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

Abstract

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 ($O_3$), particulate matter with aerodynamic diameter $\le 2.5\mu m$ (${\mathrm{PM}}_{2.5}$; excluding year-1990), particulate matter with aerodynamic diameter $\le 10\mu m$ (${\mathrm{PM}}_{10}$), 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% ($4.6\text{ppb}$)], smallest for $O_3$ [3.6% ($1.6\text{ppb}$)], 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% ($0.6{6\mu g/m}^3$; ${\mathrm{PM}}_{2.5}$) and 88% ($0.35\text{ppm}$; 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.

Figure 1.

Distribution of exposure to pollutants in years 1990, 2000, and 2010, stratified by racial/ethnic group, for (A) $\mathrm{P}{\mathrm{M}}_{2.5}$, (B) $\mathrm{N}{\mathrm{O}}_2$, (C) ${\mathrm{O}}_3$, (D) $\mathrm{S}{\mathrm{O}}_2$, (E) $\mathrm{P}{\mathrm{M}}_{10}$, and (F) CO. For all panels, the highest/lowest bound represents the 90th/10th percentile value, the box shows the 25th and 75th percentiles, and the horizontal line in the box represents the median. Color circles indicate the national population-weighted mean. ${\mathrm{PM}}_{2.5}$ has no estimates in 1990 because of a lack of monitoring data prior to 1999. Note: CO, carbon monoxide; Hispanic, Hispanic people of any race(s); NH, non-Hispanic; ${\mathrm{NO}}_2$, nitrogen dioxide; ${\mathrm{O}}_3$, ozone; ${\mathrm{PM}}_{2.5}$, fine particulate matter with aerodynamic diameter less than or equal to $2.5\text{\hspace{0.17em}micrometers}$; ${\mathrm{PM}}_{10}$ $10\text{\hspace{0.17em}micrometers}$; ${\mathrm{SO}}_2$, sulfur dioxide.

Figure 2.

Relationship between the proportion of racial/ethnic minority residents in census block groups and average criteria air pollution concentrations in the years 1990, 2000, and 2010 for (A) $\mathrm{P}{\mathrm{M}}_{2.5}$, (B) $\mathrm{N}{\mathrm{O}}_2$, (C) ${\mathrm{O}}_3$, (D) $\mathrm{S}{\mathrm{O}}_2$, (E) $\mathrm{P}{\mathrm{M}}_{10}$, and (F) CO. For each panel, the thicker portion of the line indicates the 25th to 75th percentile of census block groups, the thin line indicates the 10th to 90th percentiles, the dashed line indicates the 1st to 99th percentiles, and the diamond icon indicates the median. Note: CO, carbon monoxide; Hispanic, Hispanic people of any race(s); NH, non-Hispanic; ${\mathrm{NO}}_2$, nitrogen dioxide; ${\mathrm{O}}_3$, ozone; ${\mathrm{PM}}_{2.5}$, fine particulate matter with aerodynamic diameter less than or equal to $2.5\text{\hspace{0.17em}micrometers}$; ${\mathrm{PM}}_{10}$ $10\text{\hspace{0.17em}micrometers}$; ${\mathrm{SO}}_2$, sulfur dioxide.

Figure 3.

Population-weighted criteria air pollution concentration in 2010 for 16 household income groups, stratified by race/ethnicity, for (A) $\mathrm{P}{\mathrm{M}}_{2.5}$, (B) $\mathrm{N}{\mathrm{O}}_2$, (C) ${\mathrm{O}}_3$, (D) $\mathrm{S}{\mathrm{O}}_2$, (E) $\mathrm{P}{\mathrm{M}}_{10}$, and (F) CO. For all panels, each data point represents pollution exposure for one income category and racial/ethnic group. Values plotted for household income are, for values below $\$\mathrm{200,000}$ (i.e., for the first 15 income categories), the midpoint value; for the highest income category (“$>\$\mathrm{200,000}$”), the value plotted is the low end of the range ($\$\mathrm{200,000}$). Note: Asian, Hispanic and non-Hispanic Asian people; Black, Hispanic and non-Hispanic Black people; CO, carbon monoxide; Hispanic, Hispanic people of any race(s); NH White, non-Hispanic White people; ${\mathrm{NO}}_2$, nitrogen dioxide; ${\mathrm{O}}_3$, ozone; ${\mathrm{PM}}_{2.5}$, fine particulate matter with aerodynamic diameter less than or equal to $2.5\text{\hspace{0.17em}micrometers}$; ${\mathrm{PM}}_{10}$ $10\text{\hspace{0.17em}micrometers}$; ${\mathrm{SO}}_2$, sulfur dioxide.

Figure 4.

State racial/ethnic disparities in pollution exposure in 2010, showing the difference between (1) NH White vs. state average, (2) NH Black vs. state average, (3) Hispanic vs. state average, (4) NH Asian vs. state average, and (5) Minority vs. NH White for the six pollutants. (A) $\mathrm{P}{\mathrm{M}}_{2.5}$, (B) $\mathrm{N}{\mathrm{O}}_2$, (C) ${\mathrm{O}}_3$, (D) $\mathrm{S}{\mathrm{O}}_2$, (E) $\mathrm{P}{\mathrm{M}}_{10}$, and (F) CO, and (G) average across the six pollutants. Columns 1–4: exposure disparity relative to state average; calculated as mean exposure for a racial/ethnic group in that state minus the overall mean for that state, then divided by the national overall mean. Column 5: exposure disparity for racial/ethnic minorities relative to the racial/ethnic majority group; calculated as mean exposure for racial/ethnic minorities minus mean exposure for non-Hispanic White people, then divided by the national overall mean. Mean values are population-weighted. States displayed in white indicate that the disparity is within $\pm 5\%$ of the national overall mean. Purple shading indicates that mean exposures are higher than average by more than 5% of the national overall mean (columns 1–4) or that mean exposures are higher for racial/ethnic minorities than for non-Hispanic White people, by more than 5% of the national overall mean (column 5). Orange shading indicates the reverse: mean exposures are lower than average for that group (columns 1–4) or mean exposures are lower for racial/ethnic minorities than for non-Hispanic White people (column 5), and the disparity is greater than 5% of the national overall mean. See Excel Table S1 for corresponding numeric data. Note: CO, carbon monoxide; Hispanic, Hispanic people of any race(s); NH, non-Hispanic; ${\mathrm{NO}}_2$, nitrogen dioxide; ${\mathrm{O}}_3$, ozone; ${\mathrm{PM}}_{2.5}$, fine particulate matter with aerodynamic diameter less than or equal to $2.5\text{\hspace{0.17em}micrometers}$; ${\mathrm{PM}}_{10}$ $10\text{\hspace{0.17em}micrometers}$; ${\mathrm{SO}}_2$, sulfur dioxide.