The document discusses indoor and outdoor air pollution. It notes that indoor air pollution is usually a greater threat than outdoor pollution, as indoor pollution levels can be up to 70 times higher. Major indoor pollutants in developed countries include tobacco smoke, formaldehyde, radon gas, and fine particles. Unventilated burning of biomass in developing countries for cooking and heating leads to high indoor pollution levels and over 1.6 million deaths per year globally. Reducing indoor pollution requires using low-toxicity building materials, monitoring air quality, and allowing better mixing of indoor and outdoor air.