Air pollution is responsible for approximately 9 million premature deaths globally each year, which is double the number caused by war, other forms of violence, HIV/AIDS, tuberculosis, and malaria combined. Fine particulate matter air pollution poses significant dangers as these tiny particles can easily penetrate the lungs, bloodstream, and brain, leading to serious health issues such as infant mortality, reduced life expectancy for adults, cancer, lung disease, and heart disease. The concentration of fine particulate matter pollution in the United States has decreased by about 70% since 1981.
However, newly published research shows that the most polluted areas in 1981 remain the most polluted today, while the least polluted areas have retained their status. Areas that were predominantly white and wealthier in 1981 have experienced a relative reduction in pollution over time. Furthermore, areas that became whiter and wealthier from 1981 to 2016 have also seen a relative decrease in pollution levels. In contrast, communities and groups that were most exposed to fine particle pollution 40 years ago—often low-income and minority communities—continue to face high pollution levels. As experts in environmental economics and public policy, we believe that the persistence of air pollution disparities is important. We are concerned with who benefits and who bears disadvantages.
Additionally, these findings have implications for environmental public policy. If the goal of policy is to lessen pollution disparities, there is still much work to be done. It has been well-documented that air pollution varies by location due to factors such as economic activities and climate. It is also known that lower-income households, people of color, and other disadvantaged communities face higher exposure to air pollution. Since research links air pollution with premature death, lower educational achievement, and reduced lifetime earning potential, these disparities contribute to economic, health, and social inequalities. What hasn’t been entirely clear is how much these air pollution disparities have shifted over time. We aimed to analyze these particulate matter pollution disparities across the U.S. systematically over several years.
The necessary data to answer this question was unavailable until recently. The U.S. Environmental Protection Agency monitors nationwide levels of fine particle pollution, known as PM2.5, but these monitors provide sparse coverage, primarily in urban areas. In our study, we used newly available data tracking PM2.5 concentrations in over 8.6 million different U.S. locations from 1981 to 2016. This data was gathered from satellite observations, pollution transport modeling, and records from pollution monitors.
It offers a detailed annual view of fine particulate matter concentrations for each of the roughly 65,000 Census tracts, or neighborhoods, in the U.S. Our analysis indicates some progress over the past 35 years in closing the gaps between the most and least polluted locations. In 1981, PM2.5 concentrations in the most polluted 10% of census tracts were 34 micrograms per cubic meter on average, while the least polluted 10% registered 13 micrograms per cubic meter—a difference of 22 micrograms per cubic meter.
By 2016, PM2.5 concentrations in the most polluted 10% were down to 10 micrograms per cubic meter, and those in the least polluted 10% averaged 4 micrograms per cubic meter, leaving a difference of 6 micrograms per cubic meter. These reduced gaps likely suggest that disparities in pollution-related health, economic standings, and productivity among different locations are also narrowing. Nevertheless, while pollution gaps have diminished for some disadvantaged groups, this has not uniformly been the case. We decided next to examine whether specific locations had more or less pollution than others and if the most polluted areas remained consistent over time. For this, we ranked each neighborhood annually from most to least polluted using our data. We then assessed how these rankings changed from 1981 to 2016 and found a surprising persistence. Areas that were most polluted in 1981 are still the most polluted now, while those with the least pollution originally continue to be the least polluted.
Communities disadvantaged in 1981 continue to be exposed to high pollution levels today. If anything, relative disparities have become worse for poorer and Hispanic communities. Over the past 40 years, Southern California has accounted for a large portion of the most polluted areas, while the least polluted areas are spread across the U.S. For instance, a child born in Los Angeles County in 2016 faced 42% more fine particle pollution exposure than the average American child and 26% more than a child in New York City.
There have been changes in the relative pollution standings of some areas. Ohio, West Virginia, eastern Kentucky, and the Northeast Corridor saw relative declines in pollution between 1981 and 2016. Conversely, California’s Central and Imperial valleys, southwestern Arizona, southern Texas, and parts of Arkansas and Oklahoma became relatively more polluted. Our findings highlight the extent and persistence of air pollution disparities in the U.S. Although particulate matter air quality has generally improved over time—leading to health, economic, and productivity gains for most Americans—relative disparities between some locations remain a concern. In our opinion, persistent disparities between more and less polluted communities are important because concepts like fairness, equity, and justice are inherently relative. We evaluate these based on who is advantaged and who is not at any given time. Pollution disparities translate into disparities in health, economy, and society.
For decades, federal and state environmental policies have aimed to ensure all Americans receive equal protection from environmental hazards. The EPA’s definition of environmental justice states that “no group of people should bear a disproportionate share of the negative environmental consequences.” Our research, however, suggests that the U.S. is lagging in achieving this goal.