The city authorities had targeted a clear sky for 227 days in 2004, or 62 percent of the year, but this objective now seems unlikely to be met, the China Daily reported. Authorities have not defined what qualifies as a clear sky.

The explanation given by the municipal government is projections of a milder winter, which they said would lead to worse-than-expected pollution, according to the report.

"A warm winter will have less cold air, fewer windy days and more foggy weather, which will make it more difficult for pollutants to be dispelled," said Shi Hanmin, head of the city's environmental protection administration.

The China Daily newspaper attributed the expected warmer winter to El Nino, a disruption of the ocean-atmosphere system in the Pacific Ocean that sometimes wreaks havoc on the weather in other parts of the globe.

But scientists cautioned that it was still too early to say what kind of impact El Nino would have on China, according to the newspaper.

The biggest causes of air pollution in Beijing are attributed to industry, traffic fumes and sandstorms from the Gobi desert.

The poor air quality is blamed for health risks ranging from asthma to cancer. According to one previous Chinese media report, children in some big cities live in conditions equivalent to smoking two packs of cigarette a day.

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