The Great Smog of 1952

Since Roman times, if not before, Britain has been known to people abroad as a land of mists and fogs. Until recently, indeed, visitors to the capital could take home with them tins of 'London fog'!

For hundreds of years, the mists and fogs of Britain's major cities were all too often polluted and noxious, with London especially badly affected. The fogs endangered health and also posed a threat to travellers who lost their way and thus became an easy prey to robbers. Around 1807, the smoke-laden fog of the capital came to be known as a 'London particular', i.e. a London characteristic. Charles Dickens used the term in Bleak House (published in 1853) and provided graphic descriptions of London's fogs in this and other novels.

Fig 1: Hazardous driving conditions due to smog

The smoke-laden fog that shrouded the capital from Friday 5 December to Tuesday 9 December 1952 brought premature death to thousands and inconvenience to millions. An estimated 4,000 people died because of it, and cattle at Smithfield, were, the press reported, asphyxiated. Road, rail and air transport were almost brought to a standstill and a performance at the Sadler's Wells Theatre had to be suspended when fog in the auditorium made conditions intolerable for the audience and performers.

The death toll of about 4,000 was not disputed by the medical and other authorities, but exactly how many people perished as a direct result of the fog will never be known. Many who died already suffered from chronic respiratory or cardiovascular complaints. Without the fog, they might not have died when they did. The total number of deaths in Greater London in the week ending 6 December 1952 was 2,062, which was close to normal for the time of year. The following week, the number was 4,703. The death rate peaked at 900 per day on the 8th and 9th and remained above average until just before Christmas. Mortality from bronchitis and pneumonia increased more than sevenfold as a result of the fog.

Fig 2: The London smog disaster of 1952.
Death rate with concentrations of smoke

The fog of December 1952 was by no means the first to bring death and inconvenience to the capital. On 27 December 1813 fog was so dense that the Prince Regent, having set out for Hatfield House, was forced to turn back at Kentish Town. The fog persisted for almost a week and on one day was so thick that the mail coach from London to Birmingham took seven hours to reach Uxbridge. Contemporary accounts tell of the fog being so thick that the other side of the street could not be seen. They also tell of the fog bearing a distinct smell of coal tar. After a similar fog during the week of 7–13 December 1873, the death rate in the Administrative County of London increased to 40% above normal. Marked increases in death rate occurred, too, after the notable fogs of January 1880, February 1882, December 1891, December 1892 and November 1948. The worst affected area of London was usually the East End, where the density of factories and domestic dwellings was greater than almost anywhere else in the capital. The area was also low-lying, which inhibited fog dispersal.

At the beginning of January 1900, when he reported for duty as the newly appointed Director of The Meteorological Office, Dr (later Sir) Napier Shaw received from the Bishop of London a 'letter of condolence', expressing sorrow that he (Shaw) should have to work in 'this place of darkness' - a reference to the smoke-laden fogs of London and the fogginess of that winter in particular. One of the projects initiated by Shaw soon after he became Director, was an inquiry into the occurrence and distribution of fog in the capital. The investigation confirmed that smoke from the chimneys of London served to aggravate fog problems.

As long ago as the 13th century, air pollution was recognised as a public-health problem in the cities and large towns of the British Isles, and the burning of coal was identified as the principal source. Four centuries later, in his Fumifugium, published in 1661, John Evelyn wrote of the 'Hellish and dismall cloud of sea-coale' that lay over London and recommended that all noisome trades be banished from the city. The authorities did not, however, take his advice. The burning of coal continued and the pall of soot over London grew worse.

The industrial revolution brought factory chimneys that belched gases and huge numbers of particles into the atmosphere. Some of these particles caused lung and eye irritations. Others were poisonous. All were potentially condensation nuclei, the tiny hygroscopic particles on which condensation forms. From the gases, corrosive acids were formed, notably sulphuric acid, which is produced when sulphur dioxide combines with oxygen and water.

As if it were not enough that they brought on agues, rheumatism and fevers and carried particles of soot from coal fires, the fogs of the British Isles now became even more unpleasant, for the noxious emissions from factory chimneys gave them an acrid taste, an unpleasant odour and a dirty yellow or brown colour. These fogs, so different from the clean white fogs of country areas, came to be known as 'pea soupers', not only in London but also in other industrial areas of the British Isles. The particles in the atmosphere made buildings dirty and the acids attacked ironwork, stonework and fabrics.

