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HBr emissions from volcanoes lead rapidly to the formation of BrO within volcanic plumes and have an impact on tropospheric chemistry, at least at the local and regional scales. The motivation of this paper is to prepare a framework for further 3D modelling of volcanic halogen emissions in order to determine their fate within the volcanic plume and then in the atmosphere at the regional and global scales. The main aim is to evaluate the ability of the model to produce a realistic partitioning of bromine species within a grid box size typical of MOCAGE (Model Of atmospheric Chemistry At larGE scale) 3D (0.5∘ × 0.5∘). This work is based on a 1D single-column configuration of the global chemistry-transport model MOCAGE that has low enough computational cost to allow us to perform a large set of sensitivity simulations. This paper uses the emissions from the Mount Etna eruption on 10 May 2008. Several reactions are added to MOCAGE to represent the volcanic plume halogen chemistry. A simple plume parameterisation is also implemented and tested. The use of this parameterisation tends to only slightly limit the efficiency of BrO net production. Both simulations with and without the parameterisation give results for the partitioning of the bromine species, of ozone depletion and of the BrO/SO2 ratio that are consistent with previous studies. A series of test experiments were performed to evaluate the sensitivity of the results to the composition of the emissions (primary sulfate aerosols, Br radical and NO) and to the effective radius assumed for the volcanic sulfate aerosols. Simulations show that the plume chemistry is sensitive to all these parameters. We also find that the maximum altitude of the eruption changes the BrO production, which is linked to the vertical variability of the concentrations of oxidants in the background air. These sensitivity tests display changes in the bromine chemistry cycles that are generally at least as important as the plume parameterisation. Overall, the version of the MOCAGE chemistry developed for this study is suitable to produce the expected halogen chemistry in volcanic plumes during daytime and night-time.

To estimate the effect of vegetation stress and changes in biogenic volatile organic compound (BVOC) emissions on urban ozone (O3) levels we perform a systematic, observation-based analysis of the relationship between formaldehyde (HCHO) mixing ratios, meteorological parameters, measurement-based drought indicators and O3 over the central European city of Vienna, Austria. In addition, numerical models SURface EXternalisée (SURFEX), Model of Emissions of Gases and Aerosols from Nature (MEGAN) Vers.2.1 and 3 and MOdèle de Chimie A Grande Echelle (MOCAGE) are combined to estimate the soil moisture, the spatial distribution and drought response of isoprene emissions, and the resulting distribution of HCHO in the atmosphere. To analyse the effect of drought during spring and summer we contrast observations during dry and reference years. Our results show that the observed HCHO can be explained using the simulated isoprene emissions as well as observed and simulated vegetation drought responses. HCHO mixing ratios differ strongly between dry and reference seasons. Spring-time precipitation deficits facilitate reduced HCHO mixing ratios due to delayed and weakened plant growth. In consequence also O3 burdens are lowered due to reduced BVOC precursor emissions. These reductions occur despite radiation levels being higher than during the reference year, illustrating the strong potential of spring-time BVOC emissions to modulate urban O3 burdens. Conversely, during summer elevated O3 levels occur during local drought conditions. These are driven by advected isoprene originating from nearby forest areas, which are not affected by drought. Our results regarding elevated summer-time O3 burdens under vegetation heat and drought stress are in good agreement with previous work.

Volcanoes are known to be important emitters of atmospheric gases and aerosols, which for certain volcanoes can include halogen gases and in particular HBr. HBr emitted in this way can undergo rapid atmospheric oxidation chemistry (known as the bromine-explosion) within the volcanic emission plume leading to the production of bromine oxide (BrO) and ozone depletion. In this work, we present the results of a modelling study of a volcanic eruption from Mt Etna that occurred around Christmas 2018 that lasted 6 days. The aims of this study are to demonstrate and evaluate the ability of the regional 3D Chemistry Transport Model MOCAGE to simulate the volcanic halogen chemistry in this case study, to analyse the variability of the chemical processes during the plume transport, and to quantify its impact on the composition of the troposphere at a regional scale over the Mediterranean basin. The comparison of the tropospheric SO2 and BrO columns from 25 to 30 December 2018 from the MOCAGE simulation with the columns derived from the TROPOMI satellite measurements shows a very good agreement for the transport of the plumeand a good consistency for the concentrations if considering the uncertainties in the flux estimates and the TROPOMI columns. The analysis of the bromine species’ partitioning and of the associated chemical reaction rates provides a detailed picture of the simulated bromine chemistry throughout the diurnal cycle and at different stages of the volcanic plume’s evolution. The partitioning of the bromine species is modulated by the time evolution of the emissions during the 6 days of the eruption, by the meteorological conditions, and by the distance of the plume from the vent/the time since the emission. As the plume travels further from the vent, the halogen source gas HBr becomes depleted, BrO production in the plume becomes less efficient, and ozone depletion (proceeding via the Br + O3 reaction followed by the BrO self-reaction) decreases. The depletion of HBr relative to the other prevalent hydracid HCl leads to a shift in the relative concentrations of the Br− and Cl− ions, which in turn leads to reduced production of Br2 relative to BrCl. The MOCAGE simulations show a regional impact of the volcanic eruption on the oxidants OH and O3 with a reduced burden of both gases that is caused by the chemistry in the volcanic plume. This reduction in atmospheric oxidation capacity results in a reduced CH4 burden. Finally, sensitivity tests on the composition of the emissions carried out in this work show that the production of BrO is higher when the volcanic emissions of sulfate aerosols are increased but occurs very slowly when no sulfate and Br radicals are assumed to be in the emissions. Both sensitivity tests highlight a significant impact on the oxidants in the troposphere at the regional scale of these assumptions. All the results of this modelling study are consistent with the previous studies carried out on the volcanic halogens modelling.

Well constrained volcanic emissions inventories in chemistry transport models are necessary to study the impacts induced by these sources on the tropospheric sulfur composition and on sulfur species concentrations and depositions at the surface. In this paper, the changes induced by the update of the volcanic sulfur emissions inventory are studied using the global chemistry transport model MOCAGE (MOdele de Chimie Atmospherique a Grande Echelle). Unlike the previous inventory ( Andres and Kasgnoc , 1998 ) , the updated one ( Carn et al. , 2016 , 2017 ) uses more accurate information and includes contributions from both passive degassing and eruptive emissions. Eruptions are provided as daily total amounts of sulfur dioxide ( SO2 ) emitted by volcanoes in the Carn et al. ( 2016 , 2017 ) inventories, and degassing emissions are provided as annual averages with the related mean annual uncertainties of those emissions by volcano. Information on plume altitudes is also available and has been used in the model. We chose to analyze the year 2013, for which only a negligible amount of eruptive volcanic SO2 emissions is reported, allowing us to focus the study on the impact of passive degassing emissions on the tropospheric sulfur budget. An evaluation against the Ozone Monitoring Instrument (OMI) SO2 total column and MODIS (Moderate-Resolution Imaging Spectroradiometer) aerosol optical depth (AOD) observations shows the improvements of the model results with the updated inventory. Because the global volcanic SO2 flux changes from 13 Tg yr−1 in Andres and Kasgnoc ( 1998 ) to 23.6 Tg yr−1 in Carn et al. ( 2016 , 2017 ) , significant differences appear in the global sulfur budget, mainly in the free troposphere and in the tropics. Even though volcanic SO2 emissions represent 15 % of the total annual sulfur emissions, the volcanic contribution to the tropospheric sulfate aerosol burden is 25 %, which is due to the higher altitude of emissions from volcanoes. Moreover, a sensitivity study on passive degassing emissions, using the annual uncertainties of emissions per volcano, also confirmed the nonlinear link between tropospheric sulfur species content with respect to volcanic SO2 emissions. This study highlights the need for accurate estimates of volcanic sources in chemistry transport models in order to properly simulate tropospheric sulfur species.

