Nitrogen oxides (NOx) is a family of seven different nitrogen-oxide compounds, of which nitrogen dioxide (NO2) is the form that is most prevalent
and of most environmental concern.
Nitrogen diooxide is formed when nitrogen and oxygen (both naturally occurring in the air) react at high temperatures, i.e. in
different types of combustion processes. NO2 is harmful to the respiratory system and reacts with other chemicals in the air to form both ozone and particulate matter.
It is also a source of acidification and eutrophication in aquatic systems. NOx have a relatively short lifetime in the atmosphere and NOx concentrations are thus dependent
on the proximity of sources.