Development of a "²²²Rn incremented method" for the rapid determination of air exchange rate using soil gas

The air exchange rate (AER) is a critical parameter that governs the levels of exposure to indoor pollutants impacting occupants' health. It has been recognized as a crucial metric in spreading COVID-19 disease through airborne routes in shared indoor spaces. Assessing the AER in various human habitations is essential to combat such detrimental exposures. In this context, the development of techniques for the rapid determination of the AER has assumed importance. AER is generally determined using CO₂ concentration decay data or other trace gas injection methods. We have developed a new method, referred to as the "²²²Rn incremented method", in which ²²²Rn from naturally available soil gas was injected into the workplace for a short duration (∼30 min), homogenized and the profile of decrease of ²²²Rn concentration was monitored for about 2 h to evaluate AER. The method was validated against the established ²²²Rn time-series method. After ascertaining the suitability of the method, several experiments were performed to measure the AER under different indoor conditions. The AER values, thus determined, varied in a wide range of 0.36-4.8 h^-1 depending upon the ventilation rate. The potential advantages of the technique developed in this study over conventional methods are discussed.