UK Smoke and Sulphur Dioxide Network

Executive Summary

This report presents the results from the UK Smoke and Sulphur Dioxide Network for the year April 1997 to March 1998, providing a summary of data from the 204 sites comprising the Network this year. These data are compared with the standards and objectives specified in the UK National Air Quality Strategy, and with the standards and guidelines specified in the existing and draft EC Directives on sulphur dioxide and suspended particles. Concentration trends and spatial distributions throughout the UK are also discussed. A computer disk, which contains the full year's dataset for all Network sites, accompanies this report (see inside back cover).

The year beginning April 1998 was the fifth consecutive year in which no site exceeded any of the limit values of the original EC Directive (80/779/EEC) on Sulphur Dioxide and Suspended Particulate Matter. There was still, however, widespread exceedence of the 24 hour guide values of the Directive, and some exceedence of the annual average sulphur dioxide lower guide value.

The original EC Directive is to be superceded in 2001 by the Framework Directive on ambient air quality assessment and management, and Daughter Directive on SO₂, NO₂, PM₁₀ and lead. Seven sites exceeded the proposed Daughter Directive 24 hour limit for SO₂ during 1997; four in Belfast, two in South Yorkshire and one in Newcastle.

Daily average measurements from this Network cannot be used for direct comparison with the standards and objectives set for 15 minute average SO₂ concentrations in the UK National Air Quality Strategy. However, applying surrogate relationships to the Network data indicates that exceedence of the UK Strategy Objective for SO₂ is currently widespread. The Objective is to be met by 2005.

There is also a UK standard for particulate, but this specifically applies to PM₁₀, not black smoke, and the UK National Air Quality Strategy acknowledges that these two techniques are not the same. However, PM₁₀ concentration is usually higher than black smoke except at very high "episode" concentrations, and hence, if smoke exceeds the PM₁₀ limit, it is likely that PM₁₀ has also done so. This was the case at many sites during 1997 - 98.

UK average concentrations in 1997 - 98 were 9.4 µg m^-3 for smoke and 20.6 µg m^-3 (7.7ppb) for SO₂. These averages are both slightly lower than last years' UK averages of 9.9 µg m^-3 and 22.4 µg m^-3 (8.4 ppb) for smoke and SO₂ respectively, as measured by this Network.

The spatial distributions for black smoke and SO₂ in 1997 - 98 were similar to those observed in previous years. Concentrations of black smoke were typically highest in areas where the use of coal for domestic heating is still relatively widespread, such as parts of Yorkshire and Northern Ireland, and also at some sites in large cities. Highest concentrations of SO₂ were also found in areas with widespread domestic coal burning, in particular, Northern Ireland, where natural gas currently has limited availability.