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In this paper, we present the first multiyear time series of atmospheric ammonia (NH3) ground-based measurements in the Paris region (Créteil, 48.79∘ N, 2.44∘ E, France) retrieved with the midresolution “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 down to the atmospheric 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 have been 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 0.1×1016 molec. cm−2 in winter to 10×1016 molec. cm−2 for spring peaks, probably due to springtime spreading of fertilizers on surrounding croplands.

The Limb Profile Monitor of the Asmosphere (LPMA) instrument is a balloon-borne Fourier transform spectrometer designed to operate on a stratospheric gondola and to record high spectral resolution atmospheric spectra in absorption using the sun as a source. It is used to perform remote sensing measurements of atmospheric trace species in the mid-infrared and can also contribute to detailed validations of line-by- line atmospheric radiative transfer codes.

IAGOS (www.iagos.org) is a European Research Infrastructure using commercial aircraft (Airbus A340, A330, and soon A350) for automatic and routine measurements of atmospheric composition including reactive gases (ozone, carbon monoxide, nitrogen oxides, volatile organic compounds), greenhouse gases (water vapour, carbon dioxide, methane), aerosols and cloud particles along with essential thermodynamic parameters. The main objective of IAGOS is to provide the most complete set of high-quality essential climate variables (ECV) covering several decades for the long-term monitoring of climate and air quality. The observations are stored in the IAGOS data centre along with added-value products to facilitate the scientific interpretation of the data. IAGOS began as two European projects, MOZAIC and CARIBIC, in the early 1990s. These projects demonstrated that commercial aircraft are ideal platforms for routine atmospheric measurements. IAGOS then evolved as a European Research Infrastructure offering a mature and sustainable organization for the benefits of the scientific community and for the operational services in charge of air quality and climate change issues such as the Copernicus Atmosphere Monitoring Services (CAMS) and the Copernicus Climate Change Service (C3S). IAGOS is also a contributing network of the World Meteorological Organization (WMO). IAGOS provides measurements of numerous chemical compounds which are recorded simultaneously in the critical region of the upper troposphere – lower stratosphere (UTLS) and geographical regions such as Africa and the mid-Pacific which are poorly sampled by other means. The data are used by hundreds of groups worldwide performing data analysis for climatology and trend studies, model evaluation, satellite validation and the study of detailed chemical and physical processes around the tropopause. IAGOS data also play an important role in the re-assessment of the climate impact of aviation. Most important in the context of weather-related research, IAGOS and its predecessor programmes provide long-term observations of water vapour and relative humidity with respect to ice in the UTLS as well as throughout the tropospheric column during climb-out and descending phases around airports, now for more than 25 years. The high quality and very good resolution of IAGOS observations of relative humidity over ice are used to better understand the role of water vapour and of ice-supersaturated air masses in the tropopause region and to improve their representation in numerical weather and climate forecasting models. Furthermore, CAMS is using the water vapour vertical profiles in near real time for the continuous validation of the CAMS atmospheric models.

This paper describes the 2020 release of the GEISA database (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information), developed and maintained at LMD since 1974. GEISA is the reference database for several current or planned Thermal and Short-Wave InfraRed (TIR and SWIR) space missions IASI (Infrared Atmospheric Sounding Interferometer), IASI-NG (IASI New Generation), MicroCarb (Carbon Dioxide Monitoring Mission), Merlin (MEthane Remote sensing LIdar missioN). It is actually a compilation of three databases: the “line parameters database”, the “cross-section sub-database” and the “microphysical and optical properties of atmospheric aerosols sub-database”. The new edition concerns only the line parameters dataset, with significant updates and additions implemented using the best available spectroscopic data. The GEISA-2020 line parameters database involves 58 molecules (145 isotopic species) and contains 6,746,987 entries, in the spectral range from 10−6 to 35877 cm−1. In this version, 23 molecules have been updated (with 10 new isotopic species) and 6 new molecules have been added (HONO, COFCl, CH3F, CH3I, RuO4, H2C3H2 (isomer of C3H4)) corresponding to 15 isotopic species. The compilation can be accessed through the AERIS data and services center for the atmosphere website (https://geisa.aeris-data.fr/), with the development of a powerful graphical tool and convenient searching, filtering, and plotting of data using modern technologies (PostgreSQL database, REST API, VueJS, Plotly). Based on four examples (H2O, O3, O2 and SF6), this paper also shows how the LMD in house validation algorithm SPARTE (Spectroscopic Parameters And Radiative Transfer Evaluation) helps to evaluate, correct, reject or defer the input of new spectroscopic data into GEISA and this, thanks to iterations with researchers from different communities (spectroscopy, radiative transfer).

