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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 (${\mathrm{NO}}_2$), ozone (${\mathrm{O}}_3$), particulate matter with aerodynamic diameter $\le 2.5\mathrm{\mu }\mathrm{m}$ (${\mathrm{PM}}_{2.5}$; excluding year-1990), particulate matter with aerodynamic diameter $\le 10\mathrm{\mu }\mathrm{m}$ (${\mathrm{PM}}_{10}$), and sulfur dioxide (${\mathrm{SO}}_2$). 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 ${\mathrm{NO}}_2$ [54% ($4.6\text{\hspace{0.17em}ppb}$)], smallest for ${\mathrm{O}}_3$ [3.6% ($1.6\text{\hspace{0.17em}ppb}$)], and intermediate for the remaining pollutants (13%–19%). The disparities varied by U.S. state; for example, for ${\mathrm{PM}}_{2.5}$ 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% ($0.6{6\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$; ${\mathrm{PM}}_{2.5}$) and 88% ($0.35\text{\hspace{0.17em}ppm}$; CO); relative disparities declined to between $0.99\times$ (${\mathrm{PM}}_{2.5}$; i.e., nearly zero change) and $0.71\times$ (CO; i.e., a $\sim 29\%$ 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