An inflatable membrane stadium is built in a school in Beijing on Dec.1, 2015. Its PM2.5 filter system can screen the air flowing inside and transfer the clean air into the pneumatic membrane through air-ducts. In addition, the air pressure in the membrane is greater than outdoor air pressure, which keeps the fine particles out of the door.
Thick smog persisted in Beijing and much of northern China on Tuesday. (Photo/CNS)
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