Two case studies on the interaction of large-scale transport, mesoscale photochemistry, and boundary-layer processes on the lower tropospheric ozone dynamics in early spring

摘要

The vertical distributionof ozone in the lower troposphere over the Swiss Plateau is investigated indetail for two episodes in early spring (February 1998 and March 1999). Profilemeasurements of boundary-layer ozone performed during two field campaigns with atethered balloon sounding system and a kite are investigated using regularaerological and ozone soundings from a nearby site, measurements from monitoringstations at various altitudes, backward trajectories, and synoptic analyses ofmeteorological fields. Additionally, the effect of photochemistrywas estimated for one of the episodes employing the Metphomod Eulerianphotochemical model. Although the meteorological situations were completelydifferent, both cases had elevated layers with high ozone concentrations, whichis not untypical for late winter and early spring. In the February episode, thehighest ozone concentrations of 55 to 60 ppb, which were found at around 1100 masl, were partly advected from Southern France, but a considerable contributionof photochemistry is also predicted by the model. Belowthat elevation, the local chemical sinks and surface deposition probablyovercompensated chemical production, and the vertical ozone distribution wasgoverned by boundary-layer dynamics. In the March episode, the results suggestthat ozone-rich air parcels, probably of stratospheric or upper troposphericorigin, were advected aloft the boundary layer on the Swiss Plateau.Atmospheric compositionand structure (pollution – urban and regional; troposphere – compositionand  chemistry) – Meteorology and atmospheric dynamics (mesoscalemeteorology)