There are many sources of indoor air pollution. These can include:
-Fuel-burning combustion appliances
-Tobacco products
– Building materials and furnishings as diverse as:
-Deteriorated asbestos-containing insulation
– Newly installed flooring, upholstery or carpet
– Cabinetry or furniture made of certain pressed wood products
– Products for household cleaning and maintenance, personal care, or hobbies
-Central heating and cooling systems and humidification devices
– Excess moisture
-Outdoor sources such as:
. Radon
. Pesticides
. Outdoor air pollution.
The relative importance of any single source depends on how much of a given pollutant it emits and how hazardous those emissions are. In some cases, factors such as how old the source is and whether it is properly maintained are significant. For example, an improperly adjusted gas stove can emit significantly more carbon monoxide than one that is properly adjusted.
Some sources, such as building materials, furnishings and products like air fresheners, can release pollutants more or less continuously. Other sources, related to activities like smoking, cleaning, redecorating or doing hobbies release pollutants intermittently. Unvented or malfunctioning appliances or improperly used products can release higher and sometimes dangerous levels of pollutants indoors.
Pollutant concentrations can remain in the air for long periods after some activities.