Nitrogen Dioxide

Nitrogen oxides (NOx) are a group of highly reactive gasses. The “x” in NOx stands for one or more oxygen atoms connected to the nitrogen atom. Nitrogen dioxide (NO2) is used as the indicator for the larger group of nitrogen oxides. Nitrogen dioxide is a reddish-brown gas with a pungent, irritating odor. For more general information about NO2, please read EPA’s Nitrogen Dioxide Information page.

NO2 also contributes to the formation of ground-level ozone, particle pollution, acid rain (deposition) and regional haze.

Health Concerns
Short-term exposure to NO2 is linked to adverse respiratory effects, including airway inflammation. NOx can react with ammonia, moisture, and other compounds to form small particles that can penetrate deeply into sensitive parts of the lungs and can cause or worsen respiratory disease. High levels can produce fatal lung damage. 

Environmental Concerns
NOx reactions can produce ozone, which can cause damage to plants and trees. Another product of NOx reactions is particle pollution, which can form haze that reduces visibility in scenic areas. NOx also contributes to acid deposition, damaging forests, lakes and wetlands.

Sourcesimage of cars in traffic
NOx is commonly emitted in our everyday lives. Sources include power plants, gasoline and diesel engines (vehicles, generators, yard equipment, snowmobiles, power boats, etc.), home furnaces, and industrial processes. Please see EPA’s Air Emissions Sources page for more about NOx sources.

Please see Nitrogen Dioxide Attainment Status and Trends for more information.