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Volcanic activity is an important source of atmospheric sulfur dioxide (SO2), which, after conversion into sulfuric acid, induces impacts on rain acidity, human health, meteorology and the radiative balance of the atmosphere, among others. This work focuses on the conversion of SO2 into sulfates (SO4(p)2-, S(+VI)) in the mid-tropospheric volcanic plume emitted by the explosive eruption of Mount Etna (Italy) on 12 April 2012, using the CHIMERE chemistry transport model. As the volcanic plume location and composition depend on several often poorly constrained parameters, using a chemistry transport model allows us to study the sensitivity of SO2 oxidation to multiple aspects, such as volcanic water emissions, transition metal emissions, plume diffusion and plume altitude. Our results show that two pathways contribute to sulfate production in the mid-troposphere: (1) the oxidation of SO2 by OH in the gaseous phase (70 %) and (2) aqueous oxidation by O2 catalysed by Mn2+ and Fe3+ ions (25 %). Oxidation in the aqueous phase is the faster process, but liquid water is scarce in the mid-troposphere; therefore, the relative share of gaseous oxidation can be important. After 1 d in the mid-troposphere, about 0.5 % of the volcanic SO2 was converted to sulfates via the gaseous process. Because of the nonlinear dependency of the kinetics in the aqueous phase on the amount of volcanic water emitted and on the availability of transition metals in the aqueous phase, several experiments have been designed to determine the prominence of different parameters. Our simulations show that, during the short time that liquid water remains in the plume, around 0.4 % of sulfates manage to quickly enter the liquid phase. Sensitivity tests regarding the advection scheme have shown that this scheme must be chosen wisely, as dispersion will impact both of the oxidation pathways explained above.

The atypical huge forest fires observed in France during the summer of 2022 are modelled using the CHIMERE model. Scenario simulations are performed without and with these fires to quantify the impact of these extra emissions on air quality thresholds exceedances. Additional processes are added in the model to better simulate fire emissions and then have more realistic simulations. The fires influence the characteristics of the surface by destroying the vegetation and creating new erodible surfaces. This increases the mineral dust emissions, but also reduces the Leaf Area Index, then decreases the biogenic emissions and the dry deposition of gases such as ozone. Results show that the fires induce numerous increases in surface ozone and Particulate Matter concentrations close to the sources but also in downwind remote sites such as the Paris area. During the period of the most intense fires in July, the impact of concentrations is mainly due to emissions themselves, when later, in August, ozone and PM concentrations continue to increase but this time due to changes in the burnt surfaces.

The ADRIMED campaign provides measurements of all key parameters regarding atmospheric composition in the Mediterranean area during the summer 2013. This is an opportunity to quantify the ability of current models to adequately represent the atmospheric composition in this complex region, which is influenced by anthropogenic emissions from Europe, Africa, the Middle-East and from shipping activities as well as mineral dust emissions mostly from the arid areas in Africa, sea-salt emissions, biomass burning emissions and biogenic emissions from the vegetation. The CHIMERE model in its present version is a chemistry-transport model which takes into account all these processes. We show here by simulating the period from 5 June to 15 July 2013 with the CHIMERE model and comparing the results to both routine and specific ADRIMED measurements that this model allows an adequate representation the atmospheric composition over the western Mediterranean, in terms of ozone concentration, particulate matter (PM) and aerosol optical depth (AOD). It is also shown that the concentrations of PM on all the considered area is dominated by mineral dust, even though local dust emissions in Europe are certainly overestimated by the model. A comparison with sulphate concentrations at Cape Corsica exhibits some discrepancies related to the regridding of shipping emissions.

This study displays a novel method to estimate the performance of advection schemes in numerical experiments along with a semi-realistic non-linear, stiff chemical system. This method is based on the examination of the "signature function", an invariant of the advection equation. Apart from exposing this concept in a particular numerical testcase, we show that a new numerical scheme based on a combination of the Piecewise Parabolic Method (PPM) with the flux adjustments of Walcek outperforms both the PPM and the Walcek schemes, for inert tracer advection as well as for advection of chemically active species. From a fundamental point of view, we think that our evaluation method, based on the invariance of the signature function under the effect of advection, offers a new way to evaluate objectively the performance of advection schemes in the presence of active chemistry. More immediately, we show that the new PPM+W ("Piecewise Parabolic Method + Walcek") advection scheme offers chemistry-transport modellers an alternative, high-performance scheme designed for Cartesian-grid Eulerian Chemistry-transport models, with improved performance over the classical PPM scheme. The computational cost of PPM+W is not higher than that of PPM. With improved accuracy and controlled computational cost, this new scheme may find applications in other fields such as ocean models or atmospheric circulation models.

Air pollution in the central zone of Chile not only is a public health concern, but also threatens water resources and climate, in connection with the transport and deposition of black carbon (BC) from urban centers onto the glaciers of the Andes Cordillera. Chemistry-transport simulations reveal a seasonal dichotomy in the flux and latitudinal pattern of BC deposition on glaciers of the central Chilean Andes. The average deposition flux of BC on glaciers between 30° S and 37° S is 4 times larger in winter, affecting mostly low elevation glaciers, whereas the smaller summertime flux affects glaciers evenly, irrespective of their elevation. The contribution of emissions from Santiago city is dominant in summertime with more than 50 % along the Andes, but minor in wintertime with less than 20 % even close to the capital city. Transport at larger scales and more local sources likely account for the remaining flux. The superimposition of synoptic-scale circulation and local mountain-valley circulation along the Andes cordillera drives the differences between summertime and wintertime deposition fluxes and generates a greater meteorological export potential during summer months. Future emissions and climate projections suggest that under the RCP8.5 scenario the gap between summertime and wintertime BC export and deposition flux could decrease, thereby pointing to summertime emission control gaining relevance. The chemistry-transport modeling approach for BC deposition on the Andes sheds light on the importance of the often disregarded summertime emissions on the radiative balance of its glaciers, particularly in the vicinity of Santiago.

This study introduces AerSett v1.0 (AERosol SETTling version 1.0), a model giving the settling speed of big spherical aerosols in the atmosphere without going through an iterative equation resolution. We prove that, for all spherical atmospheric aerosols with diameter D up to 1000 µm, this direct and explicit method including the drag coefficient formulation of Clift and Gauvin (1971) and the Davies (1945) slip correction factor gives results within 2 % of the exact solution obtained from the numerical resolution of a non-linear fixed-point equation. This error is acceptable considering the uncertainties on the drag coefficient formulations themselves. For D, the error is below 0.5 %. We provide a Fortran implementation of this simple and straightforward model, hoping that more chemistry–transport models (CTMs) and general circulation models will be able to take into account large-particle drag correction to the settling speed of big spherical aerosol particles in the atmosphere, without performing an iterative and time-consuming calculation.

