Impact of subgrid-scale spatial heterogeneity in the urban canopy on pollutant turbulent dispersion and chemical reactions

The complex structure of the urban canopy and the high spatial heterogeneity of emission sources significantly influence the turbulent dispersion, mixing, and chemical reactions of atmospheric pollutants. However, due to the limitation of model resolutions and insufficient understanding of these processes, current mesoscale atmospheric chemical models struggle to accurately represent these interactions, contributing to major uncertainties in urban air quality simulations. To address this issue, this study employs high-resolution computational fluid dynamics (CFD) simulations with explicitly resolved buildings and large-eddy simulations (LES) coupled with an urban canopy model to systematically investigate the synergistic effects of spatial heterogeneity in building morphology and emission distributions on pollutant turbulent dispersion and chemical reactions. The research will quantify the impact of subgrid-scale heterogeneity on effective chemical reaction rates and develop parameterization schemes for subgrid-scale pollutant turbulent diffusion coefficients and effective chemical reaction rates, designed for mesoscale models.