A Numerical Simulation Study On Environmental Impacts Of Mercury Emissions And Depositions In Pearl River Delta

Mercury is a toxic contaminant that can be bio-accumulated.Mercury deposition in the environment is the most serious mercury pollution problem in nowadays China.The Pearl River Delta(PRD)region is one of the largest atmospheric mercury emitters in China.Quantifying the contributions of emission sources from local,regional and global areas to mercury pollution in the region helps to provide a scientific basis for control strategies.In this study,local anthropogenic mercury emission inventory was updated to 2014 and applied in the CMAQ-Hg model with latest regional and global emission results to simulate the mercury concentrations and depositions in the PRD.Then we designed different simulated programs to simulate and identify sources of mercury pollution in PRD.With an understanding of the study results,we provided a practical mercury control strategies to mitigate mercury pollution in the PRD region effectively.The total anthropogenic mercury emissions in the PRD for 2014 were estimated around 11,939.6 kg,of which 55.0% was released as GEM,42.0% as GOM and 3.0% as PBM.Power plants and industrial boilers were dominant sectors,responsible for 29.4 and 22.7% of the total.Other important industrial sources,including municipal solid waste incineration,non-ferrous metals production,iron and steel production and cement production were responsible for 4.8-22.2%.Non-industrial anthropogenic sources,including on-road mobile,residential boilers and biomass incineration,were less than 1.0%.First,we used the CMAQ-Hg Model to simulate characteristics of mercury pollution in the PRD,and that the model predictions agreed well with the observations.Then power plants(PP),municipal solid waste incineration(MSWI),industrial point sources(IP),natural sources(NAT),and boundary conditions(BCs)were zeroed out separately for simulation and comparison with the base case.BCs was responsible for 31.6 and 30.8% of annual average mercury concentration and total deposition,while NAT contributed 15.0 and 19.5%.Among the anthropogenic sources,IP dominated the variations of mercury concentration and deposition with a contribution over 20.0%.PP and MSWI were the second and third largest contributors,whose contributions to mercury concentration and deposition were 18.9 and 18.2,11.3 and 10.3%,respectively.Results showed that power plants were the most important emission sources in the central PRD,so the ultra-low emission(ULE)for thermal power units need to be strengthened.In the northern and western PRD,the contributions of non-ferrous metal production,iron and steel production and cement production were the most significant,which were priorities of mercury control.The fast growth of municipal solid waste incineration were also a key factor in the densely populated and developed areas for future mercury control.In addition,a coordinated regional mercury emission control was important for effectively reducing the deposition in the PRD due to the considerable contribution to mercury transport from outside the local.As industrial mercury emission control measures are strengthened,it is foreseeable that mercury emissions will decrease in the future,but more attention should be paid to the mercury deposition around the large point sources as high pollution and large influence is observed.