Stratospheric intrusion events recorded at Mt. Cimone station (Italy) : analysis of six years of ozone and carbon dioxide observations

The study of stratospheric intrusion events represents one of the main activities performed at Mt. Cimone GAW station (44º11’ N, 10º42’ E; 2165 m asl), the highest mountain peak of the Italian northern Apennines. Within the frame of different EU research projects, the frequency of such events has been analysed and their contribution to the background tropospheric ozone concentration has been investigated since 1996. These analyses permitted to asses that a not negligible amount of O3 recorded at Mt. Cimone was due to stratospheric intrusion events. Being one of the most important greenhouse gases, CO2 concentration has been continuously monitored at Mt. Cimone since 1979 by General Office for Meteorology. At this measurement site, considered representative of the European continental free troposphere, the CO2 behaviour reflects the continental influence of biogenic and anthropic sources. Because neither sources nor sinks for this atmospheric compound are present in stratosphere, when stratospheric air masses intrude into the troposphere, changes in CO2 concentration can be recorded, so that it can be considered a non-conventional stratospheric tracer. In this work, in order to investigate the variations of ozone and carbon dioxide concentration recorded at Mt. Cimone during stratospheric intrusion episodes, we have analysed 6-years (1998 – 2003) of O3, CO2 and 7Be activity concentrations as well as meteorological parameters and FLEXTRA three-dimensional back-trajectories. The results are presented and discussed.