The Copernicus Atmosphere Monitoring Service (CAMS) provides routine analyses and forecasts of trace gases and aerosols on a global scale. The core is the European Centre for Medium Range Weather Forecasts (ECMWF) Integrated Forecast System (IFS), where modules for atmospheric chemistry and aerosols have been introduced and which allows for data assimilation of satellite retrievals of composition. We have updated both the homogeneous and heterogeneous NOx chemistry applied in the three independent tropospheric–stratospheric chemistry modules maintained within CAMS, referred to as IFS(CB05BASCOE), IFS(MOCAGE) and IFS(MOZART). Here we focus on the evaluation of main trace gas products from these modules that are of interest as markers of air quality, namely lower-tropospheric O3, NO2 and CO, with a regional focus over the contiguous United States. Evaluation against lower-tropospheric composition reveals overall good performance, with chemically induced biases within 10 ppb across species for regions within the US with respect to a range of observations. The versions show overall equal or better performance than the CAMS reanalysis, which includes data assimilation. Evaluation of surface air quality aspects shows that annual cycles are captured well, albeit with variable seasonal biases. During wintertime conditions there is a large model spread between chemistry schemes in lower-tropospheric O3 (∼ 10 %–35 %) and, in turn, oxidative capacity related to NOx lifetime differences. Analysis of differences in the HNO3 and PAN formation, which act as reservoirs for reactive nitrogen, revealed a general underestimate in PAN formation over polluted regions, likely due to too low organic precursors. Particularly during wintertime, the fraction of NO2 sequestered into PAN has a variability of 100 % across chemistry modules, indicating the need for further constraints. Notably, a considerable uncertainty in HNO3 formation associated with wintertime N2O5 conversion on wet particle surfaces remains. In summary, this study has indicated that the chemically induced differences in the quality of CAMS forecast products over the United States depends on season, trace gas, altitude and region. While analysis of the three chemistry modules in CAMS provide a strong handle on uncertainties associated with chemistry modeling, the further improvement of operational products additionally requires coordinated development involving emissions handling, chemistry and aerosol modeling, complemented with data-assimilation efforts.

Volcanoes are known to be important emitters of atmospheric gases and aerosols, both through explosive eruptions and persistent quiescent degassing (von Glasow et al., 2009). The most abundant gases in volcanic emissions are H2O, CO2, SO2 and halogens (HCl, HBr, HF). In general, halogens play an important role in the atmosphere by modifying air composition and oxidizing capacity in the troposphere (von Glasow et al., 2004). The chemical processes occurring within the plume lead to the formation of BrO following the ‘bromine explosion’ mechanism as evidenced from both observations and modelling (e.g. Bobrowski et al., 2003; Roberts et al., 2009). Oxidized forms of bromine (BrO) are formed during daytime within the plume due to heterogeneous reactions of HBr on volcanic aerosols leading to ozone depletion. So far, modelling studies mainly focused on spatial scales ranging from 10m to ~1km and processes occurring within a few hours after eruption.The objective of this study is to go a step further by analysing the impact at the regional scale namely over the whole Mediterranean basin of a single Mt Etna eruption event in December 2018. For this, we have further developed the MOCAGE model (Guth et al., 2016), a chemistry transport model run at a resolution of 0.2°× 0.2°, to quantify the impacts of the halogen species emitted by the volcano on air composition. We selected here the case of the eruption of Mt Etna around Christmas 2018 characterised by large amounts of emissions over several days. The results show that MOCAGE represents the halogen chemistry in the volcanic plume quite well. The bromine-explosion cycle takes place during the day of the eruption, with a rapid increase in BrO concentration leading to a strong depletion in ozone and NO₂ concentrations across the Mediterranean as well as to changes in the air composition in particular for bromine compounds such as Br, HOBr, BrONO₂, Br2 and BrCl. Adding to this, BrO is formed again on the following day (25/12/2018) during daytime from the bromine reservoir species from night time leading to additional ozone depletion.The comparison of the tropospheric columns of BrO and SO2 retrievals from the TROPOMI spaceborne instrument with the MOCAGE simulations shows that the tropospheric BrO and SO₂ columns have the same order of magnitude and that the locations of the simulated and observed plumes are overall in good agreement during the main eruption period and the following six days. The comparison shows also the similarity of the order of magnitude of the BrO/SO2 ratio between MOCAGE and TROPOMI, especially for the 25th of December 2018.

Deep convection overshooting the lowermost stratosphere is well known for its role in the local stratospheric water vapour (WV) budget. While it is seldom the case, local enhancements of WV associated with stratospheric overshoots are often published. Nevertheless, one debatable topic prevails on the global impact of this event with respect to the temperature-driven dehydration of air parcels entering the stratosphere. As a first step, it is crucial to quantify their role at a local scale before assessing their impact at a large-scale in a meteorological model. It would lead to a forcing scheme for overshoots in the global models. This paper reports on the local enhancements of WV linked to stratospheric overshoots, observed during the TRO-Pico campaign conducted in March 2012 in Bauru, Brazil, using the BRAMS (Brazilian version of RAMS) mesoscale model. Since numerical simulation depends on the choice of several preferred parameters, each having its uncertainties, we vary the microphysics or the vertical resolution while simulating the overshoots. Thus, we produce a set of simulations illustrating the possible variations in representing the stratospheric overshoots. To resolve better the stratospheric hydration, we opt for simulations with the 800-m-horizontal-grid-point presentation. Next, we validate these simulations against the Bauru S-band radar echo tops and the TRO-Pico balloon-borne observations of WV and particles. Two of the three simulations' setups yield results compatible with the TRO-Pico observations. From these two simulations, we determine approximately 333 t to 2000 t of WV mass prevailing in the stratosphere due to an overshooting plume depending on the simulation setup. About 70 % of the ice mass remains between the 380 K to 385 K isentropic levels. The overshooting top comprises pristine ice and snow, while aggregates only play a role just above the tropopause. Interestingly, the horizontal cross-section of the overshooting top is about 450 km2 at 380 K isentrope, which is similar to the horizontal-grid-point resolution of a simulation that cannot compute overshoots explicitly. These results could establish a forcing scheme of overshooting hydration or dehydration in a large-scale simulation.

We report on an evaluation of tropospheric ozone and its precursor gases in three atmospheric chemistry versions as implemented in the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS), referred to as IFS(CB05BASCOE), IFS(MOZART) and IFS(MOCAGE). While the model versions were forced with the same overall meteorology, emissions, transport and deposition schemes, they vary largely in their parameterisations describing atmospheric chemistry, including the organics degradation, heterogeneous chemistry and photolysis, as well as chemical solver. The model results from the three chemistry versions are compared against a range of aircraft field campaigns, surface observations, ozone-sondes and satellite observations, which provides quantification of the overall model uncertainty driven by the chemistry parameterisations. We find that they produce similar patterns and magnitudes for carbon monoxide (CO) and ozone (O3), as well as a range of non-methane hydrocarbons (NMHCs), with averaged differences for O3 (CO) within 10 % (20 %) throughout the troposphere. Most of the divergence in the magnitude of CO and NMHCs can be explained by differences in OH concentrations, which can reach up to 50 %, particularly at high latitudes. There are also comparatively large discrepancies between model versions for NO2, SO2 and HNO3, which are strongly influenced by secondary chemical production and loss. Other common biases in CO and NMHCs are mainly attributed to uncertainties in their emissions. This configuration of having various chemistry versions within IFS provides a quantification of uncertainties induced by chemistry modelling in the main CAMS global trace gas products beyond those that are constrained by data assimilation.

