Mercury Pollution from Wildfires
As thousands of acres continue to burn across the western
United States, scientists from The National Center for
Atmospheric Research and the University of Washington are
flying over the wildfires to measure mercury emissions in their
smoke.
During a wildfire, mercury stored in the foliage and ground
litter is released and carried into the atmosphere, says NCAR
scientist Hans Friedli. He and Lawrence Radke are conducting
research flights over wildfires and prescribed burns. Scientists
are trying to understand the global sources of atmospheric
mercury, as well as how much of the dangerous substance
ends up in the food chain.
About 6,500 tons of gaseous mercury is circulating in the
atmosphere at all times. About half comes from natural
sources, such as soil, oceans, and volcanoes, and the other
half comes from human activity. The U.S. Environmental
Protection Agency estimates that 41 tons are sent into the
atmosphere annually from U.S. coal-fired plants. The same
kind of mercury release occurs when land is cleared for
agriculture by burning.
Mercury is carried in the atmosphere for about a year, then
rains or falls out of the air onto the earth. ?Mercury is picked
up by the surfaces--the leaves or needles--and it stays
there,? says Friedli. At least until those trees burn.
Friedli and Radke conducted laboratory tests to find out how
much mercury a fire could release. They set fire to forest
samples from across the United States at the Forest Service
Fire Science Laboratory?s burn facility in Missoula, Montana.
Sensors immediately detected a large amount of mercury. All
the samples released from 94% to 99% of the mercury they
had stored.
Friedli and Radke will aim ground-based sensors at a planned
burn site in Prince Albert National Park in Saskatchewan,
Canada, in September. Last summer, when the team flew
over a wildfire in Quebec, the mercury emissions were higher
than in the lab experiment,
?presumably because mercury in real fires is also emitted from
heated soil,? says Friedli, ?a source not yet considered in our
experiments.?
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