Combustion generates H2O, NO, NO2, CO, CO2 and patriculate. Combustion can also emit hydrocarbon gases, vapors, and organic particles. Impurities such as metals, mercaptans, sulfur oxides, and other particles can be emitted. Many of the particles are large and settle out, but submicron particles remain suspended in the air for long periods of time.
Burning of gas heaters produces NO2 and CO which must be vented to the outdoors. Space heaters emit particles, CO, NO2, and sometimes SO2. Gas stoves emit particles as well as gases. Wood and coal stoves emit particles when the stove is open for loading. Fireplaces emit particles constantly.
Internal combustion engines can be a source of indoor air pollution in offices, schools, hospitals, hotels, shopping centers and stores where garages are attached. The use of automobiles has certainly increased the levels of gas phase and particulate matter in the outdoor air invironment.