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| Titel |
Measurement of atmospheric sesquiterpenes by proton transfer reaction-mass spectrometry (PTR-MS) |
| VerfasserIn |
S. Kim, T. Karl, D. Helmig, R. Daly, R. Rasmussen, A. Guenther |
| 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 ; 2, no. 1 ; Nr. 2, no. 1 (2009-04-09), S.99-112 |
| Datensatznummer |
250000431
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| Publikation (Nr.) |
 copernicus.org/amt-2-99-2009.pdf |
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| Zusammenfassung |
| The ability to measure sesquiterpenes (SQT; C15H24) by a
Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) was investigated. SQT
calibration standards were prepared by a capillary diffusion method and the
PTR-MS-estimated mixing ratios were derived from the counts of product ions
and proton transfer reaction constants. These values were compared with
mixing ratios determined by a calibrated Gas Chromatograph (GC) coupled to a
Flame Ionization Detector (GC-FID). Product ion distributions from
soft-ionization occurring in a selected ion drift tube via proton transfer
were measured as a function of collision energies. Results after the
consideration of the mass discrimination of the PTR-MS system suggest that
quantitative SQT measurements within 20% accuracy can be achieved with
PTR-MS if two major product ions (m/z 149+ and 205+), out of seven
major product ions (m/z 81+, 95+, 109+, 123+, 135+,
149+ and 205+), are accounted for. Considerable fragmentation of
bicyclic sesquiterpenes, i.e. β-caryophyllene and α-humulene,
cause the accuracy to be reduced to 50% if only the parent ion (m/z 205+)
is considered. These findings were applied to a field dataset collected
above a deciduous forest at the PROPHET (Program for Research on Oxidants:
Photochemistry, Emissions, and Transport) research station in 2005. Inferred
average daytime ecosystem scale mixing ratios (fluxes) of isoprene, sum of
monoterpenes (MT), and sum of SQT exhibited values of 15 μg m−3
(4.5 mg m−2 h−1), 1.2 μg m−3 (0.21 mg m−2 h−1),
and 0.0016 μg m−3 (0.10 mg m−2 h−1), respectively. A
range of MT and SQT reactivities with respect to the OH radical was
calculated and compared to an earlier study inferring significantly
underestimated OH reactivities due to unknown terpenes above this deciduous
forest. The results indicate that incorporating these MT and SQT results can
resolve ~30% of missing OH reactivity reported for this site. |
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