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U.S. air pollution levels have dropped, but not for everyone

There has been a significant decline in U.S. air pollution levels in recent decades, but a new study emphasizes that this decrease is not distributed evenly across communities. 

The research, conducted by experts at the Columbia University Mailman School of Public Health, highlights persistent inequities in environmental health impacts.

Environmental justice 

The researchers investigated the complex interaction between air pollution emission reductions and socio-demographic factors, shedding light on an aspect of environmental justice that has been less explored.

“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 study first author Dr. Yanelli Nunez.

Focus of the research 

The study was focused on changes in U.S. air pollution emissions over a 40-year period following the Clean Air Act (CAA) in 1970. 

Unlike previous studies that concentrated on air pollution disparities at a single time point and focused more on pollutant concentrations, this research takes a new approach by examining emissions. This focus is crucial as emissions have more direct implications for regulations and policy-making.

How the research was conducted

The researchers utilized county-level data across the contiguous U.S. to assess racial/ethnic and socioeconomic disparities in the changes in air pollution emissions from 1970 to 2010. 

The team analyzed emissions data from the Global Burden of Disease Major Air Pollution Sources inventory, covering six pollution source sectors: industry, energy, agriculture, on-road transportation, commercial, and residential.

Key findings

The findings revealed that, on average, U.S. air pollution emissions have declined significantly from most source sectors. 

The experts found notable reductions in sulfur dioxide from industrial and energy generation activities, and moderate decreases in nitrogen oxide emissions from transportation, commercial activities, and energy generation. 

However, emissions from agriculture (ammonia) and residential sectors (organic carbon particles) did not follow this downward trend. Residential emissions are primarily associated with the use of solid biofuels for indoor heating.

Disproportionate benefits

A concerning aspect of the study’s findings is the uneven nature of these reductions. The researchers found that counties with higher percentages of Hispanic or Indian American populations experienced relative increases in emissions from various sectors. 

Furthermore, higher median family incomes within a county were linked to greater reductions in emissions across nearly all sectors, except agriculture. These disparities indicate that certain populations have not benefited equally from the overall improvements in air quality.

“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 study senior author Professor Marianthi-Anna Kioumourtzoglou.

Broader implications 

“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,” explained Professor Kioumourtzoglou.

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

The study is published in the journal Nature Communications.

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