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

Abstract

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)

A vertical profile of PM10 dust concentrations measured during a regional dust event identified by MODIS Terra, western Queensland, Australia

“…The kite is flown using a 300 kg breaking strain spectra line tether which is attached to a hand operated winch. While kites have been used previously to sample aerosols from biomass burning [ Mims and Mims , 2004], sea salts [ Daniels , 1989], and urban air pollutants [ Brönnimann et al , 2001], this is the first time we believe that a kite has been used to sample a dust plume.…”

Sub-continental transport mechanisms and pathways during two ozone episodes in northern Spain

“…Among other abilities, this type of modelling system can reproduce adequately the onset and decay of land and sea-breezes, the topographic forcing, the fine-scale layering of the lower troposphere, and the sharp variations in both time and space of stability within the planetary boundary layer over a non-homogeneous surface. Global, lower resolution meteorological data provided by the National Centers for Environmental Prediction (NCEP) and the European Centre for Medium-Range Weather Forecasting (ECMWF), among others, have also been used to track passive tracers using Lagrangian particle dispersion models with the aim of documenting the IC and regional transport of pollutants (Brönnimann et al, 2001;Draxler, 2003).…”