Highly Precise Atmospheric Oxygen Measurements as a tool to detect Leaks of Carbon Dioxide

On 27 November 2015 Charlotte van Leeuwen defended her thesis successful at the Rijksuniveriteit Groningen. The title of her thesis is 'Highly Precise Atmospheric Oxygen Measurements as a tool to detect Leaks of Carbon Dioxide'. (Download).

Carbon Capture and Storage (CCS) is considered to be an important option in combatting global climate change. Although geological storage of CO2 is considered to be very safe, leakage of the gas from the storage reservoir back to the atmosphere is an important concern, from a public health but even more from a climate change combat perspective. Detecting and quantifying leaks of CO2 in the atmosphere is difficult due to the rapid mixing of the emitted CO2 with the surrounding air masses, in combination with the high natural variability of the CO2 concentration in the atmosphere.
In this thesis two strategies are presented to nevertheless be able to detect leaks of CO2 by atmospheric measurements.
In the first technique, multiple CO2 sensors were placed in close proximity of each other. Although the variation of the CO2 concentration is high in time, it is low in terms of space, at least on small scales. When placed in a small area, all sensors should in principle measure the same CO2 concentration, unless there is a source of CO2 in the area under investigation.
The second technique presented in this thesis to detect a leak of CO2 from a CCS site is much more sophisticated: it combines highly precise atmospheric CO2 measurements with atmospheric oxygen (02) measurements. It is based on the observation that sources and sinks of CO2 and 02 are coupled in almost all processes on earth. In photosynthesis, plants take up CO2 and release 02 at the same time. In fossil fuel burning and biosphere respiration this is the other way around.
In case of a leak of CO2 from a CCS site, there is no such coupling and changes in CO2 concentration are not accompanied by changes in 02 concentration. Combined measurements of CO2 and 02 over a specific time interval and determination of the 02 - CO2 trend for that interval may help to mark this time interval as suspicious (that is, a leak might be present).