In wintertime, high concentrations of atmospheric fine particulate matter (PM2.5) are commonly observed in the metropolitan area of Santiago, Chile. Hourly peaks can be very strong, up to 10 times above average levels, but have barely been studied so far. Based on atmospheric composition measurements and chemistry-transport modeling (WRF-CHIMERE), the chemical signature of sporadic skyrocketing wintertime PM2.5 peaks is analyzed. This signature and the timing of such extreme events trace their origin back to massive barbecue cooking by Santiago's inhabitants during international soccer games. The peaks end up evacuated outside Santiago after a few hours but trigger emergency plans for the next day. Decontamination plans in Santiago focus on decreasing emissions from traffic, industry, and residential heating. Thanks to the air quality network of Santiago, this study shows that cultural habits such as barbecue cooking also need to be taken into account. For short-term forecast and emergency management, cultural events such as soccer games seem a good proxy to prognose possible PM2.5 peak events. Not only can this result have an informative value for the Chilean authorities but also a similar methodology could be reproduced for other cases throughout the world in order to estimate the burden on air quality of cultural habits.

Volcanic activity is an important source of atmospheric sulphur dioxide (SO2), which, after conversion into sulphuric acid, induces impacts on, among others, rain acidity, human health, meteorology and the radiative balance of the atmosphere. This work focuses on the conversion of SO2 into sulphates (, S(+VI)) in the mid-tropospheric volcanic plume emitted by the explosive eruption of Mount Etna (Italy) on Apr. 12, 2012, using the CHIMERE chemistry-transport model. Since volcanic plume location and composition depend on several often poorly constrained parameters, using a chemistry-transport model allows us to study the sensitivity of SO2 oxidation to multiple aspects such as volcanic water emissions, transition metal emissions, plume diffusion and plume altitude. Our results show that in the mid-troposphere, two pathways contribute to sulphate production, the oxidation of SO2 by OH in the gaseous phase (70 %), and the aqueous oxidation by O2 catalyzed by Mn2+ and Fe3+ ions (25 %). The oxidation in aqueous phase is the faster process, but in the mid-troposphere, liquid water is scarce, therefore the relative share of gaseous oxidation can be important. After one day in the mid-troposphere, about 0.5 % of the volcanic SO2 was converted to sulphates through the gaseous process. Because of the nonlinear dependency of the kinetics in the aqueous phase to the amount of volcanic water emitted and on the availability of transition metals in the aqueous phase, several experiments have been designed to determine the prominence of different parameters. Our simulations show that during the short time that liquid water remains in the plume, around 0.4 % of sulphates manage to quickly enter the liquid phase. Sensitivity tests regarding the advection scheme have shown that this scheme must be chosen wisely, as dispersion will impact both oxidation pathways explained above.

In the framework of the FAIRMODE initiative, a set of simulations was performed using the WRF and CHIMERE models. The simulation period is chosen to cover a Particulate Matter (PM) pollution episode that happened in February 2015 over the Parisian area. A thorough validation of the reference simulation is presented, showing a good agreement between the measurements and the model both for PM components and major gaseous species. The PM composition analysis shows that the major contributors to the PM total concentration are nitrates and organic aerosols, followed by ammonium. An analysis of emission reduction scenarios compared to the reference simulation is also presented and different configurations of these scenarios are analyzed. Exceedances regarding to the last World Health Organization (WHO) guidelines are assessed, concluding that even if the most severe mitigation analyzed here (−50% emissions reduction) was applied over Paris, exceedances would still happen for PM. Emission reduction scenarios show that ozone concentrations are sensitive to NOx reductions inside the city with an increase in concentrations, while for PM a systematic decrease is observed whichever precursor emission is reduced. Coupling effects are explored and the impact of PM concentrations on the radiative and thermodynamic budgets is quantified. Scenarios are repeated both with different durations and different intensities and the most efficient configuration leading to exceedances reduction is discussed.

Assimilation of observational data from ground stations and satellites has been identified as a technique to improve air quality model results. This study is an evaluation of the maximum benefit expected from data assimilation in chemical transport models. Various tests are performed under real meteorological conditions; the injection of various subsets of “simulated observational data” at the initial state of a forecasting period is analyzed in terms of benefit on selected criteria. This observation dataset is generated by a simulation with perturbed input data. Several criteria are defined to analyze the simulations leading to the definition of a “tipping time” to compare the behavior of simulations. Assimilating three-dimensional data instead of ground observations clearly adds value to the forecast. For the studied period and considering the expected best favorable data assimilation experiment, the maximum benefit is higher for particulate matter (PM) with tipping times exceeding 80 h; for ozone (O3) the gain is on average around 30 h. Assimilating O3 concentrations with a delta calculated on the first level and propagated over the vertical direction provides better results on O3 mean concentrations when compared with the expected best experiment corresponding to the injection of the O3 “observations” 3D dataset, but for maximum O3 concentrations the opposite behavior is observed. If data assimilation of secondary pollutant concentrations provides an improvement, assimilation of primary pollutant emissions can have beneficial impacts when compared with an assimilation of concentrations, after several days on secondary pollutants like O3 or nitrate concentrations and more quickly for the emitted primary pollutants. An assimilation of ammonia concentrations has slightly better performances on nitrate, ammonium, and PM concentrations relative to the assimilation of nitrogen or sulfur dioxides.

We developed a new retrieval algorithm based on the Infrared Atmospheric Sounding Interferometer (IASI) observations, called AEROIASI-H2SO4, to measure the extinction and mass concentration of sulphate aerosols (binary solution droplets of sulphuric acid and water), with moderate random uncertainties (typically ∼35% total uncertainty for column mass concentration estimations). The algorithm is based on a self-adapting Tikhonov–Phillips regularization method. It is here tested over a moderate-intensity eruption of Mount Etna volcano (18 March 2012), Italy, and is used to characterise this event in terms of the spatial distribution of the retrieved plume. Comparisons with simultaneous and independent aerosol optical depth observations from MODIS (Moderate Resolution Imaging Spectroradiometer), SO2 plume observations from IASI and simulations with the CHIMERE chemistry/transport model show that AEROIASI-H2SO4 correctly identifies the volcanic plume horizontal morphology, thus providing crucial new information towards the study of volcanic emissions, volcanic sulphur cycle in the atmosphere, plume evolution processes, and their impacts. Insights are given on the possible spectroscopic evidence of the presence in the plume of larger-sized particles than previously reported for secondary sulphate aerosols from volcanic eruptions.

