Factors influencing radon transport in the soils of Moscow

This article delves into the factors that may influence radon flux, such as soil properties and weather conditions, on the example of two experimental locations with different soil compositions, composed primarily of clay and sand, respectively. The experimental location with sandy soil was previously observed to have anomalously high radon flux levels. Radon monitoring was performed routinely, approximately at the same time of day and in parallel on both of these locations to exclude the influence of diurnal variations. The results show that radon transport in these locations differs in mechanism: Location with clay soil has diffusive radon transport, with an average radon flux density of 37.4 ± 24.9 mBq m^-2 s^-1 and a range of 0.3-167.8 mBq m^-2 s^-1, while the location with sandy soil has convective radon transport with an average radon flux density of 93.6 ± 51.2 mBq m^-2 s^-1 and a range of 9.8-302.2 mBq m^-2 s^-1. This corresponds to about 8.3% of RFD measurements on site with clay soils exceeding the national reference level of 80 mBq m^-2 s^-1 and 45.6% exceeding them on the site with sandy soils. Average radon flux density values were then compared to meteorological variables using Pearson correlation analysis with Student's t-test. It was observed that radon flux density correlates the most with ambient air temperature both for diffusive and convective radon transport mechanisms, while a weaker inverse correlation is observed with atmospheric precipitation and wind speed for the diffusive mode of radon transport, but not for the convective. Radon activity concentration in soil air correlates with the radon flux density and air temperature in the case of convective radon transport, but does not correlate in the case of diffusive transport.