WATER-ABSORPTION BY ORGANICS - SURVEY OF LABORATORY EVIDENCE AND EVALUATION OF UNIFAC FOR ESTIMATING WATER ACTIVITY

The composition of organic material in atmospheric particles and the i nfluence of these organics on aggregate particle properties have remai ned less well characterized than that of the inorganic ionic fraction. While laboratory and atmospheric studies strive to quantify the forma tion rates and concentrations of water-soluble and other organic compo unds in atmospheric particles, concerted efforts are being devoted by many scientists to develop models for simulating the formation and gas -particle distribution of condensible organics in the atmosphere. With in this research milieu, as a first step toward developing a capabilit y to simulate the thermodynamics of aqueous, organic-containing submic ron droplets under atmospheric conditions, in this paper we (i) synthe size published laboratory data to evaluate the water absorption behavi or of multifunctional oxygenated organic compounds and (ii) test the r eliability of the UNIFAC group contribution method (1) for estimating water activities of aqueous organic solutions. The laboratory data sho w that multifunctional oxygenated compounds can absorb water over the entire range of relative humidities. For a wide variety of compounds ( e.g., glycols, dicarboxylic acids, keto acids) and a wide range of sol ute concentrations (0 to >90% by wt), we find that, in most cases, wat er activities can be estimated to within approximately 15%.