Carbon monoxide, from motor vehicle exhausts. All these compounds, as well as others form air pollution and smog. If you live in an area that gives alerts for high levels of smog, take heed and stay indoors during times with high pollution levels. As homes and offices become more energy efficient, the indoor air quality often suffers. See the section on occupational asthma for more information.
Tobacco smoke is the most common and deadly source of indoor air pollution.
People with asthma need to live in a smoke-free environment. Their lungs are already challenged by other substances and conditions. Once inhaled, even as second-hand smoke, carbon monoxide competes with oxygen in the blood. It can also cause the lungs to collapse. Tobacco smoke contains a multitude of poisons.