The Great Smog of London

The fog in Dickens, the fog through which Sherlock Holmes hears a carriage he cannot see, was not a literary invention. Londoners had lived inside it for centuries. From the medieval period onwards the city burned coal, and by the nineteenth century it burned it on an industrial scale, in hundreds of thousands of household grates as well as in factories and gasworks. On still, cold days the smoke did not rise and blow away; it hung at street level and mixed with river mist into something thicker and dirtier than fog. Londoners named it — a "pea-souper", a "London particular" — with the grim affection people reserve for a familiar nuisance. Its colour came from the coal itself: yellow-brown, sometimes almost black, and always sulphurous. Bad fogs had killed before: in the 1870s, 1880s and 1890s London's death rate jumped sharply during long fogs, and doctors noticed. But the deaths were absorbed into the ordinary mortality of a crowded city, and no government saw reason to curb the fuel on which national wealth was built.

By 1952 the smoke was, if anything, dirtier than before. Post-war Britain was broke, and coal was one of the few things it could sell abroad. Much of the better, cleaner-burning coal was exported to earn foreign currency, which resulted in households being left with the cheap, dusty, high-sulphur residue known as "nutty slack", burned in millions of open fires. Meanwhile the capital generated much of its electricity inside its own boundaries: coal-fired power stations at Battersea, Bankside and Fulham stood among the houses they lit, emptying their chimneys into the air Londoners breathed. The air was changing in another way too. London's electric tram network had been wound up earlier that same year and the trams replaced by diesel buses, whose exhaust added its own sharp, oily smell. So the city entered the winter of 1952 with more sulphur in its fuel, its power stations still in its streets, and new fumes on those streets.

None of this was secret. Medical officers published the figures; campaigners had argued for decades that smoke abatement was possible and cheap. But the fog was so ordinary that it had stopped registering as a danger. Washing hung outdoors came in grey; a white collar turned black by lunchtime. Children with weak chests were kept indoors in December, and the winter rise in respiratory illness was treated as a fact of London life, like rain. There was a settled complacency about it: smoke was the price of warmth, and warmth was not negotiable in a country still using ration books. Successive governments accepted that the problem stemmed from millions of individual fireplaces, concluded that no minister could tell people how to heat their homes, and left it there. What was missing was not knowledge but a shock large enough to make it impossible to ignore — and that shock was five days away.

On Friday 5 December 1952 an anticyclone settled over the Thames valley, bringing exactly what London did not need: clear skies, no wind, hard frost. Two things followed. First, the cold led to people banking up their fires, so more coal burned than usual. Second, and far more dangerous, the calm air produced a temperature inversion. Normally air grows colder as you climb, so warm smoke rises, cools and disperses; that day the order was reversed. A layer of warmer air sat several hundred feet up and sealed in the freezing air below it, like a lid on a pan. Everything the city emitted — smoke, soot, sulphur dioxide from a million chimneys, exhaust from the new diesel buses — rose a little way, met the lid and stopped. Over four to five days the pollutants went on accumulating in a shallow layer of motionless air. Chemistry then made it worse: the sulphur dioxide reacted with moisture and oxygen in the fog to form droplets of dilute sulphuric acid, which people drew into their lungs with every breath.

The result was a fog unlike any within living memory. It was not grey but yellow-black, and it had a taste — sour, metallic, acrid. Visibility fell to a few metres, and in places to almost nothing: people reported being unable to see their own feet, and felt their way home along kerbs and railings. Traffic gave up. Cars were abandoned where they stood; buses ran only with a conductor walking ahead with a lamp, and then not at all. Ambulances could not reach the sick, so patients made their own way to hospital through streets no one could find. At the Smithfield Show, the annual cattle exhibition, prize animals began to gasp and choke, and some died. Indoors was scarcely better. The fog seeped into buildings, and cinema and theatre performances were abandoned because the audience could not see the stage through the murk. People came home with black rings round their nostrils and found the fog waiting in their own hallways.

What no one could see at the time was the dying. Hospitals filled with people fighting for breath — the elderly, the bronchitic, the very young — and undertakers ran out of coffins. On Tuesday 9 December the wind at last returned and swept the whole mass out to sea; the smog vanished as suddenly as it had come, and London went back to work. It was the statisticians who found the disaster. Comparing the mortality registers with a normal December, officials calculated roughly four thousand excess deaths, and that figure entered the history books. Later analyses of the same data, taking in the weeks that followed, have put the total considerably higher — commonly around twelve thousand — because deaths went on rising long after the air cleared. That higher figure comes from reanalysis rather than from anything counted at the time, and remains an estimate; but on any reckoning the smog ranks among the deadliest peacetime disasters in British history.

The government's first instinct was to play the whole thing down. Ministers pointed out that London had always had fogs, questioned whether the deaths could fairly be attributed to smoke, and suggested that an influenza epidemic explained much of the rise — an argument the medical evidence did not support. Behind the defensiveness lay a real fear: cleaning the air meant interfering with how millions heated their homes. What broke the deadlock was persistence from an unexpected quarter. Gerald Nabarro, a Conservative backbencher with no ministerial career to protect, kept the issue alive in Parliament and pushed a private member's bill on air pollution, forcing the government to legislate or explain why not. It took a third path first and appointed a committee of inquiry under the industrialist Sir Hugh Beaver. The Beaver Committee reported in 1954 that smoke abatement was both necessary and achievable, and its recommendations brought about the legislation resisted for a century: the Clean Air Act of 1956.

The Act was modest in language and radical in effect. It empowered local authorities to declare "smoke control areas" — smokeless zones — in which emitting dark smoke from a chimney became an offence. It met the practical objection head-on with a subsidy towards converting household grates to smokeless fuel, gas or electricity, so the burden did not fall entirely on poor families. And it pushed power stations and heavy industry out of city centres, or up much taller chimneys. Change was gradual — smoke control areas spread borough by borough, and a further Act followed in 1968 — but the direction was set and never reversed. Within a generation the London pea-souper had ceased to exist. Something that had defined the city for three hundred years, and shaped its literature, vanished so completely that visitors now arrive expecting fog and find none. Few pieces of environmental legislation have produced so visible a result.

The physics, however, did not disappear; it merely moved. Los Angeles, ringed by mountains and prone to inversions, developed its own photochemical smog from traffic exhaust and sunlight. Beijing has endured winters of "airpocalypse", and Delhi still faces annual episodes when a cold, windless spell traps smoke from vehicles, industry and crop burning. Each stems from the same recipe: too much combustion, and air that will not move. Yet the greater modern danger is the pollution that never announces itself. Fine particulates and nitrogen dioxide, largely from traffic, kill without obscuring the view; they trigger asthma attacks, strokes and heart disease, and millions of premature deaths each year are attributed to them — but they leave the sky looking blue. That is the uncomfortable echo of 1952: it took a catastrophe you could taste to overcome a century of complacency. The open question is whether governments can act on a killer nobody can see, or whether they will always wait for a fog thick enough to stop the traffic.