I have yet to play a game that gets to this point on the latest patches, but I am under the impression that you can never completely remove all pollution unless you nix your factory.
Here's what I see.
1) As population rises pollution rises, so when you create a mass transit center it cancells that out.
2) As you build a factory and your production rises, so does pollution, so you build a recycling center. HOWEVER, 2 pollution icons on the largest producers are always left.
3) Adding a hydro dam, nuclear plant or solar plant does not affect this. In reality a nuclear plant increases production and reduces pollution, but since the increased production increases pollution more than any other power plant, the nuclear plant pollution effect is negated.
Is this still true? If this is the case then there really is no way to beat pollution except by conquering the world and killing off your production.