By Katrina Marland

More often than not, you expect a park or forest to have pretty clean air. Even more so if it happens to be a well-known place, located far from the nearest urban center that could be smogging up its air. But sadly, this is not always the case. Sequoia National Park, home to some of the biggest and oldest trees in the U.S., is also home to a higher level of air pollution than any other national park.

There are 52 national parks in the U.S. that monitor their air quality each day to make sure that it is safe for visitors. High temperatures, levels of smog and levels of certain allergens or pollutants can all add up to make a bad air-quality day. Ozone in particular can be a nasty problem, capable of literally causing lungs to blister when it’s found at high enough concentrations. That national parks — the places we go to get away from cities and their many urban problems — also have to monitor for air pollution is a bit alarming. This week, the EPA and the National Park Service released a list of the 10 national parks with the worst pollution in 2011 based on ozone levels and days that failed to meet EPA standards for air quality, and Sequoia National Park topped the list.

Despite its reputation for immense trees and remote forests, Sequoia had a total of 87 days that failed to meet federal air-quality standards in 2011 — and it’s hardly a new problem. Park employees and volunteers have come to expect regular lectures on the dangers of air pollution and watch as once-clear vistas have become routinely wreathed in smog. In fact, according to the National Park Conservation Association (NPCA), Sequoia National Park has levels of ozone comparable to those in major cities like Los Angeles. Already this year, though summer has just begun, the park has seen levels of ozone well beyond those set by federal health standards.

How can this be the case when the park is miles away from the closest city? Unfortunately, it comes down to a quirk of geography. The park lies north of the San Joaquin Valley, which contains several major trucking highways, a number of power and food-processing plants and acres upon acres of farmland overseen by diesel-powered machinery. Pollution from this region is pushed north by winds off San Francisco Bay and meets the cooler air moving south, creating an eddy that traps the polluted air in the region, which gives it a chance to seep into the area where the park is located.

Human safety is certainly important, but such severe air pollution in what is supposed to be a remote, natural location also begs the question, what about the trees? Scientists are uncertain what effect long-term exposure to these levels of ozone might have on the environment in these locations, though foresters do see needles turn yellow as the trees soak up ozone, which interferes with their ability to photosynthesize. Young seedlings also struggle to survive and grow with such obstacles to overcome.

With this disturbing news about air pollution in national parks, we can only hope that Sequoia and other parks will benefit from legislation like the Clean Air Act, through which officials aim to give the region pure, clean air by the year 2064. The problem is that the only way to cut down on the pollution that enters Sequoia is to cut down on the pollution in the entire San Joaquin Valley air basin — a tall order given the sheer number of sources of pollution.