A staff member checks the air filtration system as pupils have PE inside a specially-built dome for athletic activities at Yuxing Campus of Huaxing Primary School in Shijiazhuang, capital of north China's Hebei Province, Jan. 4, 2017. The dome, which is pressurized, has built-in filtration systems. Heavy smog continued to shroud north China on Wednesday. (Xinhua/Wang Xiao)
