Fluxes of carbon dioxide (CO2), being a major greenhouse gas, are of great importance to understand and monitor. Findings have shown that while CO2 emissions enhanced by humans triggered the greenhouse gas effect, several significant CO2 fluxes in nature that are climate sensitive may still be poorly constrained, especially those from inland waters and its surrounding soils and sediments. This including different processes such as decomposers degrading organic material. At present, direct measurements of CO2 from soils, waters or CO2 concentrations in surface water, are typically labour intensive or require costly equipment. Therefore, small inexpensive CO2 mini loggers, originally made for indoor air quality monitoring, are for this project being developed further for field use, as a convenient equipment to measure CO2 emissions. However, a requirement is that the mini loggers are stable and robust against interference by other air components, including water vapour, and physical factors such as temperature. Therefore, the mini loggers were for this project studied further under different environmental conditions such as temperature and humidity in a controlled environment. The results were analysed using multiple regression analysis where the CO2 concentration (CO2), measured by the LGR instrument, versus the logger IR signal (IR), temperature (T) and relative humidity (RH) were studied. Unlike some previous studies, this project studied a large CO2 concentration interval (400 – 10 000 ppm).  The results show that there was a strong regression for IR versus CO2. The regression for both RH and the T was on the other hand very weak. However, there were factors that could have affected the mini logger. This since it was noticed that the mini loggers’ ability to calculate the CO2 concentration was worsened when the humidity was increased during the experiments. It is believed that the cause was condensed water, gathering in the inner parts of the mini logger. This because the sensor chamber had a lower temperature than the hot air entering the sensor chamber from the humidity bottle, together with the CO2, leading to condensation. Hence, prevention of condensation inside the measurement cell is important. However, the results from the analysis shows that the factors; RH and T do not need to be taken into account when studying the CO2 concentration over a larger interval, as long as the conditions are not condensing.

L'augmentation des émissions de CO2 entraîne un réchauffement de la planète préjudiciable aux équilibres écologiques terrestres. Dans ce contexte, le stockage de CO2 dans des formations géologiques terrestres et sous-marines se pose comme un moyen intéressant de limiter les conséquences de ces émissions. Cependant cette solution nécessite une surveillance continue afin de détecter d'éventuelles fuites au niveau d'une zone de stockage. Les travaux de thèse présentés concernent le développement d'un capteur optique en fibre de chalcogénures pour la détection de CO2 gazeux fonctionnant dans le moyen infrarouge. Cette détection est basée sur un phénomène de luminescence, jouant le rôle de source déportée et partiellement absorbée en présence de CO2. Le développement de ces fibres optiques a demandé un important travail en sciences des matériaux et en caractérisation spectroscopique. Un prototype a été fabriqué et utilisé avec succès sur le terrain lors de campagnes de mesure menées in-situ. / The increase of CO2 emissions causes global warming harmful to ecological balances in earth. In this context, CO2 storage in geological formations is an interesting way to limit the consequences of these emissions. However, this solution requires continuous monitoring to detect possible leaks at storage area. The presented work involves the development of an optical fiber sensor based on chalcogenide glasses for the CO2 gas detection operating in the infrared. This detection is based on a luminescent phenomenon, acts as a remote source and partly absorbed in the presence of CO2. The development of these fiber optic asked important work in materials science and spectroscopic characterization. A prototype was manufactured and successfully used in the field during measurement campaigns in situ.

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