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Knowledge of sulfur dioxide layer height (SO2 LH) is important to understand volcanic eruption processes, the climate impact of SO2 emissions and to mitigate volcanic risk for civil aviation. However, the estimation of SO2 LH from ground-based instruments is challenging in particular for rapidly evolving and sustained eruptions. Satellite wide-swath nadir observations have the advantage to cover large-scale plumes and the potential to provide key information on SO2 LH. In the ultraviolet, SO2 LH retrievals leverage the fact that, for large SO2 columns, the light path and its associated air mass factor (AMF) depends on the SO2 absorption (and therefore on the vertical distribution of SO2), and SO2 LH information can be obtained from the analysis of measured back-scattered radiances coupled with radiative transfer simulations. However, existing algorithms are mainly sensitive to SO2 LH for SO2 vertical columns of at least 20 DU. Here we develop a new SO2 LH algorithm and apply it to observations from the high spatial resolution TROPOspheric Monitoring Instrument (TROPOMI). It is based on an SO2 optical depth look-up-table and an iterative approach. The strength of this scheme lies in the fact that it is a Covariance-Based Retrieval Algorithm (COBRA; Theys et al., 2021). This means that the SO2-free contribution of the measured optical depth is treated in an optimal way, resulting in an improvement of the SO2 LH sensitivity to SO2 columns as low as 5 DU, with a precision better than 2 km. We demonstrate the value of this new data through a number of examples and comparison with satellite plume height estimates (from IASI and CALIOP), and back trajectory analyses. The comparisons indicates an SO2 LH accuracy of 1–2 km, expect for some difficult observation conditions.

40 pags., 22 figs., 13 tabs., In September 2016, 36 spectrometers from 24 institutes measured a number of key atmospheric pollutants for a period of 17¿d during the Second Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI-2) that took place at Cabauw, the Netherlands (51.97¿¿N, 4.93¿¿E). We report on the outcome of the formal semi-blind intercomparison exercise, which was held under the umbrella of the Network for the Detection of Atmospheric Composition Change (NDACC) and the European Space Agency (ESA). The three major goals of CINDI-2 were (1) to characterise and better understand the differences between a large number of multi-axis differential optical absorption spectroscopy (MAX-DOAS) and zenith-sky DOAS instruments and analysis methods, (2) to define a robust methodology for performance assessment of all participating instruments, and (3) to contribute to a harmonisation of the measurement settings and retrieval methods. This, in turn, creates the capability to produce consistent high-quality ground-based data sets, which are an essential requirement to generate reliable long-term measurement time series suitable for trend analysis and satellite data validation. The data products investigated during the semi-blind intercomparison are slant columns of nitrogen dioxide (NO2), the oxygen collision complex (O4) and ozone (O3) measured in the UV and visible wavelength region, formaldehyde (HCHO) in the UV spectral region, and NO2 in an additional (smaller) wavelength range in the visible region. The campaign design and implementation processes are discussed in detail including the measurement protocol, calibration procedures and slant column retrieval settings. Strong emphasis was put on the careful alignment and synchronisation of the measurement systems, resulting in a unique set of measurements made under highly comparable air mass conditions. The CINDI-2 data sets were investigated using a regression analysis of the slant columns measured by each instrument and for each of the target data products. The slope and intercept of the regression analysis respectively quantify the mean systematic bias and offset of the individual data sets against the selected reference (which is obtained from the median of either all data sets or a subset), and the rms error provides an estimate of the measurement noise or dispersion. These three criteria are examined and for each of the parameters and each of the data products, performance thresholds are set and applied to all the measurements. The approach presented here has been developed based on heritage from previous intercomparison exercises. It introduces a quantitative assessment of the consistency between all the participating instruments for the MAX-DOAS and zenith-sky DOAS techniques., CINDI-2 received funding from the Netherlands Space Office (NSO). Funding for this study was provided by ESA through the CINDI-2 (ESA contract no. 4000118533/16/ISbo) and FRM4DOAS (ESA contract no. 4000118181/16/I-EF) projects and partly within the EU 7th Framework Programme QA4ECV project (grant agreement no. 607405). The BOKU MAX-DOAS instrument was funded and the participation of Stefan F. Schreier was supported by the Austrian Science Fund (FWF): I 2296-N29. The participation of the University of Toronto team was supported by the Canadian Space Agency (through the AVATARS project) and the Natural Sciences and Engineering Research Council (through the PAHA