China's Four Day Pollution Reduction Experiment

Successful:

China hails car trial a 'success'
A four-day scheme that took 1.3 million cars off Beijing's streets reduced air pollution by 15-20%, officials in the Chinese capital say.

Not successful:

China prays for Olympic wind as car bans fail to shift Beijing smog
More than a million cars were taken off the roads for the four-day test period, but there was no improvement in the air quality, according to city officials.