Study on the influence of sampling methods for measuring soil radon exhalation rates

Soil is the primary source of radon in the atmosphere, and soil radon exhalation rate (E) is a key indicator to evaluate the radon hazard in soil. Radon can also be used as a tracer to analyze atmospheric processes and monitor greenhouse gas emissions. Therefore, improving the accuracy of measuring E is significant for radon protection and radon pollution management as well as public health. In this study, three different sampling methods were compared to determine the most suitable sampling method for E measurement under different conditions. The results indicated that the closed-loop gas-flow method can be used to measure E and required correction for leakage and counterdiffusion; E was found to vary from 13.25 ± 1.44 to 30.46 ± 2.19 mBq·m−2 s−1. For the open-loop gas-flow method, a low sampling flow rate was selected, and the sampling flow rate derived from this experiment was less than 0.2 l min−1; E varied from 36.11 ± 0.99 to 52.67 ± 1.68 mBq·m−2 s−1. For the activated-carbon adsorption method, the counterdiffusion effect had a negligible influence on the measurement results, and the measurement error due to the uneven distribution of radon in the carbon layer could be eliminated by changing the waiting time for the measurement; the measurement showed E of about 23 mBq·m−2 s−1. Moreover, the influence of water absorption of the activated carbon on the measurement results should be considered, and the water absorption rate should be less than 9%. The obtained values will serve as a reference for the rapid and accurate measurement of E.