Across the Northeastern and mid-Atlantic regions, Latino, Asian American, and African American residents are disproportionately exposed to dangerous air pollution, a new study from a science research and advocacy group suggests.

And in Pennsylvania, the burden for some communities is especially profound, with concentrations of air pollution in parts of Philadelphia and Pittsburgh three times higher than the regional average.

The report, released this week by the Union of Concerned Scientists (UCS), is based on data from the U.S. Environmental Protection Agency on the average concentration of a type of air pollution, known as particulate matter (PM) 2.5, in 12 states and Washington, D.C.

PM2.5 consists of airborne particles that are less than 2.5 micrometers, or 1/30th the width of a human hair. Their small size makes them especially dangerous, as they can enter the bloodstream. A number of studies have linked exposure to PM2.5 with lung and heart diseases, asthma attacks, and premature death.

The UCS study found that, on average, Latinos in the 12 states studied are exposed to 75 percent more PM2.5 pollution than white residents. Asian Americans are exposed to 73 percent higher levels, and African Americans to 61 percent higher levels.

“The disparity is quite blatant,” said Maria Cecilia Pinto de Moura, who researches transportation energy and emissions for UCS and co-authored the report. “Communities of color have known for a very long time that they breathe bad air. We are just providing quantitative evidence to show that.”

In Philadelphia, which the report cited as the most polluted county in Pennsylvania, the findings reflect long-established concerns around environmental justice — many of which have risen to the forefront again since the explosion at a refinery in South Philadelphia last week.

Although the city health department said air tests following the fire show no immediate cause of alarm for workers at the refinery or residents nearby, many are skeptical. The refinery has long been the single biggest polluter in the city, and in 2017, the NAACP and Clean Air Task Force issued a joint report that singled out refineries as having an outsize impact on African American communities regarding air quality. Of all metro areas in the United States, Philadelphia had the eighth highest number of asthma attacks for African American children.

The UCS study didn’t look at PM2.5 pollution created by power plants. The researchers focused solely on pollution caused by cars, trucks, and buses. That means the findings may be an underestimate, they said.

PM2.5 pollution can be generated from indoor sources such as tobacco smoke, cooking, and fireplaces as well as outdoor sources, such as vehicle exhaust or forest fires.

Vehicles are problematic because they produce PM2.5 in two ways, Pinto de Moura said. One is the combustion of fossil fuels that emits PM2.5 directly from tailpipes. The second is from chemical reactions that occur when other substances emitted in exhaust, like nitrous oxide, combine with chemicals in the atmosphere to produce PM2.5.

In Pennsylvania, areas where PM2.5 pollution is less than half the state average are overwhelmingly white, the report found. In areas where pollution levels are more than twice the state average, the majority of residents are people of color. African Americans, Latinos, and Asian Americans live in areas where the air is, on average, 40 percent to 50 percent more polluted.

While the disparity is slightly less in New Jersey, people of color are still exposed to air that is 15 percent to 30 percent more polluted than that in areas with predominantly white populations.

The report points to a history of public policy decisions that placed communities of color farther from public transit and closer to junctions of major interstates as the cause.

But communities of color are not the only ones affected.

The areas of highest pollution across the region are often in major cities, which have high numbers of residents of all demographics. For instance, in New York City, African American and Latino residents in the Bronx are exposed to some of the highest levels of pollution in the region, but the significantly white population of Manhattan also breathes highly polluted air.

Pinto de Moura hopes the report motivates cities and states to invest in cleaner transportation. That could include switching to electric buses, creating rebate programs to make electric cars affordable for low- and middle-income people, and improving public transit.

"It’s not enough to have a clean transportation system,” she said. “We have to put them in the communities that need them most.”