Seasonal variations of radon concentration in soil air in different geological conditions on the example of Estonia

Abstract

Radon risk in Estonia is among the highest in Europe, influencing human health in many areas. The measured radon level in soil air differs considerably between spring– summer and autumn–winter periods at the same measuring point. Such variations are an obvious obstacle in interpreting reliably the radon risk level in the soil. To tackle with this problem, a monitoring system was established. Radon (²²²Rn) concentrations in soil air were investigated in four geologically different sites at three depths during three years every 26–40 days. The results showed that at every site the concentration of radon in soil air depended on the eU (²³⁸U) concentration in Quaternary deposits and underlying bedrock, on rock types, as well as on aeration circumstances during measuring, such as temperature, topsoil aeration, precipitation and air pressure. The measured radon level concentration starts to increase in autumn when the topsoil turns wet, air humidity increases and ground begins to freeze. It reached the maximum in late winter, when the ground is most frozen. The radon concentration is at its lowest during the warm and dry summer period when topsoil aeration and radon permeability are at their maximum.