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Mercury is a potent neurotoxin causing major impacts to both human health and ecosystems.East Asia is the largest source region of anthropogenic mercury emission into the global atmosphere.Although the observational programs and the associated modeling assessments of atmospheric mercury in the region started relatively recently,significant advancements have been made in the past decade regarding the emission sources,temporal and spatial distribution,transport characteristics and mass budget of mercury in the regional atmosphere.This presentation synthesizes the principal findings and current knowledge gaps of speciated atmospheric mercury in East Asia,and projects the research needs in the future monitoring and modeling efforts.Speciated concentrations of atmospheric mercury observed by previous and ongoing monitoring programs exhibit large spatial and temporal variations depending on the locations of monitoring sites,with highly elevated levels at many urban sites.Continuous observation of speciated mercury in the region is scarce and uncertain,given the analytical uncertainty and the high level of expertise required for GOM and PBM measurements.There is clear evidence for trans-boundary transport of atmospheric mercury within the region,although the inference regarding emission source strength remains relatively weak based on the monitoring data and meteorological/statistical receptor modeling.Results from multiple modeling assessments using first-principle atmospheric models suggest that approximately 70%of mercury emissions end up in the outflow entering the global background of atmospheric mercury pool,and that the mercury emission quantity in the region is likely larger than the emission inventory estimated from the statistics of human activities.However,the implications of model results are also weakened due to a general lack of wet deposition data for model verification and of GIS data for reliably estimating the air-surface exchange(dry deposition and evasion)of different mercury species.Additional monitoring efforts are warranted for better understanding the emission strength and speciation in South Asia.Co-observation of CO,NOx,aerosol and atmospheric oxidants at the existing monitoring sites will greatly enhance the source-receptor analysis.Modeling investigations will benefit from a strong regional program of wet deposition observation and further development of models that incorporate recent findings on isotopic fractionation and air-surface exchange of mercury.