US air pollution rates on the decline but pockets of inequities remain

The research provides a national investigation of air pollution emission changes in the 40 years following the enactment of the Clean Air Act (CAA). Until now, studies have primarily focused on evaluating air pollution disparities at a single time point, focusing on pollutant concentrations instead of emissions. A focus on emissions, however, has more direct implications for regulations and policies. In this study, the researchers used county-level data to evaluate racial/ethnic and socioeconomic disparities in air pollution emissions changes in the contiguous U.S. from 1970 to 2010.

"The analyses provide insight on the socio-demographic characteristics of counties that have experienced disproportionate decreases in air pollution emissions over the last forty years," said Yanelli Nunez, PhD, the study's first author, who is a scientist in the Department of Environmental Health Sciences at Columbia Mailman School of Public Health and affiliated with PSE Healthy Energy. Additionally, by analyzing air pollution emissions, the researchers identified specific pollution source sectors that are potentially important contributors to air pollution exposure disparities.

Nunez and colleagues leveraged air pollution emissions data from the Global Burden of Disease Major Air Pollution Sources inventory to analyze air pollutant emissions from six pollution source sectors: industry (sulfur dioxide), energy (sulfur dioxide and nitrogen oxides), agriculture (ammonia), on-road transportation (nitrogen oxides), commercial (nitrogen oxides), and residential (particles of organic carbon).

On average, national U.S. air pollution emissions declined substantially from 1970 to 2010 from all source sectors the researchers considered except for ammonia emissions from agriculture and organic carbon particle emissions from the residential sector, which the researchers indicate is primarily from using solid biofuels for indoor heating. The most pronounced emission decreases were observed for sulfur dioxidefrom industrial and energy generation activities. Nitrogen oxide emissions from transportation, commercial activities, and energy generation decreased moderately.

Despite the overall downward trends for most pollutants, the researchers found that certain populations experienced relatively smaller reductions or even increases in air pollution emissions. For instance, an increase in a county's average Hispanic or Indian American population percentage resulted in a relative increase in sulfur dioxide, nitrogen oxides, and ammonia emissions from the industry, energy generation, and agriculture sectors, respectively. Additionally, an increase in the county median family income was linked with an increase in the magnitude of emissions reductions in every pollution source sector the researchers analyzed, except agriculture.

"Air pollution emissions do not perfectly capture population air pollution exposure, and we also know that neighborhood-level air pollution inequities are common, which we were not able to analyze in this study given the data at hand," noted Marianthi-Anna Kioumourtzoglou, ScD, associate professor of environmental health sciences at Columbia Mailman School, and senior author. "In this study, we provide information about potential racial/ethnic and socioeconomic inequalities in air pollution reductions nationwide from major air pollution sources, which can inform regulators and complement local-level analysis."

"Policies specifically targeting reductions in overburdened populations could support more just reductions in air pollution and reduce disparities in air pollution exposure," observed Dr. Nunez. "This is an important lesson gained from 53 years of Clean Air Act implementation, which is particularly relevant as we develop policies to transition to renewable energy sources, which will have a collateral impact on air quality and, as a result, on public health."

Co-authors are Jaime Benavides^, Jenni A. Shearston, Misbath Daouda, and Jeff Goldsmith, Columbia University Mailman School of Public Health; Joan Casey, Columbia Mailman School and the University of Washington; Elena Krieger, PSE Healthy Energy; Lucas R.F. Henneman, George Mason University; and Erin McDuffie, University of Washington.

The study was supported by National Institute of Environmental Health Sciences, (P30 ES009089, R01 ES030616, R01 ES028805 and T32 ES007322), The Thomas F. and Kate Miller Jeffress Memorial Trust, Bank of America; and Health Effects Institute (HEI, R-82811201).