Large-eddy simulation of reactive pollutant dispersion for the spatial instability of photostationary state over idealised 2D urban street canyons
by Tracy N.H. Chung; Chun-Ho Liu
International Journal of Environment and Pollution (IJEP), Vol. 50, No. 1/2/3/4, 2012

Abstract: Dispersion of chemically reactive pollutants in the urban canopy layer (UCL) over twelve idealised two-dimensional (2D) street canyons of unity aspect ratio in isothermal conditions is examined. The reversible NO_x-O₃ mechanism is integrated into a large-eddy simulation (LES) model. The ground-level NO emission in the first street canyon and the background O₃ in the prevailing wind initiate the NO₂ production. The chemical equilibrium is measured by the photostationary state (PSS) which is a function of the time scales of turbulent mixing and chemical reactions. PSS of the first street canyon increases with increasing NO emission. For small amount of ground-level NO emission and background O₃ in the prevailing flows, (say NO/O₃ = 1/1), PSS increases gradually from the second to last street canyons. It increases faster if the NO-to-O₃ ratio is raised, say 1,000/30. Further increasing the NO-to-O₃ ratio, say 10,000/1, PSS exhibits a non-linear behaviour in which a trough is observed in the fifth street canyon.

Online publication date: Wed, 19-Nov-2014

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