New University of Washington research suggests mercury can be carried long distances in the atmosphere, combining with other airborne chemicals as it travels. These compounds are much more water-soluble and therefore are more easily removed from the air in rainfall.

Mercury generally is present in the atmosphere in only very small amounts compared with other pollutants, said Philip Swartzendruber, a University of Washington doctoral student in atmospheric sciences. But mercury does not break down and after it washes out of the atmosphere it can be converted to a more toxic form, methyl mercury. Even in places thought to be pristine, the more toxic form can become very concentrated as it is passed up the food chain.

"By the time mercury gets to the top of the food chain, it can increase by a factor of a million," he said. "It can go from being nearly undetectable in the air to being toxic to larger organisms."

Swartzendruber presents his team's findings Thursday during the American Geophysical Union's fall meeting in San Francisco. He is part of a team that began taking measurements of atmospheric mercury levels early this year atop Mount Bachelor, near Bend, Ore. At about 9,000 feet, the station is high enough to take readings from the bottom of the free troposphere, where substances such as mercury, carbon dioxide and ozone can travel great distances and remain for a long time. The free troposphere extends from about 5,000 feet in altitude to about 40,000 feet.

The researchers recorded mercury levels that included significant concentrations of a type called reactive gaseous mercury. "After nearly half a year of results, it is pretty clear things are going on up there," Swartzendru
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Contact: Vince Stricherz
vinces@u.washington.edu
206-543-2580
University of Washington
7-Dec-2005