Introduction

In the introduction to the First Report of the Advisory Group the way in which the major problems of air pollution by smoke and sulphur dioxide (SO2). Principally form the burning of coal, had been largely overcome in the wake of the Clean Air Acts of 1956 and 1968 was noted. That first report dealt with a separate problem that had emerged meanwhile namely ozone, a photochemical pollutant arising form reactions in the air between pollutants derived largely from motor vehicle emissions, and confined, in the United Kingdom, to sunny periods in the summer.

There remain however residual problems regarding the “traditional” Pollutants, sulphur dioxide, smoke or other suspended particulates, especially in the winter months. In some localities in the United Kingdom, where the Clean Air Acts have not been fully implemented and coal is used for domestic heating purposes, appreciable amounts of black, tarry smoke are generated along with sulphur dioxide. In other areas the principal concern is with the latter pollutant, derived form the large scale, more efficient, combustion of coal air heavy oil in power stations, commercial or industrial premises. Dispersion from these sources is sufficient, in most weather conditions, to avoid concentrations at ground level that would be of concern in relation to health. Limit values have been set, in terms of 24 hour, seasonal and annual averages, linked with concentrations of smoke by regulations as required in an EC Directive. There are a few localities, notably in Northern Ireland, where smoke control areas have been established under the Clean Air Acts. But where in the absence of piped gas supplies reliance has to be placed partly on solid smokeless fuels for domestic heating purposes. These can then contribute to local levels of sulphur dioxide, even it there is little smoke.

Because much of the evidence on adverse effects on health relates to the situation in earlier decades when the air of urban areas of the United Kingdom and of other places abroad was pervaded by coal smoke as well as sulphur dioxide, most prior assessments of such effects considered this complex as a whole. Information related to present day conditions, in which the particulate matter associated with sulphur dioxide in the air is proportionately less than hitherto, and is of changed composition, is more limited.

While the present report covers the sulphur dioxide/particulates complexcollectively the emphasis is on sulphur dioxide and on the secondary acid aerosols derived from it which form part of the particulate component. A further aspect is that attention has been turned more to the peak values that may occur during the day, raising possibilities of at least transient effects on health even when longer term average values are low and EC Directive limit values are complied with. Thus in a more recent World Health Organization review air quality guidelines based on ten minute and one hour averages were provided as well as ones based on longer averaging periods. For this purpose reliance has to be placed more on findings form controlled inhalation studies (generally with sulphur dioxide, or acid aerosols, alone) rather than on epidemiological studies.