SAN FRANCISCO — A 10-year study of smog in national parks has found that air quality is improving in western states but continuing to deteriorate in the East, despite tougher laws aimed at halting air pollution.
In the summertime, remote parks and wilderness areas in the East share the same hazy air as cities such as Washington. In fact, the study found, visible air pollution in the two eastern parks studied is worse than in Los Angeles during the summer.
Researchers at UC Davis, who conducted the study of a dozen national parks, came to the unexpected conclusion that the West is doing a better job of controlling the sulfur emissions that cause visible air pollution and acid rain. The findings were published in the latest issue of the journal Atmospheric Environment.
"The measures used in the East to clean up the air aren't working the way they should and the air quality is getting worse," said physicist Thomas Cahill, head of the UC Davis Air Quality Group. "The measures used in the West are working, and the air is getting better."
Cahill called for tougher laws to reduce sulfur emissions, particularly in the East. "The bottom line is that the Clean Air Act may not accomplish all that it was supposed to do, which is to clean up the air of the eastern United States," he said.
The research--the first of its kind--found that the United States is divided down the middle into two distinct zones of sulfur emissions, which can travel hundreds of miles from their sources.
In the East, the level of sulfate pollutants is often eight times as high as in the West because there are many more power plants, fewer emission controls and higher humidity, which accelerates the conversion of sulfur emissions into visible acidic particles.
Sulfate pollution is the primary cause of visible smog and, in heavy concentrations, can severely damage trees. By contrast, ozone, which is not visible, is the main component of smog that causes health problems in humans and can also damage vegetation.
To see how air pollution is affecting visibility in some of the most remote and pristine spots in the country, the UC Davis researchers took air samples at scenic spots, such as the mountains above Yosemite Valley and the bottom of the Grand Canyon.
The researchers found that the air quality improved in national parks in Arizona, Colorado, Utah and Oregon between 1982 and 1992, while holding steady in Yosemite, the Grand Canyon, Bryce Canyon National Park in Utah and two national parks in Texas.
However, visible pollution at Shenandoah National Park in Virginia and Great Smoky Mountains National Park in Tennessee jumped nearly 40% during the same period.
"On many days in the summer, visitors have no view at all except a strange, gray fog from many of the most popular lookouts," Cahill said. "But it's not fog. It's mostly sulfate particles, with lots of water attached. At times in the East, it is almost pure dilute sulfuric acid."
Cahill said the UC Davis findings support the theory that the sulfate haze hanging over much of the eastern United States and Europe is countering the effect of global warming in that region by scattering light that would otherwise heat the Earth.
He said this finding could explain why temperatures have not increased as much in the Northern Hemisphere as expected under scientific models of global warming.