Active Monitoring of Residential Radon in Rome: A Pilot Study.

We present an overview of the potential of active monitoring techniques to investigate the many factors affecting the concentration of radon in houses. We conducted two experiments measuring radon concentration in 25 apartments in Rome and suburban areas for two weeks and in three apartments in the historic center for several months. The reference levels of 300 and 100 Bq/m3 are overcome in 17% and 60% of the cases, respectively, and these percentages rise to 20% and 76% for average overnight radon (more relevant for residents' exposure). Active detectors allowed us to identify seasonal radon fluctuations, dependent on indoor-to-outdoor temperature, and how radon travels from the ground to upper floors. High levels of radon are not limited to the lowest floors when the use of heating and ventilation produces massive convection of air. Lifestyle habits also reflect in the different values of gas concentration measured on different floors of the same building or in distinct rooms of the same apartment, which cannot be ascribed to the characteristics of the premises. However, the finding that high residential radon levels tend to concentrate in the historic center proves the influence of factors such as building age, construction materials, and geogenic radon.

Multi-level continuous monitoring of indoor radon activity.

We present the results of an experiment taking place inside the geophysical museum of Rocca di Papa (Rome, Italy), where the high radon levels detected might pose a risk to the health of workers and of the public audience. As a first step towards the mitigation of potential exposure risk, four active sensors were installed at different floors of the building, in order to continuously monitor not only radon exhalation from the soil but also its transport from the ground up to elevated floors. Collecting more than three years of data of radon concentration enables us to identify fluctuations over both short and seasonal scales and to elucidate the relation between radon variations and changes of internal temperature and relative humidity. The analysis of such dataset reveals how the healthiness of indoor environments in terms of radon concentration is controlled by a number of factors, including the environmental conditions and the use of heating and ventilation systems. Finally, the continuous radon monitoring at different levels of the building provides a unique chance to trace the vertical radon diffusion, allowing to make a first-order estimate of upward radon velocity.

Monitoring soil radon during the 2016-2017 central Italy sequence in light of seismicity.

The radioactive nature of radon makes it a powerful tracer for fluid movements in the crust, and a potentially effective marker to study processes connected with earthquakes preparatory phase. To explore the feasibility of using soil radon variations as earthquakes precursor, we analyse the radon concentration data recorded by two stations located close to the epicentre of the strongest mainshock (Mw 6.5 on October 30, 2016) of the seismic sequence which affected central Italy from August 2016. The two stations CTTR and NRCA operate in the framework of the permanent Italian Radon monitoring Network and recorded almost continuously since 2012 and 2016, respectively, the latter being installed just after the first mainshock of the sequence (Mw 6.0 on August 24, 2016). An increase of radon emanation is clearly visible about 2 weeks before the Mw 6.5 event on both the time series, more pronounced on NRCA, nearer to the epicentre, suggesting the possibility of a direct association with the earthquake occurrence. An independently developed detection algorithm aimed at highlighting the connections between radon emission variations and major earthquakes occurrence succeeds in forecasting the Mw 6.5 mainshock on NRCA time series. The resulting time advance of the alarm is consistent with that obtained using a Bayesian approach to compute the a posteriori probability of multiple change points on the radon time series of NRCA. Moreover, it is in agreement with the delay time which maximizes the correlation between radon and seismic anomalies. Applying the detection algorithm to CTTR time series returns alarms for both the Mw 6.0 event, with epicentre closer to this station, and the stronger Mw 6.5 event, but with a higher number of false detections. Finally, we found that a preliminary correction of the bias introduced by variations of meteorological parameters does not affect our main finding of an increase in radon concentration before the major mainshocks. Our study confirms that, although much work is still needed, a monitoring approach based on a permanent dense network is crucial for making radon time series analysis an effective complement to traditional seismological tools.

Implementing soil radon detectors for long term continuous monitoring.

The employment of different instruments for radon continuous measurements within the Italian Radon mOnitoring Network (IRON), mostly INGV, Algade AER and Airthings Corentium instruments, requires a uniform characterization and calibration protocol for the results to be comparable in a rigorous way. A 56 L stainless steel radon chamber with a sensitivity of 0.95 ±â€¯0.01 Bq m-3 per pulse h-1 has been used and validation of Algade AER, Airthings Corentium and Durridge RAD7 radon monitors equipped with solid-state detectors operated at different absolute humidity values has been performed, extending their operative range. Robustness to atmospheric electromagnetic phenomena of INGV and Algade AER instruments has been investigated and, for the former instrument, improved.

Multiple seasonality in soil radon time series.

The dynamics governing the movement of the radon are complex and dependent on many factors. In the present study, we characterise the nature of temporal variations of 2-hourly and daily radon measurements in several monitoring sites of the Italian Radon mOnitoring Network (IRON) in Italy. By means of continuous wavelet transformation, a spectral analysis in time-frequency domain is performed. The results reveal that there are sub-daily, daily and yearly persistent periodicities that are common for all the stations. We observe structural seasonal breaks, that occur at the same frequency but at distinct time. Variations in radon concentration and local temperature are studied in terms of frequency contents and synchronicity. When analysing several long time series together, it is evident that the phase difference at low frequency movements (365-day period) between the radon and local temperature time series is depending on the sites' location and therefore strongly controlled by local factors. This could at least partially explain the apparently contrasting results available in the literature obtained investigating smaller dataset about the relationships between temperature and radon variations. On the other hand, results show that all radon time series are characterised by marked cycles at 1 and 365-days and less evident cycles at 0.5-day and 180-days. They would be all ascribable to environmental-climatic factors: the short-period cycles to temperature and pressure variations, the long-period cycles also to seasonal rainfall variations.