Urban aerodynamics and turbulent dispersion

Exposure to poor air quality in urban areas is one of the largest environmental health risks in the UK. Accurate pollution dispersion models are important for air quality forecasting and to inform urban planning and policy. There is currently a gap in understanding in how air pollution spreads at local scales (those relevant to pedestrians) and how it can be affected by heterogeneous urban terrain. This talk describes high-fidelity experiments of urban aerodynamics using scale models in a water flume facility and a passive dye as a surrogate for air pollution. Simultaneous Particle Image Velocimetry (PIV) and Planar Laser-Induced Fluorescence (PLIF) capture full two-dimensional quantitative images of the velocity and concentration at the fine scales near the pollution sources and at the city scale. The results highlight the role of tall buildings and local geometry on the relative importance of advection and turbulent diffusion processes. In this context, the strengths and limitations of current turbulent dispersion models are discussed for simplified, urban, and indoor applications.