BEIJING, July 15 -- Beijing saw the density of PM2.5, fine particulate matter causing smog, decrease by 17.9 percent in the first half of 2016 year on year, the local environment watchdog said on Friday.

The capital enjoyed 107 days with sound air quality during the six months, 19 more than in the same period last year, according to the city's environmental protection bureau.

The density of other pollutants PM10, sulfur dioxide and nitrogen dioxide dropped 19.3 percent, 27.8 percent and 12 percent respectively.

Beijing is aiming to keep the average level of PM2.5 below 60 micrograms per cubic meter in 2017. In 2015, the level was 80.6 micrograms, down from 95.7 micrograms in 2012.

A report by the Chinese Academy of Engineering earlier this month said Beijing faces an arduous task to meet the 2017 goal, which requires tougher controls on pollutant emissions and better coordination with neighboring regions.