Indoor carbon dioxide (CO2) level varied in the range from 500 ppm to 11231 ppm
during school time. Formaldehyde (HCHO) and total volatile organic compounds (TVOCs) concentrations were low and at
acceptable levels, but indoor PM1.0, PM2.5 and PM10 levels were the same as outdoor, up to 325 μg/m3 332 μg/m3 and 411 μg/m3
in autumn, and 899 μg/m3 927 μg/m3 and 1090 μg/m3 in winter, respectively.