What has been called the world’s largest air purifier by its operators is now up and running in the Chinese city of Xian in Shaanxi province. The 100-meter (328 feet) tall tower has already improved the local air quality, lead scientist Cao Junji told the South China Morning Post, adding that it could prove to be a valuable tool in the country’s fight against urban air pollution. “The tower has no peer in terms of size … the results are quite encouraging,” he said. Greenhouses covering the size of half a soccer field surround the base of the tower, into which polluted air is pulled. The smog is heated in the greenhouse by solar energy, then rises through the tower, passing through several layers of cleaning filters.
Because Xian largely relies on coal for heating, smog can become exceptionally thick and harmful during the cold months. Despite the lower level of solar energy available during the winter, a special coating on the tower’s greenhouses allows it to absorb what is available more efficiently and continue to pull smog all year long. To determine the tower’s impact on local air quality, Cao and his team erected over a dozen monitoring stations. The team found that the average reduction in PM2.5, the most harmful particles in smog, was 15 percent during times of heavy pollution.
Cao stresses that the results are only initial while further details will be released in the spring. A comprehensive scientific assessment of the tower’s effectiveness is also forthcoming. Nonetheless, what is known is promising. While there have been other similar smog-removing towers, many of which were powered by coal-fueled electricity, the Xian tower is unique in its very limited electricity needs. “It barely requires any power input throughout daylight hours. The idea has worked very well in the test run,” said Cao. While locals have marveled at the tower’s size, it is in fact a miniature version of smog-removing towers that Cao and his team hope to install throughout China’s dense, massive cities. The full-size version could reach as high as 500 meters (1,640 feet) while the surrounding greenhouses could cover nearly 30 square kilometers (11.6 square miles).