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| Titel |
Concentrations and fluxes of isoprene and oxygenated VOCs at a French Mediterranean oak forest |
| VerfasserIn |
C. Kalogridis, V. Gros, R. Sarda-Estève, B. Langford, B. Loubet, B. Bonsang, N. Bonnaire, E. Nemitz, A.-C. Genard, C. Boissard, C. Fernández, E. Ormeño, D. Baisnée, I. Reiter, J. Lathière |
| 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 ; 14, no. 18 ; Nr. 14, no. 18 (2014-09-22), S.10085-10102 |
| Datensatznummer |
250119057
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| Publikation (Nr.) |
 copernicus.org/acp-14-10085-2014.pdf |
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| Zusammenfassung |
The CANOPEE project aims to better understand the biosphere–atmosphere
exchanges of biogenic volatile organic compounds (BVOCs) in the case of
Mediterranean ecosystems and the impact of in-canopy processes on the
atmospheric chemical composition above the canopy. Based on an intensive
field campaign, the objective of our work was to determine the chemical
composition of the air inside a canopy as well as the net fluxes of reactive
species between the canopy and the boundary layer. Measurements were carried
out during spring 2012 at the field site of the Oak Observatory of the
Observatoire de Haute Provence (O3HP) located in the southeast of
France. The site is a forest ecosystem dominated by downy oak,
Quercus pubescens Willd., a typical Mediterranean species which
features large isoprene emission rates. Mixing ratios of isoprene, its
degradation products methylvinylketone (MVK) and methacrolein (MACR) and
several other oxygenated VOC (OxVOC) were measured above the
canopy using an online proton transfer reaction mass spectrometer (PTR-MS),
and fluxes were calculated by the disjunct eddy covariance approach. The
O3HP site was found to be a very significant source of isoprene
emissions, with daily maximum ambient concentrations ranging between
2–16 ppbv inside and 2–5 ppbv just above the top of the forest canopy.
Significant isoprene fluxes were observed only during daytime, following
diurnal cycles with midday net emission fluxes from the canopy ranging
between 2.0 and 9.7 mg m−2 h1. Net isoprene normalized flux (at
30 °C, 1000 μmol quanta m−2 s−1) was
estimated at 7.4 mg m−2 h−1. Evidence of direct emission of
methanol was also found exhibiting maximum daytime fluxes ranging between 0.2
and 0.6 mg m−2 h−1, whereas flux values for monoterpenes and
others OxVOC such as acetone and acetaldehyde were below the
detection limit.
The MVK+MACR-to-isoprene ratio provided useful information on the
oxidation of isoprene, and is in agreement with recent findings proposing
weak production yields of MVK and MACR, in remote forest regions where the
NOx concentrations are low. In-canopy chemical oxidation of isoprene was
found to be weak and did not seem to have a significant impact on isoprene
concentrations and fluxes above the canopy. |
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