Carbon monoxide (CO)
Nitrogen dioxide (NO2)
Secondhand tobacco smoke
Volatile organic compounds (VOCs)
Potential sources of indoor air pollution
Indoor air levels of many pollutants may be 2-5 times, and occasionally, more than 100 times higher than outdoor levels. Indoor air pollutants are of particular concern because most people spend as much as 90% of their time indoors.
Common sources can include burning kerosene, wood or oil, smoking tobacco products, releases from household cleaners, pesticides, building materials, and radon.