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 staysthere,? 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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