Why is smoking one of the main sources of pollution in the living room?

Smoking is harmful to human health, but the number of smokers is increasing. The U.S. Environmental Protection Agency (EPA) lists cigarette smoke as a "Class A carcinogen to people". Since 1989, the World Health Organization (WHO) has designated May 3 1 day as the World No Tobacco Day, and in 20001year, the slogan was "Clean the air, reject second-hand smoke", which widely publicized the harm of smoking to human body. In fact, smoking is not only harmful to yourself, but also harmful to people around smokers. According to each cigarette a smoker smokes, it can be divided into three steps: inhalation, stopping and breathing. When inhaling, all cigarette smoke is inhaled into the human body, which is called mainstream smoke. When smoking stops, the smoke burns by itself, and the smoke emitted into the air is called sidestream smoke; When exhaling, smokers exhale a part of mainstream smoke, which enters the air environment and forms second-hand smoke together with sidestream smoke, making non-smokers smoke passively. Indoor environmental pollution caused by smoking has aroused widespread concern.