Cap and trade, scrubbers, catayltic converters made a big dent
That is an interesting example of what we can do with ingenuity and technology when confronted with a real problem and allowed to apply real solutions (well, maybe not C&T, although I see how that could be beneficial in the short-term.)
I have heard my brother-in-law (TVA engineer) discuss how difficult it is to get government approval for making small changes that would improve air quality. On one hand, the gov't likes to complain about the pollution while, on the other hand, they refuse to allow them the freedom to do what the gov't demands.