The study of diffusion processes of trace gases inside a plant canopy is challenging to experimental efforts due to its tremendously high cost and complication in instrumentation, and such field tracer experimental work is very rare. Modeling approaches such as analytical solutions to diffusion equations have been hammered by the frequent failure of K-theory and similarity theory in a canopy environment.
Here the large-eddy simulation (LES) technique is used as an alternative tool, which directly resolves three-dimensional turbulent motions with scales larger than the grid size, and parameterizes the subgrid scale processes. A reasonable assumption is made that large coherent structures dominate the transport and diffusion processes inside a plant canopy, as supported by many previous field and wind tunnel observations and large-eddy simulations.
In this study, a numerical tracer experiment is performed within and above a model forest using an LES in neutral condition. The spatial distribution and the budgets of concentrations, variances and fluxes of tracers as a function of downwind distance from line sources located at different heights inside the forest will be presented, and compared against wind tunnel data.
The limitations of the LES technique will also be examined