HR: 09:15h
AN: A41G-05    [Abstracts]
TI: Enhanced Surface Photochemistry in Chloride-Nitrate Ion Aerosol Mixtures
AU: * Wingen, L M
EM: wingenit@uci.edu
AF: University of California, Irvine, Department of Chemistry, Irvine, CA 92697-2025,
AU: Moskun, A C
EM: amymoskun@gmail.com
AF: University of California, Irvine, Department of Chemistry, Irvine, CA 92697-2025,
AU: Thomas, J L
EM: jenniet@uci.edu
AF: University of California, Irvine, Department of Chemistry, Irvine, CA 92697-2025,
AU: Roeselova, M
EM: martina.roeselova@uochb.cas.cz
AF: Academy of Sciences of the Czech Republic, Center for Biomolecules and Complex Molecular Systems, Institute of Organic Chemistry and Biochemistry, Flamingovo nam. 2, Prague, 16610, Czech Republic
AU: Tobias, D J
EM: dtobias@uci.edu
AF: University of California, Irvine, Department of Chemistry, Irvine, CA 92697-2025,
AU: Finlayson-Pitts, B J
EM: bjfinlay@uci.edu
AF: University of California, Irvine, Department of Chemistry, Irvine, CA 92697-2025,
AB: Heterogeneous reactions of sea salt aerosol with various oxides of nitrogen often lead to replacement of chloride ion by nitrate ion. Photolysis of aqueous nitrate at wavelengths > 290 nm leads to the production of nitrogen dioxide, hydroxyl radicals and other oxidants. The photochemistry of aerosols containing NO₃^- and Cl^-, however, has not been investigated. Aerosols containing mixtures of NaCl and NaNO3 were used as a model system for processed sea salt aerosol. Photolysis experiments (λ_max = 306 nm) were performed in 55 L Teflon chambers that contained deliquesced aerosols and production of gas phase NO₂ was measured as a function of time using chemiluminescence detection. Simple alkanes were added in some experiments to probe OH radical and Cl atom production. Molecular dynamics simulations were also carried out on mixed aqueous NaCl and NaNO₃ slabs to help understand ion solvation in these mixed salt systems. The simulations showed that as the Cl^- to NO₃^- ratio increases, nitrate ions are drawn toward the interface due to the large double layer of interfacial Cl^- and subsurface Na⁺. The systems explored both experimentally and computationally included pure NaNO3 and mixtures of Cl^- and NO₃^- in molar ratios of 1:9, 1:1, and 9:1. The photolysis experiments showed an enhanced yield of gas phase NO₂ as the chloride to nitrate ratio increased. We attribute the observed enhanced NO₂ yields to an increased interfacial concentration of under-coordinated nitrate ion as the ratio of Cl^- to NO₃^- increases. The implications of these enhanced NO₂ yields as sea salt aerosols become processed in the atmosphere will also be discussed.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0365 Troposphere: composition and chemistry
DE: 3307 Boundary layer processes
DE: 4852 Photochemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting