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| Titel |
A comparison of GC-FID and PTR-MS toluene measurements in ambient air under conditions of enhanced monoterpene loading |
| VerfasserIn |
J. L. Ambrose, K. Haase, R. S. Russo, Y. Zhou, M. L. White, E. K. Frinak, C. Jordan, H. R. Mayne, R. Talbot, B. C. Sive |
| 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 ; 3, no. 4 ; Nr. 3, no. 4 (2010-07-23), S.959-980 |
| Datensatznummer |
250001212
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| Publikation (Nr.) |
 copernicus.org/amt-3-959-2010.pdf |
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| Zusammenfassung |
| Toluene was measured using both a gas chromatographic system (GC), with a
flame ionization detector (FID), and a proton transfer reaction-mass
spectrometer (PTR-MS) at the AIRMAP atmospheric monitoring station Thompson
Farm (THF) in rural Durham, NH during the summer of 2004. Simultaneous
measurements of monoterpenes, including α- and β-pinene, camphene, Δ
3-carene, and d-limonene, by GC-FID demonstrated large enhancements in
monoterpene mixing ratios relative to toluene, with median and maximum
enhancement ratios of ~2 and ~30, respectively. A detailed
comparison between the GC-FID and PTR-MS toluene measurements was conducted
to test the specificity of PTR-MS for atmospheric toluene measurements under
conditions often dominated by biogenic emissions. We derived quantitative
estimates of potential interferences in the PTR-MS toluene measurements
related to sampling and analysis of monoterpenes, including fragmentation of
the monoterpenes and some of their primary carbonyl oxidation products via
reactions with H3O+, O2+ and NO+ in the PTR-MS
drift tube. The PTR-MS and GC-FID toluene measurements were in good
quantitative agreement and the two systems tracked one another well from the
instrumental limits of detection to maximum mixing ratios of ~0.5 ppbv. A correlation plot of the PTR-MS versus GC-FID toluene measurements
was described by the least squares regression equation y=(1.13±
0.02)x−(0.008±0.003) ppbv, suggesting a small ~13% positive
bias in the PTR-MS measurements. The bias corresponded with a ~0.055
ppbv difference at the highest measured toluene level. The two systems
agreed quantitatively within the combined 1σ measurement precisions for
60% of the measurements. Discrepancies in the measured mixing ratios were
not well correlated with enhancements in the monoterpenes. Better
quantitative agreement between the two systems was obtained by correcting
the PTR-MS measurements for contributions from monoterpene fragmentation in
the PTR-MS drift tube; however, the improvement was minor (<10%).
Interferences in the PTR-MS measurements from fragmentation of the
monoterpene oxidation products pinonaldehyde, caronaldehyde and α-pinene
oxide were also likely negligible. A relatively large and variable toluene
background in the PTR-MS instrument likely drove the measurement bias;
however, the precise contribution was difficult to accurately quantify and
thus was not corrected for in this analysis. The results from THF suggest
that toluene can be reliably quantified by PTR-MS using our operating
conditions (drift tube pressure, temperature and voltage of 2.0 mbar, 45 °C and 600 V, respectively) under the ambient compositions probed. This work
extends the range of field conditions under which PTR-MS validation studies
have been conducted. |
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