project). The instrument was primarily funded by the Canada Foundation for Innovation and is usually operated at the Polar Environment Atmospheric Research Laboratory (PEARL) by the Canadian Network for the Detection of Atmospheric Change (CANDAC). Funding for CISC was provided by the UVAS (“Ultraviolet and Visible Atmospheric Sounder”) projects SEOSAT/INGENIO, ESP2015-71299- R, MINECO-FEDER and UE. The activities of the IUP-Heidelberg were supported by the DFG project RAPSODI (grant no. PL 193/17-1). SAOZ and Mini-SAOZ instruments are supported by the Centre National de la Recherche Scientifique (CNRS) and the Centre National d’Etudes Spatiales (CNES). INTA recognises support from the National funding projects HELADO (CTM2013-41311-P) and AVATAR (CGL2014-55230-R). AMOIAP recognises support from the Russian Science Foundation (grant no. 16-17-10275) and the Russian Foundation for Basic Research (grant nos. 16-05- 01062 and 18-35-00682). Ka L. Chan received transnational access funding from ACTRIS-2 (H2020 grant agreement no. 654109). Rainer Volkamer recognises funding from NASA’s Atmospheric Composition Program (NASA-16-NUP2016-0001) and the US National Science Foundation (award AGS-1620530). Henning Finkenzeller is the recipient of a NASA graduate fellowship. Mihalis Vrekoussis recognises support from the University of Bremen and the DFG Research Center/Cluster of Excellence “The Ocean in the Earth System-MARUM”. Financial support through the University of Bremen Institutional Strategy in the framework of the DFG Excellence Initiative is gratefully appreciated for Anja Schönhardt. Pandora instrument deployment was supported by Luftblick through the ESA Pandonia Project and NASA Pandora Project at the Goddard Space Flight Center under NASA Headquarters’ Tropospheric Composition Program. The article processing charges for this open-access publication were covered by BK Scientific.

Comparisons between satellite and ground-based measurements of the atmosphere are inevitably affected by natural variability due to mismatches in spatial and temporal co-location. These additional terms in the comparison error budget are quantified here for total ozone column comparisons using an Observing System Simulation Experiment. Even when using tight co-location criteria, atmospheric variability is found to impact the comparisons significantly. Part of this work was funded by the Belgian Science Policy O ce (BELSPO) and ESA via the ProDEx projects A3C and ACROSAT, and by the EU H2020 project GAIA-CLIM (Ares(2014)3708963/Project 640276). Finally, the 20 authors acknowledge the pioneering research carried out in 2008–2012 by C. De Clercq and S. Vandenbussche and funded by the EU FP6 project GEOmon (FP6-2005-Global-4-036677) and ProDEx project SECPEA.

This document is the final report of the Intercalibration of ground-based spectrometers and Lidars - Extension 2012-2013. It summarizes the activities performed in the period from November 2012 until December 2013 and the main results obtained.

This document summarizes activities and achievements during the second part of the ESA CEOS Intercalibration project. The period covered by this report extends from February 2011 until January 2012.

Atmospheric formaldehyde (H2CO) is an intermediate product common to the degradation of many volatile organic compounds and therefore it is a central component of the tropospheric chemistry. While the global formaldehyde background is due to methane oxidation, emissions of non-methane volatile organic compounds (NMVOCs) from biogenic, biomass burning and anthropogenic continental sources result in important and localised enhancements of the H2CO concentration. Recent spaceborne nadir sensors provide an opportunity to quantify the abundance of tropospheric formaldehyde at the global scale, and thereby to improve our knowledge of NMVOC emissions. This is essential for a better understanding of the processes that control the production and the evolution of tropospheric ozone, a key actor in air quality and climate change, but also of the hydroxyl radical OH, the main cleansing agent of our troposphere. For this reason, H2CO satellite observations are increasingly used in combination with tropospheric chemistry transport models to constrain NMVOC emission inventories in so-called top-down inversion approaches. Such inverse modelling applications require well characterised satellite data products consistently retrieved over long time periods. This work reports on global observations of formaldehyde columns retrieved from the successive solar backscatter nadir sensors GOME, SCIAMACHY and GOME-2, respectively launched in 1995, 2002 and 2006. The retrieval procedure is based on the differential optical absorption spectroscopy technique (DOAS). Formaldehyde concentrations integrated along the mean atmospheric optical path are derived from the recorded spectra in the UV region, and further converted to vertical columns by means of calculated air mass factors. These are obtained from radiative transfer simulations, accounting for cloud coverage, surface properties and best-guess H2CO profiles, the latter being derived from the IMAGES chemistry transport model. A key task of the thesis has consisted in the optimisation of the H2CO retrieval settings from