| Atmospheric mercury?Hg?poses human health and ecological risks once deposited and bio-accumulated through food chains or webs.Source contribution analysis of Hg deposition is essential to formulating effective emission control strategies to alleviate the adverse impact of Hg release from anthropogenic sources.In this study,firstly,the Hg concentrations of the plume from point sources and its impacts on surrounding environment were briefly analyzed based on the Hg observation data.Secondly,the anthropogenic Hg emission inventory of the central region of Pearl River Delta?cPRD?was compiled by using available emission factors.Then,for the first time,California Puff Dispersion Modeling system?CALPUFF?was enhanced to a Hg version?denoted as CALPUFF-Hg?to simulate the transport,diffusion,oxidation and deposition processes of Hg.Finally,the WRF-CALPUFF-Hg air quality system was established to simulate the Hg concentration and deposition in the cPRD at 1 km×1 km resolution.The model results were evaluated with observations,and then compared to the CMAQ-Hg results to assess the performance of near-field deposition.Scenarios of the different sectors and individual point sources were simulated to evaluate the contributions of source sectors and point sources to Hg deposition of cPRD by appling a widely used Brute-Force method.The source contributions to deposition of receptors near the large point sources were also evaluated.Additionally,the simulations of uncertainty cases were conducted,according to the uncertainty range of the Hg speciation distribution,to briefly assess the implication on the simulation results.The results show that the Hg emission concentration in the flue gas from the point sources is still high after air pollution control devices and it has a great impact on the Hg concentration in the surrounding atmosphere,soil,and plants.The five-year observation of soil shows that the average concentration in soil around Likeng municipal solid waste incinerator is 0.125±0.098mg kg-1 with increasing year by year.The three-year observation of plants shows that the average concentration in plants around Likeng is 0.038±0.032 mg kg-1.In 2014,the total anthropogenic Hg emission in the cPRD was 8301 kg with 99.9%of emission from point sources.In terms of the three forms of Hg,gaseous elemental mercury?GEM?,gaseous oxidized mercury?GOM?,and particulate-bound mercury?PBM?accounted for 54.1%,43.6%,and 2.3%,respectively.The WRF-CALPUFF-Hg simulation system was verified by comparing available observation,literature data,and CMAQ-Hg results,it predicts that the Hg concentration and deposition are higher near large point sources than CMAQ-Hg results and met reasonable well with observed data.The model results also indicate that the boundary transport contributes 64.4%to Hg deposition in the domain;The emission from cement production in the local source sectors was the largest contributor to Hg deposition,accounting for 13.0%,followed by coal-fired power plants?6.5%?,non-ferrous metal smelting?5.4%?,iron and steel production?3.5%?,and municipal solid waste incineration?3.4%?.The point sources that released a higher fraction of gaseous oxidized mercury,such as cement production and municipal solid waste incineration,were the most significant contributors to local deposition.At the investigated receptors,large point sources that are closest with high Hg emissions contributed 67-94%of total Hg deposition.Based on the source apportionment results,cement production and the rapidly growing municipal solid waste incineration are identified as priority sectors for Hg emission control in the cPRD region. |
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