<p>A continuous, 36-year measurement record of atmospheric carbon dioxide (CO<sub>2</sub>) at three measurement sites of Mount Zugspitze, Germany was studied. The CO<sub>2</sub> trend and seasonality were analyzed by decomposing the long-term time series into trend and seasonal components. The mean CO<sub>2</sub> annual growth rate over the 36 year period at Zugspitze is 1.8 ppm yr<sup>−1</sup>, which is in good agreement with the Mauna Loa station and the global means. The peak-to-trough amplitude of the mean CO<sub>2</sub> seasonal cycle is 11.67 ppm at Mount Zugspitze, which is significantly less than nearby measurement sites at Mount Wank and Schauinsland, but which follow similar patterns. To characterize this mountain site better, analyses of weekly periodicity and the diurnal cycle were performed to provide evidence of local sources and sinks of CO<sub>2</sub>. Together, with an atmospheric trace gas (CO and NO) and the number of site visitor case study, clear weekday–weekend differences were detected, indicating potential CO<sub>2</sub> sources in the near vicinity.</p>