What caused racial disparities in particulate exposure to fall? New evidence from the Clean Air Act and satellite-based measures of air quality

What is this research about and why did you do it?

It is widely believed that low income and racial minority groups face disproportionately high exposure to environmental harm. However, the evidence has been piecemeal given the limited quality of the data. Leveraging newly available data, we ask what are the gaps in exposure between racial groups, and how have they evolved over time? We show that the gap between the non-Hispanic white population and African Americans is narrowing over time, and investigate what is the specific contribution of the Clean Air Acts.

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How did you answer this question?

We combine new, high-resolution pollution data for the entire U.S. with over 30 million individual responses from the Census and American Community Surveys to provide a new national picture of disparities in U.S. pollution exposure by race and their evolution over time. We then use quantile regression methods to examine determinants of exposure to pollution at different points in the distribution. Finally, we use event study methods to examine the extent to which reductions in racial gaps in pollution were due to tougher standards on particulates that came into effect in 2005.

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What did you find?

We show that there is a racial gap in pollution exposure because Black Americans are systematically more likely to live in the most polluted areas. However, this gap decreased markedly between 2000 and 2015. A small share of the convergence (~10 percent) was due to mobility, especially white Americans moving to more polluted, central city areas. The largest component was due to the tightening of Clean Air Acts standards in 2005. The CAA targets the most polluted areas for clean up, and since Black Americans disproportionately live in these areas, the law helped close gaps in pollution exposure.

National US racial differences in exposure to PM2.5. This figure plots the author’s estimate of mean PM2.5 exposure by year, separately for African-Americans and the non-Hispanic White population. The observed Black-White gap in mean pollution exposure was 1.6 μg/m³ in 2000, narrowing to 0.54 μg/m³ in 2015. Although African American exposure fell more, it was higher to begin with, so that the percentage reduction is similar for both Black and White people. PM2.5 stands for particulate matter 2.5 (PM_2.5), and refers to tiny particles or droplets in the air that are two and one half microns or less in width.

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What implications does this have for the research on wealth concentration or economic inequality?

Air pollution has pervasive negative effects on human populations including higher risk of death, greater morbidity, and reductions in cognitive ability and labor productivity, as well as negative effects on property values. If poor and minority neighborhoods are differentially exposed to pollution, then that may be an important cause of differences in these outcomes. Since children are especially vulnerable to pollution, these disparities could also have a significant effect on the next generation.

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What are the next steps in your agenda?

We plan to continue to investigate disparities in exposure to pollution and the negative effects that they can have on a wide range of outcomes.

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Citation

This paper can be cited as follows: Currie, J., Voorheis, J., and Walker, R. (2023). "What Caused Racial Disparities in Particulate Exposure to Fall? New Evidence from the Clean Air Act and Satellite-Based Measures of Air Quality." American Economic Review, 113(1), pp. 71-97.