Modelling and measuring transport processes within urban surface layer at high spatio-temporal resolutions
The transport of momentum, heat, and other atmospheric quantities in the urban surface layer (USL), the lowest part of the urban boundary layer (UBL), mediates the exchanges between urban landscapes and the atmosphere. High-resolution modelling and observational data are essential to understand urban surface layer transport processes, but many widely-used approaches struggle with urban variability. By covering both state-of-the-art modelling and novel observational approaches, this thesis provides a wide perspective on transport processes within the USL, advancing both methodological tools and fundamental understanding of urban–atmosphere interactions from a scale of a single street canyon to city-scale.
Large-eddy simulations (LES) were used to examine the effects of urban vegetation on street canyon ventilation and subsequently local air quality. The results show that vegetation reduces ventilation, increasing pollutant concentrations at the pedestrian level. By analysing the relationship between the structure of the vegetation canopy and ventilation, strategies to mitigate these effects are proposed. To address the need for an integrated micro-to-mesoscale UBL modelling, a new urban canopy model for the PALM model system was developed and evaluated, demonstrating its ability to capture key urban-atmosphere exchanges of momentum, heat, and moisture. High-resolution fibre-optic distributed temperature sensing (DTS) was employed to measure the USL thermal structure and mixing, revealing transient meteorological effects and the limitations of widely used surface layer similarity theory in urban environments.
The findings contribute to the advancement of UBL modelling, knowledge of the performance of novel measurement techniques, and support evidence-based urban planning decisions. The methodological advancements of the thesis pave the way for novel integrated studies of the USL and the UBL.
