5C Chemistry Seminar


Laboratory and Field Studies of Hydroxyl Radical on Ice
Dr. Cort Anastasio
Department of Land, Air & Water Resources, UC Davis
From: 11:00 AM To: 11:50 AM
Tuesday, Sep 18, 2007
Keck Science Center, Burns Lecture Hall
Atmospheric/Environmental Chemistry
In the past decade there has been an explosion of scientific interest in the chemical reactions that occur on sunlit snow and ice. These reactions can affect both the composition of the atmosphere (because of release of pollutants from the snow) as well as the composition of the snow/ice (which complicates ice core records of past atmospheres). One of the key players in this chemistry appears to be hydroxyl radical (OH), a strong oxidant that can initiate the degradation of pollutants in the environment. While OH is typically the most important oxidant in the atmosphere and in surface waters (such as lakes and the ocean), little is known about the formation or kinetics of OH on ice surfaces. We have investigated the OH chemistry on snow and ice using both laboratory and field work. In the laboratory we characterized the direct photolysis of two major OH-forming species nitrate and hydrogen peroxide on ice surfaces. Based on our results we conclude that nitrate is a major source of nitrogen oxides (NO and NO2) in polar snow, but that hydrogen peroxide (HOOH) is the dominant source of OH. This laboratory-based conclusion was then tested in the field at Summit, Greenland, at the top of the Greenland glacier. In agreement with the laboratory data, at Summit we found that HOOH accounted for nearly all of the OH that is formed on snow. Furthermore, the rate of OH formation at Summit is large enough that it likely initiates a suite of reactions, including the formation and release of formaldehyde and other organic compounds.
FMI: Contact Dr. Anna G. Wenzel At 909-607-0912
Seminar Registered by: Anna Wenzel


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