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Exploring the application of Earth Observation datasets for SEEA carbon accounting and its comparison with national GHG reporting to the UNFCCC
No full textInternational audienceGlobal biomass and carbon datasets derived from Earth Observation (</div
Estimation des émissions de CO2 dans l'aire urbaine de Paris à partir de mesures de colonnes totales
No full textUrban greenhouse gas (GHG) emissions, mainly produced by human activities, are the primary driver of climate change. Cities are therefore key areas for climate mitigation. The assessment of the performance of local emission-reduction policies relies mainly on so-called bottom-up inventories, built from activity data and emission factors. Their ability to provide short-term monitoring can be limited by their uncertainties. A complementary method that uses physical measurements to better understand surface fluxes and their variability is atmospheric inversion. This thesis aims to evaluate the capacity of surface and total-column GHG measurements in the Paris region (Île-de-France) to improve urban inventories. The first chapter presents the role of cities in climate change, current methods for quantifying emissions, and the benefits and challenges of atmospheric inversions in urban environments. The second chapter describes eight years of in-situ measurements of CO2, CH4 and CO within the Île-de-France monitoring network. The time series provide insights into variability at different time scales: growth consistent with that observed at background stations, seasonal cycles, and meteorology-driven fluctuations. Differences between CO2 concentrations measured at urban and rural sites provide a direct measure of the urban CO2 dome, which has decreased by 28% over the past decade. This signal and its drop associated with the COVID-19 pandemic (2020) are consistent with the decline in emissions estimated by the AirParif inventory, illustrating the sensitivity of the network to variations in anthropogenic emissions. The third chapter presents the remote-sensing instrument network providing total-column measurements, which since July 2022 consists of three Fourier-transform infrared (FTIR) solar spectrometers: two EM27/SUN instruments (Saclay, Gonesse) and one IFS 125 HR (Jussieu). An automated measurement-control system and processing chain ensure a seasonal data availability (share of days with valid measurements in a month) ranging from 10-20% in winter to 70-80% in summer. Instrumental uncertainties were quantified: 0.2 ppm for XCO2, 1.2 ppb for XCH4 and 2 ppb for XCO for the EM27/SUN, compared with 0.7 ppm, 3.5 ppb and 4.1 ppb respectively for the IFS 125 HR. Effects related to the vertical profiles of the gases of interest, solar angle, pressure, or a priori profiles influence the retrieved total columns. However, these are systematic errors, and therefore have no significant impact on the measurement of regional gradients between stations that share the same solar angles and a priori profiles. The final chapter analyses the measured and modelled gradients using the WRF-Chem model driven by the Origins.earth emission inventory. While the model reproduces a clear average urban plume, it is less intense (around 0.5 ppm) but better defined than in the observations. The correlation between the measured and modelled Saclay-Gonesse gradients (in both defined sectors) reaches 0.47 over the full period (maximum 0.70 in autumn, minimum 0.28 in summer), with a regression slope of 0.66. The relatively weak correlation between simulations and measurements, and the average slope inconsistent with prior knowledge, indicate that total-column measurements, in their current state, do not yet allow urban emissions to be constrained within an operational inversion framework. Importantly, measurement quality is not the only limitation. Estimating the link between concentrations and emissions also requires accurate modelling of atmospheric transport. The analysis of a specific event shows significant differences between simulated transport and that inferred from observations.Les émissions urbaines de gaz à effet de serre (GES), majoritairement issues des activités humaines, constituent le moteur principal du changement climatique. Les villes sont donc des territoires clés pour l'atténuation climatique. L'évaluation des performances des politiques locales de réduction des émissions reposent principalement sur des inventaires dits "bottom-up", établis à partir de données d'activité et de facteurs d'émission. Leur capacité de suivi à court-terme peut être limitée par leurs incertitudes. Une méthode complémentaire permettant d'utiliser des mesures physiques dans le but de mieux comprendre les flux de surface et leurs variabilités est l'inversion atmosphérique. Cette thèse vise à évaluer la capacité des mesures de surface et de colonnes totales de GES en Île-de-France pour améliorer les inventaires urbains. Le premier chapitre présente le rôle des villes dans le changement climatique, les méthodes actuelles de quantification des émissions, ainsi que les apports et défis des inversions atmosphériques en