3D Radiative and Convective Modeling of Urban Environment: An Example for the City Center of Toulouse

International audienc

Micrometerological modeling of radiative and convective effects with a building resolving code

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Identification of sensitive parameters in the modeling of SVOC reemission processes from soil to atmosphere

International audienceSemi-volatile organic compounds (SVOCs) are subject to Long-Range Atmospheric Transport because of transport–deposition–reemission successive processes. Several experimental data available in the literature suggest that soil is a non-negligible contributor of SVOCs to atmosphere. Then coupling soil and atmosphere in integrated coupled models and simulating reemission processes can be essential for estimating atmospheric concentration of several pollutants. However, the sources of uncertainty and variability are multiple (soil properties, meteorological conditions, chemical-specific parameters) and can significantly influence the determination of reemissions. In order to identify the key parameters in reemission modeling and their effect on global modeling uncertainty, we conducted a sensitivity analysis targeted on the ‘reemission’ output variable. Different parameters were tested, including soil properties, partition coefficients and meteorological conditions. We performed EFAST sensitivity analysis for four chemicals (benzo-a-pyrene, hexachlorobenzene, PCB-28 and lindane) and different spatial scenari (regional and continental scales). Partition coefficients between air, solid and water phases are influent, depending on the precision of data and global behavior of the chemical. Reemissions showed a lower variability to soil parameters (soil organic matter and water contents at field capacity and wilting point). A mapping of these parameters at a regional scale is sufficient to correctly estimate reemissions when compared to other sources of uncertainty

Modélisation du mercure, du plomb et du cadmium à l'échelle européenne

National audienceSince its adoption in 1979, the Convention on Long-Range Transboundary Air Pollution has addressed some of the major environmental problems of the UNECE region. In this framework the protocol on heavy metals, signed in 1998, gives first priority to lead (Pb), cadmium (Cd) and mercury (Hg). These heavy metals and their compounds are highly toxic substances, being likely to bio-accumulate in organisms. Understanding and modelling their transport and fate in the atmosphere allow to take more effective decision to reduce their impact on the ecosystems. POLAIR 3D is a three-dimensional chemistry-transport model developed within the modelling system POLYPHEMUS at CEREA. It is designed to handle a wide range of applications from passive transport to photo-chemistry and aerosol modelling, and has been recently extended to deal with heavy metals at European scale. Removal processes have been carefully taken into account since deposition fluxes are more worrying than air concentrations. Most of the heavy metals in the atmosphere have a passive chemical behaviour but are carried by the aerosol phase. For this reason their rate of removal are linked to those of aerosol particles. Mercury differs because of its high saturated vapour pressure and mainly being found under gaseous elemental form. However it is essential to simulate mercury chemistry in gaseous and aqueous phases since oxidised mercury species represent the main part of the deposited mercury mass. Simulated air concentrations and deposition fluxes are evaluated by comparison to data of the EMEP measurement network. Sensitivity analysis has been performed using adjoint techniques. Such investigation being required to handle in a suitable way our developed model. Moreover, these techniques allow to carry out inverse modelling to improve boundary conditions which are crucial with a restricted area model.Le mercure, le plomb et le cadmium sont actuellement un objet de préoccupations pour les instances concernées par la pollution atmosphérique. La dénomination commune de " métaux lourds " cache en fait des comportements variables de ces composés dans l'atmosphère qui influencent fortement leur transfert vers les écosystèmes. La modélisation numérique de ces comportements doit permettre de mieux comprendre leur devenir, une attention particulière devant être portée aux processus de déposition. L'utilisation pertinente d'un modèle numérique ne peut se faire sans étudier sa sensibilité aux données et paramètres qu'il utilise. Des techniques ont été développées en ce sens puis appliquées au modèle de chimie-transport POLAIR 3D. Elles permettent par ailleurs de mener à bien un travail de modélisation inverse

14 th Conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes -2-6

Abstract: City residents are subjected to modified thermal environments as well as increased air pollution. In order to better understand the phenomena occurring at urban scale and to study different scenarios more and more realistic simulation tools are developed. Nevertheless, many micrometeorological studies on flow and pollution dispersion assume a neutral atmosphere and most building energy balance models neglect the three-dimensional local variation of the flow and temperature fields. The aim of this work is to develop a three dimensional tool coupling thermal energy balance of the buildings and modelling of the atmospheric flow in urban areas. We have developed a threedimensional microscale atmospheric radiative scheme in the atmospheric module of the 3D Computational Fluid Dynamics (CFD) code Code_Saturne adapted to complex geometry. In our simulations, we use a Reynolds Averaged Navier-Stokes (RANS) approach with a k-ε turbulence closure. The full coupling of the radiative transfer and fluid dynamics models has been validated with idealized cases. In this work, we simulate surface temperatures of a district of the city of Toulouse, in the South-West part of France, taking into account the 3D effects of the flow around the buildings, in real meteorological conditions. The mesh developed for the city center and the simulation conditions for the selected day of the campaign are presented. The results are evaluated with the measurements from the CAPITOUL (Canopy and Aerosol Particles Interactions in TOulouse Urban Layer) experiment, including brightness surface temperature measured by infrared imagery

Representation of aerosol optical properties using a chemistry transport model to improve solar irradiance modelling

International audienceAtmospheric particles may attenuate solar irradiance effectively during clear-sky days, but attenuation by particles is sometimes not taken into account in numerical models, or it is often parameterised using constant or climatological values for example. This paper compares different representations of the effects of particles on direct and global solar irradiance, using the software Code_Saturne. Particle concentrations, as well as aerosol optical properties AOPs (optical thickness, asymmetry factor and single scattering albedo), are estimated using the air-quality modelling platform Polyphemus. Modelled solar irradiance is compared to measurements in greater Paris and the south of France. Accurate modelling of AOPs leads to an improvement of statistical error indicators, especially in clear-sky conditions. A simplified scheme represents AOPs integrated over the full spectral range using only 6 wavelengths, and a sensitivity study on the influence of assumptions in AOPs on solar irradiance is performed

On the Influence of a Simple Microphysics Parametrization on Radiation Fog Modelling: A Case Study During ParisFog

International audienceA detailed numerical simulation of a radiation fog event with a single column model is presented, which takes into account recent developments in microphysical parametrizations. One-dimensional simulations are performed using the computational fluid dynamics model Code_Saturne and the results are compared to a very detailed in situ dataset collected during the ParisFog campaign, which took place near Paris, France, during the winter 2006–2007. Special attention is given to the detailed and complete diurnal simulations and to the role of microphysics in the fog life cycle. The comparison between the simulated and the observed visibility, in the single-column model case study, shows that the evolution of radiation fog is correctly simulated. Sensitivity simulations show that fog development and dissipation are sensitive to the droplet-size distribution through sedimentation/deposition processes but the aerosol number concentration in the coarse mode has a low impact on the time of fog formation

Effect of Atmospheric Stability on the Atmospheric Dispersion Conditions Over a Industrial Site Surrounded by Forests

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Numerical simulations of the microscale heterogeneities of turbulence observed on a complex site

International audienc

Experimental and Numerical Study of Wind and Turbulence in a Near-Field Dispersion Campaign at an Inhomogeneous Site

International audienc