Nitrogen Dioxide (NO2)
A reddish-brown gas produced primarily by vehicle engines and power plants that contributes to smog and respiratory problems.
Detailed Explanation
Nitrogen dioxide is a highly reactive gas that forms primarily from the burning of fossil fuels in vehicles, power plants, and industrial facilities. It is one of a group of gases called nitrogen oxides (NOx). NO2 is both a significant air pollutant on its own and a key precursor in the formation of ground-level ozone and fine particulate matter. Short-term exposure can aggravate respiratory diseases, particularly asthma, leading to symptoms such as coughing, wheezing, and difficulty breathing. Long-term exposure is associated with the development of asthma in children and may increase susceptibility to respiratory infections. NO2 concentrations are typically highest near major roadways and in urban areas with heavy traffic. The EPA's annual standard for NO2 is 53 parts per billion. Vehicle emissions are the largest source, which is why NO2 levels have generally declined as vehicle emission standards have tightened and electric vehicle adoption has increased. However, some cities near major highway corridors and freight hubs continue to show elevated NO2 levels. AirHistory data shows NO2 is rarely the dominant pollutant for an entire city but contributes to overall AQI readings in many urban areas.
Related Terms
Ozone (O3)
A reactive gas formed at ground level when sunlight triggers chemical reactions between nitrogen oxides and volatile organic compounds.
Smog
Visible air pollution, primarily composed of ground-level ozone and fine particles, that reduces visibility and harms health.
Criteria Pollutants
The six common air pollutants regulated by the EPA under the Clean Air Act: ozone, PM2.5, PM10, CO, NO2, and SO2.
Emissions Inventory
A comprehensive accounting of air pollutant emissions from all sources in a geographic area, used for regulation and planning.
Frequently Asked Questions
A reddish-brown gas produced primarily by vehicle engines and power plants that contributes to smog and respiratory problems.
Nitrogen dioxide is a highly reactive gas that forms primarily from the burning of fossil fuels in vehicles, power plants, and industrial facilities. It is one of a group of gases called nitrogen oxides (NOx). NO2 is both a significant air pollutant on its own and a key precursor in the formation of ground-level ozone and fine particulate matter.
this entity is one of the U.S. air quality and pollution monitoring concepts that recurs across this site. The definition above is the technical answer; the paragraphs below add the practical context for how the concept connects to the the EPA Air Quality System (AQS) data behind every per-entity page on the site.
In the the EPA Air Quality System (AQS) data, this concept shapes one or more of the fields that drive the per-entity grades and rankings on this site. The methodology page describes which fields feed into which output; this glossary entry documents the underlying term.