A method of the determination of sulfur dioxide in air with a detection tube is described. The tube contains a chromogenic reagent, 2,2'-dinitro-5,5'-disulfanediyldibenzoic acid, dimethyl sulfoxide, ammonium acetate and glycerol. The method is sensitive (detection limit 1 mg.m ³) and enables colorimetric determination based on the length of the coloured indication zone.