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Ozone (O3) Standards -
Table of Historical Ozone NAAQS
History of the National Ambient Air Quality Standards for Ozone
During the Period 1971-2008
| Final Rule/Decision | Primary/ Secondary | Indicator (1) | Averaging Time | Level (2) | Form |
|---|---|---|---|---|---|
| 1971 36 FR 8186 Apr 30, 1971 |
Primary and Secondary | Total photochemical oxidants | 1-hour | 0.08 ppm | Not to be exceeded more than one hour per year |
| 1979 44 FR 8202 Feb 8, 1979 |
Primary and Secondary | O3 | 1-hour | 0.12 ppm | Attainment is defined when the expected number of days per calendar year, with maximum hourly average concentration greater than 0.12 ppm, is equal to or less than 1 |
| 1993 58 FR 13008 Mar 9, 1993 |
EPA decided that revisions to the standards were not warranted at the time | ||||
| 1997 62 FR 38856 Jul 18, 1997 |
Primary and Secondary | O3 | 8-hour | 0.08 ppm | Annual fourth-highest daily maximum 8-hr concentration, averaged over 3 years |
| 2008 73 FR 16483 Mar 27, 2008 |
Primary and Secondary | O3 | 8-hour | 0.075 ppm | Annual fourth-highest daily maximum 8-hr concentration, averaged over 3 years |
(1) O3 = ozone
(2) Units of measure are in parts per million (ppm).