Impacts radiatifs des aérosols sur la dynamique en couche limite urbaine : application à la campagne CAPITOUL

La modélisation de l'aérosol se pose actuellement comme un point de passage obligé pour la compréhension du système atmosphérique. Son rôle multiple le place au centre de préoccupations environnementales comme météorologiques. Aujourd'hui, de nombreuses études attestent que de par ses propriétés physico-chimiques, l'aérosol a un impact direct complexe sur le bilan radiatif du fait de ses propriétés diffusantes et absorbantes. Il a été également montré qu'il avait un fort impact indirect lorsqu'on considère sa capacité d'activation en gouttelettes nuageuses. Enfin et selon différents rapports de l'Organisation Mondiale de la Santé, l'aérosol fin et ultra fin (particules fines inhalables) pose un vrai problème de santé publique (cancers, asthmes,...). Cette étude s'inscrit dans ce contexte et a pour principal objectif d'étudier les impacts radiatifs de l'aérosol urbain sur la couche limite. L'un des objectifs est d'étudier et d'évaluer les rétroactions des aérosols sur la dynamique de la couche limite urbaine au travers des interactions entre les particules atmosphériques et le rayonnement. La campagne de mesure CAPITOUL qui eut lieu entre 2004 et 2005 à Toulouse a servi de cadre à cette étude. Un cadastre d'émissions des aérosols et des gaz a tout d'abord été établi. Puis, une modélisation de l'aérosol urbain, principalement émis par des sources anthropiques (trafic routier et industries), a permis l'étude de l'évolution granulométrique et chimique, ainsi que l'analyse de la distribution spatiale des particules, fortement dépendante de la résolution adoptée. Ensuite, un module permettant de prendre en compte les caractéristiques des aérosols (taille, composition, concentration) calculées en chaque point et à chaque pas de temps lors du calcul des flux radiatifs a été développé. Ce module a permis de calculer les flux radiatifs influencés par la nature absorbante ou diffusante des aérosols. Les impacts sur ces flux et sur la température de la couche limite dans le cas réel de la campagne CAPITOUL sont présentés et comparés aux impacts dus à la surface urbaine seule.Nowaday, aerosol modelling is an absolute interest for the understanding of the complex atmospheric system. The role of aerosol particles is considered crucial for air quality, meteorological and climatical purpose. Several studies show that the aerosol physical and chemical behaviours affect the atmospheric radiative budget by scaterring and aborbing the radiative fluxes. Moreover, it has also been shown that the physical and chemical description of the aerosol is necessary to give shape to water droplets. Finally, several reports from the World Health Organisation show that the fine aerosol particles can cause major diseases as cancer or pulmonary diseases, and should be now considered as a public health matter. This study takes place in this context, and aims at estimating the radiative feedbacks of urban aerosol on the boundary layer. The CAPITOUL field experiment, which took place in the city of Toulouse during one year from march 2004 to february 2005, is the framework of a modelling study during a 2-day IOP. First, an emission inventory has been set up to reproduce the gaz and particles emissions. Then, a simulation exercise aims at reproduce the aerosol evolution at the fine scale of 500 m, and the very specific spatial distribution at different resolutions. In order to estimate the impact of aerosol particles on radiation, a radiative module has been developped to compute online the aerosol optical properties depending on the complex aerosol physical and chemical parameters. The radiative fluxes are then impacted by the aerosol scaterring and aborbing behaviour, leading to change in the urban dynamics. Those feedbacks on radiative fluxes lead to a change of the boundary layer's temperature. The impacts are also compared to the urban surface impacts

3D direct impacts of urgan aerosols on dynamics during the CAPITOUL field experiment

International audienceEvaluating the radiative impacts of aerosol particles is of great interest for understanding atmospheric physics and processes feedbacks. To respond to such objectives, the online fully coupled model Meso-NH is applied to a real case during a two-day Intensive Observation Period (IOP) of the CAPITOUL campaign. The aerosol optical properties are computed from the chemical composition and the size distribution of the particle population, and are compared to observations and analysed at local and regional scales. The differences between two simulations are then studied in order to isolate the direct radiative impacts of aerosols on dynamics. Results show that the aerosol particles generate a forcing on shortwave flux by a decrease of the amount reaching the surface up to 30 Wm−2. The resulting feedbacks lead to a cooling up to 0.6 K on the 2-meter temperature over the city of Toulouse and over the larger 125 km by 125 km area around Toulouse. This cooling is also modeled along the whole boundary layer, leading to a decrease of the boundary layer height up to −50 m during the afternoon and a decrease of the vertical velocities with an average of −3 %

High resolution modelling of aerosol dispersion regimes during the CAPITOUL field experiment: from regional to local scale interactions

High resolution simulation of complex aerosol particle evolution and gaseous chemistry over an atmospheric urban area is of great interest for understanding air quality and processes. In this context, the CAPITOUL (Canopy and Aerosol Particle Interactions in the Toulouse Urban Layer) field experiment aims at a better understanding of the interactions between the urban dynamics and the aerosol plumes. During a two-day Intensive Observational Period, a numerical model experiment was set up to reproduce the spatial distribution of specific particle pollutants, from the regional scales and the interactions between different cities, to the local scales with specific turbulent structures. Observations show that local dynamics depends on the day-regime, and may lead to different mesoscale dynamical structures. This study focuses on reproducing these fine scale dynamical structures, and investigate the impact on the aerosol plume dispersion. The 500-m resolution simulation manages to reproduce convective rolls at local scale, which concentrate most of the aerosol particles and can locally affect the pollutant dispersion and air quality

