Some new thermal data and interpretations for the system SO2-NHS-H2O-O2

Thermal data have been obtained for gas-phase reactions in systems consisting of NH₃ and SO₂; of NH₃, SO₂ and O₂; of NH₃, SO₂, and H₂O (vapor); and of NH₃, SO₂, O₂ and H₂O (vapor). A special calorimeter was constructed with capability for rapid injection of gases, magnetically driven stirrer, and a fast-reacting thermocouple. Results yield reaction enthalpies of –30 kcal mole^–1 for the anhydrous reaction of SO₂ with NH₃, with the presence of oxygen having no effect on that value. With water vapor present the enthalpy goes to –34 and –45 kcal mole^–1 in the absence and presence of oxygen, respectively, indicating the importance of water to rapid oxidation in the system. The relationship of these results to other thermal information, together with implications for the atmospheric SO₂ cycle and particulate formation, is discussed.