U.S. Air Pollution Rates Down, but Vary by Demographics

Air pollution emissions in the United States have decreased considerably since the Clean Air Act of 1970 was enacted, but the benefits have not always been equally felt.

According to a new study by researchers at Columbia University Mailman School of Public Health, the amount of the improvements is largely dependent on demographics, with socioeconomic and racial/ethnic inequalities in air pollution reductions felt especially in the energy and industry sectors, a press release from the Columbia Mailman School said.

The study was an examination of changes in emissions from air pollution in the U.S. over the past four decades. Previous studies have looked mostly at imbalances in concentrations of pollutants at a given point in time, rather than at emissions.

In looking into the socioeconomic and racial/ethnic disparities regarding changes in air pollution emissions, the research focused on data from counties in the contiguous U.S. during the period 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 lead author of the study Yanelli Nunez, who is an environmental health scientist in the Columbia Mailman School of Public Health’s Department of Environmental Health Sciences, in the press release.

By focusing on air pollution emissions, Nunez and colleagues were able to pinpoint sectors that are potentially contributing to disparities in exposure.

The researchers used Global Burden of Disease Major Air Pollution Sources data in analyzing emissions from six air pollution source sectors, including energy (nitrogen oxides and sulfur dioxide), road transportation (nitrogen oxides), industry (sulfur dioxide), agriculture (ammonia); residential (organic carbon particles) and commercial (nitrogen oxides).

Average air pollution emissions in the U.S. have decreased markedly during the 40-year study period from every source sector except residential organic carbon particles — mostly from solid biofuels used for indoor heating — and agricultural ammonia emissions.

The biggest emissions decreases were for sulfur dioxide from energy generation and the industrial sectors. Nitrogen oxide emitted by energy generation, commercial activities and transportation showed moderate decreases.

Although emissions from most pollutants had gone down, the research team discovered that certain populations had increases in emissions or relatively smaller reductions. One example is that an increase in the average Indian American or Hispanic population percentage in a county was associated with a relative increase in nitrogen oxides, sulfur dioxide and ammonia emissions from energy generation, industry and the agricultural sectors, respectively.

“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,” said Marianthi-Anna Kioumourtzoglou, senior author of the study and a Columbia Mailman School associate professor of environmental health sciences, in the press release.

An increase in the amount of emissions reductions was also associated with an increase in the median family income in a county in all pollution source sectors examined by the researchers except agriculture.

“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,” Kioumourtzoglou added.

The findings of the study were published in the journal Nature Communications.

“Policies specifically targeting reductions in overburdened populations could support more just reductions in air pollution and reduce disparities in air pollution exposure,” Nunez explained. “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.”