A THERMODYNAMIC MODEL OF THE SYSTEM HCL-HNO3-H2SO4-H2O, INCLUDING SOLUBILITIES OF HBR, FROM LESS-THAN-200 TO 328 K

A multicomponent mole-fraction-based thermodynamic model, together wit h 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 . nH(2)O, HNO3 . nH(2)O, and HCl . 3H(2)O) in the system HCl-HBr-HNO3 -H2SO4-H2O. The model is valid from 328 to <200 K, and up to similar t o 40 mol kg(-1) total solute molality for solutions containing mainly H2SO4 and HNO3. Model parameters for pure aqueous H2SO4 were adopted f rom a previous study, and values for HNO3-H2O, HCl-H2O, and HBr-H2O we re obtained by fitting to activity and osmotic coefficients, electromo tive force (emf) measurements, vapor pressures, freezing points, and t hermal (enthalpy and heat capacity) data. The model was tested using m easured partial pressures and solubilities of HCl in aqueous H2SO4 fro m >328 to 200 K, HBr solubilities in aqueous H2SO4 from similar to 240 to 205 K, and HNO3 partial pressures and freezing points for HNO3-H2S O4-H2O mixtures from 273.15 to <200 K. Ternary (mixture) parameters we re required only for HNO3-H2SO4-H2O. Solubilities of HNO3, HCl, and HB r in liquid stratospheric aerosols are calculated.