The distribution of tracers in the atmosphere results from the presence and emission of gaseous and particulate matter, as well as their transport, sedimentation and (photo-)chemical transformations. Understanding and quantifying these processes in the atmosphere can be addressed through the use of global-scale or regional-scale chemistry-transport numerical models such as CHIMERE (Mailler et al., 2016). While possible in principle, it is impractical to use this model to represent long-range transport of dense plumes of gas and aerosols, resulting for instance from massive emissions by volcanic eruptions, forest fires and desertic aerosol tempests. Indeed such studies requiring both large domains and high resolution have a prohibitive numerical cost due to the formulation of CHIMERE on a regular Cartesian mesh. This limitation is shared by all currently operational chemistry-transport models. Additionally, traditional Cartesian meshes pose a numerical singularity at the poles, where the longitude lines converge. These limitations may be lifted by replacing CHIMERE’s Cartesian mesh by a fully unstructured mesh. This would allow modelers to vary resolution in space, and hence to focus computational resources in key regions with sharp variations (e.g. volcanic eruptions) where high spatial and temporal resolution is required. As a first step in this direction, we compare the numerical performance of transport schemes formulated on Cartesian meshes and schemes formulated on unstructured meshes (Dubey et al., 2015). To focus on differences due to numerics, the unstructured mesh is a quasi-uniform icosahedral mesh such as the one used by global dynamical core DYNAMICO (Dubos et al., 2015). Spatial and temporal coupled and de-coupled schemes of various order are implemented in each mesh framework. A suite of test cases is used to evaluate different properties of the mesh-scheme pairings.To avoid the Cartesian pole singularity, the Cartesian mesh covers a limited domain excluding the poles. Analytical wind fields adapted to this limited domain are used. Metrics are evaluated using the quantities obtained in the simulations, such as convergence using root mean square errors, shape preservation using non-linear tracer relations, and diffusion using total entropy. The stability and monotonicity of the used schemes are also numerically validated. We find that a scheme of the Van Leer family on the unstructured mesh has a performance slightly inferior to a similar scheme on a Cartesian mesh. However, since this loss in quality remains moderate, it should be possible to more than compensate for it with a variable resolution. We are currently investigating this question and will present variable-resolution results if this ongoing work is timely completed. If successful, fully unstructured meshes would be a significant step forward in the modeling of scale interactions in atmospheric chemistry, and would potentially allow breakthrough for the understanding of such interactions.

The configuration of the Santiago basin, Chile (33.5°S 70.65°W) is quite unique in that it combines very strong emissions of urban anthropogenic pollutants with the steep topography of the coastal and Andes cordilleras surrounding the Metropolitan area. Interactions between atmospheric pollution and mountain meteorology are therefore exacerbated, and the potential for black carbon (BC) deposition on glaciers is strong. Based on chemistry-transport modeling with WRF-CHIMERE, we investigate (i) the pathways leading to deposition of BC from Santiago up to Andean glaciers in wintertime and (ii) the differences in magnitude and time dynamics of such deposition between wintertime and summertime.Ice and snow in the central Andes contain significant amounts of BC often attributed to emissions from Santiago. However, given the usually stable conditions in wintertime and the height of the obstacle to overcome for urban air masses (Santiago is 500 m a.s.l., summits are above 4000 m a.s.l.) the pathways for such deposition are not straightforward. We find that, for a typical winter month, up to 40% of BC dry deposition on snow- or ice-covered areas in the central Andes directly downwind from the Metropolitan area can indeed be attributed to emissions from Santiago. The adjacent network of canyons plays a key role in this export: for the case of the Maipo canyon, polluted urban air masses follow gentle slopes upward in the afternoon, consistently with mountain-valley circulation, before being vertically exported when reaching the tip of the main canyon. Statistical analysis shows that zonal wind speed in the urban area and vertical diffusion deep into the canyon account for most of the variance in BC deposition.In summertime, more intense convection takes place, and mountain-valley circulation is seldom perturbed by cloud cover, resulting in a greater export potential. Accordingly, summertime dry deposition of BC on glaciers occurs on a regular basis with equivalent amounts each day, contrarily to a more chaotic time series in wintertime. The contribution of wet deposition in winter (nonexistent in summer) exacerbates this irregularity. However, as a consequence of weaker emissions, average monthly dry deposition of BC over the central Andes glaciers (29°S to 38°S) is found to be less than half in summertime (135 µg/m2) compared to wintertime (320 µg/m2). Given the lesser role played by wood burning for residential heating in summertime, emissions from Santiago through traffic and industry dominate the signal leading to 55% of dry deposition, while it accounts for only 14% in wintertime, at the regional scale, due to more scattered sources.

Central Chile faces atmospheric pollution issues all year long, in relation with elevated concentrations of fine particulate matter during the cold months and tropospheric ozone during the warm season. In addition to public health issues, environmental problems regarding vegetation growth and water supply, as well as meteorological feedback are at stake. Sharp spatial gradients in regional emissions along with a complex geographical situation make for variable and heterogeneous dynamics in the localization and long-range transport of pollutants, with seasonal differences. Based on chemistry-transport modeling with WRF-CHIMERE, this work studies for one winter period and one summer period: (i) the contribution of emissions from the Santiago Metropolitan Area to air pollution in central Chile, (ii) the reciprocal contribution of regional pollutants transported into the Santiago basin. The underlying 3-dimensional advection patterns are investigated. We find that on average for the winter period 5 μg m−3 to 10 μg m−3 of fine particulate matter in Santiago come from regional transport, corresponding to 13 % to 15 % of average concentrations. In turn, emissions from the Metropolitan Area contribute to 5 % to 10 % of fine particulate matter pollution as far as 4° north and 4° south. Wintertime transport occurs mostly close to the surface. In summertime, exported precursors from Santiago, in combination with mountain-valley circulation dynamics, are found to account for most of ozone formation in the adjacent Andes cordillera and to create a persistent plume of ozone of more than 50 ppb, extending along 80 km horizontally and 1.5 km vertically, and located several hundred meters above ground, slightly north of Santiago. This work constitutes the first description of such an ozone bubble formation mechanism. Emissions of precursors from the capital city also affect daily maxima of surface ozone hundreds of kilometers away. In parallel, cutting emissions of precursors in the Santiago basin results in an increase of surface ozone mixing ratios in its western area.

