mhching

I did something like you before, and after that happened, to keep the CBD where it belongs (the commercial city), I zoned low-density commercial in the suburb (much like a supermarket just across the street), while keeping all mid and high density commercial to that city. Anyway, that will provide a boost for your demand for residential development too.

It may be helpful to use your taxes pane to check if there's any dirty manufacturing unit left. Sometimes I accidentally left one or two of them behind, and they continue bringing pollution. A little combing when comes to that.