Disparities in PM 2.5 air pollution in the United States

Particulate air pollution in the contiguous United States has decreased considerably over recent decades, but where exactly has that progress been made? Colmer et al. analyzed 36 years of data and found that the spatial distribution of fine particulate matter concentrations has remained largely unchanged over that interval (see the Perspective by Ma). Although, fine particulate pollution levels have dropped overall, those areas that were most and least polluted in 1981 remain so today. We may have made important strides in pollution control, but we have been less successful in addressing disparities of exposure between communities. Science , this issue p. 575 ; see also p. 503 Particulate air pollution in the United States has fallen substantially over the past four decades, but the relative pattern persists. Air pollution at any given time is unequally distributed across locations. Average concentrations of fine particulate matter smaller than 2.5 micrometers in diameter (PM 2.5 ) have fallen over time. However, we do not know how the spatial distribution of PM 2.5 has evolved. Here, we provide early evidence. We combine 36 years of PM 2.5 concentrations measured over ~8.6 million grid cells with geographic, economic, and demographic data from ~65,000 U.S. census tracts. We show that differences in PM 2.5 between more and less polluted areas declined substantially between 1981 and 2016. However, the most polluted census tracts in 1981 remained the most polluted in 2016. The least polluted census tracts in 1981 remained the least polluted in 2016. The most exposed subpopulations in 1981 remained the most exposed in 2016. Overall, absolute disparities have fallen, but relative disparities persist.