The Act contains key provisions to control common pollutants which, at the time of the 1970 amendments, formed dense, visible smog in many of the nation’s cities and industrial centers.  To protect public health and welfare nationwide, the law requires EPA to establish national ambient air quality standards based on the latest science, and requires states to adopt enforceable plans to achieve the standards. State plans also must control emissions that drift across state lines and harm air quality in downwind states. Congress designed the law to minimize pollution increases from growing numbers of motor vehicles, and from new or expanded stationary sources (i.e., power plants, industrial plants, and other facilities that are not mobile). The law calls for new stationary sources to be built with best technology, and allows less stringent standards for existing stationary sources.

• The Clean Air Act in a Nutshell: How It Works (PDF)(23 pp, 250 K, March 22, 2013)