Monitoring CO₂ concentration to control the infection probability due to airborne transmission in naturally ventilated university classrooms

Due to the increasing amount of time that people are spending indoors, the need to ensure adequate ventilation has become a priority. The confirmed airborne transmission of COVID-19 highlights the necessity to consider the effect of ventilation on the reduction of the infection risk. In naturally ventilated buildings, the ventilation rate is not easy to determine, and it is difficult to estimate the risk to implement preventive measures. This paper presents a method to estimate the infection probability from CO2 concentration monitoring, which was applied to university classrooms. The effects of people’s activity, classroom characteristics, occupancy and protective masks were also investigated. From the method, it is possible to calculate the infection probability using CO2 dataloggers that can be adopted as ‘alarm’ systems to keep the infection probability below a critical value. The method will enhance healthy conditions indoors and reduce the risk of infectious diseases in the future.