Continuous monitoring of ozone in air by reflectiometry

Abstract

A porous cellulose tape containing silica gel as an absorbent and impregnated with a processing solution that includes potassium iodide, starch, buffer solution, glycerin and methanol was developed for the detection of ozone in air. When the sample is passed through the tape, ozone is absorbed on the surface of the tape, and reacts with potassium iodide to form a colour stain. The intensity of the colour stain is proportional to the concentration of ozone at a constant sampling time and flow rate, and was recorded by measuring the intensity of reflected light (555 nm). The detection limit was 5 ppb of ozone with a sampling time of 60 s and a flow rate of 400 ml min^–1. The sensitivity of the tape could be maintained for at least 1 month when stored in a desiccator. Reproducibility tests showed that the relative standard deviations of the response (n= 10) were 2.4 and 4.2% for 0.2 and 0.05 ppm of ozone, respectively. No interference was observed from ethanol (1 vol.-%), acetone (1 vol.-%), trichloroethylene (1 vol.-%), carbon dioxide (4.9 vol.-%), carbon monoxide (100 ppm), sulfur dioxide (30 ppm), hydrogen chloride gas (5 ppm), acetylene (120 ppm) or ammonia (40 ppm). The relative intensities of chlorine, nitrogen dioxide and hydrogen peroxide gas were 25, 2 and 1.1% of that of ozone, respectively.