The potential interest of the antidiffusive transport scheme proposed by Després et Lagoutière (1999) for resolving vertical transport in chemistry-transport models is investigated in an idealized framework with very encouraging results. We show that, compared to classical higher-order schemes, the Després et Lagoutière (1999) scheme reduces numerical diffusion and improves accuracy in idealized cases that are typical of atmospheric transport of tracers in chemistry-transport models. Increased accuracy and reduced diffusion is spectacular when, and only when vertical resolution is insufficient to properly resolve vertical gradients, which is very frequent in chemistry-transport models. Therefore, we think that this scheme is an extremely promising solution for reducing numerical diffusion in chemistry-transport models.

Recent studies based on observations have shown the impact of lockdown measures taken in various European countries to contain the Covid-19 pandemic on air quality. However, these studies are often limited to compare situations without and with lockdown measures, which correspond to different time periods and then under different meteorological conditions. We propose a modelling study with the WRF-CHIMERE modelling suite for March 2020, an approach allowing to compare atmospheric composition with and without lockdown measures without the biases of meteorological conditions. This study shows that the lockdown effect on atmospheric composition, in particular through massive traffic reductions, has been important for several short-lived atmospheric trace species, with a large reduction in NO2 concentrations, a lower reduction in Particulate Matter (PM) concentrations and a mitigated effect on ozone concentrations due to non-linear chemical effects., Graphical abstract Unlabelled Image, Highlights • Air pollution modelling • COVID19 epidemy • Regional modelling • Anthropogenic emissions scenario • Impact of emissions reduction

NOx emissions from lightning have been added to the CHIMERE v2020r1 model using a parameterization based on convective clouds. In order to estimate the impact of these emissions on pollutant concentrations, two simulations, using the online coupled WRF-CHIMERE models with and without NOx emissions from lightning, have been carried out over the months of July and August 2013 and over a large area covering Europe and the northern part of Africa. The results show that these emissions modify the pollutant concentrations as well as the meteorology. The changes are most significant where the strongest emissions are located. Adding these emissions improves Aerosol Optical Depth in Africa but has a limited impact on the surface concentrations of pollutants in Europe. For the two-month average we find that the maximum changes are localized and may reach &plusmn, 0.5 K for 2 m temperature, &plusmn, 0.5 m s&minus, 1 for 10 m wind speed, 10 W m&minus, 2 for short wave radiation surface flux, and 50 and 2 &mu, g m&minus, 3 for dust and sea salt surface concentrations, respectively. This leads to maximum changes of 1 &mu, 3 for surface concentrations of PM2.5.

Ice and snow in the Central Andes contain significant amounts of light-absorbing particles such as black carbon. The consequent accelerated melting of the cryosphere is not only a threat from a climate perspective but also for water resources and snow-dependent species and activities, worsened by the mega-drought affecting the region since the last decade. Given its proximity to the Andes, emissions from the Metropolitan Area of Santiago, Chile, are believed to be among the main contributors to deposition on glaciers. However, no evidence backs such an assertion, especially given the usually subsident and stable conditions in wintertime, when the snowpack is at its maximum extent. Based on high-resolution chemistry-transport modeling with WRF-CHIMERE, the present work shows that, for the month of July 2015, up to 40% of black carbon dry deposition on snow or ice covered areas in the Central Andes downwind from the Metropolitan area can be attributed to emissions from Santiago. Through the analysis of aerosol tracers we determine (i) that the areas of the Metropolitan Area where emissions matter most when it comes to export towards glaciers are located in Eastern Santiago near the foothills of the Andes, (ii) the crucial role of the network of Andean valleys that channels pollutants up to remote locations near glaciers, following gentle slopes. A direct corollary is that severe urban pollution, and deposition of impurities on the Andes, are anti-correlated phenomena. Finally, a two-variable meteorological index is developed that accounts for the dynamics of aerosol export towards the Andes, based on the zonal wind speed over the urban area, and the vertical diffusion coefficient in the valleys close to ice and snow covered terrain. Numerous large urban areas are found along the Andes so that the processes studied here can shed light on similar investigations for other glaciers-dependent Andean regions.

A well-known drawback of Eulerian models is excessive numerical diffusion of the transported species. This applies to chemical species but also to water vapor. We present a new way of dealing with this problem in the vertical direction by using the Després and Lagoutière (1999) scheme – hereinafter DL99, a simple 1st-order advection scheme with antidiffusive properties. These authors have only studied this scheme in the context of 1d transport. Here we test the applicability of this scheme in atmospheric modelling by applying it to tracer transport in the vertical direction in idealized 2d (zonal-vertical) atmospheric circulations and quantify the gain compared to classical advection schemes. In this idealized framework, we have tested the efficiency of DL99 in two cases representative of important situations for atmospheric transport : - Formation of a thin plume from an initially thick column of tracer (e.g. volcanic plume, biomass burning plume etc.) under the effect of zonal wind shear in presence of large-scale variations in vertical wind - Long-range advection of a thin polluted layer under the action of zonal wind in presence of large scale oscillations in the vertical wind. In these idealized case studies, we show that using DL99 in the vertical direction yields dramatically improved performance compared to any other scheme we have tested, including the 3rd-Order Piecewise Parabolic Method (PPM). As an example, in a simulation with a vertical resolution of 500m and a zonal resolution of 25 km initialized by a 1000m-thick, zonally uniform layer of tracer, after being transported horizontally over 2000km over 48 hours by a uniform zonal wind ~11.5ms-1 together with an oscillating vertical wind of +-0.05ms-1, maximal tracer concentration at the end of the simulation with DL99 is 94% of its initial value instead of 51% with PPM, l2 relative error is 10% instead of 61%, and 92% of the tracer mass is still confined in the correct 1000m-thick envelope instead of 50%.This and other numerical experiments shows that, by design, DL99 reduces numerical diffusion, but it also proves it to be able to preserve the areas of uniform tracer concentration even if these areas cover only a very small number of cells in the vertical direction. We argue that this unique set of properties, along with the simplicity of its formulation and its minimal computational cost make the DL99 an extremely attractive candidate for a robust and non-diffusive representation of vertical advection in Eulerian meteorological and chemistry-transport models. This scheme has been implemented in the state-of-the-art CHIMERE chemistry-transport model (Mailler et al., 2017), and we have shown that it brings a clear improvement in the representation of the structure of a volcanic plume from the Etna volcano (Lachâtre et al., 2020, Atmos. Chem. Phys.)Main references:Després, B., and F. Lagoutière, 1999, Un schéma non linéaire anti-dissipatif pour l'équation d'advection linéaire, Comptes Rendus de l’Académie des Sciences

