1. http://www.environment.detr.gov.uk/airq/aqinfo.htm.
2. Gas Turbine Theory;Saravanamuttoo,1994
3. Polymer Films in Sensor Applications—Technology, Materials, Devices and their Characteristics;Harsanyi,1995
4. http://www.capteur.co.uk/cgi-bin/view.pl5?sensor=23.
5. Semiconducting oxides as gas-sensitive resistors