Validation and uncertainty quantification of three state-of-the-art ammonia surface exchange schemes using NH3 flux measurements in a dune ecosystem
Series / Report no.
Open Access
Type
Article
Language
en
Date
2025-05-12
Research Projects
Organizational Units
Journal Issue
Title
Validation and uncertainty quantification of three state-of-the-art ammonia surface exchange schemes using NH3 flux measurements in a dune ecosystem
Translated Title
Published in
Atmos Chem Phys 2025; 25(9)4943-4963
Abstract
Deposition of reactive nitrogen causes detrimental environmental effects, including biodiversity loss, eutrophication, and soil acidification. Measuring and modelling the biosphere–atmosphere exchange of ammonia, the most abundant reduced nitrogen species, is complex due to its high reactivity and solubility, often leading to systematic discrepancies between model predictions and observations. This study aims to determine whether three state-of-the-art exchange schemes for NH3 can accurately model NH3 exchange in a dune ecosystem (Solleveld) and detect factors causing the uncertainties in these schemes. The selected schemes are DEPAC (DEPosition of Acidifying Compounds) by van Zanten et al. (2010) and the schemes by Massad et al. (2010) and Zhang et al. (2010). Validation against 1 year of gradient flux measurements revealed that the Zhang scheme represented the NH3 deposition at Solleveld best, whereas the DEPAC scheme overestimated the total deposition, while the Massad scheme underestimated the total deposition. Yet none of these schemes captured the emission events at Solleveld, pointing to considerable uncertainty in the compensation point parameterization and possibly in the modelling of NH3 desorption processes from wet surface layers. The sensitivity analysis further reinforced these results, showing how uncertainty in essential model parameters in the external resistance (Rw) and compensation point parameterization propagated into diverging model outcomes. These outcomes underscore the need to improve our mechanistic understanding of surface equilibria represented by compensation points, including the adsorption–desorption mechanism at the external water layer, and specific recommendations are provided for future modelling approaches and measurement setups to support this goal.