Imperial College London

ProfessorHelenApSimon

Faculty of Natural SciencesCentre for Environmental Policy

Professor of Air Pollution Studies
 
 
 
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Contact

 

+44 (0)20 7594 9292h.apsimon

 
 
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Location

 

305Weeks BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

57 results found

Woodward H, Stettler M, Pavlidis D, Aristodemou E, ApSimon H, Pain Cet al., 2019, A large eddy simulation of the dispersion of traffic emissions by moving vehicles at an intersection, Atmospheric Environment, Vol: 215, Pages: 1-16, ISSN: 1352-2310

Traffic induced flow within urban areas can have a significant effect on pollution dispersion, particularly for traffic emissions. Traffic movement results in increased turbulence within the street and the dispersion of pollutants by vehicles as they move through the street. In order to accurately model urban air quality and perform meaningful exposure analysis at the microscale, these effects cannot be ignored. In this paper we introduce a method to simulate traffic induced dispersion at high resolution. The computational fluid dynamics software, Fluidity, is used to model the moving vehicles through a domain consisting of an idealised intersection. A multi-fluid method is used where vehicles are represented as a second fluid which displaces the air as it moves through the domain. The vehicle model is coupled with an instantaneous emissions model which calculates the emission rate of each vehicle at each time step. A comparison is made with a second Fluidity model which simulates the traffic emissions as a line source and does not include moving vehicles. The method is used to demonstrate how moving vehicles can have a significant effect on street level concentration fields and how large vehicles such as buses can also cause acute high concentration events at the roadside which can contribute significantly to overall exposure.

Journal article

Song J, Fan S, Lin W, Mottet L, Woodward H, Wykes MD, Arcucci R, Xiao D, Debay J-E, ApSimon H, Aristodemou E, Birch D, Carpentieri M, Fang F, Herzog M, Hunt GR, Jones RL, Pain C, Pavlidis D, Robins AG, Short CA, Linden PFet al., 2018, Natural ventilation in cities: the implications of fluid mechanics, BUILDING RESEARCH AND INFORMATION, Vol: 46, Pages: 809-828, ISSN: 0961-3218

Journal article

O'Driscoll R, Stettler MEJ, Molden N, Oxley T, ApSimon HMet al., 2017, Real world CO2 and NOx emissions from 149 Euro 5 and 6 diesel, gasoline and hybrid passenger cars., Science of the Total Environment, Vol: 621, Pages: 282-290, ISSN: 0048-9697

In this study CO2 and NOx emissions from 149 Euro 5 and 6 diesel, gasoline and hybrid passenger cars were compared using a Portable Emissions Measurement System (PEMS). The models sampled accounted for 56% of all passenger cars sold in Europe in 2016. We found gasoline vehicles had CO2 emissions 13-66% higher than diesel. During urban driving, the average CO2 emission factor was 210.5 (sd. 47) gkm-1 for gasoline and 170.2 (sd. 34) gkm-1 for diesel. Half the gasoline vehicles tested were Gasoline Direct Injection (GDI). Euro 6 GDI engines <1.4ℓ delivered ~17% CO2 reduction compared to Port Fuel Injection (PFI). Gasoline vehicles delivered an 86-96% reduction in NOx emissions compared to diesel cars. The average urban NOx emission from Euro 6 diesel vehicles 0.44 (sd. 0.44) gkm-1 was 11 times higher than for gasoline 0.04 (sd. 0.04) gkm-1. We also analysed two gasoline-electric hybrids which out-performed both gasoline and diesel for NOx and CO2. We conclude action is required to mitigate the public health risk created by excessive NOx emissions from modern diesel vehicles. Replacing diesel with gasoline would incur a substantial CO2 penalty, however greater uptake of hybrid vehicles would likely reduce both CO2 and NOx emissions. Discrimination of vehicles on the basis of Euro standard is arbitrary and incentives should promote vehicles with the lowest real-world emissions of both NOx and CO2.

