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EPA Strengthens Smog Standards to Better Protect Human Health and the Environment

Release Date: 03/12/2008
Contact Information: Jonathan Shradar, (202) 564-4355 / or Cathy Milbourn, (202) 564-4355 /; En español: Lina Younes, (202) 564-4355 /

(Washington, D.C. – March 12, 2008) EPA today met its requirements of the Clean Air Act by signing the most stringent 8-hour standard ever for ozone, revising the standards for the first time in more than a decade. The agency based the changes on the most recent scientific evidence about the effects of ozone, the primary component of smog.

"America's air is cleaner today than it was a generation ago. By meeting the requirement of the Clean Air Act and strengthening the national standard for ozone, EPA is keeping our clean air progress moving forward," said EPA Administrator Stephen L. Johnson.

The new primary 8-hour standard is 0.075 parts per million (ppm) and the new secondary standard is set at a form and level identical to the primary standard. The previous primary and secondary standards were identical 8-hour standards, set at 0.08 ppm. Because ozone is measured out to three decimal places, the standard effectively became 0.084 ppm: areas with ozone levels as high as 0.084 ppm were considered as meeting the 0.08 ppm standard, because of rounding.

In announcing the new ozone standard Administrator Johnson also announced that he will be sending Congress four principles to guide legislative changes to the Clean Air Act.

"The Clean Air Act is not a relic to be displayed in the Smithsonian, but a living document that must be modernized to continue realizing results. So while the standards I signed today may be strict, we have a responsibility to overhaul and enhance the Clean Air Act to ensure it translates from paper promises into cleaner air," Johnson concluded.

The four principles outlined by the Administrator recommend that the Clean Air Act and the National Ambient Air Quality Standards (NAAQS)

  1. must protect the public health and improve the overall well-being of our citizens;
  2. should allow decision-makers to consider benefits, costs, risk tradeoffs, and feasibility in making decisions about how to clean the air;
  3. should provide greater accountability and effective enforcement to ensure not only paper requirements but also air quality requirements are met, especially in areas with the furthest to go in meeting our standards;
  4. should allow the schedule for addressing NAAQS standards to be driven by the available science and the prioritization of health and environmental concerns, taking into account the multi-pollutant nature of air pollution.
While the Administrator stated that these changes are needed to modernize the Clean Air Act, the nation will still benefit from the new standard.

The United States has made significant progress reducing ground-level ozone across the country. Since 1980, ozone levels have dropped 21 percent as EPA, states and local governments have worked together to improve the quality of the nation's air. EPA expects improvement to continue, as a result of landmark regulations such as the Clean Air Interstate Rule, to reduce emissions from power plants in the East, and the Clean Diesel Program, to reduce emissions from highway, nonroad and stationary diesel engines nationwide.

Ozone can harm people's lungs, and EPA is particularly concerned about individuals with asthma or other lung diseases, as well as those who spend a lot of time outside, such as children. Ozone exposure can aggravate asthma, resulting in increased medication use and emergency room visits, and it can increase susceptibility to respiratory infections.

Ground-level ozone is not emitted directly into the air, but forms when emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs) "cook" in the sun. Power plants, motor vehicle exhaust, industrial facilities, gasoline vapors and chemical solvents are the major human-made sources of these emissions.

EPA estimates that the final standards will yield health benefits valued between $2 billion and $19 billion. Those benefits include preventing cases of bronchitis, aggravated asthma, hospital and emergency room visits, nonfatal heart attacks and premature death, among others. EPA's Regulatory Impact analysis shows that benefits are likely greater than the cost of implementing the standards. Cost estimates range from $7.6 billion to $8.5 billion.

EPA selected the levels for the final standards after reviewing more than 1,700 peer-reviewed scientific studies about the effects of ozone on public health and welfare, and after considering advice from the agency's external scientific advisors and staff, along with public comment. EPA held five public hearings and received nearly 90,000 written comments.

As part of today's action, EPA also has updated the Air Quality Index (AQI) for ozone to reflect the change in the health standard. The AQI is EPA's color-coded tool for communicating daily air quality to the public.

More details on the revised standards:
More on the AQI and to see daily air quality forecasts

March 14, 2008 update: Statement by the U.S. EPA Press Secretary about the smog standards