Disparities in Air Pollution Exposure in the United States by Race/Ethnicity and Income, 1990–2010

BACKGROUND: Few studies have investigated air pollution exposure disparities by race/ethnicity and income across criteria air pollutants, locations, or time. OBJECTIVE: The objective of this study was to quantify exposure disparities by race/ethnicity and income throughout the contiguous United States for six criteria air pollutants, during the period 1990 to 2010. METHODS: We quantified exposure disparities among racial/ethnic groups (non-Hispanic White, non-Hispanic Black, Hispanic (any race), non-Hispanic Asian) and by income for multiple spatial units (contiguous United States, states, urban vs. rural areas) and years (1990, 2000, 2010) for carbon monoxide (CO), nitrogen dioxide ([Formula: see text]), ozone ([Formula: see text]), particulate matter with aerodynamic diameter [Formula: see text] ([Formula: see text]; excluding year-1990), particulate matter with aerodynamic diameter [Formula: see text] ([Formula: see text]), and sulfur dioxide ([Formula: see text]). We used census data for demographic information and a national empirical model for ambient air pollution levels. RESULTS: For all years and pollutants, the racial/ethnic group with the highest national average exposure was a racial/ethnic minority group. In 2010, the disparity between the racial/ethnic group with the highest vs. lowest national-average exposure was largest for [Formula: see text] [54% ([Formula: see text])], smallest for [Formula: see text] [3.6% ([Formula: see text])], and intermediate for the remaining pollutants (13%–19%). The disparities varied by U.S. state; for example, for [Formula: see text] in 2010, exposures were at least 5% higher than average in 63% of states for non-Hispanic Black populations; in 33% and 26% of states for Hispanic and for non-Hispanic Asian populations, respectively; and in no states for non-Hispanic White populations. Absolute exposure disparities were larger among racial/ethnic groups than among income categories (range among pollutants: between 1.1 and 21 times larger). Over the period studied, national absolute racial/ethnic exposure disparities declined by between 35% ([Formula: see text]; [Formula: see text]) and 88% ([Formula: see text]; CO); relative disparities declined to between [Formula: see text] ([Formula: see text]; i.e., nearly zero change) and [Formula: see text] (CO; i.e., a [Formula: see text] reduction). DISCUSSION: As air pollution concentrations declined during the period 1990 to 2010, absolute (and to a lesser extent, relative) racial/ethnic exposure disparities also declined. However, in 2010, racial/ethnic exposure disparities remained across income levels, in urban and rural areas, and in all states, for multiple pollutants. https://doi.org/10.1289/EHP8584