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| Titel |
Accuracy of cuticular resistance parameterizations in ammonia dry deposition models |
| VerfasserIn |
Frederik Schrader, Christian Brümmer, Undine Richter, Chris Flechard, Roy Wichink Kruit, Jan Willem Erisman |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250129035
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| Publikation (Nr.) |
 EGU/EGU2016-9097.pdf |
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| Zusammenfassung |
| Accurate representation of total reactive nitrogen (Nr) exchange between ecosystems and the
atmosphere is a crucial part of modern air quality models. However, bi-directional exchange
of ammonia (NH3), the dominant Nr species in agricultural landscapes, still poses a major
source of uncertainty in these models, where especially the treatment of non-stomatal
pathways (e.g. exchange with wet leaf surfaces or the ground layer) can be challenging.
While complex dynamic leaf surface chemistry models have been shown to successfully
reproduce measured ammonia fluxes on the field scale, computational restraints and the lack
of necessary input data have so far limited their application in larger scale simulations. A
variety of different approaches to modelling dry deposition to leaf surfaces with simplified
steady-state parameterizations have therefore arisen in the recent literature. We present
a performance assessment of selected cuticular resistance parameterizations by
comparing them with ammonia deposition measurements by means of eddy covariance
(EC) and the aerodynamic gradient method (AGM) at a number of semi-natural
and grassland sites in Europe. First results indicate that using a state-of-the-art
uni-directional approach tends to overestimate and using a bi-directional cuticular
compensation point approach tends to underestimate cuticular resistance in some cases,
consequently leading to systematic errors in the resulting flux estimates. Using the
uni-directional model, situations where low ratios of total atmospheric acids to NH3
concentration occur lead to fairly high minimum cuticular resistances, limiting
predicted downward fluxes in conditions usually favouring deposition. On the other
hand, the bi-directional model used here features a seasonal cycle of external leaf
surface emission potentials that can lead to comparably low effective resistance
estimates under warm and wet conditions, when in practice an expected increase in
the compensation point due to an equilibrium shift towards ammonia in the gas
phase would be expected to limit deposition fluxes. We highlight the respective
strengths and shortcomings of both approaches and propose suggestions for the future
treatment of this part of the non-stomatal deposition pathway in air quality models. |
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