India’s capital Delhi is blanketed under a hazardous shroud of air pollution.
City authorities have imposed a car rationing scheme in a bid to bring levels down, but experts believe the real blame lies with crop burning by farmers in neighbouring states.
Delhi is the latest city to try to come up with ways to tackle increasingly dangerous pollutants in the air.
This is what other cities have done in a bid to beat air pollution.
When was pollution at its worst?
Thick smog used to frequently blanket the UK capital in the 19th and 20th centuries, when people burned coal to warm homes and heavy industry in the city centre pumped chemicals into the air.
Referred to as “pea-soupers”, the most famous of these events was the so-called Great Smog of London in 1952. It was recently dramatised in the first series of the Netflix drama, The Crown.
Cold weather in the preceding days meant people had burned more coal – often of low quality, which released more sulphur dioxide – while inner-city coal power stations added to the haze. An anticyclone then settled over London, trapping cold air under a layer of warm air.
The smog lowered visibility to a few feet and, over four days, is thought to have killed more than 10,000 people.
What was the solution?
In 1956 the UK passed the Clean Air Act.
It regulated both industrial and domestic smoke, imposing “smoke control areas” in towns and cities where only smokeless fuels could be burned and offering subsidies to households to convert to cleaner fuels.
The act was extended in 1968, and air quality substantially improved in London through the following decades.
What’s it like now?
Air pollution remains at hazardous levels in London.
The city recently introduced an Ultra Low Emission Zone, which charges drivers of more polluting vehicles. London City Hall said in October that toxic air pollution had dropped by a third in the six months since the measure came into place.
But the UK capital still has some of the highest pollution levels in Europe. Particulate matter and nitrogen dioxide remain the greatest concern, and thousands are thought to die prematurely every year because of pollutants in the air.