Experts sbaid it's a common practice to start a national market from imposing caps on carbon dioxide emissions from utilities and industry, as some regional pilot programs have done.

Top 10 cities with worstsmogin China

Future points to carbon trading

In South Korea, carbon dioxide emissions from power generators and manufacturers will be capped at 1.64 billion metric tons in the 2015-17 period, the country said last month.

"Experience both abroad and in China has proved that trading can only be effective under a robust cap, which contributes to and helps deliver the establishment of an economy-wide emissions management program," said Dan Dudek, vice-president of the Environmental Defense Fund, a United States environmental group.

Pilot trading projects have been ongoing in six cities and provinces in Beijing, Shenzhen, Shanghai and Tianjin and the provinces of Hubei and Guangdong since 2003. The southwestern city of Chongqing will be the latest region to launch carbon trading later this month.

"They are individual projects," Sun said. "Even if we expand the pilot projects to more regions, they are still not a connected and whole market, so it's not the most effective and rapid path to take."

The average trading price of carbon permits in the pilot cities and provinces range from 27 yuan ($4.4) in Tianjin to 70 yuan in Shenzhen.

Li Junfeng, director of the National Center for Climate Strategy and International Coordination, said the varying carbon prices indicate the regions' unequal stages of development and quota allocation systems.

China launches carbon trading in Hubei	Tianjin starts carbon trading market