Stratospheric ozone intrusion episodes recorded at Mt. Cimone during the VOTALP project: case studies

Continuous measurements of ozone concentrations performed at baseline stations on high mountain summits allow stratosphere–troposphere exchange events to be monitored and their variability over small scales to be studied. In this paper we present two characteristic episodes related to lower stratosphere/upper troposphere vertical transport registered at Mt. Cimone during the VOTALP project and we highlight the use of carbon monoxide (CO) and carbon dioxide (CO2) as non-conventional tracers of lower stratospheric air masses. In this way, stratosphere–troposphere exchange events transporting high ozone concentration into the troposphere have been identified by an accurate analysis of the CO and CO2 behaviour. Moreover, three-dimensional ensemble trajectories, satellite maps (water vapour and total ozone), ground-based ozone measurements and ozone-soundings have been analysed together with conventional tracers as 7Be and relative humidity as well as the normalised fraction f (7Be, 210Pb) in order to fully characterise the examined events.