We have developed a new statistical approach (M3Fusion) for combining surface ozone observations from thousands of monitoring sites around the world with the output from multiple atmospheric chemistry models to produce a global surface ozone distribution with greater accuracy than can be provided by any individual model. The ozone observations from 4766 monitoring sites were provided by the Tropospheric Ozone Assessment Report (TOAR) surface ozone database, which contains the world's largest collection of surface ozone metrics. Output from six models was provided by the participants of the Chemistry-Climate Model Initiative (CCMI) and NASA's Global Modeling and Assimilation Office (GMAO). We analyze the 6-month maximum of the maximum daily 8 h average ozone value (DMA8) for relevance to ozone health impacts. We interpolate the irregularly spaced observations onto a fine-resolution grid by using integrated nested Laplace approximations and compare the ozone field to each model in each world region. This method allows us to produce a global surface ozone field based on TOAR observations, which we then use to select the combination of global models with the greatest skill in each of eight world regions; models with greater skill in a particular region are given higher weight. This blended model product is bias corrected within 2∘ of observation locations to produce the final fused surface ozone product. We show that our fused product has an improved mean squared error compared to the simple multi-model ensemble mean, which is biased high in most regions of the world.

Alkyl hydroperoxides are essential intermediates in the atmospheric oxidation of hydrocarbons and in low-temperature combustion processes [1]. Chlorinated alkyl hydroperoxides play a similar role in the atmospheric oxidation of chlorinated hydrocarbons. It is important to study the thermodynamic parameters for these species to understand and predict the reaction pathways, rate constants, and equilibrium constants. There are relatively few experimental studies on the thermodynamic properties of alkyl hydroperoxides due to their rapid interconversion and instability, which makes the studies of these species complex.The main objective of this work is to provide reliable kinetic and thermodynamic data for the gas phase reaction of hydroxyl radicals with chloromethyl hydroperoxyl (CH2ClOOH). Several possible reaction pathways could be feasible: H-abstraction, Cl-abstraction, and OH-abstraction. The reaction mechanism involves many stationary points on the potential energy surface and reveals some unusual features for the H-abstraction. Theoretical calculations were performed with the augmented correlation consistent basis sets aug-cc-pVTZ for H and O atoms and the aug-cc-pV(T+d)Z for Cl atom including tight d polarization functions. The potential energies have been calculated at the DK-CCSD(T)/ANO-RCC (VTZP and VQZP) level of theory on the geometries optimized previously.Implications for atmospheric chemistry are presented and discussed.References[1] H. Sun, C. Chen, and J. Bozzelli, “Structures, Intramolecular Rotation Barriers, and Thermodynamic Properties (Enthalpies, Entropies and Heat Capacities) of Chlorinated Methyl Hydroperoxides (CH2ClOOH, CHCl2OOH, and CCl3OOH)”, The Journal of Physical Chemistry A, 2000; 104 (35): 8270-8282, https://doi.org/10.1021/jp0013917

International audience

Estimates of ground-level ozone concentrations are necessary to determine the human health burden of ozone. To support the Global Burden of Disease Study, we produce yearly fine resolution global surface ozone estimates from 1990 to 2017 through a data fusion of observations and models. As ozone observations are sparse in many populated regions, we use a novel combination of the M3Fusion and Bayesian Maximum Entropy (BME) methods. With M3Fusion, we create a multimodel composite by bias-correcting and weighting nine global atmospheric chemistry models based on their ability to predict observations (8834 sites globally) in each region and year. BME is then used to integrate observations, such that estimates match observations at each monitoring site with the observational influence decreasing smoothly across space and time until the output matches the multimodel composite. After estimating at 0.5° resolution using BME, we add fine spatial detail from an additional model, yielding estimates at 0.1° resolution. Observed ozone is predicted more accurately (R2 = 0.81 at the test point, 0.63 at 0.1°, and 0.62 at 0.5°) than the multimodel mean (R2 = 0.28 at 0.5°). Global ozone exposure is estimated to be increasing, driven by highly populated regions of Asia and Africa, despite decreases in the United States and Russia.

Volcanoes emit different gaseous species, SO₂ and in particular halogen species especially bromine and chlorine compounds. In general, halogens play an important role in the atmosphere by contributing to ozone depletion in the stratosphere (WMO Ozone assessment, 2018) and by modifying air composition and oxidizing capacity in the troposphere (Von Glasow et al. 2004). The halogen species emitted by volcanoes are halides. The chemical processing occurring within the plume leads to the formation of BrO from HBr following the ‘bromine explosion’ mechanism as evidenced from both observations and modelling (e.g., Bobrowski et al. Nature, 2003; Roberts et al., Chem. Geol. 2009). Oxidized forms of chlorine and bromine are modelled to be formed within the plume due to the heterogenous reaction of HOBr with HCl and HBr, forming BrCl and Br₂ that photolyses and produces Br and Cl radicals. So far, modelling studies were mainly focused on the very local scale and processes occurring within a few hours after eruption.In this study, the objective is to go a step further by analyzing the impact at the regional scale over the Mediterranean basin of a Mt Etna eruption event. For this, we use the MOCAGE model (Guth et al., GMD, 2016), a chemistry transport model run with a resolution of 0.2°x 0.2°, to quantify the impacts of the halogens species emitted by the volcano on the tropospheric composition. We have selected here the case of the eruption of Mount Etna around Christmas 2018 characterised by large amounts of emissions over several days (Calvari et al., remote sensing 2020; Corrdadini et al., remote sensing 2020). The results show that MOCAGE represents rather well the chemistry of the halogens in the volcanic plume because it established theory of plume chemistry. The bromine explosion process takes place on the first day of the eruption and even more strongly the day after, with a rapid increase of the in-plume BrO concentrations and a corresponding strong reduction of ozone and NO2 concentrations.We also compared MOCAGE results with the WRF-CHEM model simulations for the same case study. We note that the tropospheric column of BrO and SO₂ in the two models have the same order of magnitude with more rapid bromine explosion occurring in WRF-CHEM simulations. Finally, we compared the MOCAGE results to tropospheric columns of BrO and SO2 retrieved from TROPOMI spaceborne instrument.