Atmospheric modelling allows to study large spatial scale events such as volcanic eruptions, which can emit large amounts of plume-confined particulate matter and gases, to evaluate their transport in the atmosphere and their subsequent impacts. However, to study more precisely these events, different issues have to be addressed. One notable example of these issues is the well-known excessive numerical diffusion in the atmospheric column in Eulerian models leading to excessive plume dispersion misrepresentation of the plume three-dimensional morphology and subsequent geographical extent of its impacts. Mount Etna volcano’s moderate eruption of March 18, 2012, which released about 3kT of sulphure dioxide in the atmosphere, has been simulated in this study with the CHIMERE chemistry-transport model. The simulated plume has been observed and tracked with satellite instruments (OMI and IASI) for several days during its transport over the Mediterranean Sea in order to compare with model outputs.Sensitivity tests have been performed to evaluate the impact of injection altitude and profile shape on the subsequent trajectory of the plume. It was shown that altitude is the most sensitive parameter when results remain weakly sensitive to the vertical shape of injection.In order to effectively address the problem of excessive numerical diffusion, we have included a new antidiffusive transport scheme in the vertical direction and a new strategy to use directly the vertical wind field provided by the forcing meteorological model. We show that both these improvements permit a substantial reduction in numerical diffusion. The use of the new antidiffusive vertical scheme has brought the strongest improvement in our model outputs. To a lesser extent, a more realistic representation of the vertical wind field has also been shown to reduce volcanic plume spreading. In summary, we show that these two improvements bring an improvement in the representation of the plume which is as strong as the improvement brought by increasing the number of vertical levels, but without an additional burden in computational power.This study has been supported by AID (Agence de l'Innovation de Défense) under grant TROMPET.

In wintertime, high background concentrations of atmospheric fine particulate matter (PM2.5) are commonly observed in the metropolitan area of Santiago, Chile. Although the frequency of alert events has been decreasing in the recent years, two short-lived peak events reaching up to 600µg/m3 for a few hours were observed in the city on June 18th and June 26th 2016, triggering emergency measures for the next day.The observed meteorological conditions at the time of these peaks are not unusual. In addition, a high-resolution meteorology and chemistry-transport simulation with the WRF meteorological model and the CHIMERE chemistry-transport model reproduces fairly well the meteorology and levels of PM for June 2016, except for those two particular events that are not captured by the model. The combination of these elements leads to the conclusion that sporadic strong emissions are at play.The analysis of recorded concentration ratios of PM2.5, NOx and CO points to a specific source, departing significantly from the average signal for the season. Based on the literature and HTAP emission ratios, usual sources of PM such as traffic, residential heating and industry can be ruled out. The temporal correlation of the events with soccer games of the Chilean team and the recorded chemical footprint lead to conclude to the dominant contribution of massive barbecue cooking at the peak times.Following the source identification via surface stations analysis, the next question was to quantify the potential transport and impact of such pollution peaks in the Santiago Metropolitan area. An additional source term was added in the chemistry-transport simulation, and maps of PM changes were analyzed. For both events, the same region in the Southwest of Santiago was impacted by the plume.A natural continuation of this work is the study through modeling of the dispersion patterns of polluted plumes outside of the Santiago basin on a longer time scale. In particular, significant deposition of light-absorbing particles has been measured on glaciers near the capital city, without a clear identification of their source or the underlying processes of transport.

International audience; Nearly all regions in the world are projected to become dryer in a warming climate. Here, we investigate the Mediterranean region, often referred to as a climate change “hot spot”. From regional climate simulations, it is shown that although enhanced warming and drying over land is projected, the spatial pattern displays high variability. Indeed, drying is largely caused by enhanced warming over land. However, in Northern Europe, soil moisture alleviates warming induced drying by up to 50% due to humidity uptake from land. In already arid regions, the Mediterranean Sea is generally the only humidity source, and drying is only due to land warming. However, over Sahara and the Iberian Peninsula, enhanced warming over land is insufficient to explain the extreme drying. These regions are also isolated from humidity advection by heat lows, which are cyclonic circulation anomalies associated with surface heating over land. The cyclonic circulation scales with the temperature gradient between land and ocean which increases with climate change, reinforcing the cyclonic circulation over Sahara and the Iberian Peninsula, both diverting the zonal advection of humidity to the south of the Iberian Peninsula. The dynamics are therefore key in the warming and drying of the Mediterranean region, with extreme aridification over the Sahara and Iberian Peninsula. In these regions, the risk for human health due to the thermal load which accounts for air temperature and humidity is therefore projected to increase significantly with climate change at a level of extreme danger.

International audience; Excessive numerical diffusion is one of the major limitations in the representation of long-range transport by chemistry-transport models. In the present study, we focus on excessive diffusion in the vertical direction, which has been shown to be a major issue, and we explore three possible ways to address this problem: increase vertical resolution, use an advection scheme with antidiffusive properties, and represent more accurately the vertical wind. This study is done with the CHIMERE chemistry-transport model, for the March 18, 2012 eruption of Mount Etna, which has released about 3 kt of sulphur dioxide in the atmosphere into a plume that has been observed by satellite instruments (IASI and OMI) for several days. The change from the classical Van Leer et al., (1977) scheme to the Després and Lagoutière (1999) antidiffusive scheme in the vertical direction has been shown to bring the largest improvement to model outputs in terms of preserving the thin plume emitted by the volcano. To a lesser extent, improved representation of the vertical wind field has also been shown to reduce plume dispersion. Both these changes help reducing vertical diffusion in the model as much as a brute-force approach (increasing vertical resolution).; L'excès de diffusion numérique est l'une des limitations majeures pour la représentation du transport à longue distance dans les modèles de chimie-transport. La présente étude se concentre sur l'excès de diffusion verticale, dont il a été démontré que c'est un problème majeur. Nous explorons trois façons possibles d'aborder ce problème: raffiner la résolution verticale, utiliser un schéma de transport antidiffusif, et représenter le vent vertical de façon plus exacte. Cette étude est réalisée avec le modèle de chimie-transport CHIMERE pour l'éruption de l'Etna du 18 mars 2012, qui a libéré environ 3kT de dioxyde de soufre dans l'atmosphère, formant un panache qui a été observé par les instruments spatiaux IASI et OMI durant plusieurs jours. C'est la substitution du schéma classique de Van Leer (1977) par le schéma antidiffusif de Després et Lagoutière (1999) dans la direction verticale qui a apporté l'amélioration la plus substantielle dans les sorties du modèle, en termes de préservation du panache mince émis par le volcan. Dans une moindre mesure, la représentation améliorée du champ de vent vertical a également réduit la diffusion du panache. Ces deux changements ont réduit la diffusion verticale de façon aussi efficace qu'une approche en force brute (raffinement de la résolution verticale).

