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 (ϕ_SOA). Flow reactor measurements of the <i>trans</i>-β-isoprene epoxydiol (<i>trans</i>-β-IEPOX) and methacrylic acid epoxide (MAE) aerosol reaction probability (γ) were performed on atomized aerosols with compositions similar to those used in chamber studies. Observed γ ranges for <i>trans</i>-β-IEPOX and MAE were 6.5 × 10^–4−0.021 and 4.9–5.2 × 10^–4, respectively. Through the use of a time-dependent chemical box model initialized with chamber conditions and γ measurements, ϕ_SOA values for <i>trans</i>-β-IEPOX and MAE on different aerosol compositions were estimated between 0.03–0.21 and 0.07–0.25, respectively, with the MAE ϕ_SOA showing more uncertainty