Beijing saw a total of 226 "good air" days in 2017, with 12 instances of warnings for severe air pollution covering 26 days, according to a statement released by city environmental authorities on Wednesday.

"Good air" days account for 62.1 percent of the year, 28 days more than last year and 50 more than five years ago.

The annual average concentration of PM2.5 is 58 micrograms per cubic meter, 35.6 percent down from the 2013 level. Compared with last year, the number of "severely polluted" days fell by 16 to 23, 35 fewer than the level five years ago.

Environmental law enforcement was also strengthened. 5,238 cases of stationary polluters were fined 187 million yuan ($29.4 million), increases of 78 percent and 32 percent respectively from the previous year.