Air pollution monitoring using semiconductor toxic gas sensors

The SnO/sub 2/ toxic gas sensors, which are usually used in alarm systems, were integrated in air pollution monitoring systems for ammonia, hydrogen sulphide, carbon monoxide and freon (R113 and R22). The sensitivity curves were extended for small concentrations using a parameter extraction method based on a simple semiconductor theory and on a n-dimensional minimisation algorithm. The sensors are working in real-time regime, 100 concentration values for each sensor were measured in 30 minutes. Concentrations lower than EPA limits have been measured.<>