In-depth review of atmospheric mercury: sources, transformations, and potential sinks

Mercury is a toxic heavy metal that is found naturally throughout the global environment. During the last 100 years, there has been a 70% rise in atmospheric mercury levels over the natural background measured prior to industrialization due to anthropogenic emissions. This increase in mercury levels represents a global threat to the health of ecosystems and humans worldwide. Atmospheric mercury chemistry is complex and its sources and sinks involve equilibrium interactions between the atmosphere, the hydrosphere, and the geosphere. This review outlines the fundamental chemistry of mercury in gas, aqueous, and solid phases, including inorganic, organic, and complexed mercury species. An understanding of this chemistry is important for understanding the cycling between the various environmental compartments as it affects atmospheric loadings. Further, many of these reactions can also occur in the atmosphere in heterogeneous gas/cloud/aerosol interactions. The sources and fate of mercury in the atmosphere, including the cycling of mercury through soil and water as it impacts atmospheric loadings are therefore examined. The sources of major uncertainties in our understanding of mercury in the atmosphere are also discussed, along with recommendations for future studies that include both homogeneous and heterogeneous reactions of the various mercury species.