Green Leaf Volatiles on Atmospheric Air/Water Interfaces: A Combined Experimental/Molecular Simulation Study

Green leaf volatiles (GLVs) are a family of oxygenated hydrocarbons emitted by plants, especially under mechanical stress or damage. GLVs are believed to react with atmospheric oxidants both at the surface and within the bulk of water droplets (fog, mist, and rain), which can significantly contribute to the formation of secondary organic aerosols (SOAs). Both molecular simulation and experiments were conducted to investigate the properties of four selective GLVs, 2-methyl-3-buten-2-ol (MBO), methyl salicylate (MeSA), cis-3-hexen-1-ol (HxO), and cis-3-hexenylacetate (HxAc) in the air/water systems. Our simulations show that all the four GLVs have a thermodynamic preference to be adsorbed to the water droplets and stay at the air/water interface, as indicated by the deep free energy minima at those interfaces, and the stability of the GLV solutes at the air/water interface is mainly driven by energetic interactions between these solutes and water molecules. These results suggest that the air/water interface is the most likely reaction site for GLVs and atmospheric oxidants. Furthermore, the surface tension at the air/water interface is affected by adding those GLVs. These findings are relevant to the kinetics and mechanisms of the reactions between GLVs and atmospheric oxidants, which can be significantly different from those observed when the reactions take place in the gas phase or in the bulk of water phases.