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

该项目解决了在格陵兰Summit的大气化学中卤素的作用。最近对阳光照射下的雪上和雪内化学过程的研究表明，极地地区具有光化学活性和强氧化性。在Summit之前的测量活动中，发现HO2（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）水平显著升高。这种情况主要发生在大风期间。这就提出了两种并非相互排斥的假设：(1)来自海洋边界层或自由对流层的反应性卤素的偶发性运输可能通过非均相反应导致雪中的卤素活化；(2)在有风期间，在光化学活性的积雪或空气中的冰中局部形成反应性卤素。该项目涉及对格陵兰山顶表层各种化学物质的测量，包括O3（臭氧）、NO（氮氧化物）、NO2（二氧化氮）、H2O（水蒸气）、HONO（亚硝酸）、RONO2（有机硝酸盐）、HCHO（甲醛）、HCOOH（甲酸）、CH3COOH（乙酸）、CO（一氧化碳）、CH4（甲烷）、活性NMHCs（非甲烷碳氢化合物）和各种卤素物质，包括BrO（一氧化溴）、IO（一氧化碘）、OIO（二氧化碘），以及可溶气相溴化物。光化学反应的速率将在雪上和雪内测定。计划在2007年夏季（日照最多的时候）和2008年春季（温度快速变化的时候）进行密集采样。在广泛的环境条件下以及运输制度下的测量将有助于区分卤素对活性氢自由基（HOx）光化学循环的相对重要性。现场测量结果将借助反轨迹工具（特别是FLEXPART模型）进行解释，并采用光化学稳态盒模型来确定峰顶边界层内的HOx循环。如果成功，该项目将对极地典型环境中的化学过程产生新的见解，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众宣传方案。

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.