How Laws, Regulations Cleaned Our Air

The Clean Air Act (CAA) was signed by President Richard Nixon on Dec. 31, 1970, to regulate air emissions from stationary and mobile sources. Before its passage, smog—a combination of ground-level ozone and particle pollution—posed a significant problem for many U.S. cities.

Congress charged the newly formed Environmental Protection Agency (EPA) with the primary role of carrying out the law. Revisions to the act in 1977 and 1990 strengthened the EPA’s enforcement ability to ensure states met their clean air goals.

The Clean Air Act required the EPA to set National Ambient Air Quality Standards (NAAQS) for widespread and common pollutants, based upon the latest science at the time. That was all designed to protect the health and welfare of the public. NAAQS are in place for these six criteria pollutants:

  • Carbon monoxide
  • Lead
  • Nitrogen dioxide
  • Ozone (ground-level)
  • Particulate matter
  • Sulfur dioxide

States are required to adopt implementation plans to achieve and maintain the air quality standards for these pollutants. Various provisions were put in place to minimize pollution from stationary sources like expanding industrial plants, as well as from mobile sources like cars, trucks and buses.

The 1990 Clean Air Act amendments were considerable and targeted three major threats to public health and the environment: acid rain, urban air quality issues and toxic emissions. A national permits program was established for polluting industries, and greater EPA enforcement authority allowed it to make further improvements in air quality. The 1990 amendments also targeted protection of the stratospheric ozone layer.

Since then, the EPA and state governments have made significant progress in reducing polluting benzene and toluene emissions from cars and trucks as well as from various other mobile sources. This has been done by requiring reformulated gasoline to be used and placing limits on tailpipe emissions. Those new controls on fuel and vehicles are expected to reduce the amount of air toxic emissions by more than 75 percent, from 1990 to 2020.

The EPA has also issued rules for more than 80 categories of major industrial sources, ranging from aerospace manufacturers to steel mills, as a way to control toxic products from industrial and commercial sources. Projected reductions in toxic air emissions from those rules are estimated to be approximately 1.5 million tons per year.

Over the past 40 years, the EPA has made great strides in reducing toxic emissions from both mobile and stationary sources. It has also developed a variety of mapping tools to let the public identify sources of pollution near homes, schools, etc., to better protect public health. Federal agencies along with the EPA and the private sector have also begun to understand more about indoor air pollution and have implemented programs focused on reducing air pollutants within homes, schools and offices.


In 2002 North Carolina passed landmark legislation known as the Clean Smokestacks Act to address pollution from older coal plants still in operation three decades after the 1970 Clean Air Act. Legislators set caps on total annual emissions of nitrogen oxide and sulfur dioxide, both of which contribute to acid rain. Nitrogen oxide also contributes to ground-level ozone pollution, especially in urban areas. Sulfur dioxide is the culprit behind haze in the North Carolina mountains. The Clean Smokestacks Act required Progress Energy and Duke Energy to reduce their total year-round emissions of nitrogen oxides by 77 percent and sulfur dioxide by 73 percent over a 10-year period. Those stringent caps required either retiring or modernizing the 45 coal-fired electric generating units.

Another aspect of the act allowed North Carolina’s attorney general to use all available resources, including negotiation and lawsuits, to induce other states to achieve similar reductions in emissions.

A 2006 lawsuit by Attorney General Roy Cooper said the Tennessee Valley Authority (TVA), the largest public power company at the time, was violating the Clean Air Act with its fleet of coal plants. The case went all the way to the U.S. Supreme Court, and in 2011 TVA agreed to phase out 18 units of its coal plants, totaling 2,700 MW, and to install modern pollution controls on three dozen other units. TVA also agreed to invest an estimated $3 billion to $5 billion on pollution controls, $350 million on clean energy projects, and pay a civil penalty of $10 million. This was a significant public health win for residents of North Carolina mountain communities and led to the development of federal interstate air pollution control regulations by the EPA designed to address issues similar to North Carolina’s problems with pollution caused by the Tennessee Valley Authority.

This post was written by Terry Lansdell, Program Director for Clean Air Carolina.

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