The smog is so bad even the statues wear masks. Or at least they do in photos of a campus stunt circulating online as parts of northern China suffered a sixth straight day of severe pollution.

A Peking University student placed the masks on statues of Spanish novelist Miguel de Cervantes, Communist Party co-founder Li Dazhao and a sage practicing tai chi.

Hazardous white pollution hid much of Beijing's skyline Tuesday, despite announced closures or production cuts at 147 of the city's industrial plants.

The National Meteorological Center said readings of particulate matter known as PM2.5, a key measure of pollution, reached 444 micrograms per cubic meter in central Beijing. WHO considers 25 micrograms a safe level.