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Arctic Haze: An Uninvited Spring Guest

While squinting through spring sunshine, Alaskans sometimes notice that the sky doesn't seem very blue, and that distant mountains seem a bit out-of-focus. Don't blame your contact lenses; the culprit is arctic haze, an unwanted visitor that can make the skies above Alaska dirtier than the air above California.

Arctic haze is a soup of pollutants housed within the polar air mass. Geophysical Institute Professor of Physics Glenn Shaw compares the polar air mass to an amoeba the size of Africa that hovers over the top of the earth. As the cold air mass drifts around, it picks up air pollution from one northern part of the globe and escorts it to another.

"Arctic haze" is a phrase invented in 1956 by Murray Mitchell, a U.S. Air Force officer stationed in Alaska who wrote about murky bands of pollution on the horizon noticed by pilots flying arctic missions.

Since Alaska isn't the home of many industrial smokestacks, the origin of arctic haze was a mystery for years. Researchers sampled the haze in the 1970s to find where it came from. They found that sulfur compounds and black carbon particles--the products of iron, nickel and copper smelters and inefficient coal-burning plants--made up a large proportion of arctic haze. Later studies showed much of the pollution was coming from the former Soviet Union and other areas of Eurasia.

Arctic haze is unique because its chemical ingredients hang around for a long time, especially when compared to other weather-system carried pollutants. In the case of acid rain, for example, sulfur and nitrogen compounds belched into the atmosphere from coal- burning plants in the U.S. midwest survive for about a week before rain or snow rinses them out of the air over northeastern states and Canada.

Arctic haze can endure for more than a month because there is not much snow, rain, or turbulent air to flush it out of the polar air mass in spring.

"Spring is the time when the washing machine of nature shuts down," Shaw said.

It also is the time when the Northern Hemisphere tilts toward the sun. The sun triggers chemical reactions that change sulfur compounds and other pollutants from gases to microscopic solids and liquids. These arctic haze particles scatter sunlight, robbing the air of its transparency and the sky of its blue.

This spring, Geophysical Institute researchers have seen surprisingly little arctic haze hovering over Alaska. Shaw and Geophysical Institute Assistant Professor of Chemistry Richard Benner have found the air to be cleaner than in years past. Shaw thinks it might be due to the fact that this year the polar air mass rested more over northern Canada, where there isn't much industry, than it did over the former Soviet Union and Eurasia.

While scientists have proven the existence of arctic haze, the final resting place of arctic haze pollutants that have been washed out of the air is still unknown. Benner said that snow above the Arctic Circle is remarkably clean despite the polluted air mass that hangs above it in spring. The clean snow means the chemicals are falling to earth somewhere else, probably farther south.

Benner and Shaw plan to measure the fallout of arctic haze sulfur compounds over the Interior during the next two years. They hope to determine the final resting place of springtime pollutants over Alaska that were donated by dirty smokestacks on another continent