A critical evaluation and validation of the complete set of previously published experimental rotational–vibrational line positions is reported for the four stable sulphur isotopologues of the semirigid SO2 molecule – i.e., 32S16O2, 33S16O2, 34S16O2, and 36S16O2. The experimentally measured, assigned, and labeled transitions are collated from 43 sources. The 32S16O2, 33S16O2, 34S16O2, and 36S16O2 datasets contain 40,269, 15,628, 31,080, and 31 lines, respectively. Of the datasets collated, only the extremely limited 36S16O2 dataset is not subjected to a detailed analysis. As part of a detailed analysis of the experimental spectroscopic networks corresponding to the ground electronic states of the 32S16O2, 33S16O2, and 34S16O2 isotopologues, the MARVEL (Measured Active Rotational–Vibrational Energy Levels) procedure is used to determine the rovibrational energy levels. The rovibrational levels and their vibrational parent and asymmetric-top quantum numbers are compared to ones obtained from accurate variational nuclear-motion computations as well as to results of carefully designed effective Hamiltonian models. The rovibrational energy levels of the three isotopologues having the same labels are also compared against each other to ensure self-consistency. This careful, multifaceted analysis gives rise to 15,130, 5852, and 10,893 validated rovibrational energy levels, with a typical accuracy of a few 0.0001 cm − 1 , for 32S16O2, 33S16O2, and 34S16O2, respectively. The extensive list of validated experimental lines and empirical (MARVEL) energy levels of the S16O2 isotopologues studied are deposited in the Supplementary Material of this article, as well as in the distributed information system ReSpecTh ( http://respecth.hu ).

A Fourier transform spectrum of phosgene (Cl2CO) has been recorded in the 17.3-μm spectral region at a temperature of 180 K and at a resolution of 0.00102 cm−1 using a Bruker IFS125HR spectrometer coupled to synchrotron radiation, leading to the observation of the ν2 and ν4 vibrational bands of the two isotopologues 35Cl2CO and 35Cl37ClCO. The corresponding upper-state ro-vibrational levels were fit using a Hamiltonian model accounting for the A-type Coriolis interaction linking the rotational levels of the 21 and 41 vibrational states. In this way, it was possible to reproduce the upper-state ro-vibrational levels to within the experimental uncertainty, i.e. ∼0.30 × 10−3 cm−1. Very accurate rotational and centrifugal distortion and interaction constants were derived from the fit, together with the following band centres: ν0(ν2, 35Cl2CO) = 572.526299(30) cm−1, ν0(ν4, 35Cl2CO) = 582.089026(30) cm−1, ν0(ν2, 35Cl37ClCO) = 568.951791(35) cm−1 and ν0(ν4, 35Cl37ClCO) = 581.758279(35) cm−1.

A Fourier transform spectrum of sulfur dioxide 33S16O2 has been recorded in the 18.3 μm spectral region at a resolution of 0.002 cm−1 using a Bruker IFS 125HR spectrometer leading to the observation of the ν2 and 2ν2-ν2 vibrational bands of the 33S16O2 molecule. The corresponding upper state ro-vibrational levels were fit using Watson-type Hamiltonians. In this way it was possible to reproduce the upper state ro-vibrational levels to within the experimental uncertainty; i.e., ∼0.20 × 10−3 cm−1. Very accurate rotational and centrifugal distortion constants were derived from the fit together with the following band centers: ν0 (ν2) = 515.659089(50) cm−1, ν0 (2ν2) = 1030.697723(20) cm−1.

HighlightsHigh-resolution spectra of 33S16O2 have been recorded for the first time in the 8 and 4 µm spectral regions.The ν1, ν3 and ν1 + ν3 bands of the 33S16O2 have been analysed up to very high quantum numbers.Accurate ro-vibrational upper states constants have been determined.

A Fourier transform spectrum of phosgene (Cl2CO) has been recorded in the 11.8 μm spectral region at low temperature and at a resolution of 0.00102 cm−1 using a Bruker IFS125HR spectrometer coupled to synchrotron radiation leading to the observation of the ν5 vibrational band of the isotopologue 37Cl2CO. The corresponding upper state rovibrational levels were fit using a Watson-type Hamiltonian. In this way it was possible to reproduce the upper state rovibrational levels almost to within the experimental uncertainty i.e. ∼0.50 × 10−3 cm−1. Very accurate rotational and centrifugal distortion constants were derived from the fit together with the following band center: ν0 (ν5, 37Cl2CO) = 848.970769 (20) cm−1.

In 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.

The 12.6 µm region of nitryl chloride (ClNO2) has been recorded at high resolution (0.00102 cm−1) using a Fourier transform spectrometer and the SOLEIL synchrotron light source. ClNO2 was found during our studies of chlorine nitrate and, after fractional distillations it was introduced into a multipass White cell made of inert materials, with an optical path length of 5.4 m. 320 scans were recorded for the range 600–980 cm−1 at a total pressure of 0.23 hPa and a temperature of 250 K. A thorough analysis of the ν2, 2ν6 and 2ν3 bands of 35ClNO2 and of the ν2 band of 37ClNO2 falling in this region has been carried out using a Hamiltonian model which takes explicitly into account the numerous resonances affecting the ro-vibrational energy levels; especially the C-type Coriolis resonance between the ν2 and the ν3 + ν6 modes. These two modes are only separated by less than 20 cm−1 and are thoroughly mixed. From the fittings, the following band centers were derived: νo(ν2) = 792.761264(60) cm−1, νo(ν3 + ν6) = 775.8923(20) cm−1, νo(2ν3) = 734.183576(20) cm−1 and νo(2ν6) = 819.836727(90) cm−1 for 35ClNO2 and νo(ν2) = 792.258284(30) cm−1 and νo(ν3 + ν6) = 774.6826(30) cm−1 for 37ClNO2 where the uncertainties are one standard deviation. Due to their sharp Q branches falling into an atmospheric “window”, the detection of the ν2 bands might be an advantageous route for future attempts to quantify atmospheric ClNO2, using infrared techniques.

MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) is a Fourier transform spectrometer designed for measuring the earth atmospheric emission at limb in the 685-2410 cm-1 range. It flew onboard the polar orbit ENVISAT satellite for approximately 10 years, from June 2002 to April 2012, performing measurements during both day and night with an unprecedented spectral resolution from space (0.025 cm-1 in the first part of the mission and 0.0625 cm-1 in the second part). MIPAS measurements on ENVISAT represent a unique database for the study of the vertical distribution and time variation of the atmospheric composition on a global scale. While the focus of the instrument is the study of the chemistry and the physics of the stratosphere, also information on constituents in the upper troposphere has been derived. The ESA products include more than 20 minor atmospheric constituents [1]. The retrieval of the vertical profiles of atmospheric constituents is performed by fitting the observations to a full-physics model taking into account emission and absorption of all molecules. As a consequence the possibility of performing the retrievals is directly linked to the availability of the spectroscopic parameters and the quality of the retrieval depends on their quality. Indeed, in the estimation of the total error budget of the retrieved profiles the error due to the spectroscopic database is often one of the largest ones. The need of exploiting the information contained in the measurements of MIPAS, as well as of other instruments operating in the same spectral region like ACE-FTS, has driven studies for improving spectroscopic parameters in the middle infrared spectral region. MIPAS measurements provided not only the motivation, but also the guideline and the validation of the spectroscopic studies. Thanks to the their high spectral resolution and broadband coverage, the differences between observations and simulations of MIPAS measurements have been used to detect inconsistencies and validate subsequent improvements in the spectroscopic database (obtained with laboratory measurements and new calculations). In some cases MIPAS measurements have been used to convert the relative line intensities of a given spectral band to absolute intensities by comparing the retrieved profiles from MIPAS radiances from two different regions covering the two different spectral bands [2]. In this talk we will show how MIPAS measurements were used to validate the most recent improvements in the spectroscopic database of HNO3 and COCl2.

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a Fourier transform spectrometer that measured mid-infrared atmospheric limb emission spectra from July 2002 to April 2012 on board the polar-orbiting satellite ENVISAT. We have used MIPAS data to study the latitudinal variations of phosgene (COCl2 or carbonyl chloride) and, for the first time, its seasonal variation in the upper troposphere/lower stratosphere region (UTLS). Retrievals of phosgene were made using the 830–860 cm−1 region, corresponding to the ν5 bands of COCl2. Unfortunately, in that region, the ν4 band of CFC-11, which is much stronger than COCl2 ν5, hides the phosgene emission. In order to evaluate seasonality and latitudinal distribution of phosgene we have analysed all the measurements made by MIPAS on days 18 and 20 of each month of 2008 with the optimized retrieval model (ORM) recently upgraded with the multi-target retrieval technique and with the optimal estimation functionality to apply external constraints to the state vector. Average seasonal profiles of phosgene show an evident latitudinal variability with the largest values observed in the tropical regions (maximum ≈ 35 parts per trillion by volume (pptv) at about 300 hPa). In the midlatitude and polar regions, the volume mixing ratio (VMR) values do not exceed 30 pptv and the vertical distributions are less peaked. Our analysis highlights that COCl2 seasonal variability is fairly low, apart from the polar regions.

The high-resolution absorption spectra of phosgene (Cl 2 CO) has been recorded at 0.001 cm −1 resolution in the 250–350 cm −1 region by Fourier transform spectroscopy at synchrotron SOLEIL. To reduce the spectral congestion, the spectra have been recorded at low temperature (197 K) using a 93.14 m optical path length cryogenic cell. This enables the first detailed infrared analysis of the ν 3 bands of the 35 Cl 2 CO and 35 Cl 37 ClCO isotopologues of phosgene. Using a Watson-type Hamiltonian, it was possible to reproduce the upper state rovibrational infrared energy levels, together with, for 35 Cl 2 CO, the available microwave data in the 3 1 excited state (Yamamoto et al. 1984) to within their experimental accuracy. In this way, accurate rotational and centrifugal distortion constants together with the following band centers: ν 0 ( ν 3 , 35 Cl 2 CO) = 301.545622(17) cm −1 and ν 0 ( ν 3 , 35 Cl 37 ClCO) = 298.199194(81) cm −1 , were derived for the ν 3 bands of 35 Cl 2 CO and 35 Cl 37 ClCO.

