Reactive Uptake of an Isoprene-Derived Epoxydiol to Submicron Aerosol Particles

The reactive uptake of isoprene-derived epoxydiols (IEPOX) is thought to be a significant source of atmospheric secondary organic aerosol (SOA). However, the IEPOX reaction probability (gamma(IEPOX)) and its dependence upon particle composition remain poorly constrained. We report measurements of gamma(IEPOX) for trans-beta-IEPOX, the predominant IEPOX isomer, on submicron particles as a function of composition, acidity, and relative humidity (RH). Particle acidity had the strongest effect. gamma(IEPOX) is more than 500 times greater on ammonium bisulfate (gamma similar to 0.05) than on ammonium sulfate (gamma pound 1 x 10(-4)). We could accurately predict gamma(IEPOX) using an acid-catalyzed, epoxide ring-opening mechanism and a high Henry's law coefficient (1.7 x 10(8) M/atm). Suppression of gamma(IEPOX) was observed on particles containing both ammonium bisulfate and poly(ethylene glycol) (PEG-300), likely due to diffusion and solubility limitations within a PEG-300 coating, suggesting that IEPOX uptake could be self-limiting. Using the measured uptake kinetics, the predicted atmospheric lifetime of IEPOX is a few hours in the presence of highly acidic particles (pH < 0) but is greater than 25 h on less acidic particles (pH > 3). This work highlights the importance of aerosol acidity for accurately predicting the fate of IEPOX and anthropogenically influenced biogenic SOA formation.