The major sources of indoor air pollution worldwide include indoor combustion of solid fuels, tobacco smoking, outdoor air pollutants, emissions from construction materials and furnishings, and improper maintenance of ventilation and air conditioning systems. Although some indoor air pollutants, such as environmental tobacco smoke, are of concern globally, profiles of indoor air pollutants and the resulting health risks are generally very different in developed and developing countries. In developing countries, the most significant issue for indoor air quality is pollutants released during the combustion of solid fuels—including biomass (wood, dung and crop residues) and coal (mainly in China)—that are used.
