HR: 0800h
AN: A11B-0047    [Abstracts]
TI: Comparison of Spring and Summer Hydroxyl Concentrations in the Snowpack at Summit, Greenland
AU: * Beyersdorf, A
EM: abeyersd@uci.edu
AF: Department of Chemistry, University of California Irvine, 570 Rowland Hall, Irvine, CA 92697 United States
AU: Blake, N
EM: nblake@uci.edu
AF: Department of Chemistry, University of California Irvine, 570 Rowland Hall, Irvine, CA 92697 United States
AU: Swanson, A
AF: Cooperative Institute for Research in Environmental Science, University of Colorado Boulder, Boulder, CO 80309 United States
AU: Meinardi, S
AF: Department of Chemistry, University of California Irvine, 570 Rowland Hall, Irvine, CA 92697 United States
AU: Dibb, J
AF: Climate Change Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Morse Hall, , Durham, NH 03824 United States
AU: Blake, D R
EM: drblake@uci.edu
AF: Department of Chemistry, University of California Irvine, 570 Rowland Hall, Irvine, CA 92697 United States
AU: Rowland, F
AF: Department of Chemistry, University of California Irvine, 570 Rowland Hall, Irvine, CA 92697 United States
AB: The concentration of hydroxyl radical in near-surface snowpack at Summit, Greenland (72\deg34' N, 38\deg28' W) was estimated during two field campaigns. The first took place in the summer (2003) when hydroxyl radical should be at its peak due to 24 hours of sunlight. The second occurred in the spring (mid-March through April) of 2004, a period when Summit goes from 12 hours of sunlight to near complete sunlight and experiences rapidly changing photochemistry. The experiment consisted of adding a carefully selected mixture of hydrocarbon gases, with a wide variety of radical reactivities, to a UV and visible transparent flow chamber containing undisturbed natural firn. The relative decrease in mixing ratios of these gases allowed estimation of the mixing ratio of hydroxyl radicals in the near- surface snowpack. Hydrocarbon samples were collected in 2L stainless steel canisters and analyzed in Irvine, CA. The residence time of gases in the chamber was characterized by injection of SF$_{6}$ and monitored by an on-site GC. Graphing the decay of 1-butene, i-butene, cis-2-butene, and trans-2-butene versus their respective rate constants with hydroxyl yields a straight line with a slope equal to -[OH]$\times$$\tau$ where [OH] is the gaseous hydroxyl concentration in the firn pore spaces and $\tau$ is the residence time of the gases in the firn. During the summer of 2003, the calculated OH mixing ratios followed a diurnal cycle. The peak hourly average was 5.0$\times$10$^{6}$ molecules/cm$^{3}$ between 1PM and 2PM local time. The minimum hourly average was 1.6$\times$10$^{6}$ molecules/cm$^{3}$ between 8PM and 9PM. Initial results from spring 2004 will be presented, and are expected to show hydroxyl radical concentrations that are significantly lower.
DE: 5462 Polar regions
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting