Analysing the seasonal cycle and inter-annual variability of ammonium and nitrate in precipitation across Germany / Gutachter: Prof. Dr. Martijn Schaap, Prof. Dr. Peter Builtjes
Barbara Szénási / Masterarbeit – 2016
Atmospheric deposition of reactive nitrogen causes acidification and eutrophication of soils and fresh water negatively affecting the biodiversity in terrestrial and aquatic ecosystems. The German Advisory Council on the Environment (SRU) recommends that the federal government and the German Länder jointly elaborate a national nitrogen strategy (SRU, 2015) to reduce the reactive nitrogen input into the environment in Germany. Developing a nitrogen strategy requires robust chemical transport models to quantify the actual nitrogen deposition as well as to investigate the effectiveness of mitigation strategies and estimate impacts on climate change. The aim of this master thesis is to improve the understanding of the seasonal cycle and inter-annual variability of ammonium and nitrate in precipitation across Germany. Measurement data of wet deposition flux and rain water concentration of ammonium and nitrate of 311 measurement sites in total, spanning a thirteen-year period 2000-2013, were provided by the Umweltbundesamt within the framework of the PINETI-III research project. The measurements were compared to the model data of the LOTOS-EUROS model in order to investigate the simulating performance of the considered chemical compounds. On average, the measured wet deposition fluxes and rain water concentrations of ammonium and nitrate are underestimated by the model by 7-23%. Furthermore, the model does not capture the seasonal cycles correctly. Increasing the dry deposition velocity of ammonia by 30% results in a minor decrease of the ammonium wet deposition fluxes and rain water concentrations, whereas changing the temporal profile leads to seasonal cycles that are in better agreement with the measurements. The influence of the sensitivity runs is negligible on the wet deposition fluxes and rain water concentrations of nitrate. It is advised to develop temporal profiles tailored to the regional emission variabilities to further enhance the model performance.