Identifying solid-aqueous phase transitions in atmospheric aerosols—I. Neutral-acidity solutions

The composition of aerosol particles is an important factor in understanding atmospheric phenomena such as cloud formation and visibility degradation. To predict the phase state and water content of aerosol particles as a function of relative humidity, one needs to understand the thermodynamics of multicomponent solutions at saturation. The goal of this paper is to determine the composition and deliquescence relative humidity for mixtures of salts, given the mole fraction of the respective ions and the relative humidity. Three sets of neutral acidity aerosol compositions are analyzed; the first set consists of aqueous solution of Na+, NH4+, SO42− and Cl−, the second set consists of Na+, NH4+, SO42− and NO3− and the third set contains Na+, NH4+, N03− and Cl−. For each set, contours of the deliquescence surfaces are plotted along; with path lines describing the compositional variation with relative humidity and phase boundaries. These diagrams can be used to predict the equilibrium phase state of aerosol particles as a function of composition and relative humidity.