HR: 1340h
AN: A53B-1158    [Abstracts]
TI: Photochemistry of PAHs on Arctic Snow Grains
AU: * Ram, K
EM: kerram@ucdavis.edu
AF: Department of Land, Air, and Water Resources, University of California, Davis, One Shields Ave., Davis, CA 95616,
AU: Anastasio, C
EM: canastasio@ucdavis.edu
AF: Department of Land, Air, and Water Resources, University of California, Davis, One Shields Ave., Davis, CA 95616,
AB: Photochemical reactions can greatly influence the chemistry of surface snow and transform many of the organic pollutants in snowpacks. Little is known about the rates and mechanisms of these photochemical processes, but they likely play a large role in determining lifetimes of many pollutants in snow. Our goal here is to understand the fate of one class of organic pollutants, polycyclic aromatic hydrocarbons (PAH's), in snow and ice. PAH's are ubiquitous in the environment and have well-studied toxicities. We have focused on the degradation kinetics of phenanthrene, pyrene, and fluoranthene on ice, as these are the most abundant PAH's found in Arctic snow. Laboratory photochemistry experiments were conducted using frozen solutions of PAH's illuminated with simulated solar light. Direct photolysis rates were measured using frozen solutions of the PAH's in Milli-Q with added solutes, whereas indirect photo-oxidation reactions with hydroxyl radical were measured in similar frozen solutions with added hydrogen peroxide as a source of ·OH. Using data from our group's previous and ongoing research on the levels of hydroxyl radical in Summit snow, we have been able to begin to assess the relative significance of indirect photo-oxidation and direct photolysis of PAH's as mechanisms of degradation for these compounds on snow and ice. Summit field data indicate that direct photolysis is the main mechanism of phenanthrene degradation, and laboratory experiments confirm this finding for all three PAH compounds. Data extrapolated to Summit conditions suggests that indirect photo-oxidation via ·OH accounts for only a small fraction (about 2 to 4%) of PAH degradation on ice. Our direct photolysis data suggest that PAH lifetimes on snow and ice under Arctic conditions are on the order of 1 to 7 hours during mid-summer. These results are based on photolysis experiments conducted on ice pellets made from PAH solutions. Actual snowpack lifetimes are likely to be longer, given that PAH's are most likely to be associated with particulate matter (e.g, deposited atmospheric aerosols) in the snow.
DE: 0317 Chemical kinetic and photochemical properties
DE: 0478 Pollution: urban, regional and global (0345, 4251)
DE: 1863 Snow and ice (0736, 0738, 0776, 1827)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting