| Volatile halocarbons (VHCs) are important atmospheric trace gases, potential greenhouse gases and ozone destructors, which play important roles in global climatic change and environment. Sources of volatile halogenated hydrocarbons in the atmosphere are mainly from natural production and human activities, while the ocean is the important natural source of volatile halogenated hydrocarbons. Ocean interface layer is one of the important places of gases exchange between water and atmosphere, so the ocean may be the source of atmospheric VHCs, it also may become the sink of them. Ocean plays an important role in the geochemical cycling of VHCs, so it is of great significance in global buget of VHCs to study the occurrences of VHCs in the marine environment.In the present dissertation, we choose the East China Sea (ECS), the Yellow Sea (YS) and the Northern South China Sea (NSCS) as the study areas. Several common VHCs are obversed in these waters. The concentration distribution, spatial and temporal variations, sea-to-air fluxes, and factors influencing them are systematically studied. The purpose of this study is to estimate the contribution of the China Sea to the regional and global environmental change. The main conclusions are drawn as follows:(1) Based on the gas-stripping chromatographic systems of seawater VHCs in our laboratory,6 VHCs were determined, which are chloroform (CHCl3), carbon tetrachloride (CC14), trichloroethylene (C2HC13), bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl) and bromoform (CHBr3), respectively. The detection limits of the analytical method in this study were 0.25 pmol L-1 CHCl3,0.03 pmol L"1 CCl4,0.08 pmol L"1 C2HC13,0.01 pmol L-1 CHBrCl2,0.16 pmol L-1 CHBr2Cl and 0.12 pmol L"1 CHBr3, respectively. The relative standard deviations and recoveries were 1.82%-3.98% and 87.3%-109.4%, respectively, which are quite similar to foreign study results in the same method.(2) The distributions and sea-to-air fluxes of 6 VHCs were determined in the East China Sea (ECS) and the Yellow Sea (YS) during April-May,2009. The surface water concentrations of CHC13, CCl4, C2HC13, CHBrCl2, CHBr2Cl and CHBr3 in spring were 42.19 (2.57-139.76),2.91 (0.06-13.49),17.85 (2.67-41.99),24.47 (7.17-45.71),6.31 (0.47-30.45) and 10.09 (5.54-21.93) pmol L-1, respectively. The horizontal distributions of 6 VHCs present certain characteristics in the ECS and the YS. The surface concentrations of CHCl3, CCl4 and C2HCl3 showed higher concentritions in the coast and lower values off the coast. Lower concentrations were observed in the eastern part of the ECS due to the influence of Kuroshio waters, with low concentrations of nutrients and Chl-a and high temperature and salinity. The higher concentrations of CHBrCl2, CHBr2Cl and CHBr3 mainly by biology production occurred in the red tide-prone areas off the Yangtze River estuary. Vertical profiles along different transects displayed that 6 VHC presented diffrent distributions in every transect. The diurnal variations generally showed 5 VHCs by biogenic production may be significantly affected by light and temperature, while human activities production CCl4 may not be related to the sunshine radiation. Correlation analysis suggested that there is a significant negative correlation between seawater temperature and CHBrCl2, salinity and CHBr2Cl, respectively. There was a certain positive correlation only between CHBrCl2 and Chl-a in the 6 VHCs study. The results of sea-to-air fluxes of VHC showed that the ECS and the YS were a sink of CCl4 and a source of CHBrCl2, CHBr2Cl and CHBr3. For CHC13 and CHBr3, the most part of the ECS and the YS were also a source with the exception of some stations. Therefore, although China's continental shelf waters account for only a small part of the world's oceans, but its role can not be ignored for estimating sea-to-air fluxes of 6 VHCs in the global oceans emission.(3) The distributions and sea-to-air fluxes of 4 VHCs were determined in the Northern South China Sea (NSCS) during March-April,2009. The surface water concentrations of CHC13, C2HCl3, CHBrCl2 and CHBr3 in spring were 6.47 (0.88-27.02),1.44 (0.31-6.79),3.12 (0.35-6.76) and 23.39 (5.84-32.12) pmol L-1, respectively. The horizontal distributions of 4 VHCs presented certain characteristics in the NSCS. The highest concentrations of CHC13, CHBrCl2 and C2HC13 located NO1, N02 and N03 stations, respectively. The highest concentration of CHBr3 appeared in the QB4 station. Furthermore, Lower values of CHCl3, CHBrCl2 and CHBr3 were observed in the Kuroshio area, while higher values of C2HCl3 appeared in this area. The diurnal variation of 4 VHCs generally showed their higher levels in day and lower ones at night, indicating that the production processes of these compounds may be related to the sunlight and water temperature. Correlation analysis suggested that there is a significant positive correlation between CHBrCl2 and C2HCl3. But there is an obvious negative correlation between seawater temperature and CHBrCl2. Sea-to-air fluxes showed generally that the NSCS was a source for CHCl3, C2HCl3, CHBrCl2 and CHBr3.
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