Beijing embarked on a four-day experiment yesterday to see if taking 1.3 million cars off the city's streets will substantially reduce air pollution at next year's Beijing Olympics.
While officials said it would take some time to judge the impact of the measures, the hazy skies above the Chinese capital suggested they may need to do more to ensure good air when the world's best athletes arrive next August.
Beijing is closing down the worst-polluting factories and switching thousands of homes from coal to gas use but air quality remains the biggest concern for organisers.
Beijing's car tally hit the 3 million mark in May and more than 1,000 more are registered every day, snarling up the roads and pumping nitrogen dioxide, carbon monoxide and particulate matter into the air.
"The traffic restrictions will definitely reduce vehicle pollutants and will work effectively," Du Shao-zhong, spokesman for Beijing's Environmental Bureau, said.
"The exact evaluation of the facts of the transportation control will not be released until relevant data is collected and analysed by the experts."
International Olympic Committee (IOC) president Jacques Rogge said last week some endurance events at next year's Games might have to be postponed if the air quality is not good enough.
"Today's air quality is National Standard Grade 2 - Grades 1 and 2 are suitable for any activity," said Du.
Heart problems
An air pollution expert at the World Health Organisation (WHO), however, was yesterday quoted as saying people with heart problems should think twice about visiting Beijing as they could face "serious problems" because of the pollution.
Dr Michal Krzyzanowski said he doubted there would be much improvement in the city's air quality by Games' time and that the car control measures might not have too great an effect.
"Particles have the ability of travelling thousands of kilometres in the air," he told the BBC.
"So it's possible the beneficial effect of cutting the traffic in the city will be compensated by the transport of pollution from other parts of China."
From 6 a.m. until midnight yesterday and tomorrow, drivers with an even final digit on their licence plate face fines if they take to the city roads. Odd-numbered cars will be banned today and Monday.
Yesterday, at least, the plan appeared to be working, with fewer cars along the broad, tree-lined avenues.
One traffic policeman told Reuters television he had only picked up one even-numbered car plate in one and a half hours.
Some coaches and athletes are concerned air quality tests in China and the National Standards do not record levels of ozone and smaller particulate matter.
"Our National Standard is based on our own situation, our own needs," Du explained. "But when setting it we also learnt from international practice."