Ozone in a state of gas is colorless. When thin film forms, ozone shows blue sky. Ozone in a state of liquid shows dark brown or almost black.
Ozone in a state of solid shows purple. Ozone smells unique. When there is ozone of 0.015PPM (0.01mg/Kg), most people can smell it.
Right after ightning, people can smell ozone. (because ozone is generated by electric discharge.)

You may smell ozone because office machines such as copier, facsimile and laser printer which use high voltage power supplies generate ozone though the amount is small. As ozone is very unstable and it is not possible to store ozone. Ozone is very unstable and impossible to be used with it stored like other gases and thus it is used by generating it through corona discharge or UV source.


Ozone has wavelength absorption characteristics of 200-300 nanometer UV Spectrum called Hartely Band.
The highest absorption wavelength is 255.3NM in gas and 260NM in water (molar extinction coefficient 3.292/M.cm).

Ozone is decomposed easily in air or water as it is very unstable. Rate of decomposition of ozone depends on temperature,
concentration and pressure. Ozone in a state of liquid is very unstable and it is decomposed to oxygen and water in a short time
(half life: 20-30 min. temperature: 20°C). Rate of decomposition of ozone is greatly influenced by pH. Ozone is decomposed by OH-.
In other words, ozone is relatively stable in a state of acid. However, it becomes unstable in a state of alkali and its rate of decomposition increases.