Mechanism for intense photochemical NOx fluxes from ice surfaces

在南极、格陵兰岛、加拿大北极和许多其他永久或季节性积雪地区，观测到的强烈光化学NOx通量的来源是被雪束缚的硝酸盐的光解。但目前的数值模式未能对这一控制极地边界层氧化势的现象提供足够的解释。这突显了我们在分子水平上对机制的认识不足，以及缺乏适当的物理参数来描述冰中硝酸盐的异质光解速率。此外，有几个迹象表明，可能有相当大的倾向于从吸附或分离到雪粒表面的硝酸盐产生光产物。我们建议调查控制冰面光解速率的因素，并量化它们的表面特异度。在使用薄冰膜替代品的情况下，我们将调查最重要的物理参数，试图提供对这种现象的分子水平的机制描述。这将使光化学通量的定量评估成为可能，并改进对冰芯气候指标的解释。因此，这些基于实验室的定量调查在2007-2008年国际极地年的黎明是重要和及时的。

Photolysis of snow-bound nitrates has been identified as the source for intense photochemical NOx fluxes that have been observed to emanate for the sunlit snow pack in Antarctica, Greenland, the Canadian arctic and many other permanently or seasonally snow covered regions.  Numerical models have failed to provide an adequate interpretation for this phenomenon which controls the oxidative potential of the polar boundary layer.  This highlights our poor understanding of the mechanisms at the molecular level and the lack of appropriate physical parameters to describe the heterogeneous photolysis rates of nitrates in ice.  Furthermore, there are several indications that there might be a considerable bias favouring photoproducts from nitrates adsorbed or segregated to the surface of snow grains.  We propose to investigate the factors that control the photolysis rate at ice surfaces and quantify their surface specificity.  Using thin ice film surrogates, we will investigate the most important physical parameters in an attempt to provide a molecular-level mechanistic description of this phenomenon.  This will enable a quantitative evaluation of the photochemical fluxes and improve the interpretation of climate proxies from ice cores.  These quantitative laboratory-based investigations are important and timely at the dawn of the International Polar Year 2007-2008.