Journal article

Aristodemou E, Boganegra LM, Mottet L, Pavlidis D, Constantinou A, Pain C, Robins A, ApSimon Het al., 2017, How tall buildings affect turbulent air flows and dispersion of pollution within a neighbourhood, Environmental Pollution, Vol: 233, Pages: 782-796, ISSN: 0269-7491

The city of London, UK, has seen in recent years an increase in the number of high-rise/multi-storey buildings (“skyscrapers”) with roof heights reaching 150 m and more, with the Shard being a prime example with a height of ∼310 m. This changing cityscape together with recent plans of local authorities of introducing Combined Heat and Power Plant (CHP) led to a detailed study in which CFD and wind tunnel studies were carried out to assess the effect of such high-rise buildings on the dispersion of air pollution in their vicinity. A new, open-source simulator, FLUIDITY, which incorporates the Large Eddy Simulation (LES) method, was implemented; the simulated results were subsequently validated against experimental measurements from the EnFlo wind tunnel. The novelty of the LES methodology within FLUIDITY is based on the combination of an adaptive, unstructured, mesh with an eddy-viscosity tensor (for the sub-grid scales) that is anisotropic. The simulated normalised mean concentrations results were compared to the corresponding wind tunnel measurements, showing for most detector locations good correlations, with differences ranging from 3% to 37%. The validation procedure was followed by the simulation of two further hypothetical scenarios, in which the heights of buildings surrounding the source building were increased. The results showed clearly how the high-rise buildings affected the surrounding air flows and dispersion patterns, with the generation of “dead-zones” and high-concentration “hotspots” in areas where these did not previously exist. The work clearly showed that complex CFD modelling can provide useful information to urban planners when changes to cityscapes are considered, so that design options can be tested against environmental quality criteria.

Journal article

O'Driscoll R, ApSimon H, Oxley T, Molden N, Stettler M, Thiyagarajah Aet al., 2016, A portable emissions measurement system (PEMS) study of NOx and primary NO2 emissions from Euro 6 diesel passenger cars and comparison with COPERT emission factors, Atmospheric Environment, Vol: 145, Pages: 81-91, ISSN: 1352-2310

Real world emissions of oxides of nitrogen (NOx) often greatly exceed those achieved in the laboratory based type approval process. In this paper the real world emissions from a substantial sample of the latest Euro 6 diesel passenger cars are presented with a focus on NOx and primary NO2. Portable Emissions Measurement System (PEMS) data is analysed from 39 Euro 6 diesel passenger cars over a test route comprised of urban and motorway sections. The sample includes vehicles installed with exhaust gas recirculation (EGR), lean NOx traps (LNT), or selective catalytic reduction (SCR). The results show wide variability in NOx emissions from 1 – 22 times the type approval limit. The average NOx emission, 0.36 (sd. 0.36) g km-1, is 4.5 times the Euro 6 limit. The average fraction primary NO2 (fNO2) is 44 (sd. 20) %. Higher emissions during the urban section of the route are attributed to an increased number of acceleration events. Comparisons between PEMS measurements and COPERT speed dependent emissions factors show PEMS measurements to be on average 1.6 times higher than COPERT estimates for NOx and 2.5 times for NO2. However, by removing the 5 most polluting vehicles average emissions were reduced considerably.

Journal article

Dore A, Reis S, Oxley T, ApSimon H, Hall J, Vieno M, Kryza M, Green C, Tsagatakis I, Tang S, Braban C, Sutton Met al., 2016, Calculation of Source-Receptor Matrices for Use in an Integrated Assessment Model and Assessment of Impacts on Natural Ecosystems, 34th International Technical Meeting on Air Pollution Modelling and its Application (ITM), Publisher: SPRINGER INT PUBLISHING AG, Pages: 107-112

Conference paper

Dore A, Reis S, Oxley T, ApSimon H, Hall J, Vieno M, Kryza M, Green C, Tsagatakis I, Tang S, Braban C, Sutton Met al., 2016, Calculation of Source-Receptor Matrices for Use in an Integrated Assessment Model and Assessment of Impacts on Natural Ecosystems, 34th International Technical Meeting on Air Pollution Modelling and its Application (ITM), Publisher: SPRINGER-VERLAG BERLIN, Pages: 107-112

Conference paper

Oxley T, ApSimon HM, de Nazelle A, 2015, Investigating the sensitivity of health benefits to focussed PM2.5 emission abatement strategies, ENVIRONMENTAL MODELLING & SOFTWARE, Vol: 74, Pages: 268-283, ISSN: 1364-8152

