A Chinese environmental official Thursday urged hastening the national elimination of high-emission vehicles to help curb urban air pollution.

"The automobile emissions have become main sources of air pollution in Chinese large and medium-sized cities," said Li Xinmin, an official with the Ministry of Environmental Protection.

"High-emission cars and trucks only make up 28 percent of all automobiles in China, but they are responsible for 75 percent of the pollutant emissions," Li said.

Automobiles which fail to meet the National Emission Standard I are listed as high-emission vehicles in China.

The Standard I, equivalent to the Euro I standard, allows an average petrol sedan to emit a maximum of 2.7 grams of carbon monoxide a kilometer among other exhausts, whereas Standard IV requires less than 1 gram of carbon monoxide and 0.08 gram of nitrogen oxide per kilometer.

China introduced Standards I, II and III respectively in 2000, 2005, and 2007. Standard IV is scheduled to be adopted nationwide in 2010.

The pollutant amount discharged by a high-emission vehicle is 30 times as much as a Standard IV automobile, according to Li.

"We encourage local governments to increase financial support in eliminating high-emission vehicles, especially in big cities like Beijing and Shanghai. It's good for reducing air pollution and introducing more automobiles of low pollution," Li said.

China had more than 64 million automobiles by the end of 2008, among which 18 million were high-emission vehicles.

The ministry has built an online inquiry system for the public to check whether a certain automobile belongs to the high-emission category, according to Li.

Urban air pollution has been a growing concern for governments at all levels as the number of automobiles rises in cities and towns all over the country, and big cities turn to different ways to lower vehicle exhaust emissions.

During the Olympics and Paralympics last year, Beijing limited the use of most vehicles through an odd-even license plate system. The initiative took 45 percent of the cars off the roads and helped keep skies clean.

In April, the city implemented a new restriction, also based on license plates, which forces a fifth of privately-owned vehicles off the roads each week day.