Air pollution in 33 of America's national parks — including some of its most heavily visited, like Yellowstone, Yosemite, and Acadia — is on par with air quality in the nation's 20 biggest cities, according to a new study.
In the study published Wednesday in Science Advances, researchers found from 1990 to 2014, ozone levels — a key component of smog — in 33 national parks was "statistically indistinguishable" from levels in the country's 20 largest metropolitan areas.
And the pollution is making a dent in park attendance, the researchers found.
According to the study, since 1990, the number of days in which the parks had unhealthy ozone concentrations haven't declined as dramatically as they have in cities, despite air pollution regulations.
Some of the parks included in the study are Acadia in Maine, Great Smoky Mountains in Tennessee, and Yellowstone in Wyoming.
The study found the highest average ozone concentrations were at Sequoia National Park in California — and were at higher levels than in Los Angeles in all but two years since 1996.
The pollution keeps visitors away, the study found, stating a 1 part per billion increase in maximum ozone levels met with a 2 percent visitation reduction in summer – and a 1.5 percent visitation reduction in the fall.
Cornell economics professor and study co-author Ivan Rudik told Axios this suggests "[p]eople value having better air quality in parks . . . there was a clear negative relationship between ozone and visitation."
"Ultimately, you're going to have to reduce emissions of pollutants that end up in parks," Rudik said, which could include reductions in personal vehicle use or the removal of fossil fuel power plants that are upwind of national parks, Axios noted.
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