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Nitrogen Dioxide (NO2) Standards -
Table of Historical NO2 NAAQS

History of the National Ambient Air Quality Standards for Oxides of Nitrogen
During the Period 1971-2010

Final Rule/Decision Primary/ Secondary Indicator (1) Averaging Time Level (2) Form


36 FR 8186
Apr 30, 1971

Primary and Secondary



53 ppb (3)

Annual arithmetic average


50 FR 25532
Jun 19, 1985

Primary and secondary NO2 standards retained, without revision.


61 FR 52852
Oct 8, 1996

Primary and secondary NO2 standards retained, without revision.


75 FR 6474
Feb 9, 2010 (4)




100 ppb

98th percentile, averaged over 3 years (5)

Primary annual NO2 standard retained, without revision.

(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.


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