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| Titel |
A modified micrometeorological gradient method for estimating O3 dry depositions over a forest canopy |
| VerfasserIn |
Z. Y. Wu, L. Zhang, X. M. Wang, J. W. Munger |
| 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 ; 15, no. 13 ; Nr. 15, no. 13 (2015-07-10), S.7487-7496 |
| Datensatznummer |
250119883
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| Publikation (Nr.) |
 copernicus.org/acp-15-7487-2015.pdf |
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| Zusammenfassung |
| Small pollutant concentration gradients between levels above
a plant canopy result in large uncertainties in estimated air–surface
exchange fluxes when using existing micrometeorological gradient methods,
including the aerodynamic gradient method (AGM) and the modified Bowen ratio
method (MBR). A modified micrometeorological gradient method (MGM) is
proposed in this study for estimating O3 dry deposition fluxes over a
forest canopy using concentration gradients between a level above and a
level below the canopy top, taking advantage of relatively large gradients
between these levels due to significant pollutant uptake in the top layers of
the canopy. The new method is compared with the AGM and MBR methods and is
also evaluated using eddy-covariance (EC) flux measurements collected at the
Harvard Forest Environmental Measurement Site, Massachusetts, during
1993–2000. All three gradient methods (AGM, MBR, and MGM) produced
similar diurnal cycles of O3 dry deposition velocity (Vd(O3)) to
the EC measurements, with the MGM method being the closest in magnitude to
the EC measurements. The multi-year average Vd(O3) differed
significantly between these methods, with the AGM, MBR, and MGM method being
2.28, 1.45, and 1.18 times that of the EC, respectively. Sensitivity experiments
identified several input parameters for the MGM method as first-order
parameters that affect the estimated Vd(O3). A 10% uncertainty in
the wind speed attenuation coefficient or canopy displacement height can
cause about 10% uncertainty in the estimated Vd(O3). An unrealistic
leaf area density vertical profile can cause an uncertainty of a factor of
2.0 in the estimated Vd(O3). Other input parameters or formulas for
stability functions only caused an uncertainly of a few percent. The new
method provides an alternative approach to monitoring/estimating long-term
deposition fluxes of similar pollutants over tall canopies. |
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