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Neighborhood Differences in Air Pollution Persist for Decades

The most and least polluted U.S. neighborhoods in 1981 remained the most and least polluted more than 30 years later. | Jonathan Colmer, Ian Hardman, Jay Shimshack, John Voorheis

While the overall amount of air pollution above the United States has declined considerably over the past several decades, meaningful disparities in access to clean air across the nation continue to persist.

The most and least polluted U.S. neighborhoods in 1981 remain the most and least polluted more than 30 years later, according to a study published in the July 31 issue of Science. Despite the great progress made in controlling air pollution, socioeconomically disadvantaged communities are far more likely to have had higher levels of exposure to harmful fine particulate air pollution at any given time.

"Reducing environmental disparities has been a stated objective of U.S. environmental policy for decades. Federal and state guidelines aim for all people to enjoy the same degree of protection from environmental hazards and argue that no groups should bear a disproportionate share of pollution," said the study's lead author Jonathan Colmer, a researcher at the University of Virginia.

"Our results suggest that we are falling short on this front."

Fine particulate air pollution — ambient airborne particles smaller than 2.5 microns in size — is one of the largest environmental risk factors for human health worldwide. Formed in the surrounding atmosphere as various chemicals from burning fuels and emissions interact, the particles are small enough to make their way deep into the lungs when inhaled. This type of air pollution is associated with a wide variety of acute and chronic illnesses, including deadly lung cancers and cardiovascular diseases.

Overall improvements in air quality worldwide are commonly associated with greater health and economic well-being. However, like other types of pollution and environmental hazards, increased levels of fine particulate air pollution are often closely correlated with disparities between different demographic and socioeconomic groups. Whether through geographical location, proximity to emissions sources, or underlying poor health, disadvantaged people around the world bear a disproportionate amount of potentially harmful fine particulate air pollution exposure relative to others.

The concentration of fine particulate air pollution in the U.S. has decreased by roughly 70% since 1981. According to Colmer and colleagues, these conclusions are derived from studies that have focused on air pollution averages across broad regions. There is little evidence documenting the distribution of pollution concentration on a more localized scale or how that distribution relates to underlying social and economic factors.

"We know that air quality has consequences for health, wealth and productivity, and that air pollution is unequally distributed across locations and populations. However, we haven't really known how disparities have changed over time," said Colmer. "We wanted to understand the problem in a systematic way."

The research team combined high-resolution air pollution data spanning 1981-2016 with economic and demographic data for nearly 65,000 neighborhoods across the U.S. to evaluate the relative disparities in fine particulate exposure.

Unlike absolute disparities, which are concerned with the differences in pollution concentrations between more and less polluted areas, relative disparities identify where particular locations and population subgroups fall within the spectrum of pollution concentrations.

For each year, the distribution of pollution in neighborhoods across the U.S was ranked according to its fine particulate concentration, which provided each neighborhood's relative standing in the spectrum of least polluted to most polluted areas in the nation.

While the results show that the differences in fine particulate concentrations between more and less polluted areas declined over time, the neighborhoods and communities most polluted in 1981 remained the most polluted in 2016. In contrast, those areas that were least polluted in 1981 remained the least polluted in 2016.

What's more, areas that were whiter and richer in 1981 as well as those that became whiter and richer between 1981 and 2016 have become relatively less polluted over time, said Colmer.

"We still don't have a full understanding of why disparities exist in the first place, let alone why they persist so much through time. Better answers to these questions will lead to sharper policy recommendations," he said.

"We think this paper calls attention to the scope, scale and remarkable persistence of air pollution disparities in the United States," said Colmer. "We aren't the first word, and we won't be the last, on this important topic."

[Credit for associated image: Thomas Hawk/ Flickr]