19 research outputs found
The CO2 –broadened H2O continuum in the 100–1500 cm -1 region: Measurements, predictions and empirical model
Transmission spectra of H2O + CO2 mixtures have been recorded, at 296, 325 and 366 K, for various pres- sures and mixture compositions using two experimental setups. Their analysis enables to retrieve values of the “continuum”absorption by the CO2 -broadened H2O line wings between 100 and 1500 cm-1 . The results are in good agreement with those, around 1300 cm-1 , of the single previous experimental study available. Comparisons are also made with direct predictions based on line-shape correction factors χ calculated, almost thirty years ago, using a quasistatic approach and an input H2O –CO2 intermolecular potential. They show that this model quite nicely predicts, with slightly overestimated values, the con- tinuum over a spectral range where it varies by more than three orders of magnitude. An empirical cor- rection is proposed, based on the experimental data, which should be useful for radiative transfer and climate studies in CO2 rich planetary atmospheres
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The CO₂–broadened H₂O continuum in the 100–1500cm-1 region: Measurements, predictions and empirical model
Transmission spectra of H₂O+CO₂ mixtures have been recorded, at 296, 325 and 366 K, for various pressures and mixture compositions using two experimental setups. Their analysis enables to retrieve values of the “continuum” absorption by the CO₂-broadened H2₂O line wings between 100 and 1500 cm-1. The results are in good agreement with those, around 1300 cm-1, of the single previous experimental study available. Comparisons are also made with direct predictions based on line-shape correction factors χ calculated, almost thirty years ago, using a quasistatic approach and an input H₂O—CO₂ intermolecular potential. They show that this model quite nicely predicts, with slightly overestimated values, the continuum over a spectral range where it varies by more than three orders of magnitude. An empirical correction is proposed, based on the experimental data, which should be useful for radiative transfer and climate studies in CO2 rich planetary atmospheres
The 2 ν 6 / ν 2 + ν 3 / ν 3 + ν 5 band system of CH 3 Br revisited: Modeling anharmonic and Coriolis interactions in a three-level system near 2000 cm −1
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The 2ν3/ν2/ν5/ν3 + ν6 band system of CH3Br revisited: Anharmonic and Coriolis interactions in a four-level system near 1400 cm−1
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Ground-based lidar measurements within the framework of AEROCLO-SA
International audienceA specific instrumental synergy, associating ground-based lidar, airborne and spaceborne remote sensing measurements, was set up as part of the field campaign of the AErosol, RadiatiOn and CLOuds in southern Africa (AEROCLO-sA) project. The overarching objective of AEROCLO-sA is to improve our knowledge about the role of atmospheric aerosols on the specific climate of southern Africa. For this reason, the Henties Bay experimental site of the Research Centre of the University of Namibia (22° 6' S, 14° 17' E) in the Orongo region has been selected to implement a ground-based lidar between 22 August and 12 September, 2017. The geographical position of the site is favorable for such a study, it is bounded on its western side by the Atlantic Ocean and by the Namibia desert ( 800 m amsl) on its eastern side. A big part of the year, as the west coast of South Africa, Henties Bay is covered with low clouds of stratocumulus type with very frequent fogs, and often overflown by air masses loaded with aerosol of various origins: forest fires, pollution, desert and/or ocean. Strong contributors to the aerosol load are the forest fires occurring during the dry season between August and October. Biomass burning aerosols exert a strong influence on the Earth's radiation budget by scattering and absorbing solar radiation, and influence the cloud formation and life time. The vertical distribution of absorbing aerosols is of paramount importance as it significantly influences the vertical profile of radiative heating in the atmosphere and, by this way, the stability of the atmosphere, thereby modifying convective and turbulent motions and clouds. The main vertical aerosol structures observed by lidar will be present and discussed. Passive (MODIS) and active (CALIPSO, CATS) space-borne observations coupled with back trajectory studies will allow for regionalized the local lidar observations
Ground-based lidar measurements within the framework of AEROCLO-SA
International audienceA specific instrumental synergy, associating ground-based lidar, airborne and spaceborne remote sensing measurements, was set up as part of the field campaign of the AErosol, RadiatiOn and CLOuds in southern Africa (AEROCLO-sA) project. The overarching objective of AEROCLO-sA is to improve our knowledge about the role of atmospheric aerosols on the specific climate of southern Africa. For this reason, the Henties Bay experimental site of the Research Centre of the University of Namibia (22° 6' S, 14° 17' E) in the Orongo region has been selected to implement a ground-based lidar between 22 August and 12 September, 2017. The geographical position of the site is favorable for such a study, it is bounded on its western side by the Atlantic Ocean and by the Namibia desert ( 800 m amsl) on its eastern side. A big part of the year, as the west coast of South Africa, Henties Bay is covered with low clouds of stratocumulus type with very frequent fogs, and often overflown by air masses loaded with aerosol of various origins: forest fires, pollution, desert and/or ocean. Strong contributors to the aerosol load are the forest fires occurring during the dry season between August and October. Biomass burning aerosols exert a strong influence on the Earth's radiation budget by scattering and absorbing solar radiation, and influence the cloud formation and life time. The vertical distribution of absorbing aerosols is of paramount importance as it significantly influences the vertical profile of radiative heating in the atmosphere and, by this way, the stability of the atmosphere, thereby modifying convective and turbulent motions and clouds. The main vertical aerosol structures observed by lidar will be present and discussed. Passive (MODIS) and active (CALIPSO, CATS) space-borne observations coupled with back trajectory studies will allow for regionalized the local lidar observations