Journal article

Smith AC, Holland M, Korkeala O, Warmington J, Forster D, Apsimon H, Oxley T, Dickens R, Smith SMet al., 2015, Health and environmental co-benefits and conflicts of actions to meet UK carbon targets, Climate Policy, Vol: 16, Pages: 253-283, ISSN: 1752-7457

Journal article

Oxley T, Dore AJ, ApSimon H, Hall J, Kryza Met al., 2013, Modelling future impacts of air pollution using the multi-scale UK Integrated Assessment Model (UKIAM), ENVIRONMENT INTERNATIONAL, Vol: 61, Pages: 17-35, ISSN: 0160-4120

Journal article

Tzanidakis K, Oxley T, Cockerill T, ApSimon Het al., 2013, Illustrative national scale scenarios of environmental and human health impacts of Carbon Capture and Storage, ENVIRONMENT INTERNATIONAL, Vol: 56, Pages: 48-64, ISSN: 0160-4120

Journal article

Oxley T, ApSimon HM, Hall J, 2013, Application of a protectability index to assess habitat eutrophication in designated areas, 20th International Congress on Modelling and Simulation (MODSIM), Publisher: MODELLING & SIMULATION SOC AUSTRALIA & NEW ZEALAND INC, Pages: 1875-1881

Conference paper

Oxley T, de Nazelle A, Katara C, ApSimon HMet al., 2013, Bridging the gap between air pollution models and epidemiological studies, 20th International Congress on Modelling and Simulation (MODSIM), Publisher: MODELLING & SIMULATION SOC AUSTRALIA & NEW ZEALAND INC, Pages: 1882-1888

Conference paper

Oxley T, Elshkaki A, Kwiatkowski L, Castillo A, Scarbrough T, ApSimon Het al., 2012, Pollution abatement from road transport: cross-sectoral implications, climate co-benefits and behavioural change, ENVIRONMENTAL SCIENCE & POLICY, Vol: 19-20, Pages: 16-32, ISSN: 1462-9011

Journal article

Reis S, Grennfelt P, Klimont Z, Amann M, ApSimon H, Hettelingh JP, Holland M, LeGall AC, Maas R, Posch M, Spranger T, Sutton MA, Williams Met al., 2012, From Acid Rain to Climate Change, Science, Vol: 338, Pages: 1153-1154, ISSN: 0036-8075

The Convention on Long-Range Transboundary Air Pollution (CLRTAP) under the United Nations Economic Commission for Europe (UNECE) was established in 1979 to control damage to ecosystems and cultural heritage from acid rain, initially in Europe (1). Extended by eight protocols, most recently the Gothenburg Protocol (GP) signed in 1999, it has been key for developing cross-border air pollution control strategies over the UNECE region, which includes the United States and Canada. We describe how recent amendments to the GP reflect improved scientific knowledge on pollution, environmental relations, and links between regional air pollution and global climate change.

Journal article

Wang H, Colvile RN, Pain C, Aristodemou E, ApSimon HMet al., 2011, Understanding peak pedestrian exposures due to traffic emissions within the urban environment, TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT, Vol: 16, Pages: 392-401, ISSN: 1361-9209

Journal article

Jamieson IA, Jamieson SS, ApSimon HM, Bell JNBet al., 2011, Grounding & human health - a review, 13th International Conference on Electrostatics, Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588

Conference paper

Oxley T, ApSimon H, 2011, A conceptual framework for mapping uncertainty in integrated assessment, MSSANZ 19th Biennial Congress on Modelling and Simulation (MODSIM), Publisher: MODELLING & SIMULATION SOC AUSTRALIA & NEW ZEALAND INC, Pages: 1803-1809

Conference paper

Oxley T, Hall J, ApSimon H, 2011, Spatialities and temporalities of metrics calculated by Integrated Assessment Models: Exceedance of ecosystem-specific Critical Loads, MSSANZ 19th Biennial Congress on Modelling and Simulation (MODSIM), Publisher: MODELLING & SIMULATION SOC AUSTRALIA & NEW ZEALAND INC, Pages: 1795-1802

Conference paper

Oxley T, ApSimon H, Valiantis M, 2011, Modelling national air quality strategy scenarios with UKIAM: uncertainties emerging from the integration of multiple spatial scales, INTERNATIONAL JOURNAL OF ENVIRONMENT AND POLLUTION, Vol: 44, Pages: 54-61, ISSN: 0957-4352

