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

萨尔茨曼极地冰芯中的气体是研究古大气成分和变异性的独特而宝贵的档案。到目前为止，努力的重点是二氧化碳、氧气、甲烷和一氧化二氮，它们在空气中的混合比率为十亿分之一或更高。在浓度较低的冰芯中存在着更多的痕量气体，这些冰芯包含了大量关于生物地球化学循环和大气化学的信息。特别是，冰芯可能含有甲基氯(CH3Cl)和甲基溴(CH3Br)等卤素的自然可变性记录，这些卤素是大气卤素负荷和平流层臭氧损失的主要贡献者。冰芯还记录了古大气中的羰基硫化物(OCS)，这是大气中最丰富的硫磺气体，也是平流层硫酸盐层的前驱物质。首席调查员将测量来自格陵兰浅冰芯和深冰芯的冰芯样品中的CH3Cl、CH3Br3和其他一些痕量气体。微量气体将通过机械粉碎冰芯样品来提取，并通过气相色谱-质谱仪检测进行分析。初步的冰芯测量表明：1)用干法提取冰芯样品，并用气相色谱/质谱仪进行分析，可以获得古大气中CH3Cl和OCS的水平；2)冰芯CH3Br值的解释更为复杂，因为这种气体既包含在气泡中，也包含在冰基质中。将进行实验，以区分储存在空气中的气体和储存在冰基质中的气体，并了解控制这些气体在这些相之间分配的因素。其目的是为工业化前北半球空气中卤代烃和其他气体的浓度提供新的基线数据。这些数据将对人类活动对其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变化很大和气候变化迅速的时期，大气中的卤代烃水平与气候变异性之间的关系。就更广泛的社会影响而言，这项研究将有助于为规范臭氧消耗和气候活性气体的生产和使用的政策决策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.