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History of Ground-level Ozone Standards
Ground-level Ozone triggers a variety of health problems even at very low levels and may cause permanent lung damage after long-term exposure. It is one of six common pollutants for which the Clean Air Act requires EPA to set National Ambient Air Quality Standards (NAAQS). Vehicle exhaust and industrial emissions are major sources of nitrogen oxides (NOx) and volatile organic compounds (VOC) that help to form ozone.
| 1971 | EPA established a 1-hour NAAQS ozone standard
of 0.08 ppm. |
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| 1979 | EPA revised the 1-hour standard to 0.12 ppm. |
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| 1991 | The number of counties designated for non-attainment reached 371. Concerned about the new science indicating adverse effects at levels allowed by that NAAQS, the American Lung Association went to court to compel EPA to act. |
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| 1994 | EPA obtained a voluntary remand based on a promise to consider the newer studies. |
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| 1995 | EPA and 37 eastern states form the Ozone Transport Assessment Group
- work with stakeholders to study ozone transport for two years. |
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| 1996 | EPA issued a three-volume criteria document encompassing hundreds of new scientific studies, finding "strong" scientific evidence of adverse health effects from ozone at levels allowed by the 1979 NAAQS. |
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| 1997 | (July) EPA revised the air quality standards for ozone replacing the 1979 standard with an 8-hour standard set at 0.08 ppm. Three states and dozens of industry plaintiffs quickly challenged the new standards. (October) EPA acted on the work of the Ozone Transport Assessment Group and proposes NOx regional reductions in the eastern US. |
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| 1998 | EPA issued the final rule on regional NOx reductions, known as the NOx SIP Call. |
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| 1999 | The DC Circuit Court of Appeals sent the 1997 standards back to EPA for further study. EPA appealed. |
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| 2001 | The U.S. Supreme Court unanimously upheld the constitutionality of the Clean Air Act as EPA had interpreted it in setting the 1997 health-protective air quality standards. The Supreme Court also reaffirmed EPA's long-standing interpretation that it must set these standards based solely on public health considerations without consideration of costs. |
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| 2002 | EPA began the process by which states (governors) and tribes submit recommendations for what areas would be designated non-attainment (failing to meet the 1997 standard). |
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| 2003 | (June) EPA proposed the clean air ozone implementation rule with options for how areas would transition from the 1-hour ozone standard to the 8-hour ozone standard. (July) States and tribes recommended designations - 412 counties were included. (December) EPA responded to states and tribes describing intended modifications to their recommended designations - 506 counties were included. (December) EPA proposed the Clean Air Interstate Rule to help areas in the US meet the 8-hour ozone standard. |
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| 2004 | (April 15) EPA finalized the Clean Air Ozone designations and basic implementation rule.
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| 2007 | (June) State plans for meeting the 1997 health-based 8-hour ozone standard were submitted to EPA. (July) EPA proposed revisions to the National Ambient Air Quality Standards (NAAQS) for ground-level ozone. |
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| 2008 | (March) EPA significantly strengthens the National Ambient Air Quality Standards for ground-level ozone. |