Numerical modelling of microorganisms dispersion in urban area : application to legionella

International audienceDispersion modelling is often used to estimate potentially contaminated areas in case of accidental release of microorganisms in the atmosphere. In the specific case of Legionella, accidental spread in the atmosphere due to contaminated cooling towers system may occur over distance larger than 10km. In addition, most cooling towers are located in urban areas where dispersion due to obstacles is complex. In this case, dispersion models have to take into account complex flows and microphysical processes that occur within the plume and may have an impact on the survival of the microorganisms. To estimate the concentration of microorganisms in these areas, a specific module has been developed within the lagrangian dispersion model Micro Swift Spray (MSS, Aria technologies). This module takes into account microorganisms outside or inside water liquid droplets and microphysical interaction inside the plume. A simple biological module governing the survival of airborne microorganisms has also been implemented in the dispersion model

Modélisation du panache odorant de Lubrizol

On 21-22 January 2013, an odour of natural gas was smelled by many people in the region extending from Paris to London. Quick investigations showed that a significant release of sulphur compounds in the Lubrizol industrial facility, located in the city of Rouen, was responsible of numerous complaints for uncomfortable odours. These complaints, including spatial and temporal information were collected by the French institute for public health surveillance and a regional air quality association (Air Normand). INERIS was asked by the French Ministry in charge of Ecology to model the temporal evolution of the plume. After reconstruction of the source term, dispersions modelling were carried out on both regional and local scales. The CHIMERE air quality model was driven by Météo-France model for the regional scale. Simulations at local scale were conducted by using Micro Swift SPRAY model fed by both AROME fields and observations. At regional scale, modelling results show that the odorant part of the plume is well consistent with the occurrence of complaints. At local scale, using the same set of meteorological input data, correlation between simulations and complaints is slightly lower. Ground meteorological observations used as input data for the local scale modelling give better agreement with the complaints.Le 21 janvier 2013 sur le site de Lubrizol de Rouen, une instabilité des produits contenus dans le bac d’ajustage final de la fabrication du di-alkyl dithiophosphate de zinc (ZDDP) est constatée. Des rejets de composés soufrés ont été émis à l’atmosphère dans des proportions entraînant des nuisances olfactives. Des plaintes de riverains invoquant de mauvaises odeurs, des maux de tête ou des nausées ont ainsi été recueillies par les centres antipoison et de toxicovigilance (CAPTV) et Air normand entre le 21 et le 22 janvier. Le panache a aussi été détecté à Paris dans la nuit du 21 au 22 janvier ainsi qu’au sud de Londres le 22 janvier dans la matinée. L’INERIS, dans le cadre d’un appui technique au ministère chargé de l’écologie, a été chargé de reconstruire l’évolution temporelle du panache issu du site durant les 24 à 48 premières heures de l’accident, à partir des données disponibles sur les conditions météorologiques et le terme source

New lagrangian approach for wet plume modelling

International audienceA new version of the lagrangian dispersion modelling system Micro-SWIFT-SPRAY (MSS developed by ARIA Technologies and ARIANET) has been developed in order to allow simulation of wet plume, microorganisms, insecticide or pesticide dispersion. For all these applications, it is necessary to take into account both gas and liquid phase evolution including mass and heat transfer. In the particular case of microorganisms distinct behaviors potentially occur when transported by the liquid and/or the gas phase. Following the MSS lagrangian approach, it is easy to define a mass quantity of vapor and a large number of droplets of the same diameter by a virtual particle. Hence a spectrum of different size of droplets can be model using several virtual particles. The development of the new module consists of modelling the physical phenomenon of evaporation and condensation inside a wet plume taking into account temperature and humidity of ambient atmosphere. Microphysics of droplet is solved using the classical laws of evaporation/condensation processes in the surrounding atmosphere. The calculated evaporation rate allows to estimate the diameter evolution and the temperature inside the droplet. The difficulty consists in characterizing the surrounding atmosphere. The interaction between droplets and ambient humidity has been performed on an eulerian frame. Two methods of two way coupling have been tested on academic cases (0D). The proposed paper will present the two approaches and the obtained results

Statistical analysis of PM2.5 data in urban and suburban environments in France

As a result of the Clean Air for Europe program and the implementation of the new thematic strategy on air pollution, fine particles PM2.5 are bound to take an increasing part in future European and national regulations. Limit values and long term quality objectives will be set for this pollutant which raises concerns for public health. In that context a better knowledge of the sources and behaviour of PM2.5 appears essential for the design of relevant monitoring strategies and efficient pollution control policies. This study is based on three years of continuous measurement of PM2.5 in French cities and suburban areas. Through a statistical analysis, it aims at characterizing PM2.5 pollution according to the urban environment and to identify the contribution of the city to the observed concentrations. Descriptive statistics (histograms, time series) are computed for a selection of monitoring stations located in different French regions. Wherever possible, pairs of urban/suburban stations are examined to compare concentration levels inside and outside the city. Relationships between PM 2.5 concentrations and other species (PM10, NOx, SO2, CO) collocated measurements are investigated as well as correlation with variables indicative of PM2.5 sources and dispersion processes. This investigation is performed for each season of the year to highlight possible seasonal influences

