Studies of the Role of Sea Ice in Arctic Tropospheric Ozone Chemistry

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ABSTRACT9818257ShepsonThis project is focused on studies of the atmospheric chemistry of tropospheric ozone production and removal. Ozone is both a necessary component of the atmosphere that helps regulate its' ability to oxidize and remove potentially hazardous pollutants, but is also toxic to the human respiratory system and to vegetation. Thus there must be a reasonably delicate balance of ozone in the troposphere. However, it appears that ozone has increased significantly over the past century. This is of concern not only because ozone is toxic, but also because it is an important "greenhouse" gas.This project will investigate the surprising observation that at polar sunrise, ozone is completely removed in the Arctic marine boundary layer. This observation points out that our current understanding of tropospheric ozone is quite incomplete. Researcher have recently obtained evidence that this process may be initiated by oxidation of halide ions in the Arctic Ocean ice/snow pack, to produce molecular halogens (Br2 and Cl2) that then volatilize into the atmosphere. They then photolyze to initiate a free radical chain mechanism that results in destruction of ozone near the surface. During the Polar Sunrise Experiment 1998, striking evidence was obtained that formaldehyde (HCHO) is produced photochemically in the snow pack, and then volatilizes, and that this process is responsible for the relatively high levels of HCHO in the marine boundary layer at sunrise in the Arctic. This is quite important, as HCHO photolysis represents one of the most important sources of free radicals in the relatively dry polar atmosphere. This project will pursue in detail the hypothesis that much of the gas phase photochemistry that occurs actively at sunrise in the Arctic is initiated at the air/snow/ice interface. To do this, it is necessary to set up an ice camp on the Arctic Ocean surface, near Alert, N.W.T., as a key component of the Polar Sunrise Experiment 2000. This project will conduct measurements of key reactive trace gases, and measure the fluxes of these gases from the surface, over a period covering early February (continuous darkness) through April (continuous sunlight) in the winter/spring of 2000. This project represents an exciting first step in the process of examining the role of air/snow/ice interfacial photochemistry and its impact on important tropospheric gases such as HCHO and O3. This work also ties directly to efforts to improve our understanding of the role of snow surface chemistry and physics on ice core concentrations and the associated historical