Modelling Atmospheric CO2 in Denmark for Remote Sensing applications

The Copernicus sentinel expansion missions include the first European CO₂ measuring satellite, CO2M, scheduled to be launched in late 2027. To utilize the CO2M satellite data, it requires a good knowledge of the variation in anthropogenic and natural sources of CO₂ from models and observations. In this project, we present new modelling results of the temporal and spatial variation in atmospheric CO₂ across Denmark. This is done by employing an updated version of the DEHM-SPA-CO2 model system, being developed.

The DEHM-SPA-CO2 model system consists of the Danish Eulerian Hemispheric Model (DEHM) adapted for CO₂ and coupled to the mechanistic biosphere flux model Soil-Plant-Atmosphere (SPA). The model has been updated with a new high-resolution emissions dataset for Denmark, as well as simulated traffic activity from COMPASS, following different experimental policies for impacting emissions. The model system is evaluated against the ICOS station network, and preliminary results show good agreement.

Additionally, data from a new urban observation site in Copenhagen are used together with satellite data from OCO-2 and GOSAT-2 to evaluate the modelling results. GOSAT-1 was also considered but only few observations are available for Denmark. The Urban CO₂ station is located on top of a building in Copenhagen and will be used to evaluate the model representation of Traffic emissions. The OCO-2 and GOSAT-2 data are used to fit a seasonal variation for Denmark.

Lastly, we present a discussion of the possibility of doing mass flux estimates for emissions from Copenhagen using OCO-2 overpasses in optimal wind conditions. This, however, still faces the challenge of a low signal-to-noise ratio. While it is typically manageable for point sources, the more diffuse emissions from a city such as Copenhagen result in a lower ratio, complicating the inference of CO₂ signals.