Racial-ethnic disparities in exposure to NO2 and PM2.5 in the United States: Insights from spatial decomposition of ambient concentrations

Abstract

BACKGROUND AND AIM: In the US, average exposure to ambient NO2 and PM2.5 is higher for racial-ethnic minorities (Hispanic, Black, and Asian people) than for the majority (White people). We investigate spatially decomposed concentrations, and how differences among racial-ethnic groups shed light on patterns underlying existing disparities. METHODS: We use Census data for demographic information and national empirical models for ambient concentrations. We employ two approaches for spatially decomposed concentrations, subdividing concentration prediction by (1) length scale of variability (1 km, 1-10 km, 10-100 km, and 100 km), and (2) political boundaries: (a) across-state; then, the remaining (i.e., within-state) component is divided into (b) urban versus rural, (c) within-rural, (d) across-urban (i.e., differences across urban areas within one state), and (e) within urban (i.e., differences within that urban area). We calculate national racial-ethnic exposure disparities using those decomposed concentrate surfaces. RESULTS:The largest contributors to absolute disparities are the between-state and within-urban components: racial-ethnic minority populations live in the more-polluted cities within their state and in the more-polluted part of their city (exception: PM2.5 for Asian people). The 1-100 km component contributes the most to disparities (exception: for NO2 for Black people, 1 km contributes the most). For PM2.5, the 100 km and between-state components lead to higher-than-average concentrations for Black people and lower-than-average for Hispanic, Asian people; this finding reflects, in part, in which regions of the US people live. CONCLUSIONS:Within-urban disparities, which are the focus of substantial research on environmental justice, are important but are only one contributor to national disparities. Overall, disparities for NO2 come mostly from local variability (within-state; 1-100 km range) while for PM2.5 they relate more with regional sources (across-state; 100 km). KEYWORDS: Environmental Justice, Air Pollution, Spatial Decomposition