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| Titel |
Eddy covariance emission and deposition flux measurements using proton transfer reaction – time of flight – mass spectrometry (PTR-TOF-MS): comparison with PTR-MS measured vertical gradients and fluxes |
| VerfasserIn |
J.-H. Park, A. H. Goldstein, J. Timkovsky, S. Fares, R. Weber, J. Karlik, R. Holzinger |
| 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 ; 13, no. 3 ; Nr. 13, no. 3 (2013-02-06), S.1439-1456 |
| Datensatznummer |
250017639
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| Publikation (Nr.) |
 copernicus.org/acp-13-1439-2013.pdf |
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| Zusammenfassung |
| During summer 2010, a proton transfer reaction – time of flight – mass
spectrometer (PTR-TOF-MS) and a quadrupole proton transfer reaction mass
spectrometer (PTR-MS) were deployed simultaneously for one month in an
orange orchard in the Central Valley of California to collect continuous
data suitable for eddy covariance (EC) flux calculations. The high time
resolution (5 Hz) and high mass resolution (up to 5000 m/Δm) data
from the PTR-TOF-MS provided the basis for calculating the concentration and
flux for a wide range of volatile organic compounds (VOC). Throughout the
campaign, 664 mass peaks were detected in mass-to-charge ratios between 10
and 1278. Here we present PTR-TOF-MS EC fluxes of the 27 ion species for
which the vertical gradient was simultaneously measured by PTR-MS. These EC
flux data were validated through spectral analysis (i.e., co-spectrum,
normalized co-spectrum, and ogive). Based on inter-comparison of the two PTR
instruments, no significant instrumental biases were found in either mixing
ratios or fluxes, and the data showed agreement within 5% on average for
methanol and acetone. For the measured biogenic volatile organic compounds
(BVOC), the EC fluxes from PTR-TOF-MS were in agreement with the
qualitatively inferred flux directions from vertical gradient measurements
by PTR-MS. For the 27 selected ion species reported here, the PTR-TOF-MS
measured total (24 h) mean net flux of 299 μg C m−2 h−1. The
dominant BVOC emissions from this site were monoterpenes (m/z 81.070 + m/z
137.131 + m/z 95.086, 34%, 102 μg C m−2 h−1) and methanol
(m/z 33.032, 18%, 72 μg C m−2 h−1). The next largest fluxes
were detected at the following masses (attribution in parenthesis): m/z 59.048
(mostly acetone, 12.2%, 36.5 μg C m−2 h−1), m/z 61.027
(mostly acetic acid, 11.9%, 35.7 μg C m−2 h−1), m/z 93.069
(para-cymene + toluene, 4.1%, 12.2 μg C m−2 h−1),
m/z 45.033 (acetaldehyde, 3.8%, 11.5 μg C m−2 h−1), m/z 71.048
(methylvinylketone + methacrolein, 2.4%, 7.1 μg C m−2 h−1), and
m/z 69.071 (isoprene + 2-methyl-3-butene-2-ol, 1.8%, 5.3 μg C m−2 h−1). Low levels of emission and/or deposition
(<1.6% for each, 5.8% in total flux) were observed for the
additional reported masses. Overall, our results show that EC flux
measurements using PTR-TOF-MS is a powerful new tool for characterizing the
biosphere-atmosphere exchange including both emission and deposition for a
large range of BVOC and their oxidation products. |
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