One of the CORSO project focus areas is to determine the added value of supplementary observations for the observation-based operational anthropogenic CO2 emissions Monitoring and Verification Support (MVS) (CO2MVS). In WP3, we focus on two atmospheric tracers that inform about the separation of the anthropogenic and natural components in the CO2 signal: radiocarbon (14CO2) and atmospheric oxygen (O2).
Fossil fuels do not contain radiocarbon (14C), and their combustion releases CO2 that dilutes the 14C/C ratio of the atmosphere compared to other CO2 sources (e.g., biospheric) that contain 14CO2. This dilution induces a measurable depletion of the 14C/C isotope ratio in atmospheric CO2, and therefore provides a measure for the fossil fuel CO2 component (ffCO2). Atmospheric O2 is inversely coupled to CO2 in carbon cycle processes, through the O2/CO2 exchange ratio (ER). Using this coupling and process specific ERs allow to extract ffCO2 using combined atmospheric O2 and CO2 measurements.
CORSO facilitated measurements of 14CO2 and O2, specifically in the intensive sampling year 2024. CORSO enabled the expansion of the capacity of the ICOS Central Radiocarbon Laboratory in Heidelberg. This allows for measuring every flask collected in 2024 at 10 selected stations in the ICOS network for 14CO2. A new flask sampler was installed at the Białystok station in Poland. Furthermore, samples at Heathfield in the UK were analysed at University of Bristol. In total, 1363 samples have been collected and analysed.
Figure 1: sampling locations
Figure 2: 14CO2 observations and calculated ffCO2 signals at Cabauw in the Netherlands
CORSO also made it possible to install continuous O2 and CO2 measurements at the Cabauw station in the Netherlands, as the third continuous record in Europe. These measurements are performed by University of Groningen and Wageningen University in the Netherlands. The first results show a good agreement to the ICOS continuous CO2 measurements, and ICOS CO2 and O2 flask measurements. O2 and CO2 can be combined into Atmospheric Potential Oxygen which is defined as: O2 + 1.1 x CO2. This removes the influence of the biospheric processes assuming its ER is 1.1. This allows to derive a continuous ffCO2 signal.
Figure 3: first continuous O2, CO2 and APO observations at Cabauw in the Netherlands.
More information is provided in Deliverable 3.3: CORSO-D3-3-V1-3.pdf
Images and figures courtesy of the project team.