In the field of IAQ research, the term "volatile organic compound" or "VOC" refers to any of dozens or even hundreds of carbon-containing chemicals that are gases at room temperature. Inorganic carbon-containing gases such as carbon dioxide and carbon monoxide are excluded from this definition. The specific VOCs that can be detected in indoor air vary depending on the methods used for measurements.
Semi-volatile organic compounds or SVOCs are VOCs that are present indoors partly as gaseous airborne chemicals and partly as chemicals adsorbed on indoor surfaces and onto microscopic airborne and settled particles. SVOCs tend to have a higher molecular weight and higher boiling point temperature than other VOCs.
Because of the complexity and high cost of measuring airborne concentrations of large numbers of individual VOCs, researchers have often employed measurement methods that indicate the total concentration of a broad range of indoor airborne VOCs. The term "total volatile organic compound" or "TVOC" concentration refers to the resulting concentration of multiple airborne VOCs; however, different measurement methods can result in obtaining substantially different TVOC concentrations for identical VOC mixtures.
A large number of VOCs are emitted into indoor air from building materials, furnishings, cleaning compounds, office equipment, personal care products, air fresheners, pesticides, people, and unvented combustion processes such as tobacco smoking or cooking with gas stoves [1-4]. Some of these same sources emit SVOCs. VOCs are also produced indoors from chemical reactions of indoor ozone with other VOCs, SVOCs, or materials (such as carpeting) . Outdoor air is normally the major source of the indoor ozone, although ozone generators (marketed as air cleaners), electronic air cleaners (that unintentionally produce ozone as a by-product), and some types of office equipment can be additional sources of ozone. VOCs also enter buildings with outdoor air; however, for many types of VOCs and SVOCs, indoor air concentrations far exceed outdoor air concentrations [1, 2].
Some VOCs and SVOCs are odorous and some are suspected causes of adverse health effects. The suspected health effects cover a broad range including, but not limited to, sensory irritation symptoms, allergies and asthma, neurological and liver toxicity, and cancer. The following text briefly summarizes the current knowledge about the linkages of indoor VOCs with sensory irritation, allergic and asthmatic effects, and cancer.