Improved line positions and intensities have been generated for the 7.6 µm spectral region of nitric acid. They were obtained relying on a recent reinvestigation of the nitric acid band system at 7.6 µm and comparisons of HNO3 volume mixing ratio profiles retrieved from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) limb emission radiances in the 11 and 7.6 µm domains. This has led to an improved database called MIPAS-2015. Comparisons with available laboratory information (individual line intensities, integrated absorption cross sections, and absorption cross sections) show that MIPAS-2015 provides an improved description of the 7.6 µm region of nitric acid. This study should help to improve HNO3 satellite retrievals by allowing measurements to be performed simultaneously in the 11 and 7.6 µm micro-windows. In particular, it should be useful to analyze existing MIPAS and IASI spectra as well as spectra to be recorded by the forthcoming Infrared Atmospheric Sounding Interferometer – New Generation (IASI-NG) instrument.

International audience; A new investigation of the ν3 bands of 35ClNO2 and 37 ClNO2, located around 370 cm−1 has been performed using a high resolution (0.00102 cm−1) Fourier transform spectrum recorded at SOLEIL with highly improved experimental conditions as compared to previous work [Orphal J, Morillon-Chapey M, Klee S, Mellau GC, Winnewisser M. J Mol Spectrosc 1998;190:101–6]: (i) the use of synchrotron radiation which resulted in a better signal-to-noise ratio; (ii) a resolution twice better; (iii) a low temperature (221 K) with an optical path length of 8.16 m, allowing low pressure (0.025 hPa) in the sample leading to a well resolved spectrum. As a consequence, significantly better results than previously were obtained. Thanks to the new experimental conditions, the line assignments were pursued up to higher J and Ka quantum number values, J = 83 and Ka = 44. For both isotopomers, a total of 6331 transitions were reproduced with a root-mean-square deviation of 2 × 10−4 cm−1 using a Watson-type A-reduced Hamiltonian. Improved rotational and centrifugal distortion constants for the ν3 fundamental bands of 35ClNO2 and 37 ClNO2 have been determined. The band centers are 370.1510773(92) cm−1 for the ν3 fundamental band of 35ClNO2 and 364.5218094(96) cm−1 for the ν3 fundamental band of 37ClNO2. The synthetic line list obtained in this study could be interesting for future measurements of ClNO2 in the atmosphere, e.g. using the new space mission FORUM which is one of the concepts chosen by ESA to be developed further and which opens up a new window (150–1400 cm−1 ) for understanding and quantifying the radiative processes, as well as air quality and pollution effects

This paper presents the first high resolution (Δν = 0.00096 cm−1) IR investigation of 2–13C-propane. Spectra of the ν9(A1) CCC skeletal bending mode near 336.767 cm−1 (a b-type band) and the ν26(B2) methylene (CH2) rocking mode near 746.614 cm−1 (a c-type band) were recorded at the Canadian Light Source (CLS) synchrotron. The spectra were assigned both traditionally and with the aid of the pgopher program. As only limited microwave data are available for this molecule the present data was used to determine a new set of ground state constants that included centrifugal distortion terms. Upper state constants for both bands have been determined that provide a good simulation of the spectra. The analysis also included the strong a-type Coriolis resonance between the ν26 and 2ν9 states that causes strong perturbation-allowed transitions to appear in the spectrum. Lines of the 2ν9-ν9 hot band were also assigned and included in our analysis of the bending region. This data will be useful in identifying isotopic propane lines in Titan and other astrophysical objects.

We present the first investigation of the ν8 band (C–C symmetric stretch at 870.3137 cm−1), together with an extended analysis of the neighbouring ν21 band (CH3 rock at 921.3756 cm−1) of propane (C...

A high resolution (0.0015 cm −1 ) IR spectrum of propane, C 3 H 8 , has been recorded with synchrotron radiation at the French light source facility at SOLEIL coupled to a Bruker IFS-125 Fourier transform spectrometer. A preliminary analysis of the ν 21 fundamental band (B 1 , CH 3 rock) at 921.382 cm −1 reveals that the rotational energy levels of 21 1 are split by interactions with the internal rotations of the methyl groups. The AA, EE and AE + EA components of this A-type band have their band centers at 921.3724(38), 921.3821(33) and 921.3913(44) cm −1 , respectively. These torsional splittings most probably are due to anharmonic and/or Coriolis resonance couplings with nearby highly excited states of both internal rotations of the methyl groups. In addition, several vibrational–rotational resonances were observed that affect the torsional components in different ways.