Biomass burning emissions are a major source of trace gases and aerosols. Wildfires being highly variable in time and space, calculating emissions requires a numerical tool able to estimate fluxes at the kilometer scale and with an hourly time step. Here, the APIFLAME model version 2.0 is presented. It is structured to be modular in terms of input databases and processing methods. The main evolution compared to version 1.0 is the possibility of merging burned area and fire radiative power (FRP) satellite observations to modulate the temporal variations of fire emissions and to integrate small fires that may not be detected in the burned area product. Accounting for possible missed detection due to small fire results in an increase in burned area ranging from ∼5% in Africa and Australia to ∼30% in North America on average over the 2013-2017 time period based on the Moderate-Resolution Imaging Spectroradiometer (MODIS) Collection 6 fire products. An illustration for the case of southwestern Europe during the summer of 2016, marked by large wildfires in Portugal, is presented. Emissions calculated using different possible configurations of APIFLAME show a dispersion of 80% on average over the domain during the largest wildfires (8-14 August 2016), which can be considered as an estimate of uncertainty of emissions. The main sources of uncertainty studied, by order of importance, are the emission factors, the calculation of the burned area, and the vegetation attribution. The aerosol (PM10) and carbon monoxide (CO) concentrations simulated with the CHIMERE regional chemistry transport model (CTM) are consistent with observations (good timing for the beginning and end of the events, ±1d for the timing of the peak values) but tend to be overestimated compared to observations at surface stations. On the contrary, vertically integrated concentrations tend to be underestimated compared to satellite observations of total column CO by the Infrared Atmospheric Sounding Interferometer (IASI) instrument and aerosol optical depth (AOD) by MODIS. This underestimate is lower close to the fire region (5%-40% for AOD depending on the configuration and 8%-18% for total CO) but rapidly increases downwind. For all comparisons, better agreement is achieved when emissions are injected higher into the free troposphere using a vertical profile as estimated from observations of aerosol plume height by the Multi-angle Imaging SpectroRadiometer (MISR) satellite instrument (injection up to 4km). Comparisons of aerosol layer heights to observations by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) show that some parts of the plume may still be transported at too low an altitude. The comparisons of the different CTM simulations to observations point to uncertainties not only on emissions (total mass and daily variability) but also on the simulation of their transport with the CTM and mixing with other sources. Considering the uncertainty of the emission injection profile and of the modeling of the transport of these dense plumes, it is difficult to fully validate emissions through comparisons between model simulations and atmospheric observations., SCOPUS: ar.j, info:eu-repo/semantics/published

Biomass burning emissions are a major source of trace gases and aerosols. Wildfires being highly variable in time and space, calculating emissions requires a numerical tool able to estimate fluxes at the kilometer scale and with an hourly time-step. Here, the APIFLAME model version 2.0 is presented. It is structured to be modular in terms of input databases and processing methods. The main evolution compared to the version v1.0 is the possibility to merge burned area and fire radiative power (FRP) satellite observations to modulate the temporal variations of fire emissions and to integrate small fires that may not be detected in the burned area product. Accounting for possible missed detection due to small fires results in an increase ranging from ∼ 5 % in Africa and Australia to ∼ 30 % in North America, on average over the 2013–2017 time period based on the Moderate-Resolution Imaging Spectroradiometer (MODIS) collection 6 fire products. An illustration for the case of south-western Europe during the summer of 2016, marked by large wildfires in Portugal, is presented. Emissions calculated using different possible configurations of APIFLAME show a dispersion of 75% on average over the domain during the largest wildfires (8–14/08/2016), which can be considered as an estimate of uncertainty on emissions (excluding the uncertainty on emission factors). Corresponding enhancements of aerosols and carbon monoxide (CO) simulated with the regional chemistry transport model CHIMERE are consistent with observations (good timing for the beginning and end of the events, ± 1 day for the timing of the peak values) but tend to be overestimated compared to observations at surface stations. On the contrary, vertically integrated concentrations tend to be underestimated compared to satellite observations of total column CO by the Infrared Atmospheric Sounding Interferometer (IASI) instrument and aerosol optical depth (AOD) by MODIS, which allow regional scale evaluation. This underestimate is lower close to the fire region (5 % to 40 % for AOD depending on the configuration, and 8–18 % for total CO) but rapidly increases downwind. For all comparisons, better agreement is achieved when emissions are injected higher into the free troposphere using a vertical profile as estimated from observations of aerosol plume height by the MISR satellite instrument (injection up to 4 km). The overestimate compared to surface sites and underestimate compared to satellite observations point to uncertainties not only on emissions (total mass and daily variability) but also on their injection profile and on the modelling of the transport of these dense plumes.

In wintertime, high background concentrations of atmospheric fine particulate matter (PM2.5) are commonly observed in the metropolitan area of Santiago, Chile. Hourly peaks can be very strong, up to ten times average levels, but have barely been studied so far. Based on atmospheric composition measurements and chemistry-transport modeling (WRF-CHIMERE), the chemical signature of sporadic skyrocketing wintertime PM2.5 peaks is analyzed. This signature and the timing of such extreme events traces their origin back to massive barbecue cooking by Santiago's inhabitants during international soccer games. The peaks end up evacuated outside Santiago after a few hours but trigger emergency plans for the next day. Decontamination plans in Santiago focus on decreasing traffic, industrial and residential heating emissions. Thanks to the air quality network of Santiago, this study shows that cultural habits such as barbecue cooking also need to be taken into account. For short-term forecast and emergency management, cultural events such as soccer games seem a good proxy to prognose possible PM2.5 peak events. Not only this result can have an informative value for the Chilean authorities, but a similar methodology could also be reproduced for other cases throughout the world in order to estimate the burden on air quality of cultural habits. In particular, the present study shows that investigating the atmospheric composition in large cities during major events is key for the design of effective air pollution mitigation policies.

