The chemical compound dinitrogen trioxide (chemical formula: N2O3) is a pale blue liquid, and is unstable above 3°C (37° F) at standard pressure. It melts at -102°C (-152°F) and boils/decomposes at 3°C (37°F). The liquid at 2°C has the density 1.4 g/cm3.
Dinitrogen trioxide is produced by mixing equal parts of nitric oxide (NO) and nitrogen dioxide (NO2), and cooling the mixture below -21°C (-6°F). The gases react, forming the blue liquid N2O3. Dinitrogen trioxide is only stable in the liquid and solid phases, and decomposes back to NO and NO2 when heated above 3°C.