Evaluation of atmospheric pollution by two semiconductor gas sensors

After a brief introduction about: the different gaseous pollutants present in the atmosphere; the cause of their concentration rise: their consequence s on human health; and the different devices used to monitor each gas, two types of semiconductor gas sensors are presented. The first of them is a si mple InP-based resistive sensor. The sensitive layer is a thin n-type InP e pitaxial layer grown on a semi-insulating InP substrate. The electrical res istance, increasing in the presence of oxidising gases, is measured between two ohmic contacts. The second sensor is a thin film of copper phthalocyan ine deposited by sublimation on an alumina substrate. The conductivity of t he phthalocyanine layer increases in the presence of oxidising gases. Influ ence of NO2 and O-3, especially at low concentration, is investigated. Infl uence of other parameters like operating temperature or interfering gases i s also studied. In conclusion, optimisation of sensor characteristics to im prove the evaluation of oxidising air pollutants concentrations is discusse d. (C) 2001 Elsevier Science B.V. All rights reserved.