Car emissions have replaced coal burning to become the leading contributor of PM2.5 particles in Beijing, according to a study released by Beijing's environment watchdog on May 14.
The new findings come as Beijing is encouraging the use of natural gas instead of coal for winter heating and shutting down polluting smokestack factories.
Emissions from vehicles, ships, and construction machinery are the top sources of PM2.5, contributing as much as 45 percent of the total PM2.5 in Beijing, according to the study by Beijing Municipal Environmental Protection Bureau.
Beijing has the highest level of car ownership in the country, with 5.64 million privately owned cars at the end of 2017. The city has cut the number of license plates issued annually from 240,000 in 2013 to 100,000 in 2017.
However, despite reports that vehicles and dusts are contributing a higher percentage of pollutants than before, figures of pollutants from these major sources of pollution show an overall decline.
The study also shows that Beijing's surrounding regions contributed to approximately one-third of pollutants in the city on average, and to 55 to 75 percent during heavily polluted days when the air quality index (AQI) exceeded 200 in the city.
Air samples were gathered daily in 11 different locations around Beijing, and more than 300,000 sets of data were analyzed, said Liu Baoxian, deputy director of Beijing Municipal Environmental Protection Monitoring Center, a subsidiary of Beijing Municipal Environmental Protection Bureau.
The level of PM2.5 in Beijing has dropped to its lowest level since 2013 when the national air pollution control campaign began. Across the country, average PM2.5 density in 338 cities fell by 6.5 percent in 2017.
The study suggests that the city should shift focus to diesel vehicles, dust and volatile organic compounds, while enhancing regional pollution control.