Tracer concentration profiles measured in central London as part of the REPARTEE campaign

There have been relatively few tracer experiments carried out that have looked at vertical plume spread in urban areas. In this paper we present results from two tracer (cyclic perfluorocarbon) experiments carried out in 2006 and 2007 in central London centred on the BT Tower as part of the REPARTEE (Regent’s Park and Tower Environmental Experiment) campaign. The height of the tower gives a unique opportunity to study vertical dispersion profiles and transport times in central London. Vertical gradients are contrasted with the relevant Pasquill stability classes. Estimation of lateral advection and vertical mixing times are made and compared with previous measurements. Data are then compared with a simple operational dispersion model and contrasted with data taken in central London as part of the DAPPLE campaign. This correlates dosage with non-dimensionalised distance from source. Such analyses illustrate the feasibility of the use of these empirical correlations over these prescribed distances in central London

Fluid tunnel research for challenges of urban climate

Experimental investigations using wind and water tunnels have long been a staple of fluid mechanics research for a large number of applications. These experiments often single out a specific physical process to be investigated, while studies involving multiscale and multi-physics processes are rare due to the difficulty and complexity in the experimental setup. In the era of climate change, there is an increasing interest in innovative experimental studies in which fluid (wind and water) tunnels are employed for modelling multiscale, multi-physics phenomena of the urban climate. High-quality fluid tunnel measurements of urban-physics related phenomena are also much needed to facilitate the development and validation of advanced multi-physics numerical models. As a repository of knowledge in modelling these urban processes, we cover fundamentals, recommendations and guidelines for experimental design, recent advances and outlook on eight selected research areas, including (i) thermal buoyancy effects of urban airflows, (ii) aerodynamic and thermal effects of vegetation, (iii) radiative and convective heat fluxes over urban materials, (iv) influence of thermal stratification on land-atmosphere interactions, (v) pollutant dispersion, (vi) indoor and outdoor natural ventilation, (vii) wind thermal comfort, and (viii) urban winds over complex urban sites. Further, three main challenges, i.e., modelling of multi-physics, modelling of anthropogenic processes, and combined use of fluid tunnels, scaled outdoor and field measurements for urban climate studies, are discussed

Numerical and experimental investigation of air pollutant dispersion in urban areas

Air pollution is predominantly an urban problem affecting residents living in or around cities. According to the 2014 report of the World Health Organization (WHO), air pollution is now the world’s largest single environmental health risk (WHO 2016). This problem is exacerbated by rapid global population growth (Wania, Bruse et al. 2012), and densely populated urban areas are hotspots of this high risk due to outdoor air pollutant exposure, which also affects indoor air quality. Despite the advancements in urban policies necessary for curtailing air pollutant emissions, it is vital to adopt appropriate strategies in urban planning to manage and reduce outdoor air pollution to minimise the negative impact on public health (Li, Shi et al. 2020). Natural ventilation in the built environment is associated with enhancing outdoor and indoor air quality due to its air pollutant mitigation capacity (Li, Ming et al. 2021). Therefore, natural ventilation capacity deserves special attention from a fundamental perspective, resulting in novel solutions for combating this global problem. This research project focuses on the underlying wind-structure interaction mechanisms involved in the air pollutant dispersion process around buildings. The effect of building cross-section shape and air pollutant density are investigated, and a new fundamental concept of air pollutant emission regions is introduced. The effect of building cross-section shape is further investigated in an idealised generic building cluster based on the fundamental flow structure. Additionally, mean and transient features of air pollutant dispersion based on both continuous air pollutant emission and stagnant air pollutants around a generic isolated building are explored in detail. Finally, two new indices based on air pollutant exposure time in a scaled model are proposed to capture full-scale air pollutant time integrated with air pollutant concentration