The Ministry of Environmental Protection has signed "responsibility pledges" with 31 municipalities, provinces, and autonomous regions to achieve air pollution reduction targets by 2017, according to an announcement published on the ministry's website on Tuesday.

The pledges came after the government's release on Sept 12 of an action plan to combat air pollution nationwide. The plan sets tough targets in key regions for the reduction of fine particles, known as PM2.5, and inhalable particles, known as PM10.

"The pledges feature differentiated targets to reduce PM2.5 and PM10 levels, and also detail measures to be adopted by local governments to complete the tasks," said Wang Jian, deputy head of the ministry's Pollution Prevention and Control Department, in an interview in September when the first batch of pledges were signed by regions from the most polluted Beijing-Tianjin-Hebei cluster.

Reduction targets for the annual concentration of PM2.5 ranged from 10 percent for the Inner Mongolia autonomous region to 25 percent each for Beijing, Tianjin and Hebei province.

Eleven regions out of a total 31 will be evaluated based on reductions of PM2.5, while the performance of 20 other regions will be weighed by reductions in PM10.

Hainan province, the Tibet autonomous region and Yunnan province, where the air quality is already much better than the national standard, received no specific requirements to bring down local PM10 levels as long as they keep going down.

PM10 reduction targets for other regions varied from 5 percent to 15 percent.

Detailed measures that were to meet the pledge targets include control of coal consumption and cutbacks in steel production, the announcement said.

The central government will issue evaluation criteria that connect local government officials' achievement of the targets to their political futures, the announcement said.