Etude de l'impact du mécanisme chimique et des taux de photolyse "online" sur les simulations 3D d'épisodes de pollution régionale. (Exercice ESCOMPTE d'intercomparaison de modèles)

This work focus on of the main physico-chemical processes driving the redistribution of photochemical pollutants and oxidizing capacity of the atmosphere, using the modelling way with the comprehensive RAMSChemistry meso-scale model. These studies were done in the framework of the ESCOMPTE models intercomparison modelling exercise. This experiment took place over the southern France, including the Marseilles urban area and close to the Fos-Berre industrial area. With the coupling of a chemical mechanism interpreter, a dry deposition module and an "online" photolysis rates calculation code, we were able to study the impact of these various processes on the distribution of pollutants and on the oxidizing capacity of the atmosphere. We shows that an "online" calculation for photolysis rates is necessary in order not to modify radicals redistribution, and that a simplified chemical mechanism is sufficient for processes studies, but not for air quality or oxidizing capacity prediction. Finally, the participation on the ESCOMPTE modelling exercise gave us the possibility to test in real conditions the RAMS-Chemistry model, and to compare it with reference models. It also permitted to focus on strong and weak points of this kind of exercises.Ce travail porte sur l'étude des principaux processus physico-chimiques dirigeant la redistribution des polluants photochimiques et la capacité oxydante de l'atmosphère, grâce à une approche par la modélisation méso-échelle à l'aide du modèle RAMS-Chimie. Ces études ont été réalisées dans le cadre de l'exercice ESCOMPTE d'intercomparaison de modèles de transport chimie. Cette campagne s'est déroulé dans le sud-est de la france, à proximité de la zone urbanisée de Marseille et du site industriel de Fos-Berre. Grâce au développement et au couplage d'un interprét- eur de mécanismes chimiques, d'un module de dépôt sec, et d'un code de calcul "online" des taux de photolyse, nous avons pu étudier l'impact de ces différents processus dans la répartition des polluants et de la capacité oxydante de l'atmosphère. Nous montrons que le calcul "online" des taux de photolyse est nécessaire pour ne pas modifier la représentation des radicaux et qu'un mécanisme chimique simplifié est suffisant dans le cadre d'études de processus, mais pas pour des études de qualité de l'air ou de capacité oxydant

Gas emissions due to magma-sediment interactions during flood magmatism at the Siberian Traps: gas dispersion and environmental consequences.

International audienceWe estimate the fluxes of extremely reduced gas emissions produced during the emplacement of the Siberian Traps large igneous province, due to magma intrusion in the coaliferous sediments of the Tunguska Basin. Using the results of a companion paper (Iacono-Marziano et al. submitted to EPSL), and a recent work about low temperature interaction between magma and organic matter (Svensen et al., 2009), we calculate CO-CH4-dominated gas emission rates of 7×1015-2×1016 g/yr for a single magmatic/volcanic event. These fluxes are 7 to 20 times higher than those calculated for purely magmatic gas emissions, in the absence of interaction with organic matter-rich sediments. We investigate, by means of atmospheric modelling employing present geography of Siberia, the short and mid term dispersion of these gas emissions into the atmosphere. The lateral propagation of CO and CH4 leads to an important perturbation of the atmosphere chemistry, consisting in a strong reduction of the radical OH concentration. As a consequence, both CO and CH4 lifetimes in the lower atmosphere are enhanced by a factor of at least 3, at the continental scale, as a consequence of 30 days of magmatic activity. The short-term effect of the injection of carbon monoxide and methane into the atmosphere is therefore to increase the residence times of these two species and, in turn, their capacity of geographic expansion. The estimated CO and CH4 volume mixing ratios (i.e. the number of molecules of CO or CH4 per cm3, divided by the total number of molecules per cm3) in the low atmosphere are 2-5 ppmv at the continental scale and locally higher than 50 ppmv. The dimension of the area affected by these high volume mixing ratios decreases in the presence of a lava flow accompanying magma intrusion at depth. Complementary calculations for a 10-year duration of the magmatic activity suggest (i) an increase in the mean CH4 volume mixing ratio of the whole atmosphere up to values 3 to 15 times higher than the current one, and (ii) recovery times of 100 years to bring back the atmospheric volume mixing ratio of CH4 to the pre-magmatic value. Thermogenic methane emissions from the Siberian Traps has already been proposed to crucially contribute to end Permian-Early Triassic global warming and to the negative carbon isotopic shift observed globally in both marine and terrestrial sediments. Our results corroborate these hypotheses and suggest that concurrent high temperature CO emissions also played a key role by contributing to increase (i) the radiative forcing of methane and therefore in its global warming potential, and (ii) the input of isotopically light carbon into the atmosphere that generated the isotopic excursion. We also speculate a poisoning effect of high carbon monoxide concentrations on end-Permian fauna, at a local scale

