The quality of the air in China's urban areas is notoriously poor. And while the country did cut air pollution levels by 4.5 percent last year, this marked the smallest decline since 2013. To help combat the problem, a 328-foot air purification tower, supposedly the biggest in the world, has been built in Xian, in the Shaanxi province of northern China.

As much of Xian's heating relies on coal, the city experiences heavy pollution during the winter months. But one of the scientists working on the tower said it has already resulted in a noticeable improvement in the air quality over an area of 10 square kilometers (3.86 miles), according to the South China Morning Post.

Scientists at the Institute of Earth Environment at the Chinese Academy of Sciences continue to test the tower. The head of research, Cao Junji, said it had produced over 353 million cubic feet of clean air every day since it launched a few months ago.

The system uses the greenhouses around the base of the construction; these suck up the polluted air, which is then heated by solar energy. The hot air rises through the tower and passes through multiple cleaning filters on its way up, before the final, clean result is pumped out the top.

"The tower has no peer in terms of size [...] the results are quite encouraging," said Cao.

The last large smog tower in China ran on electricity powered by coal-fired plants, which defeated its purpose slightly, but the one in Xian requires little power to run. "It barely requires any power input throughout daylight hours. The idea has worked very well in the test run," added Cao.

As large as it is, the tower will be dwarfed by those that Cao and his team aim to build in other Chinese cities. According to a patent they filed in 2014, the full-sized versions will reach 1640 feet into the air, have a 656 diameter, and the greenhouses will cover an area of 11.6 miles.

Image credit: South China Morning Post