An aerial view of sandstone formations May 2, 2012 in Bryce Canyon National Park, Utah.

(Ethan Miller/Getty Images)

At a Glance

The air in U.S. national parks is as polluted with ozone as the air found in major cities, a new study found.Unhealthy ozone levels have persisted into the 2000s, even as ozone pollution has declined in recent decades.The study also found California's Sequoia National Park averages more days per year with unhealthy ozone levels than Los Angeles.

Getting out of the stinky, smoggy city and escaping into the fresh air of our country's national parks isn't what it used to be.

According to a new study , ozone levels were virtually the same at United States national parks and the country's 20 biggest cities in measurements taken from 1990 to 2014. Unhealthy ozone concentrations are the biggest concern, and the study found 35 percent of visits to national parks occur when levels of the pollutant are elevated.

"Even though the national parks are supposed to be icons of a pristine landscape, quite a lot of people are being exposed to ozone levels that ,"Ivan Rudik, an assistant professor of applied economics at Cornell University and co-author of the study, told USA Today.

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The study singled out California's Sequoia National Park, which welcomes more than 1.2 million visitors per year, because of the alarming pollution levels the researchers found. Because of pollution that blows infrom the San Francisco Bay Area and cities closer to the park, Sequoia averages more days per year with unhealthy ozone levelsthanLos Angeles, which has the highest ozone concentration of any city in the nation.

"You can see this in the park's Twitter feed, where pretty much every day in the summer, there is an air quality warning where it is unhealthy for sensitive groups ," Rudik told CNN.com.

To get their data, the researchers studied 33 of the largest national parks in the U.S.

Ozone pollution can cause respiratory health problems and premature death, and can also , according to the Conversation. Although ozone levels have declinedin the U.S. since the 1980s, the Environmental Protection Agency said residents several weeks per year, on average.