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

In Houston, Texas, nitrogen dioxide (NO₂) air pollution disproportionately affects Black, Latinx, and Asian communities, and high ozone (O₃) days are frequent. There is limited knowledge of how NO₂ inequalities vary in urban air quality contexts, in part from the lack of time-varying neighborhood-level NO₂ measurements. First, we demonstrate that daily TROPOspheric Monitoring Instrument (TROPOMI) NO₂ tropospheric vertical column densities (TVCDs) resolve a major portion of census tract-scale NO₂ inequalities in Houston, comparing NO₂ 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 NO₂ inequalities (May 2018–November 2022). This includes explaining differences between mean daily NO₂ inequalities and those based on TVCDs oversampled to 0.01° × 0.01° and showing daily NO₂ column-surface relationships weaken as a function of observation separation distance. Second, census tract-scale NO₂ inequalities, city-wide high O₃, and mesoscale airflows are found to covary using principal component and cluster analysis. A generalized additive model of O₃ mixing ratios versus NO₂ inequalities reproduces established nonlinear relationships between O₃ production and NO₂ concentrations, providing observational evidence that neighborhood-level NO₂ inequalities and O₃ are coupled. Consequently, emissions controls specifically in Black, Latinx, and Asian communities will have co-benefits, reducing both NO₂ disparities and high O₃ days city wide.

Most neighborhood-level NO₂ inequalities can be observed with daily TROPOspheric Monitoring Instrument (TROPOMI) observations; the unequal NO₂ distribution affects O₃ chemistry in Houston, Texas.