Développements d'instrumentations lasers (QCL, DFG) dédiés à la métrologie d'espèces d'intérêt atmosphérique (CH₄, HONO)

I report in this PhD thesis on the development of two mid-infrared laser spectrometers, based on difference-frequency generation (DFG) and quantum cascade laser (QCL), for application to trace gas monitoring. The DFG spectrometer (2.78 µm) was coupled with the QCL spectrometer (8 µm) to simultaneously measure nitrous acid (HONO) absorption spectra of the v₁ and v₃ bands respectively. Such crossing measurements allow us to determine experimentally, for the first time, the line strengths of 31 absorption lines of the ν1 band of trans isomer of nitrous acid that significantly impacts the air quality and climate change because of its crucial role in the atmospheric oxidation capacity. The QCL spectrometer is also deployed for continuous monitoring of methane (CH₄) during January 2013 in Dunkirk. Methane concentration variation is analyzed with the help of the simultaneously recorded meteorological parameters. In order to identify the sources of CH₄ emission, I developed an Isotope Ratio Laser Spectrometry (IRLS) technique to measure the isotopic ratio of ¹³CH₄/¹²CH₄. Preliminary results are presented.Nous reportons dans ces travaux de thèse le développement de deux spectromètres à lasers fonctionnant dans la région spectrale du moyen infrarouge (2,78 µm et 8 µm) correspondant aux deux fenêtres atmosphériques pour la détection de traces de gaz. Le premier spectromètre, basé sur la génération de différence de fréquences (DFG) vers 2,78 µm, est couplé à un spectromètre utilisant un laser à cascade quantique (QCL) vers 8 µm dans une cellule multipassages. Ce montage croisé nous a permis de déterminer pour la première fois expérimentalement les intensités de 31 raies d’absorption les plus intenses de la branche Q de la bande fondamentale ν₁ de l’isomère trans de l’acide nitreux (trans-HONO), considéré comme espèce clé pour la capacité d'oxydation atmosphérique. Nous avons exploité le spectromètre à QCL lors d’une campagne de mesures ciblée sur la surveillance continue du méthane (CH₄) pendant le mois de janvier 2013 à Dunkerque. Les observations de la variation de la concentration du CH₄ ont été analysées à l'aide des paramètres météorologiques simultanément enregistrées. Face au besoin d’identification de ses sources d’émission, nous avons développé la technique IRLS (Isotope Ratio Laser Spectrometry) pour la mesure du taux isotopique de ¹³CH₄/¹²CH₄. Les résultats préliminaires sont présentés

Developments of laser-based instrumentation (QCL, DFG) dedicated to optical monitoring of atmospheric species (CH₄, HONO)

Nous reportons dans ces travaux de thèse le développement de deux spectromètres à lasers fonctionnant dans la région spectrale du moyen infrarouge (2,78 µm et 8 µm) correspondant aux deux fenêtres atmosphériques pour la détection de traces de gaz. Le premier spectromètre, basé sur la génération de différence de fréquences (DFG) vers 2,78 µm, est couplé à un spectromètre utilisant un laser à cascade quantique (QCL) vers 8 µm dans une cellule multipassages. Ce montage croisé nous a permis de déterminer pour la première fois expérimentalement les intensités de 31 raies d’absorption les plus intenses de la branche Q de la bande fondamentale ν₁ de l’isomère trans de l’acide nitreux (trans-HONO), considéré comme espèce clé pour la capacité d'oxydation atmosphérique. Nous avons exploité le spectromètre à QCL lors d’une campagne de mesures ciblée sur la surveillance continue du méthane (CH₄) pendant le mois de janvier 2013 à Dunkerque. Les observations de la variation de la concentration du CH₄ ont été analysées à l'aide des paramètres météorologiques simultanément enregistrées. Face au besoin d’identification de ses sources d’émission, nous avons développé la technique IRLS (Isotope Ratio Laser Spectrometry) pour la mesure du taux isotopique de ¹³CH₄/¹²CH₄. Les résultats préliminaires sont présentés.I report in this PhD thesis on the development of two mid-infrared laser spectrometers, based on difference-frequency generation (DFG) and quantum cascade laser (QCL), for application to trace gas monitoring. The DFG spectrometer (2.78 µm) was coupled with the QCL spectrometer (8 µm) to simultaneously measure nitrous acid (HONO) absorption spectra of the v₁ and v₃ bands respectively. Such crossing measurements allow us to determine experimentally, for the first time, the line strengths of 31 absorption lines of the ν1 band of trans isomer of nitrous acid that significantly impacts the air quality and climate change because of its crucial role in the atmospheric oxidation capacity. The QCL spectrometer is also deployed for continuous monitoring of methane (CH₄) during January 2013 in Dunkirk. Methane concentration variation is analyzed with the help of the simultaneously recorded meteorological parameters. In order to identify the sources of CH₄ emission, I developed an Isotope Ratio Laser Spectrometry (IRLS) technique to measure the isotopic ratio of ¹³CH₄/¹²CH₄. Preliminary results are presented

A Quantum Cascade Laser-Based Optical Sensor for Continuous Monitoring of Environmental Methane in Dunkirk (France)

