Invited Paper HC+SA+SS-WeA3
Gas-Liquid Scattering Studies of Atmospheric Reactions at the Surfaces of Sea-Spray Mimics

Wednesday, November 1, 2017, 3:00 pm, Room 24

Heterogeneous reactions between atmospheric gases and sea-spray aerosols are fascinating examples of complex interfacial processes involving water, ions, and surface-active molecules. These reactions are also important because of the controlling role they play in regulating pollution and greenhouse gases in the troposphere. Of particular interest is the atmospheric molecule N₂O₅, created indirectly by fossil fuel burning. During the day, N₂O₅ is photolyzed to NO₂ and NO₃, ultimately producing O₃ and then OH· radicals that destroy CH₄. During the night, N₂O₅ can be removed by dissolving into sea-spray aerosols near coastal regions. This dissolution is followed by rapid hydrolysis to HNO₃ or reaction with Cl^- to produce ClNO₂, a gas that potentially supplies reactive Cl atoms and returns half of the NO₂ to the atmosphere. The fate of N₂O₅ upon collision with an aerosol droplet is enormously difficult to predict because the droplets are chemically diverse and often possess an outer layer of lipid-like organic molecules. Such surface-active species can inhibit or even enhance uptake and reactivity by orders of magnitude.

We have implemented gas–liquid scattering experiments to investigate the dynamics of these interfacial N₂O₅ reactions. By directing a well-defined beam of N₂O₅ at a stream of salty water emerging from a liquid microjet in vacuum, we can track the uptake and reactivity of N₂O₅ with seawater and sea-spray mimics. We have also used similar experiments involving liquid glycerol to explore the ability of cationic and zwitterionic surfactants to increase ion concentrations of Br^– or Cl^– at the surface and to stabilize reaction intermediates created by N₂O₅. These studies provide insight into interfacial ionization and bimolecular reactions at the surfaces of complex liquids found in the atmosphere.