Beijing's Olympic organisers are launching last-ditch measures to clean up the city's air in time for the games in August, amid fears that some endurance events may be postponed if pollution continues to cast its yellow-tinged pall over the city.
While the International Olympic Committee repeatedly says how delighted it is with the efforts the city has made for the games and indeed, the new facilities for the two-week event are among some of the architectural wonders of the world there have been warnings that cycling events and marathon running may have to be postponed if the air quality is not up to scratch by the time the games open on 8 August.
The Olympics are seen here as symbolising China's emergence on to the world stage, and there is huge anticipation growing in this vibrant city of 17 million people. But pollution is a vicious circle when the capital disappears inside a haze of yellow clouds, a mix of coal smoke, particulate matter and ozone, people leave their bicycles at home and opt for an air-conditioned car instead.
The host city has already spent 120 billion yuan (8.4bn) on environmental programmes to combat pollution, and city officials say that more efforts are planned.
They include closing factories and taking 1.3 million of the city's three million cars off the roads for the duration of the games. Some 300,000 cars with high emissions will be taken out of circulation; coal-burning furnaces are being converted to natural gas in the city centre; millions of trees are being planted and dust clouds from building sites kept under control.
Late last year, the IOC president, Jacques Rogge, said: "Despite all these efforts, time may be running out, and the conditions required for the athletes competing in endurance disciplines might not be met 100 per cent on a given day. For this reason, we may have to reschedule some events so that the health of athletes is scrupulously protected." Fearful of the embarrassment postponement or even cancellation of events could cause, the government is pushing ahead with the building of miles of urban rail lines and has cut bus fares to discourage driving. Other steps will include cloud-seeding, where chemical-infused rockets are fired into clouds to induce rain and clear the polluted skies.
The government has introduced tough new fuel standards for cars, which require service stations to supply petrol and diesel equivalent to the Euro IV standard. This will cut emissions of sulphur dioxide, which causes acid rain, by 1,840 tons, according to Beijing's Environmental Protection Bureau.
The capital's top five power plants, all coal-fired, which provide a third of Beijing's electricity and thermal energy, have committed to cutting emissions. They include the Huaneng plant, which has installed a nitrogen oxide reduction system to cut emissions of the gas by 75 per cent, or 10,000 tons, a year, while the other main plants will also curb emissions over the coming months.
China has pitched the Olympics as the "Green Games" to showcase the country's efforts to combat pollution and encourage sustainable energy use. However, Beijing is one of the world's dirtiest cities, choked with smog that is often two or three times the maximum allowed for by the World Health Organisation. The World Bank says China is home to 16 of the world's 20 most polluted cities.
The United Nations Environmental Programme (UNEP) has issued a report which says Beijing was on course to hold a Green Olympics as it originally promised it would, but warning that air quality remains a problem. The UN's environment wing is particularly worried about the high levels of small particulate matter (PM10), which are sometimes at more than double recommended safe amounts.
Casual tourists visiting during heavily polluted periods complain of sore throats, allergic reactions and asthma, so it is no wonder that marathon runners and cyclists forced to race through the streets are concerned about the air quality. An endurance athlete inhales up to 150 litres of air a minute, about 10 times that of an average office worker.
There was much official celebration at news that the capital had squeaked past its target of 245 "blue-sky days" in 2007 by just one day. In 2006 Beijing had 241 clear-sky days, and local media said 2007's figure of 246 marked a steady improvement for nine straight years, even if many international scientists do not recognise Beijing's standard for a "blue-sky day".
"We anticipated the last 'blue-sky' day more than 10 days ago, but lingering fog and sandstorms frustrated us in the past week," Du Shaozhong, deputy director of the Municipal Bureau of Environmental Protection, told local media. Crucially, the data recorded only three heavily polluted days last year, in sharp contrast with 13 appallingly smoggy days in 2006, and city officials are setting a more ambitious target of at least 256 days with relatively good air quality in 2008.
The Beijing Olympics will not be the first games where smog is a problem one in five US athletes complained they had problems with smog in Athens, while British runner Steve Ovett collapsed with breathing problems at Los Angeles in 1984, blaming pollution.
During the marathon in St Louis in 1904, only 14 of the 32 competitors finished the course through the city's dirty streets, and one American runner died after inhaling too much dust.
Last year China's government staged a huge experiment where it took one million cars from the streets to see if it reduced pollution. Beijing said it was a success, although residents did not notice much improvement in air quality.
Still, it's a brave bookmaker who would take a bet on a new world record being set during the marathon in Beijing.