Nitrogen gas, N₂, makes up approximately 79% of the Earth's atmosphere. Compounds of nitrogen, and in particular its oxides (although only present in trace quantities), play an important role in the chemistry of the atmosphere and its pollution.

• Nitric oxide, NO, is highly reactive and and a major combustion product. It combines readily (with a lifetime of tens of minutes) with ozone, O₃, to produce nitrogen dioxide, NO₂.
• Nitrogen dioxide, NO₂ is also reactive and plays an important role in the creation and destruction of O₃, because of which it is known as an O₃ precursor. It is also readily photolysed into NO and an oxygen atom.
• Nitrous oxide, N₂O is a stable compound that can have a liftime of about 20 years. Because of its stability it can be carried into the stratosphere, where it can be destroyed, usually by photolysis into N₂ and an oxygen atom.
• Nitric acid, HNO₃ is very soluble in water and is generally created in the atmosphere by the reaction of NO₂ with the hydoxyl radical, OH. Dissolved HNO₃ is responsible for the nitrogen contribution to the phenomenon of 'acid rain'.

The nitrogen oxides, NO and NO₂, are rapidly converted into one another and are therefore commonly considered together and generically termed NO_x. Both NO and NO₂ are free radicals, and as such are sometimes termed 'odd electron nitrogen oxides'.