In the United States, despite the passage of the Clean Air Act in 1970, in 2002 at least 146 million Americans were living in non-attainment areas—regions in which the concentration of certain air pollutants exceeded federal standards.
在美国，虽然洁净空气法案于1970年通过，但在2002年至少有1.46亿名美国人居住在未达标区域里，即该区域空气污染物浓度超过联邦标准。