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Ketzel M.,University of Aarhus | Jensen S.S.,University of Aarhus | Lorentz H.,Ingenieurbuero Lohmeyer GmbH and Co. KG | Becker T.,University of Aarhus | Lofstrom P.,University of Aarhus
Proceedings of the 15th International Conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes, HARMO 2013 | Year: 2013

In this paper we present an evaluation of the latest GIS-based version of OML-Highway for both NO2 and NOx for various datasets from Denmark and Norway.

Belalcazar L.C.,National University of Colombia | Zamudio A.,National University of Colombia | Clappier A.,University of Strasbourg | Blond N.,University of Strasbourg | Flassak T.,Ingenieurbuero Lohmeyer GmbH and Co. KG
Proceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA | Year: 2011

The CFD model WinMISKAM was evaluated using the results of a roadside tracer experiment conducted in Ho Chi Minh City, Vietnam. The uncertainty associated with the emission was eliminated from the validation process because the tracer emission rate was known. The impact of different parameters (wind direction and grid size) on model performance was analyzed. N-propane contained commercial LPG was used as a passive tracer. In most cases, WinMISKAM reproduced very well the trends and levels of the measured tracer concentrations. A grid size of 1×1×1 m, or even 2×2×2 m were more suitable for air quality CFD modeling at roadside level. The validated models can be used to estimate vehicle emission factors to accurately calculate population exposure levels and to evaluate air pollution abatement strategies. This is an abstract of a paper presented at the 104th AWMA Annual Conference and Exhibition 2011 (Orlando, FL 6/21-24/2011).

Belalcazar L.C.,Ecole Polytechnique Federale de Lausanne | Clappier A.,University of Strasbourg | Clappier A.,French National Center for Scientific Research | Blond N.,University of Strasbourg | And 3 more authors.
Atmospheric Environment | Year: 2010

Road traffic emission factors (EFs) are one of the main sources of uncertainties in emission inventories; it is necessary to develop methods to reduce these uncertainties to manage air quality more efficiently. Recently an alternative method has been proposed to estimate the EFs. In that work the emission factors were estimated from a long term tracer study developed in Ho Chi Minh City (HCMC) Vietnam. A passive tracer was continuously emitted from a finite line source placed in one side of an urban street canyon. Simultaneously, the resulting tracer concentrations were monitored at the other side of the street. The results of this experiment were used to calculate the dispersion factors and afterwards, these dispersion factors were used to estimate the EFs. In this paper we use the Computational Fluids Dynamics (CFD) model WinMISKAM to critically evaluate the proposed methodology.In a first step, we use the results of the tracer study to validate the CFD model. Results show that the model is able to simulate quite well the tracer dispersion in most of the cases. The model is then used to evaluate the effect of varying the source configuration and to correct the EFs. A comparison with available studies shows that the corrected EFs are within the range of the EFs reported in other studies. Finally, the CFD model is used to find a source configuration that better represents the vehicle emissions and that may be used in future studies to estimate the EFs more accurately. Results show that a 200 m line placed in the center of the street would represent very well the vehicle emissions. This work shows that it is possible to accurately estimate the EFs from tracer studies. © 2010 Elsevier Ltd.

Park S.-B.,Seoul National University | Baik J.-J.,Seoul National University | Raasch S.,Leibniz University of Hanover | Letzel M.O.,Leibniz University of Hanover | Letzel M.O.,Ingenieurbuero Lohmeyer GmbH and Co. KG
Journal of Applied Meteorology and Climatology | Year: 2012

Thermal effects on turbulent flow and dispersion in and above an idealized street canyon with a street aspect ratio of 1 are numerically investigated using the parallelized large-eddy simulation model ("PALM"). Each of upwind building wall, street bottom, and downwind building wall is heated, and passive scalars are emitted from the street bottom. When compared with the neutral (no heating) case, the heating of the upwind building wall or street bottom strengthens a primary vortex in the street canyon and the heating of the downwind building wall induces a shrunken primary vortex and a winding flow between the vortex and the downwind building wall. Heating also induces higher turbulent kinetic energy and stronger turbulent fluxes at the rooftop height. In the neutral case, turbulent eddies generated by shear instability dominate mixing at the rooftop height and appear as band-shaped perturbations in the time-space plots of turbulent momentum and scalar fluxes. In all of the heating cases, buoyancy-generated turbulent eddies as well as shear-generated turbulent eddies contribute to turbulent momentum and scalar fluxes and band-shaped or lump-shaped perturbations appear at the rooftop height.Aquadrant analysis shows that at the rooftop height, in the neutral case and in the case with upwind building-wall heating, sweep events are less frequent but contribute more to turbulent momentum flux than do ejection events. By contrast, in the case with street-bottom and downwind building-wall heating, the frequency of sweep events is similar to that of ejection events and the contribution of ejection events to turbulent momentum flux is comparable to that of sweep events. © 2012 American Meteorological Society.

Letzel M.O.,Leibniz University of Hanover | Letzel M.O.,Ingenieurbuero Lohmeyer GmbH and Co. KG | Helmke C.,Leibniz University of Hanover | Ng E.,Chinese University of Hong Kong | And 3 more authors.
Meteorologische Zeitschrift | Year: 2012

Hong Kong is one of the most densely built-up and populated cities in the world. An adequate air ventilation at pedestrian level would ease the thermal stress in its humid subtropical climate, but the high-density city severely reduces the natural ventilation. This case study investigates pedestrian level ventilation in two neighbourhoods in Kowloon, downtown Hong Kong using the parallelized large-eddy-simulation (LES) model PALM. The LES technique is chosen here for a city quarter scale pedestrian comfort study despite of its high computational cost. The aims of the paper are a) to get a comprehensive overview of pedestrian level ventilation and a better understanding of the ventilation processes in downtown Hong Kong, b) to test the LES technique on this urban scale compared to the wind tunnel and c) to investigate how numerical/physical parameters influence ventilation. This case study is restricted to neutral stratification in order to allow a direct comparison with the wind tunnel. A sensitivity study quantifies the dependence of site-averaged ventilation on numerical and physical parameters and determines an appropriate urban LES set-up for two 1 km2 neighbourhoods in Kowloon (Tsim Sha Tsui, Mong Kok) that are investigated for prevailing E and SW wind. The results reveal the critical dependence of ventilation on the urban morphology. Air paths, street orientations, ground coverage, sites fronting the water, inter connectivity of spaces, building podium size and building heights can all affect the pedestrian wind environment. Isolated tall buildings may have a pronounced impact on ventilation both locally and downstream. © 2012 by Gebrüder Borntraeger.

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