Modeling water content and solute activities of atmospheric aerosols
Authors
Cari Dutcher — University of California
Xinlei Ge — University of California
Anthony S. Wexler — University of California
Simon L Clegg — University of California
Category
Aerosol Properties
Description
Multilayer adsorption isotherm models describe a lattice adsorption of a solvent (e.g., water) molecule on to sites on a substrate (e.g., an electrolyte). In this work, statistical mechanics is used to modify the seminal Brunauer-Emmett-Teller (BET) adsorption isotherm to include distinct energies of adsorption of the solvent on to n layers in the hydration shell surrounding the solute molecule. Equations for the excess Gibbs energy, solute activity, and solute concentration are derived. The inclusion of additional hydration layers of distinct energy results in remarkable agreement of the solute concentration and osmotic coefficients for solutions at water activities (aw, equivalent to the equilibrium relative humidity) as high as 0.9 to 0.95. Even further extension of the isotherm to the aw = 1 limit can be achieved through incorporating electrostatic limiting law behavior. The model is shown to be consistent with the Zdanovskii-Stokes-Robinson (ZSR) mixing model, which is commonly used in atmospheric science for estimating water contents of aerosols containing more than one solute. The model will be incorporated into the Extended Aerosol Inorganics Model (E-AIM) and made available on the Internet.
