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An air-purifying device shaped like a bus stop has been installed at Tsinghua University in Beijing as part of a pilot trial.

The device was tested for four months in downtown Hong Kong before being moved to Beijing on Wednesday. It can get rid of 30 to 70 percent of PM2.5 (airborne particles smaller than 2.5 microns in diameter) and PM10 in the air, depending on the severity of real-time air pollution.

On its first day in Beijing, the device reduced the PM2.5 density around it to 1 microgram per cubic meter, considerably lower than the 20 micrograms per cubic meter present in the area.

It took seven months and more than 600,000 HKD (about $77,400) to develop the device, which serves not only as an air purifier, but also as a bus stop. Experts say the construction cost would be significantly lower if air purifying systems were added to existing bus stops instead of building new ones.

The air purifying system allows air to enter the device at the bottom and exit at the top. As the air travels through the bus stop, air purifying structures in the middle remove much of the pollution.

Thanks to hydromechanics, the device also maintains positive air pressure over its surroundings, extending a "shield" of clean air to protect whoever stands within it.

If this version of the "oxygen bar" performs well in its trial run, future versions will be tested in other crowded areas in Beijing.