Reviewing National Ambient Air Quality Standards (NAAQS)
Nitrogen Dioxide (NO2) Standards -
Table of Historical NO2 NAAQS
History of the National Ambient Air Quality Standards for Oxides of Nitrogen
During the Period 1971-2012
| Final Rule/Decision | Primary/ Secondary | Indicator (1) | Averaging Time | Level (2) | Form |
|---|---|---|---|---|---|
1971 36 FR 8186 |
Primary and Secondary |
NO2 |
Annual |
53 ppb (3) |
Annual arithmetic average |
1985 50 FR 25532 |
Primary and secondary NO2 standards retained, without revision. |
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1996 61 FR 52852 |
Primary and secondary NO2 standards retained, without revision. |
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2010 75 FR 6474 |
Primary |
NO2 |
1-hour |
100 ppb |
98th percentile, averaged over 3 years (5) |
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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(1) NO2 = nitrogen dioxide
(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 1-hour NO2 standard added in 2010 is a primary standard. The revision of the NO2 NAAQS in 2010 did not affect the secondary standard, which remains an annual standard with a level of 53 ppb.
(5) 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.