Atmospheric nitrogen deposition in Switzerland

Increased atmospheric nitrogen (N) deposition into sensitive ecosystems is leading to soil acidification, nutrient imbalances and biodiversity losses. Therefore, N depositions were quantified throughout Switzerland in 2000, 2014, 2019 and 2024 measuring the concentrations of seven different inorganic N compounds in wet and dry gravitational as well as in dry non-gravitational deposition. For data collection passive (diffusion tubes and bulk sampler) and active sampling systems (denuder and filter sampler) were used. From the obtained measurement data, N depositions were calculated. The wet and dry gravitational deposition was obtained directly from the bulk samples. The dry non-gravitational deposition was calculated using the inferential method. By summing up the gravitational and non-gravitational N deposition, the total N deposition was obtained and compared to the critical loads for N (CLN). The results show that N inputs in Switzerland are largely around or above the CLN, regardless of the sensitive ecosystems considered. Considerable exceedances have been found near intensive agriculture. In the long-term comparison, a decrease in oxidized N components was observed. However, the total N deposition remained stable over time. The most important processes for the N deposition are the precipitation and the dry deposition of ammonia (NH₃). In summary, the atmospheric N inputs into sensitive ecosystems in Switzerland are largely too high and therefore further measures to reduce N emissions are necessary.

We would like to thank to the Swiss Federal Office for the Environment (FOEN), Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Ostluft, the Swiss cantons and the University of Basel for financial support of the measurement campaigns. A special thank goes to the Swiss Federal Laboratories for Materials Science and Technology (EMPA) for the valuable cooperation.