Sulphur Dioxide
The main sources of SO2 emissions are electricity generation, industry and domestic fuel combustion. Over the past 20 years there has been a reduction in the emissions from low level sources including domestic combustion, so that emissions are now dominated by a few large high level sources. Ground-level concentrations of SO2 in the UK have fallen so much that there is no longer a threat to plant health.
Total SO2 emissions have decreased substantially, in line with changes in fuel use and commitments to international agreements within the UNECE Convention on Long Range Transboundary Air Pollution (CLRTAP) and the European Union ("Sulphur Protocols"). However, the reductions in deposition corresponding to this change have been observed mostly near sources, rather than in long range transported S deposition (Smith et al.2000, NEGTAP 2001). The explanation of this effect is an area of uncertainty at present and has important consequences for the upland areas of the UK, since these are clean areas receiving deposition from long range transport. The result is that the reductions in emissions are not currently matched by reductions in deposition and impacts in the most sensitive areas of the UK. These impacts include both soil and freshwater acidification.
References:
NEGTAP (National Expert Group on Transboundary Air Pollution) 2001: Transboundary Air Pollution: Acidification, Eutrophication and Ground-Level Ozone in the UK. ISBN 1 870393 61 9. Available online at http://www.nbu.ac.uk/negtap.
Smith R.I., Fowler D., Sutton M.A., Flechard C. and Coyle M. (2000): Regional Estimation of Gas Deposition in the UK: model description, sensitivity analyses and output. Atmospheric Environment 34: 3757 - 3777.