夏季长江口及其邻近海域海水及大气中挥发性卤代烃的分布与海-气通量研究

挥发性卤代烃(Volatile halocarbons,VHCs)是大气中重要的痕量温室气体,在全球变暖和大气化学中扮演着重要的角色.运用吹扫-捕集气相色谱法于2016年7月4—16日对长江口及其邻近海域6种常见的挥发性卤代烃(CFC-11、CFC-12、CH2Cl2、CCl_4、C_2Cl_4、CHBr3)的浓度进行了测定.同时,测定了大气中的CCl_4、CFC-11、CFC-12和C_2Cl_4浓度.结果表明,受陆源输入、水团及生物作用因素的影响,海水中6种VHCs的浓度分布总体呈现出近岸高、远海低的趋势.受地理位置和水文等条件影响,不同的VHCs垂直分布有所差别,但浓度的高值区出现在0~20 m水体中.相关性分析表明,CHBr3与Chl-a之间存在显著正相关,说明CHBr3分布受到浮游植物生物量的影响;CCl_4、C_2Cl_4与CFC-11显著正相关,推测三者拥有相似的来源.另外,分析结果显示,CHBr3与pH之间没有相关性.大气中除CFC-11外,CCl_4、CFC-12和C_2Cl_4的平均浓度均高于全球平均值.大气中4种VHCs浓度分布表现出近岸高、外海低的趋势.后向轨迹分析表明,近岸的陆源污染及大气的扩散输送是长江口及其附近海域上方大气VHCs的重要来源.采用双膜模型估算了卤代烃的海-气通量,结果表明,夏季长江口及其邻近海域是大气中CCl_4、C_2Cl_4、CHBr3、CH2Cl2的源.

Distributions and sea-to-air fluxes of volatile halocarbons in the Yangtze River Estuary and adjacent area in summer

Volatile halocarbons (VHCs) are important atmosphere trace gases, which play significant roles in the global warming and atmospheric chemistry. The concentrations of six VHCs including CFC-11, CFC-12, CH₂Cl₂, CCl₄, C₂Cl₄ and CHBr₃ in the seawater of the Yangtze River Estuary and adjacent area were determined by purge and trap-chromatography during the period of 4-16 July 2016. Furthermore, CCl₄, CFC-11, CFC-12 and C₂Cl₄ concentrations in the marine atmosphere were determined. The results showed that the concentrations of six VHCs in the coastal waters were higher than those in the open sea, due to the impact of terrestrial input, water mass and biological production. Influenced by geographical position and hydrological conditions, the concentrations of six VHCs were different in the vertical distributions, although they had a common feature with the maxima appearing in the 0~20 meters of sea water. Significant positive correlations were observed among the CCl₄, C₂Cl₄ and CFC-11 concentrations, suggesting that they might have some common sources. Besides, a positive correlation was found between the CHBr₃ and chlorophyll a (Chl-a) concentrations in the surface seawater, indicating that phytoplankton biomass might play an important role in controlling the distribution of CHBr₃ in the study area. No correlation was observed between the CHBr₃ and pH. The atmospheric concentrations of CCl₄, CFC-12 and C₂Cl₄ in the study area were higher than the global averages except CFC-11. According to the analytical results of backward trajectories, the atmospheric diffusion and transport of the nearshore terrigenous pollutants were the main source of CCl₄, CFC-11 and CFC-12. The sea-to-air flux data indicated that the Yangtze River and adjacent area acted as a source for atmospheric CCl₄, C₂Cl₄, CHBr₃ and CH₂Cl₂ during the study period.