Mercury In Precipitation And Its Deposition Fluxes In Main Urban Area Of Chongqing

Mercury, a highly toxic heavy metal, is recognized as a global pollutant due to its long distance transport. After entering the atmosphere, various mercury species finally deposit to water or terrestrial ecosystem by wet and dry deposition, and then end the atmospheric cycling process. Mercury in the water or terrestrial ecosystem can harm the human healthy by methylation and bioaccumulation. What's more, atmospheric deposition is one of the main sources of mercury in water or terrestrial ecosystem. Atmospheric mercury wet deposition is the primary type at mid and low latitude regions that have more precipitation days and large precipitation.Recently, some countries such as North America and Japan have established more mature sites for measuring mercury wet deposition fluxes. However, there were few regions monitoring mercury wet deposition in China except Beijing,Changchun,Guiyang,especially for methylmercury. The terrain of valleys, hills and mountains and the weather of no wind or breeze in Chongqing arouse the increased atmospheric stability and radiation inversion, which is easy to lead trouble in mercury spreading and local atmospheric mercury pollution. With the washing of precipitation, the increasing mercury entering into the water and terrestrial ecosystem can endanger the living creature. In order to understand the distribution characteristics of mercury in precipitation in main urban areas Chongqing, make up for the deficiency in domestic wet deposition field, APS-3A/2B automatic sampler was used to collect rain in three different measurement sites, and DMA-80 and distill-ethylize-CVAF equipment to measure total mercury (THg) and methylmercury(MeHg) in rain, The conclusions as follows:(1) During study period (July.2010—Feb.2011), the range of THg and MeHg concertrations in rain, higher than that in America and simlar to the result measured in Wujing basin,Guiyang, were 8.14-157.58 ng/L and 0.04-3.7 ng/L,respectively. The THg and MeHg mean VMW concentrations were 34.86 ng/L and 0.36 ng/L.(2) The mercury distribution in precipitation had spatial characteristics.The mean VMW concentrations of THg decreased in order of NA(38.85 ng/L)>XD(37.44 ng/L)>JY(29.58 ng/L),which illustrated that the THg concentration in precipitation in city center is higher than that in urban and human activities had influence on mercury wet deposition; The mean VMW concentrations of MeHg decreased in order of XD(0.64 ng/L)>NA(0.38 ng/L)>JY(0.16 ng/L).(3) The mercury in precipitation showed obvious time variation.The maximal monthly mean THg (69.31 ng/L) and MeHg (0.62 ng/L) VMW concentration respectively appeared in January and Octorber; the minimum value of THg (26.26 ng/L) and MeHg (0.21 ng/L) both appeared in July.(4) Ratio range of MeHg accounted for THg was 0.10%-16.46%, with mean percentage 1.59%.(5) There were significantly linear positive correlations between THg concentration and SO42-concentration in precipitation in JY,NA measurement sites(r=0.377*,r=0.412**),which illustrated that the mercury in precipitation in both measurement sites were mainly from the combustion of coal.(6) The THg and MeHg deposition fluxes respectively were 18.47μg/m2 and 0.19μg/m2, having significant difference with rainfall.In order to obtain more integrated deposition datas and mechanism, the researches in the future we need to do are that estimating the sources of mercury in precipitation by mastering more details of meteorological datas, estimating the dry deposition fluxes by grasping calculation model of atmospheric dry deposition, analyzing the effect of matters in atmospherer or rain and meteorological conditionon on methylation and demethylation by laboratory experiment and discussing preliminarily the sources of MeHg in atmosphere.