Space-Based Observational Constraints on NO₂ Air Pollution Inequality From Diesel Traffic in Major US Cities

Air pollution disproportionately burdens communities of color and lower-income communities in US cities. We have generally lacked city-wide concentration measurements that resolve the steep spatiotemporal gradients of primary pollutants required to describe intra-urban air pollution inequality. Here, we use observations from the recently launched TROPospheric Ozone Monitoring Instrument (TROPOMI) satellite sensor and physics-based oversampling to describe nitrogen dioxide (NO₂) disparities with race, ethnicity, and income in 52 US cities (June 2018–February 2020). We report average US-urban census tract-level NO₂ inequalities of 28 ± 2% (race-ethnicity and income combined), with many populous cities experiencing even greater inequalities. Using observations and inventories, we find diesel traffic is the dominant source of NO₂ disparities, and that a 62% reduction in diesel emissions would decrease race-ethnicity and income inequalities by 37%. We add evidence that TROPOMI resolves tract-scale NO₂ differences using relationships with urban segregation patterns and spatial variability in column-to-surface correlations.