ORIGIN OF OZONE IN VIENNA AND SURROUNDINGS, AUSTRIA

A statistical analysis of local scale ground-level trajectories during three summer half years was made to determine the influence of Vienna on the ozone concentrations in the surroundings. It was possible to show that on average, Vienna does not act as an ozone source for sites in the surroundings. Only on the hottest days of each year around noon is it a strong source of ozone. Therefore, long-range transport of ozone must be important for the average ozone concentrations. This was investigated by a statistical analysis of isobaric backward trajectories. In summer, high ozone concentrations in Vienna and surroundings are often associated with trajectories arriving from areas in Europe which agree reasonably well with those having high anthropogenic emissions of precursors. In winter, an important source of ozone in eastern Austria is transport from the Atlantic Ocean. Tropospheric background ozone concentrations in Vienna and surroundings were estimated from surface measurements during periods of high wind speed. A mean summertime tropospheric background concentration of 30-40 ppb ozone was found for air masses of maritime origin, while it was 70-75 ppb for continental air masses.