We developed a new retrieval algorithm based on the Infrared Atmospheric Sounding Interferometer (IASI) observations, called AEROIASI-Sulphates, to measure vertically-resolved sulphate aerosols (SA) extinction and mass concentration profiles, with limited theoretical uncertainties (typically ~25 % total uncertainty for SA mass column estimations). The algorithm, based on a self-adapting Tikhonov-Phillips regularization method, is applied to a medium-sized-intensity eruption of Mount Etna volcano (18 March 2012). Comparisons with simultaneous and independent SO2 plume observations and simulations show that AEROIASI-Sulphates correctly identifies the volcanic plume morphology both horizontally and vertically. This method provided, for the first time, crucial information pieces to describe the gaseous-to-particulate volcanic sulphur mass balance (60 % of the injected sulphur mass is converted to particulate matter, after ~24 hours) and to estimate the regional shortwave direct radiative forcing (a regional forcing of −0.8 W/m2 is exerted in the eastern Mediterranean) for moderate volcanic eruptions.

During the monsoon season, pollutants emitted by large coastal cities and biomass burning plumes originating from Central Africa have complex transport pathways over Southern West Africa (SWA). The Dynamics–Aerosol–Chemistry–Cloud–Interactions in West Africa (DACCIWA) field campaign has provided numerous dynamical and chemical measurements in and around the super site of Savè in Benin (≈ 185 km away from the coast), which allows quantifying the relative contribution of advected pollutants. Through the combination of in-situ ground measurements with aircraft, radio-sounding, satellite and high-resolution chemistry-transport modeling with the CHIMERE model, the source attribution and transport pathways of pollutants inland (here, NOx and CO) are carefully analyzed for the 1–7 July 2016 period. The relative contributions of different sources (i.e. emissions from several large coastal cities) on the air quality in Savè are characterized. It is shown that a systematic diurnal cycle exists with high surface concentrations of pollutants from 18:00 to 22:00 UTC. This evening peak is attributed to pollution transport from the coastal city of Cotonou (Benin). Numerical model experiments indicates that the anthropogenic pollutants are accumulated during the day close to the coast, and transported northward as soon as the daytime convection in the atmospheric boundary layer ceases after 16:00 UTC, reaching 8° N at 21:00 UTC. When significant biomass burning pollutants are transported into continental SWA, they are mixed with anthropogenic pollutants along the coast during the day, and this mixture is then transported northward. At night, most of the coastal anthropogenic plumes are transported within the planetary boundary layer (below about 500 m above ground level), whereas the biomass burning pollutants are mostly transported above it, thus generally not impacting ground level air quality.

The city of Santiago experiences extreme pollution events during winter due to particulate matter and the associated health impact depends on the exposure to this pollutant, particularly to PM2.5. We present and apply a method that estimates the exposure of users of the public transport system of Santiago by combining smart card mobility data with measured surface concentrations from the monitoring network of Santiago and simulated concentrations by the CHIMERE model. The method was applied between July 20th and 24th of 2015 to 105,588 users corresponding to 12% of the frequent users of the public transport system and approximately 2% of the total population of Santiago. During those five days, estimated exposure based on measured concentrations varied between 44 and 75 μg/m3 while exposure based on simulated concentrations varied between 45 and 89 μg/m3. Furthermore, including socioeconomic conditions suggests an inverse relationship between exposure and income when measured concentrations are used, i.e. the lower the income the higher the exposure, whereas no such relationship is observed when using simulated concentrations. Although only exposure to PM2.5 was considered in this study, the method can also be applied to estimate exposure to other urban pollutant such as ozone.

The Mediterranean basin is characterized by large concentrations of aerosols from both natural and anthropogenic sources. These aerosols affect tropospheric photochemistry by modulating the photolytic rates. Three simulations of the atmospheric composition at basin scale have been performed with the CHIMERE chemistry-transport model for the period from 6 June to 15 July 2013 covered by the ADRIMED campaign, a campaign of intense measurements in the western Mediterranean basin. One simulation takes into account the radiative effect of the aerosols on photochemistry, the second one does not, and the third one is designed to quantify the model sensitivity to a bias in the ozone column. These simulations are compared to satellite and ground-based measurements, with a particular focus on the area of Lampedusa. Values of the aerosol optical depth (AOD) are obtained from the MODIS instrument on the AQUA and TERRA satellites as well as from stations in the AERONET network and from the MFRSR sun photometer deployed at Lampedusa. Additional measurements from instruments deployed at Lampedusa either permanently or exceptionally are used for other variables: MFRSR sun photometer for AOD, diode array spectrometer for actinic fluxes, LIDAR for the aerosol backscatter, sequential sampler for speciation of aerosol and Brewer spectrophotometer for the total ozone column. It is shown that CHIMERE has a significant ability to reproduce observed peaks in the AOD, which in Lampedusa are mainly due to dust outbreaks during the ADRIMED period, and that taking into account the radiative effect of the aerosols in CHIMERE considerably improves the ability of the model to reproduce the observed day-to-day variations of the photolysis rate of ozone to O2 and O(1D), J(O1D), and that of NO2 to NO and O(3P), J(NO2). While in the case of J(O1D) other variation factors such as the stratospheric ozone column are very important in representing correctly the day-to-day variations, the day-to-day variations of J(NO2) are captured almost completely by the model when the optical effects of the aerosols are taken into account. Finally, it is shown that the inclusion of the direct radiative effect of the aerosols in the CHIMERE model leads to reduced J(O1D) and J(NO2) values over all the simulation domain, which range from a few percents over continental Europe and the north-east Atlantic Ocean to about 20 % close to and downwind from Saharan dust sources. The effect on the modelled ozone concentration is 2-fold: the effect of aerosols leads to reduced ozone concentrations over the Mediterranean Sea and continental Europe, close to the sources of NOx, but it also leads to increased ozone concentrations over remote areas such as the Sahara and the tropical Atlantic Ocean.

