Ozone Levels at America's National Parks Match Those of Big Cities

Heading to a National Park this summer? You might not get that breath of fresh air you’re expecting.

A new study from researchers at Iowa State and Cornell University, and published in Science Advances, found that average ozone levels in 33 of America’s national parks were “statistically indistinguishable” from the levels in nation’s 20 largest metropolitan areas.

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“The U.S. has spent billions of dollars over the last three decades to improve air quality,” said David Keiser, assistant professor of economics at Iowa State. “Given the popularity of national parks, as well as the fact that people go to parks to be outside, we believed it was worth better understanding air quality trends in these areas and whether people, through their actions, respond to changes in air quality in parks.”

The study, which collected information from 1990 to 2014, at the nation’s largest national parks, including the Great Smoky Mountains, Yellowstone and Yosemite.

used the same data points that previously led to the passing of the Clean Air Act (CAA) Amendments of 1977 and 1990.

Interestingly, after the passage of those regulations, metropolitan areas saw an improvement in ozone levels starting as early as 1990. National parks, however, have taken a little longer to catch up. Their ozone levels only started to improve in the early 2000s, an uptick which corresponds to the 1999 implementation of the Regional Haze Rule, which strengthened air quality protections for national parks and wilderness areas.

Even so, national parks have only seen a modest reduction in number of days with ozone concentrations exceeding 70 parts per billion, a level called “unhealthy” by the EPA.

Researchers also cross-matched air pollution data with visitation statistics and found that visits to national parks tend to slow down when the air quality is lower.

Analysts, which surmised that the reduced visitor numbers could be sparked by air quality warnings (AQI) issued by parks or by low visibility, collected more data and found that visitation fluctuations are more likely to be associated with potential health warnings and less so with visibility.

Despite the decrease in visitation during months with high ozone levels, America’s national parks are busier than ever. Research showed that some 35 percent of all visitor days occurred when ozone levels in the parks had attained a “moderate” 55 ppb AQI. Nearly 9 percent of visitor days occurred when ozone levels exceeded 70 ppb.

According to the study, exposure to ozone at these levels can have serious health implications, including increased chances of being hospitalized for respiratory symptoms.