Industry and a yellow sky background

NOx is the collective term for the nitrogen oxides NO and NO2, which are significant components of harmful air pollution.


NOx is formed in combustion processes such as engines, power plants, and boilers, as well as industrial processes with very high temperatures (e.g., in smelters). NOx emissions in Norway mainly come from transportation (especially road transport and shipping), oil and gas activities, and land-based industry.

Harmful Effects

NOx contributes to respiratory diseases, the formation of ground-level ozone, and acid rain.

  • The direct harmful effects of NOx are associated with impaired lung function and worsening of asthma, as well as respiratory diseases (e.g., COPD) and cardiovascular disease.
  • Ground-level ozone is harmful to both humans and vegetation.
  • Acid rain is harmful to ecosystems and vegetation and can lead to, among other things, fish mortality.
  • In addition to environmental and health damage, NOx also contributes to damage to materials and buildings through acid rain and ground-level ozone.

NOx emissions are particularly a local/regional problem, but NOx can also be transported over longer distances with air currents. In the upper atmosphere, NOx is involved in various processes that are important for the greenhouse gas budget, with both cooling and warming effects. NOx is a significant component of visible pollution (smog) that can be seen over large cities.

According to the Norwegian Institute of Public Health, over 4 million deaths globally in 2019 were caused by complex pollution from particulate matter, nitrogen dioxide, and ozone.