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High-resolution impacts of traffic on air pollution
Speaker Name
Dr. Marc Stettler
Speaker Detail

Senior Lecturer
Faculty of Engineering, Department of Civil and Environmental Engineering
Imperial College London

G4701, 4/F, Yeung Kin Man Academic Building (YEUNG), City University of Hong Kong, Kowloon Tong, Kowloon, Hong Kong

School of Energy and Environment
City University of Hong Kong


Most cities suffer from elevated concentrations of pollution as a result of road traffic exhaust emissions. Our picture of personal exposure is improving and measurements indicate that exposure to ambient air pollution in cities is highly variable in time and space. This talk will discuss methods to estimate vehicle emissions using real-world emissions data and machine learning approaches. Secondly, the talk will describe recent research comparing the results from two air quality models. The large-eddy simulation (LES) model DALES-Urban is used to evaluate the predictive skill of the operational air quality model SIRANE. The use of LES in this study presents a novel approach to air quality model evaluation, avoiding the uncertainty associated with field and experimental validations and providing numerical control that permits systematic analysis of targeted parametrisations and assumptions. A case study is conducted over South Kensington, London under steady-state, neutral conditions, simulating the dispersion of both inert (NOx) and reactive (NO, NO2 and O3) pollutants. SIRANE is shown to successfully capture the dominant trends with respect to canyon-averaged concentrations and along-canyon velocities. The prediction of along-canyon velocities is shown to exhibit sources of systematic error dependant on the angle of incidence of the mean wind. The validity of the uniform in-canyon concentration is assessed by analysing the pedestrian, leeward and windward concentrations resolved in DALES-Urban. Vertical variations in concentrations within the urban canopy are shown to be more significant than directional asymmetry, particularly for primary pollutants. A correction factor of ~1.66 is proposed in order to avoid significant underestimations of pedestrian level exposure. The prevalence of intersections and advective nature of the shear layer are highlighted as important differences between modelling real heterogeneous urban topology and idealised infinite canyons.

About the Speaker

Dr Marc Stettler is a Senior Lecturer in Transport and the Environment in the Centre for Transport Studies and Director of the Transport & Environment Laboratory at Imperial College London. Marc's research aims to quantify and reduce environmental impacts from transport using a range of emissions measurement and modelling tools. Examples of recent research projects include: quantifying real-world vehicle emissions; using real-world vehicle emissions data to improve emissions models; evaluating economic and environmental benefits of Kinetic Energy Recovery Systems (KERS) for road freight; quantifying aircraft emissions at airports; and improving global estimates of aviation black carbon emissions and their impacts. Prior to joining Imperial, Marc was a Research Associate in the Centre for Sustainable Road Freight and Energy Efficient Cities Initiative at the University of Cambridge, where he also completed his PhD.