The simultaneous solubility of sulfur dioxide and ammonia in aqueous solutions of (ammonium sulfate or sodium sulfate) was measured by a synthetic method in the temperature range from 313.6 to 373.2 K and at pressures up to 2.5 MPa. Furthermore, the enthalpy change upon diluting aqueous solutions of sulfur dioxide, ammonia and (ammonium sulfate or sodium sulfate) in aqueous solutions of the same salt was measured in a batch calorimeter at about 313 and 352 K. The experimental results are used for comparison with predictions from a thermodynamic model for the vapor-liquid equilibrium and the enthalpy of dilution of those chemical reacting systems. In that model, activity coefficients are calculated from Pitzer's molality-scale-based Gibbs excess energy model, where all interaction parameters are either adopted from previous investigations on the properties of the binary and ternary sub-systems (if available) or they are neglected (if they are not available). (c) 2006 Elsevier B.V. All rights reserved.