Beijing motorists hardly notice the nondescript white van parked at one of the city’s biggest motorway junctions. But, as each car passes, a board on top of the van flashes up its licence plate number and a verdict on whether its exhaust fumes meet city standards. This is just one of Beijing’s moves to clean up its notorious pollution before the Olympics.

Equipped with the latest computer technology, Liu Shuang said it takes just 0.8 of a second to measure each passing car. Between 8am and 4pm yesterday he tracked 1,321 vehicles and estimated the pass rate at between 80 and 90 per cent.

Drivers who fail will be fined 100 yuan (£7) and ordered to get their engines retuned.

Athletes around the world are nervous that the city’s filthy air will take its toll when they compete in the humid heat of August. Because of this, the city is desperate to clean up its air and its reputation.

It has ordered factories to close, is taking cars off the road and introduced cleaner petrol on March 1. Ancient coal-heated homes are being switched over to electricity.

Expense seems to be no obstacle to ensuring that the Games, starting on August 8, will be a success. A single van, the words “Environmental Monitor” painted down its side, costs 1.3 million yuan (£90,000) and the city environmental protection bureau has put 22 into operation so far this year.

Wang Xiaoming, chief information officer of the bureau, told The Times that motor vehicles were the greatest source of pollution after coal emissions. “If a vehicle can’t get its ‘green’ licence, then it won’t be allowed on the roads,” he said.

He was cautious not to be overconfident about whether Beijing’s air would be clean enough for athletes to run and jump in the city’s stifling summer heat. “We have done everything we can do,” is all he would say.

Beijing in summer is a city where the thick air catches in your throat and skyscrapers disappear into a brown smog. The authorities have occasionally issued pollution warnings to the old and very young, advising them not to venture outside and everyone else to avoid vigorous exercise.

China’s capital is not the first Olympic host city to take drastic measures to clean up its air for the Games. Smog scares haunted Los Angeles in 1984, Seoul in 1988 and Athens in 2004, but schemes to suppress traffic and close factories were largely effective.

The pall of dust from the Gobi desert and fumes from industries fuelling China’s economic boom may be difficult to control. China has already poured at least 120 billion yuan (£8 billion) into clearing the smog.

A plan implemented at the start of the year, but made public only this month thanks to traditional Chinese secrecy, will require four provinces and a big city near Beijing to cut industrial pollution for two months from late July.

Du Shaozhong, spokesman for the Beijing bureau, said that even with all these measures in place, he would be keeping his fingers crossed: “To improve the air quality in Beijing needs both people’s effort and a little luck.”

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