Extraction and Analysis of Halocarbons and Other Trace Gases in Greenland Ice Cores

0221480萨尔茨曼极地冰芯中捕获的气体是研究古大气成分和变化的独特而宝贵的档案。到目前为止，人们的努力集中在二氧化碳、氧气、甲烷和一氧化二氮上，它们在空气中的混合比例为十亿分之几或更高。在冰芯中存在更多浓度较低的痕量气体，这些气体含有丰富的地球化学循环和大气化学信息。特别是，冰芯可能含有氯甲烷（CH 3Cl）和溴甲烷（CH 3Br）等卤烃的自然变异记录，这些卤烃是大气卤素负担和平流层臭氧损失的主要贡献者。冰芯还含有古大气羰基硫化物（OCS）的记录，这是大气中最丰富的含硫气体，也是平流层硫酸盐层的前身。 首席研究员将测量来自格陵兰岛浅层和深层冰芯的冰芯样本中的CH 3Cl，CH 3Br和其他一些痕量气体。痕量气体将通过机械切碎冰芯样品来提取，并通过气相色谱和质谱检测进行分析。初步冰芯测量表明：1）可以从冰芯样品中获得CH 3Cl和OCS的古大气水平，使用干提取并通过气相色谱/质谱检测分析，2）冰芯CH 3Br测量结果的解释更复杂，因为这种气体包含在气泡和冰基质中。将进行实验以区分储存在空气中和冰基质中的气体，并了解控制这些气体在这些相之间分配的因素。目的是提供工业化前北方半球空气中卤化碳和其他气体浓度的新基线数据。这些数据将对人类活动对大气预算的贡献提供强有力的限制。这项研究还将深入了解在气候条件大不相同和气候变化迅速的时期内，大气中的卤代烃含量与气候变异性之间的关系。就对社会的更广泛影响而言，这项研究将有助于为管理消耗臭氧层气体和气候活性气体的生产和使用的政策决定提供更有力的科学依据。

0221480SaltzmanThe gases trapped in polar ice cores are a unique and invaluable archive for investigating paleoatmospheric composition and variability. To date, efforts have focused on carbon dioxide, oxygen, methane, and nitrous oxide, which occur at mixing ratios in air of parts-per-billion and above. There are many more trace gases present at lower concentrations in ice cores that contain a wealth of information about biogeochemical cycles and atmospheric chemistry. In particular, ice cores potentially contain a record of natural variability of halocarbons such as methyl chloride (CH3Cl) and methyl bromide (CH3Br) that are major contributors to the atmospheric halogen burden and to stratospheric ozone loss. Ice cores also contain a record of paleoatmospheric carbonyl sulfide (OCS), the most abundant sulfur gas in the atmosphere and a precursor to the stratospheric sulfate layer. The Principal Investigator will measure CH3Cl, CH3Br, and a number of other trace gases on ice core samples from shallow and deep Greenland ice cores. Trace gases will be extracted by mechanically shredding ice core samples, with analysis by gas chromatography with mass spectrometric detection. Preliminary ice core measurements indicate that: 1) paleoatmospheric levels of CH3Cl and OCS can be obtained from ice core samples using dry extraction with analysis by gas chromatography/mass spectrometric detection, and 2) the interpretation of ice core CH3Br measurements is more complex, as this gas is contained both in gas bubbles and in the ice matrix. Experiments will be carried out to differentiate between gas stored in the air and in the ice matrix, and to understand the factors controlling the partitioning of this gas between these phases. The objective is to provide new baseline data for the concentration of halocarbons and other gases in pre-industrial northern hemisphere air. These data will provide strong constraints on the anthropogenic contribution to their atmospheric budgets. This study will also provide insight into the relationship between the atmospheric levels of halocarbons and climate variability, over periods of widely varying climate conditions and rapid climate change. In terms of broader impacts on society, this research will help to provide a stronger scientific basis for policy decisions regulating the production and use of ozone-depleting and climate-active gases.