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| Titel |
Selective measurements of isoprene and 2-methyl-3-buten-2-ol based on NO+ ionization mass spectrometry |
| VerfasserIn |
T. Karl, A. Hansel, L. Cappellin, L. Kaser, I. Herdlinger-Blatt, W. Jud |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 24 ; Nr. 12, no. 24 (2012-12-17), S.11877-11884 |
| Datensatznummer |
250011666
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| Publikation (Nr.) |
 copernicus.org/acp-12-11877-2012.pdf |
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| Zusammenfassung |
| Biogenic VOC emissions are often dominated by 2-methyl-1,3-butadiene
(isoprene) and 2-methyl-3-buten-2-ol (232 MBO). Here we explore the
possibility to selectively distinguish these species using NO+ as a
primary ion in a conventional PTR-MS equipped with an SRI unit. High purity
of NO+ (>90%) as a primary ion was utilized in
laboratory and field experiments using a conventional PTR-TOF-MS. Isoprene
is ionized via charge transfer leading to the major product ion
C5H8+ (>99%) (e.g. Spanel and Smith, 1998). 232
MBO undergoes a hydroxide ion transfer reaction resulting in the major
product ion channel C5H9+ (>95%) (e.g. Amelynck
et al., 2005). We show that both compounds are ionized with little
fragmentation (>5%) under standard operating conditions. Typical
sensitivities of 11.1 ± 0.1 (isoprene) and 12.9 ± 0.1 (232 MBO)
ncps ppbv−1 were achieved, which correspond to limit of detections of 18 and
15 pptv respectively for a 10 s integration time. Sensitivities decreased at
higher collisional energies. Calibration experiments showed little humidity
dependence. We tested the setup at a field site in Colorado dominated by
ponderosa pine, a 232 MBO emitting plant species. Our measurements confirm
232 MBO as the dominant biogenic VOC at this site, exhibiting typical
average daytime concentrations between 0.2–1.4 ppbv. The method is able to
detect the presence of trace levels of isoprene at this field site (90–250 ppt) without any interference from 232 MBO, which would not be feasible
using H3O+ ionization chemistry, and which currently also remains
a challenge for other analytical techniques (e.g. gas chromatographic
methods). |
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