linked to power plant activity
The amount of mercury emitted into the atmosphere in the Northeast fluctuates annually depending on activity in the electric power industry, according to researchers at the School of Forestry & Environmental Studies.
Xuhui Lee, professor of meteorology, and Jeffrey Sigler, a recent Yale Ph.D. graduate and now a postdoctoral researcher at the University of New Hampshire, co-authored the Yale study, published this summer in the Journal of Geophysical Research-Atmospheres.
They found that between 2000 and 2002 the emission rate of mercury decreased by 50%, but that between 2002 and 2004 the rate increased between 50% and 75%. During that five-year period, overall emissions declined by 20%.
The dramatic annual changes in mercury emissions, the study's authors say, cannot be explained climatologically by air flow patterns that would bring either clean or polluted air into the region.
Mild winters and a correspondent decrease in the need for regional power plants to burn coal could partially explain the decline in mercury emissions, according to the authors. They estimate that power plants account for up to 40% of total emissions in New Jersey, New York and Pennsylvania and in New England.
"The study highlights just how important power plants are in influencing regional mercury emission," says Sigler.
Lee cautions that other factors are also important when considering how to reduce the amount of mercury in the atmosphere, saying, "We should not forget other source categories when formulating abatement policies, since they also contribute significant amounts to the total emissions."
Mercury, which converts to highly toxic methyl mercury in ground water, is found in fish and can cause neurological problems in developing fetuses as well as dementia and organ failure in adults who eat fish in large amounts and over long periods.
The Yale study was conducted at Great Mountain Forest in northwestern Connecticut. The measurements were restricted to wintertime so data on carbon dioxide, which comes from the same combustion sources as mercury, would not be distorted by photosynthesis. The researchers used carbon dioxide to trace mercury back to its sources with a unique method called "tracer analysis."
"To our knowledge, using the carbon dioxide to trace mercury over a long time period hasn't been done before," say the authors. "We started with actual mercury that's in the atmosphere, worked back to sources that emit it, then calculated the emission rate."
The U.S. Environmental Protection Agency, which does not regulate mercury emissions, determines the mercury emission rate by taking an inventory of existing sources.
"Although the EPA's approach is highly useful, it requires accurate measurements of mercury emitted from the smokestack per ton of fuel burned," says Sigler. "These data are hard to come by. Our top-down technique circumvents those rather cumbersome problems and allows for much more timely estimates of mercury emission. It's difficult to get annual changes in the emission rate with the inventory approach."
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