Toward a general parameterization of N2O5 reactivity on aqueous particles: the competing effects of particle liquid water, nitrate and chloride

The heterogeneous reaction of N2O5 on mixed organic-inorganic aerosol particles was investigated using an entrained aerosol flow tube coupled to a custom-built chemical ionization mass spectrometer. Laboratory results on aqueous particles confirm a strong dependence of the reactive uptake coefficient (gamma) on particle liquid water, for particle water concentrations below 15 M, and the molar ratio of particle water to nitrate. Measurements of gamma(N2O5) on mixed chloride-nitrate particles indicate that the presence of trace chloride can negate the suppression of gamma(N2O5) at high nitrate loadings with implications for polluted coastal regions. These results are used to construct a new parameterization for gamma(N2O5), that when coupled to an aerosol thermodynamics model, can be used within regional and/or global chemical transport models.