Determining the sulfur dioxide content of air

The acidimetric method, the colorimetric method with the p-rosaniline/formaldehyde reagent, or the measurement of the consumption of an oxidizing reagent after contact with the SO2 contained in the air gave only mean values covering sampling periods of several hrs. A coulometric method based on the oxidn. of SO2 by Br was used for short sampling periods and for continuous measurements. The air flowed through a soln. contg. H2SO4 4, KBr 0.1, and Br 10-6 moles/l. The Br concn. was measured by the voltage difference between a Pt electrode and a reference one. H2SO4 and Br- were formed by the reaction of SO2 with the soln. The decrease of the Br concn. involved a decrease of the voltage difference. This change was amplified and transformed in a current that generated Br at the anode and H at the cathode. The Br formed prevented a future decrease of the Br concn. As an equil. occurred, the reaction with SO2 consumed as much Br as was formed by electrolysis of the soln. The current was then proportional to the SO2 concn. in the air. The effect of reducing and oxidizing agents could be eliminated by the use of filters. The app. was fitted with a calibrated source of SO2 for the standardization and could be commanded by telephone from a computer. The detection limit was .apprx.0.004 ppm. SO2. [on SciFinder (R)