A thermodynamic model of mixed organic-inorganic aerosols to predict activity coefficients A. Zuend, C. Marcolli, B. P. Luo, and T. Peter Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland
Abstract. Tropospheric aerosols contain mixtures of inorganic salts, acids, water, and
a large variety of organic compounds. Interactions between these substances in
liquid mixtures lead to discrepancies from ideal thermodynamic behaviour. By
means of activity coefficients, non-ideal behaviour can be taken into account.
We present here a thermodynamic model named AIOMFAC (Aerosol Inorganic-Organic
Mixtures Functional groups Activity Coefficients) that is able to calculate activity
coefficients covering inorganic, organic, and organic-inorganic interactions in aqueous
solutions over a wide concentration range. This model is based on the activity coefficient
model LIFAC by Yan et al. (1999) that we modified and reparametrised to better describe atmospherically
relevant conditions and mixture compositions.
Focusing on atmospheric applications we considered H+, Li+, Na+, K+,
NH+4, Mg2+, Ca2+, Cl−, Br−, NO−3, HSO−4,
and SO2−4 as cations and anions and a wide range of alcohols/polyols composed of the functional
groups CHn and OH as organic compounds. With AIOMFAC, the activities of the components
within an aqueous electrolyte solution are well represented up to high ionic strength. Most notably,
a semi-empirical middle-range parametrisation of direct organic-inorganic interactions in
alcohol+water+salt solutions strongly improves the agreement between experimental and modelled activity coefficients.
At room temperature, this novel thermodynamic model offers the possibility to compute equilibrium relative
humidities, gas/particle partitioning and liquid-liquid phase separations with high accuracy. In further studies,
other organic functional groups will be introduced. The model framework is not restricted to specific ions or
organic compounds and is therefore also applicable for other research topics.
Citation: Zuend, A., Marcolli, C., Luo, B. P., and Peter, T.: A thermodynamic model of mixed organic-inorganic aerosols to predict activity coefficients, Atmos. Chem. Phys., 8, 4559-4593, doi:10.5194/acp-8-4559-2008, 2008.