Abstract
Abstract. The contribution from different emission sources and atmospheric processes to gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), particulate bound mercury (PBM) and mercury deposition in eastern China were quantified using the Community Multi-scale Air Quality (CMAQ-Hg) modeling system run with a nested domain. Natural sources (NAT) and six categories of anthropogenic mercury sources (ANTH) including cement production (CEM), domestic life (DOM), industrial boilers (IND), metal production (MET), coal-fired power plants (PP) and traffic (TRA) were considered for source apportionment. NAT were responsible for 36.6 % of annual averaged GEM concentration, which was regarded as the most important source for GEM in spite of obvious seasonal variation. Among ANTH, the influence of MET and PP on GEM were most evident especially in winter. ANTH dominated the variations of GOM and PBM concentrations with contributions of 86.7 and 79.1 %, respectively. Among ANTH, IND were the largest contributor for GOM (57.5 %) and PBM (34.4 %) so that most mercury deposition came from IND. The effect of mercury emitted from out of China was indicated by a > 30 % contribution to GEM concentration and wet deposition. The contributions from nine processes – consisting of emissions (EMIS), gas-phase chemical production/loss (CHEM), horizontal advection (HADV), vertical advection (ZADV), horizontal advection (HDIF), vertical diffusion (VDIF), dry deposition (DDEP), cloud processes (CLDS) and aerosol processes (AERO) – were calculated for process analysis with their comparison in urban and non-urban regions of the Yangtze River delta (YRD). EMIS and VDIF affected surface GEM and PBM concentrations most and tended to compensate each other all the time in both urban and non-urban areas. However, DDEP was the most important removal process for GOM with 7.3 and 2.9 ng m−3 reduced in the surface of urban and non-urban areas, respectively, in 1 day. The diurnal profile variation of processes revealed the transportation of GOM from urban area to non-urban areas and the importance of CHEM/AERO in higher altitudes which partly caused diffusion of GOM downwards to non-urban areas. Most of the anthropogenic mercury was transported and diffused away from urban areas by HADV and VDIF and increased mercury concentrations in non-urban areas by HADV. Natural emissions only influenced CHEM and AERO more significantly than anthropogenic. Local emissions in the YRD contributed 8.5 % more to GEM and ~ 30 % more to GOM and PBM in urban areas compared to non-urban areas.
Highlights
Mercury (Hg) pollution in the atmosphere attracts increasing concern globally in view of its neurotoxicity and bioaccumulation along the food chain posing risks to human health (Schroeder and Munthe, 1998; Rolfhus et al, 2003)
The results indicate that two major processes dominate surface gaseous elemental mercury (GEM) concentration, namely EMIS and vertical diffusion (VDIF), and their contributions were comparable in urban and non-urban areas (Fig. 6a)
The base model results were consistent with the measurements of atmospheric mercury including the concentrations of total gaseous mercury (TGM) and particulate bound mercury (PBM) as well as the wet deposition in most sites of eastern China
Summary
Mercury (Hg) pollution in the atmosphere attracts increasing concern globally in view of its neurotoxicity and bioaccumulation along the food chain posing risks to human health (Schroeder and Munthe, 1998; Rolfhus et al, 2003). Atmospheric mercury is divided into three species according to various physical and chemical properties: gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM) and Published by Copernicus Publications on behalf of the European Geosciences Union. J. Zhu et al.: Source attribution and process analysis for atmospheric mercury particulate bound mercury (PBM). GEM is the predominant form (> 95 %) in atmosphere; it is very stable and well mixed hemispherically with a long lifetime of 0.5–2 years (Selin et al, 2007). Mercury is a multi-scale pollutant able to be transported at local-, regional- and larger-scale distances from its sources, and mercury emission speciation has a great impact on the processes and spatial distribution of mercury in the atmosphere (Bieser et al, 2014; Quan et al, 2009; Pai et al, 1999)
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