The biggest event on the global sporting calendar will be hosted in one of the world's most polluted cities unless there are dramatic improvements in air quality over the next 809 days.

The helter-skelter pace of economic growth in China has come at a cost, and in the capital that price is the dirty, yellow-brown haze that restricts visibility and clogs the lungs.

The International Olympic Committee's (IOC) Hein Verbruggen said last week that, while it was definitely a challenge, he was certain the air would be cleaner by the time the Games start.

"They have an interest, they have a genuine straightforward vested interest in presenting this city in the best possible way during the Olympics and that is, for me, more than enough guarantee," he told Reuters at the end of the IOC inspection.

"They voted a budget of $12.3 billion before they won the right to host the Olympics to clean up the air and I'm absolutely sure they're spending it," he said.

"It's an uphill battle but they will deliver. I'm absolutely sure."

Measures such as the relocation of industry out of the city, a switch to the use of gas from coal in homes and the phasing out of old public transport vehicles have made inroads into the problem.

But the economic boom has brought with it an explosion in car ownership and the 400,000 or so new vehicles that hit the road in Beijing last year have caused more than congestion.

Athens, Beijing's predecessor as host of the Summer Games, had similar pollution problems in the years before their Olympic year of 2004, as Verbruggen recalled.

"This was also a big discussion point about Athens," he added. "It was not easy, but they delivered."

"GREEN OLYMPICS"

Jiang Xiaoyu, vice president of the Beijing Organising Committee for the Olympic Games (BOCOG), said last week the 'Green Olympics, High-Tech Olympics and People's Olympics' slogan reflected how much stock BOCOG placed on the environment.

"Since 1998, Beijing has done a lot to improve the air quality in Beijing," he said, pointing out that official statistics showed there were 234 "clean air" days last year to just 100 back in 1998.

This year started badly, however, with 13 days of the worst measure of pollution by mid-April and frequent sand storms further depleting the air quality.

Failing a permanent solution to the problem, Beijing authorities may at least ensure the air is clean for the 16 days of the Games.

Jiang confirmed limiting car usage -- a measure adopted by Athens in the early 1980s -- was being discussed, while there has also been talk of seeding clouds to cause rain, factory closures and extended holidays for public employees in August 2008.

Ultimately though, as Verbruggen pointed out, should Beijing fail to meet the commitments they have made to the IOC on air pollution, there are unlikely to be any serious repurcussions.

"Even if they did not attain their targets, what can you do?" he asked. "Let's be open about this, we can't say tomorrow, we go somewhere else."