This latest effort, led by Beijing Municipal Environmental Protection Bureau, means that the buses will discharge 60 per cent less nitrogen oxide, or 2,800 tons, annually, state-run Xinhua news agency reported.
The project follows standards on automobiles and their emissions, released by the city in 2013, that aimed to address loopholes in diesel vessel standards.
Observers and officials say vehicles are a major contributor to Beijing's air pollution.
The city has 5.57 million vehicles, which churn out 700,000 tons of pollutants annually.
