Modeling radon behavior for characterizing and forecasting geophysical variables at the atmosphere-soil interface

As well known, noble gases are often used as stable tracers in several geophysical environments, due to their basic property of being chemical noninteracting. Among these noble gases, the attention of researchers in the last decades has been focused on radon. Here, we review the use of radon data in characterizing and forecasting geophysical variables at the atmosphere-soil interface. In particular, we analyze the applications to the study of the diffusive properties of the low atmosphere, to the research in the fields of pedology and sedimentology, where radiogenic nuclides are employed as stratigraphic markers, and to the investigations on radon exhalations in the framework of earthquake characterization and forecasting. In doing so, particular attention is paid to modeling and statistical approaches based on radon data. In an atmospheric framework, it has been shown that radon concentration can be a good tracer of stability of the boundary layer (BL) (the lowest part of the atmosphere). In particular, this led to working out diagnostic models for the estimation of the mixing depth from radon data and prognostic neural network (NN) models for forecasting its future behavior, thus giving important information about the meteorological influences on air pollution and its possible peak events. Here, we briefly review these studies and present the structure of an improved model. Furthermore, the interaction between radon by-products, pedosphere, and hydrosphere is commonly assumed to be an important tool for the characterization of soil and of sediment dynamics. Radon daughters are an efficient stratigraphic marker that is useful for modeling accumulation and erosion rates associated to the recent evolution of landscapes. Considering the wide range of box model approaches proposed for geomorphological purposes in the last years, a review of such applications will be illustrated. Finally, in the framework of studies about earthquakes, we briefly review the use of statistical analyses based on radon data for characterizing and, possibly, forecasting these phenomena. Thus, the present paper supplies a review of radon detection and the related modeling activities and statistical analyses at the atmosphere-soil interface. It clearly shows the importance of these studies for a better understanding of processes and phenomena that occur at this delicate and complex interface.