The analyses of air quality using chromatography or optical methods are very accurate but rather expensive. A cheaper solution consists of using solid state chemical sensors in easy-to- use portable and rugged equipment or distributed systems to achieve a continuous monitoring of pollution. Nevertheless it is difficult to discriminate among a set of gases because these sensors have poor selectivity. Measurements on thick-film tin oxide gas sensors have shown that their conductance transient, when they are exposed to a step change in gas concentration, is diffusion limited. The analysis and characterization of this transient enables a rise time to be obtained, which is independent of the final conductance value and depends, among other parameters, on the diffusion coefficient of gases into the porous structure of the sensor. This parameter is easily measurable and gives useful information for gas/vapor recognition. In particular in this work we have shown that it is possible to discriminate among a set of three volatile organic compounds VOCs (benzene, toluene and o-xylene) using a commercial Taguchi Inc. semiconductor gas sensor.
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