Table 1.

The detailed reference range of indoor air quality indices of this study.

Air quality indices	Acceptable range	Tolerable range	Poor quality range
Carbon dioxide	400–800 ppm	800–1500 ppm	>1500 ppm
Volatile organic compounds	0–400 ppb	400–800 ppb	>800 ppb
Particulate matter	<50 mg/m3	50–100 mg/m3	>100 mg/m3
Nitrogen dioxide	<100 ppb	100–250 ppb	>250 ppb