Partner und Internationale Organisationen
(Englisch)
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B, CH, CRO, CZ, D, DK, E, F, FIN, GR, H, I, N, S, SK, UK
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Abstract
(Englisch)
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AirObsGeneva was a continuing effort to document and analyze tropospheric ozone production ('summer smog'), its precursors, and meteorological background in the urban plume of Geneva. The tool to achieve the three-dimensional in-situ-measurements was an instrumented light aircraft with sensors for position, wind, temperature, dewpoint (humidity), aerosols, ozone, nitrogen dioxide, about 30 species of hydrocarbons (C4..C10), and hydrogen peroxide. In addition to measuring campaigns in 1991 and 1992 (BUWAL Umwelt-Materialien Luft Nr. 24 und 63), two observation periods of four and five days in 1996, and 1997 took place. Newly measured parameters such as speciated NMHC (Non-Methane Hydrocarbons), aerosols, and peroxides should give more insight into the sources and chemical processes in the diluted air above and behind the city of Geneva. Another aim was to collect more 'typical' cases of enhanced ozone levels in the region around Geneva (6 since 1991 was not so much). With meanwhile 15 observation days, we can give a better estimate of the ratio between 'regionally enhanced ozone levels' (i.e. regional possibilities for abatement) and 'large scale events'. Within this ensemble, we have found two cases of extreme regional ozone production in the lee of Geneva (both around 40 ppb above background concentrations), and at least two more remarkable urban plumes. For the rest of the days, the net sum of advection, production, deposition, and destruction of ozone is less obvious to interpret. In order to quantify the net regional emission of precursors, and the net production of ozone, 'flux budget calculations' were performed. For this purpose, the measured wind- and concentration fields, and the mixing heights were used. The latter were calculated with an orography-sensitive convection model which extended the observed mixing heights to diurnal evolutions. t is not yet clear what effects are causing the few extreme ozone pollution events. The relative concentrations between the precursor concentrations (NO2, and NMHC) of the different days is not so much varying, and cannot be purely explained by the non-linearity of the chemical reactions. The most obvious differences were in the windfields. Other criteria such as ratios between different species of NMHC's, and of NMHC's versus NO2 or NOx will further be studied. Another question is about local precursor pollution maxima between the two cities of Lausanne, and Geneva, which persisted independently of wind direction, and which cannot be an urban plume of Geneva.
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