(298c) Integrated Raoult's And Henry's Law Approach For Multiphase Organic Aerosol Partitioning

Organic gas-aerosol partitioning has been described in atmospheric models using Raoult's Law (typically for a primarily organic aerosol phase) and/or Henry's Law (typically for an aqueous aerosol phase). In both cases, activity coefficients are needed to account for nonideal behavior in the aerosol solution. Saturation vapor pressures, Henry's law constants, and activity coefficients for organic aerosol compounds must typically be estimated. As a result, thermodynamic inconsistencies can arise when using Raoult's and Henry's Law approaches together due to errors in estimation methods. Comparison of known and estimated parameters for representative semivolatile organics suggest overall uncertainties of 2-3 orders of magnitude, resulting in dramatic shifts in predicted gas-aerosol partitioning for many compounds. Results also indicate that activity coefficient estimates are the largest source of uncertainty. By appropriately scaling estimated activity coefficient values, Raoult's Law and Henry's Law can be integrated in a thermodynamically consistent manner, despite uncertainties in estimation methods.