Many substances found in the workplace may also occur in the home as a result of hobby or craft activities. For example, paint strippers contain methylene chloride, cleaning solvents comprise a mixture of aliphatic hydrocarbons and certain glues can release toluene. Exposure to metal fumes may result from welding, soldering and metal working operations. Human metabolic activity itself influences air quality by reducing the concentration of oxygen and increasing levels of carbon dioxide. Respiration, perspiration and food preparation add water vapour as well as odour-producing substances to the indoor environment.
Smoking is a major source of indoor air pollutants.
While smokers subject themselves to mainstream smoke, bystanders can be involuntarily exposed to significant amounts of respirable particles, carbon monoxide and oxides of nitrogen in side stream smoke. Other potentially harmful contaminants in side stream smoke include PAHs, phenols, nicotine, nitrosamines and aldehydes. More than 3,000 constituents have been identified in cigarette smoke, of which about 150 are biologically active. Typically, oven and pilot light emissions are not vented and can contribute significantly to indoor levels of carbon monoxide, nitrogen oxides and formaldehyde. Of emerging interest as a potential source of indoor air pollution is the wood burning stove.