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Multi-walled carbon nanotube (MWNT) networks were investigated as resistive gas sensors for nitrogen dioxide detection. Sensor films were fabricated by airbrushing MWNT dispersions on alumina substrates. Sensors were characterized by resistance measurements from 25 to 250degC in air atmosphere, in order to find the optimum detection temperature. The best response to NO2 was obtained at 25degC. The tested MWNT sensors were sensitive to low NO2 concentrations in air atmosphere. Moreover, these sensors provided no response to interfering gases such as H2, NH3, toluene and octane. Thermal treatments, based in repeated heating and cooling of the films, increased the sensor response to NO2.