Air pollution

Abstract

As people have become more aware of the hazards associated with the pollutants that are emitted into the atmosphere as gases or particles, interest has grown in measuring concentrations in air, both in polluted environments and in ‘clean’ environments. Such interest is not new; as long ago as the 17th century, the air of London was obviously unpleasant to even a casual observer. Urban air quality was the major focus of interest, because of the potential effect on human health, but by the end of the 19th century it was also apparent that plants were suffering, and not only in cities. The first ‘Alkali Inspector’ in Britain, R.A. Smith, made a systematic study of the chemical composition of rainfall (Smith, 1872), and did much to bring about the regulation of gaseous and particle emissions from industrial processes. Experimental evidence was also accumulating on the deleterious effects of pollution on agriculture and forestry, with measurements of the effects of polluted rain (Russell and Richards, 1919) on the growth of grasses in industrial regions (Crowther and Ruston, 1912), and the description of the covering of conifer needles by ‘soot’ (Rhine, 1924). In Britain, the severe winter smog (smoke + fog) in London in 1952, which caused many deaths and which could not be ignored even by healthy citizens, led to the introduction of the Clean Air Acts of 1956 and 1968, which greatly reduced the emission of particulate material (soot) from coal combustion. The obvious improvement in visual air quality was not matched, however, by an improvement in gaseous pollution, which only began to decrease as coal combustion switched from domestic grates and small industries (being replaced by gas) to large electricity generating plants (Department of Environment, 1994). The large power stations, usually situated outside cities, emitted the pollutant gases at much higher levels in the atmosphere and so alleviated the episodes of high concentrations of pollutants at ground level caused by the trapping of emissions below stable atmospheric inversion layers in winter.