A room-temperature continuous-wave (CW) quantum cascade laser (QCL)-based methane (CH4) sensor operating in the mid-infrared near 8 μm was developed for continuous measurement of CH4 concentrations in ambient air. The well-isolated absorption line (7F2,4 ← 8F1,2) of the ν4 fundamental band of CH4 located at 1255.0004 cm−1 was used for optical measurement of CH4 concentration by direct absorption in a White-type multipass cell with an effective path-length of 175 m. A 1σ (SNR = 1) detection limit of 33.3 ppb in 218 s was achieved with a measurement precision of 1.13%. The developed sensor was deployed in a campaign of measurements of time series CH4 concentration on a site near a suburban traffic road in Dunkirk (France) from 9th to 22nd January 2013. An episode of high CH4 concentration of up to ~3 ppm has been observed and analyzed with the help of meteorological parameters combined with back trajectory calculation using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model of NOAA

Atmospheric Measurements by Ultra-Light SpEctrometer (AMULSE) Dedicated to Vertical Profile in Situ Measurements of Carbon Dioxide (CO2) Under Weather Balloons: Instrumental Development and Field Application

The concentration of greenhouse gases in the atmosphere plays an important role in the radiative effects in the Earth’s climate system. Therefore, it is crucial to increase the number of atmospheric observations in order to quantify the natural sinks and emission sources. We report in this paper the development of a new compact lightweight spectrometer (1.8 kg) called AMULSE based on near infrared laser technology at 2.04 µm coupled to a 6-m open-path multipass cell. The measurements were made using the Wavelength Modulation Spectroscopy (WMS) technique and the spectrometer is hence dedicated to in situ measuring the vertical profiles of the CO2 at high precision levels (σAllan = 0.96 ppm in 1 s integration time (1σ)) and with high temporal/spatial resolution (1 Hz/5 m) using meteorological balloons. The instrument is compact, robust, cost-effective, fully autonomous, has low-power consumption, a non-intrusive probe and is plug & play. It was first calibrated and validated in the laboratory and then used for 17 successful flights up to 10 km altitude in the region Champagne—Ardenne, France in 2014. A rate of 100% of instrument recovery was validated due to the pre-localization prediction of the Météo—France based on the flight simulation software

A Quantum Cascade Laser-Based Optical Sensor for Continuous Monitoring of Environmental Methane in Dunkirk (France)

International audienceA room-temperature continuous-wave (CW) quantum cascade laser (QCL)-based methane (CH4) sensor operating in the mid-infrared near 8 μm was developed for continuous measurement of CH4 concentrations in ambient air. The well-isolated absorption line (7F2,4 ← 8F1,2) of the ν4 fundamental band of CH4 located at 1255.0004 cm−1 was used for optical measurement of CH4 concentration by direct absorption in a White-type multipass cell with an effective path-length of 175 m. A 1σ (SNR = 1) detection limit of 33.3 ppb in 218 s was achieved with a measurement precision of 1.13%. The developed sensor was deployed in a campaign of measurements of time series CH4 concentration on a site near a suburban traffic road in Dunkirk (France) from 9th to 22nd January 2013. An episode of high CH4 concentration of up to ~3 ppm has been observed and analyzed with the help of meteorological parameters combined with back trajectory calculation using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model of NOAA

Laser absorption spectroscopy applied to monitoring of short-lived climate pollutants (SLCPs)

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The development of the Atmospheric Measurements by Ultra-Light Spectrometer (AMULSE) greenhouse gas profiling system and application for satellite retrieval validation

International audienceWe report in this paper the development of an embedded ultralight spectrometer (<3 kg) based on tuneable diode laser absorption spectroscopy (with a sampling rate of 24 Hz) in the mid-infrared spectral region. This instrument is dedicated to in situ measurements of the vertical profile concentrations of three main greenhouse gases – carbon dioxide (CO2), methane (CH4) and water vapour (H2O) – via standard weather and tethered balloons. The plug and play instrument is compact, robust, cost-effective, and autonomous. The instrument also has low power consumption and is non-intrusive.It was first calibrated during an in situ experiment on an ICOS (Integrated Carbon Observation System) site for several days, then used in two experiments with several balloon flights of up to 30 km altitude in the Reims region of France in 2017–2018 in collaboration with Météo-France CNRM (Centre National de Recherches Météorologiques).This paper shows the valuable interest of the data measured by the AMULSE (Atmospheric Measurements by Ultra-Light Spectrometer) instrument during the APOGEE (Atmospheric Profiles of Greenhouse Gases) measurement experiment, specifically for the vertical profiles of CO2 and CH4, measurements of which remain very sparse. We have carried out several experiments showing that the measured profiles have several applications: the validation of simulations of infrared satellite observations, evaluating the quality of chemical profiles from chemistry transport models (CTMs) and evaluating the quality of retrieved chemical profiles from the assimilation of infrared satellite observations. The results show that the simulations of infrared satellite observations from IASI (Infrared Atmospheric Sounding Interferometer) and CrIS (Cross-track Infrared Sounder) instruments performed in operational mode for numerical weather prediction (NWP) by the radiative transfer model (RTM) RTTOV (Radiative Transfer for the TIROS Operational Vertical Sounder) are of good quality. We also show that the MOCAGE (Modèle de Chimie Atmosphérique de Grande Echelle) and CAMS (Copernicus Atmospheric Monitoring Service) CTMs modelled ozone profiles fairly accurately and that the CAMS CTM represents the methane in the troposphere well compared to MOCAGE. Finally, the measured in situ ozone profiles allowed us to show the good quality of the retrieved ozone profiles by assimilating ozone-sensitive infrared spectral radiances from the IASI and CrIS