Non-stomatal exchange in ammonia dry deposition models: comparison of two state-of-the-art approaches
Item
Title (Dublin Core)
Non-stomatal exchange in ammonia dry deposition models: comparison of two
state-of-the-art approaches
state-of-the-art approaches
Description (Dublin Core)
The accurate representation of bidirectional ammonia (NH<sub>3</sub>) biosphere–atmosphere exchange is an important part of modern air quality models. However, the cuticular (or external leaf surface) pathway, as well as other non-stomatal ecosystem surfaces, still pose a major challenge to translating our knowledge into models. Dynamic mechanistic models including complex leaf surface chemistry have been able to accurately reproduce measured bidirectional fluxes in the past, but their computational expense and challenging implementation into existing air quality models call for steady-state simplifications. Here we qualitatively compare two semi-empirical state-of-the-art parameterizations of a unidirectional non-stomatal resistance (<i>R</i><sub>w</sub>) model after Massad et al. (2010), and a quasi-bidirectional non-stomatal compensation-point (<i>χ</i><sub>w</sub>) model after Wichink Kruit et al. (2010), with NH<sub>3</sub> flux measurements from five European sites. In addition, we tested the feasibility of using backward-looking moving averages of air NH<sub>3</sub> concentrations as a proxy for prior NH<sub>3</sub> uptake and as a driver of an alternative parameterization of non-stomatal emission potentials (Γ<sub>w</sub>) for bidirectional non-stomatal exchange models. Results indicate that the <i>R</i><sub>w</sub>-only model has a tendency to underestimate fluxes, while the <i>χ</i><sub>w</sub> model mainly overestimates fluxes, although systematic underestimations can occur under certain conditions, depending on temperature and ambient NH<sub>3</sub> concentrations at the site. The proposed Γ<sub>w</sub> parameterization revealed a clear functional relationship between backward-looking moving averages of air NH<sub>3</sub> concentrations and non-stomatal emission potentials, but further reduction of uncertainty is needed for it to be useful across different sites. As an interim solution for improving flux predictions, we recommend reducing the minimum allowed <i>R</i><sub>w</sub> and the temperature response parameter in the unidirectional model and revisiting the temperature-dependent Γ<sub>w</sub> parameterization of the bidirectional model.
Creator (Dublin Core)
Schrader, Frederik
Brümmer, Christian
Flechard, Chris R.
Wichink Kruit, Roy J.
Zanten, Margreet C.
Zöll, Undine
Hensen, Arjan
Erisman, Jan Willem
Date (Dublin Core)
2018-09-10
Type (Dublin Core)
Text
Format (Dublin Core)
application/pdf
Identifier (Dublin Core)
10.5194/acp-16-13417-2016
https://acp.copernicus.org/articles/16/13417/2016/
Source (Dublin Core)
eISSN: 1680-7324
Language (Dublin Core)
eng
