Ozone levels across the country's national parks are virtually indistinguishable from the smog and pollution found in major metropolitan areas according to new research.

Every year, more than 300 million people visit America’s national parks for a breath of fresh air. But if it’s quality they’re after, they might as well have traveled to the heart of a metropolitan smog.

Researchers at Iowa State and Cornell universities have discovered that the ozone concentrations in America’s national parks are statistically indistinguishable from those of the 20 largest cities in the US. Combing through data from 1990 to 2014, David Keiser and his colleagues’ compared daily ozone measurements from 33 national parks—including Acadia, Yellowstone, and Yosemite—against 20 major U.S. metropolitan areas, such as Los Angeles, New York City and Chicago, and found results on either side were “largely indistinguishable” from each other.

Since the Clean Air Act was passed in 1970, law enforcers have been trying to curtail the number of pollutants entering our atmosphere; namely carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide. But the law wasn’t just created to spare our lungs; it was brought about to help our eyes too. Seven years after it was established, Class I and II sites were tacked on to the legislation as a way of preserving the clean, clear views of national parks larger than 6,000 acres. Then in 1999, the EPA Regional Haze Rule was introduced to help direct states in how to improve the visibility and air quality of their national parks. The recent figures seem to show these additions been actioned to little or no avail.

“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.”

If our areas of natural beauty are already enveloped by heavy pollution, then the current administration’s attitude towards the issue of regional haze doesn’t bode well for their future. Back in April, in a White House press release Trump said, “aspects of the National Ambient Air Quality Standards (NAAQS) program are outdated, inefficient and in need of reform.” His reason? Because air quality standards are an “unnecessary barrier to growth.” Even the recently resigned head of the EPA Scott Pruitt has previously filed a lawsuit against the EPA regional haze rule. All this recent piece of research does is illustrate the severity of the problem, at a time when those trying to protect our national parks are having to do it against the tide of Trump.