BACKGROUND: Disparities in exposure to air pollution by race-ethnicity and by socioeconomic status have been documented in the United States, but the impacts of declining transportation-related air pollutant emissions on disparities in exposure have not been studied in detail. OBJECTIVE: This study was designed to estimate changes over time (2000 to 2010) in disparities in exposure to outdoor concentrations of a transportation-related air pollutant, nitrogen dioxide (NO2), in the United States. METHODS: We combined annual average NO2 concentration estimates from a temporal land use regression model with Census demographic data to estimate outdoor exposures by race-ethnicity, socioeconomic characteristics (income, age, education), and by location (region, state, county, urban area) for the contiguous United States in 2000 and 2010. RESULTS: Estimated annual average NO2 concentrations decreased from 2000 to 2010 for all of the race-ethnicity and socioeconomic status groups, including a decrease from 17:6 ppb to 10:7 ppb (−6:9 ppb) in nonwhite [non-(white alone, non-Hispanic)] populations, and 12:6 ppb to 7:8 ppb (−4:7 ppb) in white (white alone, non-Hispanic) populations. In 2000 and 2010, disparities in NO2 concentrations were larger by race-ethnicity than by income. Although the national nonwhite–white mean NO2 concentration disparity decreased from a difference of 5:0 ppb in 2000 to 2:9 ppb in 2010, estimated mean NO2 concentrations remained 37% higher for nonwhites than whites in 2010 (40% higher in 2000), and nonwhites were 2.5 times more likely than whites to live in a block group with an average NO2 concentration above the WHO annual guideline in 2010 (3.0 times more likely in 2000). CONCLUSIONS: Findings suggest that absolute NO2 exposure disparities by race-ethnicity decreased from 2000 to 2010, but relative NO2 exposure disparities persisted, with higher NO2 concentrations for nonwhites than whites in 2010.
Bibliographical noteFunding Information:
The authors are grateful for support from the National Science Foundation (NSF; Sustainability Research Network award 1444745 and grant 0853467) and the U.S. Environmental Protection Agency (EPA; Assistance Agreement RD83587301). This article has not been formally reviewed by the NSF or the U.S. EPA; views expressed herein are solely those of authors and do not necessarily reflect those of either agency.