Coal power generation is largely responsible for the smog in China, not automotive exhaust. They're barking up the wrong tree.
In 2007 I was invited to Suzhou to train engineers in our China division. Suzhou prohibits all two-cycle engines so most of its vehicular traffic is comprised of bicycles and electric scooters. There were autos, but even at the height of rush, they were outnumbered 30 to one.
I arrived the day after the remnants of a typhoon had swept the air clear. My colleagues retracted accusations of altering photos I had sent them to highlight the blue skies. They were taking snaps like crazy to record these days for posterity.
The visibility from my 45th floor hotel room was phenominal. I could make out much of the landscape as much as eight miles distant. Three miles away, however, with smoke stacks that towered as high as my hotel room, was the nearest coal generation plant belching brown/grey smoke.
By the third day of my visit, the smog had reduced my hotel room window visibility to the point where the smoke stacks were merely hazy outlines. By day six, I couldn't see the stacks and the air has a dusty taint. As I got used to the persistant odor, food started tasting bland.
The last day of my stay was uncomfortatble. I started to experience respiratory heaviness and while washing up, I started hacking up brown-colored sputum. A majority of cyclists and pedestrians we passed as we left the city had donned particle masks. The air quality improved markedly and incrementally as we made our way to Shanghai. Shanghai, though far more densely populated, is not nearly as polluted due to the ocean breeze.
China is doing their damnedest to promote green energy -- all new highrise construction we passed featured pv and thermal solar panels on southern facades, some even shaded the room air conditioners that jutted from each apartment. They are just growing too fast to surrender coal generation and they are paying the price with diminishing public health.