Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 6 4 2006 10.5194/acp-6-975-2006 http://www.atmos-chem-phys.net/6/975/2006/ http://www.atmos-chem-phys.net/6/975/2006/acp-6-975-2006.html http://www.atmos-chem-phys.net/6/975/2006/acp-6-975-2006.pdf 975 992 2006-03-28 A new inorganic atmospheric aerosol phase equilibrium model (UHAERO) N. R. Amundson A. Caboussat J. W. He A. V. Martynenko V. B. Savarin J. H. Seinfeld K. Y. Yoo Department of Mathematics, University of Houston, Houston, USA Ecole Nationale Supérieure de Techniques Avancées, Paris, France Departments of Chemical Engineering and Environmental Science and Engineering, California Institute of Technology, Pasadena, USA Department of Chemical Engineering, Seoul National University of Technology, Seoul, Korea A variety of thermodynamic models have been developed to predict inorganic gas-aerosol equilibrium. To achieve computational efficiency a number of the models rely on a priori specification of the phases present in certain relative humidity regimes. Presented here is a new computational model, named UHAERO, that is both efficient and rigorously computes phase behavior without any a priori specification. The computational implementation is based on minimization of the Gibbs free energy using a primal-dual method, coupled to a Newton iteration. The mathematical details of the solution are given elsewhere. The model computes deliquescence behavior without any a priori specification of the relative humidities of deliquescence. Also included in the model is a formulation based on classical theory of nucleation kinetics that predicts crystallization behavior. Detailed phase diagrams of the sulfate/nitrate/ammonium/water system are presented as a function of relative humidity at 298.15 K over the complete space of composition.