The aim of this paper is to model the simultaneous absorption mass transfer of NO2 and SO2 with chemical reactions. The absorption has been studied at low temperature (25 degrees C) in a gas-liquid stirred tank reactor, open for the gas flow and closed for the liquid phase. The kinetics of the reactions between sulphite and nitrite ions, obtained respectively from the absorption Of SO2 and NO2, depend mainly on the pH of the solution. With a weakly acid solution (4 < pH < 5), at low temperature, after the simultaneous absorption and interaction between the ions generated, it is possible to transform NO2 and SO2 into two products: N2O and hydroxylamine disulfonic acid (HADS). In the first time, the mass transfer during the absorption of the two gases, without chemical reaction was characterized separately. Then the mass transfer during the simultaneous absorption with chemical reaction was quantified. The experimental conditions have been fixed at pH 4 and 5 for different gas flow rates. The mass transfer for NO2 was clearly improved by the interaction between nitrite and sulphite ions. The modelling of mass transfer in the liquid phase of the reactor allowed to specify the hydration kinetics of nitrogen dioxide. (c) 2005 Elsevier B.V. All rights reserved.