Monitoring radon concentration in roman catacombs: a long-term analysis across different geological settings

Radon concentration monitoring was conducted in three Roman catacombs characterized by distinct geological settings, motivated by the anticipated high radon levels in indoor underground spaces-some of them carved into volcanic deposits-and the associated potential health risks for workers and visitors. The study was also inspired by the interest in an environment that is generally difficult to access and consequently little studied. Radon studies in catacombs existing in literature primarily focus on average radon levels; in this study, active monitoring instruments were employed to analyze radon concentrations both spatially and temporally across multiple time scales, enabling the detection of the gas's full dynamics, including diurnal and seasonal variations as well as long-term trends. The extreme conditions of the catacombs, including high humidity, and elevated radon levels, posed significant challenges for accurate and continuous measurements. A considerable part of our work was devoted to finding the optimal configuration and installation of the instruments to mitigate environmental interference and operational issues and to ensure the recording of long and reliable time series of radon concentration. The results revealed notable differences in radon levels across the three catacombs, with clear correlations to the geological characteristics of each site. Temporal analyses indicated significant seasonal patterns, likely driven by temperature changes between summer and winter periods. Short-term fluctuations were also observed at some sites, providing insights into the dynamic behavior of radon influenced by environmental conditions. The study expands our understanding of radon dynamics in catacombs, with practical implications for the protection of individuals who frequently access such sites and for the development of effective radon mitigation strategies in underground cultural heritage environments. In addition, it highlights the importance of devising proper methodological adjustments when monitoring radon in such unique underground environments.