Dr Omduth Coceal, University of Reading, UK

Dr Omduth Coceal is a Senior Research Scientist in the National Centre for Atmospheric Science (NCAS) and is based at the University of Reading, UK. He obtained his bachelor's degree from Imperial College London and his PhD from Queen Mary, University of London. He joined the Department of Meteorology at the University of Reading in 1998, and is a Fellow of the Royal Meteorological Society (FRMetS). In the last 15 years or so, his research has focused on numerical simulation and modelling of turbulent flow and dispersion in urban areas. He was the lead author of the first DNS (direct numerical simulation) over groups of building-like obstacles and has made important contributions to clarifying the structure of turbulence over very rough surfaces. He has a number of publications focusing on turbulence and dispersion in urban areas, including direct numerical simulations and the development of a novel street network approach to modelling dispersion in city centres. He was a co-author of two extensive reviews on urban turbulence and on urban dispersion modelling, commissioned by the UK Met Office and the UK Atmospheric Dispersion Modelling Liaison Committee (ADMLC) respectively. He is the lead PI of a major EPSRC project (DIPLOS, www.diplos.org) involving several institutions in the UK and France and aiming to undertake underpinning scientific studies to improve the capability for fast modelling of dispersion in cities.

“Urban dispersion: problems, processes and modelling approaches”

Air pollution is one of the world’s biggest killers, responsible for around 3 million deaths annually. London’s air quality regularly breaches EU standards – for instance, the annual maximum permitted number of 18 breaches of hourly limits of nitrogen dioxide was exceeded in the first week of 2016 alone (The Guardian, 8 Jan 2016). Outdoor pollution, mostly due to traffic emissions, are well known to have detrimental health impacts, leading to an estimated 40,000 deaths in the UK. Much less is known about the effects of indoor pollution, but it is acknowledged that it has been overlooked and needs studying. Cities in Europe now face a heightened threat from terrorist attacks; potential terrorist scenarios include releases of harmful air-borne substances, such as toxic chemicals, biological agents or ‘dirty bombs’ in densely populated areas. Similar risks exist from accidental releases or explosions within or in the vicinity of urban areas.

In all these applications, impact assessment and mitigation measures depend on the ability to model the turbulent dispersion of pollutants in a highly heterogeneous urban environment. This in turn requires detailed knowledge of key dispersion processes and how to represent them in operational models. This talk will review the current state of the art in our understanding of urban dispersion, focusing on recent advances made by wind-tunnel studies, direct numerical simulations (DNS) and large-eddy simulations (LES). It will then examine and contrast a number of modelling approaches suitable for simplified operational dispersion modelling, including classical tools such as Gaussian models, computational fluid dynamics (CFD), and Lagrangian stochastic models as well as novel approaches such as street network and reduced-order models. The presentation will be illustrated by recent results from the DIPLOS (Dispersion of Localised Releases in a Street Network) project.