Semiconductor gas sensors for environmental monitoring

Atmospheric pollution is still a topical problem in most European cities; it injures human health and greatly damages monuments and historical buildings. Atmospheric pollution control is today performed by means of traditional analytical techniques, which are expensive and require cumbersome devices. Thereby, low cost, portable and versatile equipment is an issue. Recently developments in the European legislation have caused a general change in the management of air quality assessment, making proposable the use of reliable solid state gas sensors. This work aims to analyze the most important semiconductor oxides for gas sensing. Aspects, such as the role of nanostructures to improve gas sensor performance, addition of catalysts and/or dopants to obtain a better selectivity, theoretical models to justify the size-dependent behaviour of the gas response of nanocrystalline oxides will be described. Array of these sensors, assembled in small remotely controlled monitoring units, have been used for on-field tests. The results of a long term field trial, performed locating several units closely to conventional monitoring stations, will be reported, as well as the experiments aimed to evaluate the concentrations of the same pollutants at different heights. These experiments are crucial to investigate air quality inside buildings, since the pollution of the outdoor air is one of the main factors affecting the indoor atmosphere.