Ion-induced reorientation and distribution of pentanone in the air-water boundary layer

Organic material at the surface of atmospheric aerosols is ubiquitous and plays an important role in Earth's atmosphere. Small ketones, such as 3-pentanone, are found in aerosols and as surface-active species on aerosols. This study uses 3-pentanone as a model ketone to understand how such molecules adsorb at the vapor-water interface on aqueous solutions containing sulfate, carbonate, or chloride ions. By combining surface spectroscopic experiments with computational methods, very detailed information about the molecular bonding, geometries, and surface orientation of 3-pentanone as a function of depth has been obtained. The results show that, for pure water, 3-pentanone resides at the topmost surface of water with the carbonyl pointing into the aqueous phase where it is weakly solvated. For Na2SO4-containing solutions, we found that sulfate ions in the boundary layer provoke changes in the geometry and interfacial position of 3-pentanone that are not seen in solutions containing sodium chloride or sodium carbonate. The results provide important insight into the behavior of ketones in the presence of salts at the surface of aerosols in the atmosphere.