AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM10
Surface Segregation of Bromine in Bromide Doped NaCl: Implications for the Seasonal Variations in Arctic Ozone

Tuesday, October 3, 2000, 11:20 am, Room 208

Session: Reactions on Oxides and Environmental Chemistry
Presenter: S. Ghosal, University of California, Irvine
Authors: S. Ghosal, University of California, Irvine
J.C. Hemminger, University of California, Irvine
Correspondent: Click to Email
Episodes of ozone depletion attributed to chemistry of gas phase bromine compounds in marine regions of the Arctic boundary layer have been reported at polar sunrise. Models for the source of brominated compounds in the marine Arctic troposphere have focussed on surface chemistry of sea salt ice and aerosols even though the molar ratio of Cl@super-@ to Br@super-@ in sea salt is expected to be ~660 to 1. X-ray photoelectron spectroscopy (XPS) studies described here show, for the first time, substantial segregation of Br@super-@ to the surface of NaCl samples with low level Br@super-@ dopant. Water exposure plays an important role as it provides enhanced ionic mobility in such systems allowing the surface segregation as the system approaches thermodynamic equilibrium. Our XPS results are confirmed by scanning electron microscopy (SEM) imaging of the salt sample surface after water vapor exposure, which shows NaBr crystallites that form at the surface. Our experiments provide the first experimental evidence of surface segregation in mixed alkali halide solids.@footnote 1@ The segregation phenomenon displayed here is likely to play an important role in a wide range of atmospheric phenomena that involve surface reactions of sea salt particles and aerosols. @FootnoteText@ @footnote 1@ This work was supported by the NSF Grant ATM-9707285.