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 (f6hn) 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 •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 f6hn episodes. The NO x values exhibit an even larger increase. Depending on the season, the O3 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 NO x 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.

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Abstract. The vertical distribution of ozone in the lower troposphere over the Swiss Plateau is investigated in detail for two episodes in early spring (February 1998 andMarch 1999). Profile measurements of boundary-layer ozone performed during two field campaigns with a tethered balloon sounding system and a kite are investigated using regular aerological and ozone soundings from a nearby site, measurements from monitoring stations at various altitudes, backward trajectories, and synoptic analyses of meteorological fields. Additionally, the effect of in situ photochemistry was estimated for one of the episodes employing the Metphomod Eulerian photochemical model. Although the meteorological situations were completely different, both cases had elevated layers with high ozone concentrations, which is not untypical for late winter and early spring. In the February episode, the highest ozone concentrations of 55 to 60 ppb, which were found at around 1100 m asl, were partly advected from Southern France, but a considerable contribution of in situ photochemistry is also predicted by the model. Below that elevation, the local chemical sinks and surface deposition probably overcompensated chemical production, and the vertical ozone distribution was governed by boundarylayer dynamics. In the March episode, the results suggest that ozone-rich air parcels, probably of stratospheric or upper tropospheric origin, were advected aloft the boundary layer on the Swiss Plateau.Key words. Atmospheric composition and structure (pollution -urban and regional; troposphere -composition andCorrespondence to: S. Brönnimann (broenn@giub.unibe.ch) chemistry) -Meteorology and atmospheric dynamics (mesoscale meteorology)

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