Beijing residents wear masks to combat the smog on December 8.
Under the citys first-ever red alert， which was in effect from December 8 to 10， the authorities advised kindergartens， primary and high schools to suspend classes， shut down construction sites and required some industrial plants to limit or stop production， among other measures.
The red alert is the highest in Beijings four-tier emergency response system to be implemented when pollution levels hit a certain point.
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