| Volatile halocarbons (VHCs) are significiant trace gases in the atmosphere,which are part of greenhouse gases and ozone depleting substances and take importantroles in global climatic change and environment change. The VHCs in the atmosphereare mainly from natural production and anthropogenic activities. Previous researcheshave showed that the ocean may be the source or sink of VHCs. Ocean, whichoccupies the71percents of the Earth’s area, takes an important and complex role inthe biological balance of the atmospheric VHCs. Marine boundary layer is animportant field in which the gases in water exchange with those in the atmosphere,thus, it is important to investigate the distributions of the VHCs in sea surfaceseawater.In the present dissertation, the East China Sea (ECS), the Yellow Sea (YS), theBohai Sea (BS) and the Jiaozhou Bay (JZB) are investigated. The distributions,saturation anomalies (SA) and sea-to-air fluxes of the VHCs are analysised anddiscussed systematically. The main research conclusions are drawn as follows:(1) The results showed that the concentrations for CH3Br, C2H2Cl2, CHCl3,CH3CCl3, CCl4and C2HCl3in surface water were0.24~10.22,1.11~15.8,0.67~49.22,1.59~14.46,1.31~6.34and5.59~71.68pmol/L, respectively, with theaverage concentrations of1.57,4.14,8.44,4.59,3.54and19.30pmol/L, in the YS andthe Yangtze River Estuary (YRE) during Nov-Dec2009. The individual VHCs hadtheir own distribution patterns in this survey area, because that the concentrations ofVHCs were influenced by the Yellow Sea circulation, the East Sea circulation andbiological activities et al. The highest concentrations of VHCs in the Northern YellowSea (NYS) usually were observed in the coastal area in which the river current flowedinto sea, the highest concentrations of VHCs were observed outer the Yangtze estuaryin the YRE, and the concentrations for VHCs decreased from inshore to offshore in the Southern Yellow Sea (SYS). The results showed that the SA of CH3Br, CCl4andC2H3Cl3were-96.34~645.52%,74.77~1987.11%and-75.99~10.30%,respectively, with the average values of9.32%,436.78%and-39.22%. The sea-to-airfluxes of VHCs were computed as Wanninkhof relationship (Wan92) and two-layermodel theory. The results showed that fluxes of CH3Br, CCl4, C2H3Cl3, CHCl3andC2HCl3were-16.76~38.55,-25.72~0.72,0.19~48.87,-174.79~153.50and0.72~154.92nmol m-2d-1, respectively, with the average fluxes of-1.27,-6.01,9.75,-33.24and36.88nmol m-2d-1. These results demonstrated that the study area was the sourceof CH3Br, CCl4and CHCl3, and the sink of C2H3Cl3and C2HCl3. The fluxes of VHCswere influenced by the wind speed in situ and the difference concentrations in air andthose in seawater.（2）The concentrations of7kinds of VHCs, the fluxes and the SAof4kinds ofVHCs were investigated in BS and YS during Sept,2010. The results showed that theconcentrations of CH3Cl, CH3Br, C2H2Cl2, CHCl3, C2H3Cl3, CCl4, C2HCl3were51.69~156.26,1.14~4.34,5.15~18.79,3.79~124.43,0.35~7.82,1.17~11.61and5.63~43.39pmol/L, the average concentrations of them were89.87,2.34,12.12,28.31,5.49,2.99and25.07pmol/L, respectively. In general, the lowest concentrations ofVHCs were observed in the middle of BS with little anthropogenic influences, thehighest concentrations of VHCs were observed in the coastal of SYS. The SA ofCH3Br, CH3Cl, CCl4and C2H3Cl3were-27.61~185.69%,-29.31~125.66%,-69.43~263.22%and-76.25~463.04%, the average of them were46.85%,25.65%,-16.85%and296.72%. The VHCs SA had their own distribution pattern, due to thecomplexity hydrological conditions and environmental factors. The fluxes of CH3Cl,CH3Br, CCl4and C2H3Cl3were-71.94~266.05,-3.67~11.80,-13.38~16.77and-0.15~52.96nmol m-2d-1, the average of them were27.28,1.36、-0.61and12.86nmol m-2d-1. Therefore, the BS and YS was the source for CH3Cl, CH3Br andC2H3Cl3, and the sink for CCl4. The fluxes of VHCs were influenced by theconcentrations of VHCs, in situ wind speed and water temperature. The fluxes ofVHCs had similar distribution patterns with the SA of VHCs.