I don't think it's as simple as that, although I also advocate people walk and/or bike whenever possible and have plants. Americans love their cars and they'd rather have them than cleaner air.

As Thomas Sowell says, "There are no solutions. There are only tradeoffs."

Undisciplined

econ

A 'smart city' is a city plagued by high taxes and central planning

The clean air initiative, if you took a lot of cars off the road, it would seriously help. 
People can walk and bike, especially if they live and work in the city. 
Look at denmark and their bike routes!
Also, singapore has done a lot on their clean air initiative. 
They want every household to have a green plant, and many people plant them on their balconies!
If everyone works together, its very possible for cheap. 