Nitrogen oxides are formed during high temperature combustion processes from the oxidation of nitrogen in the air or fuel. The principal source is road traffic. Other important sources are power stations, heating plants and industrial processes. They interact with volatile organic carbon in the presence of sunlight and contribute to the ozone formation. There are many different nitrogen oxides: Nitric oxide or nitrogen monoxide (NO), Nitrogen dioxide (NO2), Nitrous oxide (N2O), Nitrosylazide (N4O), Oxatetrazole (N4O), Dinitrogen trioxide (N2O3), Dinitrogen tetroxide (N2O4), Dinitrogen pentoxide (N2O5), Trinitramide (N4O6), etc.