China's pollution claims disputed ahead of Games

You wouldn't know it to look out the window at the yellow-tinged fug masking Beijing's spectacular Olympic buildings, but with less than a month to go until the Games, China's government says pollution in the host city is falling.

Levels of sulphur dioxide and COD, or chemical oxygen demand, both fell significantly last year, according to China's environmental watchdog, which hailed the news as a sign that the war on pollution is being won. Sulphur dioxide emissions, which belch out of factories and cause acid rain, fell by 4.7 per cent last year, while COD, a measure of water pollution, dropped by 3.2 per cent, said the watchdog's official report.

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Anecdotal and unofficial evidence suggests otherwise – the air in downtown Beijing was appalling yesterday and when the sun came out on Sunday it was for the first time in weeks. The sight of a massive, stinking algae bloom in the sailing venue Qingdao has also highlighted the environmental threat.

The BBC used a hand-held detector to test for airborne particles known as PM10 and found that Beijing's air failed to meet the World Health Organisation's air quality guidelines on six days out of seven. The results are sure to anger the Beijing authorities, which tightly control pollution monitoring.

China failed to meet pollution-control targets in 2006 but the government promises the air will be fine by the time the athletes arrive for the Games, which start on 8 August and run until the end of the Paralympics a month later.

While China's pollution watchdog described the recent results as "heartening" it warned: "The environmental situation is still grim. We are still under enormous pressure to meet the targets in the [five-year] plan."

Some athletes are taking no chances. The Olympic gold medallist and world record holder Haile Gebrselassie of Ethiopia has pulled out of the Beijing marathon because he suffers from asthma and believes the pollution in China threatens his health. He still intends to participate in the 10,000-metre run.

Athletics Australia has said its team would not march in the opening ceremony because of pollution. Their athletes had come back from a test event with respiratory problems and are now staying in the training venue in Hong Kong for as long as possible.

Beijing has already spent 120bn yuan (£8.9bn) to combat pollution and city officials say more efforts are planned. On 20 July an odd-even licence plate system will start taking 1.3 million vehicles off the roads for the duration of the Games, and 300,000 cars with high emissions will be taken out of circulation. The city has also demanded that factories in surrounding provinces stop work or cut production.

In an embarrassing statement last year, the International Olympic Committee (IOC) president, Jacques Rogge, warned that time may be running out to meet the conditions necessary. "For this reason, we may have to reschedule some events so that the health of athletes is scrupulously protected," he said.

Fearful of any disruption, the government has pushed ahead with the building of miles of urban rail lines and has cut bus fares to discourage driving.

This week, the IOC's chief inspector, Hein Verbruggen, backed preparations by saying Beijing "looked ready" but he warned that the committee needed "to see how temporary measures in the city will make an impact on air quality".