THE URBAN PLUME OF VIENNA - COMPARISONS BETWEEN AIRCRAFT MEASUREMENTSAND PHOTOCHEMICAL MODEL RESULTS

A Lagrangian photochemical box model (IMPO model) developed for ozone forecasts and longterm scenario calculations was evaluated by comparin g simulated ozone and nitrogen dioxide concentrations with aircraft me asurements done around Vienna/Austria during episodes of high ozone co ncentrations in 1995. The major aim oi these measurements was to recor d position, extent and intensity of the urban ozone plume. The Lagrang ian model simulations were done on a grid covering Vienna and surround ings. The simulated concentrations were interpolated to the aircraft p ositions. In most cases, the horizontal position of the plume was reas onably well reproduced by the model, demonstrating that despite of all the necessary simplifications, a box model based on air-mass trajecto ries can be a valuable tool in describing the transport of pollutants. The ozone production in the plume was underpredicted by a factor of 2 . High nitrogen dioxide concentrations measured near the city centre w ere reproduced by the model, but there are strong indications that nit rogen dioxide concentrations were underpredicted by the model in rural areas. A clear quantification proved to be impossible due to uncertai nties in the measurement data. (C) 1998 Elsevier Science Ltd. All righ ts reserved.