Temporal And Spatial Distribution Characteristics Of Mercury And Major Inorganic Ions In Wet Deposition On The Northern Slope Of Taibai Mountain

Mercury(Hg)is a toxic heavy metal and a global pollutant with special physical and chemical properties.The wet Hg deposition plays a very important role for the entrance of atmospheric Hg to earth surface,and thus may constitute a menace to terrestrial ecosystem.As an environmental media between atmosphere and terrestrial ecosystem,precipitation is regarded as a key process in global Hg biogeochemical cycling.In addition,under the current conditions of global warming and complex air pollution in China,the constant inorganic ions in atmospheric wet deposition also carry certain atmospheric pollutant transport information.This study takes the northern slope of the main peak of Taibai Mountain in Qinling Mountains as the main research area,through a systematic study of the total mercury in the atmospheric wet deposition in the study area,the temporal and spatial variations and the controlling factors of total mercury concentration and deposition flux of atmospheric wet deposition in the study area were analyzed.At the same time,by combining the concentration of inorganic ions in the atmospheric wet deposition of the study area,the basic features and sources of wet deposition chemical composition in the north slope of Taibai Mountain were explored using correlation analysis method,enrichment factor method and sea salt tracer method.The main conclusions of this study are:(1)The pH value of atmospheric wet deposition on the northern slope of Taibai Mountain ranges from 3.80 to 8.29.The values in autumn and winter seasons are higher than those in spring and summer,and the range of change is relatively large,and increases as the altitude rises.The electrical conductivity values have the same trend with the pH value,ranges from 1.4-360?S·cm-1,80%wet deposition events are lower than 60 ?S·cm-1.There is a significant negative correlation between pH value and electrical conductivity.There is a positive correlation between wet deposition and pH value,and there is a negative correlation between electrical conductivity and wet deposition.(2)The seasonal variation ranges of total mercury concentration in wet deposition on the northern slope of Taibai Mountain ranged from 3.99 to 26.20 ng·L-1.The value was significantly higher in autumn and winter than in spring and summer.Overall the monsoon period was higher than the non-monsoon period,and the low altitude region is far higher than the high altitude area.In 2015,the total mercury deposition on the northern slope of Taibai Mountain was 10.21 ?g·m-2,the settlement in August to October accounted for 64%of the whole year,total mercury deposition shows an increasing trend during the interannual period.Correlation analysis showed that there was a negative correlation between wet deposition and total mercury concentration in wet deposition,but there was a positive correlation between total mercury deposition and wet deposition.(3)The analysis of airflow trajectory model shows that the wet depositional air mass on the northern slope of Taibai Mountain mainly comes from the northwest,southeast,and southwest directions.Influenced by the distance of the transmission path,human activities,natural conditions,and meteorological factors,the chemical characteristics of mercury in the wet deposition under different paths of air flow transmission are differences,in general,the total mercury concentration of wet deposition under the northwest air mass is the highest.(4)The total inorganic ion concentration of wet deposition in the north slope of Taibai Mountain is 321.18 ?eq·L-1,and the average cation concentration is 221.70 ?eq·L-1,and the main positive and anion are Ca2+ and NH4+,SO42-and NO3-.In general,the wet deposition is Ca2+-SO42-type.The total concentration of ions in autumn and winter was apparently higher than that in the spring and summer.The total and each ion concentration have an obviously tendency to decrease with the increase of altitude on the whole.The results of statistical analysis showed that,the correlation between ions in wet deposition on the northern slope of Taibai Mountain is good,NO3-,SO42-,F-and NH4+ are mainly contributed by human activities,Mg2+ and Ca2+ are highly correlated,all from the land source,K+ mainly comes from local biomass combustion and gneiss weathering.The non-sea source contribution rate of Na+ is as high as 60.73%,showing obvious characteristics of wet deposition of continental mountain stations.