Indoor air pollution

Definition: Contamination of the air contained within buildings

Pollutants in indoor air are believed to cause thousands of deaths each year—mainly from lung cancer caused by radon and carbon monoxide poisoning—as well as a considerable amount of illness and discomfort.

Because most people in developed nations spend more time indoors than outdoors, the air quality in homes, offices, stores, and other buildings can have a greater effect on human health than the quality of outdoor air. The term “sick building syndrome” is used when a majority of a building’s occupants experience health and comfort problems caused by a variety of indoor pollutants that are difficult to identify.

Outdoor air is one source of indoor air pollution, because the ventilation systems in buildings bring in air from the outside. Fortunately, some pollutants are trapped as they enter buildings; particulate matter, for example, may stick to walls and pass no further than entryways.

Carbon Monoxide and Carbon Dioxide

Far more important to indoor air are activities that occur inside buildings. One significant contributor to indoor air pollution is combustion; such pollution may come from appliances or from tobacco-smoking building occupants. An unvented or improperly vented furnace or water heater or a cracked heat exchanger in a furnace may allow combustion products such as carbon monoxide to enter the indoor space. Carbon monoxide, which can also enter buildings from garages in which motor vehicle engines are running and result in carbon monoxide poisoning, causes hundreds of accidental deaths annually in the United States and produces a large amount of often-unrecognized illness. Tobacco smoke is known to be harmful not only to smokers but also to nonsmokers exposed to a significant amount of secondhand smoke; tobacco smoke is also a major source of annoyance and discomfort to most people.

Carbon dioxide, normally regarded as nontoxic, causes nausea and headaches at elevated levels and should not exceed 5,000 parts per million (ppm). Even at 1,000 ppm, however, a buildup of carbon dioxide will make a room seem stuffy. Unvented gas or kerosene space heaters should never be used indoors because they necessarily lead to high carbon dioxide levels and often produce high levels of carbon monoxide, nitrogen oxide, and sulfur oxide (the last of these is a particularly severe problem with kerosene heaters, because kerosene contains sulfur).

Building Materials and Volatile Compounds

Building materials can also contribute to indoor air pollution. Asbestos, a known cause of lung cancer and asbestosis , may be present in indoor air if insulation or other materials containing asbestos have broken down; exposure to these materials can be especially dangerous when the materials are being removed or otherwise disturbed, such as during building renovation. Formaldehyde, a major component of urea-formaldehyde foam insulation, particle board, and some packaging materials, can produce acute eye, nose, and throat irritation at levels below 1 ppm. Formaldehyde is mainly a concern during the first few years after building construction or renovation, after which it eventually disappears.

A variety of other volatile organic compounds may contribute to poor indoor air quality. These include acetone and other ketones, alcohols, aromatic hydrocarbons (such as benzene and toluene), and halogenated hydrocarbons (such as methylene chloride) found in adhesives, household cleaners, enamels, glues, paints, solvents, and varnishes. Indoor hobbies or renovations involving such compounds should be undertaken only in areas that are well ventilated.

Microorganisms such as bacteria, fungi, molds, and viruses can be dangerous in buildings that are not kept clean. They appear to be most troublesome in buildings with low relative humidity, but some thrive in moist areas. The organism responsible for Legionnaires’ disease has been found to be capable of growing in improperly maintained cooling and ventilation systems.

Ventilation

The ventilation rate of a building plays an important role in its indoor air quality. The concentration of air pollutants can rise at a rapid rate in a poorly ventilated building because the pollutants generated inside the building are not being removed quickly enough. This problem has been aggravated since the energy crisis of the 1970s by the practice of making buildings airtight in order to reduce energy costs associated with the heating or cooling of outdoor air that has entered a building. It is possible for a building to be ventilated well and yet have low energy costs if an air-to-air heat exchanger is used; this device allows the incoming and outgoing airstreams to pass near each other across a thin conducting barrier, so that a large fraction of the heat from the outgoing air in winter is transferred to the incoming air. On the other hand, a building in which there is little indoor generation of air pollutants can be airtight and still have superior air quality; increasing the ventilation rate in such a building may actually decrease indoor air quality by bringing in outdoor pollution.

Radon levels are particularly and subtly dependent on the way a building is ventilated. Radon is normally present in underground air in concentrations sufficient to cause concern if even a small percentage of the air in the building comes from underground; the ventilation of the lower level of a building may actually increase this percentage.

Bibliography

Burroughs, H. E., and Shirley Hansen. Managing Indoor Air Quality. 3d ed. Lilburn, Ga.: Fairmont Press, 2004. Print.

Godish, Thad. Indoor Environmental Quality. Boca Raton, Fla.: CRC Press, 2001. Print.

Hines, Anthony L., et al. Indoor Air: Quality and Control. Englewood Cliffs, N.J.: Prentice Hall, 1993. nPrint.

Moffat, Donald W. Handbook of Indoor Air Quality Management. Englewood Cliffs, N.J.: Prentice Hall, 1997. Print.

Vallero, Daniel. “Indoor Air Quality.” In Fundamentals of Air Pollution. 4th ed. Boston: Elsevier, 2008. Print.