High altitude balloons used by Environment Canada to measure O3 levels in the atmosphere also use a similar idiometric titration where the iodine liberated is measured by back titration with sodium thiosulfate. In this case, the iodine is generated by oxidation of iodide by ozone:
O3 (g) + 2I- (aq) + 2H+ (aq) - I2 (aq) + O2 (g) + H2O (l)
If 10,000 L of air were bubbled through an acidic iodide solution (at STP) and was then back titrated with 19.4 mL of a 1.2x10-4 M Na2S2O3 solution to reach equivalence, what is the concentration of ozone in that sample of air (in ppm)?