In the 20 years since the Clean Air Act (C A A) Amendments of 1990, U.S. electric power companies have deployed pollution-control technologies, new power plants with relatively low emissions, and demand-side measures to reduce electricity production air emissions. The Environmental Protection Agency (EPA) has found, however, that despite this significant progress in reducing emissions, in 2008 some 127 million Americans still lived in counties with unhealthy air, many of which are along the Ohio River Valley in the Middle Atlantic and Southeast.
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机译：自1990年《清洁空气法》（C A A）修订以来的20年中，美国电力公司已经部署了污染控制技术，排放量相对较低的新电厂，以及减少电力生产空气排放的需求方措施。然而，环境保护署（EPA）发现，尽管在减少排放方面取得了显着进展，但2008年仍有约1.27亿美国人居住在空气不健康的县，其中许多沿中大西洋和东南部的俄亥俄州河谷。
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