Heterogeneous Reactions of Isoprene-Derived Epoxides: Reaction Probabilities and Molar Secondary Organic Aerosol Yield Estimates

A combination of flow reactor studies and chamber modeling is used to constrain two uncertain parameters central to the formation of secondary organic aerosol (SOA) from isoprene-derived epoxides: (1) the rate of heterogeneous uptake of epoxide to the particle phase and (2) the molar fraction of epoxide reactively taken up that contributes to SOA, the SOA yield (phi(SOA)). Flow reactor measurements of the trans-beta-isoprene epoxydiol (trans-beta-IEPOX) and methacrylic acid epoxide (MAE) aerosol reaction probability (gamma) were performed on atomized aerosols with compositions similar to those used in chamber studies. Observed gamma ranges for trans-beta-IEPOX and MAE were 6.5 x 10(-4)-0.021 and 4.9-5.2 X 10(-4), respectively. Through the use of a time-dependent chemical box model initialized with chamber conditions and gamma measurements, phi(SOA) values for trans-beta-IEPOX and MAE on different aerosol compositions were estimated between 0.03-021 and 0.07-025, respectively, with the MAE phi(SOA) showing more uncertainty.