HR: 15:10h
AN: V12E-07    [PDF]
TI: Organics and Halocarbons in Volcanic Gas Emissions: Sampling, Analysis, and Estimates of Source Strengths for Diffuse and Fumarolic Gas Emissions
AU: * Schwandner, F M
EM: florimax@erdw.ethz.ch
AF: Institute of Mineralogy and Petrography, ETH Z\"{u}rich, Z\"{u}rich, 8092 Switzerland
AU: Seward, T M
EM: tseward@erdw.ethz.ch
AF: Institute of Mineralogy and Petrography, ETH Z\"{u}rich, Z\"{u}rich, 8092 Switzerland
AU: Gi\.{z}e, A P
EM: andy_gize@msn.com
AF: Department of Earth Sciences, University of Manchester, Manchester, M13 9PL United Kingdom
AU: Hall, K
EM: keith@hallanalytical.co.uk
AF: Hall Analytical Ltd., Millbrook Business Centre, Floats Road, Manchester, M23 9YJ United Kingdom
AB: The well-established interest in organic compounds in volcanic emissions, emerging in the early 1800?s and continuing through modern times, has led to a long history of method development for the analysis of trace organics in volcanic gases. Both the sampling and analysis techniques have often been hampered by strong matrix effects, such as interferences by aerosol and ash scattering in spectroscopy, or the adverse impact of sulfur, acids and water on chromatographic and wet chemical techniques. Established methods exist for the ground-based sampling of fumaroles and diffuse degassing structures, whereas remote OP-FTIR spectroscopy appears promising for the detection and quantification of organic compounds during dangerous eruptive phases. The most successful collection techniques are based on a multiple-fold enrichment of the analytes during sampling, either by the absorption flask technique (''Giggenbach bottle''), or by in-line separation of water and sulfur from the analytes with subsequent trapping onto solid adsorbents. For organic analytes present at relatively high concentrations (e.g., C$_{1}$-C$_{6}$ hydrocarbons), the first technique has been used extensively. For labile and trace compounds (pptv to ppbv abundance), the latter technique has proven more reliable provided that the gas is dried sufficiently during sampling and that suitable dry gas volumes are sampled. A poor choice of sampling technique, or its incorrect application, may lead to erroneous results. These are often obvious by the finding of near-air concentrations, since volcanic gases are strongly enriched with respect to ambient air for a large range of compounds. Quantitative and independent testing of the air fraction possibly entrained during sampling must be performed in order to achieve reliable results. By using gas chromatography coupled with mass spectrometric detection (GC-MS), unambiguous simultaneous identification of compounds can be achieved by two independent analytical techniques. Unlike with ion trap MS, relatively soft electron impact ionization with either sector scanning or quadrupole MS instruments yields characteristic mass fragment spectra for a large range of compound types, from saturated and cyclic hydrocarbons to more labile iodocarbons. Detection limits of 10 to 50 pptv can be achieved routinely. Data are available from several volcanoes around the world, ranging in emission temperatures from 100 to 900$\deg$C. Global fumarolic fluxes (volcanic source strengths) for certain halocarbons are estimated to be on the order of up to 10$^{-5}$ Tgy$^{-1}$. Although this represents only a small fraction of the total releases including anthropogenic sources, the global fumarolic fluxes for some halocarbons account for a comparatively more significant fraction of natural sources. For example, CCl$_{3}$F (CFC-11) has been detected in volcanic gases with an estimated flux of 1.3 x 10$^{-5}$ Tgy$^{-1}$, making subaerial volcanism the sole natural source currently known for this compound. Diffuse degassing appears to emit amounts similar to those of high-temperature fumarolic discharges, whereas the output by explosive emissions is not known. During pre-industrial times, volcanic emissions would have represented a larger fraction of global emissions, since the anthropogenic burden at the time was negligible.
UR: http://www.geochem.ethz.ch
DE: 0322 Constituent sources and sinks
DE: 0330 Geochemical cycles
DE: 8409 Atmospheric effects (0370)
DE: 8424 Hydrothermal systems (8135)
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting