Mercury concentrations in soils, fish, and wildlife have increased 300-1000% since the preindustrial era, harming people, especially children, and wildlife. Control measures focus on reducing current atmospheric emissions from coal combustion, waste incineration, and mining, but emissions from soils and the ocean, largely a legacy of past anthropogenic releases, are about twice the current direct anthropogenic sources. The grand challenge for mercury science is to trace the causal links from smokestacks to stomachs, accounting for cycling between atmosphere, ocean, soils, vegetation, and food webs.
Our past work has revised our understanding of atmospheric chemistry that drives the fate and transport of mercury, showing that halogens are key oxidants for gaseous elemental mercury. Our current work is developing and improving the global GEOS-Chem model, which simulates mercury cycling in the atmosphere, ocean, and land.
Atmospheric mercury wet deposition (left) and emissions (right) for the eastern United States.
The southeastern US has greater atmospheric mercury deposition than the northeastern US, despite having lower mercury emissions. With an innovative combination of precipitation composition measurements and remote sensing of individual rain storms, we showed that thunderstorms, which are frequent in the southeastern US, are responsible for the high deposition. The reason is that oxidized mercury, which is water soluble, accumulates in the upper troposphere. Thunderstorms scavenge from that high-altitude pool of mercury, but non-convective storms cannot. Using radar and satellites that sense cloud tops, we found that mercury concentrations in Florida rainfall increase 5% for each 1 km increase in cloud top height.