Processes controlling the seasonal variations of 210Pb and 7Be at the Mt. Cimone WMO-GAW global station, Italy: A model analysis

We apply the Global Modeling Initiative (GMI) chemistry and transport model 14 driven by the NASA’s MERRA assimilated meteorological data to simulate the seasonal variations of two radionuclide aerosol tracers (terrigenous 210Pb and cosmogenic 7 15 Be) at the 16 WMO-GAW station of Mt. Cimone (44°12’ N, 10°42’ E, 2165 m asl, Italy), which is 17 representative of free-tropospheric conditions most of the year, during 2005 with an aim to 18 understand the roles of transport and precipitation scavenging processes in controlling their 19 seasonality. The total precipitation field in the MERRA data set is evaluated with the Global 20 Precipitation Climatology project (GPCP) observations, and a generally good agreement is found. The model reproduces reasonably the observed seasonal pattern of 210 21 Pb concentrations, characterized by a wintertime minimum due to lower 222 22 Rn emissions and weaker uplift from the boundary layer and summertime maxima resulting from strong convection over the continent. The observed seasonal behavior of 7Be concentrations shows a winter minimum, a summer maximum, and a secondary spring maximum. The model captures the observed 7Be 4 pattern in winter-spring, which is linked to the larger stratospheric influence during spring. However, the model tends to underestimate the observed 7Be concentrations in summer, 6 partially due to the sensitivity to spatial sampling in the model. Model sensitivity experiments 7 indicate a dominant role of precipitation scavenging (versus dry deposition and convection) in controlling the seasonality of 210Pb and 7 Be concentrations at Mt. Cimone.