Volatile Organic Compounds: Definitions Matter

The term "volatile organic compound" (VOC) means different things to different people. In high school or college chemistry class we learned that VOCs are a class of carbon-based compounds that readily become volatile (gaseous) under ordinary (atmospheric) conditions. Thus, we learned that VOCs are any of those carbon-based compounds that smell strong and readily evaporate—stuff like acetone, rubbing alcohol, and propane.

As used by ambient air quality regulators, the term VOC has a quite different definition. According to the U.S. Environmental Protection Agency (EPA) and other regulatory bodies, VOCs are organic compounds that readily volatilize under atmospheric conditions and that react in sunlight to generate smog. Thus, from a regulator’s standpoint, compounds are VOCs only if they contribute to certain type of outdoor air pollution.