One group of scientists on the south side of Xi’an are fighting back against Xi’an’s rising PM2.5, and they did so in true China style — by building something big, a huge air purifier tower to be precise. But locals are left to wonder, does it actually work?
That makes Xi’an China’s current PM2.5 “champion” (among major cities) and a bad place to be an air-breather.
Prior failures give reason to be pessimistic
This isn’t the first project in China to create a huge air purifier to try to purify outdoor air. Dutch artist Daan Roosegaarde built an ionizing tower in Beijing and Tianjin, claiming it would clean air the air pollution outdoors.
Yet independent tests of the air filter tower found it was not providing clean air even within 10 meters of the tower. Even a careful look at the team’s own modeling estimated only a 20% drop among large particles (PM10, not PM2.5), assuming zero wind, and only up to 20 meters from the tower. Thus, the tower is more art than science.
Is the Xi’an Tower Just as Much Smoke and Mirrors?
Given the Dutch artist’s failure, Xi’an residents can be forgiven for being skeptical. However, the Xi’an tower works completely differently from the artist’s towers.
First, the sun heats up the air inside a large greenhouse. Next, that warm air rises through a chimney and passes through huge air filters. Reports don’t say what type of filters those are.
So does it work? Without data, we can only make an educated guess.
Pro: The tower uses a different process from earlier failed towers and doesn’t use ionization (the science behind why ionizers are largely ineffective).
Con #1: Greenhouses work the best when the sun is strong. Smog is worst in Xi’an in the winter, when the sun is the weakest.
Con #2: The tower would have to move a LOT of air to have any noticeable impact. The team claims the massive air purifier tower cleans 10 million cubic meters a day. That’s a big number, but the team is analyzing a 10 square kilometer area. Even at the smallest air mixing height of 100 meters, the tower would have to clean 1 billion cubic meters of air. Thus, the tower would be cleaning only 1/100th of the air. And that assumes the air doesn’t move or receive new pollution.
Bottom Line: Xi’an’s smog tower should work in principle, but rough calculations suggest it’s unlikely to have a major impact. We hope to see real-life test data.
Help Solve This Question and Collect Independent Test Data!
The data nerds at Smart Air would love to test the tower! Do you own a particle counter and live in Xi’an? If so, email Joseph at firstname.lastname@example.org, and we’ll coordinate tests, analyze the data, and publish the results.
Thomas is a new Assistant Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.