Nitrogen Dioxide (NO2) Pollution

Timeline of Nitrogen Dioxide (NO2) National Ambient Air Quality Standards (NAAQS)

History of the NO2 National Ambient Air Quality Standards
Final Rule/Decision	Primary/ Secondary	Indicator ⁽¹⁾	Averaging Time	Level ⁽²⁾	Form
1971 36 FR 8186 Apr 30, 1971	Primary and Secondary	NO₂	Annual	53 ppb⁽³⁾	Annual arithmetic average
1985 50 FR 25532 Jun 19, 1985	Primary and secondary NO₂ standards retained, without revision.
1996 61 FR 52852 Oct 8, 1996	Primary and secondary NO₂ standards retained, without revision.
2010 75 FR 6474 Feb 9, 2010	Primary	NO₂	1 hour	100 ppb	98th percentile, 1-hour daily maximum, averaged over 3 years ⁽⁴⁾
2010 75 FR 6474 Feb 9, 2010	Primary	Primary annual NO₂ standard retained, without revision.
2012 77 FR 20218 April 3, 2012	Secondary	Existing secondary NO₂ standard (annual) retained, without revision.
2018 83 FR 17226 April 18, 2018	Primary	Existing primary NO₂ standards 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 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.