Despite Smoke and Manmade Invaders, Alaska Air Still Good Stuff
Smoke from wildfires has drowned interior Alaska this summer, fuzzing views of distant hills and turning the sun into an orange Frisbee. Though the outdoors smells like a campfire, Alaska's air is still among the cleanest in the nation according to an air-monitoring station in Denali Park.
The station, a vacuum pump system near the entrance to Denali Park that pulls air through four filters, traps less gunk than any similar system installed in 70 other national parks around the country. The air in Hawaii, at 11,000 feet on Mauna Loa, is a close second, according to the National Park Service. The station that traps the most specks of pollution is located on the roof of a park service building in Washington, D.C. These statistics about air quality are part of a Park Service study on visibility. The Denali station is the clean-air champ based on the 1994-1998 average of trapped particles less than 2.5 micrometers in size. It takes dozens of specks that small to bridge the width of a human hair, but scientists are interested in them for several reasons: small particles get past the mouth and nose and into the lungs, and the tiny flecks also scatter sunlight to create haze and cut viewing distances.
Alaska's air is pristine when compared with Lower 48 air, but we have regular episodes of pollution, said Cathy Cahill, an atmospheric chemist at the Geophysical Institute. Residents of the Fairbanks North Star Borough walk the tightrope with air quality every winter, when one of the most severe temperature inversions on the planet sets up in the Tanana Valley. Cold air trapped beneath a lid of warm air confines vehicle emissions and wood smoke with a severity that sometimes violates federal air quality standards. Anchorage has a similar but less extreme problem.
By looking at seasonal results from the Denali air-monitoring station, Cahill has found other pulses of air pollution that aren't caused by humans, or at least humans living in Alaska. Operational since 1988, the Denali station pulls in the most particles in June, July and August. Cahill said those peaks correspond to fire season, when more than one million acres of the state's forest and tundra can go up in flames each year. In late April and early May the station catches specks of iron and silicon. Cahill and others have traced the elements to an unexpected source-giant dust storms that form over the Gobi Desert in China and Mongolia. The storms are large enough that they march over China and Japan, picking up pollutants along the way. The squalls blow out over the Pacific Ocean, where they mate with other storms that quickly carry the particulates to the West Coast and Alaska. "When those storms hit the jet stream, they often take a direct line across the Pacific," Cahill said. "They can get from Asia to Washington state in five days."
The Denali station also catches arctic haze. Named by an Air Force pilot who in 1956 saw murky bands in the sky while flying up north, arctic haze is a soup of pollutants from the former Soviet Union and Eurasia. Researchers such as the Geophysical Institute's Glenn Shaw found that the sulfur compounds and black carbon particles come from metal-smelting factories and inefficient coal-burning plants. The Denali station catches arctic haze in different concentrations from November through March depending on the location of the polar air mass, which Shaw describes as an ameba the size of Africa that hovers over the northern part of the globe and picks up pollution during its movement.
Though these winter invaders gunk up Alaska's atmosphere, Alaskans still have some of the best air around. Cahill said the smokiest day at Denali National Park allows better views than the average day at Shenandoah National Park, which is 75 miles west of Washington, D.C. "We have amazingly good visibility," she said, citing Alaskans' ability to see Mt. McKinley from Fairbanks and Anchorage on clear days. "Our normal visibility is about 160 miles. We're spoiled because we're used to that."
