Observations and box-model analysis of Radon-222 in the atmospheric surface layer at L’Aquila, Italy: March 2009 case study

Two years of Radon-222 observations collected at L’Aquila (Italy) in the atmospheric surface layer during 2004-2006 have been analysed in correlation with meteorological data and other atmospheric tracers. 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, with a 0.8 average correlation coefficient between hourly values for the whole period of radon observations. Measurements taken during March 2009 have been analysed 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. Contrary to professed (and unpublished) dramatic increases of radon activity unofficially announced to the inhabitants at that time, the study presented here shows that no radon activity increase was taking place in L’Aquila with respect to a previous ‘seismically-unperturbed’ year (same month with similar meteorological conditions), but also experienced an average 30% decrease. This conclusion is reached from a direct comparison of observed data, but also as a result of the previously validated radon box model constrained by actual meteorological data, where an indirect estimate of a 17% reduction of the radon soil flux is obtained from.