Congress amended the Clean Air Act that year to set up a market for the permits that power plants must have to release sulfur dioxide (SO2) -a major culprit in acid rain-out of their smokestacks.

美国国会修订空气清净法案，建立了二氧化硫(SO2)排放许可的市场，电厂都必须持有执照，才能从烟囱排出这种造成酸雨的元凶。

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For a decade now, the Environmental Protection Agency has been using a provision of the Clean Air Act to force dirty, older power plants to clean up.

NPR: EPA Proposal Eases Rules on Pollution Controls

But what they really are looking at is the EPA to soon release or formalize, finalize its carbon-based pollution regulations for future power plants and then to get quickly on the task of putting together some of the regulatory rules under the Clean Air Act for existing power plants.

WHITEHOUSE: Press Briefing by Press Secretary Jay Carney,

Jim Jeffords, R-Vermont, author of the Clean Energy Act, a bill to clean up the polluting power plants, joined PIRG in releasing the report.

CNN: Nature - America's most wanted: Power plants urged to clean up their act