Given a text, write a compressed version of it in a single sentence.
Q: Power generators are a significant source of three key emissions: sulfur dioxide (SO2), nitrogen oxide (NOx), and mercury (Hg). The Clean Air Act has been, and will continue to be, a successful tool in reducing these emissions.
A:
3 key emissions: sulfur dioxide, nitrogen oxide, and mercury. The Clean Air Act has been, and will continue to be, a successful tool in reducing these emissions.