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| Titel |
The Chemistry of Atmosphere-Forest Exchange (CAFE) Model – Part 2: Application to BEARPEX-2007 observations |
| VerfasserIn |
G. M. Wolfe, J. A. Thornton, N. C. Bouvier-Brown, A. H. Goldstein, J.-H. Park, M. McKay, D. M. Matross, J. Mao, W. H. Brune, B. W. LaFranchi, E. C. Browne, K.-E. Min, P. J. Wooldridge, R. C. Cohen, J. D. Crounse, I. C. Faloona, J. B. Gilman, W. C. Kuster, J. A. Gouw, A. Huisman, F. N. Keutsch |
| 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. 3 ; Nr. 11, no. 3 (2011-02-15), S.1269-1294 |
| Datensatznummer |
250009307
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| Publikation (Nr.) |
 copernicus.org/acp-11-1269-2011.pdf |
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| Zusammenfassung |
In a companion paper, we introduced the Chemistry of Atmosphere-Forest
Exchange (CAFE) model, a vertically-resolved 1-D chemical transport model
designed to probe the details of near-surface reactive gas exchange. Here,
we apply CAFE to noontime observations from the 2007 Biosphere Effects on
Aerosols and Photochemistry Experiment (BEARPEX-2007). In this work we
evaluate the CAFE modeling approach, demonstrate the significance of
in-canopy chemistry for forest-atmosphere exchange and identify key
shortcomings in the current understanding of intra-canopy processes.
CAFE generally reproduces BEARPEX-2007 observations but requires an enhanced
radical recycling mechanism to overcome a factor of 6 underestimate of
hydroxyl (OH) concentrations observed during a warm (~29 °C)
period. Modeled fluxes of acyl peroxy nitrates (APN) are quite sensitive to
gradients in chemical production and loss, demonstrating that chemistry may
perturb forest-atmosphere exchange even when the chemical timescale is long
relative to the canopy mixing timescale. The model underestimates peroxy
acetyl nitrate (PAN) fluxes by 50% and the exchange velocity by nearly a
factor of three under warmer conditions, suggesting that near-surface APN
sinks are underestimated relative to the sources. Nitric acid typically
dominates gross dry N deposition at this site, though other reactive
nitrogen (NOy) species can comprise up to 28% of the N deposition
budget under cooler conditions. Upward NO2 fluxes cause the net
above-canopy NOy flux to be ~30% lower than the gross
depositional flux. CAFE under-predicts ozone fluxes and exchange velocities
by ~20%. Large uncertainty in the parameterization of cuticular and
ground deposition precludes conclusive attribution of non-stomatal fluxes to
chemistry or surface uptake. Model-measurement comparisons of vertical
concentration gradients for several emitted species suggests that the lower
canopy airspace may be only weakly coupled with the upper canopy. Future
efforts to model forest-atmosphere exchange will require a more mechanistic
understanding of non-stomatal deposition and a more thorough
characterization of in-canopy mixing processes. |
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