Highly precise atmospheric oxygen measurements as a tool to detect leaks of carbon dioxide from Carbon Capture and Storage sites

In Carbon Capture and Storage (CCS), carbon dioxide (CO2) from fossil fuel combustion is stored underground into a geological formation. Although the storage of CO2 is considered as safe, leakage to the atmosphere is an important concern and monitoring is necessary. Detecting and quantifying leaks of CO2 in the atmosphere is, however, difficult due to the rapid mixing of the emitted CO2 with the surroundings and the high natural variability of the CO2 concentration. In this thesis we present two leak detection strategies. The first uses multiple simple CO2 sensors that are placed in close proximity to each other. Although the variability of atmospheric CO2 is high in time, it is low in space. The sensors will all measure the same concentration unless there is a source of CO2 in the area under investigation. The second technique is much more sophisticated: it combines highly precise atmospheric oxygen (O2) measurements with atmospheric CO2 measurements. Sources and sinks of CO2 and O2 are –inversely- coupled in almost all processes on earth (e.g. photosynthesis and fossil fuel burning) but not in case of a CO2 leak. Combining O2 and CO2 allows unambiguous identification of CO2 leaks. Measuring atmospheric O2 accurately is very challenging. This thesis presents a newly designed, transportable, O2 – CO2 instrument that can be used in CO2 leak detection. Atmospheric O2 measurements also have merits for studying the global carbon cycle. This thesis presents the 15 year long records for atmospheric O2 from stations Lutjewad (NL) and Mace Head (IE)