Abstract
Abstract. Atmospheric levels of reactive nitrogen have increased substantially during the last century resulting in increased nitrogen deposition to ecosystems, causing harmful effects such as soil acidification, reduction in plant biodiversity and eutrophication in lakes and the ocean. Recent developments in the use of atmospheric remote sensing enabled us to resolve concentration fields of NH3 with larger spatial coverage. These observations may be used to improve the quantification of NH3 deposition. In this paper, we use a relatively simple, data-driven method to derive dry deposition fluxes and surface concentrations of NH3 for Europe and for the Netherlands. The aim of this paper is to determine the applicability and the limitations of this method for NH3. Space-born observations of the Infrared Atmospheric Sounding Interferometer (IASI) and the LOTOS-EUROS atmospheric transport model are used. The original modelled dry NH3 deposition flux from LOTOS-EUROS and the flux inferred from IASI are compared to indicate areas with large discrepancies between the two. In these areas, potential model or emission improvements are needed. The largest differences in derived dry deposition fluxes occur in large parts of central Europe, where the satellite-observed NH3 concentrations are higher than the modelled ones, and in Switzerland, northern Italy (Po Valley) and southern Turkey, where the modelled NH3 concentrations are higher than the satellite-observed ones. A sensitivity analysis of eight model input parameters important for NH3 dry deposition modelling showed that the IASI-derived dry NH3 deposition fluxes may vary from ∼ 20 % up to ∼50 % throughout Europe. Variations in the NH3 dry deposition velocity led to the largest deviations in the IASI-derived dry NH3 deposition flux and should be focused on in the future. A comparison of NH3 surface concentrations with in situ measurements of several established networks – the European Monitoring and Evaluation Programme (EMEP), Meetnet Ammoniak in Natuurgebieden (MAN) and Landelijk Meetnet Luchtkwaliteit (LML) – showed no significant or consistent improvement in the IASI-derived NH3 surface concentrations compared to the originally modelled NH3 surface concentrations from LOTOS-EUROS. It is concluded that the IASI-derived NH3 deposition fluxes do not show strong improvements compared to modelled NH3 deposition fluxes and there is a future need for better, more robust, methods to derive NH3 dry deposition fluxes.
Highlights
Reactive nitrogen (Nr) emissions have substantially increased during the last century to around 4 times the preindustrial levels (Erisman et al, 2008; Fowler et al, 2013)
This paper shows the first use of the Infrared Atmospheric Sounding Interferometer (IASI)-NH3 product for the derivation of NH3 dry deposition fluxes, together with validation of the derived NH3 surface concentrations with in situ measurements
The computation of the IASI-derived NH3 surface concentrations and dry deposition fluxes is described in detail
Summary
Reactive nitrogen (Nr) emissions have substantially increased during the last century to around 4 times the preindustrial levels (Erisman et al, 2008; Fowler et al, 2013). Atmospheric deposition of reactive nitrogen to both terrestrial and aquatic ecosystems has increased. Excessive nitrogen deposition to sensitive ecosystems can cause harming effects such as soil acidification, reduction in plant biodiversity and eutrophication in water bodies (Erisman et al, 2015). Ammonia (NH3) is one form of reactive nitrogen and constitutes an important part of the total amount of Nr emissions. Up to 50 % of global reactive nitrogen emissions consist of NH3 (Reis et al, 2009), and NH3 contributes significantly to these adverse effects. Atmospheric ammonia is deposited to surfaces by two processes: dry and wet deposition
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