'World's biggest air purifier' is improving China's air, scientist says

Author: Lynsey Free

A massive tower dubbed the "world's biggest air purifier" has improved air quality in China’s Xian, according to the scientist leading the experimental project. The "encouraging" result comes as the country continues to struggle with crippling smog.

Xian. PurpleImages

The construction of the tower, which measures over 100 meters (328 feet), started in the city of Xian, Shaanxi province in 2015 and was finished last year. The project was aimed at developing a successful, low-cost way to remove pollutants from the atmosphere.

Its placement in Xian was strategic, as industrial coal burning has left the historic city with dangerously polluted air. That could be changing, however, if preliminary results are anything to go by.

Cao Junji, who leads a team of researchers at the Institute of Earth Environment at the Chinese Academy of Scientists, said improvements in air quality have been measured over an area of 10 square kilometers (3.86 square miles) in Xian over the past few months.

The tower has managed to produce more than 10 million cubic meters (353 million cubic feet) of clean air each day since it was installed. Even on extremely polluted days, it was able to reduce smog to moderate levels, Cao told the  South China Morning Post. On average, levels of PM2.5 – the smallest and most harmful particles in the air – fell 15 percent during heavy pollution.

The reported success of the "world's biggest air purifier" is owed to greenhouses which cover about half the size of a football field around the base of the tower. Polluted air is sucked into the greenhouses and heated up by solar energy. From there, the hot air rises through the tower and passes through numerous layers of cleaning filters.

As if air purification wasn't enough, the tower also boasts another great feature – it requires very little power to run. "It barely requires any power input throughout daylight hours. The idea has worked very well in the test run,” Cao said.

The results – deemed "encouraging" by Cao – aren't just apparent to the researchers behind the project. Xian's citizens have noticed a positive change too, the South China Morning Post reports.

Meanwhile, monitoring of the tower's performance will continue for Cao and his team, who have set up more than a dozen pollution monitoring stations in the area. The researchers plan to release more detailed data in March, which will include a full scientific assessment of the tower's overall performance.

If all goes well, such towers could become commonplace in Chinese cities, with Cao and his colleagues ultimately hoping to build much bigger towers across the country.

A full-sized tower would measure 500 meters (1,640 feet) tall and have a diameter of 200 meters (656 feet), according to a patent application filed in 2014. The size of the greenhouses would also expand to cover nearly 30 square kilometers (11.6 square miles), and each installed system would have the capability of purifying air for a small sized city.

Such towers could be a game changer for notoriously smog-plagued China. While the country's pollution has been blamed on a number of factors, coal burning has been linked to the most premature deaths – 366,000 in 2013, according to a study published in 2016. Other culprits include China's rapid and unrestricted growth over the course of a few decades, and the lack of green technologies to handle it.

The country announced a "war on pollution" in 2014, which included detaining people and imposing fines. However, enforcement has been a challenge, with the Ministry of Environmental Protection (MEP) stating this week that officials in the cities of Xinyu, Jiangxi province, and Xinyang, Henan province, had tried to reduce emissions readings by spraying water on their air quality sensors. Officials in Xian were also found to be stuffing sensors with cotton and removing surveillance tapes. 

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