Distributions and sea-to-air fluxes of volatile halocarbons in the East China Sea in early winter

Abstract

The concentrations of six volatile halogenated organic compounds (VHOC)–chloroform (CHCl3), trichloroethylene (C2HCl3), tetrachloroethylene (C2Cl4), carbon tetrachloride (CCl4), methylchloroform (CH3CCl3), and bromoform (CHBr3) in the East China Sea (ECS) in November and December 2010 were measured by a purge and trap system coupled to a gas chromatograph with an electron capture detection (ECD). Mean (range) concentrations of CHCl3, C2HCl3, C2Cl4, CH3CCl3, CCl4 and CHBr3 in the surface water were 16.90 (0.40–62.92), 16.27 (2.78–83.33), 2.40 (0.39–9.33), 32.29 (19.72–57.68), 1.70 (0.39–8.73) and 17.11 (4.33–34.46) pM, respectively. With the exception of C2HCl3, the concentrations of other five kinds of VHOC generally exhibited a decreasing trend with distance from the coast, with the low values found in the open sea. The anthropogenic sources contributed to the elevated levels of CCl4 and CH3CCl3, whereas a combination of the anthropogenic and biogenic sources might be responsible for the elevated levels of CHCl3, C2HCl3, C2Cl4 and CHBr3. In the depth profiles, vertical distributions of the six VHOC in the water column were complicated, with the maxima occurring at 0–100m depths. The mean sea-to-air fluxes of CHCl3, C2HCl3, C2Cl4 and CHBr3 were estimated to be 21.08, 29.94, 2.05 and 35.50nmolm−2d−1, respectively, indicating that the ECS was a source for the four VHOC in the atmosphere.