Air pollution is known to have negative -- even deadly -- effects on our health, and studies have shown that breathing pollution can kill, even at levels below air quality guidelines.
Now, a new study shows that air pollution produced in one state often blows across state lines, and can contribute to health issues and even premature deaths hundreds of miles away.
The study, published Wednesday in the journal Nature, found that, on average, around half of the early deaths in the US linked to pollution actually occur outside the borders of the state where the toxic air originated.
"This situation is a bit like secondhand smoke, but on a national scale," said Steven Barrett, director of the Laboratory for Aviation and the Environment at the Massachusetts Institute of Technology and a co-author of the study.
The importers and exporters of dirty air
The study found that the northern Midwest states are the largest net "exporters" of pollution-related early deaths outside state lines, due to their to low local populations, high emissions and the large populations that are located downwind.
On the other hand, a group of states in the Northeast are significant "importers" of air pollution premature deaths, meaning many of the deaths that occur there are from toxic particles that originated elsewhere.
Of the 48 contiguous states studied, New York had the largest percentage of premature deaths from out-of-state pollution in all three of the years examined.
Overall, Barrett and his colleagues found that cross-state premature deaths from air pollution have fallen over time -- from 53% in 2005 to 41% in 2018 -- a decline they say is due to a drop in emissions from electric power generation during this period.
Electricity generation had been the largest source of air pollution from human activity tied to early deaths, but since 2018, emissions from commercial and residential activity have become the biggest contributor.
"While it was known that electric power generation resulted in long-range pollution, it wasn't obvious that other emissions had such reach too," Barrett said.
Why emissions reductions are needed
Barrett said that it will likely get harder to lower the percentage of deadly air pollution crossing state lines, at least by current measures.
"Significant interventions to reduce commercial, residential and car emissions will be needed," Barrett said.
The US Environmental Protection Agency has a rule that aims to reduce cross-state air pollution, but it only regulates air pollution that comes from power generation, Barrett said.
"EPA regulations have been very successful at improving air quality in the US. It's important that these aren't rolled back, and indeed the cross-state rule could be enhanced to include other sectors."
Under President Trump's administration, the EPA has moved to slash several rules aimed at regulating emissions, including a plan to freeze an Obama-era rule mandating that automakers work to make cars more fuel efficient.