In order to point out and study transports of ozone rich air masses in the lower troposphere from the stratosphere/upper troposphere, continuous measurements of several parameters have been undertaken at Mt. Cimone during the European Community VOTALP project (Vertical Ozone Transport in the Alps). Several high values of surface ozone concentration due to vertical stratospheric-tropospheric exchanges have been recorded in the four mountain peak stations involved in this project (Jungfraujoch, Sonnblick, Zugspitze and Mt. Cimone) in 1996–1997. This paper presents and analyses data concerning the Mt. Cimone ground-based station, which is the highest peak of the Italian Northern Apennines and the most representative WMO-GAW site in Italy. Episodes of vertical exchange in the lower stratosphere, as tropopause folding, or in the upper troposphere, as down draft transport, have been registered at Mt. Cimone since March 1996 and subsequently studied. In fact, the comparison between the behaviours of different background trace gases at a mountain baseline station, the weather situations and the backward trajectory analyses can bring to light these events and be very useful for a better knowledge of transport phenomena. Correlation between high level of ozone concentration, chemical and meteorological parameters and three-dimensional backward trajectories relative to two particular events are herein presented.

In order to evaluate the background ozone concentration at Mt. Cimone (2165 m a.s.l.), the contribution of air masses characterised by different provenances is analysed in this paper. The analysis method is based on identification of background air masses which travelled above the 780 hPa pressure level for at least 48 h before arriving at Mt. Cimone. Not being recently mixed with boundary layer air, these air masses are characterised by a chemical age greater than 2 days. This analysis has shown that under background conditions the yearly principal maximum of ozone is recorded in spring and a secondary maximum is recorded in summer. In contrast, if we consider non-background conditions, the principal maximum is found in late summer and a secondary one in spring. In addition, the analysis indicates the presence of a smooth latitudinal gradient of background ozone concentrations in air masses arriving at Mt. Cimone, with higher concentrations coming from the north and lower ones from the south.

In order to point out and study transports of ozone rich air masses in the lower troposphere from the stratosphere/upper troposphere, continuous measurements of several parameters have been undertaken at Mt. Cimone during the European Community VOTALP project (Vertical Ozone Transport in the Alps). Several high values of surface ozone concentration due to vertical stratospheric-tropospheric exchanges have been recorded in the four mountain peak stations involved in this project (Jungfraujoch, Sonnblick, Zugspitze and Mt. Cimone) in 1996–1997. This paper presents and analyses data concerning the Mt. Cimone ground-based station, which is the highest peak of the Italian Northern Apennines and the most representative WMO-GAW site in Italy. Episodes of vertical exchange in the lower stratosphere, as tropopause folding, or in the upper troposphere, as down draft transport, have been registered at Mt. Cimone since March 1996 and subsequently studied. In fact, the comparison between the behaviours of different background trace gases at a mountain baseline station, the weather situations and the backward trajectory analyses can bring to light these events and be very useful for a better knowledge of transport phenomena. Correlation between high level of ozone concentration, chemical and meteorological parameters and three-dimensional backward trajectories relative to two particular events are herein presented.