Despite a rise in the number of automobiles, China has experienced a slight decrease in the amounts of four major air pollutants emitted by vehicles last year, according to an annual report from the Ministry of Ecology and Environment.

Following growth of 6.2 percent from 2020, the number of motor vehicles nationwide hit 395 million last year, according to the report on mobile emission source management, which was unveiled on Wednesday.

It's the third straight year China has experienced an annual increase of over 6 percent in car numbers.

The vehicles emitted a total of 15.6 million metric tons of carbon monoxide, hydrocarbon, nitrogen oxides and particulate matter in 2021, compared with 15.9 million tons in 2020.

The decrease is the result of as "significant progress" on a series of actions to strengthen the management of emissions from mobile sources, according to a media release from the ministry.

Many regions, for example, rolled out measures to promote adjustments to transportation, improvements to oil quality and enhancement of the management of mobile emission sources, it said.