The quality of coal on sale is being checked to ensure that its sulphur content does not exceed 0.5 percent, the city's new standard, said deputy director of the municipal environmental protection bureau Du Shaozhong.

Violators would face a maximum fine of 30,000 yuan (3,623 dollars) and could lose their business licence, he told Xinhua news agency.

China's slogan for the 2008 Games is "Green Olympics" and it has earmarked 5.4 billion dollars to make Beijing an "ecological city" with "green hills, clear water, grass-covered ground, and blue sky".

The capital set a target of achieving 227 "blue sky days" this year, but with a gritty haze regularly hanging over the city the target appears to be out of reach.

Du acknowledged Beijing must switch to cleaner energy if it wants to achieve the goal.

Most residents who live in crumbling houses in the capital's old districts have no access to central heating and have to rely on burning coal in the winter to keep warm.

Beijing started promoting coal with low sulphur content in 1998 but most citizens still prefer using high-sulphur coal because it is cheaper.

Authorities have also renovated more than 56,000 boilers but more than 3,000 still run on coal.

British Prime Minister Tony Blair issued an urgent warning Tuesday about global warning and called on China, in particular, to do more to meet its growing energy needs sustainably.

China's State Environment Protection Administration had no comment.

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