This project addresses the role of halogens in atmospheric chemistry at Summit, Greenland. Recent studies of chemical processing above and within sunlit snow have shown that polar regions are photochemically active and strongly oxidizing. In previous measurement campaigns at Summit, HO2 (peroxy radical) concentrations were found to be high and consistent with photochemical models; however, levels of OH (hydroxyl radical) were significantly elevated compared to steady-state model simulations. This occurred primarily during periods of high wind. This suggests two, not mutually exclusive, hypotheses: (1) episodic transport of reactive halogens from the marine boundary layer or free troposphere could lead to halogen activation in firn by heterogeneous reactions, and (2) local formation of reactive halogens in the photochemically active snow pack or on airborne ice during windy periods.
This project involves measurements of a variety of chemical species in the Summit Greenland surface layer, including O3 (ozone), NO (nitrogen oxide), NO2 (nitrogen dioxide), H2O (water vapor), HONO (nitrous acid), RONO2 (organic nitrates), HCHO (formaldehyde), HCOOH (formic acid), CH3COOH (acetic acid), CO (carbon monoxide), CH4 (methane), reactive NMHCs (non-methane hydrocarbons), and a variety of halogen species, including BrO (bromine monoxide), IO (iodine monoxide), and OIO (iodine dioxide), as well as soluble gas phase bromide. Rates of photochemical reactions will be determined above and within the snow. Intensive sampling seasons are planned for summer 2007 (when sunlight is at a maximum), and spring 2008 (during rapid temperature changes). Measurements over a wide range of environmental conditions as well as transport regimes will help to discriminate the relative importance of halogens on the photochemical cycling of reactive hydrogen radicals (HOx). Field measurements will be interpreted with the aid of back trajectory tools (specifically, the FLEXPART model) and by employing a photochemical steady-state box model to determine the HOx cycling within the Summit boundary layer.
If successful, this project will produce novel insights in chemical processes in an environment typical of polar regions, and improve our understanding of fundamental processes involving halogen compounds. The project will provide opportunities for graduate and undergraduate students to gain research experience. A broad program of public outreach is planned as well.