Journal article

Kumar P, Robins A, ApSimon H, 2010, Nanoparticle emissions from biofuelled vehicles - their characteristics and impact on the number-based regulation of atmospheric particles, ATMOSPHERIC SCIENCE LETTERS, Vol: 11, Pages: 327-331, ISSN: 1530-261X

Journal article

Pavlidis D, Aristodemou E, Gomes JLMA, Pain CC, ApSimon Het al., 2010, Numerical Simulation of Air Flows in Street Canyons Using Mesh-Adaptive LES, Direct and large-eddy simulation VII, Editors: Armenio, Geurts, Fröhlich, Publisher: Springer Verlag, ISBN: 9789048136513

This book is of interest to scientists and engineers both at an early level in their career as well as at more senior levels.

Book chapter

Pavlidis D, Gomes JLMA, Gorman GJ, Aristodemou E, Pain CC, ApSimon H, Robins AGet al., 2010, Novel Mesh Adaptive LES Simulations for Multi-Scale Atmospheric Flows: Application to the Urban Environment, 30th NATO/SPS International Technical Meeting on Air Pollution Modeling and Its Applications, Publisher: SPRINGER, Pages: 63-+, ISSN: 1871-465X

Conference paper

Jamieson IA, Holdstock P, ApSimon HM, Bell JNBet al., 2010, Building Health: The Need for Electromagnetic Hygiene?, Conference on Electromagnetic Phenomena and Health - A Continuing Controversy, Publisher: IOP PUBLISHING LTD, ISSN: 1755-1307

Conference paper

Garcia X, Pavlidis D, Gorman GJ, Gomes JLMA, Piggott MD, Aristodemou E, Mindel J, Latham JP, Pain CC, ApSimon Het al., 2010, A two-phase adaptive finite element method for solid–fluidcoupling in complex geometries, International Journal for Numerical Methods in Fluids

In this paper we present a method to solve the Navier–Stokes equations in complex geometries, suchas porous sands, using a finite-element solver but without the complexity of meshing the porous space.The method is based on treating the solid boundaries as a second fluid and solving a set of equationssimilar to those used for multi-fluid flow. When combined with anisotropic mesh adaptivity, it is possibleto resolve complex geometries starting with an arbitrary coarse mesh. The approach is validated bycomparing simulation results with available data in three test cases. In the first we simulate the flow pasta cylinder. The second test case compares the pressure drop in flow through random packs of sphereswith the Ergun equation. In the last case simulation results are compared with experimental data on theflow past a simplified vehicle model (Ahmed body) at high Reynolds number using large-eddy simulation(LES). Results are in good agreement with all three reference models.

Journal article

Pavlidis D, Gorman GJ, Gomes JLMA, Pain CC, ApSimon Het al., 2010, Synthetic-Eddy Method for Urban Atmospheric Flow Modelling, Boundary-Layer Meteorology, Vol: 136, Pages: 285-299

Journal article

Aristodemou E, Bentham T, Pain C, Colvile R, Robins A, ApSimon Het al., 2009, A comparison of mesh-adaptive LES with wind tunnel data for flow past buildings: Mean flows and velocity fluctuations, ATMOSPHERIC ENVIRONMENT, Vol: 43, Pages: 6238-6253, ISSN: 1352-2310

Journal article

Apsimon H, Amann M, Astrom S, Oxley Tet al., 2009, Synergies in addressing air quality and climate change, CLIMATE POLICY, Vol: 9, Pages: 669-680, ISSN: 1469-3062

Journal article

Haygarth PM, ApSimon H, Betson M, Harris D, Hodgkinson R, Withers PJAet al., 2009, Mitigating Diffuse Phosphorus Transfer from Agriculture According to Cost and Efficiency, JOURNAL OF ENVIRONMENTAL QUALITY, Vol: 38, Pages: 2012-2022, ISSN: 0047-2425

Journal article

Oxley T, Valiantis M, Elshkaki A, ApSimon HMet al., 2009, Background, Road and Urban Transport modelling of Air quality Limit values (The BRUTAL model), ENVIRONMENTAL MODELLING & SOFTWARE, Vol: 24, Pages: 1036-1050, ISSN: 1364-8152

Journal article

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