A thermodynamic model of the system HCl-HNO₃-H₂SO₄-H₂O, including solubilities of HBr, from

A multicomponent mole-fraction-based thermodynamic model, together with Henry's law constants and the vapor pressure of pure water, is used to represent aqueous phase activities, vapor pressures (of H₂O, HNO₃, HCl, and HBr), and saturation with respect to solid phases (ice, H₂SO₄·nH₂O, HNO₃·nH₂O, and HCl·H₂O) in the system HCl-HBr-HNO₃-H₂SO₄-H₂O. The model is valid from 328 to -1 total solute molality for solutions containing mainly H₂SO₄ and HNO₃. Model parameters for pure aqueous H₂SO₄ were adopted from a previous study, and values for HNO₃-H₂O, HCl-H₂O, and HBr-H₂O were obtained by fitting to activity and osmotic coefficients, electromotive force (emf) measurements, vapor pressures, freezing points, and thermal (enthalpy and heat capacity) data. The model was tested using measured partial pressures and solubilities of HCl in aqueous H₂SO₄ from >328 to 200 K, HBr solubilities in aqueous H₂SO₄ from ∼240 to 205 K, and HNO₃ partial pressures and freezing points for HNO₃-H₂SO₄-H₂O mixtures from 273.15 to 3-H₂SO₄-H₂O. Solubilities of HNO₃, HCl, and HBr in liquid stratospheric aerosols are calculated. © 1995 American Chemical Society.