A systematic study of the SO2 solubility of binary systems (SO2 + water + 1 electrolyte) and of the complex mixtures seawater and brine was performed. The experimental setup allowed a comprehensive description of the equilibrium state by a UV spectroscopic measurement of the partial pressure of SO2 in the gas phase and the concentration of sulfur compounds in the liquid phase. The influence of main ions present in the brine (e.g., Na+, Cl-, K+, Mg2+, Ca2+, HCO3-) was studied at 298 and 323 K. The experiments revealed considerable deviations of already existing models from experimental data mainly at higher temperatures. A thermodynamic model based on caloric data and a Pitzer and a Sechenov approach for the calculation of activity coefficients was fitted to experimental data. This work demonstrates that fitting selected Pitzer parameters improves the model performance very much. The new model provides a reliable prediction of SO2 solubility over the entire investigated range of temperature and concentrations. (C) 2015 Published by Elsevier B.V.