multiple sensors, taking into account the instrumental specificities of each sounder. As a result of these efforts, a homogeneous dataset of formaldehyde columns covering the period from 1996 to 2010 has been created. This comes with a comprehensive error budget that treats errors related to the spectral fit of the columns as well as those associated to the air mass factor evaluation. The time series of the GOME, SCIAMACHY and GOME-2 H2CO observations is shown to be consistent and stable over time. In addition, GOME-2 brings a significant reduction of the noise on spatiotemporally averaged observations, leading to a better identification of the emission sources. Our dataset is used to study the regional formaldehyde distribution, as well as its seasonal and interannual variations, principally related to temperature changes and fire events, but also to anthropogenic activities. Moreover, building on the quality of our 15-year time series, we present the first analysis of long-term changes in the H2CO columns. Positive trends, in the range of 1.5 to 4% yr-1, are found in Asia, more particularly in Eastern China and India, and are related to the known increase of anthropogenic NMVOC emissions in these regions. Finally, our dataset has been extensively used in several studies, in particular by the BIRA-IASB modelling team to constrain NMVOC emission fluxes. The results demonstrate the high potential of satellite data as top-down constraint for biogenic and biomass burning NMVOC emission inventories, especially in Tropical ecosystems, in Southeastern Asia, and in Southeastern US. Le formaldéhyde (H2CO) joue un rôle central dans la chimie de la troposphère en tant que produit intermédiaire commun à la dégradation chimique de la plupart des composés organiques volatils dans l’atmosphère. L’oxydation du méthane est responsable de plus de la moitié de la concentration moyenne globale du formaldéhyde. Sur les continents en revanche, les hydrocarbures non-méthaniques (NMVOCs) émis par la végétation, les feux de biomasse et les activités humaines, augmentent de façon significative et localisée la concentration de H2CO. Les récents senseurs satellitaires à visée nadir offrent la possibilité de quantifier à l’échelle globale l’abondance du formaldéhyde dans la troposphère et de ce fait, d’améliorer notre connaissance des émissions de NMVOCs. Ceci est essentiel à la compréhension des mécanismes contrôlant la production et l’évolution de l’ozone troposphérique, élément clé pour la qualité de l’air et les changements climatiques, mais aussi du composé hydroxyle OH, le principal agent nettoyant de notre troposphère. C’est pourquoi, une méthode de plus en plus répandue pour améliorer les inventaires d’émissions des NMVOCs consiste en l’utilisation d’observations satellitaires de H2CO en combinaison avec un modèle de chimie et de transport troposphérique, dans une approche appelée modélisation inverse. Ce genre d’application demande des produits satellitaires bien caractérisés et dérivés de façon cohérente sur de longues périodes de temps. Le travail présenté dans ce manuscrit porte sur l’inversion des colonnes de formaldéhyde à partir de spectres de la radiation solaire rétrodiffusée par l’atmosphère terrestre, mesurés par les senseurs GOME, SCIAMACHY et GOME-2, lancés successivement en 1995, 2002 et 2006. La méthode d’inversion est basée sur la spectroscopie d’absorption optique différentielle (DOAS). Les concentrations de formaldéhyde intégrées le long du chemin optique moyen dans l’atmosphère sont dérivées à partir des spectres mesurés, et ensuite transformées en colonnes verticales par le biais de facteurs de conversion appelés facteurs de masse d’air. Ces derniers sont calculés à l’aide d’un modèle de transfert radiatif, en tenant compte de la présence de nuages, des propriétés de la surface terrestre et la distribution verticale supposée du formaldéhyde, fournie par le modèle IMAGES. Un des objectifs principaux de la thèse a été d’optimiser les paramètres d’inversion pour H2CO, et ceci pour les trois senseurs, tout en tenant compte des spécificités de chaque instrument. Ces efforts ont conduit à la création d’un jeu de données homogène, couvrant la période de 1996 à 2010. Les colonnes sont fournies avec un bilan d’erreur complet, incluant les erreurs liées à l’inversion des concentrations dans les spectres, ainsi que celles provenant de l’évaluation des facteurs de masse d’air. La série temporelle des observations de GOME, SCIAMACHY et GOME-2 présente une bonne cohérence et stabilité sur toute la période. Nous montrons aussi que la meilleure couverture terrestre de GOME-2 entraîne une réduction significative du bruit sur les observations moyennées, permettant une meilleure identification des sources d’émission. Notre jeu de données est exploité pour étudier la distribution régionale du formaldéhyde, ainsi que ses variations saisonnières et interannuelles, principalement liées aux variations de température et aux feux de végétation, mais aussi aux activités anthropiques. De plus, en s’appuyant sur la qualité de la série temporelle de 15 ans, nous présentons la première analyse des variations à long terme des concentrations de H2CO. Des tendances positives, de l’ordre de 1.5 à 4% par an, sont observées en Asie, en particulier dans l’est de la Chine et en Inde, liées à l’augmentation des émissions anthropiques d’hydrocarbures dans ces régions. Finalement, nos données ont été largement exploitées par le groupe de modélisation de l’IASB pour faire des études de modélisation inverse des émissions de NMVOCs. Les résultats démontrent le haut potentiel des données satellitaires pour contraindre les inventaires d’émissions dues à la végétation et aux feux de biomasse, particulièrement dans les écosystèmes tropicaux, en Asie du sud-est, et dans le sud-est des Etats-Unis., Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/published

