Global deposition of speciated atmospheric mercury to terrestrial surfaces: an overview

Abstract

<p><strong>Abstract.</strong> One of the most important processes in the global mercury biogeochemical cycling is the deposition of atmospheric mercury, including gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate-bound mercury (PBM), to terrestrial surfaces. In this paper, methods for the observation of wet, dry, litterfall, throughfall, and cloud/fog deposition and models for mercury dry deposition are reviewed. Surrogate surface methods with cation exchange membranes are widely used for GOM dry deposition measurements, while observation methods for GEM dry deposition are more diverse. The methodology for Hg wet deposition is more mature, but the influence of cloud/fog scavenging is easy to neglect. Dry deposition models for speciated mercury have high uncertainties owing to the presence of sensitive parameters related to GOM chemical forms. Observation networks for mercury wet deposition have been developed worldwide, with the Global Mercury Observation System (GMOS) covering the northern hemisphere, the tropics, and the southern hemisphere. Wet deposition implies the spatial distribution of atmospheric mercury pollution, while GOM dry deposition depends highly on the elevation. Litterfall Hg deposition is crucial to forests. Urban areas have high wet deposition and PBM dry deposition because of high reactive mercury levels. Grasslands and forests have significant GOM and GEM dry deposition, respectively. Evergreen broadleaf forests bear high litterfall Hg deposition. Future research needs have been proposed based on the current knowledge of global mercury deposition to terrestrial surfaces.</p>