Nitrogen oxides are very important in the formation and loss of tropospheric ozone. They are involved in catalytic cycles and continuously react and reform. Nitrogen dioxide (NO2) is broken down by sunlight to form nitrogen monoxide (NO). This NO then re-reacts to form more NO2. Ozone and unstable oxygen compounds known as peroxy-radicals can also be involved in this cycle. We will look at these reactions in more detail later.
We emit far too much of these nitrogen oxides during combustion proceses, particularly from vehicles. The main aim of fitting catalytic converters to cars is to reduce the emission of these compounds into the air.
Other important nitrogen gases in the atmosphere include:
Nitrous oxide (N2O) which is formed during microbiological degradation processes. It is an important greenhouse gas but does not react in the troposphere. In the stratosphere it destroys ozone.
Ammonia (NH3) is the most important basic gas in the atmosphere. It comes mainly from agriculture, both from the storage of animal wastes and from fertiliser use. It reacts in the atmosphere with acid species like nitric acid to form aerosol particles.