Abstract
A wide range of pollutants cannot be perceived with human senses, which is why theuse of gas sensors is indispensable for an objective assessment of air quality. Sincemany pollutants are both odorless and colorless, there is a lack of awareness, inparticular among high school students. The project SUSmobil (funded by DBU –Deutsche Bundesstiftung Umwelt) aims to change this. In three modules on the topic ofgas sensors and air quality, the students (1) are familiarized with the functionality of ametal oxide semiconductor (MOS) gas sensor, (2) perform a sensor calibration and (3)carry out environmental measurements with calibrated sensors. Based on theseintroductory experiments, the students are encouraged to develop their ownenvironmental questions. In this contribution, we focus on the experimental andmodeling approach which explains the function principle of a MOS gas sensor in a waysuitable for high school students. This includes a qualitative and quantitativedescription of a simplified sensor model explaining the main processes on the sensorsurface. In addition, an HTML-based self-learning course is presented in which thestudents investigate the sensor behavior in the presence of different substancesdepending on the sensor temperature.
Highlights
Introduction and MotivationAir pollution is the single largest environmental health risk in Europe with over 400.000 deaths per year in 2018 [1]
CO2 can serve as indicator for poor indoor air quality, because other pollutants like volatile organic compounds (VOC) correlate with the CO2 concentration, when there is no other source of VOCs besides humans [6]
The current paper focuses on module 1 – the function principle of a metal oxide semiconductor (MOS) gas sensor
Summary
Air pollution is the single largest environmental health risk in Europe with over 400.000 deaths per year in 2018 [1]. According to [13] the description of the conductivity σ of the sensor based on the grain boundary model can be reduced to the temperature-dependent function (4). A simplified model adapted to the level of learning and knowledge of high school students was developed This model is intended to describe as adequately as possible a) The sensor behavior at different operating temperatures b) The processes taking place on the sensor surface with and without reducing gas as the core of the sensor reaction. The assumed dependence of the conductance on temperature corresponds to the exponential decrease of the resistance typical for an NTC thermistor, a widely used temperature sensor, cf Fig. 5 [18] This model presentation qualitatively replaces the temperature influence of the grain boundaries of the physical model. The surface coverage remains almost constant at very high temperatures, where the fast adsorption of oxygen dominates over the reaction with the reducing gas, decreasing the response to the reducing gas, see Fig. 9
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