Evaluation on different sampling schemes for assessing indoor radon level in Hong Kong

In order to maintain an acceptable indoor air quality (IAQ), policies, strategies and guidelines on achieving the required IAQ have been developed worldwide. In Hong Kong, the Environmental Protection Department (HKEPD) has launched an IAQ certification scheme to promote an acceptable IAQ in workplaces. For the practical radon measurement, an 8-h continuous monitoring is proposed for the assessment purpose. However, the uncertainties and measurement efforts associated with the method have not been detailed. In this study, the probable errors and measurement efforts in measuring the indoor radon concentration by three proposed sampling schemes of various sampling periods have been investigated. Scheme A is to obtain an average concentration over a sampling period in an occupied period; Scheme B is to obtain an average concentration in two sampling periods from two sessions of the occupied period; and for Scheme C, the average concentration in two structural sampling periods from two sessions of the occupied period. In particular, a 1-year measurement of indoor radon concentration in a typical office building has been used as basis to evaluate the probable errors between the long-term average and those obtained by the three measurement schemes. At a certain confidence level, the results show that the measurement time required for Schemes B and C could be reduced significantly, when compared with Scheme A using continuous monitoring. It is recommended to specify the measurement uncertainty and effort in future codes, and the sampling schemes could be considered in determining the practical strategies for radon measurement.