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Origin, properties and effects of NO2

NO2 or nitrogen dioxide is a substance released by combustion processes.

Over three-quarters (78%) of the air we breathe is composed of nitrogen (N2). At high temperatures, nitrogen reacts with oxygen (O2) to form nitrogen monoxide (NO) and nitrogen dioxide NO2. NO is further converted to NO2 in the atmosphere. The collective name for NO and NO2 is nitrogen oxides (NOx).  

N2 + O2 → NO (→ NO2) and partly NO2

NO2 is a reactive gas ("strong oxidant") involved in the formation of ozone and particulate matter (smog) and is known to be irritating to the human respiratory system. It has a significant effect on human health and contributes to respiratory problems:

  • irritation nose, throat, eyes, lungs
  • asthma attacks
  • respiratory complaints

NO2 sources from human activity (65% of total nitrogen dioxide emissions)

Nitrogen dioxide in the atmosphere has both natural and anthropogenic sources, with humans causing the vast majority (65%), through emissions from:

  • cars
  • ships
  • airplanes
  • industrial processes
  • power plants

The combustion of oil, coal and gas is responsible for increasing levels of carbon dioxide (CO2) in the atmosphere, one of the main causes of global warming. In addition to large amounts of NO2 and CO2, those combustion processes of heating systems, power generation and engines (transportation) also release other pollutants into the atmosphere, such as:

Despite increased awareness around the carbon footprint and the impact of energy consumption, the use of non-renewable fossil fuels continues to increase worldwide for the time being.

Natural sources of NO2 (35% of total nitrogen dioxide emissions)

Nitrogen dioxide is also released from natural combustion processes such as forest fires and lightning. In addition, plants and bacteria can also produce NO2 in the soil or water.

Combustion processes of heating systems, power generation and engines (transportation) release large amounts of CO2 and other pollutants into the atmosphere, such as nitrogen dioxide (NO2) and sulfur dioxide (SO2). Image credits National Maritime Foundation.
The main source of NO2 is of human origin. NO2 is mainly caused by emissions from cars, ships, aircraft, industrial processes and power plants. Credits pxfuel.
Amount of nitrogen dioxide averaged over a 3-year period (2018-2020), measured by the TROPOMI instrument. Pollution from smaller cities and individual power plants is visible. The color is an indication of the amount of gas in the atmosphere (with more blue colors indicating low concentrations, red/purple shades indicating high concentrations). Credits BIRA-IASB Tropomi.