Introduction to Volatile Organic Compounds

Volatile Organic Compounds (or Hydrocarbons) are composed primarily of hydrogen and carbon. Within the category of VOC, there are several select groups. Methane (CH₄), is the most abundent VOC in the atmosphere, other compounds can be classified as NMHC's (Non-methane hydrocarbons). Some of the major VOC that we will study include methane, formaldehyde, PAN (peroxyacyl nitrate), alkanes, alkenes, and aldehydes.

Sources of VOC

VOC can arise from a number of different sources, some of them natural, some of them anthropogenic. The following chart shows major anthropogenic sources of VOC:

Natural sources of VOC include vegetation in wooded and agricultural areas,as well as emissions from wetlands, and animal wastes. The biogenic VOC that is emitted the most is isoprene (C₅H₈), which is emitted from deciduous plants in the presence of photosynthetically active radiation. To see a movable model of isoprene, make sure you have chemchime on your plug-ins(if you don't, go to MDL to download it), then go to the isoprene model! Isoprene emissions are especially large in the southeast, and contribute to growing problems with VOC and Ozone. Biogenic VOC emissions vary from region to region, with the highest emissions coming from the tropics, and isoprene composing the largest percentage of these emissions. The following chart shows global emissions of biogenic VOC, in Tg/yr:

Chart adapted from Seinfeld et. al

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