Cao Junji, Chinese Academy of Sciences, Laboratory of Aerosol Chemistry and Physics. Xian, China, and colleagues are testing a 60-meter-high chimney that filters air in Xian, one of China’s most polluted cities, as part of a pilot project. The concrete chimney sits on top of a large open structure with a glass roof. Solar radiation heats the air underneath the glass, it rises towards the base of the tower, and then passes through filters before leaving the top of the chimney.

The US$ 2 million prototype filters between 5 and 8 million m³ air a day. PM_2.5 concentrations were 19 % lower compared to other parts of the city. According to the researchers, half a dozen larger chimneys need to be distributed around urban centers to reduce air pollution significantly. The running costs of the pilot project are estimated to be about US$ 30,000 a year.

The researchers are preparing their results for publication, have submitted a proposal for a 300-meter tower in Xian, and are negotiating proposals for the towns Guangzhou, Hebei, and Henan.

• China tests giant air cleaner to combat smog,
  David Cyranoski,
  Nature 2018, 555, 152–153.