Indoor radon concentration measurements in dwellings of Riobamba Canton, Central Andes of Ecuador

This study aimed to evaluate indoor radon concentrations in Riobamba canton, Ecuador's central Andean region, and to analyze two factors influencing their variability: surface geology and the age of the dwelling. Radon measurements were conducted in 225 homes using passive monitoring systems, while continuous laboratory monitoring with a Lucas Pylon cell was employed to assess temporal patterns. Concentrations ranged from 9.4 to 152.8 Bq/m3, with an arithmetic mean of 49.5 ± 26.6 Bq/m3. Ninety-four percent of the homes had radon concentrations below the World Health Organization's recommended reference level of 100 Bq/m3. The calculated average annual effective dose was 1.3 ± 0.7 mSv/year, well below the International Commission on Radiological Protection action level of 10 mSv/year. A statistically significant association was identified between radon levels and the age of the homes; however, no relationship was found between radon levels and the surface geology beneath the buildings. The highest concentrations were observed in houses built before 1925 using traditional techniques such as bahareque, adobe and cancagua. Seasonal analysis revealed minimal variability throughout the year (dry season mean/rainy season mean = 1.04), a result that differs from the well-documented behavior in regions with marked seasonal variability and suggests that seasonal correction factors are not necessary. In addition, a diurnal pattern was evident, which was inversely correlated with indoor temperature and directly correlated with relative humidity. These findings enhance the understanding of radon behavior in the tropical Andean climates characterized by low seasonal variability.