Factors influencing surface atmosphere exchange of gaseous elemental mercury in western Maryland

The purpose of this study was to examine the dynamics of the surface -- atmosphere exchange of gaseous elemental mercury (GEM) in western Maryland. The site studied was the Piney Reservoir Ambient Air Monitoring Station (PRAAMS) in Garrett County. I used several different techniques to quantify the exchange, including a soil pore air sampling system that I developed, dynamic flux chambers, and the modified Bowen ratio (MBR) technique. I found that GEM exchange dynamics vary widely from the small scale (< 1 m²) of the flux chambers to the large scale of the MBR technique. When I scaled the flux chamber measurements up to the annual time scale, I predicted a net GEM emission of 2.0 to 5.3 mug m² yr-1 to the atmosphere from PRAAMS, while with the MBR technique I estimated a GEM deposition of 3.3 mug m² y-1. The differences in these estimates highlight the difficulties with measuring the exchange of a substance that can be both deposited to and emitted from soils. It also shows how uncertain the current estimates of this exchange can be. On the other hand, I was able to quantify soil redox potential as an important driver of GEM fluxes and soil pore total gaseous mercury (TGM) concentrations. This had not been previously reported. I was also able to show the importance of soil organic matter (SOM) and soil pore TGM concentration gradients on the surface -- atmosphere exchange of GEM. This work opens the door for other studies on the dynamics of GEM fluxes in all sites with background concentrations of GEM.