Carbonyl Sulphide (COS) is emitted from the ocean and from anthropogenic activities, and is taken up by the biosphere and destructed in the stratosphere. COS uptake proceeds in a similar way as Carbon dioxide (CO2), through plant stomata. Therefore, COS uptake can be used as a proxy to CO2 assimilation in biosphere, and could be key to understand the global carbon cycle. However, the COS budget is also poorly known. This project will estimate an accurate COS budget, focusing on the uptake by the biosphere. We will use a land surface model and a chemical transport model, in which we simulate both CO2 and COS. By comparison to observations, and inverse modelling we aim to learn more about the coupled uptake of CO2 and COS by the biosphere.