Haze returns to Beijing with four days to go

Beijing Olympic Games banners hang from poles along along a main road as cars drive past on a hazy day in Beijing July 28, 2008.

BEIJING (Reuters) - A grey haze clogged Beijing's skies on Monday as the city returned to work after a weekend of the clear weather, just four days before the opening ceremony for the Olympic Games.

Beijing's chronic pollution has been one of the biggest headaches for organizers who have closed dozens of factories and pulled more than half the city's 3.3 million cars off the roads in a bid to ensure blue skies during the competition.

Officials said China was still considering some man-made help to ensure dry weather and clean air for Friday.

China has two methods of controlling rainfall. Weather stations outside Beijing could try to induce rain before it reaches the centre of the city, by firing a chemical seeding agent into clouds with anti-aircraft guns, a common practice in arid northern China.

Or it could fire a coolant into clouds that increases the number of water droplets, causing heavier droplets to fall ahead of the big show.

Smog shrouded the city for much of last week, prompting the government to draw up a last-resort plan to clear more vehicles from the roads of Beijing and surrounding cities, and shut down over 200 more factories.

The International Olympic Committee (IOC) has said it may reschedule endurance events such as the marathon to prevent health risks if pollution is bad.

Data from the Beijing Environmental Protection Bureau showed that air pollutants were well within limits for a "blue sky day" at all monitoring stations in the 24 hours to midday on Sunday, although they do not provide an overall summary.

But a visible haze only started to gather on Sunday afternoon and the city meteorological bureau forecast cloudy, hot weather with just a light breeze on Monday.

(Reporting by Emma Graham-Harrison; Editing by Nick Macfie)

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