NH₃ concentrations were measured at 11 LWF plots (1999/2000) with Zürcher passive samplers (Palmes-type diffusion tubes with an acidic solution as absorbent) during one year. Three samplers per site and period (usually 14 days) were installed in the open area of the LWF plots and, at Beatenberg, Novaggio and Vordemwald, under the forest as well (weather station). In 2014, NH₃ concentrations were measured again at 14 plots, using two Radiello samplers per site and period (usually 28 days). At Lausanne and Vordemwald, concentrations were also measured below the canopy. ### Purpose: ### To assess air concentrations of ammonia (NH₃) and, using deposition velocities available from the literature, to quantify the dry deposition of NH₃ (alternative method to the throughfall method). The LWF plots were part of a larger network covering the main regions of Switzerland. One objective of this larger network was to compare measured and modelled concentrations.