Modeling of multicomponent aerosol thermodynamics

When modeling behavior of atmospheric aerosols, equilibrium or non-equilibrium conditions are calculated for mixtures of solid particles, liquid droplets and condensable atmospheric gases. Normally dilute solutions, solid and gas phases are considered to behave ideally. However, in concentrated solutions, activities are needed instead of concentrations. Activity is a product of concentration and an activity coefficient, which gives deviation from ideal behavior. Activity coefficients can be calculated with activity coefficient models, which are thermodynamic models containing fitting parameters. Accurate non-electrolyte and electrolyte models can be found from the literature, but there are very few models for multicomponent aerosols containing both electrolytes and organic species. In this study, we did some modifications and fitted parameters for three published and one new activity coefficient models. Now these models are suitable for atmospheric aqueous organic-electrolyte mixtures.

Vapor pressures over curved surfaces are bigger than vapor pressures over flat surfaces. In addition to droplet radius, another important factor affecting to the pressure increase is solution surface tension. Some dissolved species can reduce the surface tension substantially even at low concentrations, but some species can increase the surface tension. Usually surface tensions are calculated using simple parameterizations fitted to experimental values. The third solution property, which is usually fitted to experimental data, is solution density. In this study, we fitted parameterizations for solution surface tension and density. These solution properties are needed in many thermodynamics models, e.g. cloud microphysics models and models predicting hygroscopic growth.