Establishment Of A High-resolution Atmospheric Mercury Emission Inventory And Simulation Of Mercury Pollution With CMAQ-Hg At Regional Scale

A better understanding of the discrepancies in multi-scale inventories could give an insight on their approaches and limitations,and provide indications for further improvements;international,national and plant-by-plant data sources are primarily obtained to compile those inventories.Moreover,in order to get a better understanding of mercury pollution and its behavious in atmosphere,we conduct a continuous measurement of speciated atmospheric mercury at Nanjing University campus from August 2014 to July 2015,and develop a CMAQ-Hg mdeling system to simulate the regional mercury pollution for southern Jiangsu.In this study we develop a high-resolution inventory of Hg emissions at 0.05°×0.05° for Jiangsu China using a bottom-up approach and then compare the results with available global/national inventories.With detailed information on individual sources and the updated emission factors from field measurements incorporated,the annual Hg emissions of anthropogenic origin in Jiangsu 2010 are estimated at 39 105 kg,of which 51%,47%and 2%were released as Hg0,Hg2+,and HgP,respectively.This provincial inventory is thoroughly compared to the downscaled results from three national inventories(NJU,THU and BNU)and two global inventories(AMAP/UNEP and EDGARv4.tox2).Attributed to varied methods and data sources,clear information gaps exist in multi-scale inventories,leading to differences in the emission levels,speciation and spatial distributions of atmospheric Hg.The total emissions in the provincial inventory are the largest,i.e.,28%,7%,19%,22%,and 70%higher than NJU,THU,BNU,AMAP/UNEP,and EDGARv4.tox2,respectively.For major sectors including power generation,cement,iron&steel and other coal combustion,the Hg contents(HgC)in coals/raw materials,abatement rates of air pollution control devices(APCD)and activity levels are identified as the crucial parameters responsible for the differences in estimated emissions between inventories.Regarding speciated emissions,larger fraction of Hg2+ is found in the provincial inventory than national and global inventories,resulting mainly from the results by the most recent domestic studies in which enhanced Hg2+ were measured for cement and iron&steel plants.Inconsistent information of big power and industrial plants is the main source of differences in spatial distribution of emissions between the provincial and other inventories,particularly in southern and northwestern Jiangsu where intensive coal combustion and industry are located.Quantified with Monte-Carlo simulation,uncertainties of provincial Hg emissions are smaller than those of NJU national inventory,resulting mainly from the more accurate activity data of individual plants and the reduced uncertainties of HgC in coals/raw materials.Average concentrations(relatively standard deviation)of GEM,RGM and PBM are 3.85(45%)ng/m3,43.0(274%)pg/m3 and 127.4(188%)pg/m3 respectively.The major pollution concentration ranges of GEM,RGM and PBM are 3-4 ng/m3,10-50 pg/m3 and 10-20 pg/m3,and the frequencies are 31%,36%and 27%respectively.GEM exhibits incresing concentrations from early morning in spring,autum and winter,which is attributable to downward mixing of air masses from aloft.Due to the formation of temperature inverse layer,PBM increases from 4:00 and decreases during day time.GOM measurements displays diurnal trend with increasing concentrations during daytime mainly resulted from the anthropogenic sources and photochemical oxidation.GEM concentration has a positive correlation with CO,PM2.5 and SO2concentration due to their homology.RGM concentration is positively related to O3 concentration and temperature in summer,while has a more significant positive correlation with SO2 in winter.It reveals that RGM is more impacted by photochemical oxidation in summer while derived more from anthropogenic emissions in winter.The observation station is influenced by regional transpotation and local emission.Southern Jiangsu and Shanghai area are the most important contributors.The cement plants around the observation point contribute significantly to the heavy RGM pollution episodes.CMAQ-Hg simulation with a spatial resolution of 3 km×3 km can well reflect the overall pollution level of our observation station,while the hourly simulation results have a weak correlation with observation values,therefore the simulation results need to be further improved.Due to the different estimation results and spatial distribution of input multi-scale inventories,the simulated regional mercury concentration and its spatial distribution patterns differ a lot.