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

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

International audienc

The 2ν3/ν2/ν5/ν3 + ν6 band system of CH3Br revisited: Anharmonic and Coriolis interactions in a four-level system near 1400 cm−1

International audienc

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)

Atmospheric ammonia (NH₃) over the Paris megacity: 9 years of total column observations from ground-based infrared remote sensing

International audienceIn this paper, we present the first multi-year time series of atmospheric NH3 ground-based measurements in the Paris region (Créteil, 48.79° N, 2.44° E, France) retrieved with the mid-resolution “Observations of the Atmosphere by Solar absorption Infrared Spectroscopy” (OASIS) ground-based Fourier Transform infrared solar observatory. Located in an urban region, OASIS has previously been used for monitoring air quality (tropospheric ozone and carbon monoxide), thanks to its specific column sensitivity across the whole troposphere including the planetary boundary layer. A total of 4920 measurements of atmospheric total columns of ammonia have been obtained from 2009 to 2017, with uncertainties ranging from 20 % to 35 %, and are compared with NH3 concentrations derived from the Infrared Atmospheric Sounding Interferometer (IASI). OASIS ground-based measurements show significant interannual, and seasonal variabilities of atmospheric ammonia. NH3 total columns over the Paris megacity (12 million people) vary seasonally by 2 orders of magnitude, from approximately 1015 molecules cm−2 in winter to 1017 molecules cm−2 for spring peaks, probably due to springtime spreading of fertilizers on surrounding croplands. Also, we observe a correlation of daily NH3-OASIS total columns with daily PM2.5 in situ measurements from the closest Airparif surface station in springtime