Volatile Organic Compounds

VOC is a general term for a class of organic compounds primarily made up of hydrocarbons. Hydrocarbons contain not only carbon, as all organic compounds do, but also, hydrogen. Some examples of VOCs are benzene, formaldehyde, chlorofluorocarbons (CFC's), and methane. Methane, as a pollutant, is becoming more important due to increased concentrations in the Southeastern United States. The major source of methane in that region is livestock. Methane is one of several greenhouse gases. We will discuss the effects of greenhouse gases later in this section. With the exception of methane, the primary sources of VOCs are industry, vehicle emissions, refrigerants, and cleansers. Many VOCs are not primary pollutants and are not harmful in and of themselves. However, many VOCs do react with other chemicals to produce secondary pollutants such as ozone.

The graphic at the left (click on graphic to see full-sized) shows sources of VOCs by total percentage. Notice that a significant percentage of VOC emissions come from mobile sources, that is, cars and trucks. The category labeled "fuel marketing" represents VOC emissions from the transport of fuel products from refineries to delivery points, such as gas stations. Spillage of fuel during transport represents as much as 6% of the total emissions of VOCs!

The graphic at the right shows the density of VOC emissions throughout the United States. Where might you expect to see the highest density levels, given that VOCs are primarily transportation-related? In areas with high population densities, which is what you should see on this particular map.

Graphic from US EPA