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Étude d’un système à base de micro-capteurs de gaz pour le suivi et la cartographie de la pollution atmosphérique

Abstract : The objective of this thesis is to design a low-cost gas sensor array for outdoor gas pollutants monitoring and to develop adapted standardization and data analysis methods. The device aims is to contribute to the densification of the current atmospheric pollution-monitoring network for better spatial and temporal resolution. First, we select electrochemical and metal oxide gas sensors capable to detecting and quantifying low concentrations of nitrogen dioxide and ozone in ambient air near a highway. We have characterized these micro-sensors in the laboratory using a diffusing controller system and tested them in the field by following procedures inspired from the evaluation protocol of low cost gas sensors proposed by the European Joint Research Center (JRC). The individual analysis of the data from each sensor highlights the need to merge the responses of all the sensors as well as the values of the temperature and the humidity of the atmosphere using multivariate methods of classification. The performance of several classification methods generally used in the field of multi-sensor gas systems was studied. This comparison leads us to choose Support Vector Machine regression (SVM) thanks to its performance in terms of precision and robustness. We also conduct a study on the optimization of the SVM hyper-parameters using optimization algorithms. The Generalized Pattern Search algorithm (GPS) was chosen among other algorithms due to its simplicity and reliability. Then, we highlight the problem of sensor drift over time and the need for periodic calibration. We proposed a standardization method based on SVM regression, thereby reducing the cost and the effort of full recalibration. This standardization method was also used for calibration transfer between several identical systems in order to avoid individual calibration of each system. The research work elaborated in this PhD was published in two journal papers and two IEEE conference papers.
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https://hal.univ-lorraine.fr/tel-02940704
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Rachid Laref. Étude d’un système à base de micro-capteurs de gaz pour le suivi et la cartographie de la pollution atmosphérique. Micro et nanotechnologies/Microélectronique. Université de Lorraine, 2020. Français. ⟨NNT : 2020LORR0048⟩. ⟨tel-02940704⟩

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