(730g) Green Leaf Volatiles and Reactive Oxygen Species On Atmospheric Air/Water Interfaces

Atmospheric aerosols play an important role in climate, air quality and fate of pollutants under atmospheric conditions. However, many knowledge gaps still remain for secondary organic aerosols (SOAs), which are particulate matter formed by compounds that originated from chemical reactions of organics in the atmosphere. SOAs are an important factor in the well-known smog-fog-smog cycle, where fog forms by condensation of water on submicron atmospheric particles, which then uptake organics and reactive oxygen species (ROSs, e.g., ozone and radicals such as •OH). These compounds undergo chemical reactions within the fog droplets, yielding products that contribute to the formation of more SOAs. Many recent efforts have concentrated on characterizing the organic fraction in samples of fog water. A significant fraction of these organics are emitted by microbes, bacteria and plants. Some of these compounds include green leaf volatiles (GLVs), which is a group of very reactive oxygenated hydrocarbons emitted in large quantities by plants, especially when they are injured or under stress conditions (e.g., grass cutting, animal grazing, local weather changes). These GLVs can react with ROSs in a fog environment, but the mechanisms and kinetics of these reactions depend on whether the reactions take place within the bulk of the water droplets, in the air/water interface or in gas phase. Here we investigated the adsorption of GLVs and ROSs on atmospheric air/water interfaces, as well as the interactions between these species, using potential of mean force (PMF) calculations and classical molecular dynamics (MD) simulations. Our results indicate that both GLVs and ROSs have a strong thermodynamic preference to remain at the air/water interface, and thus chemical reactions between atmospheric GLVs and ROSs are more likely to take place at the interface, rather than in the water phase or in the gas phase. Relevant interfacial properties (free energies, density profiles, orientations, dynamics and number of contacts between GLVs and ROSs) are investigated and discussed in this study.