HR: 0800h
AN: A21A-0834    [Abstracts]
TI: The Effect of Surface Active Organics on Halogen Activation via N2O5 Reaction on Aqueous Sub-micron NaCl Aerosol
AU: * McNeill, V F
EM: vfm@atmos.washington.edu
AF: Department of Atmospheric Sciences, University of Washington, Box 351-640, Seattle, WA 98195 United States
AU: Thornton, J A
EM: thornton@atmos.washington.edu
AF: Department of Atmospheric Sciences, University of Washington, Box 351-640, Seattle, WA 98195 United States
AU: Patterson, J
EM: jpchem@u.washington.edu
AF: Department of Chemistry, University of Washington, Box 351-700, Seattle, WA 98195 United States
AU: Wolfe, G M
EM: gwolfe@u.washington.edu
AF: Department of Chemistry, University of Washington, Box 351-700, Seattle, WA 98195 United States
AB: The heterogeneous reaction of N₂O₅ with sea salt aerosol surfaces is a sink for nitrogen oxides and a potential source of the chlorine radical in the troposphere. Recent observations have detected surface active organics in sea salt aerosol. To test the effect of a thin film (~ 1 monolayer) of surfactant molecules on the aerosol surface, we have studied the reaction of N₂O₅ on NaCl aerosol containing trace amounts (< 8 wt %) of sodium dodecyl sulfate, SDS. SDS was chosen as a proxy for natural organic surfactant molecules due to its solubility in water and its well-characterized surface properties. Experiments were performed using a recently constructed aerosol flow tube coupled to a chemical ionization mass spectrometer for monitoring the gas phase, and a differential mobility analyzer/condensation particle counter for determining aerosol surface area. We have observed that the presence of ~ 8 wt % SDS in the aerosol suppresses the N₂O₅ reaction probability by approximately a factor of ten at relative humidities above 60 %, and also suppresses ClNO₂ product generation. We attribute this suppression to the partitioning of SDS to the gas-aerosol interface forming a thin film that slows mass accommodation and/or surface reactivity of N₂O₅. Reaction probabilities and product yields measured as a function of aerosol surface area, relative humidity, and SDS content are presented, and implications for NO_x-induced halogen chemistry are discussed.
DE: 0317 Chemical kinetic and photochemical properties
DE: 0322 Constituent sources and sinks
DE: 0365 Troposphere: composition and chemistry
DE: 0368 Troposphere: constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005