China builds ‘world’s biggest air purifier’


An experimental tower over 100 metres (328 feet) high in northern China – dubbed the world’s biggest air purifier by its operators – has brought a noticeable improvement in air quality, according to the scientist leading the project, as authorities seek ways to tackle the nation’s chronic smog problem.





The tower has been built in Xian in Shaanxi province and is undergoing testing by researchers at the Institute of Earth Environment at the Chinese Academy of Sciences.

The head of the research, Cao Junji, said improvements in air quality had been observed over an area of 10 square kilometres (3.86 square miles) in the city over the past few months and the tower has managed to produce more than 10 million cubic metres (353 million cubic feet) of clean air a day since its launch. Cao added that on severely polluted days the tower was able to reduce smog close to moderate levels.


The system works through greenhouses covering about half the size of a soccer field around the base of the tower.

Polluted air is sucked into the glasshouses and heated up by solar energy. The hot air then rises through the tower and passes through multiple layers of cleaning filters.

Xian can experience heavy pollution in winter, with much of the city’s heating relying on coal.
The tower’s operators say, however, that the system still works in the cold months as coatings on the greenhouses enable the glass to absorb solar radiation at a much higher efficiency.
Cao’s team set up more than a dozen pollution monitoring stations in the area to test the tower’s impact.
The average reduction in PM2.5 – the fine particles in smog deemed most harmful to health – fell 15 per cent during heavy pollution.

The seven-metre (23-feet) tall tower produced about eight cubic metres (282.5 cubic feet) of clean air per second. It was entirely powered by electricity, most of which is generated by coal-fired power plants in China.
However, a teacher at the Meilun Tiancheng Kindergarten on the edge of the 10-square-kilometre (3.86-square-mile) zone said she had felt no change. “It’s just as bad as elsewhere,” she said.
The experimental facility in Xian is a scaled-down version of a much bigger smog tower that Cao and his colleagues hope to build in other cities in China in the future.
A full-sized tower would reach 500 metres (1,640 feet) high with a diameter of 200 metres (656 feet), according to a patent application they filed in 2014.
The size of the greenhouses could cover nearly 30 square kilometres (11.6 square miles) and the plant would be powerful enough to purify the air for a small sized city.

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