HR: 14:10h
AN: A33C-03    [Abstracts]
TI: Interfacial Segregation of Halogen Ions in Alkali Halide Solutions - A Model for Sea Salt Aerosols.
AU: * Ghosal, S
EM: sghosal@uci.edu
AF: University of California, Irvine, Department of Chemistry, Irvine, CA 92697 United States
AU: Mun, B S
EM: BSMun@lbl.gov
AF: Lawrence Berkeley National Laboratory, Advanced Light Source, Berkeley, CA 94720 United States
AU: Ogletree, F
EM: ogletree@lbl.gov
AF: Lawrence Berkeley National Laboratory, Materials Science Division, Berkeley, CA 94720 United States
AU: Salmeron, M
EM: MBsalmeron@lbl.gov
AF: Lawrence Berkeley National Laboratory, Materials Science Division, Berkeley, CA 94720 United States
AU: Hemminger, J C
EM: jchemmin@uci.edu
AF: University of California, Irvine, Department of Chemistry, Irvine, CA 92697 United States
AB: The chemistry of sea salt particles in the marine troposphere has recently generated substantial interest in the atmospheric chemistry community. Reactions of gas phase atmospheric constituents at the surfaces of such sea salt aerosols and particles have been shown to extract halogens into the marine troposphere. Recent reaction studies have led to the suggestion that the surface composition of sea salt aerosols is enriched in chloride ion[1]. This suggestion has been supported by Molecular Dynamics (MD) simulations[2,3]of alkali halide solutions which have predicted the surface segregation of polarizable halogen ions. The proposed enhanced surface availability of halogen ions would mean that gas surface reactions involving these ions would be much more important than previously expected. We present here results from our studies of the surface composition of saturated salt solutions. Using a novel high pressure photoelectron spectroscopy (HPPES) system at beamline 9.3.2 of the ALS synchrotron radiation source, we have compared the surface composition of KBr and NaCl crystals cleaved in vacuum with the surface composition of the saturated solutions formed at the deliquescence point, in equilibrium with water vapor. Our results show that the anion/cation ratio in the saturated solution is significantly enhanced within one nanometer of the surface. This is consistent with the predictions from the MD simulations by Jungwirth et al1,[2, 3] regarding halogen surface segregation. While a number of research groups are carrying out experiments aimed at the verification of this theoretical prediction, the experiments described here are the first direct experimental measurement of the enhanced halogen concentration at the surface of a salt solution in equilibrium with water vapor. References : 1. E.M. Knipping, M. J. Lakin, K. L. Foster, P. Jungwirth, D. L. Tobias, R. B. Gerber, D. Dabdub, B. J. Finlayson-Pitts, Science, 288, pg 301-306, 2000. 2. Jungwirth, P.; Tobias, D. J. J. Physical Chemistry 2002, 106(2), 379. 3. Jungwirth, P.; Tobias, D. J. J. Phys. Chem. B 2002, 106, 6361.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0317 Chemical kinetic and photochemical properties
DE: 0365 Troposphere--composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting