Nitrogen Dioxide - Overview

This page last reviewed July 21, 2011

What is Nitrogen Dioxide?
Nitrogen dioxide (NO2) is a reactive, oxidizing gas capable of damaging cells lining the respiratory tract. This pollutant is also an essential ingredient in the formation of ground-level ozone pollution. NO2 is one of the nitrogen oxides emitted from high-temperature combustion processes, such as those occurring in trucks, cars and power plants. In the presence of sunlight, complex reactions of nitrogen oxides with ozone and other air pollutants produce the majority of NO2 in the atmosphere. Indoors, home heaters and gas stoves also produce substantial amounts of NO2.
Health and Welfare Effects from Exposure to Ambient Levels of Nitrogen Dioxide
Exposure to NO2 along with other traffic-related pollutants, is associated with respiratory symptoms, episodes of respiratory illness and impaired lung functioning. Studies in animals have reported biochemical, structural, and cellular changes in the lung when exposed to NO2 above the level of the current state air quality standard. Clinical studies of human subjects suggest that NO2 exposure to levels near the current standard may worsen the effect of allergens in allergic asthmatics, especially in children.
Ongoing Review of NO2 Standard
In February 2007, the Air Resources Board established a new annual average NO2 standard of 0.030 ppm and lowered the one-hour NO2 standard to 0.18 ppm, after an extensive review of the scientific literature. For information on the nitrogen dioxide standards, click here.

Ambient Air Quality Standards for Nitrogen Dioxide

Averaging Time

California Standard

Federal Standard


0.030 ppm

0.053 ppm

1 hour

0.18 ppm

0.100 ppm

* Annual Arithmetic Mean

For a brief history of the ambient air quality standards, click here.

For more information on Ambient Air Quality Standards, please contact Linda Smith
at (916) 327-8225.