BEIJING - A total of 12,500 cars registered outside Beijing that violated pollution standards have been barred from the city following the launch, on Feb 9, of a campaign to monitor vehicle exhaust emissions, the city’s environment watchdog said on Tuesday.

The campaign is part of the city’s efforts to reduce PM 2.5, particulate matter smaller than 2.5 micrometers in diameter, a major component of smog.

“Car exhaust contributed 22.2 percent to the city’s PM 2.5 reading, as vehicles hit five million on Beijing’s roads,” Yao Hui, an official with the Beijing Municipal Environmental Protection Bureau, said.