International audience; The region of Valencia in Spain has historically been affected by heavy precipitation events (HPEs). These HPEs are known to be modulated by the sea surface temperature (SST) of the Balearic Sea. Using an atmosphere-ocean regional climate model, we show that more than 70 % of the HPEs in the region of Valencia present a SST cooling larger than the monthly trend in the Northwestern Mediterranean before the HPEs. This is linked to the breaking of a Rossby wave preceding the HPEs: a ridge-trough pattern at mid-levels centered over western France associated with a low-level depression in the Gulf of Genoa precedes the generation of a cut-off low over southern Spain with a surface depression over the Alboran Sea in the lee of the Atlas. This latter situation is favourable to the advection of warm and moist air towards the Mediterranean Spanish coast, possibly leading to HPEs. The depression in the Gulf of Genoa generates intense northerly (Mistral) to north-westerly (Tramontane/Cierzo) winds. In most cases, these intense winds trigger entrainment at the bottom of the oce-anic mixed layer which is a mechanism explaining part of the SST cooling in most cases. Our study suggests that the SST cooling due to this strong wind regime then persists until the HPEs and reduces the precipitation intensity.

Carbon monoxide, CO, and fine atmospheric particulate matter, PM2.5, are analyzed over the Guinean gulf coastal region using the WRF-CHIMERE modeling system and observations during the beginning of the monsoon 2006 (from May to July), corresponding to the Africa Multidisciplinary Monsoon Analysis (AMMA) campaign period. Along the Guinean gulf coast, the contribution of long-range pollution transport to CO or PM2.5 concentrations is important. For PM2.5, desert dust decreases from ≈38 % in May to ≈5 % in July; biomass burning aerosol from Central Africa increases from ≈10 % in May to ≈52 % in July. The anthropogenic contribution is ≈30 % for CO and ≈10 % for PM2.5. When focusing only on anthropogenic pollution, frequent northward transport events from the coast to the Sahel are associated with periods of low wind and no precipitation. In June, anthropogenic PM2.5 and CO concentrations are higher than in May or July over the Guinean coastal region. Over the Sahel, air masses dynamics concentrate pollutants emitted locally and remotely at the coast due to a meridional atmospheric cell. Refining the analysis on the period 8–15 June, anthropogenic pollutants emitted along the coastline are exported toward the North especially at the beginning of the night (18 UTC to 00 UTC) with the establishment of the nocturnal low level jet. Plumes originating from different cities overlay for some hours at the coast, leading to high pollution level, because of specific disturbed meteorological conditions.

In the Mediterranean area, aerosols may originate from anthropogenic or natural emissions (biogenic, mineral dust, fire and sea salt) before undergoing complex chemistry. In case of a huge pollution event, it is important to know whether European pollution limits are exceeded and, if so, whether the pollution is due to anthropogenic or natural sources. In this study, the relative contribution of emissions to surface PM10, surface PM2.5 and total aerosol optical depth (AOD) is quantified. For Europe and the Mediterranean regions and during the summer of 2012, the WRF and CHIMERE models are used to perform a sensitivity analysis on a 50 km resolution domain (from −10° W to 40° E and from 30° N to 55° N): one simulation with all sources (reference) and all others with one source removed. The reference simulation is compared to data from the AirBase network and two ChArMEx stations, and from the AERONET network and the MODIS satellite instrument, to quantify the ability of the model to reproduce the observations. It is shown that the correlation ranges from 0.19 to 0.57 for surface particulate matter and from 0.35 to 0.75 for AOD. For the summer of 2012, the model shows that the region is mainly influenced by aerosols due to mineral dust and anthropogenic emissions (62 and 19 %, respectively, of total surface PM10 and 17 and 52 % of total surface PM2.5). The western part of the Mediterranean is strongly influenced by mineral dust emissions (86 % for surface PM10 and 44 % for PM2.5), while anthropogenic emissions dominate in the northern Mediterranean basin (up to 75 % for PM2.5). Fire emissions are more sporadic but may represent 20 % of surface PM2.5, on average, during the period near local sources. Sea salt mainly contributes for coastal sites (up to 29 %) and biogenic emissions mainly in central Europe (up to 20 %). The same analysis was undertaken for the number of daily exceedances of the European Union limit of 50 μg m−3 for PM10 (over the stations), and for the number of daily exceedances of the WHO recommendation for PM2.5 (25 μg m−3), over the western part of Europe and the central north. This number is generally overestimated by the model, particularly in the northern part of the domain, but exceedances are captured at the right time. Optimized contributions are computed with the observations, by subtracting the background bias at each station and the specific peak biases from the considered sources. These optimized contributions show that if natural sources such as mineral dust and fire events are particularly difficult to estimate, they were responsible exclusively for 35.9 and 0.7 %, respectively, of the exceedances for PM10 during the summer of 2012. The PM25 recommendation of 25 μg m−3 is exceeded in 21.1 % of the cases because of anthropogenic sources exclusively and in 0.02 % because of fires. The other exceedances are induced by a mixed contribution between mainly mineral dust (49.5–67 % for PM10 exceedance contributions, 4.4–13.8 % for PM2.5), anthropogenic sources (14.9–24.2 % and 46.3–80.6 %), biogenic sources (4.1–15.7 % and 12.6–30 %) and fires (2.2–7.2 % and 1.6–12.4 %).

Mineral dust is one of the most important aerosol in mass over the world, affecting health and dynamics. This aerosol is mainly emitted over arid areas but may be long-range transported, impacting the local budget of air quality in many cities. While models were extensively used to study a single specific event, or making a global analysis at coarse resolution, the goal of our study is to simultaneously focus on several areas - Europe, North America, Central Asia, East China and the Caribbean area - for a one month period, March 2014, avoiding any parameter fitting to better simulate a given dust outbreak. The simulation is performed for the first time with the hemispheric version of the CHIMERE model, with a horizontal resolution of 10km. In this study, an overview of several simultaneous dust outbreaks over the north hemisphere is proposed to assess the capability of such modelling tools to predict dust pollution events. A quantitative and qualitative evaluation of the most striking episodes is presented with comparisons to satellite data, ground based Particulate Matter and calcium measurements. Despite some overestimation of dust concentrations far from emission areas, the model is able to simulate the timing of the arrival of dust outbreaks on observational sites. For instance, several spectacular dust storms in the US and China are perfectly captured by the models. The high resolution allows to better describe and understand the orographic effects and the long-range transport of dust plumes.