The uptake of SO 2 on aqueous surfaces was studied by directly measuring SO 2 concentration distribution above the surface by means of laser-induced fluorescence method in an impinging flow field with a 10-100 ms order contact time between the gas flow containing SO 2 and the water flow. The uptake coefficient was determined by using the eq which describes the boundary condition at the surface. The uptake coefficient increased with pH of the aqueous phase and reached the limiting value of 0.028 ( 0.010 at pH ) 13.2 at 293.5 K. Its temperature dependence was slightly negative. The present uptake coefficients could be understood satisfactorily by taking into account the rapid acid-dissociation reaction of dissolved SO 2 with the reported bulk reaction rate constant.