| Volatile halocarbons (VHC) are important atmospheric trace gases, which play improtant roles in stratospheric ozone depletion and the greenhouse effect. Global oceans are net natural sources of atmospheric VHC. Studies of VHC in the oceans are helpful to understand the contribution of the ocean to atmospheric VHC and global warming. Therefore, studies on the distribution, air-sea flux and cycling of VHC in seawater have received considerable interest over the past thirty years. In the present dissertation, the analytical methods, distributions of six kinds of VHC in the Yellow Sea (YS) and the East China Sea (ECS) are systematically studied for the first time. The main research results are showed as follows:1 Purge-and-trap technique combined with gas chromatography and electron capture detector was developed for the analysis of six kinds of VHC in sea water. The six kinds of VHC included chloroform (CHCl3), tetrachloromethane (CCl4), trichloroethylene (C2HCl3), tetrachloroethylene (C2Cl4), dichlorobromomethane (CHBrCl2) and dibromochloromethane (CHBr2Cl). The optimum conditions of purge-and-trap system were as follows: purging seawater (volume:35 ml) with high purity nitrogen at 100 mL min-1 for 15min at ambient temperature (25℃), traping temperature at -78℃during the purge, and desorpping at 180℃for 10 min. Chromatographic conditions were as follows: flow-rate of nitrogen used as the carrier gas at 0.8 mL min-1, the make-up gas for the detector at 45 mL min-1, detector at 230℃, injector at 180℃. The GC temperature programming was used. The initial tempreture was set at 50℃, then increased to 100℃at 10℃min-1, and then to 140℃at 2℃min-1, and finally raised to 180℃at 20℃min-1 (held for 3 min). Six kinds of VHC were well separated using the above optimized conditions. The detection limits were 0.76, 0.04, 0.10, 0.009, 0.37 and 0.16pM for CHCl3, CCl4, C2HCl3, CHBrCl2, C2Cl4 and CHBr2Cl, respectively. Analytical relative standard deviations were between 1.83~3.97%.2 Distributions of VHC in the East China Sea were studied during 973 cruise in July 2006. The results showed that average concentrations of CHCl3, CCl4, C2HCl3, C2Cl4, CHBrCl2 and CHBr2Cl in the surface seawater were 3.21±2.68 (0.32~8.22), 45.01±48.20 (6.34~211.36), 153.48±231.38 (12.75~894.94), 18.52±15.74 (3.52~64.86), 18.45±21.33 (4.23~91.86) and 6.81±4.87 (2.53~21.00) pM, respectively. The distributions of the six kinds of VHC in surface seawater mainly showed a gradually increasing trend from south to north of the East China Sea. The VHC concentrations appeared to be high out of the mouth of Yangtze River and showed a gradually decreasing trend from coastal zone to open sea. There was another high concentration area of CHCl3 and CCl4 in the coastal sea of Zhejiang, which might be resulted from terrestrial substance input.3 Distributions of VHC in the Yellow Sea were determined during the SOLAS cruise in April 2006. The results showed that the average concentrations of CHCl3, CCl4, C2HCl3, C2Cl4, CHBrCl2, CHBr2Cl in the microlayer and subsurface seawater were 10.31±8.07 (2.91~45.88), 0.80±0.64 (0.20~2.74), 11.43±6.53 (1.13~32.07), 17.10±15.57 (0.16~73.68), 0.43±0.34 (0.08~1.64), 4.35±3.53 (0.22~14.20)pM and 10.38±7.80 (2.02~38.55), 0.80±0.54 (0.12~2.14), 11.90±6.74 (1.50~26.80), 16.58±14.97 (0.96~73.45), 0.42±0.34 (0.06~1.88), 4.95±4.92 (0.27~25.24)pM, respectively, while those in the surface seawater were 12.26±12.14 (1.38~52.96), 0.77±0.55 (0.12~2.36), 10.53±6.34 (0.79~28.66), 15.04±13.45 (1.53~59.88), 0.45±0.41 (0.05~1.61), 6.89±6.95 (0.42~8.97)pM, respectively. The distributions of CCl4, CHCl3, C2HCl3 and C2Cl4 in microlayer, subsurface, surface seawater were similar. Their concentrations are showed a gradually decreasing trend from coastal zone to open sea and from the port of Bohai Sea to north Yellow Sea, probably due to the influence of terrestrial substance input. The decreasing trend from the station of G3 to its north was resulted from Changjiang River. The concentrations of CHBrCl2 and CHBr2Cl showed a gradually increasing trend from coastal zone to open sea and the high concentration areas of VHC are the same as that of chl-a because of the release of halobios. The concentrations of VHC in the surface seawater of the Yellow Sea in July were higher than those in April, exhibiting an obvious seasonal variation. No enrichment of VHC was found in the microlayer, due to vertical mixing of microlayer water and bulk seawater during the study. The large range of the fluxes of VHC in the Yellow Sea during the study resulted mainly from the large range of the concentrations of VHC. A preliminary estimate for average sea-to-air fluxes of VHC from the Yellow Sea were -0.88±1.72(-7.02~4.03) for CHCl3, -0.65±0.59(-3.05~-0.01) for CCl4, 2.60±4.12 (-0.43~19.97) for C2HCl3 and 4.35±8.11(-0.00049~38.99) nmol m-2 d-1 for C2Cl4, respectively.
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