Northern China's Shanxi province, a major coal-producing area, has vowed to reduce annual average PM2.5 density by 20 percent by 2020, the provincial government said Saturday.

Aiming to increase the proportion of days with good air quality to 75.4 percent per year, the province will create a pollutant discharge license system covering all polluting enterprises.

The expansion of industrial capacity will also be strictly restricted to control air pollution. No new projects in major polluting industries, such as coal, steel, cement and plate glass, will be approved.

Some major industries will undergo improvements to become more environmentally friendly. By the end of 2017, all 300,000-kW and above coal-fired units will be upgraded to lower emission.