Hebei Province has released revised emission standards for high-polluting industries in a move to improve air quality.

The stricter standards, which came into force on March 1, cover the province's key industries, including steel, cement and flat glass, and also apply to coal-burning boilers.

The requirements are even tougher than the national standards, and some have been drawn up in line with international standards.

Shijiazhuang, Tangshan, Baoding, Langfang, Xingtai, and Handan are listed as major targets, and factories in the cities will be strictly monitored.

"Air pollution is linked to pillar industries that discharge excessive emissions, such as steel production," Lyu Zhuqing, deputy director of Hebei's Environmental Protection Department, said on Thursday.

She said new factories will have to meet the standards before they are allowed to open. In addition, the new rules will force long-established companies to introduce desulphurization and denitration equipment.

A staff member at a scientific institution involved in environmental protection in Hebei told China Daily, on condition of anonymity, that most of the discharge standards for high-polluting industries meet international standards.

"Chinese factories have advanced technology to meet these standards," she added. The staff member helped to draw up the new standards.

However, some enterprises choose not to control pollutants so they can cut costs.

Lyu said installing desulphurization and denitration equipment greatly increases the amount of investment required, and added, "A large factory can spend up to 200 million yuan ($32.2 million) on these units."

She said the new requirements are compulsory.

"Factories will be forced to operate strictly in accordance with the standards."

Hebei has faced severe environmental problems in recent years, and is often shrouded in dense smog.

The province has made other moves to tackle the problem, including shutting down nearly 10,000 companies that produced pollutants last year.

It is working with Beijing and Tianjin to create a coordinated strategy to cut pollution.