighborhood-level NO 2 inequalities and O 3 are coupled. Consequently, emissions controls specifically in Black, Latinx, and Asian communities will have co-benefits, reducing both NO 2 disparities and high O 3 days city wide.