Fourier transform spectra of phosgene (Cl2CO) have been recorded in the 11.75 and 5.47 μm spectral regions using a Bruker IFS125HR spectrometer at resolutions of 0.00102 and 0.0015 cm−1, respectively, leading to the observation of the ν5 and ν1 vibrational bands of the two isotopologues 35Cl2CO and 35Cl37ClCO. The corresponding upper state ro-vibrational levels were fit using Watson-type Hamiltonians and/or a Hamiltonian matrix accounting for resonance effects when necessary. In this way, it was possible to reproduce the upper state ro-vibrational levels to within the experimental accuracy, i.e. ∼0.17 × 10−3 cm−1. Very accurate rotational and centrifugal distortion constants were derived from the fit together with the following band centres: ν0(ν5, 35Cl2CO) = 851.012737(20) cm−1, ν0(ν5, 35Cl37ClCO) = 849.995451(90) cm−1, ν0(ν2 + ν3, 35Cl37ClCO) = 864.42370(50) cm−1, ν0(ν1, 35Cl2CO) = 1828.202514(40) cm−1 and ν0(ν1, 35Cl37ClCO) = 1827.246444(20) cm−1.

The ν8 band region of BrONO2 around 14 µm has been studied at high resolution. The band structure is highly similar to the ν8 band of ClONO2: in addition to very regular Q branches at the low energy side of the band and the main ν8 Q branch located at 722.4 cm−1, a second Q branch is visible at 723.9 cm−1. When attributing this peak to the ν8+ν9 − ν9 band center (as in ClONO2), together with a very weak band observed at 835.8 cm−1, one can determine the ν9 band center to be 111.9 (7) cm−1, in agreement with ab initio calculations.

In this paper, we present performance analyses for a concept geostationary observing system called MAGEAQ (Monitoring the Atmosphere from Geostationary orbit for European Air Quality). The MAGEAQ mission is designed to include a TIR (thermal infrared) spectrometer and a broadband VIS (visible) radiometer; in this work we study only the TIR component (MAGEAQ-TIR). We have produced about 20 days of MAGEAQ-TIR tropospheric ozone pseudo-observations with a full forward and inverse radiative transfer pseudo-observations simulator. We have studied the expected sensitivity of MAGEAQ-TIR and we have found that it is able to provide a full single piece of information for the ozone column from surface to 6 km (about 1.0 DOF (degrees of freedom) and maximum sensitivity at about 3.0 km, on average), as well as a partially independent surface–3 km ozone column (about 0.6 DOF and maximum sensitivity at about 2.5 km, on average). Then, we have compared the tropospheric ozone profiles and the lower (surface–6 km) and lowermost (surface–3 km) tropospheric ozone column pseudo-observations to the target pseudo-reality, produced with the MOCAGE (MOdèle de Chimie Atmosphérique à Grande Echelle) chemistry and transport model. We have found very small to not significant average biases (< 1% in absolute value, for the surface–6 km TOC (tropospheric ozone column), and about −2 to −3 %, for the surface–3 km TOC) and small RMSEs (root mean square errors; about 1.3 DU (5%), for the surface–6 km TOC, and about 1.5 DU (10%), for the surface–3 km TOC). We have tested the performance of MAGEAQ-TIR at some selected small (0.2° × 0.2°) urban and rural locations. We have found that, while the vertical structures of the lower tropospheric ozone pseudo-reality are sometimes missed, MAGEAQ-TIR's lower and lowermost column pseudo-observations follow stunningly good the MOCAGE column pseudo-reality, with correlation coefficients reaching values of 0.9 or higher. Unprecedented retrieval performance for the lowermost tropospheric ozone column is shown. In any case, our MAGEAQ-TIR pseudo-observations are only partially able to replicate the MOCAGE pseudo-reality variability and temporal cycle at the very lowest layers (surface and 1 km altitude), especially at southern European urban locations, where the photochemistry signal is partially missed or shifted at higher altitudes. Temporal artifacts on the daily cycle are sometimes observed. Stratospheric-to-tropospheric exchanges during short time periods (of the order of 1 day) are detected by the MAGEAQ-TIR pseudo-observations.