Volcanic eruptions are events that can eject several tons of material into the atmosphere. Among these emissions, sulfur dioxide is the main sulfurous volcanic gas. It can form sulfate aerosols that are harmful to health or, being highly soluble, it can condense in water particles and form acid rain. Thus, volcanic eruptions can have an environmental impact on a regional scale.The Mediterranean region is very interesting from this point of view because it is a densely populated region with a strong anthropogenic activity, therefore polluted, in which Mount Etna is also located. Mount Etna is the largest passive SO2 emitter in Europe, but it can also sporadically produce strong eruptive events. It is then likely that the additional input of sulfur compounds into the atmosphere by volcanic emissions may have effects on the regional atmospheric sulfur composition.We are particularly investigating the eruption of Mount Etna on December 24, 2018 [Corradini et al, 2020]. This eruption took place along a 2 km long breach on the side of the volcano, thus at a lower altitude than its main crater. About 100 kt of SO2 and 35 kt of ash were released in total, between December 24 and 30. With the exception of the 24th, the quantities of ash were always lower than the SO2.The availability of the TROPOMI SO2column estimates, at fine spatial resolution (7 km x 3.5 km at nadir) and associated averaging kernels, during this eruptive period made it also an excellent case study. It allows us to follow the evolution of SO2 in the volcanic plume over several days.Using the CNRM MOCAGE chemistry-transport model (CTM), we aim to quantify the impact of this volcanic eruption on atmospheric composition, sulfur deposition and air quality at the regional scale. The comparison of the model with the TROPOMI observation data allows us to assess the ability of the model to properly represent the plume. In spite of a particular meteorological situation, leading to a complex plume transport, MOCAGE shows a good agreement with TROPOMI observations. Thus, from the MOCAGE simulation, we can evaluate the impact of the eruption on the regional concentrations of SO2 and sulfate aerosols, but also analyse the quantities of dry and wet deposition, and compare it to surface measurement stations.

Halogen halides emitted by volcanoes are known to rapidly convert within plumes into BrO while depleting ozone, as clearly shown by observations and models over the past 2 decades (e.g. review by Gutmann et al., 2018). So far, most of the modelling studies have focused on the plume processes occurring in the first few hours after the emission. The only study at the regional scale is that of Jourdain et al. (2016). They assessed the impact of volcanic halogens for a period of strong degassing of the Ambrym volcano, showing in particular its effect on the atmospheric oxidizing capacity and methane lifetime.A step further would be to quantify the impact of volcanic halogens at the global scale using global chemistry models. This type of model uses a horizontal resolution (greater than 50 km) that is much coarser than the plume size. This raises the issue of, whether at this resolution, it is possible to represent the chemistry occurring under high concentrations within the plume. To assess this, a sub-grid scale parameterization is proposed. It has been tested in the 1D version of MOCAGE global and regional chemistry transport model for a short eruption of Mt Etna on the 10th of May 2008. The results show that while using the subgrid-scale plume parameterization or not does change the timing of when the maximum BrO occurs but does not affect the predicted maximum concentration. The same finding is made when using a range of different settings in the parameterization regarding dilution of the plume with its environment. The 1D model results show a sensitivity of BrO formation to parameters other than the sub-grid scale effects: composition of the plume at the vent, injection height of the emissions, and time of the day when the eruption takes place.

A wide variety of observation data sets are used to assess long-term simulations provided by chemistry-climate models (CCMs) and chemistry-transport models (CTMs). However, the upper troposphere – lower stratosphere (UTLS) has hardly been assessed in the models yet. Observations performed in the framework of IAGOS (In-service Aircraft for a Global Observing System) combine the advantages of in situ airborne measurements in the UTLS with an almost global-scale sampling, a ~ 20-year monitoring period and a high frequency. If a few model assessments have been made using IAGOS database, none of them took advantage of the dense and high-resolution cruise data in their whole ensemble yet. The present study proposes a method to compare this large IAGOS data set to long-term simulations used for chemistry-climate studies. For this purpose, a new software (named Interpol-IAGOS) projects all IAGOS data on the 3D grid of the chosen model with a monthly resolution, since generally chemistry-climate models provide 3D outputs as monthly means. This provides a new IAGOS data set (IAGOS-DM) mapped at the model's grid and time resolution. As a first application, the REF-C1SD simulation generated by MOCAGE CTM in the framework of CCMI phase-I has been evaluated during the 1994–2013 period for ozone and the 2002–2013 period for carbon monoxide. This comparison is exclusively based on the grid cells sampled by IAGOS, thus the assessed model output (MOCAGE-M) is obtained by applying a corresponding mask onto the grid. First, climatologies are derived from the IAGOS-DM product. Good correlations are reported between IAGOS-DM and MOCAGE-M spatial distributions. As an attempt to analyse MOCAGE-M behaviour in the upper troposphere (UT) and the lower stratosphere (LS) separately, UT and LS data in IAGOS-DM were sorted according to potential vorticity. From this, we derived O3 and CO seasonal cycles in eight regions well sampled by IAGOS flights in the northern mid-latitudes. They are remarkably well-reproduced by the model for lower-stratospheric O3 and also good for upper-tropospheric CO. The data projection onto the model's grid is a necessary step for a more accurate assessment, as it allows to filter out biases only due to either spatial or temporal resolution. Beyond the MOCAGE REF-C1SD evaluation presented in this paper, the method could be used by CCMI models for individual assessments in the UTLS and for model intercomparisons with respect to IAGOS data set.

The contribution of volcanic emissions is argued as non-linear on the sulfur species burden. Thus, well constraining volcanic emissions inventories is necessary to better study the impacts induced by these pollution sources on the troposheric sulfur composition, as well as on sulfur species concentrations and depositions at the global surface. In this paper, the changes induced by the update of the volcanic sulfur emissions inventory on the global chemistry-transport model MOCAGE (MOdèle de Chimie Atmosphérique à Grande Échelle) are studied. Unlike the current inventory [Andres and Kasgnoc (1998)], the new inventory [Carn et al. (2016, 2017)] includes contributions from both passive degassing and eruptive emissions with more accu- rate information. Eruptions are provided as daily total amounts of sulfur dioxide (SO2) emitted by volcanoes, while degassing are provided as annual averages with annual uncertainties by volcanoes. Information on plumes altitudes is also available and has been used in the model. The choice is made to look at the year 2013, when a neglieable amount of eruptive volcanic SO2 emissions is referenced, allowing us to focus the study on the impact of passive degassing emissions on the tropospheric sulfur budget. A validation against GOME-2 SO2 total column and MODIS AOD observations shows the improvements of the model results with the new inventory. Because the global volcanic SO2 flux changes from 13 Tg.yr−1 in the current inventory to 23.6 Tg.yr−1 in the new inventory, the updated inventory shows significant differences in the global sulfur budget, mainly in the free troposphere and in the tropics. Even though volcanic SO2 emissions represent 15 % of the total annual sulfur emissions, the volcanic contribution to the tropospheric sulfate aerosol burden is 27 %. Moreover, a sensitivity study on passive degassing emissions, using the annual uncertainties of emissions per volcanoes, also confirmed the non-linear link between tropospheric sulfur species and volcanic emissions. This study highlights the necessity of using accurate estimates of volcanic sources in chemistry-transport models in order to properly simulate tropospheric sulfur species.

In this paper, the fate of biomass burning emissions of carbon monoxide is studied with the global chemistry–transport model MOCAGE (MOdélisation de Chimie Atmosphérique à Grande Échelle) and IAGOS (In-Service Aircraft for a Global Observing System) airborne measurements for the year 2013. The objectives are firstly to improve their representation within the model and secondly to analyse their contribution to carbon monoxide concentrations in the upper troposphere. At first, a new implementation of biomass burning injection is developed for MOCAGE, using the latest products available in Global Fire Assimilation System (GFAS) biomass burning inventory on plume altitude and injection height. This method is validated against IAGOS observations of CO made in fire plumes, identified thanks to the SOFT-IO source attribution data. The use of these GFAS products leads to improved MOCAGE skill to simulate fire plumes originating from boreal forest wildfires. It is also shown that this new biomass burning injection method modifies the distribution of carbon monoxide in the free and upper troposphere, mostly at northern boreal latitudes. Then, MOCAGE performance is evaluated in general in the upper troposphere and lower stratosphere in comparison to the IAGOS observations and is shown to be very good, with very low bias and good correlations between the model and the observations. Finally, we analyse the contribution of biomass burning to upper tropospheric carbon monoxide concentrations. This is done by comparing simulations where biomass are toggled on and off in different source regions of the world to assess their individual influence. The two regions contributing the most to upper tropospheric CO are found to be the boreal forests and equatorial Africa, in accordance with the quantities of CO they emit each year and the fact that they undergo fast vertical transport: deep convection in the tropics and pyroconvection at high latitudes. It is also found that biomass burning contributes more than 11 % on average to the CO concentrations in the upper troposphere and up to 50 % at high latitudes during the wildfire season.

