In December 1952, air pollution resulting from a toxic mix of dense and grimy fog and smoke from burning coal affected London and killed thousands of people. This event is known as the great smog of 1952. The smog was formed by the smoke from coal burning in homes and factories and an anticyclone that prevented the smoke from dispersing into the atmosphere. The fog and smoke combined to form a thick layer of smog. The event lasted for four days i.e. from December 5th to December 9th. It is still considered as one of the biggest tragedies in history. Initially, the Londoners did not realize the seriousness of this event as they were used to experiencing smogs. The impact of the event was realized when the smog started turning poisonous and things started becoming worse. The smog hovered over the city and affected visibility. The city became impassable, transportation came to a standstill and many people died. ✦ In the beginning of December 1952, a mass of cold air with high atmospheric pressure or anticyclone settled over the city. A light veil of fog was formed due to favorable weather conditions like light winds, cold air, and high humidity. ✦ People started burning more coal to prevent themselves from the chilling cold. Over time, this created dense smoke in the atmosphere, which came out of household chimneys. To add to the trouble, more smoke from combustion of coal from the industrial smokestacks started accumulating in the air. ✦ The anticyclone that prevailed in the area caused a temperature inversion where the air close to the ground became cooler than the air above it. The inversion prevented the smoke from escaping into the atmosphere. Instead, it trapped the smoke close to the ground. As a result, the concentration of pollutants increased dramatically. ✦ Additionally, the light wind caused the smoke to remain stagnant and not disperse. As a result, the smoke combined with the fog leading to an increasingly dense layer of smog. The smog began to turn to a yellow shade as it mixed with soot, sulfur particles, carbon dioxide, hydrochloric acid, tar particles, and other hazardous elements present in the smoke. The harmful elements in the smog reached exceptional levels. ✦ The smog was so dense that it affected visibility and immobilized the city. It entered homes, shops, and offices. People could not see themselves or others. Also, they could not go out for the fear of getting lost in the streets and breathing the dangerous smoke. Students could not be sent to schools or colleges. The city became impassable, concerts were canceled as the stage could not be seen, flights were grounded, trains were canceled, and boat transportation came to a standstill. People who already had been out with their cars, abandoned driving and had to walk. Shop owners closed their shops to prevent the smog from permeating indoors. However, it was almost impossible to prevent the smog particles from entering indoors. This is evident from the sheer number of people who died at home. ✦ It is estimated that around 12,000 people died and most of them were elderly, infants, and ones who suffered from pre-existing respiratory problems like bronchitis and pneumonia or cardiac disorders. About 100,000 people fell sick and suffered from health effects like chest pains, lung inflammation, breathing problems, and asthma attacks. Many animals lost their lives due to the smog. ✦ Almost the whole city was covered by the smog. There were very few places in Greater London where smog did not occur. The worst days of the smog were between December 5th and 7th. On December 8th, the smog started clearing by a light wind. On December 9, the great smog finally came to an end when cold winds from the west finally cleared the poisonous smog from all areas of London. However, the detrimental effects lingered. ✦ Following this event, air pollution was recognized as a threat to health in London. A number of laws were brought in to prevent further pollution disasters. The Parliament passed the Clean Air Act of 1956, which banned the burning of coal in urban areas and decreed the residents to use smokeless fuels like using alternative heating systems, gas, and oil. Locals were given time to get used to the laws. However, despite the passing of laws and making improvements, one more smog event took place in 1962 and a few people died. However, the impact was not as severe as the Great Smog in 1952. The Clean Air Act was amended in 1962. The laws were implemented strictly and the use of fuels and black smoke emissions was banned in the industries across London. The change from the use of coal to the use of gas, oil, and electricity was gradual. Thankfully, things have become normal now. Also, modern developments like the use of central heating for keeping the rooms warm has become popular today. Given that emissions of air pollutants today are regulated across most countries, the re-occurrence of a similar disaster is less likely. However, it has to be kept in mind that the current levels of air pollution could affect human health.