AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS2-TuA

Paper SS2-TuA2
Uptake and Reaction of Ozone on NaCl and Bromide-doped NaCl

Tuesday, November 5, 2002, 2:20 pm, Room C-110

Session: Atmospheric Surface Chemistry
Presenter: J.N. Newberg, University of California, Irvine
Authors: J.N. Newberg, University of California, Irvine
J.C. Hemminger, University of California, Irvine
Correspondent: Click to Email
Sea-salt significantly affects the chemistry and composition of the marine boundary layer. For example, gas-phase bromine compounds resulting from sea-salt aerosol particles and sea ice have been implicated in tropospheric ozone depletion events in the arctic spring time, as well as in the deposition of mercury from the atmosphere in the marine troposphere. While there have been significant advances in our knowledge of gas-phase and bulk aqueous-phase reactions of sea-salt, little is known about the fundamental surface interactions of sea-salt with important gas-phase constituents (e.g., O@sub 3@ and OH) at the air-particle interface. This is due in part to the paucity of conventional atmospheric chemistry methods with the ability to monitor surface reactions on a fundamental molecular-level. Using X-ray photoelectron spectroscopy (XPS), we monitored the surface chemistry of solid sea-salt substrates upon exposure to ozone. Past studies under steady-state conditions indicate that O@sub 3@ is essentially unreactive towards dry and aqueous NaCl in the dark. Our results show unequivocally that under UHV conditions and continuous exposure to O@sub 3@, oxygen uptake occurs on NaCl. For NaCl doped with bromide, an increase in oxygen uptake was observed. Moreover, as the amount of doped bromide increased, the total uptake of oxygen increased. Based on our experimental results and ab initio calculations, it is suggested that the products of the surface reaction of O@sub 3@ on dry bromide-doped NaCl yield ClO@super -@ and BrO@super -@. Neither of these species has been reported in the XPS literature. Exposing the bromide-doped NaCl samples to water vapor leads to the segregation of Br@super -@ to the salt surface. Exposure of this surface enriched Br@super -@ to ozone leads to enhanced uptake of oxygen, likely in the form of BrO@super -@.