HR: 1330h
AN: A52A-0774    [PDF]
TI: The Stable Carbon Isotope Ratio Analysis of Atmospheric Non-Methane Hydrocarbons in Los Angeles, California
AU: * Gotoh, A A
EM: aagotoh@uci.edu
AF: Department of Chemistry, University of California Irvine, 516 Rowland Hall, Irvine, CA 92697-2025 United States
AU: * Gotoh, A A
EM: aagotoh@uci.edu
AF: Deparment of Earth System Science, University of California Irvin, 3200 Croul Hall, Irvine, CA 92697-3100 United States
AU: Tyler, S C
EM: styler@uci.edu
AF: Deparment of Earth System Science, University of California Irvin, 3200 Croul Hall, Irvine, CA 92697-3100 United States
AU: Meinardi, S
EM: smeinard@uci.edu
AF: Department of Chemistry, University of California Irvine, 516 Rowland Hall, Irvine, CA 92697-2025 United States
AU: Gervais, K
EM: kgervais@uci.edu
AF: Department of Chemistry, University of California Irvine, 516 Rowland Hall, Irvine, CA 92697-2025 United States
AU: Blake, D R
EM: drblake@uci.edu
AF: Department of Chemistry, University of California Irvine, 516 Rowland Hall, Irvine, CA 92697-2025 United States
AU: Blake, D R
EM: drblake@uci.edu
AF: Deparment of Earth System Science, University of California Irvin, 3200 Croul Hall, Irvine, CA 92697-3100 United States
AB: Los Angeles type photochemical air pollution is caused by non-methane hydrocarbons (NMHCs) reacting with hydroxyl radicals and nitrous oxides in the presence of light. To create more effective control strategies in reducing such air pollution, it is essential to have both a better understanding of the complex photochemical processes of NMHCs and the sources of these compounds. From the past successful studies of other atmospheric trace gases such as methane and carbon monoxide, we expect that the stable carbon ratio ($^{13}$C/$^{12}$C, reported as a $\delta$$^{13}$C value) of each of these hydrocarbons will also reflect the $\delta$$^{13}$C value of the source material and/or provide formation on chemical loss processes that fractionate C isotopes. We have developed a NMHC preconcentrator system which enables us to measure $\delta$$^{13}$C values using a continuous-flow gas chromatography combustion isotope ratio mass spectrometer (cf-GC/C/IRMS). Our system is similar to the successful design pioneered in Rudolph {\it et al}. (1997), but is custom designed by our laboratory. Stable carbon isotope measurements of any of the C$_{2}$-C$_{5}$ NMHCs in field and/or lab studies are scarce to date. Our system allows us to report on $\delta$$^{13}$C measurements of ethane, ethene, ethyne, propane, propene, n-butane, i-butane, 1-butene, n-pentane, i-pentane, and methyl chloride. To see if we can learn the specific sources contributing to the emissions of a given NMHC within a region by comparing isotopic signatures of its potential sources to $\delta$$^{13}$C measurements of it within the local air mass, urban air samples were collected in 3 different cities of Los Angeles County, California, USA, during the summer of 2003 and analyzed for the concentrations and $\delta$$^{13}$C values of NMHCs. To our knowledge, this is the first $\delta$$^{13}$C analysis of ambient NMHCs conducted in the United States. We report the results of the $\delta$$^{13}$C analyses and concentration measurements for selected NMHC species from the urban air samples, and their implications for the local atmospheric chemistry of Los Angeles Basin.
DE: 0345 Pollution--urban and regional (0305)
DE: 0365 Troposphere--composition and chemistry
DE: 1040 Isotopic composition/chemistry
DE: 9350 North America
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting