Preliminary results suggest it has already helped reduce smog levels in Xian
A 100m-high cylindrical tower built in Xian, the capital of China’s central Shaanxi province, is considered to be the world’s biggest air purifier. It sucks in polluted air and funnels it into greenhouses at the base of the structure, which heat the air before it is filtered and vented. Although still under testing by researchers at the Institute of Earth Environment at the Chinese Academy of Sciences, the first indications show it has helped reduce smog levels in the city, resulting to a noticeable improvement in air quality. The idea for this massive air purifier was put forward by the academy in 2015, as an effective, low cost method to tackle air pollution and its construction was completed two years later.
More than a dozen pollution monitoring stations have been set up in the area to test the tower’s impact. According to Cao Junji, head of the research, improvements in air quality had been observed over an area of 10 km2 (3.86 mi2) in the city over the past few months and the tower has managed to produce more than 10 million m3 (353 million ft3) of clean air a day since its launch. Although these results are preliminary because the experiment is still ongoing, it is interesting that on severely polluted days, the tower was able to reduce smog close to moderate levels (the expelled air now contains 15% less fine particles (PM2.5) than it did before being scrubbed). “The tower has no peer in terms of size … the results are quite encouraging,” said Cao, while the team plans to release more detailed data in March with a full scientific assessment of the facility’s overall performance.
Apart from the cylindrical tower, there is also a large network of greenhouses at its base, covering about half the size of a soccer field, from where the polluted air enters. There, it is heated up by trapped solar energy, causing it to rise and move upwards, passing through multiple layers of cleaning filters. Because the greenhouses are powered by solar radiation which is readily available throughout the year, the system requires little power to run. “It barely requires any power input throughout daylight hours. The idea has worked very well in the test run,” Cao said.
Several residents have noticed the difference since the tower started operating. A manager at a restaurant about 1km (0.62 miles) northwest of the facility said she had noticed an improvement in air quality this winter, although she was previously unaware of the purpose of the tower. “I do feel better,” she said. A student studying environmental science at Shaanxi Normal University, also a few hundred metres from the tower, said the improvement was quite noticeable. “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,” she said. “The air quality did improve. I have no doubt about that.”
However, the notion that its operation has brought a noticeable improvement in the city’s air quality is not accepted by all. For example, a teacher at the Meilun Tiancheng Kindergarten on the edge of the 10-km2 (3.86-mi2) zone said she had felt no change. “It’s just as bad as elsewhere,” she said.
The previously considered largest smog tower was a 7m-tall one, built by Dutch artist Daan Roosegaarde. Able to produce about 8 m3 (282.5 ft3) of clean air per second, it can run either on wind or solar energy. If the project proves successful, the Chinese Academy of Sciences plans to build much bigger smog towers in other Chinese cities in the future. A full-sized tower would be 500m-high (1,640 feet) and 200m wide (656 feet), according to a patent application Cao and his colleagues filed in 2014, with greenhouses covering nearly 30 km2 (11.6 mi2). These gigantic towers would be powerful enough to purify the air for a small city.
The tower pictured while under construction in Xian.
The top of the tower pictured during building work.
Source: South China Morning Post