Seventy-three years ago today, on December 4, 1952 (October 18, 1952 lunar calendar), the London Smog Event. London, England is known as the "fog capital" of the world. On December 4, 1952, the city of London experienced one of the most serious "smog" events in the world: a continuous thick fog for nearly a week, a large amount of smoke and gas from factories and households accumulated at low altitudes, and the whole city was shrouded in thick fog and fell into a gray. During this period, more than 4,700 people died from respiratory diseases; after the fog cleared, more than 8,000 people died. At that time, there were coal-fired power plants in London, and there were many factories not far from the city center. Most households burned coal for heating, and there was little control over the exhaust gas produced by cars and trucks. During this period, London was in a state of dead wind, with a large amount of smoke and dust accumulating in the air. After a long time, the wind was too weak to carry away the various harmful soot emitted by the many factory chimneys and households. The fog cloud hovered over the city for 5 days, gradually becoming dirtier and more toxic. The amount of smog in the air in central London increased almost tenfold. The Donora Smog and the London Smog Event were the same as the Maas Valley Smog in Belgium in December 1930. They had the same factories and power plants that produced pollutants. The pollutants mainly came from the combustion of fuels such as coal and oil, as well as carbon monoxide, carbon dioxide, hydrocarbons, sulfur dioxide and nitrogen oxides produced by chemical plants. At the same time, they have the same pollution weather conditions, inversion and dead wind environment, which means that the already polluted air loses its ability to spread and cannot effectively dilute or carry away the pollutants. And more pollutants are added, and the concentration continues to increase, causing people living in it to suffer from bronchitis, asthma and other diseases that affect the lungs.