In early December 1952, the weather was cold, as it had been for some weeks. The weather of November 1952 had been considerably colder than average, with heavy falls of snow in southern England towards the end of the month. To keep warm, the people of London were burning large quantities of coal in their grates. Smoke was pouring from the chimneys of their houses and becoming trapped beneath the inversion of an anticyclone that had developed over southern parts of the British Isles during the first week of December. Trapped, too, beneath this inversion were particles and gases emitted from factory chimneys in the London area, along with pollution which the winds from the east had brought from industrial areas on the continent.

Fig 3

Early on 5 December in the London area, the sky was clear, winds were light and the air near the ground was moist. Accordingly, conditions were ideal for the formation of radiation fog. The sky was clear, so a net loss of long-wave radiation occurred and the ground cooled. The moist air in contact with the ground cooled to its dew-point temperature and condensation occurred. Cool air drained katabatically into the Thames Valley. Beneath the inversion of the anticyclone, the very light wind stirred the saturated air upwards to form a layer of fog 100–200 metres deep. Along with the water droplets of the fog, the atmosphere beneath the inversion contained the smoke from innumerable chimneys in the London area and farther afield. Elevated spots such as Hampstead Heath were above the fog and grime. From there, the hills of Surrey and Kent could be seen.

During the day on 5 December, the fog was not especially dense and generally possessed a dry, smoky character. When nightfall came, however, the fog thickened. Visibility dropped to a few metres. The following day, the sun was too low in the sky to make much of an impression on the fog. That night and on the Sunday and Monday nights, the fog again thickened. In many parts of London, it was impossible at night for pedestrians to find their way, even in familiar districts. In the Isle of Dogs, the visibility was at times nil. The fog there was so thick that people could not see their own feet! Even in the drier thoroughfares of central London, the fog was exceptionally thick. Not until 9 December did it clear. In central London, the visibility remained below 500 metres continuously for 114 hours and below 50 metres continuously for 48 hours. At Heathrow Airport, visibility remained below ten metres for almost 48 hours from the morning of 6 December.

Huge quantities of impurities were released into the atmosphere during the period in question. On each day during the foggy period, the following amounts of pollutants were emitted: 1,000 tonnes of smoke particles, 2,000 tonnes of carbon dioxide, 140 tonnes of hydrochloric acid and 14 tonnes of fluorine compounds. In addition, and perhaps most dangerously, 370 tonnes of sulphur dioxide were converted into 800 tonnes of sulphuric acid. At London's County Hall, the concentration of smoke in the air increased from 0.49 milligrams per cubic metre on 4 December to 4.46 on the 7th and 8th.

The infamous fog of December 1952 has come to be known as 'The Great Smog'; the term 'smog' being a portmanteau word meaning 'fog intensified by smoke'. The term was coined almost half a century earlier, by HA Des Voeux, who first used it in 1905 to describe the conditions of fuliginous (sooty) fog that occurred all too often over British urban areas. It was popularised in 1911 when Des Voeux presented to the Manchester Conference of the Smoke Abatement League of Great Britain a report on the deaths that occurred in Glasgow and Edinburgh in the Autumn of 1909 as a consequence of smoke-laden fogs.

Legislation followed the Great Smog of 1952 in the form of the City of London (Various Powers) Act of 1954 and the Clean Air Acts of 1956 and 1968. These Acts banned emissions of black smoke and decreed that residents of urban areas and operators of factories must convert to smokeless fuels. As these residents and operators were necessarily given time to convert, however, fogs continued to be smoky for some time after the Act of 1956 was passed. In 1962, for example, 750 Londoners died as a result of a fog, but nothing on the scale of the 1952 Great Smog has ever occurred again.

Pea-soupers have become a thing of the past, thanks partly to pollution legislation but also to slum clearance, urban renewal and the widespread use of central heating in the houses and offices of British towns and cities. As recently as the early 1960s, winter sunshine totals were thirty per cent lower in the smokier districts of London than in the rural areas around the capital. Today, there is little difference.

We should not, however, be complacent. The air now contains other types of pollutants, many of them from vehicle exhausts. Among these pollutants are carbon monoxide, nitrogen dioxide, ozone, benzines and aldehydes. They are less visible than the pollutants of yesteryear, but are equally toxic, causing eye irritation, asthma and bronchial complaints. To some extent, we have simply replaced one form of air pollution with another. We may question whether or not the major cities of the British Isles are any less polluted now than they have been for hundreds of years.