Ozone transport between Apennines and Alps: Influence of Po-basin-polluted air masses

Continuous in-situ ozone measurements (1996-1998) at the stations Mt. Cimone (2165 m a.s.l., northern Apennines) and Zugspitze (2962 m a.s.l.; northern Alps) are compared, aiming at an estimate of the contribution of polluted air from the Po Basin. While the annual average O3 concentrations are higher at Mt. Cimone by 2.9 ppb, mainly due to higher summer values, the large-scale and year-to-year O3 variations were very similar at both sites. Episodes of transport from Zugspitze to Mt. Cimone were identified by 3D-backward trajectories, with O3 concentrations at Mt. Cimone increasing as a function of travel time. The seasonal average O3 increases were maximal during summer, with a net surplus from Zugspitze to Mt. Cimone around 6 ppb. The Po Basin influence was further evidenced by O3 data seleceted by trajectories comprising this region.