§ Alun Michael
Volatile organic compounds (VOCs) include a very wide range of individual substances, such as hydrocarbons (for example benzene and toluene), polycyclic aromatic hydrocarbons (PAHs), halocarbons and oxygenates. Hydrocarbon VOCs are usually grouped into methane and other non-methane VOCs. Non-methane VOCs are emitted to air as combustion products, as vapour arising from handling or use of petroleum distillates, solvents or chemicals, and from numerous other sources. The emissions of the 50 most significant non-methane VOCs in the UK (in terms of mass emissions), together with time trends and a784W spatially disaggregated map of all sources are published annually in the National Atmospheric Emissions Inventory, available at www.naei.org.uk.
Some VOCs are harmful to human health, including benzene, PAHs and 1,3-butadiene. Benzene can cause leukaemia, if exposure is maintained over a long period of time. There are several hundred different forms of PAH, and sources can be both natural and man-made. Several of these PAHs can cause lung cancer. Sources of 1,3-butadiene include the manufacturing of synthetic rubbers, petrol driven vehicles and cigarette smoke. 1,3-butadiene exposure probably causes lymphomas or leukaemias. Other volatile organic compounds may, at high concentrations, affect the central nervous system (e.g. chloroform), cause liver damage (e.g. carbon tetrachloride) or show irritant effects (e.g. aldehydes). These effects will not necessarily be relevant at environmental levels of exposure.
VOCs also contribute to the formation of ground-level ozone that can impair lung function and cause irritation to the respiratory tract. Ozone has also been associated with increases in respiratory hospital admissions and deaths in those already ill with respiratory disease.
Total emissions of methane and non-methane VOCs have reduced significantly in England since the late 1980s, particularly those from traffic and industrial processes, and are expected to continue to do so. The UK met the requirements of the United Nations Economic Commission for Europe Convention on Long Range Transboundary Air Pollution's 1991 Geneva Protocol, which required a 30 per cent. reduction in VOC emissions by 1999 using 1988 as a basis. The EU National Emission Ceilings Directive has set a further target of a reduction to 1200kT VOC annual emissions by 2010. Latest projections suggest the UK will meet this target. The Air Quality Strategy includes objectives for ambient levels of benzene, PAHs and 1,3-butadiene to protect human health. Latest monitoring indicates that we have already met the Air Quality Strategy objectives for some of these pollutants at most sites in the UK and that levels are generally declining for all these pollutants.