Concentrations of CHCl₃, C₂HCl₃, C₂Cl₄, CHBr₃and CHBr₂Cl in the South Yellow Sea and the East China Sea during autumn

Abstract: Concentrations of five volatile halocarbons (VHCs), that is, chloroform (CHCl3), trichloroethylene (C2HCl3), tetrachloroethylene (C2Cl4), bromoform (CHBr3) and chlorodibromomethane (CHBr2Cl), were measured in the South Yellow Sea (SYS) and East China Sea (ECS) during autumn in 2011. The average (min-max) concentrations of CHCl3, C2HCl3, C2Cl4, CHBr2Cl and CHBr3 in surface seawater were 63.91 (24.63-361.23), 28.46 (1.82-85.77), 21.04 (9.85-89.31), 20.92 (7.98-59.89) and 75.91 (0.04-537.04) pmol L-1 respectively. The five VHCs exhibited a point distribution in autumn with clearly defined patterns in certain areas. In the vertical profiles, the highest concentrations of VHCs generally appeared in the upper mixing layer. Different VHCs were correlated with different environmental parameters, such as temperature, salinity, chlorophyll a (Chl-a), nutrient levels and bacteria. These results revealed that the sources of these VHCs were influenced by the Yangtze River effluent and Kuroshio waters as well as the biogenic release. Diurnal bimodal cycles were obvious in the concentrations of the five VHCs in the ECS. In general, concentrations peaked around noon, likely owing to biological production and photochemical mechanisms, and a secondary peak occurred around midnight, possibly resulting from a combination of respiration, zooplankton feeding and tidal action. The estimated sea-to-air fluxes showed that the study area was a net source of the five VHCs in the atmosphere during the study period.