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| Titel |
Seasonal variation of ozone deposition to a tropical rain forest in southwest Amazonia |
| VerfasserIn |
U. Rummel, C. Ammann, G. A. Kirkman, M. A. L. Moura, T. Foken, M. O. Andreae, F. X. Meixner |
| 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 ; 7, no. 20 ; Nr. 7, no. 20 (2007-10-18), S.5415-5435 |
| Datensatznummer |
250005235
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| Publikation (Nr.) |
 copernicus.org/acp-7-5415-2007.pdf |
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| Zusammenfassung |
Within the project EUropean Studies on Trace gases and Atmospheric CHemistry as a
contribution to Large-scale Biosphere-atmosphere experiment in Amazonia
(LBA-EUSTACH), we performed tower-based eddy covariance measurements of
O3 flux above an Amazonian primary rain forest at the end of the wet
and dry season. Ozone deposition revealed distinct seasonal differences in
the magnitude and diel variation. In the wet season, the rain forest was an
effective O3 sink with a mean daytime (midday) maximum deposition
velocity of 2.3 cm s−1, and a corresponding O3 flux of
−11 nmol m−2 s−1. At the end of the dry season, the ozone
mixing ratio was about four times higher (up to maximum values of 80 ppb)
than in the wet season, as a consequence of strong regional biomass burning
activity. However, the typical maximum daytime deposition flux was very
similar to the wet season. This results from a strong limitation of daytime
O3 deposition due to reduced plant stomatal aperture as a response to
large values of the specific humidity deficit. As a result, the average
midday deposition velocity in the dry burning season was only 0.5 cm s−1.
The large diel ozone variation caused large canopy storage
effects that masked the true diel variation of ozone deposition mechanisms
in the measured eddy covariance flux, and for which corrections had to be
made. In general, stomatal aperture was sufficient to explain the largest
part of daytime ozone deposition. However, during nighttime, chemical
reaction with nitrogen monoxide (NO) was found to contribute substantially
to the O3 sink in the rain forest canopy. Further contributions were
from non-stomatal plant uptake and other processes that could not be clearly
identified.
Measurements, made simultaneously on a 22 years old cattle pasture enabled
the spatially and temporally direct comparison of O3 dry deposition
values from this site with typical vegetation cover of deforested land in
southwest Amazonia to the results from the primary rain forest. The mean
ozone deposition to the pasture was found to be systematically lower than
that to the forest by 30% in the wet and 18% in the dry season. |
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