Different models for calculation of ²²²Rn flux and validation with experimental data in Bratislava, Slovakia

Radon exhalation rate (ERR) represents a key link between subsurface radon sources, soil processes, and atmospheric transport, with relevance for environmental tracing, radiation protection, and greenhouse gas flux estimation. Its temporal variability is mainly controlled by soil moisture and temperature through the effective diffusion coefficient (D_ef,Rn). In this study, six commonly used D_ef,Rn parameterisations (D1 - D6) and three theoretical ERR formulas (E1, E2, E4) were combined into 18 EiDj models and evaluated against continuous four-year field measurements (October 2020 - June 2024) obtained with an automated accumulation chamber in sandy-silt soil in Bratislava, Slovakia. All D_ef,Rn parameterisations showed almost identical temporal behaviour and differed mainly by a constant magnitude shift, with D1 and D5 providing the most realistic values under local soil conditions. Using a combination of statistical performance measures and agreement analyses, three EiDj formulas: E1D1, E4D1 and E4D5 were consistently identified as the most reliable in reproducing both the magnitude and temporal evolution of measured ERR. All three combinations successfully captured the characteristic annual ERR cycle as well. These findings demonstrate the importance of moisture-dependent D_ef,Rn parameterisations and highlight the strong predictive capability of combined theoretical and semi-empirical approaches for estimating radon exhalation under real environmental conditions, validated against comprehensive multi-year field observations.