Because people spend most of their time indoors, it is useful to examine the composition and quality of indoor air. Because people's time is often divided between home and work, it is important to examine air quality in both residences and workplaces. Sources of indoor air pollution include outdoor air and indoor emissions. Outdoor air contains the constituents of smog, but some of these constituents dissipate quickly indoors because of the lack of ultraviolet (UV) radiation to reproduce them indoors. Major indoor sources of pollution include stoves, heaters, carpets, fireplaces, tobacco smoke, motor vehicle exhaust from garages, building materials, and insulation. Whereas indoor air pollution in the United States is regulated in workplaces, it is not regulated in residences. In this chapter, characteristics, sources, and regulation of indoor air pollution are discussed.

POLLUTANTS IN INDOOR AIR AND THEIR SOURCES

In the United States, about 89 percent of people's time is spent indoors, 6 percent is spent in vehicles, and 5 percent is spent outdoors (Robinson et al., 1991). Another study found that in nonindustrialized countries, people in urban areas spend 79 percent of their time indoors and those in rural areas spend 65 percent of their time indoors (Smith, 1993). Because people breathe indoor air more than outdoor air, an examination of indoor air is warranted.

Table 9.1 identifies major pollutants in indoor air and their primary sources. Many of the pollutant gases in indoor air are also found in outdoor air.