Racial and ethnic minorities in the U.S. are consistently exposed to more deadly fine particulate air pollution on average than white people, a disparity that is present across virtually all regions and income levels, research published Wednesday shows.

The Science Advances paper, which quantifies the effects of air pollution from 5,000 different sources, adds significantly to researchers' understanding of racial disparities in air pollution, which is the number one environmental cause of death in the United States. Air pollution kills an estimated 85,000 to 200,000 Americans per year through heart disease, cancer, brain damage and other adverse health effects. 

This burden, however, is not spread evenly. White people in the U.S. are exposed to an average of 5.9 micrograms of fine particulate air pollution per day, compared with 7.9 micrograms for Black people, 7.2 for Hispanics and 7.7 for Asians, the researchers found. The Environmental Protection Agency says breathing an average of 12 micrograms or less of fine particulate pollution per day is safe, but exposure underneath that threshold can still cause health problems. 

While racial gaps in pollution have been acknowledged for decades, the Science Advances paper also adds to researchers' understanding of the disparities by quantifying how individual sources of pollution affect different groups. Looking at a wide variety of emissions source types, white people are exposed to lower-than-average concentrations of pollution from 60% of sources. By contrast, Black people are exposed to higher-than-average pollution from 75% of sources, Hispanics are exposed to higher-than-average pollution from 87% of sources, and Asians are exposed to higher-than-average pollution from 73% of sources.

"The vast majority of the pollution is coming from sources that disproportionately affect people of color," said lead author Christopher Tessum, an assistant professor of environmental engineering at the University of Illinois at Urbana-Champaign.

The researchers sorted the 5,000 types of air pollution sources into 14 broader sectors, such as industrial, construction and commercial cooking emissions. People of color were disproportionately exposed to 12 out of 14 of these sectors. The only sectors where white people were disproportionately exposed to pollution were agriculture and coal-fired electric utilities, the researchers found. 

Overall, this disparity exists across both rural and urban areas and when controlling for income. 

"People of color at all different income levels get more of their pollution from sources that disproportionately affect them than do white people of any income level," Tessum said.

A notable exception to this pattern is Asians in California urban areas, including Los Angeles, San Francisco and San Jose, who are less exposed to air pollution than residents overall, the researchers found, though it was unclear why this is the case. 

"If you removed California from the analysis, then you're back to the same pattern," Tessum said in regard to Asians being more exposed to air pollution than whites.

Tessum wrote the paper alongside David Paolella and Julian Marshall of the University of Washington; Sarah Chambliss of the University of Texas at Austin; Joshua Apte of the University of California, Berkeley; and Jason Hill of the University of Minnesota. 

The project was initially conceived as a study of air pollution by source, through which researchers could identify what sources of pollution should be prioritized for future regulation. However, Tessum said the sheer number of sources of pollution became overwhelming.

"The results that we got don't really support that type of approach, just because you can't really prioritize much when everything is contributing to the problem," said Tessum, who has a Ph.D. in civil, environmental and geo-engineering from the University of Minnesota. 

The researchers then decided to shift the paper into a broader discussion of racial disparities. 

While the Science Advances paper only measured exposure to air pollution, Tessum told The Academic Times that individuals' reactions to air pollution vary depending on demographic factors. Black and Hispanic people are less likely than white people to have insurance, for example, meaning that pollution-related medical issues can be deadlier for minorities.

Tessum said that disparities in health responses to air pollution should be examined in further studies and incorporated into government policy. He also said that both researchers and politicians should make better efforts to incorporate residents of the hardest-hit communities into conversations about air pollution. 

"Our results were surprising to us as researchers. They wouldn't necessarily be surprising to the people that live in these communities," he said. "We can point out the problem in an analytical sense, backed by data, but any solution to the problem really needs to have people who are most affected at the table." 

The paper, "PM2.5 polluters disproportionately and systemically affect people of color in the United States," published April 28 in Science Advances, was authored by Christopher Tessum, University of Illinois at Urbana-Champaign; David Paolella and Julian Marshall, University of Washington; Sarah Chambliss, University of Texas at Austin; Joshua Apte, the University of California, Berkeley; and Jason Hill, University of Minnesota.