Bromine compounds play an important role as catalyst of the ozone destruction in both the stratosphere and troposphere. While the impact of bromine species on the chemistry of the stratosphere is known to a large extend, a number of uncertainties remain regarding the sources and sinks of atmospheric bromine as well as the chemistry and impact of bromine species on the troposphere. This work describes remote-sensing observations of bromine monoxide (BrO) derived from scattered sunlight spectra in the ultraviolet region measured by ground-based multi-axis and satellite nadir viewing instruments (GOME and GOME-2). The method of differential optical absorption spectroscopy is used to retrieve the columnar concentration of BrO along the effective light path through the atmosphere. New algorithms to derive vertical columns of BrO resolved into their stratospheric and tropospheric contributions are developed and described. For the ground-based geometry a way was found to determine independently the stratospheric and tropospheric BrO columns from the diurnal variation of the BrO measurements. For the satellite observations, the contribution of the stratospheric BrO to the measured column is estimated using an innovative stratospheric BrO climatology. This climatology is based on a state-of-the-art stratospheric chemical transport model, and explicitly accounts for the impact of atmospheric dynamics and photochemistry on the stratospheric BrO distribution. As for the tropospheric fraction of the measured total BrO column, it is derived using a residual technique accounting for the effects of clouds and surface reflectivity. Supported by an extensive set of correlative data, the results presented here allow to study properly the spatial and temporal evolution of atmospheric BrO at the global scale and enable to better assess the significance of BrO in the polar planetary boundary layer and free-troposphere as well as the contribution from very short-lived brominated sources gases to the stratospheric bromine budget. We also report on the first satellite detection of BrO in a volcanic plume, using GOME-2 measurements. Les composés bromés jouent un rôle important dans la stratosphère et la troposphère en tant que catalyseurs de la destruction d’ozone. Bien que l’impact des espèces bromées sur la chimie de la stratosphère soit largement compris, il reste de nombreuses incertitudes en ce qui concerne les sources et les pertes de brome dans l’atmosphère ainsi qu’à propos de la chimie et de l’impact des espèces bromées sur la troposphère. Le travail présenté dans ce manuscrit porte sur la télédétection du monoxyde de brome (BrO) à partir de spectres du rayonnement solaire diffusé, mesurés dans l’ultraviolet à partir d’instruments au sol de type multi-axis et satellitaires à visée nadir (GOME et GOME-2). La méthode de spectroscopie d’absorption optique différentielle est utilisée pour inverser la colonne intégrée de BrO le long du chemin optique effectif dans l’atmosphère. Nous avons développé de nouveaux algorithmes afin de dériver les colonnes verticales de BrO résolues en leurs contributions stratosphérique et troposphérique. Pour la géométrie d’observation au sol, un moyen a été trouvé pour déterminer indépendamment les colonnes de BrO stratosphérique et troposphérique, et cela à partir de la variation diurne des mesures de BrO. Pour les observations satellitaires, la contribution de la stratosphère à la colonne mesurée de BrO est estimée à partir d’une climatologie innovante de BrO stratosphérique. Cette climatologie est basée sur un modèle de pointe de la chimie et du transport de la stratosphère; par ailleurs, elle tient compte explicitement de l’impact de la dynamique atmosphérique et de la photochimie sur la distribution du BrO dans la stratosphère. La fraction troposphérique de la colonne totale mesurée de BrO est quant à elle dérivée à partir d’une technique résiduelle tenant compte des effets des nuages et de la réflectivité de la surface. Soutenus par un vaste jeu de données corrélatives, les résultats présentés dans ce travail permettent d’étudier de manière appropriée l’évolution spatiale et temporelle du BrO atmosphérique à l’échelle globale. Ces résultats permettent également de mieux estimer l’importance du BrO dans la couche limite planétaire polaire et dans la troposphère libre ainsi que la contribution des précurseurs bromés à temps de vie court sur le budget de brome dans la stratosphère. Nous présentons également la première détection satellitaire de BrO dans un panache volcanique, à l’aide de mesures effectuées avec l’instrument GOME-2., Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/published