Summary report of the corech (COGAR) workshop on the evaluation of air pollution episodes and associated control measures

Discussions within COGAR during 1981 indicated that collective information on the types of meteorological conditions when large, single sources like power stations contributed to pollution episodes, the frequency with which they occurred and the implications for intermittent control procedures, was important to all member utilities. This paper summarizes the findings of a working group set up by COGAR to study these problems.The investigation was concerned with SO₂ episodes and how feasible it would be to reduce their intensity by such measures as a substitution of low sulphur fuel or switching generation to areas where the probability of an episode developing is less.There has been a considerable reduction in SO₂ emissions in most urban areas in the last two decades. Nevertheless, in many locations, 24-h air pollution episodes can still be attributed to small or medium-sized emissions from low or medium level stacks, rather than to power stations and other large industrial sources with tall stacks. The worst cases in flat terrain where power stations do contribute for many hours are either stagnant conditions persisting for 24 h or a steady wind blowing consistently from an area containing several power stations. Single stations can present problems when topography interferes with dispersion or the stack height is inadequate for the emissions.Data on the frequency with which episodes occur in a given location and the ability to forecast episode conditions in advance, so that if appropriate, preventative measures may be taken, are the desired objectives. Achievement of these objectives requires a detailed understanding of the role of each type of source in relation to different meteorological situations and the local topography. The end product of such studies should be either;

• 1.(a) the specification of a procedure for implementing intermittent emission control
• 2.(b) a demonstration that intermittent control is not an effective option in the area under study.

In case (a), input data required are

• 1.(i) the vertical structure of the atmosphere
• 2.(ii) ground level concentrations of pollutant plus, in complicated topography
• 3.(iii) the three-dimensional distribution of pollutant.

COGAR is a group set up to coordinate atmospheric research in the electrical supply industry in Europe.