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