Berlin 2005 – wissenschaftliches Programm

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UP: Umweltphysik

UP 1: Aerosole I

UP 1.3: Fachvortrag

Montag, 7. März 2005, 14:30–14:45, TU HFT101

REFORMULATING AEROSOL THERMODYNAMICS — •Swen Metzger — Max-Planck-Institute for Chemistry, Department of Atmospheric Chemistry, J.J. Becherweg 27, D-55128 Mainz, Germany

Modeling aerosol composition is rather complex due to the required aerosol thermodynamics computations. We show, however, that for atmospheric aerosols thermodynamics can be considerably simplified. Aerosol water, which determines the aerosol activity, is not constant but depends itself on thermodynamics, i.e. on the relative humidity (RH). In chemical and thermodynamical equilibrium, RH fixes the water activity of the aerosol and, thus, for a given aerosol concentration and type also the water content of the aerosol. The aerosol activity coefficients are then a function of RH. We show that the complex system of aerosol thermodynamics can be solved analytically, if we reformulate chemical equilibrium to include water. We demonstrate that this method provides an alternative for the computationally expensive iterative activity coefficient calculation methods presently used in thermodynamic gas/aerosol models. The gain of our method is that the entire system of the gas/aerosol equilibrium partitioning can be solved non-iteratively, a substantial advantage in aerosol composition modeling. We furthermore show that this new approach (the equilibrium simplified thermodynamic aerosol model, EQSAM) compares favorably against current state-ofthe-art equilibrium models.