Yang Keng, a member of the National Committee of the Chinese People's Political Consultative Conference, suggested during the annual meeting of the top political advisory body last month that key regions should adopt the latest standard as soon as possible to reduce sulfur pollution.

Zhuang said cities in the Beijing-Tianjin-Hebei region have greater difficulty improving air quality than cities around the Yangtze River and Pearl River deltas. The region has serious imbalances in economic development, which makes it difficult to meet a consistent standard, Zhuang said.

Whether air quality during the APEC event will be as good as it was during the Olympics is uncertain, said Zou Shoumin, head of the environmental inspection office of the Ministry of Environmental Protection.

At a news briefing on Wednesday, Zou said he was not sure the quality could be matched, considering the different pollutants and diffusion conditions at play.

In addition, the drastic anti-smog measures, including odd-even license plate rules and industrial suspensions are unconventional and can only be applied during a special period, Zou said.

Peng Yingdeng, an expert in urban environment management from the ministry, said diffusion conditions play an important role in air quality.

The 2008 Olympics took place during the city's rainy season and coincided with ideal pollutant diffusion conditions, whereas the APEC event will be held in the fall, which typically sees more adverse conditions for dispersal, he said.

Measures such as those taken during the Olympics can only be employed at an unusually important moment because of their influence on the country's economic development and people's livelihood, he said.