Parameterisation study of chemically reactive pollutant dispersion over idealised urban areas based on the Gaussian plume model

Dispersion of pollutants emitted from vehicles over urban areas largely affects pedestrian-level air quality. In this study, turbulent dispersion of reactive pollutants in the ABL over hypothetical urban areas in the form of idealised street canyons is investigated using large-eddy simulation (LES). Nitric oxide (NO) is emitted from the first street canyon into the urban ABL doped with ozone (O3). First of all, we make use of the advection-diffusion equation with chemical kinetics to derive the theoretical relation between the dispersion coefficients of tracer and reactive pollutants. Next, the source depletion analogy is used to determine the plume shape instead of the conventional Gaussian plume model. Finally, regression to the LES output unveils that the vertical dimensionless NO concentration profiles exhibit self-similarity for a range of background O3 concentrations. A new parameterisation of reactive plume dispersion over urban areas, whose performance is remarkable over the mean plume rise, is thus suggested.