How is $O_3$ estimated quantitatively?

(N/A) Quantitatively,ozone $(O_3)$ can be estimated by reacting it with an excess of potassium iodide $(KI)$ solution buffered with a borate buffer $(pH \ 9.2)$.
$1$. Ozone reacts with iodide ions to liberate iodine $(I_2)$:
$2I^- + H_2O + O_3 \to 2OH^- + I_2 + O_2$
$2$. The liberated iodine is then titrated against a standard solution of sodium thiosulphate $(Na_2S_2O_3)$ using starch as an indicator:
$I_2 + 2Na_2S_2O_3 \to Na_2S_4O_6 + 2NaI$
By measuring the volume of sodium thiosulphate used,the amount of ozone can be calculated.