Abstract View
Evidence that Halogen Bonding Catalyzes the Heterogeneous Chlorination of Alkene Aerosols
MEIRONG ZENG, Kevin R. Wilson, Lawrence Berkeley National Laboratory
Abstract Number: 627
Working Group: Aerosol Chemistry
Abstract
A key challenge in predicting the multiphase chemistry of aerosols is connecting the uptake coefficients, observed in an experiment, with the kinetics of individual elementary steps that control the chemistry that occurs across a gas/liquid interface. Here we report evidence that oxygenated molecules accelerate the heterogeneous reaction rate of chlorine gas with squalene (Sqe) aerosols. The effective uptake coefficient for Sqe is sensitive to both the aerosol composition and gas phase environment. In binary aerosol mixtures with 2-decyl-1-tetradecanol, linoleic acid and oleic acid, Sqe reacts 12-23x more rapidly than in a pure aerosol. In contrast, the reactivity of Sqe is diminished by 3x when mixed with an alkane. Additionally, small oxygenated molecules in the gas phase (water, ethanol, acetone, and acetic acid) also significantly enhance (up to 10x) the heterogeneous chlorination rate of Sqe. The formation kinetics of the chlorinated products suggest that overall reaction mechanism is not altered by the presence of these aerosol and gas phase additives, suggesting instead that they act as catalysts. Since the largest rate acceleration occurs in the presence of oxygenated molecules, we conclude that halogen bonding enhances reactivity by slowing the desorption kinetics of Cl2 at the gas/aerosols interface, in a way that is analogous to decreasing temperature. These results highlight the importance of relatively weak interactions in controlling the multiphase reactions of aerosols in the atmosphere and indoor environments.