milieu urbain. Le deuxième chapitre décrit huit années de mesures in situ de CO2, CH4 et CO dans le réseau de mesure d'Île-de-France. Les séries temporelles nous renseignent sur les variabilités à différentes échelles de temps: croissance conforme à celle mesurée dans des stations de fond, cycles saisonniers et variabilité liée à la météorologie. Les différences entre les concentrations en CO2 mesurées par les sites urbains et ruraux représentent une mesure directe du dôme urbain de CO2 qui a diminué de 28% sur la décennie écoulée. Ce signal et sa chute associée à la pandémie de COVID-19 (2020) sont cohérents avec la décroissance des émissions estimée par l'inventaire d'AirParif illustrant la sensibilité du réseau aux variations des émissions anthropiques. Le troisième chapitre présente le réseau d'instruments de télédétection donnant accès aux colonnes totales, composé depuis juillet 2022 de trois spectromètres solaires infra-rouges à transformée de Fourier (FTIR) : deux EM27/SUN (Saclay, Gonesse) et un IFS 125 HR (Jussieu). Un système automatisé de pilotage des mesures et une chaîne de traitement assurent une disponibilité (proportion des jours comportant des mesures valides dans un mois) saisonnière comprise entre 10-20% en hiver et 70-80% en été. Les incertitudes instrumentales ont été quantifiées : 0.2 ppm pour XCO2, 1.2 ppb pour XCH4 et 2 ppb pour XCO pour les EM27/SUN contre 0.7 ppm, 3.5 ppb et 4.1 ppb respectivement pour l'IFS 125 HR. Les effets liés au profil vertical des gaz d'intérêt, à l'angle solaire, à la pression ou aux profils a priori influent sur les colonnes totales calculées. Cependant, il s'agit là d'erreurs systématiques qui n'ont donc pas d'influence notable sur la mesure des gradients régionaux entre deux stations qui partagent les mêmes angles solaires et profils a priori. Le dernier chapitre analyse les gradients mesurés et simulés par le modèle WRF-Chem forcé par l'inventaire d'Origins.earth. Si le modèle reproduit un panache urbain moyen bien visible, celui-ci est moins intense (environ 0.5 ppm) mais mieux défini que dans les observations. La corrélation entre les gradients Saclay-Gonesse (dans les deux secteurs définis) mesurés et modélisés atteint 0.47 sur toute la période (maximum 0.70 en automne, minimum 0.28 en été), avec une pente d'ajustement de 0.66. La corrélation relativement faible entre modélisations et mesures, et la pente moyenne incohérente avec notre connaissance a priori indique que les mesures de colonnes totales ne permettent pas, en l'état, de contraindre les émissions urbaines dans un cadre d'inversion opérationnelle. Notons que la qualité des mesures n'est pas seule en cause. L'estimation du lien entre concentrations et émissions nécessite aussi une modélisation précise du transport atmosphérique. L'analyse d'un évènement particulier montre des différences notables entre le transport modélisé et celui qui peut être interprété à partir des observations
Contrasting Biogenic Isoprene Emission Responses to La Niña and El Niño Driven by Temperature: Insights from HCHO-Based Global Inversion
No full textInternational audienc
New insight on the global dynamics in the "transition region" of Venus atmosphere (80-130 km) with a 3D model
No full textInternational audienceVenus’ atmosphere layers between 80 km and 130 km mark the transition between the superrotation and the day-to-night circulation regimes. Accurately modeling this layer is essential to better understand the planet’s atmospheric dynamics. However, this re-gion remains poorly constrained by observations, and its variability is not yet fully captured by current 3D models. Here we use the latest version of the Venus Planetary Climate Model (V-PCM), a ground-to-thermosphere global circulation model, to investigate possible scenarios relevant to future EnVision observations above the cloud tops. We focus on current data-model biases and provide a tentative interpretation of their origin. Benchmark simulations by Martinez et al. (2024) overestimate the nightside O airglow emission by a factor of two and place the emission peak 5–7 km higher than observed. Furthermore, the emission distribution is not centered around midnight, but shifted to LT=4h, likely due to a strong (∼100 m/s) zonal wind component below 105 km. We performed sensitivity tests on unconstrained parameters (e.g. gravity wave drag and eddy diffusion) to evaluate their impact on the dynamical structures. Results show that reducing non-orographic gravity wave forcing below 105 km weakens that superrotation wind component, and recenter the emission around midnight. However, the altitude bias appears linked to insufficient vertical transport in the model. These findings underline the need for future space missions capable of continuously monitoring mesospheric gravity waves and O2 nightglow to better constrain their spatial and temporal variability and improve the representation of key dynamical processes in Venus’ upper atmosphere
The COVID-19 pandemic: a challenge or an opportunity for sustainable mobility? A qualitative interview study in Île-de-France
