From the coal-powered factories that contributed to the deaths of thousands in London in the 1950s to the smog caused by forest fires in Indonesia, killer air pollution has played a major role in the planet’s history. Here are some of the world’s worst smog disasters.

Belgium

On February 12, 1930, 60 people died and thousands became seriously ill when industrial air emissions from coal-powered factories were trapped over a 15-mile-long stretch of farms in the Meuse Valley.

Pennsylvania

In late October 1948, the Monongahela River Valley town of Donora was enveloped by toxic smog that killed 20 people and sickened 7,000 in five days. The cause was a deadly mixture of sulfur dioxide, carbon monoxide and metal-dust emissions from coke plants, a huge zinc smelter and coal furnaces located in the valley and town that was held in place by an unyielding layer of air. The investigation into the Donora smog disaster led to the first federal clean-air act, passed in 1955.

Mexico

A killer smog left 22 dead and hundreds hospitalized in the Gulf Coast oil city of Poza Rica in 1950. The smog was caused by gas fumes from a local oil refinery.

London

Piccadilly Circus theater lights stayed on during the day, conductors guided buses down the street with flashlights, and gas masks became a fashion item. In December 1952, London experienced a devastating smog when fog and black smoke from burning coal were trapped beneath a still, cold air mass. Some 4,000 people were killed in four days. The official death toll rose to 12,000. Many of the deaths were attributed to heart and respiratory problems. The disaster resulted in the Clean Air Act of 1956 — the first effective limit on the burning of coal.

New York City

Smog is reported to have killed more than 170 people in New York in November 1953. Officials blamed the deaths on a temperature inversion that caused extreme smog conditions, which led to respiratory failure and heart attacks.

Indonesia

In 1997, severe fires, mostly lit by farmers and logging companies to clear land, caused a choking smog that smothered Indonesia and surrounding countries, costing more than $5 billion in tourism and transport, and damaging public health. Some 1.8 million acres of bush and forest land were burned. The smog poisoned and harmed the health of more than 20 million workers and their families. Most of the smoke came from Sumatra and Indonesia’s Borneo provinces. Governments in Germany, Denmark, Belgium and the U.K. advised pregnant women, travelers with respiratory problems, the very young and the very old to avoid the region. On the Indonesian island of Sumatra, officials speculated that a plane crash that killed 234 passengers may have been caused by the massive blanket of haze over Southeast Asia. And in the Strait of Malacca, 250 miles from the air crash, 29 men went missing after two cargo vessels collided in the thick smog caused by the bush fires in the region.

Chile

The government declared an environment pre-emergency on May 19, 2004, because of the high levels of pollutants in the air, forcing the 60 percent of vehicles with improper pollution-control devices off the roads in the capital city of Santiago. Between May and August, the Andes Mountains were covered in a thick blanket of toxic smog that was caused by thermal inversions, which prevented the pollutants’ being flushed away from the city. No deaths were reported.

Malaysia

In July 2005, much of Malaysia was blanketed by smog attributed to forest
fires, many of them started by slash-and-burn farmers in Sumatra. It was considered
one of the country’s worst pollution crises in almost a decade. Two schools were
ordered closed for a week, a vessel ran aground, people wore masks in the streets,
and Kuala Lumpur’s second airport was closed temporarily, as visibility was reduced
to 100 yards. It was the first time in six years that the Malaysian government
released its air-pollution-index statistics — a heavily guarded secret for fear
the smog would scare people away.

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