Ozone Triatomic oxygen, O3, is most commonly known as ozone. It has a resonance structure, and can be drawn in two different ways: O=O- O-O=O It is a bluish, explosive gas at room temperature, and has a boiling point of -119°C. It has a melting point of -193°C, and is a blue liquid. It's critical temperature and pressure are -12.1°C and 53.8 atm, respectively. It has a pleasant odor in concentrations of less than 2 ppm, and is irritating and injurious in higher concentrations. The density of ozone gas is 2.144 g/L, and the density of ozone as a liquid is 1.614 g/mL. It is extremely unstable, and solutions containing ozone explode upon warming. It is found in varying proportions