Rapid heterogeneous oxidation of organic coatings on submicron aerosols

Laboratory studies have found that heterogeneous oxidation can affect the composition and loading of atmospheric organic aerosol particles over time scales of several days, but most studies have examined pure organic particles only. In this study, in order to probe the reactivity of organic species confined near the particle surface, the rates and products of the OH-initiated oxidation of pure squalane particles are compared to oxidation of thin coatings of squalane on ammonium sulfate particles. The squalane reaction rate constant shows a linear dependence on the organic surface area-to-volume ratio, with rate constants for coated particles up to 10 times larger than for pure particles. Changes in the carbon oxidation state and fraction of particulate carbon remaining show similar enhancements, implying that heterogeneous oxidation may exhibit a stronger effect on the loadings and properties of organic aerosol than previously estimated from laboratory studies.