Under the 1988 EC Directive on large combustion plants, the UK's emissions of SO2 from existing plants of more than 50MWth must be reduced by 60% by 2003 from a 1980 baseline. The target for NOx is a 30% reduction by 1998, also from a 1980 baseline.
In order to meet these targets, the Government has prepared a national plan which sets declining annual ceilings for both pollutants, and also allocates emission quotas to the power generators, the oil refining industry, and "other industry". These have been translated into annual emission ceilings for each plant by HM Inspectorate of Pollution and its counterparts in Scotland and Northern Ireland.
The DoE's figures for 1992 show that SO2 emissions from all large combustion plant were reduced by 78,478 tonnes, and NOx emissions by 47,491 tonnes, compared to 1991.
The 1992 targets in the national plan were 3,246,000 tonnes for SO2 and 925,000 tonnes for NOx. But actual emissions were 2,668,117 tonnes of SO2 - 18% below the target - and 701,645 tonnes for NOx - 24% below the target.
The electricity sector remains by far the biggest source of the pollutants, contributing 90.9% of the SO2 and 93.6% of the NOx emitted by large combustion plants in 1992 (see table ).
However, the biggest contribution to the fall in emissions last year was made by National Power, which cut its SO2 emissions by 72,000 tonnes and its NOx emissions by 15,000 tonnes. In contrast, refinery emissions of both pollutants increased slightly last year, as did releases from the "other industry" sector.
The downward trend is set to continue this year, with gas-fired power stations increasingly displacing older coal-fired capacity. The initial phase of the UK's first large-scale flue gas desulphurisation plant, at National Power's Drax power station, is also due to come on stream shortly, while the first stage of a similar installation at PowerGen's Ratcliffe power station is due for commissioning early in 1994.