59 results found
Woodward H, Schroeder A, Le Cornec C, et al., 2022, High resolution modelling of traffic emissions using the large eddy simulation code Fluidity, Atmosphere, Vol: 13, ISSN: 2073-4433
The large eddy simulation (LES) code Fluidity was used to simulate the dispersion of NOx traffic emissions along a road in London. The traffic emissions were represented by moving volume sources, one for each vehicle, with time-varying emission rates. Traffic modelling software was used to generate the vehicle movement, while an instantaneous emissions model was used to calculate the NOx emissions at 1 s intervals. The traffic emissions were also modelled as a constant volume source along the length of the road for comparison. A validation of Fluidity against wind tunnel measurements is presented before a qualitative comparison of the LES concentrations with measured roadside concentrations. Fluidity showed an acceptable comparison with the wind tunnel data for velocities and turbulence intensities. The in-canyon tracer concentrations were found to be significantly different between the wind tunnel and Fluidity. This difference was explained by the very high sensitivity of the in-canyon tracer concentrations to the precise release location. Despite this, the comparison showed that Fluidity was able to provide a realistic representation of roadside concentration variations at high temporal resolution, which is not achieved when traffic emissions are modelled as a constant volume source or by Gaussian plume models.
Woodward H, Oxley T, Rowe EC, et al., 2022, An exceedance score for the assessment of the impact of nitrogen deposition on habitats in the UK, ENVIRONMENTAL MODELLING & SOFTWARE, Vol: 150, ISSN: 1364-8152
Woodward H, Stettler M, Pavlidis D, et 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.
Song J, Fan S, Lin W, et al., 2018, Natural ventilation in cities: the implications of fluid mechanics, BUILDING RESEARCH AND INFORMATION, Vol: 46, Pages: 809-828, ISSN: 0961-3218
O'Driscoll R, Stettler MEJ, Molden N, et 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.
Aristodemou E, Boganegra LM, Mottet L, et 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.
O'Driscoll R, ApSimon H, Oxley T, et 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.
Dore A, Reis S, Oxley T, et 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
Dore A, Reis S, Oxley T, et 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
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
Smith AC, Holland M, Korkeala O, et 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
Oxley T, Dore AJ, ApSimon H, et 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
Tzanidakis K, Oxley T, Cockerill T, et 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
Oxley T, de Nazelle A, Katara C, et 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
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
Oxley T, Elshkaki A, Kwiatkowski L, et 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
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.
Wang H, Colvile RN, Pain C, et 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
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
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
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
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
Pavlidis D, Aristodemou E, Gomes JLMA, et 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.
Pavlidis D, Gomes JLMA, Gorman GJ, et 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
Jamieson IA, Holdstock P, ApSimon HM, et 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
Garcia X, Pavlidis D, Gorman GJ, et 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.
Pavlidis D, Gorman GJ, Gomes JLMA, et al., 2010, Synthetic-Eddy Method for Urban Atmospheric Flow Modelling, Boundary-Layer Meteorology, Vol: 136, Pages: 285-299
Aristodemou E, Bentham T, Pain C, et 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
Apsimon H, Amann M, Astrom S, et al., 2009, Synergies in addressing air quality and climate change, CLIMATE POLICY, Vol: 9, Pages: 669-680, ISSN: 1469-3062
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