Timeline of Nitrogen Dioxide (NO2) National Ambient Air Quality Standards (NAAQS)
| Final Rule/Decision | Primary/ Secondary | Indicator (1) | Averaging Time | Level (2) | Form |
|---|---|---|---|---|---|
|
1971 |
Primary and Secondary | NO2 | Annual | 53 ppb (3) | Annual arithmetic average |
|
1985 |
Primary and secondary NO2 standards retained, without revision. |
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|
1996 |
Primary and secondary NO2 standards retained, without revision. |
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|
2010 |
Primary |
NO2 |
1 hour |
100 ppb |
98th percentile, 1-hour daily maximum, averaged over 3 years (4) |
|
Primary annual NO2 standard retained, without revision. |
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|
2012 |
Secondary |
Existing secondary NO2 standard (annual) retained, without revision. |
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|
2018 |
Primary | Existing primary NO2 standards retained, without revision. | |||
(2) Units of measure are in parts per million (ppm) and parts per billion (ppb).
(3) The official level of the annual NO2 standard is 0.053 ppm, equal to 53 ppb, which is shown here for the purpose of clearer comparison to the 1-hour standard.
(4) The form of the 1-hour standard is the 3-year average of the 98th percentile of the yearly distribution of 1-hour daily maximum NO2 concentrations.
Learn more about setting and reviewing standards to control NO2 pollution.