Sources can be *reduced in number*. Emissions (from sources) can be reduced. But "sources have been reduced" sounds like a mistake to me. A source ("an origin") either exists or it doesn't; its quality of being an origin can't be "reduced" (only what it outputs). But not many people would raise an eyebrow if you said "sources have been reduced", so it's not a big deal. If you felt that "reduce" wasn't quite right in this context, Smoke, then I think you have very good instincts. "Eliminated" is a good word, though. I would say "Harmful emissions from some sources have been reduced or even eliminated altogether." Note that it's the emissions that we're saying have reduced, not the sources themselves.

Reduced is fine. I would say "some sources of harmful chemicals have been reduced or even eliminated."