Molecular simulations of green leaf volatiles and atmospheric oxidants on air/water interfaces

Green leaf volatiles (GLVs) are oxygenated hydrocarbons that are emitted by plants, especially under stress conditions such as mechanical damage and local weather changes. GLVs can react with photochemically-generated oxidants (e. g., OH radicals) in atmospheric water drops, and contribute to the formation of secondary organic aerosols (SOAs). Here we investigated the adsorption of a gas phase GLV, 2-methyl-3-buten-2-ol (MBO) and OH radicals on atmospheric air/water interfaces using classical molecular dynamics (MD) simulations and potential of mean force (PMF) calculations. Our models can reproduce experimental values of the free energy of hydration of MBO and (OH)-O-center dot, as well as 1-octanol/water partition coefficients of MBO determined experimentally in this study. Both MBO and (OH)-O-center dot have a strong thermodynamic incentive to remain at the air/water interface, with their density profiles overlapping significantly at the interface. These results suggest that chemical reactions between MBO and (OH)-O-center dot are more likely to take place at the interface, rather than inside the bulk of water droplets or in the vapor phase. We found a significant number of contacts between MBO and center dot OH in our simulations, which could lead to reactions between these two species.