Beijing has seen the density of PM2.5 drop by about 12 percent year-on-year to 51 micrograms per cubic meter in 2018, said Beijing's environmental watchdog on Friday. 

The measurements for other major air pollutants have also decreased. The concentration of sulfur dioxide reached 6 mg/cu m, decreasing by 25 percent from 2017. The density of PM10 also decreased by about 7 percent and reached 78 mg/cu m, according to the Beijing Municipal Bureau of Ecology and Environment. 

It also said the measurements for these major air pollutants were higher in the southern part than the northern part of the capital. The city's downtown and southern areas were found to have higher densities of nitrogen dioxide. 

The southwestern part of Beijing was the area most heavily polluted with PM2.5 in 2018 with an average density of 69 mg/cu m. The northeastern area saw the lowest average PM2.5 density of 41 mg/cu m. 

The bureau also said that Beijing has seen a decrease in the number of days with heavy pollution. The number of days with heavy air pollution stood at 58 in 2013, and this number went down to only 15 days in 2018. 

The past year also saw 195 consecutive days without heavy PM2.5 pollution — 108 days more than that in 2013.