The smog hangs thick over Beijing. It's a brownish haze with a vaguely smoky smell, shrouding lanes of traffic and pedestrians wearing face masks.
The main culprits are nearby steel factories and coal-burning heating plants. But the city's five million cars add much to the toxic mix, creating air that's frequently rated "hazardous" by the World Air Quality Index Project.
Since the beginning of last year, Chinese cities have been awash with 23 million GPS-equipped bicycles, part of a bike share program that has been credited with changing traffic patterns across the country and reviving a mode of transportation that was fading fast.