Abstract
Abstract. One of the most important processes in the global mercury (Hg) biogeochemical cycling is the deposition of atmospheric Hg, including gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate-bound mercury (PBM), to the land surfaces. Results of wet, dry, and forest Hg deposition from global observation networks, individual monitoring studies, and observation-based simulations have been reviewed in this study. Uncertainties in the observation and simulation of global speciated atmospheric Hg deposition to the land surfaces have been systemically estimated based on assessment of commonly used observation methods, campaign results for comparison of different methods, model evaluation with observation data, and sensitivity analysis for model parameterization. The uncertainties of GOM and PBM dry deposition measurements come from the interference of unwanted Hg forms or incomplete capture of targeted Hg forms, while that of GEM dry deposition observation originates from the lack of a standardized experimental system and operating procedure. The large biases in the measurements of GOM and PBM concentrations and the high sensitivities of key parameters in resistance models lead to high uncertainties in GOM and PBM dry deposition simulation. Non-precipitation Hg wet deposition could play a crucial role in alpine and coastal regions, and its high uncertainties in both observation and simulation affect the overall uncertainties of Hg wet deposition. The overall uncertainties in the observation and simulation of the total global Hg deposition were estimated to be ± (25–50) % and ± (45–70) %, respectively, with the largest contributions from dry deposition. According to the results from uncertainty analysis, future research needs were recommended, among which a global Hg dry deposition network, unified methods for GOM and PBM dry deposition measurements, quantitative methods for GOM speciation, campaigns for comprehensive forest Hg behavior, and more efforts in long-term Hg deposition monitoring in Asia are the top priorities.
Highlights
Mercury (Hg) is a global pollutant, characterized by its neurotoxicity, persistency, and bioaccumulation effect
We investigated results from observations and simulations of global Hg deposition, reviewed methods adopted for Hg deposition measurements and modeling, estimated the uncertainties of different methods for different Hg deposition forms, and summarized the overall uncertainty level of the global Hg deposition
Knife-edge surrogate surface (KSS) samplers with quartz fiber filters (QFFs) and dry deposition plates (DDPs) with overhead projection films were deployed for particulate-bound mercury (PBM) dry deposition measurements (Lai et al, 2011; Fang et al, 2012b, 2013)
Summary
Mercury (Hg) is a global pollutant, characterized by its neurotoxicity, persistency, and bioaccumulation effect. Forest canopy is regarded as an important sink of atmospheric Hg for its special forms of deposition, litterfall, and throughfall (Gustin et al, 2008). Litterfall is a form of indirect Hg dry deposition through foliar uptake of atmospheric Hg, and throughfall includes wet-deposited Hg above the canopy and a portion of drydeposited Hg washed off from the canopy (Wright et al, 2016). Significant efforts have been made in the past decade in quantifying atmospheric Hg deposition through both direct observations and model simulations, especially of dry deposition We investigated results from observations and simulations of global Hg deposition, reviewed methods adopted for Hg deposition measurements and modeling, estimated the uncertainties of different methods for different Hg deposition forms, and summarized the overall uncertainty level of the global Hg deposition
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