This highly unstable blue compound has not been isolated in pure form, but can be generated and observed as a short-lived component of gas, liquid, or solid systems.

[1] Nitrogen trioxide is an important intermediate in reactions between atmospheric components, including the destruction of ozone.

[1][2] The existence of the NO3 radical was postulated in 1881-1882 by Hautefeuille and Chappuis to explain the absorption spectrum of air subjected to a silent electrical discharge.

[1] Nitrogen trioxide can be prepared in the gas phase by mixing nitrogen dioxide and ozone:[1] This reaction can be performed also in the solid phase or water solutions, by irradiating frozen gas mixtures, flash photolysis and radiolysis of nitrate salts and nitric acid, and several other methods.

[1] Nitrogen trioxide is a product of the photolysis of dinitrogen pentoxide N2O5, chlorine nitrate ClONO2, and peroxynitric acid HO2NO2 and its salts.