Source And Effects

Other indoor pollutants include asbestos, bioaerosols, carbon dioxide and carbon monoxide, formaldehyde, nitrogen oxides, ozone, inhalable particulates, and VOCs.


Asbestos is a silicate mineral fiber that is flexible, durable, and incombustible and makes good electrical and thermal isolators. It has been used as insulation for heating, water, and sewage pipes; sound absorption and fireproofing materials; roof, siding, and floor tiles; corrugated paper; caulking; putty; and spackle. In short, asbestos was used extensively in all types of construction until about 1960. Once released from its binding material (by erosion, vibration, renovation, or cleaning) the fibers can remain airborne for long periods.


Biological contaminants include animal dander, cat saliva, human skin scales, insect excreta, food remnants, bacteria, viruses, mold, mildew, mites, and pollen. The sources of these contaminants include outdoor plants and trees, people, and animals. Pollens are seasonal; fungal spores and molds are prevalent at high temperatures. A central air-handling system can distribute these contaminants throughout a building.

Carbon Dioxide and Carbon Monoxide

Carbon monoxide, a colorless, odorless, toxic gas formed by the incomplete combustion of fossil fuels, is the most prevalent and dangerous indoor pollutant. It results from poorly ventilated kitchens, rooms over garages, and un-vented combustion appliances (stoves, ovens, heaters, and the presence of tobacco smoke).


Formaldehyde, the simplest of aldehydes, is a colorless gas that is emitted from various building materials, household products, or combustion processes. Indoor sources include pressed-wood products, including particle board, paneling, fiberboard, and wallboard; textiles, such as carpet backings, drapes and upholstery fabrics, linens, and clothing; urea-formaldehyde foam insulation; adhesives; paints; coatings; and carpet shampoos.

Minimal outgassing by each product can significantly increase the formaldehyde level when the ventilation rate is low. Hot and humid conditions usually cause formaldehyde to outgas at a greater rate. Product aging diminishes its emission rate although in some cases, this process can take several years.

Nitrogen Oxides

Nitrogen oxides are combustion by-products produced by the burning of natural gas or oil in oxygen-rich environments such as kitchen stoves and ovens, furnaces, and un-vented gas and kerosene heaters. When a fireplace or wood stove is used, some of these pollutants enter the room. Cracks in the stovepipe, downdrafts, or wood spillage from a fireplace can exacerbate the condition. Coal burning adds sulfur dioxide to the nitrogen oxides.


Ozone is recognizable by its strong, pungent odor. Indoors, significant ozone can be produced by electrostatic copying machines, mercury-enhanced light bulbs, and electrostatic air cleaners. Poorly ventilated offices and rooms housing photocopying machines can accumulate significant levels of ozone.

Inhalable Particulates

Particulates are not a single type of pollutant; they describe the physical state of many pollutants—that is, all suspended solid or liquid particles less than a few hundred ¡m in size. Among the pollutants that appear as particu-lates are asbestos and other fibrous building materials, radon progeny, smoke, organic compounds, infectious agents, and heavy metals, such as cadmium in cigarette smoke.

Because of the diversity of particulates and their chemical nature, considering the adverse health effects of this category as a whole is not possible.


VOCs are chemicals that vaporize readily at room temperature. High levels of organic chemicals in homes are attributed to aerosols, cleaners, polishes, varnishes, paints, pressed-wood products, pesticides, and others.

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