Disentangling carbonyl sulphide ecosystem relative uptake using (inverse) canopy modelling

Carbonyl sulphide (COS) has been used in earlier studies as a proxy for determining photosynthesis. To this end, the concepts of leaf relative uptake (LRU, ratio of COS and CO2 deposition velocities at leaf scale) and ecosystem relative uptake (ERU, ratio of COS and CO2 deposition velocities at ecosystem scale) are often used. We have constructed a new canopy model that simulates LRU and ERU. This model consists of multiple layers, each having its own air temperature, COS, CO2 and H2O mixing ratio. Sunlit and shaded leaves are modelled separately. We coupled this model to the Chemistry-Land Surface Soil Slab (CLASS) model to simulate the atmospheric mixed layer and surface layer above the canopy. An inverse modelling framework is built around these models, allowing for an optimisation of model parameters. In our presentation we will mostly focus on using this framework to analyse the differences in leaf relative uptake in the model, that together influence the overall ERU. We find large differences in LRU between sunlit and shaded leaves, to a large extent caused by differences in stomatal conductance.