Air pollution doesn’t respect borders. A power plant in one place often ends up killing people who live far downwind. Now, a detailed analysis of how air pollution moves in the United States reveals that since 2005 premature deaths caused by two of the biggest polluters—power plants and traffic—have fallen significantly. The bad news: Deaths from residential and business emissions, like those from heating and burning trash, grew nearly 40% over the same period.
Air pollution kills when particles from burning coal, wood, or natural gas react in the atmosphere to create ozone and soot. Those particles damage airways and the cardiovascular system. In the United States, such pollution causes many deaths each year; estimates range between 90,000 and 360,000.
But figuring out how all the various sources of pollution spread and threaten health is a herculean task. So Steven Barrett, an atmospheric scientist at the Massachusetts Institute of Technology; aerospace engineer Irene Dedoussi, now at Delft University of Technology; and colleagues used a computer model of winds and atmospheric chemistry. They added data from U.S. Environmental Protection Agency (EPA) air pollution surveys to study large sources of pollution, including power plants, industry, roadways, and homes and businesses. The model revealed how the pollution moves from state to state, reacting with other compounds to form harmful particles. Because people are exposed to pollution from multiple sources, the model estimated the contributions from all these sectors and their added risk of death.
There has been progress since 2005. Overall, about 30,000 fewer people died from air pollution in 2018, they report today in Nature. Deaths related to power plant emissions fell 65% to 8500, and deaths related to traffic pollution fell 50% to 18,600. Much of the former improvement, Barrett says, comes from tighter EPA regulations and economic factors that favor cleaner burning natural gas over coal.
“All those years of effort to control power plant pollution, and to some extent road transport, have dramatically reduced the contributions of those sources—and that’s good news,” says Dan Greenbaum, an air quality expert and president of the Health Effects Institute, a research organization that studies air pollution.
But the benefits depend on where you live: Forty-one percent of premature deaths from air pollution still result from out-of-state emissions, the study found. “That’s a startlingly high figure,” says John Walke, who directs the clean air, climate, and clean energy program at the Natural Resources Defense Council, an environmental advocacy organization. “This is the first time that I’ve seen such a precise estimation … attributed to upwind emissions.”
Power plants remain the dominant cause of these out-of-state deaths because those emissions travel longer distances. Greenbaum says the findings reinforce the need to tackle air pollution with a national approach, as EPA has done. Giving more power to the states to regulate air quality would jeopardize progress, he says.
Barrett says he was surprised by a different finding: the significant, and growing, impact caused by residential and commercial pollution. Such emissions caused 20,400 premature deaths in 2005, a number that rose to 28,200 by 2018. But the 38% increase isn’t due to large increases in air pollution. Instead, as less sulfur dioxide and nitrogen oxides enter the atmosphere from coal-burning power plants, the ammonia and nitrogen oxide byproducts of residential and commercial burning are more likely to form harmful particles.
Dan Goldberg, who researches air pollution at George Washington University, was also surprised by the increase. Because commercial and residential emissions are understudied compared with other sources, he’s not yet fully convinced by that trend. But given the shifting burden, the researchers calculate that a 10% reduction in air pollution from residential and commercial sources would yield more than three times the health benefits of a 10% reduction from power plants.
Still, most experts would be loath to have to choose which sector to clean up. “For me,” Barrett says, “the right answer for emissions is ultimately zero.”