Indoor environment is one of the most frequent and intimate external environments. People spend most of their lives indoors, and indoor air quality is directly related to everyone's health. Breathing natural and fresh air can promote blood circulation, enhance immunity, improve myocardial nutrition, eliminate fatigue, improve the function of human nervous system and improve work efficiency. On the contrary, poor indoor air quality may lead to a series of health problems, including respiratory diseases, allergic reactions and mental health.