Present and future satellite observations offer a great potential for monitoring air quality on daily and global basis. However, measurements from currently in orbit satellites do not allow using a single sensor to probe accurately surface concentrations of gaseous pollutants such as tropospheric ozone (Liu et al., 2010). Using single-band approaches based on spaceborne measurements of either thermal infrared radiance (TIR, Eremenko et al., 2008) or ultraviolet reflectance (UV, Liu et al., 2010) only ozone down to the lower troposphere (3 km) may be observed. A recent multispectral method (referred to as IASI+GOME-2) combining the information of IASI and GOME-2 (both onboard MetOp satellites) spectra, respectively from the TIR and UV, has shown enhanced sensitivity for probing ozone at the lowermost troposphere (LMT, below 3 km of altitude) with maximum sensitivity down to 2.20 km a.s.l. over land, while sensitivity for IASI or GOME-2 only peaks at 3 to 4 km at lowest (Cuesta et al., 2013). Future spatial missions will be launched in the upcoming years, such as EPS-SG, carrying new-generation sensors of IASI and GOME-2 (respectively IASI-NG and UVNS) that will enhance the capacity to observe ozone pollution and particularly by synergism of TIR and UV measurements. In this work we develop a pseudo-observation simulator and evaluate the potential of future EPS-SG satellite observations through IASI-NG+UVNS multispectral method to observer near-surface O3. The pseudo-real state of atmosphere (nature run) is provided by the MOCAGE (MOdèle de Chimie Atmosphérique à Grande Échelle) chemical transport model. Simulations are calibrated by careful comparisons with real data, to ensure the best consistency between pseudo-reality and reality, as well as between the pseudo-observation simulator and existing satellite products. We perform full and accurate forward and inverse radiative transfer calculations for a period of 4 days (8–11 July 2010) over Europe. In the LMT, there is a remarkable agreement in the geographical distribution of O3 partial columns, calculated between the surface and 3 km of altitude, between IASI-NG+UVNS pseudo-observations and the corresponding MOCAGE pseudo-reality. With respect to synthetic IASI+GOME-2 products, IASI-NG+UVNS shows a higher correlation between pseudo-observations and pseudo-reality, enhanced by about 11 %. The bias on high ozone retrieval is reduced and the average accuracy increases by 22 %. The sensitivity to LMT ozone is enhanced on average with 154 % (from 0.29 to 0.75, over land) and 208 % (from 0.21 to 0.66, over ocean) higher degrees of freedom. The mean height of maximum sensitivity for the LMT peaks at 1.43 km over land and 2.02 km over ocean, respectively 1.03 km and 1.30 km below that of IASI+GOME-2. IASI-NG+UVNS shows also good retrieval skill in the surface-2 km altitude range with a mean DOF (degree of freedom) of 0.52 (land) and 0.42 (ocean), and an average Hmax (altitude of maximum sensitivity) of 1.29 km (land) and 1.96 km (ocean). Unique of its kind for retrieving ozone layers of 2–3 km thickness, in the first 2–3 km of the atmosphere, IASI-NG+UVNS is expected to largely enhance the capacity to observe ozone pollution from space.

Absolute individual line intensities of numerous transitions of the fundamental ν15, ν12 and ν5 bands of oxirane (ethylene oxide, cyc-C2H4O) have been measured in the 750–950 cm−1 region using eight high-resolution Fourier transform spectra recorded at 0.002 cm−1 resolution and various pressures. These line intensities were least-squares fit using a theoretical model which takes into account the vibration–rotation interactions linking the upper state rotational levels and, therefore, accurate rotational expansions of the transition moments of the ν15, ν12 and ν5 vibrational bands were derived. Using the coefficients obtained in the fitting, a line list has been generated and used to perform comparisons with the present measurements. Also, comparisons with measurements taken at medium–low resolution of the ν15/ν12/ν5 system show excellent agreement.

Absolute individual line intensities of numerous transitions of the fundamental ν 2 and ν 10 bands of oxirane (ethylene oxide, cyc-C 2 H 4 O) have been measured in the 1420–1560 cm −1 region using seven high-resolution Fourier transform spectra recorded at 0.002 cm −1 resolution and various pressures. These line intensities were least-squares fit using a theoretical model which takes into account the vibration–rotation interactions linking the upper state rotational levels, and, therefore, accurate rotational expansion of the transition moments of the ν 2 and ν 10 vibrational bands were derived. Using the coefficients obtained in the fitting, a line list of both bands has been generated. Comparisons with measurements taken at low resolution of the ν 2 / ν 10 dyad system show excellent agreement.

To evaluate the added value brought by the next generation of IASI (Infrared Atmospheric Sounder Interferometer) instruments to monitor lower tropospheric (LT) ozone, we developed a pseudo-observation simulator, including a direct simulator of thermal infrared spectra and a full inversion scheme to retrieve ozone concentration profiles. We based our simulations on the instrumental configuration of IASI and of an IASI-like instrument, with a factor 2 improvement in terms of spectral resolution and radiometric noise. This scenario, that will be referred to as IASI/2, is one possible configuration of the IASI-NG (New Generation) instrument (the configuration called IASI-NG/IRS2) currently designed by CNES (Centre National d'Études Spatiales). IASI-NG is expected to be launched in the 2020 timeframe as part of the EPS-SG (EUMETSAT Polar System-Second Generation, formerly post-EPS) mission. We produced one month (August 2009) of tropospheric ozone pseudo-observations based on these two instrumental configurations. We compared the pseudo-observations and we found a clear improvement of LT ozone (up to 6 km altitude) pseudo-observations quality for IASI/2. The estimated total error is expected to be more than 35% smaller at 5 km, and 20% smaller for the LT ozone column. The total error on the LT ozone column is, on average, lower than 10% for IASI/2. IASI/2 is expected to have a significantly better vertical sensitivity (monthly average degrees of freedom surface–6 km of 0.70) and to be sensitive at lower altitudes (more than 0.5 km lower than IASI, reaching nearly 3 km). Vertical ozone layers of 4 to 5 km thickness are expected to be resolved by IASI/2, while IASI has a vertical resolution of 6–8 km. According to our analyses, IASI/2 is expected to have the possibility of effectively separate lower from upper tropospheric ozone information even for low sensitivity scenarios. In addition, IASI/2 is expected to be able to better monitor LT ozone patterns at local spatial scale and to monitor abrupt temporal evolutions occurring at timescales of a few days, thus bringing an expected added value with respect to IASI for the monitoring of air quality.

