National Patterns in Environmental Injustice and Inequality: Outdoor NO2 Air Pollution in the United States

Environmental injustice often places disproportionate health risks on people who are already the most vulnerable or susceptible to those risks. Since the earliest US environmental justice studies in the 1960s–1980s, disparities in exposures to environmental risks (e.g., landfills, hazardous waste sites, polluting industries, vehicle traffic) by socioeconomic status (SES) have been widely documented Air pollution is a priority environmental risk in the United States (US): urban outdoor air pollution is one of the top ten causes of death in high-income nations. Low-SES communities are often disproportionately exposed to air pollution and also may be more susceptible to air pollution owing to other underlying disparities in, for example, access to health care This paper applies a national-scale analysis to quantify US-wide NO2 concentration patterns by socioeconomic status characteristics. It provides quantitative information for understanding how environmental equality and justice for air pollution vary among communities and regions across the US. A goal of this study is to identify US locations with highest priority environmental justice and equality concerns attributable to NO2 and co-emitted air pollutants. We investigated environmental injustice and inequality in residential outdoor NO2 air pollution for the contiguous US population. Nationally, inequality in average NO2 concentration is greater than inequality in average income. Nonwhites experience 4.6 ppb (38%) higher residential outdoor NO2 concentrations than whites – an exposure gap that has potentially large impacts to public health. Within individual urban areas, after controlling for income, nonwhites are on average exposed to higher outdoor residential NO2 concentrations than whites; and, after controlling for race, lower-income populations are exposed to higher outdoor residential average NO2 concentrations than higher-income populations. Results given here provide strong US wide evidence of ambient NO2 air pollution injustice and inequality, establish a national context for studies of individual metropolitan areas and regions, and enable comprehensive tracking over time. Hopefully results given here will usefully allow policy-makers to identify counties and urban areas with highest priority NO2 air pollution environmental justice and equality concerns.