HR: 0830h
AN: A21E-1023    [PDF]
TI: Oxidation of NaBr Aerosol by Ozone and Hydroxyl Radicals: Importance of Reactions
AU: * Hunt, S W
EM: shunt@uci.edu
AF: University of California, Irvine, Department of Chemistry 516 Rowland Hall, Irvine, CA 92697-2025
AU: Wang, W
EM: wangw@uci.edu
AF: University of California, Irvine, Department of Chemistry 516 Rowland Hall, Irvine, CA 92697-2025
AU: Laskin, A
EM: alexander.laskin@pnl.gov
AF: W. R .Willey Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, PO Box 999, Richland, WA 99352
AU: Gaspar, D J
EM: Daniel.Gaspar@pnl.gov
AF: W. R .Willey Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, PO Box 999, Richland, WA 99352
AU: Wingen, L M
EM: wingenit@uci.edu
AF: University of California, Irvine, Department of Chemistry 516 Rowland Hall, Irvine, CA 92697-2025
AU: Finlayson-Pitts, B J
EM: bjfinlay@uci.edu
AF: University of California, Irvine, Department of Chemistry 516 Rowland Hall, Irvine, CA 92697-2025
AB: The release of Br atoms from photolyzable bromine species is responsible for the almost complete destruction of ground-level ozone observed in the Arctic after Polar sunrise, and likely for the partial destruction of ozone observed in the marine boundary layer at mid-latitudes. Based on previous studies of the reaction of deliquesced NaCl particles with hydroxyl radicals, a surface reaction mechanism was proposed to explain formation of photolytically active Cl$_2$. A similar reaction producing Br$_2$ should be more rapid in bromide-containing aerosols where the bromide ion concentration is expected to be enhanced at the gas-particle interface. To investigate the mechanism of the reactions of ozone and hydroxyl with NaBr aerosol, experiments were carried out at room temperature and atmospheric pressure in a 561 L aerosol chamber at relative humidity above the deliquescence point of NaBr aerosol. Fourier transform infrared spectroscopy (FTIR) and differential optical absorption spectroscopy (DOAS) were used to measure the concentrations of ozone and the intermediate species BrO. The concentration of Br$_2$ was monitored using atmospheric pressure chemical ionization mass spectrometry. Additionally, the composition of individual aerosol particles collected from the chamber was analyzed with computer controlled scanning electron microscopy with energy-dispersed analysis of x-rays (CCSEM/EDX) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). Analysis of particles collected after reaction with ozone and hydroxyl revealed bromine depletion and oxygen enrichment. The mechanism for bromine production was evaluated with a computer kinetics box model that includes gas and aqueous phase chemical reactions, gas and aqueous phase diffusion, and mass transfer between the liquid aerosol droplets and the gas phase. The modeling showed that known gas phase and aqueous phase bromine chemistry alone could not reproduce experimental results. However, with the inclusion of a reaction at the air-water interface between gaseous ozone and aqueous bromide ion, the model reproduces experimental results for bromine production reasonably well. The atmospheric implications of this type heterogeneous chemistry at interfaces will be discussed.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0317 Chemical kinetic and photochemical properties
DE: 0345 Pollution--urban and regional (0305)
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting