Collaborative Research: Radical Chemistry over Sunlit Snow at Summit, Greenland

本项目探讨卤素在格陵兰萨米特大气化学中的作用。最近对阳光照射下的雪上方和内部的化学过程的研究表明，极地地区是光化学活性和强氧化性的。在峰会之前的测量活动中，发现HO 2（过氧自由基）浓度很高，与光化学模型一致;然而，与稳态模型模拟相比，OH（羟基自由基）水平显着升高。这主要发生在大风期间。这表明了两个并不相互排斥的假设：（1）海洋边界层或自由对流层中活性卤素的间歇性输送可能会通过非均相反应导致积雪中的卤素活化，以及（2）在有风的时期，在光化学活性雪包或空中冰中局部形成活性卤素。该项目涉及测量格陵兰岛首脑会议表层的各种化学物质，包括O3（臭氧）、NO（氮氧化物），NO2（二氧化氮），H2O（水蒸气），HONO（亚硝酸），RONO 2（有机硝酸盐），甲醛（甲醛），HCOOH（甲酸），CH 3COOH（乙酸），CO（一氧化碳）、CH 4（甲烷）、反应性NMHCs（非甲烷烃）和各种卤素物质，包括BrO（一氧化溴）、IO（一氧化碘）和OIO（二氧化碘），以及可溶性气相溴化物。光化学反应的速率将在雪的上方和内部确定。计划在2007年夏季（阳光最充足时）和2008年春季（气温急剧变化时）进行密集采样。在广泛的环境条件下，以及运输制度的测量将有助于区分的相对重要性卤素的光化学循环的活性氢自由基（HOx）。现场测量将解释的帮助下，返回轨迹工具（特别是，FLEXPART模型），并通过采用光化学稳态箱模型，以确定首脑会议边界层内的HOx循环。如果成功，该项目将在极地典型环境中产生化学过程的新见解，并提高我们对涉及卤素化合物的基本过程的理解。该项目将为研究生和本科生提供获得研究经验的机会。还计划了一个广泛的公共宣传方案。

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.