Fourteen Fourier transform spectra of ethylene (C 2 H 4 ) have been recorded in the 1800–2350 cm −1 spectral domain with different path-lengths and pressures and used to derive individual line intensities for lines belonging to the ν 7 + ν 8 , ν 4 + ν 8 , ν 6 + ν 10 , ν 6 + ν 7 , ν 4 + ν 6 and ν 3 + ν 10 bands. These line intensities were satisfactorily fit leading to accurate transition moment constants. A line list of positions and intensities has been generated.

International audience

The activity “Absorption Cross-Sections of Ozone” (ACSO) started in 2008 as a joint initiative of the International Ozone Commission (IO3C), the World Meteorological Organization (WMO) and the IGACO (“Integrated Global Atmospheric Chemistry Observations”) O3/UV subgroup to study, evaluate, and recommend the most suitable ozone absorption cross-section laboratory data to be used in atmospheric ozone measurements. The evaluation was basically restricted to ozone absorption cross-sections in the UV range with particular focus on the Huggins band. Up until now, the data of Bass and Paur published in 1985 (BP, 1985) are still officially recommended for such measurements. During the last decade it became obvious that BP (1985) cross-section data have deficits for use in advanced space-borne ozone measurements. At the same time, it was recognized that the origin of systematic differences in ground-based measurements of ozone required further investigation, in particular whether the BP (1985) cross-section data might contribute to these differences. In ACSO, different sets of laboratory ozone absorption cross-section data (including their dependence on temperature) of the group of Reims (France) (Brion et al., 1993, 1998, 1992, 1995, abbreviated as BDM, 1995) and those of Serdyuchenko et al. (2014), and Gorshelev et al. (2014), (abbreviated as SER, 2014) were examined for use in atmospheric ozone measurements in the Huggins band. In conclusion, ACSO recommends: (a) The spectroscopic data of BP (1985) should no longer be used for retrieval of atmospheric ozone measurements. (b) For retrieval of ground-based instruments of total ozone and ozone profile measurements by the Umkehr method performed by Brewer and Dobson instruments data of SER (2014) are recommended to be used. When SER (2014) is used, the difference between total ozone measurements of Brewer and Dobson instruments are very small and the difference between Dobson measurements at AD and CD wavelength pairs are diminished. (c) For ground-based Light Detection and Ranging (LIDAR) measurements the use of BDM (1995) or SER (2014) is recommended. (d) For satellite retrieval the presently widely used data of BDM (1995) should be used because SER (2014) seems less suitable for retrievals that use wavelengths close to 300 nm due to a deficiency in the signal-to-noise ratio in the SER (2014) dataset. The work of ACSO also showed: • The need to continue laboratory cross-section measurements of ozone of highest quality. The importance of careful characterization of the uncertainties of the laboratory measurements. • The need to extend the scope of such studies to other wavelength ranges (particularly to cover not only the Huggins band but also the comparison with the mid-infrared region). • The need for regular cooperation of experts in spectral laboratory measurements and specialists in atmospheric (ozone) measurements.

The GEISA database (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information) has been developed and maintained by the ARA/ABC(t) group at LMD since 1974. GEISA is constantly evolving, taking into account the best available spectroscopic data. This paper presents the 2015 release of GEISA (GEISA-2015), which updates the last edition of 2011 and celebrates the 40th anniversary of the database. Significant updates and additions have been implemented in the three following independent databases of GEISA. The “line parameters database” contains 52 molecular species (118 isotopologues) and transitions in the spectral range from 10−6 to 35,877.031 cm−1, representing 5,067,351 entries, against 3,794,297 in GEISA-2011. Among the previously existing molecules, 20 molecular species have been updated. A new molecule (SO3) has been added. HDO, isotopologue of H2O, is now identified as an independent molecular species. Seven new isotopologues have been added to the GEISA-2015 database. The “cross section sub-database” has been enriched by the addition of 43 new molecular species in its infrared part, 4 molecules (ethane, propane, acetone, acetonitrile) are also updated; they represent 3% of the update. A new section is added, in the near-infrared spectral region, involving 7 molecular species: CH3CN, CH3I, CH3O2, H2CO, HO2, HONO, NH3. The “microphysical and optical properties of atmospheric aerosols sub-database” has been updated for the first time since 2003. It contains more than 40 species originating from NCAR and 20 from the ARIA archive of Oxford University. As for the previous versions, this new release of GEISA and associated management software facilities are implemented and freely accessible on the AERIS/ESPRI atmospheric chemistry data center website., SCOPUS: ar.j, info:eu-repo/semantics/published

