How To Filter Out Smog

The outdoor air purifying system chimney — Inside a chimney that releases filtered air, function of a airplane pilot projection to reduce smog in Xi'an, Communist china. Credit: David Cyranoski/Nature

A lx-metre-high chimney stands amidst a sea of loftier-rise buildings in one of China'due south most polluted cities. But instead of adding to Xian's smog, this chimney is helping to clear the air. The outdoor air-purifying arrangement, powered by the Sun, filters out baneful particles and billows clean air into the skies. Chinese scientists who designed the prototype say that the system could significantly cut pollution in urban areas in China and elsewhere.

The technology has excited and intrigued researchers — especially in China, where air pollution is a daily challenge. Early on results, which are nonetheless to be published, are promising, says the project'southward leader Cao Junji, a chemist at the Chinese Academy of Sciences' Key Laboratory of Aerosol Chemical science and Physics in Xian in central China.

"This is certainly a very interesting idea," says Donald Wuebbles, an atmospheric scientist at the University of Illinois at Urbana-Champaign, who has heard about the system but not seen information technology in activeness. "I am not aware of anyone else doing a project like this one."

The epitome, built with The states$ 2 one thousand thousand in funding from the provincial regime, has also caught the attention of the president of the Chinese University of Sciences, Bai Chunli, who visited the site final month. Cao says Chinese leaders are eager for innovative solutions to air pollution because it creates such a widespread public-health problem. The Global Burden of Affliction Study for 2015, a comprehensive effort to map the world's diseases, institute that pollution contributed to one.1 million premature deaths in People's republic of china in that yr alone.

Cao has submitted a proposal for another 300-metre tower in Xian. He is also negotiating proposals with cities in Guangzhou, Hebei and Henan.

But the technology has its sceptics, who say that there are much cheaper ways to reduce air pollution.

Stack consequence

The physical chimney sits atop a large open up structure with a glass roof. Solar radiation hitting the glass heats the air, causing it to rise towards the base of operations of the belfry. The air then passes through a wall of industrial filters before billowing out the chimney. The organisation is inspired past renewable-energy ability plants that generate electricity from solar heat.

"This is a very well-designed and well-made prototype," says Renaud de Richter, a chemical engineer at Ecole Nationale Supérieure de Chimie de Montpellier, who has worked on solar-energy towers. Richter says Cao's success could assistance to convince investors to support other applications based on the flow of solar-powered air through chimneys, a technology known as solar updraft.

Pollution peaks during winter and Cao chose this time to conduct his starting time exam of the systems' air filters over two weeks in Jan. At the tower and at 10 monitoring stations beyond a 10 square-kilometre area, he placed monitors that measured particulate thing under 2.v micrometres in diameter (PM2.5), a type of pollution that has plagued Chinese cities.

Cao found that the tower expels between 5 million and 8 million cubic metres of filtered air a day in winter. During the written report period, the surrounding air monitors registered a 19% decrease in PM2.five concentrations compared with monitors in other parts of the city. Cao is preparing the results for peer review.

Cao says the image's bear on was local, so he proposes creating arrays of about half a dozen larger chimneys distributed around urban centres. He has besides designed a 500-metre-alpine tower. "The influence of one system is small. We need multiple systems and so that significant reduction of air pollution concentration can exist achieved," he says.

Cheaper alternatives

Neil Donahue, who studies atmospheric particles at Carnegie Mellon Academy in Pittsburgh, Pennsylvania, says in that location is little doubt that pulling a large volume of air through high-efficiency particulate filters volition clean it. But Donahue wonders whether the benefits will exist worth the ecology damage caused by building and running such facilities. "I would like to see an cess of the power and resource use for the filtration," he says. Turning the aforementioned amount of power into clean electricity, or not emitting the pollution in the showtime place, might achieve the same goal of reducing pollution, says Donahue.

Wuebbles as well worries that the chimney would filter only particulate matter and non precursors to particulate thing, such as sulfur dioxide gas and nitrogen oxides, which are likewise dangerous to human health, or secondary gaseous pollutants such equally ozone. "So while the sky may expect cleaner, the air quality can still be really atrocious," he says.

Cao says that the system already removes nitrogen oxides, one of the major precursors in the formation of ultra-fine particles and ozone. He besides says that concerns about the economics are overblown. He estimates the running costs of the pilot projection to be about $30,000 a year.

Despite some reservations, researchers — such as atmospheric scientist Jose Jimenez, at the Academy of Colorado Boulder — see an advantage in pursuing the applied science. "I'd definitely say it is worth exploring it more, though I am not convinced either style at this point," he says.