No full textInternational audienceIn an effort to counter the COVID-19 pandemic, France introduced safety measures that changed people’s capacity to move around. To what extent can these changes be opportunities for more sustainable mobility in the long term? While numerous studies have analyzed the impact of the pandemic on mobility using quantitative or short-term data, few have explored how individuals themselves experienced and reinterpreted these changes over time. In this article, we address this gap by providing a qualitative, longitudinal perspective on how residents of the Paris region adjusted their mobility practices during and after the pandemic. Between March and April 2023, we conducted qualitative interviews to discover what had occurred during and after the pandemic. Through 19 biographical interviews with people from the Parisian region, we get a retrospective view of the pandemic’s impact on mobility from March 2020 to April 2023. The results show that the pandemic had very little effect on the mode of transport, but did have a long-term effect on the frequency of work-related trips (particularly with the strong growth of work from home), and to a lesser extent on the frequency of travel for leisure and non-food purchases. Even though participants share the perceived risk of using public transport, this does not lead to a modal shift. Our findings highlight the importance of situating the effects of the pandemic within broader contextual, personal, and professional dynamics, offering new insights into how crisis-driven disruptions can shape long-term mobility patterns
Assessing the artificial radionuclide Cesium-137 spatial distribution in the Southern Hemisphere from lake sediment records
No full textInternational audienceWhen supported by a reliable geochronology, lake sediments provide important archives for environmental and climatic changes. Artificial radionuclides in general, and cesium-137 (137Cs) in particular, are frequently used to validate sediment chronologies over the past century. This review and meta-analysis assessed the spatial distribution and variability of 137Cs in lake records from the Southern Hemisphere, while also identifying geographical data gaps. The 137Cs profile shapes and inventories were compared and categorized, and their relationships with environmental variables were tested. The spatial distribution of available data reveals an imbalance in studies available across the Southern Hemisphere, with South America showing the greatest research coverage. While the sedimentation rate was identified as a key factor of 137Cs variability, two groups identified from the database presented high peak activities regardless of sedimentation rate, particularly in lakes located between 40°S and 50°S in Chile and Argentina. Lake geographic location (and their distance from nuclear test sites) appears to be the most influential factor explaining disparities in 137Cs deposition. Surprisingly, neither precipitation nor lake elevation showed a significant correlation with 137Cs peak activity
Influence of simulated vs. satellite-based burned areas on modelled terrestrial carbon fluxes
No full textInternational audienceBackgroundThe Global Carbon Project provides annual updates on anthropogenic and natural components of the Global Carbon Budget. Dynamic Global Vegetation Models (DGVMs) contribute to these estimates and are used to simulate the evolution of terrestrial carbon sinks. However, DGVMs are known to poorly represent disturbances such as fire, leading to uncertainties in estimates of mean, interannual variability (IAV), and trends in land carbon fluxes. To address this issue, we propose a hybrid-process-based assessmentby constraining three DGVMs (OCN, JULES-INFERNO, and ORCHIDEE-MICT) with remotely-sensed burned areas from ESA CCI (FIRECCI51) and climate data from ERA5 reanalysis. We aim to improve the representation of the spatio-temporal variability of regional carbon budgets, namely fire emissions, above-ground biomass carbon (AGC), and vegetation-related variables-leaf area index (LAI) and gross primary productivity (GPP). ResultsPrescribing burned area (BA) in DGVMs reveals contrasting patterns between prognostic (model simulations) and diagnostic (simulations with prescribed BA) runs. As prognostic tends to overestimate BA, particularly across tropical and high-latitude regions, diagnostic simulations correct this issue, by reducing bias and improving the IAV and the agreement with satellite-based datasets of BA and fire emissions in these regions. Moreover, enhanced IAV of AGC is simulated by diagnostic runs, essentially due to better representation of biomass carbon in the mentioned regions. Although moderate improvements are found in LAI and GPP, as the differences between the two runs are more limited, the improvements between prognostic and diagnostic are more evident in their IAV, particularly for LAI, rather than on long-term means, indicating that prescribed fire can improve the representation of some variability patterns.Conclusions Prescribing remotely-sensed BA in models can lead to a better representation of global BA, fire emissions and AGC, particularly improving the IAV, reducing bias and enhancing the agreement with satellite datasets. The moderate improvements in vegetation-related variables underscore the need to better constrain fire</div
