Abstract: Volatile halocarbons (VHCs) are important atmospheric trace gases,which play significant roles in the global warming and atmospheric chemistry.The concentrations of four VHCs in the Bohai Sea (BS) and northern Yellow Sea (NYS) were measured.The results showed that the concentrations of CHBr2Cl,CHBr3,C2HCl3 and C2Cl4 in the surface seawater of the BS and NYS were 7.03 (4.23~12.63) pmol/L,19.61 (5.99~55.00) pmol/L,20.37 (1.68~58.25) pmol/L,41.03 (10.84~96.94) pmol/L,respectively.The distributions of the four VHCs in the surface water of the BS and NYS were clearly influenced by the combined actions of biological production,anthropogenic activities and riverine input,and exhibited a gradually decreasing trend from north to south in the BS,with the minimum concentrations appearing on the north of Shandong Peninsula and in the Yalu River estuary.The depth profiles of the four VHCs were characterized by the maxima in the euphotic layer due to the impacts of geographical locations and hydrological conditions.The diel variation of VHCs was investigated at a fixed station.The results showed that the lowest concentrations of the four VHCs occurred at 7:00 and 21:00,while the highest values appeared at 13:00 and 17:00,indicating that a combination of illumination and tide might be responsible for the diurnal variation of VHCs.On the basis of gas exchange model and surface concentrations of VHCs,the mean sea-to-air fluxes of four VHCs in the study area were estimated to be 36.28 (0.13~109.54) nmol/m2d,85.96 (-8.9~308.61) nmol/m2d,191.71 (0.10~386.67) nmol/m2d,285.14 (0.19~914.85) nmol/m2d,respectively,indicating that the investigated area appeared to be a source of atmospheric CHBr2Cl,CHBr3,C2HCl3 and C2Cl4 during the study time.