34 cities in north China have launched an orange alert for heavy air pollution. The second highest alert in the four-tier warning system is effective till Wednesday.

The Beijing-Tianjin-Hebei region and its surrounding areas are suffering the most. Many heavy chemical factories are located in that region, and experts from the national air pollution joint prevention and control centre said industrial emissions and cargo transportation discharge are among the main causes. With the end of the winter season, many industrial enterprises are resuming production. The Ministry of Ecology and Environment has urged relevant regions to enhance supervision to combat air pollution.