IDENTIFYING SOLID-AQUEOUS PHASE-TRANSITIONS IN ATMOSPHERIC AEROSOLS .1. NEUTRAL-ACIDITY SOLUTIONS

The composition of aerosol particles is an important factor in underst anding atmospheric phenomena such as cloud formation and visibility de gradation. To predict the phase state and water content of aerosol par ticles 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 respec tive ions and the relative humidity. Three sets of neutral acidity aer osol compositions are analyzed; the first set consists of aqueous solu tion of Na+, NH4+, SO42- and Cl-, the second set consists of Na+, NH4, SO42- and NO3- and the third set contains Na+, NH4+, NO3- and Cl-. F or each set, contours of the deliquescence surfaces are plotted along with path lines describing the compositional variation with relative h umidity and phase boundaries. These diagrams can be used to predict th e equilibrium phase state of aerosol particles as a function of compos ition and relative humidity.