2.1. Monitoring of air temperature, RH and carbon dioxide (CO2) concentrations
The data loggers with temperature and humidity sensors (T&D TR-71Ui&TR-72Ui; ESPEC Thermal Recorder
RS-11) were used to monitor air temperature and RH at an interval of 10 min for 2 weeks. In each classroom, the
data loggers were placed at three positions: 0.1 m (H0.1 m) and 1.1 m (H1.1 m) in the front of classrooms, and
outdoors in the corridor. CO2 concentration was monitored at an interval of 5 min for 2 weeks with the data logger
(Lutron MCH-383SD) placed on the ground at the corner, to avoid the direct influence of people's exhalation.
Outdoor CO2 concentration was left out because it normally varied at relatively small levels that cannot lead to the
high indoor CO2 levels of concern.