The UTLS (Upper Troposphere/Lower Stratosphere) is a key layer of the atmosphere as its chemical composition impacts both the troposphere and the stratosphere, and therefore plays a significant role in the climate system. Ozone at this altitude for instance plays a great role on surface temperature. Unlike in the stratosphere; it can be produced from the photolysis of precursors originating in the troposphere; mainly nitrous oxides (NOx) and carbon monoxide (CO) at this pressure range. Biomass burning emissions in particular are likely to play a significant role in the quantities of these species in the upper troposphere and thus impacting ozone balance. This effect is investigated thanks to the global chemistry transport model MOCAGE. Because of the strong vertical gradients in this layer of the atmosphere, well resolved in-situ observation dataset are valuable for model evaluation. As of measurements used to validate MOCAGE results, IAGOS in-situ measurements from equipped commercial aircraft were chosen for their fine vertical resolution as well as their wide geographical coverage. Using both of these tools, upper tropospheric air composition is studied, with a focus on ozone precursors and production linked to biomass burning emissions.Firstly is investigated the direct impact of biomass burning emissions on CO concentration in the upper troposphere, as it is both a good tracer of wildfire plumes in the atmosphere and it plays a role in the upper troposphere chemical balance. For this purpose MOCAGE simulations spaning over the year of 2013 where biomass burning emissions were turned on and off are compared to estimate a contribution to upper tropospheric CO. These simulations were validated using all the available data from the IAGOS database. It was found that biomass burning impacted CO levels globally, with the strongest enhancement happening above the most emitting areas (equatorial Africa and the Boreal forests). The importance of a fast vertical transport pathway above the fires was also highlighted with the possible occurrence of pyroconvection in addition to deep convection. Secondly, other chemical species related to ozone production were looked upon. Peroxyacetyl Nitrates (PAN) for instance were found to be impacted by biomass burning as it is a product of NOx oxidation as well as the main "reservoir" specie for NOx in the upper troposphere. Ultimately, ozone production resulting from biomass burning emissions is investigated, both in biomass burning plumes encountered by IAGOS aircraft, and on a more global scale using the MOCAGE simulations.

Intercomparisons between Chemistry-Climate Models (CCMs) have highlighted shortcomings in our understanding and/or modeling of long-term ozone trends, and there is a growing interest in the impact of stratospheric ozone changes on tropospheric chemistry via both ozone fluxes (e.g. from the projected strengthening of the Brewer-Dobson circulation) and actinic fluxes. Advances in this area require a good understanding of the modelling uncertainties in the present-day distribution of stratospheric ozone, and a correct attribution of these uncertainties to the processes governing this distribution: photolysis, chemistry and transport. These processes depend primarily on solar irradiance, temperature and dynamics.Here we estimate model uncertainties arising from different input datasets, and compare them with typical uncertainties arising from the transport and chemistry schemes. This study is based on four sets of tightly controlled sensititivity experiments which all use temperature and dynamics specified from reanalyses of meteorological observations. The first set of experiments uses one Chemistry-Transport Model (CTM) and evaluates the impact of using 3 different spectra of solar irradiance. In the second set, the CTM is run with 4 different input reanalyses: ERA-5, MERRA-2, ERA-I and JRA-55. The third set of experiments still relies on the same CTM, exploring the impact of the transport algorithm and its configuration. The fourth set is the most sophisticated as it is enabled by model developments for the Copernicus Atmopshere Monitoring Service, where the ECMWF model IFS is run with three different photochemistry modules named according to their parent CTM: IFS(CB05-BASCOE), IFS(MOCAGE) and IFS(MOZART).All modelling experiments start from the same initial conditions and last 2.5 years (2013-2015). The uncertainties arising from different input datasets or different model components are estimated from the spreads in each set of sensitivity experiments and also from the gross error between the corresponding model means and the BASCOE Reanalysis of Aura-MLS (BRAM2). The results are compared across the four sets of experiments, as a function of latitude and pressure, with a focus on two regions of the stratosphere: the polar lower stratosphere in winter and spring - in order to assess and understand the quality of our ozone hole forecasts - and the tropical middle and upper stratosphere - where noticeably large disagreements are found between the experiments.

Constraining emission inventories into chemistry-transport models (CTM) is essential. In addition to anthropogenic emissions, natural sources of pollutants must be considered. Among them, volcanoes are large emitters of gases, including sulfur dioxide (SO2), a volatile species, causing environmental and health issues.Volcanic SO2 emission inventories are usually integrated in global CTMs, in order to improve the modelling of chemical species in the atmosphere. Here, we use the model MOCAGE, developed at CNRM, which currently uses Andres & Krasgnoc’s inventory (1998); a temporal average of emission on some 40 volcanoes, monitored through the synergy of satellite data and surface remote sensing instruments, for 25 years (from 1970’s to 1997). However, this inventory is now quite old and is therefore no longer sufficiently accurate.Thanks to the development of new satellite observations, it has become possible to produce such inventories with an improved accuracy. The global coverage and higher sensitivity of these instruments has allowed to reference more emission sources (hard-to-access volcanoes, small eruptions or even passive degassing). Hence, a new inventory of Carn et al (2016,2017) based on satellite observations has been implemented in MOCAGE. Besides being recent (from 1978 up to 2015), it combines eruption and passive degassing over more than 160 volcanoes. Passive degassing fluxes are provided as annual averages and eruption fluxes as daily total quantities (in case of events). In addition, information on volcanoes vent altitude and eruptive plume heights is available, which has been used to better constraints the model.We focus our study at the global scale. The years 2013 and 2014 were chosen as the years with the lowest and highest total eruptive emissions respectively, in Carn's inventory. Thus, 2013 highlights mainly the impact of passive degassing, while 2014 provides additional information on eruptions.For each of the years studied, the sulfur species budget in MOCAGE simulation is increased when the inventory is updated and therefore the relative contribution of volcanic sulfur emissions is larger. We note the global increase in sulfur dioxide and sulfate aerosol burdens; an increase even more significant when the injection heights of the emissions are taken into account.