Mixing of dust aerosols into a mesoscale convective system: Generation, filtering and possible feedbacks on ice anvils

International audienceDuring the second Specific Observing Period (SOP) of the African Monsoon Multidisplinary Analyses (AMMA) campaign, several intense mesoscale convective systems (MCS) developed over Niger. An examination of a particular convective storm simulated with a mesoscale model near Banizoumbou, Niger, on 1 July, 2006, shows that this MCS generates a strong emission of dust particles at the leading edge of its density current. A fraction of these dust aerosols are uplifted by the convective core of the system and redistributed by aqueous processes. Aerosol impaction scavenging is the main process by which particles are deposited within the mesoscale convective system. However, small particles (smaller than 1 μm) that are not efficiently scavenged, are able to reach the upper troposphere at a concentration of 6 particles per cm3. This suggests that deep convection over semi-arid regions is able to create its own ice nuclei in high concentrations. This leads to the question: can deep convection over semi-arid regions affect particular ice properties such as ice anvil extension or induce possible feedbacks of dust on precipitation through ice sedimentation

Importance of transboundary transport of biomass burning emissions to regional air quality in Southeast Asia during a high fire event

10.5194/acp-15-363-2015Atmospheric Chemistry and Physics151363-37

3D direct impacts of urban aerosols on dynamics during the CAPITOUL field experiment

. [1] Evaluating the radiative impacts of aerosol particles is of great interest for understanding atmospheric physics and processes feedbacks. To respond to such objectives, the online fully coupled model Meso-NH is applied to a real case during a two-day Intensive Observation Period (IOP) of the CAPITOUL campaign. The aerosol optical properties are computed from the chemical composition and the size distribution of the particle population, and are compared to observations and analysed at local and regional scales. The differences between two simulations are then studied in order to isolate the direct radiative impacts of aerosols on dynamics. Results show that the aerosol particles generate a forcing on shortwave flux by a decrease of the amount reaching the surface up to 30 Wm À2 . The resulting feedbacks lead to a cooling up to 0.6 K on the 2-meter temperature over the city of Toulouse and over the larger 125 km by 125 km area around Toulouse. This cooling is also modeled along the whole boundary layer, leading to a decrease of the boundary layer height up to À50 m during the afternoon and a decrease of the vertical velocities with an average of À3 %. Citation: Aouizerats, B., P. Tulet, and L. Gomes (2012), 3D direct impacts of urban aerosols on dynamics during the CAPITOUL field experiment, Geophys. Res. Lett., 39

Understanding Sentinel-1 Backscatter Response to Sugarcane Yield Variability and Waterlogging

Sentinel-1 observes the whole globe every 12 days (6 days when both satellites were operational) and provides a wealth of data relevant to agriculture. Sugarcane cultivators could potentially benefit from these data by using them to assist operational and management practices. However, first, thorough understanding is needed of Sentinel-1 backscatter and its behavior over sugarcane canopies. In this study, we aimed to improve understanding of how Sentinel-1 backscatter responds to sugarcane yield variability and waterlogging. In order to do so we focused on an irrigated sugarcane plantation in Xinavane, Mozambique. In the analysis presented, we assessed different polarizations, their ratio, and benchmarked them against optical indices and passive microwave observations in different seasons. With the help of a large sugarcane yield dataset, we analyzed how backscatter relates to sucrose yield variability in different seasons. We found VV backscatter related to the stalk development, the most important reservoir for sucrose accumulation. In addition, in a season with reported waterlogging, optical and radar observations showed a delay in sugarcane crop development. Further analysis showed the presence of water underneath the canopy caused an increase in all polarizations and the cross ratio (CR). The results imply that Sentinel-1 backscatter contains information on both waterlogging under the canopy as well as sucrose development in the stalk. By isolating and quantifying the impact of waterlogging on backscatter, it will be possible to further quantify sucrose development with backscatter observations and identify waterlogging simultaneously.Peer reviewe

AEROgui: A graphical user interface for the optical properties of aerosols

Atmospheric aerosols have an uncertain effect on climate and serious impacts on human health. The uncertainty in the aerosols' role on climate has several sources. First, aerosols have great spatial and temporal variability. The spatial variability arises from the fact that aerosols emitted in a certain place can travel thousands of kilometers, swept by the winds to modify the destination region's climate. The spatial variability also means that aerosols are inhomogeneously distributed in the vertical direction, which can lead to a differential effect on the energy balance depending on the aerosols' altitude. On the other hand, aerosols experience physical and chemical transformations in the time they spend in the atmosphere, commonly known as aging, which modifies its optical properties. These factors make necessary the use of two approaches for the study of the aerosol impact on climate: global aerosol models and satellite- and ground-based measurements. The disagreement between the estimates of the two approaches is the main cause of the climate uncertainty. One way to reduce climate uncertainty is to create new tools to simulate more realistic aerosol scenarios. We present a graphical user interface to obtain aerosol optical properties: extinction, scattering, and absorption coefficients; single-scattering albedo; asymmetry parameter; and aerosol optical depth. The tool can be used to obtain the optical properties of the external and internal mixture of several aerosol components. Interface outputs have successfully been compared to a black carbon plume and to aging mineral dust

Impacts radiatifs des aérosols sur la dynamique en couche limite urbaine (application à la campagne CAPITOUL)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Modélisation et analyse de l'évolution des aérosols pendant la campagne MEGAPOLI

National audienceCommunication about Modélisation et analyse de l'évolution des aérosols pendant la campagne MEGAPOLI. Sixième réunion des utilisateurs MesoN