Implementation of an incoherent broadband cavity-enhanced absorption spectroscopy technique in an atmospheric simulation chamber for in situ NO<sub>3</sub> monitoring: characterization and validation for kinetic studies
International audienceAbstract. An incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) technique has been developed for the in situ monitoring of NO3 radicals at the parts per trillion level in the CSA simulation chamber (at LISA). The technique couples an incoherent broadband light source centered at 662 nm with a high-finesse optical cavity made of two highly reflecting mirrors. The optical cavity which has an effective length of 82 cm allows for up to 3 km of effective absorption and a high sensitivity for NO3 detection (up to 6 ppt for an integration time of 10 s). This technique also allows for NO2 monitoring (up to 9 ppb for an integration time of 10 s). Here, we present the experimental setup as well as tests for its characterization and validation. The validation tests include an intercomparison with another independent technique (Fourier-transform infrared, FTIR) and the absolute rate determination for the reaction trans-2-butene + NO3, which is already well documented in the literature. The value of (4.13 ± 0.45) × 10−13 cm3 molecule−1 s−1 has been found, which is in good agreement with previous determinations. From these experiments, optimal operation conditions are proposed. The technique is now fully operational and can be used to determine rate constants for fast reactions involving complex volatile organic compounds (VOCs; with rate constants up to 10−10 cm3 molecule−1 s−1)
Evidence of the complexity of aerosol transport in the lower troposphere on the Namibian coast during AEROCLO-sA
International audienceThe evolution of the vertical distribution and optical properties of aerosols in the free troposphere, above stratocumulus, is analysed for the first time over the Namibian coast, a region where uncertainties on aerosol-cloud coupling in climate simulations are significant. We show the high variability of atmospheric aerosol composition in the lower and middle troposphere during the AEROCLO-sA field campaign (22 August–12 September 2017) around the Henties Bay supersite, using a combination of ground-based, airborne and space-borne lidar measurements. Three distinct periods of 4 to 7 days are observed, associated with increasing aerosol loads (aerosol optical thickness at 550 nm ranging from ~ 0.2 to ~ 0.7), as well as increasing aerosol layer depth and top altitude. Aerosols are observed up to 6 km above mean sea level during the later period. Aerosols transported within the free troposphere are mainly polluted dust (dust mixed with smoke from fires in Angola) for the first 2 periods (22 August–1 September 2017) and smoke (from Angola and South America) for the last part (3–9 September) of the field campaign. Lagrangian back trajectory analyses highlight that the highest aerosol layers (between 5 and 6 km above mean sea level) come from South America (Brazil, Argentina and Paraguay) and reach Henties Bay after 4 to 5 days. They are transported eastward by the mid latitude westerlies and towards Southern Africa by the equatorward moving cut-off low originating within the westerlies. This results in a very complex mixture of aerosols over the coastal regions of Namibia that must be taken into account when investigating aerosols radiative effects above stratocumulus clouds in the south east Atlantic Ocean
Implementation of an incoherent broadband cavity-enhanced absorption spectroscopy technique in an atmospheric simulation chamber for in situ NO<sub>3</sub> monitoring: characterization and validation for kinetic studies
International audienceAbstract. An incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) technique has been developed for the in situ monitoring of NO3 radicals at the parts per trillion level in the CSA simulation chamber (at LISA). The technique couples an incoherent broadband light source centered at 662 nm with a high-finesse optical cavity made of two highly reflecting mirrors. The optical cavity which has an effective length of 82 cm allows for up to 3 km of effective absorption and a high sensitivity for NO3 detection (up to 6 ppt for an integration time of 10 s). This technique also allows for NO2 monitoring (up to 9 ppb for an integration time of 10 s). Here, we present the experimental setup as well as tests for its characterization and validation. The validation tests include an intercomparison with another independent technique (Fourier-transform infrared, FTIR) and the absolute rate determination for the reaction trans-2-butene + NO3, which is already well documented in the literature. The value of (4.13 ± 0.45) × 10−13 cm3 molecule−1 s−1 has been found, which is in good agreement with previous determinations. From these experiments, optimal operation conditions are proposed. The technique is now fully operational and can be used to determine rate constants for fast reactions involving complex volatile organic compounds (VOCs; with rate constants up to 10−10 cm3 molecule−1 s−1)
New line list for the ν4 bands of the trans (790.117 cm–1) and cis (851.943 cm–1) conformers of nitrous acid (HONO): Accurate positions and absolute intensities
International audienceThe goal of this work was to update and significantly improve the line lists that have been generated recently for 11 µm bands of the trans- and cis- conformer forms of nitrous acid (HONO) [Armante R, Perrin A, Kwabia Tchana F, Manceron L. The ν4 bands at 11 μm: linelists for the trans- and cis- conformer forms of nitrous acid (HONO) in the 2019 version of the GEISA database. Molecular Physics 2021;120:e1951860]. That 2019 version of the 11 µm line list was generated using the spectroscopic parameters that were available, at that time, in the literature. During the present study, we used high-resolution Fourier transform spectra recorded at 11 µm to perform a large investigation of line positions and intensities for the ν4 bands of the trans- and cis-conformer of HONO. The resulting set of experimental ν4 (absolute) intensities and of 41 energy levels were used to determine, by least squares fit computations, improved position and intensity parameters for the ν4 bands of the trans- and cis-conformer of HONO. For trans-HONO, the ν4 band appeared not to be perturbed, while for cis-HONO a weak high order B-type Coriolis, coupling together the 41 and 61 energy levels was evidenced for the first time. This new list is of potential interest for the IASI-NG (Infrared Atmospheric Sounding Interferometer - New Generation) instrument which will be launched on board the METOP-SG satellite in 2025