Fotios Barmpas

COST 732 in practice: the MUST model evaluation exercise

The aim of this paper is to describe the use of a general methodology tailored to the evaluation of micro-scale meteorological models applied to flow and dispersion simulations in urban areas. This methodology, developed within COST 732, has been tested through a large modelling exercise involving many groups across Europe. The major test case used is the Mock Urban Setting Test (MUST) experiment representing an idealised urban area. It is emphasised that a full model evaluation is problem-dependent and requires several activities including a statistical validation that requires a careful choice of the metrics for the comparison with measurements.

Construction of a photocatalytic de-polluting field site in the Leopold II tunnel in Brussels

Within the framework of the European Life+-funded project PhotoPAQ (Demonstration of Photocatalytic remediation Processes on Air Quality), which was aimed at demonstrating the effectiveness of photocatalytic coating materials on a realistic scale, a photocatalytic de-polluting field site was set up in the Leopold II tunnel in Brussels, Belgium. For that purpose, photocatalytic cementitious materials were applied on the side walls and ceiling of selected test sections inside a one-way tunnel tube. This article presents the configuration of the test sections used and the preparation and implementation of the measuring campaigns inside the Leopold II tunnel. While emphasizing on how to implement measuring campaigns under such conditions, difficulties encountered during these extensive field campaigns are presented and discussed. This included the severe de-activation observed for the investigated material under the polluted tunnel conditions, which was revealed by additional laboratory experiments on photocatalytic samples that were exposed to tunnel air. Finally, recommendations for future applications of photocatalytic building materials inside tunnels are given.

Impact of photocatalytic remediation of pollutants on urban air quality

In the recent years, photocatalytic self-cleaning and “depolluting” materials have been suggested as a remediation technology mainly for NOx and aromatic VOCs in urban areas. A number of products incorporating the aforementioned technology have been made commercially available with the aim to improve urban air quality. These commercial products are based on the photocatalytic properties of a thin layer of TiO2 at the surface of the material (such as glass, pavement, etc.) or embedded in paints or concrete. The use of TiO2 photocatalysts as an emerging air pollution control technology has been reported in many locations worldwide. However, up to now, the effectiveness measured in situ and the expected positive impact on air quality of this relatively new technology has only been demonstrated in a limited manner. Assessing and demonstrating the effectiveness of these depolluting techniques in real scale applications aims to create a real added value, in terms of policy making (i.e., implementing air quality strategies) and economics (by providing a demonstration of the actual performance of a new technique).

3D Numerical Simulation of the Transient Thermal Behavior of a Simplified Building Envelope Under External Flow

Understanding building envelope performance and thermal mass effects is becoming increasingly important under the scope of low energy building construction and energy conservation. In the present paper, a three-dimensional computational fluid dynamics methodology is presented for the numerical simulation of the flow and heat transfer that determine the thermal behavior of simplified building envelopes. This is dominated by a conjugate heat transfer approach, which involves conduction, convection, solar heat gains, ambient temperature variation, and the effects of thermal radiation losses to the sky. Validation results include comparison both with measurements from fundamental laboratory studies of heat transfer from surface mounted cubes and with numerical results from well established commercial building energy simulation software. Numerical issues, such as temporal and spatial discretization, are addressed, and parametric studies are performed with regard to the effect of external flow Reynolds number and temperature variation in the building envelope, depending on the individual orientation of the external walls with respect to the flow and on the thermal properties of the building materials. Results from the parametric studies performed indicate that the transient three-dimensional calculations provide important information regarding the effect of external flow properties, such as the approaching flow temperature, velocity, and direction on the thermal behavior of the building envelope. In addition, it has been clearly demonstrated that the methodology is also capable of taking into account the complex effects of parameters such as the building material properties.

Numerical study for the flow around moving cars and its effect on the dispersion of the traffic emitted pollution within a road tunnel

This paper presents results from a numerical study which was conducted in order to investigate the effect of the flow around moving vehicles on the dispersion and the concentration of traffic emitted pollution within the Traforo Umberto road tunnel in the city centre of Rome. A series of three dimensional numerical transient simulations were performed using the commercial CFD code Ansys CFX 5.7.1 employing RANS advanced CFD techniques. The results have identified the effects of the flow around moving cars on the resulting concentration fields and show that increased mixing due to the motion of vehicles inside the tunnel leads to increased concentrations.