A record of Late Pleistocene environmental conditions at the transition from central to southern Europe from the Baix loess paleosol sequence (Rhône Rift Valley, SE France)
No full textInternational audienceLoess-paleosol sequences (LPSs) provide valuable archives of Quaternary paleoenvironments. Here we present new data from the Baix LPS, comprising the entire Late Pleistocene. The Baix LPS is located at the western edge of the Rhône Rift Valley, France, in the transition zone from the presently temperate to the Mediterranean region of Europe. This LPS provides a missing link between the analyzed LPSs in the presently temperate regions farther north and those in the Mediterranean region. Reddish Btg horizons of a Stagnic Luvisol at the base of the Baix LPS represent the remains of an MIS 5 pedocomplex formed under warm and, at least temporarily, relatively moist conditions. Two brown Bw horizons of truncated Cambisols have been preserved in the overlying MIS 5a/4 to MIS 3 deposits. The upper Bw horizon is associated with large carbonate nodules, indicating that considerable amounts of calcium carbonate were leached from a former MIS 3 Cambisol and accumulated in the underlying loess unit. This truncated MIS 3 Cambisol is very similar to the MIS 3 paleosol remains in the LPS Collias that we investigated 87 km farther south in the present Mediterranean climate. No paleosols were observed in the late MIS 2 deposits
French-Speaking Network of Pharmacogenetics (RNPGx) Recommendations for Gene Panel Analysis Through Genotyping or Sequencing in Pharmacogenetics
No full textInternational audienceBACKGROUND: The implementation of pharmacogenetics in clinical practice increasingly relies on multigene panels. OBJECTIVES: The objective of this study is to develop harmonized recommendations for the design and analytical implementation of multigene pharmacogenetic panels, defining clinically relevant genes and associated regions of interest (ROIs) based on evidence strength, therapeutic applicability, and compatibility with genotyping or sequencing technologies. METHODS: The French-Speaking Network of Pharmacogenetics (RNPGx) evaluated 81 candidate genes across five therapeutic domains (i.e., oncology and supportive care, anesthesia and pain management, cardiology, neurology and psychiatry and immunology and infectious diseases) using a structured, evidence-based scoring system. Each gene was evaluated using a 25-point scoring system integrating pharmacogenetic importance, regulatory and professional society recommendations, and expert consensus. For the genes ultimately selected for the core panel, clinically relevant regions of interest were defined and assigned to one of three analytical classes. Class 1 includes variants with established clinical actionability; Class 2 adds optional variants suitable for extended testing in specialized settings; and Class 3 covers broader genomic regions mainly intended for rare variant or structural analyses. RESULTS: A 28-gene core panel was retained. Class 1 included 76 prioritized variants (including CYP2D6 CNV variants), and Class 2 comprised 62 additional variants (with extended analysis for CYP2D6). Class 3 eligibility was retained for 18 genes. CONCLUSION: The RNPGx recommendations offer a harmonized and flexible framework for pharmacogenetic panel design and for the extraction and interpretation of pharmacogenetic data from whole-exome or whole-genome sequencing
Metrological concepts applied to Total Alkalinity measurements in seawater: reference materials, inter-laboratory comparison and uncertainty budget
No full textInternational audienceAbstract. Total alkalinity (TA) measurements in seawater are crucial for characterizing and monitoring the oceanic carbonate system. While international best practices and guidelines exist, the field still lacks widely available traceable reference materials and a well-established uncertainty budget of the measurement method. In this study, we applied key metrological principles – development of reference materials, inter-laboratory comparison and uncertainty quantification – to TA measurements. We developed two reference materials, including an artificial material with a rigorously characterized reference value and an associated uncertainty budget, being traceable to the International System of units (SI). These materials were tested in an inter-laboratory comparison involving five laboratories and demonstrated the applicability of the reference materials developed for quality control. Additionally, we established an uncertainty budget for the TA measurement method using two metrological approaches. The resulting expanded uncertainty was 5 µmol kg−1 (with a coverage factor k=2) in TA, approaching the 4 µmol kg−1 target set by the Global Ocean Acidification Observing Network for climate monitoring. These findings mark a significant step toward improving the quality and comparability of TA measurements, thereby strengthening long-term ocean carbonate system monitoring