Cosmogenic isotope 7Be: A case study of depositional processes in Rio de Janeiro in 2008–2009

Abstract: We present here an investigation of the depositional processes of 7Be-carrying aerosols in the troposphere through an analysis of the isotope concentration variability measured at Rio de Janeiro (Brazil) during 2008 and 2009, with weekly resolution. By adopting a simplified description of the equilibrium scenario in the troposphere and combining our isotopic data with regional meteorological parameters and numerical CRAC:Be7 model of cosmogenic production, it was possible to quantitatively reproduce the observed seasonal variability and estimate the typical 7Be-aerosols residence time in the lower troposphere (t r ∼1day) as well as the washout coefficient for each season (wet: Λ =0.029; and dry: Λ =0.023h−1). These results allowed us to discuss the origin of the seasonal patterns of 7Be concentrations, indicating that the wet deposition modulation, caused by changes in the regional weather condition, is the most important forcing in both seasons. Even an anomaly in isotopic short-term measured variability can be explained when a detailed air-mass dynamic is considered. Our results indicate that anomalous events of tropospheric dynamic, such as occurrence of strong downward air flux, imprint information about air masses 3-D movement in the near-ground air 7Be data, making 7Be a useful tracer of its peculiar dynamics at local and synoptic scales in the troposphere. This study, limited to a single location and one year time interval, illustrates the potential of the method. A more detailed general study is planned for the future. [Copyright &y& Elsevier]