How is `O_(3)` estimated quantitatively?

Explanation

When `O_(3)` is treated with excess of KI solution buffered with borate buffer (pH 9.2), `I_(2)` is liberated, quantitatively.
`2I^(-)(aq)+H_(2)O(l)+O_(3)(g)to2OH^^(-)(aq)+I_(2)(s)+O_(2)(g)`
The `I_(2)` thus liberated, is titrated against a standard solution of sodium thiosulphate, using starch as an indicator.
`underset("Sodium thiosulphate")(2Na_(2)S_(2)O_(3))+I_(2)tounderset("Sodium tetrathionate")(Na_(2)S_(4)O_(6)+2NaI)`