Abstract
Abstract. China presently contributes the largest amount of anthropogenic mercury (Hg) emission into the atmosphere in the world. Over the past decade, numerous studies have been conducted to characterize the concentration and forms of atmospheric Hg in China, which provide insights into the spatial and temporal distributions of atmospheric Hg through ground-based measurements at widely diverse geographical locations and during cruise and flight campaigns. In this paper, we present a comprehensive review of the state of understanding in atmospheric Hg in China. Gaseous elemental mercury (GEM) and particulate-bound mercury (PBM) measured at the remote sites in China are substantially elevated compared to the background values in the Northern Hemisphere. In Chinese urban areas, the highly elevated GEM, PBM and gaseous oxidized mercury (GOM) were mainly derived from local anthropogenic Hg emissions, whereas regional anthropogenic emissions and long-range transport from domestic source regions are the primary causes of the elevated GEM and PBM concentrations at remote sites. Using 7–9 years of continuous observations at a remote site and an urban site, a slight increase in atmospheric GEM (2.4–2.5 % yr−1) was identified (paired samples test: p < 0.01), which is in agreement with the increasing domestic anthropogenic emissions. Anthropogenic GEM emission quantity in China estimated through the observed GEM / CO concentration ratios ranged from 632 to 1138 t annually over the past decade, 2–3 times larger than published values using emission activity data. Modeling results and filed measurements show dry deposition is the predominant process for removing Hg from the atmosphere, 2.5–9.0 times larger than wet deposition, due to the elevated atmospheric GEM and PBM concentrations that facilitate dry deposition to terrestrial landscapes. Further studies to reconcile the observed and simulated Hg concentrations, to understand the impact of domestic emission reduction on Hg concentration and deposition and to delineate the role of Hg emission and deposition of China in the global Hg biogeochemical cycle, are needed.
Highlights
Mercury (Hg) is a toxic air pollutant that exists in the atmosphere
Averaged gaseous elemental mercury (GEM) concentrations at remote sites were in the range of 1.60–5.07 ng m−3, generally elevated compared to those observed in North America, Europe, South Africa and South America (Table 1)
A strong spatial variation in GEM and particulate-bound mercury (PBM) concentrations was observed, with high concentrations related to regional anthropogenic Hg emissions in central and eastern China
Summary
Mercury (Hg) is a toxic air pollutant that exists in the atmosphere. There are three operationally defined Hg forms: gaseous elemental mercury (GEM), particulate-bound mercury (PBM), and gaseous oxidized mercury (GOM). The persistence of GEM makes Hg one of the most widely distributed pollutants in the atmosphere Both anthropogenic and natural sources emit GEM into the atmosphere, while anthropogenic sources emit GOM and PBM (Pirrone et al, 2010; Pacyna et al, 2010). There is a need to assess the source, transport, transformation and deposition of atmospheric Hg in China, which is critical in understanding the global biogeochemical cycle of Hg. In the past ∼ 15 years, significant understanding has been obtained regarding atmospheric Hg studies in China. The knowledge is crucial to resolve the spatial distribution of atmospheric Hg, constrain the Hg emission inventory, assess Hg transport, and evaluate the roles of China emissions in the regional- and global-scale Hg biogeochemical cycles. The trend helps explain the discrepancy between decreasing atmospheric GEM concentrations in Europe and North America and increasing global anthropogenic emissions. The implications and future research needs for further understanding of atmospheric Hg in China are presented
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