Beijing needs to adopt a compulsory vehicle idling ban to combat the hazardous air pollution in the capital, a senior official said on Thursday.

"In public spots, such as areas surrounding hospitals, schools and shopping malls, the driver would only be allowed to have the engine on for three minutes, otherwise a penalty would be given," Li Kunsheng, an official in charge of vehicle emission management with the Beijing Municipal Environmental Protection Bureau, said at a public hearing on Thursday.

The hearing discussed a proposal that encourages drivers to turn their engines off after their cars have been idling for three minutes, with the nine delegates attending the meeting all supporting the proposal.

It says running engines while a vehicle is not moving is an "inefficient use of fuel" and results in the emission of gases that have a "negative effect on both air quality and public health".

According to a study conducted by Beijing Jiaotong University, the emissions of PM2.5 — tiny particulate matter considered the most harmful to health — is at least five times higher when idling than when moving at even speed.

Researchers found 1 million idling vehicles can emit 1,000 metric tons of particulate matter into the air every year, according to Li.

He said the proposal to encourage less idling is far from enough to tackle the smog problems in the capital, where 14 days in September were shrouded in smog, more than three times the average in the past two decades, but legislation would have a better effect within a short period.

Studies show that car exhaust is a major source of air pollution in big cities like Beijing, contributing about 22 percent of the fine particulate matters in the capital's air, according to the Ministry of Environmental Protection.

"Facing such severe air pollution, any measures cutting emission are worth a try," Li said.

Li Xiaoxi, a retired teacher of the Air Force Command College of the People's Liberation Army, strongly supported the legislation, while expressing worry about the enforcement of such a ban.

"It takes time from proposal to legislation and maybe we can start with government cars, which should set an example to private car owners," she suggested.

She said government cars always keep their engines running for hours, while waiting for officials or on patrol.

Zhou Ke, a law professor at the Renmin University of China, agreed that passing legislation is a long process, and suggested the ban should start with buses and taxis.

"We could draw up a vehicle idling ban regulation for professional drivers such as bus and taxi drivers first and integrate it into the training of new drivers. After a one-year promotion, the legislation will be easily accepted by the public," Zhou said.

However, some delegates didn't think a compulsory ban is feasible.

"Beijing has more than 5 million vehicles. It is almost impossible to calculate how many minutes a car's engine is on when not moving," said Xiao Yaping with the Beijing Automotive Research Institute.

Besides the difficulty of enforcement, Yang Yanqiu, a Beijing resident, had other concerns.

"What if there is a patient inside the vehicle in summer or winter —without air conditioning, his or her health might be endangered," Yang said, adding many other conditions must be considered.

Gao Peng from Jinyinjian taxi company said taxis with passengers inside should not obey such a ban.

Huang Fei, a Beijing resident who has been driving for decades, said constantly turning engines off and on may cause safety issues.

With all these suggestions, Li Xiaojuan, deputy director of the commission of legislative affairs under the Beijing Municipal People's Congress, said amendments will be made in the proposal, which is an item of a draft regulation on preventing and tackling Beijing's air pollution.

The draft regulation will be discussed in November for the third time and the final result will come out in January, Li said.

Beijing is not the first city to come up with such a proposal. Zhuhai, a city in Guangdong province, issued a car idling ban in 2009, ruling that drivers who do not turn their engines off in public spots such as hospitals and schools will receive a penalty of up to 200 yuan ($33).

Authorities in Shenzhen of Guangdong and Chongqing are also discussing car idling bans.