A resident walks down a bridge over the Songhua River on Monday in Jilin, Northeast China’s Jilin province.

A resident walks across Jilin bridge obscured by smog.

Smog blankets the sky over the centuries-old Bell Tower in Xi’an, Northwest China’s Shaanxi province.

A resident walks across a Xi’an footbridge on a polluted day.

Smog clouds the horizon in Dalian, Northeast China’s Liaoning province.

Smog covers the Forbidden City in Beijing.

Visitors stroll around in the Forbidden City on Sunday, after Beijing issued a yellow alert for air pollution, the third-most severe warning on a tiered scale.

A visitor wears an anti-pollution mask in the Forbidden City.