Ventilation Potential in High-Rise Cities

Hazardous air pollution events periodically affect Chinese cities, putting millions of people at risk of suffering severe and often long-term health problems. With recent urbanization figures indicating that more than 100 Chinese cities now have more than 1 million inhabitants, research on causes for severe air pollution events, improvements of high-resolution air-quality models and exploration of mitigation measures has become imperative. The problem is exacerbated as megacities around the world increasingly feature tall (> 20 m) and super-tall (> 300 m) buildings and deep urban canyons. Tall buildings, in isolation or as clusters, have strong and long-distance impacts on aerodynamic and thermodynamic characteristics of the urban boundary layer. Repercussions of these effects on local air quality, street-canyon ventilation potential and overall breathability of the city, however, are currently only poorly understood and neglected in urban planning strategies. In order to adequately model air pollution or urban climate scenarios in cities with high-rise buildings, underlying urban land-surface models need to be able to capture effects of the cross-urban variability of form and function including tall buildings.

The presentation will present a review of current knowledge of tall building effects on urban flow, pollutant dispersion and air pollution based on existing field/laboratory experiments and building-resolving numerical simulations to identify key characteristics and associated modelling needs that are unique to deep urban canopies. New wind-tunnel measurements of flow in a 1:200 scale-model of a part of central London that includes several tall buildings will be presented and the impact of these structures on key parameters such as the blending height, turbulent momentum transfer and vertical exchange processes will be discussed.

The work presented is conducted as part of two multi-institutional projects between universities and research organisations in the UK and China: (i) The NERC-funded AirPro project (‘An Integrated study of Air Pollution Processes in Beijing’), set out to investigate physical, chemical and meteorological mechanisms affecting air pollution in Beijing. (ii) The ‘HighResCity’ project of CSSP China (‘Climate Science for Service Partnership China’) in cooperation with the UK Met Office, which is funded by the Newton fund to build a foundation for services in support of climate and weather resilient economic development and social welfare.