Population exposure to radon gas during a volcanic eruption: A case study of the Tajogaite volcano on the Island of La Palma, Canary Islands

Radon is a significant contributor to natural ionizing radiation and a relevant public health concern, particularly in volcanic environments. This study assesses the impact of the Tajogaite eruption on La Palma (Canary Islands), on indoor radon concentrations and associated radiation doses. A dosimetry survey was conducted using passive detectors and continuous radon monitoring, focusing on areas near the eruption center. Results show elevated radon concentrations near the volcano, decreasing exponentially with distance. However, the estimated dose in the most affected region was 0.3 mSv during the three-month eruption, well below critical health thresholds, indicating no significant public health risk to the exposed population. Temporal variations in radon were modulated by volcanic degassing and meteorological dynamics, including low wind speeds, directional shifts and height of the thermal inversion, which promoted near-surface gas accumulation. Principal Component Analysis and spectral coherence analyses confirmed the dual influence of subsurface and atmospheric processes, behaving differently during and after the eruption. Multifractal analysis of continuous radon recorded in the nearest monitoring station revealed a complex temporal behavior near the volcano, with long-range correlations and persistent behavior. Conversely, more distant monitoring stations exhibited lower complexity and stronger coupling with atmospheric variables. The estimated mean daily radon emission from the Tajogaite eruption (≈3.0 ± 1.4·107 Bq·m -2 ·day -1 ) was about 160 times higher than that reported for the quiescent Furnas volcano, and up to six orders of magnitude greater than radon emissions from natural soils worldwide. These findings highlight the importance of incorporating radon monitoring programs into volcanic hazard assessments.