The exchange of momentum, heat and matter (e.g. H2O, CO2, SO2, NO, NO2, O3, NH3, HNO3, VOC) in the soil-vegetation-atmosphere system over tall canopies is influenced by non-local transfer processes and the presence of distributed sources and sinks [1–4]. Depending on their water status tall plant canopies therefore have a microweather and a microclimate which significantly differ from those above neighbouring areas covered with bare soil or low vegetation. Thus also their nutrient budgets and especially the fluxes of trace substances between the atmosphere and the plant-soil system can be altered with respect to time and space. A number of studies suggest that chemical cycles inside the canopy can have a different behaviour compared to those from outside and can be coupled or decoupled from cycles in the overlying atmosphere by the various influences of dynamic and thermodynamic processes (e.g. [5–7]). Therefore a study was performed by the joint MIMMOL group to understand better the interaction between transport processes, trace gas emissions and deposition and chemical reactions within and above tall vegetation.
