BEIJING -?The density of PM2.5, fine particulate matter causing smog, decreased in Beijing by 12.5 percent year on year in January to August, the local environment watchdog said Monday.

The average PM2.5 reading in the first eight months was 63 micrograms per cubic meter, the city's environmental protection bureau said.

Meanwhile, the density of PM10, sulfur dioxide and nitrogen dioxide dropped 17.3 percent, 26.7 percent and 8.9 percent, respectively.

Beijing is aiming to keep average PM2.5 levels 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 released by the Chinese Academy of Engineering in July stressed that Beijing faces an arduous task to meet the 2017 goal, which will require tougher controls on pollutant emissions and better coordination with neighboring regions.

Beijing will encourage farmers in the suburbs to replace coal stoves with electric and gas, the bureau said.

Meanwhile, the city will ban old cars and encourage more people to buy electric cars. Authorities said they have installed air purifiers. which trap pollutants, on 3,600 new buses and trucks this year, helping reduce nitrogen oxide emissions by 60 percent.