A differential galvanic atmospheric ozone monitor

Abstract

An automatic atmospheric ozone analyser that has been developed in these laboratories is described. The unattended instrument can perform measurements over periods of several weeks.

The principle used involves the liberation of halogen by ozone from a phosphate-buffered solution of halide and the halogen concentration is determined galvanometrically. A differential measuring technique with a galvanic cell with two cathodes and one counter electrode is used; background and noise current of the detector are extremely low and stable. The noise is equivalent to about 0·6 µg m^–3 of ozone, and the non-cumulative drift over a period of several weeks is equivalent to not more than 6 µg m^–3 of ozone. The time constant is about 40 s.

Selectivity of the instrument for ozone has been demonstrated by laboratory experiments and in field testing and, based on an ozone-to-halogen stoicheiometry of 1:1, the instrumental results obtained in field testing are in excellent agreement with those obtained by other techniques applied to and described for the determination of ozone.