Applications of environmental radionuclides to atmospheric studies at the WMO-GAW station of Mt. Cimone

Terrigenic and cosmogenic radionuclides have been often applied in the atmospheric sciences to improve the understanding of several processes, including stratosphere-troposphere exchange (STE), interhemispheric transport, transport and/or deposition processes of atmospheric pollutants. This work presents a brief compendium of research results achieved exploiting the use of 7Be and 210Pb radiotracers at the station of Mt. Cimone (44.20°N, 10.70°E; 2165 m a.s.l.; Italy). In particular, long term observations of 7Be and 210Pb in the period of 1998-2011 enabled first of all the study of STE events at the site. STE seasonal cycle at the station is characterized by the presence of a winter maximum and a spring-summer minimum. Nonetheless, stratospheric intrusion (SI) events at Mt. Cimone are scattered all over the year. The seasonal cycle of both radiotracers is characterized by a summer maximum due to higher convection and enhanced mixing height and tropopause height, which together intensify the uplift of 210Pb from the planetary boundary layer (PBL) and the subsidence of 7Be from the upper troposphere. The secondary 7Be winter maximum is associated with the higher frequency of STE events during the cold period. The study of advection patterns through the clusters of back-trajectories highlighted that the seasonality of advection patterns at the site strongly affects the seasonal cycle of both radiotracers. Further research focused on simulations of 7Be and 210Pb conducted by a state-of-the-art chemistry and transport model (CTM), which helped understand the relative roles of wet scavenging, dry deposition, and convection (transport and scavenging) on the 7Be and 210Pb seasonalities. The results pointed out the dominant role of precipitation scavenging in the seasonal pattern of both radiotracers. Finally, 210Pb peak events at the site were studied. Meteorological conditions promoting the occurrence of these events are characterized by prolonged anticyclones, low relative humidity, high temperature, and high mixing height. In particular, the strong coupling between PBL and free troposphere seem to play a major role in promoting the occurrence of such events.