Abstract: In this talk I will review some of our recent work concerning reactions of trace atmospheric gases with aqueous aerosol. I will discuss some of the theoretical tools we have developed to study reactions in strongly heterogeneous environments, including the use of reactive intermolecular potentials and novel path sampling algorithms. When wedded to a molecular theory of mass transfer kinetics we have developed, these tools enable us to explain the dependence of gas uptake measurements on aerosol composition. Throughout, I will highlight work on the reactive uptake of O3 and N2O5 by sea spray aerosol.