The mean spherical approximation is used to describe the vapor pressure over aqueous solutions containingan electrolyte and carbon dioxide. Three electrolytes have been studied: NaOH, NaCl, and acetic acid. Agood representation is obtained with a reduced number of parameters as compared to previous models. Theseparameters account for the concentration and temperature dependence of the solute sizes and the relativepermittivity of solution. The numerical values of these physically interpretable parameters are in a reasonablerange.