HR: 0800h
AN: A41A-0005    [Abstracts]
TI: Reactive Uptake of O$_3$ on Oleic Acid - Alkanoic Acid Mixtures
AU: Anthony, L M
EM: lanthony@chem.ubc.ca
AF: University of British Columbia, Department of Chemistry, 2036 Main Mall , Vancouver, BC V6T 1Z1 Canada
AU: * Knopf, D A
EM: knopf@chem.ubc.ca
AF: University of British Columbia, Department of Chemistry, 2036 Main Mall , Vancouver, BC V6T 1Z1 Canada
AU: Bertram, A K
EM: bertram@chem.ubc.ca
AF: University of British Columbia, Department of Chemistry, 2036 Main Mall , Vancouver, BC V6T 1Z1 Canada
AB: In the atmosphere gas-phase species react on or in organic particles and potentially modify the particle composition and morphology. These reactions, often referred to as heterogeneous reactions, may change the hygroscopic and the optical properties of the aerosol particles and have a direct influence on air quality and health issues.\The heterogeneous reaction of O$_3$ with pure liquid oleic acid has been studied extensively. In the atmosphere, however, oleic acid is most likely found in mixtures with other species, and these other species may influence the reaction rates, reaction mechanisms, and lifetimes of oleic acid. One major source of oleic acid containing particles is from meat cooking operations. These aerosol particles may comprise up to 20 % of the primary fine organic carbon particle emissions in the Los Angeles area. The identified particulate organic compounds account for 20 wt% of the particle mass. The identified composition of the particles is estimated to be 45 % n-alkanoic acid, 30 % n-alkenoic acids (which is mainly oleic acid), 3 % lactones, 2 % n-alkanes, and 3 % amides. Field measurements suggest that these aerosol particles have lifetimes of several days. In contrast, the laboratory studies on pure oleic acid suggest the lifetime is a few minutes for typical O$_3$ concentrations and particle diameters. Here, we present a comprehensive study of O$_3$ uptake on binary oleic acid mixtures, i.\ e.\ oleic acid/lauric acid and oleic acid/myrisitc acid. Additionally, studies on more realistic multicomponent mixtures will be presented corresponding to compositions of meat cooking aerosols. A chemical ionization mass spectrometer coupled to a rotating flow tube system is used for the investigation.\The heterogeneous uptake coefficient of O$_3$ for the binary mixtures is measured at room temperature as a function of the concentration of the saturated acid. The uptake coefficient decreases with increasing amounts of saturated fatty acids as expected. The addition of small amounts of saturated fatty acids decreases the uptake coefficient more than expected. This may be because the addition of small amounts of saturated fatty acids decreases significantly the amount of oleic acid at the air-liquid interface. The uptake coefficient of O$_3$ is an order of magnitude lower for solid-liquid mixtures. The experiments show that the uptake reaction is affected by the morphology of the mixture. The morphology in turn depends on the method of preparation of the film. The corresponding lifetimes based on the uptake measurements can be up to 11 hours for solid-liquid particles. This may, in part, explain the long lifetimes of oleic acid in the atmosphere.
DE: 4801 Aerosols (0305)
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
DE: 0345 Pollution--urban and regional (0305)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting