A3.2.5 Volatile Organic Compounds


Volatile Organic Compounds (abbreviated to VOCs, this is not a chemical formula. The Volatile refers to the fact they readily evaporate) are a pollutant category. VOCs include a wide range of individual substances, including hydrocarbons, halocarbons and oxygenates.

  • Hydrocarbons are emitted from petrol evaporation, incomplete combustion and from leakage of natural gas from distribution systems.
  • Oxygenates arise in vehicle exhausts and via atmospheric chemical reactions.
  • Halocarbons may be released through the evaporation of solvents used in paints or industrial degreasing processes.


All are organic compounds and of sufficient volatility to exist as vapour in the atmosphere.


Chlorofluorocarbons are commonly referred to as CFCs (again this is an abbreviation, not a chemical formula). CFCs contain fluorine atoms, carbon atoms and chlorine atoms. They are non-toxic, non-flammable and non-carcinogenic.

Man-made CFCs however, are the main cause of stratospheric ozone depletion. CFCs have a lifetime in the atmosphere of about 20 to 100 years. CFCs are used as coolants in refrigeration and air conditioners, as solvents in cleaners (particularly for electronic circuit boards), as a blowing agents in the production of foam (for example fire extinguishers) and as propellants in aerosols.


Methane (CH4) is an important component of VOCs. Its environmental impact is principally related to its contribution to global warming and to the production of ozone in the troposphere (the first 10km of the atmosphere).

Non-Methane VOCs

This generic term includes substances such as benzene, toluene and xylene. These are suspected carcinogens and may lead to leukaemia through prolonged exposure.


Benzene (C6H6) is a colourless, clear liquid. It is reasonably stable but highly volatile. The vast majority of man-made emissions are from petrol-fuelled vehicles. This results from both the benzene content of the fuel and partial combustion of the petrol. Smaller sources include oil refining, the burning of wood and other organic material, and the use of benzene as a laboratory reagent.

According to http://www.airquality.co.uk, “Possible chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.”                                                     

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1,3-butadiene is another VOC emitted into the atmosphere from the combustion of petrol and diesel, therefore vehicle transport is a key source. It is also used in the manufacture of synthetic rubber.

The health effects are the same as for benzene.