How is`O_(3)` estimated quantitatively?

Explanation

Ozone `O_3` reacts with excess of KI solution, buffered with borate buffer `(pH9.2)` to liberate `I_2` quantitatively.
`O_(3(g))+2I^(ɵ)+H_2O_(1)to2^(ɵ)OH_(aq)+I_(2(s))+O_(2(g))`
The `I_2` thus liberated is titrated against `Na_2S_2O_3` solution using starch as an indicator,
`2S_2O_3^(2-)toS_4O_6^(2-)+2e^(ɵ)`
`underline(I_2+2e^(ɵ)to2I^(ɵ))`
`underline(2S_2O_3^(2-)+I_2toS_4O_6^(2-)+2I^(ɵ))`