Despite the license plate restriction, the number of vehicles in the city is still overwhelming and contributes substantially to the city's pollution. It's time the city comes up with a stricter regulation," said Yu Jianhua, who is in charge of air pollution management at the bureau.

The capital aims to reduce PM2.5 concentration to 60 micrograms per cubic meter by the end of 2017, down 25 percent from 2012.

"The government is now reducing the PM2.5 concentration by 2 to 3 percent each year, and a reduction of some 5 percent each year is a great challenge," Yu said.

The role that vehicle emissions play in the forming of PM2.5 varies as target areas change, said He Kebin, a professor of environmental science and engineering and the executive dean of Tsinghua University's graduate school.

"For example, car exhaust contributes to about 22 percent of air pollution within the areas that are under jurisdiction of the municipal government," he said. "But the figure may rise to more than one-third if we narrow the area to downtown Beijing within the Second Ring Road."

Yu said details are still being studied and will be released in the near future, and the government will learn from experiences abroad, including Milan, Paris, London and Tokyo.

"Many cities worldwide have come up with congestion charges, and most of them prove effective," he said.

"The government will hold public hearings before the implementation of the congestion fee and regional vehicle restriction, and will widely gauge public opinion," he said.

Zhang Tianlong, a 49-year-old Beijing resident, said the restriction on private vehicles would be inconvenient, yet is acceptable if the number of cars on the road is obviously reduced.

Zhang also emphasized that it is important government cars take the lead and that compensation be given to car users.

"It's unfair if you buy a car and are informed later that you are forbidden from driving," he said. "Some compensation might greatly ease the commuter's dissatisfaction."

The city will also come up with stricter rules targeting cars from other provinces.

Under the new restriction, to be carried out in 2014, vehicles from outside Beijing will be forbidden from entering the Sixth Ring Road unless with permission.

Currently, cars from other provinces are prohibited from entering the Fifth Ring Road from the morning peak hours 7 am to 9 am, and the evening peak hours 5 pm to 8 pm.

The city vows to control private car ownership within 6 million by the end of 2017, from more than 5.2 million as of early 2013.