Frederik Schrader

On 03.07.2019, Frederik Schrader successfully defended his PhD thesis entitled "Challenges and perspectives in modelling biosphere-atmosphere exchange of ammonia" at the Faculty of Science of the Vrije Universiteit Amsterdam. His work was based on research within the BMBF Junior Research Group "NITROSPHERE" and the UBA project "FORESTFLUX".

The aim of this thesis was the identification of knowledge gaps and uncertainties in the state-of-the-art of modelling atmospheric dry deposition of ammonia.

It was based on a total of four studies, each of which deals with different aspects of modelling. The first study was a literature survey on historical measured and modelled estimates of the so-called ammonia dry deposition velocity. Next, a specific part of dry deposition models that describes the non-stomatal exchange of ammonia was scrutinised with respect to its physical plasubility and validity compared to micrometeorological observations. In the third study, a potential approach for coupling C and N cycles within biosphere-atmosphere exchange models was presented. In the last study, a statistical correction method for inevitable bias introduced when working with low-resolution input data was developed and succesfully demonstrated.

In the end, it was found that there is a strong need for additional field observations of ammonia biosphere-atmosphere exchange, since the majority of the limited number of existing datasets already had to be used in model development and calibration, leaving little to no room for independent validation. Nevertheless, new progress in the parameterisation and application of deposition models, and further reduction in overall uncertainty, are promising results for future directions towards the implementation of low-cost, hybrid model-measurement based ammonia dry deposition networks.