In addition to regular controls on production and vehicle use, some cities have tightened restrictions to reduce emissions of airborne pollutants.

In 10 cities in Shanxi province, including the provincial capital Taiyuan, all plants in mining, sand excavation, processing of stones and asphalt mixing industries were required to suspend production from Dec 1 to 4.

In Langfang, Hebei province, all casting factories and cement-making plants (except those providing heating services for residential communities) are required to suspend production in December.

In Shijiazhuang, capital of Hebei, all pharmaceutical plants have been required to halt their operations since Nov 18, a measure that will last until the end of this year. In addition, another seven industries, including steel and iron, cement and glass making, have also had production suspended until Dec 31.