This paper presents the first results about the assimilation of CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) extinction coefficient measurements on-board the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite in the chemistry transport model MOCAGE (Modèle de Chimie Atmosphérique à Grande Echelle) of Météo-France. This assimilation module is an extension of the Aerosol Optical Depth (AOD) assimilation system already presented by Sic et al. (2016). We focus on the period of TRAQA (TRAnsport à longue distance et Qualité de l’Air dans le bassin méditerranéen) field campaign that took place during the summer 2012. This period offers the opportunity to have access to a large set of aerosol observations from instrumented aircraft, balloons, satellite and ground-based stations. We evaluate the added value of CALIOP assimilation with respect to the model free run by comparing both fields to independent observations issued from the TRAQA field campaign. In this study we focus on the desert dust outbreak which happened during late June 2012 over the Mediterranean Basin (MB) during TRAQA campaign. The comparison with the AERONET (Aerosol Robotic Network) AOD measurements shows that the assimilation of CALIOP lidar observations improves the statistics compared to the model free run. The correlation between AERONET and the model (assimilation) is 0.682 (0.753), the bias and the RMSE, due to CALIOP assimilation, are reduced from −0.063 to 0.048 and from 0.183 to 0.148, respectively. Compared to MODIS (Moderate-resolution Imaging Spectroradiometer) AOD observations, the model free run shows an underestimation of the AOD values whereas the CALIOP assimilation corrects this underestimation and shows a quantitative good improvement in terms of AOD maps over the MB. The correlation between MODIS and the model (assimilation) during the dust outbreak is 0.47 (0.52), whereas the bias is −0.18 (−0.02) and the RMSE is 0.36 (0.30). The comparison of in-situ aircraft and balloon measurements to both modelled and assimilated outputs shows that the CALIOP lidar assimilation highly improves themodel aerosol field. The evaluation with the LOAC (Light Optical Particle Counter) measurements indicates that the aerosol vertical profiles are well simulated by the direct model but with a general underestimation of the aerosol number concentration especially in the altitude range 2–5 km. The CALIOP assimilation improves these results by a factor of 2.5 to 5. Analysis of the vertical distribution of the desert aerosol concentration shows that the aerosol dust transport event is well captured by the model but with an underestimated intensity. The assimilation of CALIOP observations allows the improvement of the geographical representation of the event within the model as well as its intensity by a factor of two in the altitude range 1–5 km.

The Infrared Atmospheric Sounding Interferometer (IASI) is an essential instrument for numerical weather prediction (NWP). It measures radiances at the top of the atmosphere using 8461 channels. The huge amount of observations provided by IASI has led the community to develop techniques to reduce observations while conserving as much information as possible. Thus, a selection of the 300 most informative channels was made for NWP based on the concept of information theory. One of the main limitations of this method was to neglect the covariances between the observation errors of the different channels. However, many centres have shown a significant benefit for weather forecasting to use them. Currently, the observation-error covariances are only estimated on the current IASI channel selection, but no studies to make a new selection of IASI channels taking into account the observation-error covariances have yet been carried out. The objective of this paper was therefore to perform a new selection of IASI channels by taking into account the observation-error covariances. The results show that with an equivalent number of channels, accounting for the observation-error covariances, a new selection of IASI channels can reduce the analysis error on average in temperature by 3 %, humidity by 1.8 % and ozone by 0.9 % compared to the current selection. Finally, we go one step further by proposing a robust new selection of 400 IASI channels to further reduce the analysis error for NWP.

Formaldehyde (HCHO) directly affects the atmospheric oxidative capacity through its effects on HOx. In remote marine environments, such as the Tropical Western Pacific (TWP), it is particularly important to understand the processes controlling the abundance of HCHO because model output from these regions is used to correct satellite retrievals of HCHO. Here, we have used observations from the CONTRAST field campaign, conducted during January and February 2014, to evaluate our understanding of the processes controlling the distribution of HCHO in the TWP as well as its representation in chemical transport/climate models. Observed HCHO mixing ratios varied from ~500 pptv near the surface to ~75 pptv in the upper troposphere. Recent convective transport of near surface HCHO and its precursors, acetaldehyde and possibly methyl hydroperoxide, increased upper tropospheric HCHO mixing ratios by ~33% (22 pptv); this air contained roughly 60% less NO than more aged air. Output from the CAM-Chem chemistry transport model (2014 meteorology) as well as nine chemistry climate models from the Chemistry-Climate Model Initiative (free-running meteorology) are found to uniformly underestimate HCHO columns derived from in situ observations by between 4 and 50%. This underestimate of HCHO likely results from a near factor of two underestimate of NO in most models, which strongly suggests errors in NOx emissions inventories and/or in the model chemical mechanisms. Likewise, the lack of oceanic acetaldehyde emissions and potential errors in the model acetaldehyde chemistry lead to additional underestimates in modeled HCHO of up to 75 pptv (~15%) in the lower troposphere.

The Infrared Atmospheric Sounding Interferometer (IASI) onboard the Metop satellites provides 8461 channels in the infrared spectrum, covering the spectral interval 645–2760 cm−1 at a resolution of 0.5 cm−1. The high volume of data observation resulting from IASI presents many challenges. In current Numerical Weather Prediction (NWP) models, assimilating all channels is not feasible, due to data transmission, data storage and significant computational costs. One of the methods for reducing the data volume is the channel selection. Many NWP centres use a subset of 314 IASI channels including 15 ozone-sensitive channels. However, this channel selection has been carried out assuming uncorrelated observation errors. In addition, these ozone-sensitive channels have been selected only for ozone information. The objective of this study is to carry out a new selection of IASI ozone-sensitive channels from the full spectrum over a spectral range of 1000–1070 cm−1, in a direct radiance assimilation framework. This selection is done with a full observation error covariance matrix to take into account cross-channel error correlations. A sensitivity method based on the channel spectral sensitivity to variables and a statistical approach based on the Degrees of Freedom for Signal (DFS) have been chosen. To be representative of atmospheric variability, 345 profiles from around the world over a one-year period were selected. The new selection, is evaluated in a One-Dimensional Variational (1D-Var) analyses framework. This selection highlights a new set of 15 IASI ozone-sensitive channels. The results are very encouraging since by adding these 15 channels to 122 operational channels, temperature and humidity analyses are improved by 13.8 % and 20.9 % respectively. Obviously, these 15 channels significantly improve ozone analyses. In addition to considering inter-channel observation error correlations, the channel selection method uses a robust background error covariance matrix that takes into account temperature, humidity and ozone errors using a lagged forecast method over a one-year period. The new selection of IASI ozone-sensitive channels will be soon used in the global 4D-Var ARPEGE (Action de Recherche Petite Echelle Grande Echelle) data assimilation system.

International audience; Climatology and long-term evolution of ozone and carbon monoxide in the upper troposphere-lower stratosphere (UTLS) at northern midlatitudes, as seen by IAGOS from Abstract. In situ measurements in the upper troposphere-lower stratosphere (UTLS) have been performed in the framework of the European research infrastructure IAGOS (In-service Aircraft for a Global Observing System) for ozone since 1994 and for carbon monoxide (CO) since 2002. The flight tracks cover a wide range of longitudes in the northern extratropics, extending from the North American western coast (125 • W) to the eastern Asian coast (135 • E) and more recently over the northern Pacific Ocean. Several tropical regions are also sampled frequently, such as the Brazilian coast, central and southern Africa, southeastern Asia, and the western half of the Maritime Continent. As a result, a new set of climatologies for O 3 (in the upper troposphere (UT), tropopause layer, and lower stratosphere (LS) are made available, including gridded horizontal distributions on a semi-global scale and seasonal cycles over eight well-sampled regions of interest in the northern extratropics. The seasonal cycles generally show a summertime maximum in O 3 and a springtime maximum in CO in the UT, in contrast to the systematic springtime maximum in O 3 and the quasi-absence of a seasonal cycle of CO in the LS. This study highlights some regional variabilities in the UT, notably (i) a west-east difference of O 3 in boreal summer with up to 15 ppb more O 3 over central Russia compared with northeast America, (ii) a systematic west-east gradient of CO from 60 to 140 • E, especially noticeable in spring and summer with about 5 ppb by 10 degrees longitude, (iii) a broad spring/summer maximum of CO over northeast Asia, and (iv) a spring maximum of O 3 over western North Amer-ica. Thanks to almost 20 years of O 3 and 12 years of CO measurements, the IAGOS database is a unique data set to derive trends in the UTLS at northern midlatitudes. Trends in O 3 in the UT are positive and statistically significant in most regions, ranging from +0.25 to +0.45 ppb yr −1 , characterized by the significant increase in the lowest values of the distribution. No significant trends of O 3 are detected in the LS. Trends of CO in the UT, tropopause, and LS are almost all negative and statistically significant. The estimated slopes range from −1.37 to −0.59 ppb yr −1 , with a nearly homogeneous decrease in the lowest values of the monthly distribution (5th percentile) contrasting with the high interregional variability in the decrease in the highest values (95th percentile).

