China has built the world’s largest air purifier in a bid to fight the country’s smog problem.
The 100m (328ft) tower in the city of Xian in central China’s Shaanxi province can filter 353 million cubic feet (10 million cubic metres) of air per day and is already said to have improved local air quality.
Even bigger towers are reportedly being planned around the country, with researchers saying towers as tall as 500m are being mooted.
The move comes as China attempts to address its smog problem.
The purifier works by sucking air into vast greenhouses the size of half a football pitch at the tower’s base.
The polluted air is heated by the sun, causing it to expand and forcing it up through the filters in the tower.
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The giant filter’s performance is being monitored by experts from the Chinese Academy of Sciences’ Institute of Earth Environment.
Research leader Cao Junji said it had improved air purity in a six-square-mile area, filtering 353 million cubic feet (10 million cubic metres) of air per day over the past few months, but on bad days it can only reduce the pollution from “severe” to “moderate”.
Cao said: “The tower has no peer in terms of size. The results are quite encouraging. It barely requires any power input throughout daylight hours. The idea has worked very well in the test run.”
Cao said larger planned towers would have diameters of 200m (656ft), use greenhouses covering almost 12 square miles and would be able to purify the air over a whole city.
Some residents of the area reportedly told Chinese media they had noticed breathing had become easier.
An unnamed student was quoted as saying: “The air quality did improve. I have no doubt about that. I can’t help looking at the tower each time I pass. It’s very tall, very eye-catching, but it’s also very quiet. I can’t hear any wind going in or out.”