Minorities across the country are exposed to more of a dangerous air pollutant than whites, resulting in thousands of preventable deaths due to heart disease, according to a University of Minnesota study.

The study, published Tuesday in the journal PLOS ONE, found that nonwhites are exposed to 38 percent more nitrogen dioxide, one of six air pollutants for which the Environmental Protection Agency has caps and requires monitoring by states, than whites. The study is the first to look nationally at this air pollution disparity in such detail, comparing demographic data from the U.S. census to a nitrogen dioxide data set developed at the U.

Minnesota's state health commissioner, Dr. Edward Ehlinger, called the finding "disturbing" but said it wasn't surprising. "While we have on average a very healthy state," he said, "when you're dealing with populations of color, we see that some are structurally disadvantaged in our state."

Breathing nitrogen dioxide is linked to asthma symptoms and heart disease. Cars, trucks and power plants are its largest sources.

The U study looked at nitrogen dioxide levels measured across the country and compared areas within cities based on populations identified in the census as white or nonwhite.

Researchers estimated that reducing exposure levels for people of color to those for whites could prevent 7,000 heart disease deaths nationally each year.

While Minnesota has relatively low levels of nitrogen dioxide, it has one of the largest disparities between minorities and whites — 9.9 parts per billion vs. 6.8, respectively.

Nationally, race had twice as large a correlation as income did, the researchers found, even within the same city.

"On the one hand, you could say everyone knows and expected this … ," said Julian Marshall, the study's senior author and an associate professor of environmental engineering at the U. "But it's still surprising to me to see … these national patterns, and to see that environmental injustice happens almost in all states across the U.S."

In one example from Minnesota, annual average nitrogen dioxide was 22 parts per billion in south Minneapolis and 14 in central Edina. The EPA's annual standard is 53 parts per billion.

The Minnesota Pollution Control Agency has four nitrogen dioxide monitors throughout the state. Readings have decreased since the 1970s as the pollutant's levels fell, air quality specialist Cassie McMahon said.

To make further cuts, McMahon said, the MPCA is working on a number of solutions, from enforcing caps for factories to improving public transit.

This study used the 2000 census data because the 2010 results weren't available yet, Marshall said, but his group will next do the same study with the later census data to see how things changed over the decade. They also are studying more extensively the potential health effects of reducing emissions.

Dr. Keith Cavanaugh, a pediatric pulmonologist at Children's Hospital and Clinics of Minnesota, said the research is a way to bring awareness to how asthma triggers like pollution can affect patients' lives. It can also help explain why certain populations are at a higher risk for respiratory issues, he said.

A key now is "applying that clinically … how does that influence public policy, how do you get people to change their ways?" he said.

U law Prof. Myron Orfield said the disparity is another outcome of segregated neighborhoods. A possible way to reduce the inequality could be to build more affordable housing in cleaner neighborhoods, he said.

Ehlinger said the state transportation, pollution control and commerce officials will have to work together to change policy because all of these aspects affect people's health.

"Not everybody's benefiting from our overall health and our good environment," he said. "There are some people that are disproportionately affected and that's not the state that we really want to live in."

More can be found at: http://tinyurl.com/med3zz4 and http://tinyurl.com/ny5vws4

Rebecca Harrington is a University of Minnesota student reporter on assignment for the Star Tribune.