MATTHEW BROWN
Denver, US.- Visitors appear to be steering clear of some U.S. national parks or cutting visits short because of pollution levels that are comparable to what’s found in major cities, according to a study released Wednesday.

Researchers at Iowa State and Cornell universities looked at more than two decades of data on ozone pollution at 33 parks — from Shenandoah to Yellowstone, the Grand Canyon and Yosemite. They say visitor numbers dropped almost 2 percent when ozone levels went up even slightly and by at least 8 percent in months with three or more days of high ozone levels compared with months with fewer days of high ozone.

Study co-author Ivan Rudik said air quality warnings issued by parks and other government agencies may be causing the visitation drop. That’s consistent with previous research on so-called avoidance behavior in response to pollution alerts in other settings. The study sought to control for seasonal variations and daily changes in the weather.

“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 could be detrimental to their health,” said Rudik, an assistant professor of economics at Cornell.

The study was published in the journal Science Advances. It comes as national parks have seen record numbers of visitors in recent years despite any concerns over pollution. Ozone, the main ingredient in smog, is formed when small particles of pollution from cars, power plants and industrial facilities react with sunlight. It limits visibility and can cause respiratory problems.

In parks, ozone is carried in on the wind and also caused by traffic and other activities. Virginia Tech economist Kevin Boyle, who has researched ozone in parks and was a peer reviewer for the study, said it provides “strong, suggestive evidence” that air pollution is changing people’s behavior when planning a park visit. Boyle said follow-up research is needed to confirm the findings.