Air pollution: the "classical" pollutants.

Few disasters can have led to such great good as four-day London smog of December 1952. Though its extreme concentrations of smoke and sulphur dioxide appear to have caused up to 4000 extra deaths,1 it provided impetus for Clean Air Act 1956. Many lines of evidence suggest that pollution so strikingly reduced by this Act was associated with both acute and chronic illness.2 Air pollution has many components (see box) and may be of different types in different places.3 In this article I deal with smoke and sulphur dioxide pollution,4 mainly in Britain, and in next I will touch on other pollutants. Severe fogs had occurred before in Britain and elsewhere; and smoke had polluted cities for centuries?in fact, problem was past its worst well before 1952.5 In eighteenth century Benjamin Taylor lectured about the clouds of Smoke, Vapour, and corrupted Effluvia, correctly pointing to importance of temperature inversions, incomplete com? bustion of coal, and all Sooty particles . . . and cloud of Smoke, which if continued, ... its caustic quality would seize upon our lungs, restrain their vigour, and at last, render them totally incapable of their office.6 A century earlier more famous John Evelyn ascribed ill health of Londoners to fuliginous and filthy vapour7; while a commission was set up to punish those who burnt coal in City of London as long ago as 1307. Only in present century, however, could air pollution become an important cause of illness and death: earlier its effects, though suspected, were overwhelmed by those of infectious diseases.5 Moreover, potentially lethal effects of intense fog would not be so apparent until there was a large population of susceptible people: by 1952 antibiotics enabled many people to survive with precarious respiratory and cardio? vascular systems; and it was these apparently, not fit, who were killed by fog.1