Large eddy simulation study of the role of canopy density and structure in removing air pollution by dry deposition

Techno-Ecological Synergy (TES) is a technique for including ecosystems in industrial processes design. One of the main participants in TES is the forest ecosystem, which is able to reduce air pollution emitted during industrial processes. We tested the effect of density and spacing of canopy patches on dry deposition velocity of an arbitrary scalar around a virtual industrial complex with the purpose of quantifying the potential improvement to air quality downwind. We simulated the interactions between the forest patches and the atmosphere using the Parallelized Large Eddy Simulation Model (PALM). Three canopy-structures were considered: a homogeneous canopy, canopy strips parallel to the wind and canopy strips perpendicular to the wind direction. For each non-homogeneous canopy structure scenario, we considered thin, intermediate, and wide strips, while the spacing between strips was assumed equal to the strip’s width. Sparse and dense canopies were simulated for each case. The results showed that strips perpendicular to wind direction had more dry deposition than parallel strips, and sparse canopies are being more efficient in scalar deposition than dense canopies. Those results can be explained by canopy-induced turbulence that couple the air within and above the canopy and in sparser canopies lead to more effective mixing of the canopy air and consequently higher deposition per leaf area when the coupling is stronger.