Ozone (O₃) is the triatomic, allotropic form of oxygen (O₂). It is an unstable gas with a pungent odor. Since ozone is unstable, it must be generated at the point of application.

The Ozone molecule, having a molecular weight of 48, is made up of three oxygen atoms bound by equal oxygen-oxygen bonds at an obtuse angle of 116^o49’. This structure is inherently unstable and is the reason for ozone’s powerful oxidizing ability. Ozone has approximately 150% the oxidizing potential of chlorine. The physical properties of ozone and comparative oxidizing potentials for other chemical oxidants are presented in Table 1 and Table 2, respectively.