Ah spring; the season of sunny skies, longer days and... arctic haze. Decades ago scientists were surprised to learn that the skies in northern latitudes are less than pristine and crystal clear in springtime. In fact, at times the arctic air can be a highly unsavory soup of pollutants.

Northerners have been forced to learn more than we might really like to know about this problem, and the concerns it brings about contaminating food chains in the North. It is now well known that pollutants from the smokestacks of the former Soviet Union and other parts of Eurasia can dump their loads of chemicals far from home.

The good news for northerners on this continent is that ever since the U.S.S.R. split up, many of those smokestacks have gone out of commission. Since 1993 arctic haze has not been building up as much as it once did.

But that decline does not make the understanding of arctic haze any less of a challenge for the scientists who study it. They now have a good understanding of what makes up arctic haze and where it comes from, but they still do not know where it eventually ends up.

Arctic haze is a seasonal problem. During winter, pollutants collect within the cold arctic air mass that hovers over the top of the world.

As this nasty brew drifts over the polar regions, it adds ingredients, picking up sulfates from any number of smelters in Eurasia. By spring the air mass is loaded with sulfates and other chemicals which can make the air appear murky.The polar air mass disappears in summer, and then begins to rebuild again in the fall.

"The reason that we have an arctic haze, and the reason that we have all of these pollution problems is that the cold stable air has a harder time getting rid of pollutants," explains Glenn Shaw, a physics professor at the University of Alaska in Fairbanks. "The atmospheric washing machines are not working in the spring, so the pollutants keep building up."

Shaw was the first scientist to begin rigorous studies of arctic haze, but he was not the first person to notice it. Murray Mitchell was already a budding scientist when he was serving with the U.S. Air Force in Alaska in the 1950s. He was intrigued by the bands of murky air that he spotted while flying military reconnaissance flights in the arctic.

Mitchell concluded that long-distance transport must be responsible for the dirty air, and wrote an article on the phenomenon. But he was too far ahead of his time, and the topic disappeared into thin air until another young scientist headed north.

Glenn Shaw went to Barrow, Alaska, in 1972, to measure the optical transparency of the atmosphere there. Instead of the clean skies that he had been expecting, he found air that was even murkier than the dusty air he had left behind in Arizona.

Eventually Shaw began working with an atmospheric chemist, Ken Rahn, on the problem, and after a series of experiments they thought they had pinned down the source; huge dust storms in the Gobi desert were loading the air with particles.

But that quick and easy answer did not hold up; arctic haze appeared in the spring even during years that dust storms did not sweep across Asia.

Later the scientists established monitoring stations in the North that collected air samples, and found sooty particles, not sandy ones. As testing equipment became more sophisticated they were able to analyze the particles in the haze, and conclude that they were not from North America.

Shaw continues to study arctic haze, and has four stations in Alaska where air samples are collected. He still wants to know what happens to the pollutants once they filter out of the air.

"If you go up to the North Slope and collect snow in the spring, it is very very clean even when the air above is dirty. The arctic air mass is this big blob of cold air that breaks apart in spring and in the process of breaking apart we think that the stuff comes out but we do not know where," Shaw explains. "We really do not know where it is going."

Professor Glenn Shaw can be contacted through theGeophysical Institute at the University of Alaska at Fairbanks, or directly at shaw@gi.alaska.edu.