Some days the air quality in Beijing is so poor you can hardly see beyond the end of your gas mask. As skylines disappear into the murky, noxious atmosphere the city's pledge to deliver a 'Green Olympics' sounds increasingly hollow, but it would be wrong to write it off as a lost cause. Over the past couple of decades the environment has been merrily slaughtered at the altar of China's economic boom. Sixteen of the world's 20 most polluted cities are on the mainland, with Beijing always in the running for the infamous top slot. The European Satellite Agency recently named the capital as having the world's highest levels of nitrogen dioxide, a gas that is pumped out of exhaust pipes, power plants and factories, and which can cause fatal lung damage. Levels are up 50 per cent on a decade ago and still climbing. The prospect of wheezing marathon runners being carted off to hospital isn't exactly the kind of PR the hosts are hoping for, so drastic measures are currently being cooked up to clear the skies. To be fair, huge efforts and resources have already been ploughed into the environmental project over the past few years. Authorities realised something had to be done back in 1998, a year that saw only 100 'blue sky days' in Beijing. Since then the city government has invested about 100 million yuan in a host of projects. More than 4,000 old buses and 30,000 taxis have been taken out of service and replaced with new vehicles that meet stricter new standards for pollution control. Leaded fuel was phased out and catalytic converters are now compulsory for new cars. Hundreds of power plants and large factories have been moved out of the city. Coal mines in the city's outskirts have been shut down. Most homes and industries are now using natural gas or processed coal that produces low levels of sulphur emissions. The construction industry also has to adhere to strict new standards, including spraying water on sites several times a day to keep the dust down. The Olympic venues that are being built are in compliance with strict international environmental standards. Millions of trees have been planted and waterfronts have been expanded. The list goes on and on, but still the air quality remains exceptionally poor. Things have got better though. In 2004 the number of blue sky days hit 229, while last year it nudged up to 234. But the fairly humble target of enjoying low levels of pollution for 80 per cent of the year, or 292 days, still seems like a long way off. Indeed the stats often take a nosedive. January saw 20 days that were 'polluted' or 'seriously polluted', according to the local government, the worst levels for the month in six years. Part of the problem is natural. Beijing is in a basin, surrounded by mountains and miles from the sea. Sandstorms and toxins sweep in from the Mongolian plains and hang heavy in the city's air. But then the city's 13 million people seem to do their best to exacerbate the problem too. A key reason that the initiatives the city is taking are only having a limited impact is the nation's adoration of the motor car. There are currently 2.6 million cars on the streets of Beijing, with more than 1,000 new vehicles joining them every day. By the time the games come around there is expected to be 3.5 million cars in Beijing, probably generating about 30 per cent of the city's pollutants. Through regulations and incentives many of these cars will be taken off the road for the Olympic period. For the two-month term, Wang said no more than 1.85 million car owners will be allowed to drive their cars, while during the actual 16 days the games are on that number will drop to below one million. These targets will be met, Wang said. Just in case drivers are inclined to ignore the temporary rules, the majority of petrol stations will be closed down for the period so fuel will be hard to come by too. As a sweetener, they plan to give the affected residents paid holidays and free monthly passes for the public transport system. Once the party is over the cars will be back clogging the streets and the factories and power plants will be back belching out fumes, but the city chiefs have the ability to create a green world - at least for the 16 days Beijing plays host to the world.