Variability of trace gases at the high-Alpine site Jungfraujoch caused by meteorological transport processes

The influence of meteorological transport processes on trace gas concentrations at the high-Alpine site Jungfraujoch (3580 m above sea level) is investigated. These processes are subdivided into two categories: thermally driven transport, which takes place on a local scale, and transport on a regional (fohn) or synoptic scale (fronts). During thermally induced processes, which are mainly observed in summer and spring, the carbon monoxide (CO) mixing ratios show a diurnal variation with a maximum concentration at approximate to 1800 local time. Processes on the regional and synoptic scale which occur during the whole season induce large variability in the trace gas observations. The CO concentrations can be twice as large as the monthly median value during severe fohn episodes. The NOx values exhibit an even larger increase. Depending on the season, the O-3 observations during these periods show an increase in summer and a pronounced decrease in winter. In addition, it is found that the calculated trajectories using the output of a mesoscale weather prediction model are a useful tool to detect and explain episodes with high NOx or CO concentrations. Altogether, the present results imply that meteorological transport processes on different spatial and timescales are important for the interpretation of the trace gas observations at the high-Alpine site Jungfraujoch during the whole year.