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| Titel |
Forest-atmosphere exchange of ozone: sensitivity to very reactive biogenic VOC emissions and implications for in-canopy photochemistry |
| VerfasserIn |
G. M. Wolfe, J. A. Thornton, M. McKay, A. H. Goldstein |
| 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 ; 11, no. 15 ; Nr. 11, no. 15 (2011-08-04), S.7875-7891 |
| Datensatznummer |
250009980
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| Publikation (Nr.) |
 copernicus.org/acp-11-7875-2011.pdf |
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| Zusammenfassung |
| Understanding the fate of ozone within and above forested environments is
vital to assessing the anthropogenic impact on ecosystems and air quality at
the urban-rural interface. Observed forest-atmosphere exchange of ozone is
often much faster than explicable by stomatal uptake alone, suggesting the
presence of additional ozone sinks within the canopy. Using the Chemistry of
Atmosphere-Forest Exchange (CAFE) model in conjunction with summer noontime
observations from the 2007 Biosphere Effects on Aerosols and Photochemistry
Experiment (BEARPEX-2007), we explore the viability and implications of the
hypothesis that ozonolysis of very reactive but yet unidentified biogenic
volatile organic compounds (BVOC) can influence the forest-atmosphere
exchange of ozone. Non-stomatal processes typically generate 67 % of the
observed ozone flux, but reactions of ozone with measured BVOC, including
monoterpenes and sesquiterpenes, can account for only 2 % of this flux
during the selected timeframe. By incorporating additional emissions and
chemistry of a proxy for very reactive VOC (VRVOC) that undergo rapid
ozonolysis, we demonstrate that an in-canopy chemical ozone sink of ~2 × 108 molec cm−3 s−1 can close the ozone flux budget. Even in
such a case, the 65 min chemical lifetime of ozone is much longer than
the canopy residence time of ~2 min, highlighting that chemistry
can influence reactive trace gas exchange even when it is "slow" relative
to vertical mixing. This level of VRVOC ozonolysis could enhance OH and
RO2 production by as much as 1 pptv s−1 and substantially alter
their respective vertical profiles depending on the actual product yields.
Reaction products would also contribute significantly to the oxidized VOC
budget and, by extension, secondary organic aerosol mass. Given the
potentially significant ramifications of a chemical ozone flux for both
in-canopy chemistry and estimates of ozone deposition, future efforts should
focus on quantifying both ozone reactivity and non-stomatal (e.g. cuticular)
deposition within the forest. |
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