Decaying Scalars Emitted by a Forest Canopy: a Numerical Study

A large-eddy simulation is modified to include multiple scalars emitted by a plant canopy. Each of these scalars is subjected to varying rates of chemical loss. Presented is a detailed comparison between conserved species and species undergoing firstand second-order chemical loss. Profiles of mean mixing ratio, mixing-ratio variance and vertical mixing-ratio flux reveal the influence of chemical reactivity. Distribution of the scalar source through the depth of the canopy is shown to locally reduce the reaction rate for second-order species. Transport efficiencies, diffusion coefficients, and mean source heights also exhibit chemical dependencies. Budgets of mixing-ratio variance and flux elucidate the mechanisms through which chemistry modifies each. Instantaneous fields show the existence of intermittently occurring coherent structures that are thought to enhance species segregation.