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经过长时间调查研究和反复酝酿，美国环保局（以下简称EPA）终于在1997年12月19日颁布了机车和机车发动机的排放标准。EPA声称：“新的排放标准将可实现使NOx排放量减少近三分之二，这相当于从公路上取消了3000多万辆小轿车。此外，HC和PM（颗粒物质）的排放量亦将会减少50％。
After a long period of investigation and research and repeated deliberations, the United States Environmental Protection Agency (EPA) finally promulgated the emission standards for locomotives and locomotive engines on December 19, 1997. EPA said: "The new emission standards will reduce NOx emissions by nearly two-thirds, which equates to the elimination of more than 30 million cars off the road. In addition, emissions of HC and PM (particulate matter) Will be reduced by 50%.