More than half of all air-quality-related early deaths in the United States are a result of emissions originating outside of the state in which those deaths occur, MIT researchers report today in the journal Nature.

The study focuses on the years between 2005 and 2018 and tracks combustion emissions of various polluting compounds from various sectors, looking at every state in the contiguous United States, from season to season and year to year.

In general, the researchers find that when air pollution is generated in one state, half of that pollution is lofted into the air and carried by winds across state boundaries, to affect the health quality of out-of-state residents and increase their risk of early death.

“Regulators in the U.S. have done a pretty good job of hitting the most important thing first, which is power generation, by reducing sulfur dioxide emissions drastically, and there’s been a huge improvement, as we see in the results,” says study leader Steven Barrett, an associate professor of aeronautics and astronautics at MIT. “Now it’s looking like other emissions sectors are becoming important. To make further progress, we should start focusing on road transportation and commercial and residential emissions.”

Image: Chelsea Turner, MIT