Fourier transform spectra of oxirane (ethylene oxide, c-C 2 H 4 O) have been recorded in the 730–1560 cm −1 (6.4–13.7 μm) spectral region using a Bruker IFS125HR spectrometer at a resolution of 0.0019 cm −1 . A total of six vibration bands, ν 15 , ν 12 , ν 5 , ν 3 , ν 10 and ν 2 , have been observed and analyzed. The corresponding upper state ro-vibrational levels were fit using Hamiltonian matrices accounting for various interactions. Satisfactory fits were obtained using the following polyads {15 1 , 12 1 , 5 1 } and {10 1 , 2 1 } of interacting states. As a result, an accurate and extended set of Hamiltonian constants were obtained. The following band centers were derived: ν 0 ( ν 15 ) = 808.13518(60) cm −1 , ν 0 ( ν 12 ) = 822.27955(37) cm −1 , ν 0 ( ν 5 ) = 876.72592(15), ν 0 ( ν 3 ) = 1270.37032(10) cm −1 , ν 0 ( ν 10 ) = 1471.35580(50) cm −1 and ν 0 ( ν 2 ) = 1497.83309(15) cm −1 where the uncertainties are one standard deviation.

To measure accurately OCS concentrations in planetary atmospheres, it is important to know precisely nitrogen and oxygen pressure broadening and pressure-induced shift coefficients for the lines used in the retrievals. We present in this study the corresponding coefficients for lines of the P and R branches of the 4ν 2 band of the primary isotopologue of carbonyl sulfide ( 16 O 12 C 32 S). For this purpose, infrared absorption spectra of a natural carbonyl sulfide (OCS) gas sample were recorded at an unapodized resolution of 0.004 cm −1 , at room temperature for different pressures of N 2 and O 2 , using a Bruker IFS125HR spectrometer at the LISA Laboratory in France. The line parameters were derived using the multispectrum fitting method applied to the measured shapes of the lines, including the interference effects caused by the line overlaps. The results are compared with earlier measurements and with values calculated using a semi-classical model based upon the Robert and Bonamy formalism that reproduces rather well the experimental m ( m =− J for P ( J ) lines and m = J +1 for R ( J ) lines) quantum number dependence of the N 2 and O 2 broadening coefficients. On the other hand most of the lines studied here have positive shift coefficients, which do not show any systematic dependence on m. However, in previous studies of the ν 3 , 2ν 3 and ν 2 bands, these coefficients were negative for all lines.

Fourier transform spectra of ethylene (C2H4) have been recorded in the 1800–2350 cm−1 (4.3–5.6 µm) spectral region using a Bruker IFS125HR spectrometer at a resolution of 0.004 cm−1 leading to the observation of six vibrational bands, ν 7 + ν 8, ν 4 + ν 8, ν 6 + ν 10, ν 6 + ν 7, ν 4 + ν 6 and ν 3 + ν 10. The corresponding upper state ro-vibrational levels were fit using a Hamiltonian matrix accounting for numerous interactions. A satisfactory fit could be obtained using a polyad of nine interacting states {81101, 7181, 4181, 81121, 61101, 6171, 4161, 31101, 3171} of which three (81101, 81121 and 3171) are unobserved dark states. As a result a much more accurate and extended set of Hamiltonian constants were obtained than previously derived. The following band centers were determined: ν 0(ν 7 + ν 8) = 1888.9783(20) cm−1, ν 0(ν 4 + ν 8) = 1958.2850(20) cm−1, ν 0(ν 6 + ν 10) = 2047.7589(20) cm−1, ν 0(ν 6 + ν 7) = 2178.011(60) cm−1, ν 0(ν 4 + ν 6) = 2252.8026(24) cm−1 and ν 0(ν 3 + ν 10) = 2171.2397(20) cm−1....

This paper presents observing system simulation experiments (OSSEs) to compare the relative capabilities of two geostationary thermal infrared (TIR) instruments to measure ozone (O3) and carbon monoxide (CO) for monitoring air quality (AQ) over Europe. The primary motivation of this study is to use OSSEs to assess how these infrared instruments can constrain different errors affecting AQ hindcasts and forecasts (emissions, meteorology, initial condition and the 3 parameters together). The first instrument (GEO-TIR) has a configuration optimized to monitor O3 and CO in the lowermost troposphere (LmT; defined to be the atmosphere between the surface and 3 km), and the second instrument (GEO-TIR2) is designed to monitor temperature and humidity. Both instruments measure radiances in the same spectral TIR band. Results show that GEO-TIR could have a significant impact (GEO-TIR is closer to the reference atmosphere than GEO-TIR2) on the analyses of O3 and CO LmT column. The information added by the measurements for both instruments is mainly over the Mediterranean Basin and some impact can be found over the Atlantic Ocean and Northern Europe. The impact of GEO-TIR is mainly above 1 km for O3 and CO but can also improve the surface analyses for CO. The analyses of GEO-TIR2 show low impact for O3 LmT column but a significant impact (although still lower than for GEO-TIR) for CO above 1 km. The results of this study indicate the beneficial impact from an infrared instrument (GEO-TIR) with a capability for monitoring O3 and CO concentrations in the LmT, and quantify the value of this information for constraining AQ models.