Once mercury is emitted into the atmosphere from the smokestacks of power plants, the pollutant has a complicated trajectory; even after it settles onto land and sinks into oceans, mercury can be re-emitted back into the atmosphere repeatedly. This so-called “grasshopper effect” keeps the highly toxic substance circulating as “legacy emissions” that, combined with new smokestack emissions, can extend the environmental effects of mercury for decades.
Now an international team led by MIT researchers has conducted a new analysis that provides more accurate estimates of sources of mercury emissions around the world. The analysis pairs measured air concentrations of mercury with a global simulation to calculate the fraction of mercury that is either re-emitted or that originates from power plants and other anthropogenic activities. The result of this work, researchers say, could improve estimates of mercury pollution, and help refine pollution-control strategies around the world.
Once mercury is emitted into the atmosphere from the smokestacks of power plants, the pollutant has a complicated trajectory; even after it settles onto land and sinks into oceans, mercury can be re-emitted back into the atmosphere repeatedly. This so-called “grasshopper effect” keeps the highly toxic substance circulating as “legacy emissions” that, combined with new smokestack emissions, can extend the environmental effects of mercury for decades.
Now an international team led by MIT researchers has conducted a new analysis that provides more accurate estimates of sources of mercury emissions around the world. The analysis pairs measured air concentrations of mercury with a global simulation to calculate the fraction of mercury that is either re-emitted or that originates from power plants and other anthropogenic activities. The result of this work, researchers say, could improve estimates of mercury pollution, and help refine pollution-control strategies around the world.
The new analysis shows that Asia now releases a surprisingly large amount of anthropogenic mercury. While its increased burning of coal was known to exacerbate mercury emissions and air pollution, the MIT team estimates that Asia produces more than double the mercury emissions previously estimated.
Noelle Selin, the Esther and Harold E. Edgerton Career Development Associate Professor in MIT’s Institute for Data, Systems, and Society and the Department of Earth, Atmospheric and Planetary Sciences, says the new analysis can also give scientists a better idea of how long legacy emissions — mercury re-emitted by the land and ocean — stick around in the atmosphere. This is because the analysis can more accurately calculate the total amount emitted by land and ocean sources.
“The timescale under which mercury circulates in the environment tells us about how fast we’ll recover if we limit mercury emissions,” Selin says. “We can better quantify mercury cycling with this method.”
Selin and Shaojie Song, a graduate student in EAPS, have published their results in the journal Atmospheric Chemistry and Physics.
Top-down approach
The team’s analysis improves on other models that take a bottom-up approach. Such models estimate mercury emissions for a region by considering factors such as the amount of coal burned in a power plant and the types of equipment in a plant used to control emissions. Models then often extrapolate data from a few sources to apply to an entire region.
However, there are a number of uncertainties with such bottom-up modeling, and it’s often difficult to obtain the required data from individual power plants.
Instead, Selin and Song’s analysis takes a top-down approach, combining bottom-up estimates with actual measurements of mercury emissions from monitoring stations around the world.
Power plant image via Shutterstock.
Read more at MIT News.