We report on an evaluation of tropospheric ozone and its precursor gases in three atmospheric chemistry versions as implemented in ECMWF’s Integrated Forecasting System (IFS), referred to as IFS(CB05BASCOE), IFS(MOZART) and IFS(MOCAGE). While the model versions were forced with the same overall meteorology, emissions, transport and deposition schemes, they vary largely in their parameterizations describing atmospheric chemistry, including the organics degradation, heterogeneous chemistry and photolysis, as well as chemical solver. The model results from the three chemistry versions are compared against a range of aircraft field campaigns, ozone sondes and satellite observations, which provides quantification of the overall model uncertainty driven by the chemistry parameterizations. We find that they produce similar patterns and magnitudes for carbon monoxide (CO) and ozone (O3), as well as a range of non-methane hydrocarbons (NMHCs), with averaged differences for O3 (CO) within 10 % (20 %) throughout the troposphere. Most of the divergence in the magnitude of NMHCs can be explained by differences in OH concentrations, which can reach up to 50 % particularly at high latitudes. Also comparatively large discrepancies between model versions exist for NO2, SO2 and HNO3, which are strongly influenced by secondary chemical production and loss. Other, common biases in CO and NMHCs are mainly attributed to uncertainties in their emissions. This configuration of having various chemistry versions within IFS provides a quantification of uncertainties induced by chemistry modeling in the main CAMS global trace gas products beyond those that are constrained by data-assimilation.

Volcanoes are a known source of halogens to the atmosphere. HBr volcanic emissions lead rapidly to the formation of BrO within volcanic plumes as shown by recent work based on observations and models. BrO, having a longer residence time in the atmosphere than HBr, is expected to have a significant impact on tropospheric chemistry, at least at the local and regional scales. The objective of this paper is to prepare a framework that will allow 3-D modelling of volcanic halogen emissions in order to determine their fate within the volcanic plume and then in the atmosphere at the regional and global scales. This work is based on a 1-D configuration of the chemistry transport model MOCAGE whose low computational cost allows us to perform a large set of sensitivity studies. This paper studies the Etna eruption on the 10 May 2008 that took place just before night time. Adaptations are made to MOCAGE to be able to produce the chemistry occurring within the volcanic plume. A simple sub-grid scale parameterization of the volcanic plume is implemented and tested. The use of this parameterization in a 0.5° × 0.5° configuration (typical regional resolution) has an influence on the partitioning between the various bromine compounds both during the eruption period and also during the night period immediately afterwards. During the day after the eruption, simulations both with and without parameterizations give very similar results that are consistent with the tropospheric column of BrO and SO2 in the volcanic plume derived from GOME-2 observations. Tests have been performed to evaluate the sensitivity of the results to the mixing between ambient air and the magmatic air at very high temperature at the crater vent that modifies the composition of the emission, and in particular the sulphate aerosol content that is key compound in the BrO production. Simulations show that the plume chemistry is not very sensitive to the assumptions used for the mixing parameter (relative quantity of ambient air mixed with magmatic air in the mixture) that is not well known. This is because there is no large change in the compounds limiting/favouring the BrO production in the plume. The impact of the model grid resolution is also tested in view of future 3-D-simulations at the global scale. A dilution of the emitted gases and aerosols is observed when using the typical global resolution (2°) as compared to a typical regional resolution (0.5°), as expected. Taking this into account, the results of the 2° resolution simulations are consistent with the GOME-2 observations. In general the simulations at 2° resolution are less efficient at producing BrO after the emission both with and without the subgrid-scale parameterization. The differences are mainly due to an interaction between concentration effects than stem from using a reduced volume in the 0.5° resolution combined with second order rate kinetics. The last series of tests were on the mean radius assumed for the sulphate aerosols that indirectly impacts the production of BrO by heterogeneous reactions. The simulations show that the BrO production is sensitive to this parameter with a stronger production when smaller aerosols are assumed. These results will be used to guide the implementation of volcanic halogen emissions in the 3-D configuration of MOCAGE.

We have developed a new statistical approach (M3Fusion) for combining surface ozone observations from thousands of monitoring sites around the world with the output from multiple atmospheric chemistry models to produce a global surface ozone distribution with greater accuracy than can be provided by any individual model. The ozone observations from 4766 monitoring sites were provided by the Tropospheric Ozone Assessment Report (TOAR) surface ozone database which contains the world's largest collection of surface ozone metrics. Output from six models was provided by the participants of the Chemistry-Climate Model Initiative (CCMI) and NASA's Global Modeling and Assimilation Office (GMAO). We analyze the 6-month maximum of the maximum daily 8-hour average ozone value (DMA8) for relevance to ozone health impacts. We interpolate the irregularly-spaced observations onto a fine resolution grid by using integrated nested Laplace approximations, and compare the ozone field to each model in each world region. This method allows us to produce a global surface ozone field based on TOAR observations, which we then use to select the combination of global models with the greatest skill in each of 8 world regions; models with greater skill in a particular region are given higher weight. This blended model product is bias-corrected within two degrees of observation locations to produce the final fused surface ozone product. We show that our fused product has an improved mean squared error compared to the simple multi-model ensemble mean.

A three-channel laser absorption spectrometer called SPIRIT (SPectromètre InfraRouge In situ Toute altitude) has been developed for airborne measurements of trace gases in the troposphere and lower stratosphere. More than three different species can be measured simultaneously with high time resolution (each 1.6 s) using three individual CW-DFB-QCLs (Continuous Wave Distributed FeedBack Quantum Cascade Lasers) coupled to a single Robert multipass optical cell. The lasers are operated in a time-multiplexed mode. Absorption of the mid-infrared radiations occur in the cell (2.8 L with effective path lengths of 134 to 151 m) at reduced pressure, with detection achieved using a HgCdTe detector cooled by Stirling cycle. The performances of the instrument are described, in particular precisions of 1, 1 and 3 %, and volume mixing ratio (vmr) sensitivities of 0.4, 6 and 2.4 ppbv are determined at 1.6 s for CO, CH4 and N2O, respectively (at 1σ confidence level). Estimated accuracies without calibration are about 6 %. Dynamic measuring ranges of about four decades are established. The first deployment of SPIRIT was realized aboard the Falcon-20 research aircraft operated by DLR (Deutsches Zentrum für Luft- und Raumfahrt) within the frame of the SHIVA (Stratospheric Ozone: Halogen Impacts in a Varying Atmosphere) European project in November-December 2011 over Malaysia. The convective outflows from two large convective systems near Borneo Island (6.0° N–115.5° E and 5.5° N–118.5° E) were sampled above 11 km in altitude on 19 November and 9 December, respectively. Correlated enhancements in CO and CH4 vmr were detected when the aircraft crossed the outflow anvil of both systems. These enhancements were interpreted as the fingerprint of transport from the boundary layer up through the convective system and then horizontal advection in the outflow. Using these observations, the fraction of boundary layer air contained in fresh convective outflow was calculated to range between 22 and 31 %, showing the variability of the mixing taking place during convective transport.

