Time scale analysis of chemically reactive pollutants over urban roughness in the atmospheric boundary layer

Abstract

Most practical dispersion models assume inert pollutants but air pollutants are often chemically reactive. There is thus a need for including pollution chemistry in plume dispersion models. In this study, turbulent dispersion of reactive pollutants in the neutral atmospheric boundary layer (ABL) over hypothetical urban area in the form of an array 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, mixes with ozone (O3) and produces nitrogen dioxide (NO2) to model bimolecular chemical reaction. The time scales of NO oxidation and dispersion are compared in details. It is found that they are coupled with each other and so collectively modify the dispersion coefficient.