AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Adsorption-Based Chemical Thermodynamics of Atmospheric Aerosols: Electrostatic Interactions and Weakly Dissociating Organic Acids
CARI DUTCHER, Peter Ohm, University of Minnesota, Twin Cities
Abstract Number: 241 Working Group: Aerosol Chemistry
Abstract The calculation of gas-liquid-solid equilibrium partitioning of water, electrolyte, and soluble organic components is critical to accurate determination of atmospheric chemistry properties and processes such as new particle formation and activation to cloud condensation nuclei. The partitioning of the molecular species between the gas and particle phase can be predicted using thermodynamic models. Previously, a transformative model for capturing thermodynamic properties of multicomponent aqueous solutions over the entire concentration range (Dutcher et al. JPC 2011, 2012, 2013) was developed using statistical mechanics and multilayer adsorption isotherms. That model needed only a few adsorption energy values to represent the solution thermodynamics of each solute.
In this work, the energetic values are related to the dipole-dipole electrostatic forces in solute-solvent and solvent-solvent interactions, leaving the solvent-solute intermolecular distance as a lone fully adjustable parameter. The model was successfully validated using thirty-seven 1:1 electrolytes and twenty non-dissociating organic solutions (Ohm et al. JPC 2015). However, careful attention is needed for weakly dissociating semi- volatile organic acids. Dicarboxylic acids such as malonic and glutaric acid are treated here as a mixture of non-dissociated organic species (HA) and dissociated organic species (H+ + A-). It was found that the apparent dissociation was greater than that predicted by known dissociation constants alone, emphasizing the effect of dissociation on activity coefficient predictions. To avoid additional parameterization from the mixture approach, an expression was used to relate the Debye-Hückel hard-core collision diameter to the adjustable solute-solvent intermolecular distance. This work results in predictive correlations for estimation of solute and solvent solution activities for which there are little or no activity data.