Articles | Volume 9, issue 12
Biogeosciences, 9, 5261–5277, 2012

Special issue: Nitrogen and global change

Biogeosciences, 9, 5261–5277, 2012

Research article 18 Dec 2012

Research article | 18 Dec 2012

Modeling the distribution of ammonia across Europe including bi-directional surface–atmosphere exchange

R. J. Wichink Kruit1, M. Schaap1, F. J. Sauter2, M. C. van Zanten2, and W. A. J. van Pul2 R. J. Wichink Kruit et al.
  • 1TNO, Dept. of Climate, Air and Sustainability, P.O. Box 80015, 3508 TA Utrecht, The Netherlands
  • 2RIVM, P.O. Box 1, 3720 BA Bilthoven, The Netherlands

Abstract. A large shortcoming of current chemistry transport models (CTM) for simulating the fate of ammonia in the atmosphere is the lack of a description of the bi-directional surface–atmosphere exchange. In this paper, results of an update of the surface–atmosphere exchange module DEPAC, i.e. DEPosition of Acidifying Compounds, in the chemistry transport model LOTOS-EUROS are discussed. It is shown that with the new description, which includes bi-directional surface–atmosphere exchange, the modeled ammonia concentrations increase almost everywhere, in particular in agricultural source areas. The reason is that by using a compensation point the ammonia lifetime and transport distance is increased. As a consequence, deposition of ammonia and ammonium decreases in agricultural source areas, while it increases in large nature areas and remote regions especially in southern Scandinavia. The inclusion of a compensation point for water reduces the dry deposition over sea and allows reproducing the observed marine background concentrations at coastal locations to a better extent. A comparison with measurements shows that the model results better represent the measured ammonia concentrations. The concentrations in nature areas are slightly overestimated, while the concentrations in agricultural source areas are still underestimated. Although the introduction of the compensation point improves the model performance, the modeling of ammonia remains challenging. Important aspects are emission patterns in space and time as well as a proper approach to deal with the high concentration gradients in relation to model resolution. In short, the inclusion of a bi-directional surface–atmosphere exchange is a significant step forward for modeling ammonia.

Final-revised paper