Final answer:
The EPA describes tobacco smoke as a hazardous air pollutant, which is known to contain toxic substances that cause serious health risks including cancer, particularly in indoor environments.
Step-by-step explanation:
The Environmental Protection Agency (EPA) describes tobacco smoke as a hazardous air pollutant. Tobacco smoke, also known as secondhand smoke or environmental tobacco smoke (ETS), is a mixture of the smoke from the burning of tobacco products such as cigarettes, cigars, or pipes, and the smoke exhaled by smokers. This smoke contains over 7,000 substances, many of which are toxic and can cause cancer and other serious health effects. Secondhand smoke is especially concerning indoors, where it can linger and easily move between rooms and living units. The EPA has classified it as a Group A carcinogen, indicating it is known to cause cancer in humans. There is no safe level of exposure to secondhand smoke, and even non-smokers can experience a significant increase in the risk of lung cancer and heart disease when exposed.