An Integrated Numerical Methodology for the Study of Transport of Air Pollution in the Coupled Indoor and Outdoor Environment

Exposure to indoor air pollution, as a result of transport from outdoor emission sources in the vicinity of buildings, has been receiving an increasing attention over the past few years. Towards the aim of quantifying the contribution of inter-canopy transport of air pollution on the quality of the indoor environment, a holistic numerical modelling approach based on transient, three-dimensional computational fluid dynamics models has been developed and validated. Numerical issues, such as temporal and spatial discretisation are addressed and parametric studies are performed to assess the impact of the external flow on the inter-canopy transport of air pollution in the coupled indoor and outdoor environment. The contributions of the main emission sources in the vicinity of buildings are considered. The main architectural features of the built environment near the buildings of interest are explicitly resolved in order to account for their contribution on the generation of atmospheric turbulence on the lower part of the approaching atmospheric boundary layer, which dominates the transport of the external flow. The methodology is validated based on comparisons with field measurements for the concentration levels of NOx, PM2.5 and PM10 in selected locations, both indoors and outdoors in close proximity to a real building.

Application of inverse dispersion modelling for the determination of PM emission factors from fugitive dust sources in open-pit lignite mines

The operation of large open-pit lignite mines represents a significant source of fugitive dust emissions connected to energy production. Emission inventories can be used to provide operational estimates of the total dust burden in the surrounding areas attributable to mining operations. In this work, a methodology based on the inverse dispersion modelling approach, combining two different dispersion models, is used for preparing a dust emissions inventory for several activity types in the lignite mines of Western Macedonia, Greece. A three-year campaign of field measurement experiments provides the necessary meteorological data and upwind-downwind concentration levels in the area of each activity. A comparison of calculated emission rates provided by the two dispersion models indicates a very good agreement, while the normalised downwind concentration timeseries are accurately reproduced. Emission factors are calculated for each experiment and per-activity, leading to the formulation of empirical relations for the total fugitive dust emissions.

New power law inflow boundary conditions for street scale modelling

In street scale numerical simulations utilising computational fluid dynamics (CFD) models, normally the inlet flow should preserve the horizontal homogeneity upstream and downstream of the area where the resolved obstacles reside. Hence, the vertical profiles of the main atmospheric flow quantities must comply with the roughness characteristics of the ground surface. Horizontally homogenous boundary conditions do not normally agree with field measurements while at the same time the profiles obtained by measurements do not preserve the homogeneity of the flow. As a result, in recent years alternative sets of boundary conditions have been proposed in order to bridge the gap between real life vertical profiles of the atmospheric boundary layer and those applied as input boundary conditions for modelling purposes. In the present study, the homogeneity of the boundary conditions is addressed by applying the power law for the mean wind speed to obtain the appropriate vertical profiles.

Nested Multi-scale System in the PALM Large-Eddy Simulation Model

Large-Eddy Simulation (LES) of atmospheric boundary layer (ABL) is becoming an important research method for urban air-quality studies. Until very recently, it was impossible to include detailed structures, such as buildings in ABL LES. Nowadays, it is possible, but such LES is still limited to a relatively small areas because typically about 1 m resolution is required. However, for several reasons an ABL LES domain should cover a large area leading to huge computational task. A means to overcome this is to concentrate resolution to the primary area of interest by means of model nesting. The idea of nesting is to simultaneously run a series of two or more LES in domains with different sizes and resolutions. In this work, two-way nesting is implemented in the parallelized LES model PALM. The nesting system is tested for several test cases including a convective boundary layer with zero mean wind, several neutral boundary layers over both flat terrain and terrain with an array of obstacles.

Evaluation, Improvement and Guidance for the Use of Local-Scale Emergency Prediction and Response Tools for Airborne Hazards in Built Environments. Cost Action ES100 – A European Experience

Releases of hazardous agents, such as in a RDD event, in complex built environments pose a tremendous challenge to emergency first responders and authorities in charge due to casualties potentially involved and the significant environmental impact. Air motions in built-up areas are very complex and adequate modelling tools have to be applied properly in order to predict the dispersion of hazardous materials with sufficient accuracy within a very short time. Different types of tools are applied; however, it is not always clear the advantages and limitations of individual models and approaches. Therefore, it is of an exceptional interest to compile a detailed inventory of the different models and methodologies currently in use, to characterize their performance and to establish strategies for their improvement. The Action is a first cross-community initiative to join, to coordinate and to harmonize European efforts for a substantial improvement in the implementation of local-scale emergency response tools.