Nitrogen oxides, NOx

The term 'nitrogen oxides' (NOx) is usually used to include two gases-nitric oxide (NO), which is a colourless, odourless gas and nitrogen dioxide (NO2), which is a reddish-brown gas with a pungent odour. Nitric oxide reacts with oxygene or ozone in the air to form nitrogen dioxide. Inhalation of the pure gases is rapidly fatal.Other oxides of nitrogen include NO3 (nitrogen trioxide), N2O (nitrous oxide), N2O4 and N2O5. Nitrous oxide is a potent greenhouse gas and also causes damage to the ozone layer. N2O4 is a dimer in equilibrum with NO2 and N2O5 is very unstable, usually only present in significant quantities at night (it is broken by sunlight).