Pollution events at the high-altitude mountain site Zugspitze-Schneefernerhaus (2670 m a.s.l.), Germany

Within the CO₂ time series measured at the Environmental Research Station Schneefernerhaus (UFS), Germany, as part of the Global Atmospheric Watch (GAW) program, pollution episodes are traced back to local and regional emissions, identified by δ¹³C(CO₂) as well as ratios of CO and CH₄ to CO₂ mixing ratios. Seven episodes of sudden enhancements in the tropospheric CO₂ mixing ratio are identified in the measurements of mixing/isotopic ratios during five winter months from October 2012 to February 2013. The short-term CO₂ variations are closely correlated with changes in CO and CH₄ mixing ratios, achieving mean values of 6.0 ± 0.2 ppb/ppm for CO/CO₂ and 6.0 ± 0.1 ppb/ppm for CH4/CO₂. The estimated isotopic signature of CO₂ sources (δs) ranges between -35‰ and -24‰, with higher values indicating contributions from coal combustion or wood burning, and lower values being the result of natural gas or gasoline. Moving Keeling plots with site-specific data selection criteria are applied to detect these pollution events. Furthermore, the HYSPLIT trajectory model is utilized to identify the trajectories during periods with CO₂ peak events. Short trajectories are found covering Western and Central Europe, while clean air masses flow from the Atlantic Ocean and the Arctic Ocean.