Nitrogen Dioxide | American Lung Association

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Nitrogen Dioxide

What Is Nitrogen Dioxide?

Nitrogen dioxide, or NO2, is a gaseous air pollutant composed of nitrogen and oxygen. NO2 forms when fossil fuels such as coal, oil, gas or diesel are burned at high temperatures. NO2 also mixes in the outdoor air to form particle pollution and ozone. It is one of six widespread air pollutants that have national air quality standards to limit them in the outdoor air. NO2 can also form indoors when fossil fuels like wood or natural gas are burned.

What Are the Health Effects?

Nitrogen dioxide causes a range of harmful effects on the lungs, including:

  • Increased inflammation of the airways
  • Worsened cough and wheezing
  • Reduced lung function
  • Increased asthma attacks
  • Greater likelihood of emergency department and hospital admissions

New research warns that NO2 is likely to be a cause of asthma in children. 1

Looking beyond the lungs, newer research has linked NO2 to cardiovascular harm, lower birth weight in newborns and increased risk of premature death.1

What Are the Sources of Nitrogen Dioxide Emissions?

Cars, trucks, and buses are the largest sources of emissions, followed by power plants, diesel-powered heavy construction equipment and other movable engines, and industrial boilers. Manmade sources in the U.S. emitted 14 million metric tons of nitrogen oxides, mainly from burning fuels, in 2011.3 Emissions of nitrogen dioxide will decline as cleanup of many of these sources continue in future years.

Where Do High NO2 Concentrations Occur?

Monitors show the highest concentrations of outdoor NO2 in large urban regions such as the Northeast corridor, Chicago and Los Angeles.4 Levels are higher on or near heavily travelled roadways.

NO2 can be a problem indoors, as well. Kerosene or gas space heaters and gas stoves also produce substantial amounts of nitrogen dioxide. If those heaters or stoves are not vented fully to the outside, higher levels of NO2 can build up indoors.


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