e-Digest Statistics about: Air Quality
Concentrations of Volatile organic compounds (VOCs)
VOCs are ozone pre-cursors and comprise a wide range of chemical compounds including hydrocarbons (alkanes, alkenes, aromatics), oxygenates (alcohols, aldehydes, ketones, ethers) and halogen containing species. Methane (CH4) is an important component of VOCs but its environmental impact derives principally from its contribution to global warming. CH4 is therefore considered separately in the Climate Change section. The major environmental impact of non-methane VOCs lies in their involvement in the formation of ground level ozone. Most VOCs are non-toxic or are present at levels well below guideline values. Others however, such as benzene and 1,3-butadiene, are of concern because of their potential impact on human health.
Table 16 shows the trends in estimated non-methane VOC emissions by emission source, by end user and by type of fuel. Total emissions fell by 62 per cent between 1990 and 2006. Road transport emissions fell by 88 per cent over the same period, mainly as a result of the introduction of catalytic converters for petrol cars. Fuel switching from non-catalyst petrol cars to diesel cars has also had a small beneficial effect. A significant proportion of VOC emissions come from sources other than the combustion of fossil fuels, including natural gas leakage in the national distribution network, motor spirit evaporation, petrol refining, industrial processes, solvent evaporation and natural sources.
Under the UNECE Gothenburg Protocol to the Convention on Long Range Transboundary Air Pollution, the UK has agreed that by 2010 its emissions will be below 1,200 thousand tonnes [16]. Total VOC emissions (excluding natural emissions) in 2005 were 977 thousand tonnes.
The environmental impact of VOCs varies considerably from compound to compound. Almost all VOCs are precursors of ozone through photochemical oxidation, but their photochemical creation potentials (POCPs) vary widely. Table 17 provides a breakdown of the estimated 2005 VOCs emissions inventory by main species and by source. The most prevalent compounds are ethanol which is emitted from solvent use, production processes and the food industry, butane which is emitted principally from aerosols, distribution of crude oil, petrol and natural gas, chemicals manufacture and toluene which is mainly produced from petrol exhausts and from solvents. The higher volatility of butane accounts for substantial evaporative, refining and distribution losses. Butane, ethanol and toluene all represent significant sources of ozone. Although the speciated emissions by source given in Table 17 are given to the nearest ten tonnes, this should not be interpreted as indicative of their accuracy.
Further Information:
- Data Tables:
- 16 Estimated emissions of volatile organic compounds (VOCs) by UNECE source category, type of fuel and end user: 1970-2006 XLS
- 17 Estimated emissions of volatile organic compounds (VOCs) by species and by source: 2006 XLS
- References, further reading and links to other resources:
- [16] National Environmental Technology Centre, (1997). Acid Deposition Monitoring in the UK, 1986 to 1996. AEA Technology.
- [27] Department for Environment, Food and Rural Affairs (2003), The Air Quality Strategy for England, Scotland, Wales and Northern Ireland: Addendum
- Internet Links:
- UK National Atmospheric Emissions Inventory (NAEI)
- National Air Quality Information Archive
Your questions and comments about information presented on this page are welcome. Contact information and Email . Copyright of data and/or information presented or attached in this document may not reside solely with this Department. Please see guidance on Copyright.
Page last modified: 13 March 2008
Page published: 13 March 2008