(3) The concentrations of7kinds of VHCs, the fluxes and the SA of4kinds of VHCs were investigated in ECS during Jun,2010. The results showed that theconcentrations of CH3Cl, CH3Br, C2H2Cl2, C2HCl3, CHCl3, CCl4and C2H3Cl3were49.37~105.72,1.31~13.80,5.11~11.21,5.51~25.25,9.26~23.71,0.71~15.55and1.31~14.89pmol/L, the average concentrations of them were80.46,4.12,9.06,12.89,17.98,7.71and9.39pmol/L. It was the coastal current, seawater circulation,Yangtze River diluted and biological activities that all influenced the VHCsconcentrations in this survey area. The concentrations of VHCs (C2HCl3exclude)exhibited the declining from the coastal to the open sea. The SA of CH3Cl, CH3Br,CCl4and C2H3Cl3were-34.22~43.33%,-41.51~431.89%,-32.51~269.19%and-15.78~846.54%, the average of them were8.47%,65.63%,99.72%and511.29%,respectively. The fluxes of CH3Cl, CH3Br, CCl4and C2H3Cl3were-88.10~174.10,-5.08~60.59,-2.71~68.23and-0.85~78.22nmol m-2d-1, the average of them were29.48,7.42,14.70and29.56nmol m-2d-1, respectively. Therefore, the ECS were thesource to4kinds of VHCs, and in the ECS surface water VHCs were super saturationduring the survey time. The fluxes of VHCs had related with the in situ wind speed,temperature of surface water, and the difference concentrations of VHCs in water andair.(4) The concentrations of7kinds of VHCs, the fluxes of4kinds of VHCs wereinvestigated in JZB from Apr,2010to Feb,2011. The results showed that each VHCshad its own distribution pattern because that the tidal current, land runoff, sewagedischarge and marineculture et al. all co-influenced the concentrations of VHCs. Ingeneral, the highest concentrations of VHCs were observed in the east coastal and thenorth of JZB, while the lowest concentrations were observed in the middle of and themouth of JZB. The VHCs concentrations were significant variation with the season,but each of them had its own distribution pattern, such as the highest concentration ofCH3Cl and CH3Br were occurred in winter and autumn respectively, the highestconcentration of CCl4and C2HCl3were occurred in summer, the highest concentrationof C2H2Cl2, CHCl3and C2H3Cl3were occurred in spring. The fluxes of VHCs alsosignificant varied with the season. Although the concentrations of VHCs were higherthan the other survey, however, the wind speed and temperature were lower in the similarly month, thus, the average fluxes of VHCs in Sep, Dec and Nov were weakhigher than those in the other survey, the fluxes of VHCs (CH3Cl exclude) in Augustwere lower than those in ECS. The contributions of VHCs in the JZB were high to thelocal area release, but were very low to the China Sea release due to owning the smallarea.(5) There were no significant correlation between the concentrations of VHCsand environmental factors, the SA of VHCs and environmental factors, in VHCs, inthe SA of VHCs. No significant correlation was founded, even the SA of VHCs wererevised by the SA of CCl4. This indicted that VHCs had complexity sources includingnatural sources and anthropogenic sources. A lot of factors influenced the VHCsconcentrations, including surface temperature, Chl-a, bacteria, water current andcoastal release, et al., however, their influencing abilities were not deduced due toabsent factor.(6) The results showed that the annual fluxes of CH3Cl, CH3Br, CCl4andC2H3Cl3were0.60,0.22,0.62and1.33Gg/y in China Sea (ECS, YS and BS) bysimply extrapolation. The China Sea occupied0.33%of the world sea area, the CH3Cl,CH3Br, CCl4and C2H3Cl3release in the China Sea were0.09%,0.39%,4.43%and0.19%of world ocean release, respectively. This indicated that the release of CH3Cland C2H3Cl3were smaller in China Sea than in world ocean. |
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