Atmospheric N2O trends, variability, and regional emissions derived from long-term observations and the radon tracer method at Schauinsland and Zugspitze stations (Germany)

Nitrous oxide (N₂O) is the third most important long-lived greenhouse gas and the most dominant contributor to stratospheric ozone depletion. In Germany, long-term atmospheric N₂O mole fractions are measured continuously at two background stations: Schauinsland (47°55‘N, 7°55‘E, 1205 m above sea level) and Zugspitze (47°25‘N, 10°58‘E, 2656 m above sea level). In this study, high-resolution measurements from 2001 (Schauinsland) and 2003 (Zugspitze) to 2024 were subjected to a comprehensive quality control process, including consistency checks and filtering to reduce the influence of local sources.

The long-term trends of N₂O mole fractions at Schauinsland and Zugspitze stations, of 0.82 ppb/yr and 0.85 ppb/yr, respectively, agree well with the marine background observations from the AGAGE at Mace Head station, and with global tropospheric growth rates. The continental excess during the last 25 years was found to be 0.9 ppb at Schauinsland and 0.5 ppb at Zugspitze. At Schauinsland station, the amplitude of the seasonal cycle decreased from 1.0 ppb during 2001-2010 to 0.7 ppb during 2011-2024. The diurnal variability ranges from 0.1 ppb  in winter to 1.0 ppb in summer. At Zugspitze, the annual variability is 0.4 ppb. The amplitudes in the mean diurnal cycle range from 0.03 ppb during the winter months to 0.15 ppb during summer months.  Regional N₂O emissions in the vicinity of Schauinsland (Upper Rhine Valley) were quantified using the radon tracer method, based on ²²²Rn activity measurements provided by the German Federal Office for Radiation Protection. The derived N₂O fluxes from the radon tracer method were extrapolated to annual emissions and compared with different emission inventories (EDGAR, UNFCCC, and E-PRTR/IREP), focusing particularly on the differences between the inventories regarding emissions attributed to the chemical industry in the Alsace region of France.