The prestigious science publication Nature published a study that tested the air of Beijing, Xi’an, Shanghai, and Guangzhou to find out exactly what PM2.5 is made out of. They found that about 20% were chemicals like ammonium and chloride. Coal made up about 4% of PM2.5 in the different cities.
From that composition, the researchers could estimate where the particulate comes from. Pollution from vehicles (red) contributed to 6% of the PM2.5 in Beijing’s air, and under 10% in all cities.
These results fit with what researchers found after Delhi temporarily banned half of the city’s cars from its roads. PM2.5 fell by about 10%. It helped Delhi’s air, but was far from solving the problem. Instead, power plants, factories, and construction account for more pollution than cars.
How much would banning cars help Beijing? In 2017, Beijing averaged 58 micrograms of PM2.5. If we removed all the vehicles from Beijing, the PM2.5 in the air would decrease by about 6%, leaving us at 54 micrograms. That’s better, but it’s still far above the WHO 24-hour limit of 25 micrograms.
Bottom line: Banning cars would help reduce pollution in China’s major cities, but they are not the biggest source of pollution.
Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.