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| Titel |
An analytical system for the measurement of stable hydrogen isotopes in ambient volatile organic compounds |
| VerfasserIn |
T. Meisehen, F. Bühler, R. Koppmann, M. Krebsbach |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 8, no. 10 ; Nr. 8, no. 10 (2015-10-23), S.4475-4486 |
| Datensatznummer |
250116649
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| Publikation (Nr.) |
 copernicus.org/amt-8-4475-2015.pdf |
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| Zusammenfassung |
| Stable isotope measurements in atmospheric volatile organic compounds (VOCs)
are an excellent tool to analyse chemical and dynamical processes in the
atmosphere. While up to now isotope studies of VOCs in ambient air have mainly
focussed on carbon isotopes, we herein present a new measurement system to
investigate hydrogen isotope ratios in atmospheric VOCs. This system,
consisting of a gas chromatography pyrolysis isotope ratio mass
spectrometer (GC-P-IRMS) and a pre-concentration system, was thoroughly characterised
using a VOC test mixture. A precision of better than 9 ‰ (in
δ 2H) is achieved for n-pentane, 2-methyl-1,3-butadiene (isoprene),
n-heptane, 4-methyl-pentane-2-one (4-methyl-2-pentanone), methylbenzene
(toluene), n-octane, ethylbenzene, m/p-xylene and 1,2,4-trimethylbenzene. A
comparison with independent measurements via elemental analysis shows an
accuracy of better than 9 ‰ for n-pentane, n-heptane,
4-methyl-2-pentanone, toluene and n-octane. Above a minimum required
pre-concentrated compound mass the obtained δ 2H values are constant
within the standard deviations. In addition, a remarkable influence of the
pyrolysis process on the isotope ratios is found and discussed. Reliable
measurements are only possible if the ceramic tube used for the pyrolysis is
sufficiently conditioned, i.e. the inner surface is covered with a carbon
layer. It is essential to verify this conditioning regularly and to renew it
if required. Furthermore, influences of a necessary H3+ correction and
the pyrolysis temperature on the isotope ratios are discussed. Finally, the
applicability to measure hydrogen isotope ratios in VOCs at ambient levels is
demonstrated with measurements of outside air on 5 different days in
February and March 2015. The measured hydrogen isotope ratios range from
−136 to −105 ‰ forn-pentane, from −86 to
−63 ‰ for toluene, from −39 to −15 ‰ for
ethylbenzene, from −99 to −68 ‰ for m/p-xylene and from
−45 to −34 ‰ for o-xylene. |
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