Differentiating NO2 and O3 at Low Cost Air Quality Amperometric Gas Sensors

This study deals with the differentiation and quantification of both nitrogen dioxide and ozone at ppb level when using amperometric gas sensors. We investigate, here, the addition of a layer of MnO2 microparticles powder as a chemical filter for ozone in a commercial amperometric gas sensor. Experimental results show that a sensor equipped with an MnO2 powder filter is insensitive to O-3 but gives a well-defined limited current signal when exposed to NO2. In contrast, an unfiltered sensor senses both gases with a defined sensitivity for each gas. We find that the use of a pair of sensors, with one of the sensors filtered and one unfiltered, allows the quantification of both O-3 and NO2. However, the MnO2 filter confers some indirect NO cross-sensitivity to the filtered sensors. Further studies show that it is possible to minimize this unwanted cross-sensitivity by replacing the MnO2 microparticles powder filter by an MnO2/PTFE microparticle composite filter powder. We find that the developed sensors allow reproducible measurements, linear output with the concentration and significant O-3 filter capacity for an extended period of time.