Take a big breath

Xi’an’s fresh approach

At first glance, the new, white tower on the edge of Xi’an looks like it could be a source of pollution. It’s tall, cylindrical and resembles a traditional smokestack or giant cigarette.

But its appearance could not be more misleading. This is not another chimney adding to the northern city’s already terrible air.

It is in fact a large, powerful filter, capable of clearing smog for several kilometres in each direction.

The type of structure is known as a Large Solar Urban Air Cleaning System (HSALSCS) and they are currently in the test phase. Initial results look good. One of the project’s creators Cao Junji, from the Chinese Academy of Sciences recently told the South China Morning Post that the giant apparatus was able to purify air over an area of 10 square kilometres. “On severely polluted days the tower was able to reduce smog close to moderate levels,” the SCMP reported.

At 100 metres tall and 10 metres wide, the HSALSCS (we know, it’s not catchy) is thought to be the largest air purifier in the world.

In October 2016, Dutch designer Daan Roosegaarde created what was then thought to be the largest air filter – a seven-metre-high structure placed in Beijing’s 798 art district. That produced about eight cubic metres of clean air per second but was entirely powered by electricity, which in China is largely produced by the burning of highly-polluting coal.

By contrast the HSALSCS produces 115 cubic metres of clean air per second and uses only solar energy.

It works by sucking air into greenhouses at its base, heating the air up and forcing it through the “chimney” via a series of filters. Early results suggest the tower can, on average, remove 15% of PM 2.5 molecules – the fine particles in airborne pollution that are categorised as most harmful to human health.

Importantly the solar panels at the base of the tower also work in winter when China’s smog is often at its worst.

People living near to the existing tower said they could feel it’s positive effect. They were also surprised by how quiet it was. “I can’t hear any wind going in or out,” one person told the SCMP. “The air quality did improve. I have no doubt about that.”

Final result from the trial will be released in March. In the wake of these, Chinese media said the giant towers could be rolled out nationwide to contain smog.

Just to boggle your mind further, these things can be much bigger. According to a patent application that was filed in 2014, a full-size HSALSCS could be five times taller and 20 times wider…

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