HR: 10:50h
AN: A22C-03    [Abstracts]
TI: Measurements of snow grain hydroxyl radical at Summit, Greenland
AU: * Anastasio, C
EM: canastasio@ucdavis.edu
AF: Department of Land, Air, & Water Resources, University of California - Davis, 1 Shields Ave., Davis, CA 95616-8627 United States
AU: Galbavy, E
EM: esgalbavy@ucdavis.edu
AF: Department of Land, Air, & Water Resources, University of California - Davis, 1 Shields Ave., Davis, CA 95616-8627 United States
AU: Hutterli, M
EM: manuel@hwr.arizona.edu
AF: Department of Hydrology and Water Resources, The University of Arizona, 1133 E. North Campus Dr., Tucson, AZ 85721-0011 United States
AU: Friel, D
EM: frieldo@bc.edu
AF: Department of Hydrology and Water Resources, The University of Arizona, 1133 E. North Campus Dr., Tucson, AZ 85721-0011 United States
AU: Bales, R
EM: rbales@ucmerced.edu
AF: School of Engineering, University of California - Merced, 4225 N. Hospital Road, Bldg 1200, Atwater, CA 95301 United States
AB: Sunlit snowpacks release a number of volatile organic compounds (VOCs) such as formaldehyde and other carbonyls, carboxylic acids, alkenes, and alkyl halides. It has been hypothesized that this flux of VOCs to the overlying atmosphere is in part due to reactions of hydroxyl radical (OH) with snowgrain organic matter. Recent laboratory measurements by Grannas et al. support this idea by showing that the photolysis of polar snow releases formaldehyde, and that this release is enhanced by the addition of nitrate, a photochemical source of OH. In addition to its effects on organic chemistry, OH is probably also important in other snowpack reactions such as the oxidation of halides to form volatile, reactive gaseous halogens. However, the possible role of OH in these reactions has not been quantified. To begin to address the importance of OH in snowpack chemistry, we have measured the photochemical formation of hydroxyl radicals on snow grains at Summit, Greenland during the spring and summer. Measurements were made using a chemical probe technique where benzoate is added to the snow sample in order to scavenge OH and convert it into p-hydroxybenzoate, which is measured by HPLC. We found that OH is formed on snow grains during both seasons and that the rate of formation in the summer was more than an order of magnitude greater than the typical springtime value. Expressed on a bulk (melted) snow volume basis, the average summer value was approximately 200 nM/hr. Assuming that this reactivity occurs within a snowgrain "quasi-liquid layer" (QLL) that represents approximately 0.001% of the bulk liquid volume, rates of OH photoformation in the QLL are on the order of 10 mM/hr. The possible implications of this enormous rate of OH formation for snowpack chemistry (e.g., for VOC release) will be discussed. We have also examined the relative importance of nitrate and hydrogen peroxide as sources of photoformed OH on snow grains at Summit. Based on quantum yields determined in the laboratory, and measurements of hydrogen peroxide and nitrate in snow pits at Summit, we calculate that hydrogen peroxide is a much greater source of photoformed OH, accounting for approximately 40 times more OH than nitrate. Finally, we will discuss the lifetime of OH on snow grains and the calculated steady-state concentrations of OH in the quasi-liquid layer.
DE: 9315 Arctic region
DE: 1863 Snow and ice (1827)
DE: 0317 Chemical kinetic and photochemical properties
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting