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Sulphur oxides, SO2 and SO3 as SO2

sulphur dioxide

SPRI Emission Reporting Threshold
100,000 Kg/yr Pollutant Emissions to Air
This sheet is a generic summary, designed to give the reader a basic level of background information about the substance in question. Great care has been taken to represent as effectively and correctly as possible the broad range of (not necessarily consistent) information which is available from a variety of sources. The reader must accept therefore that this sheet has no legal status and cannot be relied upon in any legal proceedings. SEPA disclaims any responsibility or liability whatsoever for errors and omissions in this sheet.
What is it?
Sulphur dioxide occurs both naturally and as a result of man's activities. It is a colourless gas with a strong choking smell which easily dissolves in water to form sulphuric acid. It is relatively dense; about 2.5 times heavier than air.
What is it used for?
Sulphur dioxide is used to produce sulphuric acid, as a bleaching agent or disinfectant, as a fumigant and as a food preservative. Liquid sulphur dioxide can also be used to purify petroleum products.
Where does it come from?
The main source of sulphur dioxide into the atmosphere is from the burning of fossil fuels in power stations, oil refineries and industrial plants. Vehicles and domestic boilers also release sulphur dioxide. It is also produced naturally as a result of forest fires and from volcanoes.
How might it affect the environment?
Sulphur dioxide can damage plants and reduce crop yields. Conversely, its antifungal properties can be beneficial for some plants. When sulphur dioxide levels are sufficiently high, it can combine with water vapour in the air to produce acids which can damage sensitive buildings or monuments. Sulphur dioxide also dissolves in water droplets in clouds which then fall as acid rain - sometimes thousands of kilometres from the site of emission. Acid rain damages vegetation and wildlife and pollutes water bodies.
How might exposure to it affect human health?
Sulphur dioxide can irritate the eyes and respiratory system (air passages and lungs). Even at concentrations normally experienced in the environment it can harm sensitive individuals (such as those suffering from lung disease). Sulphur dioxide pollution contributed to the "great London smog" in 1952 which is thought to have contributed to around four thousand premature deaths of people with lung disease or bronchitis. This would not occur today as sulphur dioxide pollution has been dramatically reduced.
What steps are being taken to limit the potential impacts?
Following the "great London smog", drastic action was taken to reduce levels of sulphur dioxide in the UK. This was largely successful: levels of sulphur dioxide are now around 90% lower than in 1960. Today, the main legislation controlling levels of sulphur dioxide in the UK (including Scotland) is the National Air Quality Strategy, in which it is one of the eight main air pollutants targeted for reduction; and, from large industrial processes, through the UK's Pollution Prevention and Control (PPC) regulations. The European Directive concerned with ambient air quality assessment and management (96/62/EC); the European Integrated Pollution, Prevention and Control (IPPC) directive; and the directive on combating air pollution from industrial plants (84/360/EEC) also control sulfur dioxide releases. The UK is also a signatory to the international UNECE convention on Long-Range Transboundary Air Pollutants (LRTAP) which includes measures to combat the effects of oxides of sulphur.