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

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Air Quality Monitoring

Background:

• Nitrogen dioxide (NO2) air pollution disproportionately affects minority communities in Houston, Texas.
• High ozone (O3) days are frequent, and understanding NO2 inequalities at the neighborhood level is limited due to a lack of time-varying measurements.

Purpose of the Study:

• To assess the capability of daily TROPOspheric Monitoring Instrument (TROPOMI) NO2 tropospheric vertical column densities (TVCDs) in resolving census tract-scale NO2 inequalities in Houston.
• To evaluate the application of TROPOMI TVCDs for analyzing NO2 inequalities from May 2018 to November 2022.
• To investigate the relationship between NO2 inequalities, high ozone days, and airflows in Houston.

Main Methods:

• Comparison of TROPOMI NO2 TVCDs with airborne remote sensing data (NASA TRACER-AQ) to validate NO2 inequality measurements.
• Analysis of daily TROPOMI TVCDs for census tract-scale NO2 inequalities, including oversampling and examination of column-surface relationships.
• Application of principal component and cluster analysis to identify covariation between NO2 inequalities, high O3 days, and mesoscale airflows.
• Development of a generalized additive model to explore the relationship between O3 mixing ratios and NO2 inequalities.

Main Results:

• Daily TROPOMI NO2 TVCDs effectively capture a significant portion of census tract-scale NO2 inequalities in Houston.
• NO2 inequalities, city-wide high O3 days, and mesoscale airflows demonstrate a clear covariation.
• The study provides observational evidence linking neighborhood-level NO2 inequalities with O3 levels, confirming established nonlinear relationships in O3 production.

Conclusions:

• Emissions control strategies targeting NO2 disparities in Black, Latinx, and Asian communities in Houston can yield co-benefits.
• These targeted controls can simultaneously reduce NO2 inequalities and mitigate frequent high O3 days across the city.
• The findings highlight the interconnectedness of air pollutants and the potential for equitable environmental policy.