HR: 0800h
AN: A51C-0589    [Abstracts]
TI: Interfacial Chemistry of Aqueous Sulfur/Iodide Aerosol Microdroplets in Gaseous Ozone
AU: * Enami, S
EM: enami@caltech.edu
AF: California Institute of Technology, W. M. Keck Laboratories 138-78 Caltech, Pasadena, CA 91125, United States
AU: Vecitis, C D
EM: vecitis@caltech.edu
AF: California Institute of Technology, W. M. Keck Laboratories 138-78 Caltech, Pasadena, CA 91125, United States
AU: Cheng, J
EM: jetcheng
AF: California Institute of Technology, W. M. Keck Laboratories 138-78 Caltech, Pasadena, CA 91125, United States
AU: Colussi, A J
EM: ajcoluss@caltech.edu
AF: California Institute of Technology, W. M. Keck Laboratories 138-78 Caltech, Pasadena, CA 91125, United States
AU: Hoffmann, M R
EM: mrh@caltech.edu
AF: California Institute of Technology, W. M. Keck Laboratories 138-78 Caltech, Pasadena, CA 91125, United States
AB: The intermediates ISO₃^- (m/z = 207) and IS₂O₃^- (m/z = 239) generated in aqueous (iodide - thiosulfate) microdroplets traversing dilute ozone gas plumes at atmospheric pressure are detected via online electrospray mass spectrometry within 1 ms, and their stabilities gauged by collision-induced dissociation. The simultaneous detection of anionic reactants and the S₂O6^2-, HSO₄^-, IO₃^- and I₃^- products as a function of experimental conditions provides evidence of unique interfacial reaction kinetics. Although ozone reacts ~3-4 times faster with I^- than S₂O₃3^2- in bulk solution, only S₂O₃^2- is apparently oxidized in [I^--]_o/[S₂O₃^2- ]_o = 10 microdroplets below [O₃(g)] ~ 50 ppm. The sulfite to sulfate and iodide to triiodide and iodate oxidations in the interfacial layers of aqueous thiosulfate or mixed thiosulfate and iodide microdroplets briefly exposed to dilute O₃(g) gas mixtures are also investigated. S(IV) oxidation kinetics in sodium thiosulfate solutions, where the rates are proportional to [S(IV)] [O₃(g)] in the ranges investigated, correspond to a surface-specific reaction. I₃^-/IO₃^- yields based on interfacial I^- losses exceed their stoichiometric limits in the presence of excess S(IV), revealing that interfacial I^- is competitively replenished from the microdroplets inner layers. Present results provide unequivocal evidence of distinct interfacial chemistry in gas-aerosol reactions of atmospheric relevance.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0365 Troposphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting