Atmospheric Mercury Research:
The MRT entered into the field of atmospheric mercury studies in 2003 when it became clear it was critically important to be able to seamlessly link environmental compartments from the atmosphere to the food web and created the USGS Mobile Atmospheric Mercury Lab (MAML). With this addition, the MRT became one of the few mercury research groups anywhere that could deploy a complete (mercury speciation, plus a wide range of air quality sensors). This facility has been used continuously since then on Toxics Program supported research across a wide range of locations and settings. (MAML site map). In 2003 the MAML deployments were to the western US: the Four Corners Area (Engle et al., 2010), Yellowstone National Park (Hall et al., 2007), and the Lostwood National Wildlife Refuge in northwestern North Dakota (Engle et al., 2010). In 2004, the MRT conducted studies comparing atmospheric mercury concentrations, speciation and source tracking in rural (Mt. Horeb, WI) versus urban (East St. Louis, MO) settings (Manolopoulos et al., 2007a, and 2007b). These studies revealed what was at the time some of the highest gaseous mercury concentrations ever reported. From 2005 through 2009 the Toxics and DOI Landscapes programs supported a five-year effort to evaluate mercury deposition along the Gulf and Atlantic coasts (photo of MAML in Weeks Bay, Alabama). This effort delivered a novel observation of a diel oxidation process of gaseous atmospheric mercury in the marine boundary layer (Engle et al., 2007). Documentation of this process provides a consistent explanation for the previously observed high rates of atmospheric mercury deposition in the Gulf and southeast Atlantic coasts. Our original hypothesis for this study was that atmospheric mercury oxidation rates would be greatest in warm coastal settings and would decline in colder water regions where the injection of free halogens from the ocean surface occurs at lower rates. This hypothesis was supported by the multi-site MAML deployment, and a paper summarizing the data from this broad range of sites has recently been completed (Engle et al., 2010). Last, the MRT has recently completed (Kolker et al., 2010) a unique effort to examine the atmospheric mercury deposition field around a single emission source at several locations simultaneously (I will provide a map image of the study sites). This study demonstrated that the source-receptor relations of a perceived single source are extremely complex, and several previously held assumptions, such as plumes would arrive first and with more elevated concentrations at sites in closer proximity to the source. This study has provide a better understanding of the difficulty in performing source-receptor studies, and the need to have multiple monitoring locations to better describe the complex nature of mercury emissions, transport and deposition.