International audience; The Mediterranean Basin (MB) is at the crossroad of pollutant emissions from Western and Central Europe and of mineral dust from major sources in the Sahara and Arabian deserts. Several studies (e.g. Formenti et al., J. Geophys. Res., 2002; Pace et al., J. Geophys. Res., 2005; Ancellet et al., Atmos. Chem. Phys., 2016) have also shown the occurrence over the MB of long-range transport of air masses polluted by biomass burning aerosols. In the present study, we report two cases of long-range intercontinental transport of biomass burning products in the free troposphere over the MB in August 2014, identified with in situ measurements, and evaluate their impact on trace gas concentrations using modelling The Gradient in Longitude of Atmospheric constituents above the Mediterranean basin (GLAM) airborne campaign occurred in August 2014 (Ricaud et al., BAMS, 2018), as part of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx) project. It aimed at studying the tropospheric chemical variability of gaseous pollutants and aerosols along a West-East transect above the MB. During the GLAM campaign, several instruments were deployed onboard the Falcon-20 research aircraft (SAFIRE, INSU & Météo-France) including an infrared laser spectrometer (SPIRIT, LPC2E) able to detect weak variations in the concentration of pollutants. During two flights on 6 and 10 August, increases in CO, O3 and aerosols were measured over Sardinia at 5.4 and 9.7 km above sea level, respectively. To assess the origin of the air masses, 20-day backward trajectories were calculated with a nested-grid regional scale Lagrangian particle dispersion model (FLEXPART; Stohl et al., Atmos. Chem. Phys., 2005). Combined with emissions coming from the Global Fire Assimilation System (GFAS) inventory (Kaiser et al., Biogeosci., 2012), this allows us to quantify the biomass burning contribution to CO aircraft measured values. Biomass burning products came on 10 August from the northern American continent with air masses transported during 5 days before arriving over the MB. On 6 August biomass burning products came from Siberia with air masses travelling during 12 days and enriched in fire emission products above Canada 5 days before arriving over the MB. By estimating the injection height of the model and amplifying emission fluxes, FLEXPART was able to reproduce the contribution of those fires to CO enhancements. Our measurements show that long-range transport of biomass burning induced, at the local scale, an increase by a factor of 1.7 to 3.7 of O3 and CO with background mixing ratios of ∼25 and ∼70 ppbv respectively. To assess the biomass burning effect on ozone level at the regional scale over the MB, its tropospheric increase is estimated by using the chemical transport model MOCAGE.

Made available in DSpace on 2018-11-26T17:48:49Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-03-16 Agence Nationale de la Recherche (ANR) region Champagne-Ardenne in France Direction Generale de l'Armement (PRECIP-CLOUD project) European Union's Framework Program MUSIC project LEFE project Overshoots a grande echelle Centre National d'Etudes Spatiales (CNES) Centre de Calcul ROMEO In order to better understand the water vapor (WV) intrusion into the tropical stratosphere, a mesoscale simulation of the tropical tropopause layer using the BRAMS (Brazilian version of Regional Atmospheric Modeling System (RAMS)) model is evaluated for a wet season. This simulation with a horizontal grid point resolution of 20kmx20km cannot resolve the stratospheric overshooting convection (SOC). Its ability to reproduce other key parameters playing a role in the stratospheric WV abundance is investigated using the balloon-borne TRO-Pico campaign measurements, the upper-air soundings over Brazil, and the satellite observations by Aura Microwave Limb Sounder, Microwave Humidity Sounder, and Geostationary Operational Environmental Satellite 12. The BRAMS exhibits a good ability in simulating temperature, cold-point, WV variability around the tropopause. However, the simulation is typically observed to be warmer by approximate to 2.0 degrees C and wetter by approximate to 0.4 ppmv at the hygropause, which can be partly affiliated with the grid boundary nudging of the model by European Centre for Medium-Range Weather Forecasts operational analyses. The modeled cloud tops show a good correlation (maximum cross-correlation of approximate to 0.7) with Geostationary Operational Environmental Satellite 12. Furthermore, the overshooting cells detected by Microwave Humidity Sounder are observed at the locations, where 75% of the modeled cloud tops are higher than 11km. Finally, the modeled inertia-gravity wave periodicity and wavelength are comparable with those deduced from the radio sounding measurements during TRO-Pico campaign. The good behavior of BRAMS confirms the SOC contribution in the WV abundance, and variability is of lesser importance than the large-scale processes. This simulation can be used as a reference run for upscaling the impact of SOC at a continental scale for future studies. UFR Sci Exactes & Naturelles, GSMA, CNRS, UMR 7331, Reims, France CNRS, CNRM, Meteo France, UMR3589, Toulouse, France UPMC Univ Paris 06, Sorbonne Univ, PSL Res Univ,ENS, LMD,IPSL,CNRS,UMR 8539,Ecole Polytech,Univ Paris, Palaiseau, France Ecole Polytech, ENS, CNRS, LMD,IPSL,UPMC, Paris, France INSU, Div Tech, Pl Aristide Briand, Meudon, France UPMC Univ Paris 06, UVSQ Univ Paris Saclay, CNRS, LATMOS,IPSL, Guyancourt, France Univ Estadual Paulista, Inst Pesquisas Meteorol, Bauru, Brazil Univ Estadual Paulista, Inst Pesquisas Meteorol, Bauru, Brazil Agence Nationale de la Recherche (ANR): ANR-2010-BLAN-609-01 European Union's Framework Program: 603608 MUSIC project: ANR-14-CE01-0014 Centre de Calcul ROMEO: 669

In the frame of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx), we analyse the budget of primary aerosols and secondary inorganic aerosols over the Mediterranean Basin during the years 2012 and 2013. To do this, we use two year-long numerical simulations with the chemistry-transport model MOCAGE validated against satellite- and ground-based measurements. The budget is presented on an annual and a monthly basis on a domain covering 29 to 47° N latitude and 10° W to 38° E longitude. The years 2012 and 2013 show similar seasonal variations. The desert dust is the main contributor to the annual aerosol burden in the Mediterranean region with a peak in spring, and sea salt being the second most important contributor. The secondary inorganic aerosols, taken as a whole, contribute a similar level to sea salt. The results show that all of the considered aerosol types, except for sea salt aerosols, experience net export out of our Mediterranean Basin model domain, and thus this area should be considered as a source region for aerosols globally. Our study showed that 11 % of the desert dust, 22.8 to 39.5 % of the carbonaceous aerosols, 35 % of the sulfate and 9 % of the ammonium emitted or produced into the study domain are exported. The main sources of variability for aerosols between 2012 and 2013 are weather-related variations, acting on emissions processes, and the episodic import of aerosols from North American fires. In order to assess the importance of the anthropogenic emissions of the marine and the coastal areas which are central for the economy of the Mediterranean Basin, we made a sensitivity test simulation. This simulation is similar to the reference simulation but with the removal of the international shipping emissions and the anthropogenic emissions over a 50 km wide band inland along the coast. We showed that around 30 % of the emissions of carbonaceous aerosols and 35 to 60 % of the exported carbonaceous aerosols originates from the marine and coastal areas. The formation of 23, 27 and 27 %, respectively of, ammonium, nitrate and sulfate aerosols is due to the emissions within the marine and coastal area.