A specific spectrophotometric determination of ozone in air in the presence of sulfur dioxide and nitrogen oxides

A sensitive, specific spectrophotometric method for the determination of ozone in air by the ozonolysis of 1,1-di-phenylethylene (DPE) is described. The yield of formaldehyde from the ozonolysis of several terminal olefins was determined, and DPE was found to give the highest yield, 90%. The method was checked against the EPA iodimetric method, and gives a consistent yield of formaldehyde over the ozone range 0.05–5.00 μg g^-1 of air. As sulfur dioxide is used as a reagent, its presence in air does not interfere. Interference by nitrogen oxides and other free radical oxidants is prevented by the addition of mesitol (2,4,6-trimethylphenol). Formaldehyde in air interferes, but can be determined by using the method with DPE omitted from the sampling train, and so accounted for. In the procedure, formaldehyde is determined by the reverse of the West—Gaeke method for sulfur dioxide.