Improvement of air quality simulations over urban areas

In urban areas, meteorology is affected by the presence of buildings leading to very complex processes which makes air quality simulation particularly difficult in the near-ground layers. To improve the air quality simulation in the urban areas, a chemistry-transport model (CHIMERE) driven by a mesoscale meteorological model (WRF) is used to simulate air pollutant concentrations during the winter 2016 over the Ile-de-France region especially during a short-term pollution episode in December at a resolution of 1.67km. Three urban canopy schemes are examined in this study: (1) a reference scheme (SLAB) that does not consider urban canopy parameters; (2) a multilayer urban canopy model with considered building effect parameterization (BEP); (3) multilayer urban models including energy exchange between inside and outside of the building (BEM). Compared with observations, all the schemes cannot accurately simulate the 2 meters temperature during the pollution episode and two urban canopy schemes underestimated 10 meters wind speed for the whole episode. Nudging above PBL improved 2 meters temperature simulations but did not significantly improves the 10 meters wind speed simulation. The two urban canopy schemes show better performances than the reference scheme for surface PM2.5, PM10 and nitrogen dioxide (NO2) concentrations. All schemes massively underestimated both primary and secondary organic aerosol concentrations particularly during the short-term pollution episode. These results stress the importance of emissions inventories and meteorological input data for the quality of simulations. A new vertical diffusion parametrization under PBL with input data from WRF will be developed in the next step

Impact of Physics Parameterizations on High-Resolution Air Quality Simulations over the Paris Region

The accurate simulation of meteorological conditions, especially within the planetary boundary layer (PBL), is of major importance for air quality modeling. In the present work, we have used the Weather Research and Forecast (WRF) model coupled with the chemistry transport model (CTM) CHIMERE to understand the impact of physics parameterizations on air quality simulation during a short-term pollution episode on the Paris region. A lower first model layer with a 4 m surface layer could better reproduce the transport and diffusion of pollutants in a real urban environment. Three canopy models could better reproduce a 2 m temperature (T2) in the daytime but present a positive bias from 1 to 5 degrees C during the nighttime; the multi-urban canopy scheme "building effect parameterization" (BEP) underestimates the 10 m windspeed (W10) around 1.2 m s(-1)for the whole episode, indicating the city cluster plays an important role in the diffusion rate in urban areas. For the simulation of pollutant concentrations, large differences were found between three canopy schemes, but with an overall overestimation during the pollution episode, especially for NO(2)simulation, the average mean biases of NO(2)prediction during the pollution episode were 40.9, 62.2, and 29.7 mu g m(-3)for the Bulk, urban canopy model (UCM), and BEP schemes, respectively. Meanwhile, the vertical profile of the diffusion coefficients and pollutants indicated an important impact of the canopy model on the vertical diffusion. The PBL scheme sensitivity tests displayed an underestimation of the height of the PBL when compared with observations issued from the Lidar. The YonSei University scheme YSU and Boulac PBL schemes improved the PBL prediction compared with the Mellor-Yamada-Janjic (MYJ) scheme. All the sensitivity tests, except the Boulac-BEP, could not fairly reproduce the PBL height during the pollution episode. The Boulac-BEP scheme had significantly better performances than the other schemes for the simulation of both the PBL height and pollutants, especially for the NO(2)and PM2.5(particulate matter 2.5 micrometers or less in diameter) simulations. The mean bias of the NO2, PM2.5, and PM10(particulate matter 10 micrometers or less in diameter) prediction were -5.1, 1.2, and -8.6 mu g m(-3), respectively, indicating that both the canopy schemes and PBL schemes have a critical effect on air quality prediction in the urban region

Improvement of the vertical mixing in chemistry transport modeling based on a 1.5-order turbulence kinetic energy-based eddy diffusivity closure scheme

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Evaluation of numerical models used to simulate atmospheric pollution near roadways

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Coparison of two modelling approaches for air quality monitoring from the urban scale to the street scale

Within the general framework of the development of high resolution air quality maps over the cities areas, INERIS (National Institute for Industrial Environment and Risks), AIRPL and COPARLY (Official Air Quality Monitoring Associations for the regions of Nantes and Lyon) led a comparison of two different approaches in order to assess pollutant concentrations (NOx, NO2, PM10) due to traffic in the streets. The purpose of the proposed communication deals with this project. The methodologies will be presented as well as the results obtained. The first method consisted in a nested approach from the national scale to the urban scale. ADMS Urban forced by the regional chemistry transport model CHIMERE applied with a 10km*10km resolution has been used. The second modelling approach involved a street canyon model forced by monitored background pollution data. The streets models selected were the Danish model OSPM for Nantes and the French model SIRANE for Lyon. Simulations have been carried out over hundred streets for both city centres of Nantes and Lyon. The results were compared with the available observations using several indicators : mean concentration, P98, time series... One of the main conclusion of this work is that despite the differences in the approaches, the obtained results are quite similar in the framework of this study