Continuous measurement of sulfur dioxide in atmospheric air by means of colorimetric analysis

Abstract

Continuous determination of sulfur dioxide in the atmospheric air by the use of a modified p-rosaniline-formaldehyde reagent has been described. The measurement was made intermittently once every 60 min. by an automatic analyzer equipped with a singlepath colorimeter. The discoloration of the reagent with temperature was avoided by a specially designed bubbler in a constant-temperature chamber. The transmittance ratio method employed gave accurate results even at high blank values, hence the reagent was used repeatedly by circulation only to measure the difference in its coloration before and after the absorption of sulfur dioxide, and the analyzer could be used for long without feeding new reagent. The lower limit of the determination of sulfur dioxide with this instrument was 0.3 pphm.