Atmospheric radon in the surface layer: a box model constrained with meteorological data

In situ measurements of Radon-222 in the atmospheric surface layer collected at L’Aquila (Italy) during 2004-2009 have been analyzed in correlation with meteorological data and other atmospheric trace gases. These data have been studied in order to find the controlling mechanisms of surface radon abundance: observations of coincident meteorological parameters confirmed the important role of small-scale atmospheric dynamics. The negative correlation of hourly data of surface wind speed and radon activity concentration, as well as of ozone and radon abundances, suggests that dynamical removal of radon is one of the most important controlling processes of the tracer accumulation in the atmospheric surface layer. A box model has been developed to better understand the mechanisms for diurnal and seasonal variability of the tracer and to indirectly assess the magnitude of the monthly averaged radon soil flux in the L’Aquila measurement site. The model has been successfully validated with measurements: on average for the whole period of observations, the correlation coefficient of measured and modelled radon hourly data is 0.8. Radon data collected during March 2009 have also been analyzed to find possible signs of perturbation due to the on-going seismic activity that would have reached its peak in the April 6, 2009 destructive earthquake. However, the present study shows that no significant radon activity increase was taking place in L’Aquila at that time with respect to a previous ‘seismically-unperturbed’ year, during the same month with similar meteorological conditions.