Fig. 6 shows the concentrations of HCHO, acetaldehyde and TVOCs in air samples. The maximum HCHO
concentration was 10 μg/m3 in classrooms, lower than the limit (100μg/m3) proposed by the national standards for
indoor air quality standard (IAQ) [15]. Acetaldehyde concentration was maximized at 12.5 μg/m3, lower than 48
μg/m3, which was suggested for indoor environments by Ministry of Health, Labor and Welfare, Japan [16]. The
averages of TVOCs were less than 600 μg/m3, the limit proposed by the national standards for IAQ. Both indoor and
outdoor concentrations of HCHO, acetaldehyde and TVOCs were obviously higher in winter. Moreover, all of the
indoor concentrations of HCHO and acetaldehyde were higher than the corresponding outdoor concentration.