Etude de l'impact du mécanisme chimique et des taux de photolyse "online" sur les simulations 3D d'épisodes de pollution régionale ((Exercice ESCOMPTE d'intercomparaison de modèles))

Ce travail porte sur l'étude des principaux processus physico-chimiques dirigeant la redistribution des polluants photochimiques et la capacité oxydante de l'atmosphère, grâce à une approche par la modélisation méso-échelle à l'aide du modèle RAMS-Chimie. Ces études ont été réalisées dans le cadre de l'exercice ESCOMPTE d'intercomparaison de modèles de transport chimie. Cette campagne s'est déroulée dans le sud-est de la France, à proximité de la zone urbanisée de Marseille et du site industriel de Fos-Berre. Grâce au développement et au couplage d'un interpréteur de mécanismes chimiques, d'un module de dépôt sec, et d'un code de calcul "online" des taux de photolyse, nous avons pu étudier l'impact de ces différents processus dans la répartition des polluants et de la capacité oxydante de l'atmosphère. Nous montrons que le calcul "online" des taux de photolyse est nécessaire pour ne pas modifier la représentation des radicaux et qu'un mécanisme chimique simplifié est suffisant dans le cadre d'études de processus, mais pas pour des études de qualité de l'air ou de capacité oxydante. Enfin, la participation à l'exercice ESCOMPTE nous a donné l'occasion de tester en conditions réelles le modèle RAMS-Chimie, de le confronter aux modèles de références, mais aussi de mettre en lumière les points forts et les faiblesses d'un tel exerciceCLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF

Etude de l'impact du mécanisme chimique et des taux de photolyse "online" sur les simulations 3D d'épisodes de pollution régionale. (Exercice ESCOMPTE d'intercomparaison de modèles)

Ce travail porte sur l'étude des principaux processus physico-chimiques dirigeant la redistribution des polluants photochimiques et la capacité oxydante de l'atmosphère, grâce à une approche par la modélisation méso-échelle à l'aide du modèle RAMS-Chimie. Ces études ont été réalisées dans le cadre de l'exercice ESCOMPTE d'intercomparaison de modèles de transport chimie. Cette campagne s'est déroulé dans le sud-est de la france, à proximité de la zone urbanisée de Marseille et du site industriel de Fos-Berre. Grâce au développement et au couplage d'un interprét- eur de mécanismes chimiques, d'un module de dépôt sec, et d'un code de calcul "online" des taux de photolyse, nous avons pu étudier l'impact de ces différents processus dans la répartition des polluants et de la capacité oxydante de l'atmosphère. Nous montrons que le calcul "online" des taux de photolyse est nécessaire pour ne pas modifier la représentation des radicaux et qu'un mécanisme chimique simplifié est suffisant dans le cadre d'études de processus, mais pas pour des études de qualité de l'air ou de capacité oxydanteCLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF

Study of ozone distribution over the south-eastern France (ESCOMPTE campaign) : discrimination between ozone tendencies due to chemistry and to transport

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Regional modelling of tracer transport by tropical convection – Part 1: Sensitivity to convection parameterization

International audienceThe general objective of this series of papers is to evaluate long duration limited area simulations with ide-alised tracers as a tool to assess tracer transport in chemistry-transport models (CTMs). In this first paper, we analyse the results of six simulations using different convection closures and parameterizations. The simulations are using the Grell and Dévényi (2002) mass-flux framework for the con-vection parameterization with different closures (Grell = GR, Arakawa-Shubert = AS, Kain-Fritch = KF, Low omega = LO, Moisture convergence = MC) and an ensemble parameteriza-tion (EN) based on the other five closures. The simulations are run for one month during the SCOUT-O3 field campaign lead from Darwin (Australia). They have a 60 km horizontal resolution and a fine vertical resolution in the upper tropo-sphere/lower stratosphere. Meteorological results are compared with satellite products, radiosoundings and SCOUT-O3 aircraft campaign data. They show that the model is generally in good agreement with the measurements with less variability in the model. Except for the precipitation field, the differences between the six simulations are small on average with respect to the differences with the meteorological observations. The comparison with TRMM rainrates shows that the six parameterizations or closures have similar behaviour concerning convection triggering times and locations. However , the 6 simulations provide two different behaviours for rainfall values, with the EN, AS and KF parameterizations (Group 1) modelling better rain fields than LO, MC and GR (Group 2). The vertical distribution of tropospheric tracers is very different for the two groups showing significantly more transport into the TTL for Group 1 related to the larger av-Correspondence to: J. Arteta ([email protected]) erage values of the upward velocities. Nevertheless the low values for the Group 1 fluxes at and above the cold point level indicate that the model does not simulate significant overshooting. For stratospheric tracers, the differences between the two groups are small indicating that the downward transport from the stratosphere is more related to the turbulent mixing parameterization than to the convection parameterization

