The Ministry of Environmental Protection published an air quality report for 2016 on Friday, saying the density of main pollutants dropped compared to that of 2015, but the air pollution in winter in the northern parts of China is still serious.

All of the top ten cities with the worst air quality are in northern China, with six of them located in Hebei province.

The ten cities with the best air quality are found in the south, southwest, and on the east coast of the country.

In general, the country's air quality in 2016 improved year-on-year. Among 338 cities at prefecture level and above, 84 cities' air quality reached the national standard, 11 more than that in 2015. 78.8% of days had good air quality, 2.1 percentage points higher than the year before.

The annual average density of PM2.5, particulate measuring less than 2.5 microns, fell by 6%, reaching 47 micrograms per cubic meter. Severely polluted days accounted for 2.6% of the year, down 0.6 percentage-points year-on-year.

In the heavy polluted northern part of China, the air quality from March to October is much better than it is in winter. Since November 15th, when the Beijing-Tianjin-Hebei region generally started its heating season, the PM2.5 index has surged to an average of 135, 2.4 times that of the non-heating period.