Mercury from U.S. wildfires 
With average emissions of 44 metric tons (t) of mercury per year (yr), fires in the lower 48 states and Alaska contribute almost as much mercury to the air as coal-fired power plants, the study finds.
Previous efforts to quantify mercury emissions from wildfires were either local or regional in scale. To look at the countrywide scenario, Christine Wiedinmyer and Hans Friedli, both researchers at the National Center for Atmospheric Research, gathered the number of individual fires—natural and prescribed forest fires and agricultural burns—from 2002 to 2006 from data initially collected by NASA satellites. Then, by analyzing information on land cover from global and regional data sets, the duo estimated the amount of biomass burned at each location and by each fire. They plugged these results, along with estimates of the amounts of mercury emitted per unit of biomass burned, into a fire emissions model.
For the lower 48 states, the average mercury emitted from wildfires was estimated to be 31 t/yr, whereas for Alaska alone that number was 12 t/yr. "I think both of us are fairly surprised as to how high it was," says Wiedinmyer. "It compares on the same order of magnitude as other major industrial sources." The researchers also found that forest fires and not agricultural burns spew out most of this mercury. Put together, the average yearly emissions from the lower 48 states and Alaska are equal to nearly 30% of the 108 t/yr of human-caused mercury emissions estimated by the U.S EPA for 2002. EPA did not include emissions from fires in its calculations.
Global warming is depriving us of an important ecosystem service—"trapping and storing industrial mercury," says Turetsky. "We know that mercury can be very concentrated within soils," she says. The carbon-rich soils of the boreal forests, especially peat, have been accumulating mercury for thousands of years. "In the past, those ecosystems have been probably too wet to burn very often, but that's not the case anymore," she says.
