We use gas-liquid scattering experiments to investigate the ways in which gas molecules react with common liquids and atmospheric aerosols. These liquids include jet fuel, sulfuric acid, liquid metals, glycerol, and aqueous solutions (using water microjets), each bare or coated with surfactants. The experiments enable us to explore the interfacial analogues of bulk solvation, hydrogen bonding, the “like dissolves like” rule, proton exchange and acid-base reactions, halogen atom transfer, and electron solvation and reaction. In our most important applications, we study reactions with sea spray mimics that regulate air quality and climate change, the evaporation of fuel in combustion engines, and reactions initiated by surface solvated electrons.
Much of our research focuses on surfactant control of reactions at gas-liquid interfaces. Representative pathways are illustrated in the figures for the production of Br2 from collisions of Cl2 with surfactant-coated glycerol containing Br- (left figure) and from collisions of N2O5 with surfactant-coated water containing Br- (right figure). These systems are used to model aerosol-mediated reactions for droplets containing water and organic molecules. These experiments demonstrate the remarkable power of cationic surfactants such as tetrahexylammonium (pictured in the left figure) to catalyze reactions of gaseous Cl2 and N2O5 with halide ions through their ability to drag the anion to the surface region, where it can react with an incoming gas molecule. Reactions of N2O5 with sea spray are particularly important because the hydrolysis and halogenation of this nighttime NOx reservoir influences the global concentrations of the ozone (a pollutant), hydroxyl radical (“chemical detergent of the atmosophere”, and methane ( a greenhouse gas).