Current methods and research strategies for modeling atmospheric mercury

The atmospheric pathway of the global mercury cycle is known to be the primary source of mercury contamination to most threatened aquatic ecosystems. Current efforts toward numerical modeling of atmospheric mercury are hindered by an incomplete understanding of emissions, atmospheric transformations, and deposition processes. While much effort has been made to quantify the total mass flux of mercury to the atmosphere from various natural and anthropogenic sources, discrimination of the chemical and physical forms of these emissions is just beginning in response to early modeling exercises showing this discrimination to be critical for accurate modeling estimates of the sources responsible for observed mercury deposition. A similar discrimination of ambient concentrations of mercury throughout the atmosphere is needed in order to develop a clear understanding of atmospheric transformation processes, both chemical and physical, which govern the length scale of atmospheric mercury transport and patterns of its deposition in both wet and dry processes. In this paper, current atmospheric mercury modeling techniques and the information obtained from them are described. A strategy for future field research and numerical model development is proposed which is intended to allow a confident identification of the sources of atmospheric mercury responsible for observed contamination of aquatic ecosystems.