Impact of two chemistry mechanisms fully couples with mesoscale model on the tropospheric pollutants distribution.

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Evaluation of isoprene emissions from the coupled model SURFEX–MEGANv2.1

International audienceIsoprene, a key biogenic volatile organic compound, plays a pivotal role in atmospheric chemistry. Due to its high reactivity, this compound contributes significantly to the production of tropospheric ozone in polluted areas and to the formation of secondary organic aerosols. The assessment of biogenic emissions is of great importance for regional and global air quality evaluation. In this study, we implemented the biogenic emission model MEGANv2.1 (Model of Emissions of Gases and Aerosols from Nature, version 2.1) in the surface model SURFEXv8.1 (SURface EXternalisée in French, version 8.1). This coupling aims to improve the estimation of biogenic emissions using the detailed vegetation-type-dependent treatment included in the SURFEX vegetation ISBA (Interaction between Soil Biosphere and Atmosphere) scheme. This scheme provides vegetation-dependent parameters such as leaf area index and soil moisture to MEGAN. This approach enables a more accurate estimation of biogenic fluxes compared to the stand-alone MEGAN model, which relies on average input values for all vegetation types. The present study focuses on the assessment of the SURFEX–MEGAN model isoprene emissions. An evaluation of the coupled SURFEX–MEGAN model results was carried out by conducting a global isoprene emission simulation in 2019 and by comparing the simulation results with other MEGAN-based isoprene inventories. The coupled model estimates a total global isoprene emission of 443 Tg in 2019. The estimated isoprene is within the range of results obtained with other MEGAN-based isoprene inventories, ranging from 311 to 637 Tg. The spatial distribution of SURFEX–MEGAN isoprene is consistent with other studies, with some differences located in low-isoprene-emission regions. Several sensitivity tests were conducted to quantify the impact of different model inputs and configurations on isoprene emissions. Using different meteorological forcings resulted in a ±5 % change in isoprene emissions using MERRA (Modern-Era Retrospective analysis for Research and Applications) and IFS (Integrated Forecasting System) compared with ERA5. The impact of using different emission factor data was also investigated. The use of PFT (plant functional type) spatial coverage and PFT-dependent emission potential data resulted in a 12 % reduction compared to using the isoprene emission potential gridded map. A significant reduction of around 38 % in global isoprene emissions was observed in the third sensitivity analysis, which applied a parameterization of soil moisture deficit, particularly in certain regions of Australia, Africa, and South America. The significance of coupling the SURFEX and MEGAN models lies particularly in the ability of the coupled model to be forced with meteorological data from any period. This means, for instance, that this system can be used to predict biogenic emissions in the future. This aspect of our work is significant given the changes that biogenic organic compounds are expected to undergo as a result of changes in their climatic factors

High-Resolution air quality forecasts with MOCAGE chemistry transport model

MOCAGE is the 3D global off-line chemistry transport model (CTM) run at Météo-France since 2005 for air quality operational forecasts. Three nested domains are used, with decreasing resolutions (globe, Europe, and France), and 47 vertical levels (from the surface to 5 hPa). For the global and the European domain, input meteorological forcing fields are Météo-France ARPEGE forecasts. For France, and for the first day of forecast, MOCAGE uses the operational outputs of Météo-France non-hydrostatic AROME model. This high-resolution (2.5 km) meteorological model is supposed to better represent urban processes (e.g., the urban heat island), which are of strong interest for air quality applications. The purpose of this study is to test the increase of resolution of the CTM MOCAGE over France from 0.1° to 0.025° (i.e. the native resolution of the input meteorological fields)