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Title: Measurement of selected halogenated greenhouse gases in very small air
Authors: Sturges, WT
Worton, DR
Mani, F
Etheridge, D
MacFarling, C
Trudinger, C
Curran, M
Issue Date: 10-Jun-2013
Publisher: World Meteorological Organization and IAEA
Citation: Sturges, W. T., Worton, D. R., Mani, F., Etheridge, D., MacFarling, C., Trudinger, C., . . . Smith, A. (10-13 June 2013). Measurement of selected halogenated greenhouse gases in very small air volumes. 17th WMO/IAEA Meeting on Carbon Dioxide, Other Greenhouse Gases, and Related Tracer Measurement Techniques (GGMT-2013), Beijing, China.
Abstract: We describe our methodology for measuring a number of halogen-containing strong greenhouse gases in air volumes as small as 20 cm³. Gases measured include the very long-lived perfluorocarbon gases CF₄ and C₂F₆ as well as SF₆, and several CFCs. This technique has developed for the purpose of measuring past atmospheric composition from ice cores, but could be adapted for other purposes. In this study, gases that have been cryogenically collected in cold-fingers, after extraction from dry-crushed ice cores, are re-concentrated on a glass bead-filled trap in a liquid nitrogen headspace. The concentrated gases are desorbed in to a gas chromatograph-mass spectrometer. The methodology has been tested by transferring air samples of known composition through the trapping and analysis process. We present some exemplars of measurements performed on air extracted from ice from Law Dome, Antarctica. The air extracted is representative of atmospheric composition in the 19th and early 20th century. Most of the gases decline to diminishingly small abundances before the beginning of their industrial production in the early 20th century. We are able to detect abundances as low as 0.1 pmol mol⁻₁ (ppt), depending on the compound and in some cases below 0.01 pmol mol⁻₁ , despite the small sample size. The only fluorocarbon with a significant pre-industrial presence in the atmosphere air extracted from ice. Measurements of CF₄ in ice from Berkner Island, Antarctica show similar pre-industrial abundances in ice with ages up to 94 kyr BP. The other halocarbon species appear mostly have pre-industrial abundances close to their respective detection limits.
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