A Century-long Record of Trace Gases in the Northern Hemisphere from the NEEM Ice Core Drilling Project in Greenland

一项在格陵兰岛钻探新冰芯的国际努力正在进行：北格陵兰Eemian冰钻探项目（NEEM）。这提供了一个令人兴奋和难得的机会，从北半球（NH）的位置获得“温暖”的空气和冰芯。“冷空气”是指被困在覆盖在固体冰上的多孔雪中的空气。这种空气可以通过特殊的钻孔和泵送装置泵出。越深入积雪，空气的年代越久远：最终代表了20世纪上半叶北半球空气的组成。在冰架下面，更古老的空气被困在固体冰中的单个气泡中。我们也将提取空气并进行分析，但测量要困难得多，可以分析的化学物质也没有在公司中那么多。然而，我们应该能够研究上个世纪或更长的时间里许多气体污染物（一氧化碳（CO）及其同位素组成、碳氢化合物、卤代烃、有机硝酸盐等）的增加。深层钻探将于2008年夏天开始，届时将钻探第二个井眼，以提取坚硬的空气。将回收大量的公司空气量，以便测量大量的微量气体，并允许对CO （delta13C， delta18O和Delta17O）的同位素比率进行全面分析。测量将集中在有人为来源的微量气体上，我们预计在上个世纪将观察到这方面的显著增加。我们将进一步集中研究在大气中存在时间相对较短的气体（寿命从几周到几年），因为以前的南极研究只提供了部分或根本没有提供这些气体的趋势，而这些气体主要排放在北半球。目标气体包括对平流层臭氧具有重要意义的气体、对流层臭氧的前体气体或其他物种的代用气体（例如，烷基硝酸盐作为活性氮、氮氧化物的代用气体：全球尺度化学的重要驱动力）。通过测量delta13C（CO）来确定CO的趋势和稳定同位素组成，以探测过去CO的来源（例如，生物质燃烧与甲烷氧化），并通过研究delta18O（CO）和Delta17O（CO）来研究过去羟基自由基（OH）的水平。羟基自由基是大气化学的重要组成部分，通常被称为大气的“清洁剂”。在过去的一百年里，污染的增加是否导致了OH的变化，目前还没有什么共识。任何显著的减少都会引起人们对这种重要分子未来水平的关注。

An international effort is underway to drill a new ice core in Greenland: the North Greenland Eemian Ice Drilling project (NEEM). This presents an exciting and rare opportunity to obtain 'firn' air and ice cores from a Northern Hemispheric (NH) location. 'Firn air' is air trapped in the porous snow overlying solid ice. This air can be pumped out with a special drilling and pumping arrangement. As one moves deeper in to the snow, the older the air is: eventually representing the composition of air in the NH in the first half of the 20th century. Below the firn, even older air is trapped in individual bubbles in solid ice. We will also extract this air and analyse it, but the measurement is much more difficult and not as many chemicals can be analysed as in the firn. We nevertheless should be able to study the rise of numerous gaseous pollutants (carbon monoxide (CO) and its isotopic composition, hydrocarbons, halocarbons, organic nitrates, etc.) over the last century or more. Deep drilling will begin in the summer of 2008, with a second borehole drilled at that time to extract firn air. Large firn air volumes will be retrieved to enable an extensive suite of trace gases to be measured, and also to permit comprehensive analysis of the isotopes ratios of CO (delta13C, delta18O, and Delta17O). Measurements will concentrate on trace gases with anthropogenic sources, for which we expect to observe significant increases over the last century. We will further concentrate on gases that are relatively short-lived in the atmosphere (lifetimes of weeks to a few years), since prior Antarctic studies have only partly / or not at all - delivered trends of such gases which are emitted largely in the NH. The target gases include those of importance to stratospheric ozone, and those which are precursors of tropospheric ozone, or are proxies of other species (e.g. alkyl nitrates as proxies of reactive nitrogen, NOx: an important driver of global-scale chemistry). The trend and stable isotopic composition of CO will be determined to probe both the past sources of CO (e.g. biomass burning versus methane oxidation) from measurement of delta13C(CO), and past levels of hydroxyl radical (OH) by studying delta18O(CO) and Delta17O(CO). Hydroxyl radical is a crucial component of atmospheric chemistry: often referred to as the 'detergent' of the atmosphere. There is presently little consensus on whether OH has changed over the last hundred years as a result of increased pollution. Any significant decrease would be a cause for concern for future levels of this important molecule.