Abstract
Ammonium sulfate is an important component of aqueous atmospheric aerosols in both remote and urban regions. Equilibrium water vapor pressures over supersaturated aqueous ammonium sulfate have been determined from 278.15 to 313.15 K using an electrodynamic balance. Partial molar enthalpies of water (L{sub 1} to {approximately}25 mol/kg) and partial molar heat capacities (J{sub 1}, to {approximately}8 mol/kg) have been calculated from the measurements, together with enthalpies of solution, heat capacities, and boiling point elevations. The results have been used to parameterize a mole-fraction-based activity coefficient model. Equilibrium constants for the reaction (NH{sub 4}){sub 2}SO{sub 4}{sub (cr)} {l_reversible} 2NH{sub 4}{sup +} (aq) + SO{sub 4}{sup 2{minus}} aq have been evaluated from 373.15 K to the eutectic point (5.00 mol/kg, 254.21 K). The model satisfactorily represent water vapor pressures and saturations with respect to solid phases ice and ammonium sulfate from 253 to 373.15K and up to 8--10 mol/kg, and water vapor pressures from 278.15 to 313.15 K and up to {approximately}25 mol/kg.
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