On the diurnal, weekly, and seasonal cycles and annual trends in atmospheric CO<sub>2</sub> at Mount Zugspitze, Germany, during 1981–2016

Abstract

<p><strong>Abstract.</strong> A continuous, 36-year measurement composite of atmospheric carbon dioxide (<span class="inline-formula">CO₂</span>) at three measurement locations on Mount Zugspitze, Germany, was studied. For a comprehensive site characterization of Mount Zugspitze, analyses of <span class="inline-formula">CO₂</span> weekly periodicity and diurnal cycle were performed to provide evidence for local sources and sinks, showing clear weekday to weekend differences, with dominantly higher <span class="inline-formula">CO₂</span> levels during the daytime on weekdays. A case study of atmospheric trace gases (CO and NO) and the passenger numbers to the summit indicate that <span class="inline-formula">CO₂</span> sources close by did not result from tourist activities but instead obviously from anthropogenic pollution in the near vicinity. Such analysis of local effects is an indispensable requirement for selecting representative data at orographic complex measurement sites. The <span class="inline-formula">CO₂</span> trend and seasonality were then analyzed by background data selection and decomposition of the long-term time series into trend and seasonal components. The mean <span class="inline-formula">CO₂</span> annual growth rate over the 36-year period at Zugspitze is <span class="inline-formula">1.8±0.4</span><span class="thinspace"></span>ppm<span class="thinspace"></span>yr<span class="inline-formula">⁻¹</span>, which is in good agreement with Mauna Loa station and global means. The peak-to-trough amplitude of the mean <span class="inline-formula">CO₂</span> seasonal cycle is <span class="inline-formula">12.4±0.6</span><span class="thinspace"></span>ppm at Mount Zugspitze (after data selection: <span class="inline-formula">10.5±0.5</span><span class="thinspace"></span>ppm), which is much lower than at nearby measurement sites at Mount Wank (<span class="inline-formula">15.9±1.5</span><span class="thinspace"></span>ppm) and Schauinsland (<span class="inline-formula">15.9±1.0</span><span class="thinspace"></span>ppm), but following a similar seasonal pattern.</p>