Comparison of ground-based FTIR and Brewer O3 total column with data from two different IASI algorithms and from OMI and GOME-2 satellite instruments

An intercomparison of ozone total column measurements derived from various platforms is presented in this work. Satellite data from Infrared Atmospheric Sounding Interferometer (IASI), Ozone Monitoring Instrument (OMI) and Global Ozone Monitoring Experiment (GOME-2) are compared with data from two ground-based spectrometers (Fourier Transform Infrared spectrometer FTIR and Brewer), located at the Network for Detection of Atmospheric Composition Change (NDACC) super-site of Izaña (Tenerife), measured during a campaign from March to June 2009. These ground-based observing systems have already been demonstrated to perform consistent, precise and accurate ozone total column measurements. An excellent agreement between ground-based and OMI/GOME-2 data is observed. Results from two different algorithms for deriving IASI ozone total column are also compared: the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT/ESA) operational algorithm and the LISA (Laboratoire Inter-universitaire des Systèmes Atmosphériques) algorithm. A better agreement was found with LISA's analytical approach based on an altitude-dependent Tikhonov-Philips regularization: correlations are 0.94 and 0.89 compared to FTIR and Brewer, respectively; while the operational IASI ozone columns (based on neural network analysis) show correlations of 0.90 and 0.85, respectively, compared to the O3 columns obtained from FTIR and Brewer

Tropospheric and total ozone columns over Paris (France) measured using medium-resolution ground-based solar-absorption Fourier-transform infrared spectroscopy

Ground-based Fourier-transform infrared (FTIR) solar absorption spectroscopy is a powerful remote sensing technique providing information on the vertical distribution of various atmospheric constituents. This work presents the first evaluation of a mid-resolution ground-based FTIR to measure tropospheric ozone, independently of stratospheric ozone. This is demonstrated using a new atmospheric observatory (named OASIS for "Observations of the Atmosphere by Solar absorption Infrared Spectroscopy"), installed in Créteil (France). The capacity of the technique to separate stratospheric and tropospheric ozone is demonstrated. Daily mean tropospheric ozone columns derived from the Infrared Atmospheric Sounding Interferometer (IASI) and from OASIS measurements are compared for summer 2009 and a good agreement of −5.6 (±16.1) % is observed. Also, a qualitative comparison between in-situ surface ozone measurements and OASIS data reveals OASIS's capacity to monitor seasonal tropospheric ozone variations, as well as ozone pollution episodes in summer 2009 around Paris. Two extreme pollution events are identified (on the 1 July and 6 August 2009) for which ozone partial columns from OASIS and predictions from a regional air-quality model (CHIMERE) are compared following strict criteria of temporal and spatial coincidence. An average bias of 0.2%, a mean square error deviation of 7.6%, and a correlation coefficient of 0.91 is found between CHIMERE and OASIS, demonstrating the potential of a mid-resolution FTIR instrument in ground-based solar absorption geometry for tropospheric ozone monitoring

Ground-based FTIR measurements of O3- and climate-related gases in the free troposphere and lower stratosphere

In the frame of the EC project UFTIR (Time series of Upper Free Troposphere observations from a European ground-based FTIR network), a common strategy for an optimal determination of the chemical composition in the free troposphere and lower stratosphere with ground-based Fourier-transform infrared (FTIR) spectrometers is being developed. The project focuses on 6 target species that are O3, CO, CH4, N2O, C2H6 and CHClF2 (HCFC-22). The strategy consists in selecting the most appropriate parameters to retrieve vertical concentration profiles from solar FTIR spectra. Among the important parameters are the spectral microwindows: they have been optimised to maximise the information content and to minimize the influence of poorly known spectroscopic data and interfering species

Emission line broadening in combustion products. Static and dynamic studies of gas mixtures

Because of the new restrictions on pollutant levels in industrial combustion processes, it is necessary to determine and monitor the concentration and temperature distributions of combustion products. Emission and absorption spectroscopy have been investigated for passive and non-intrusive measurements to provide information about species concentrations and gas temperatures under severe conditions (T > 2000 K). The physics governing radiation emission and propagation are directly influenced by gas species, composition and concentrations, hence a high degree of theoretical and experimental analysis of typical gas samples is required to elaborate emission models. This paper intends to study high pressure effects on H2O line broadening. An experimental laboratory setup for high temperature and high pressure dynamic gas analysis is presented. The H2O vapor is produced as a burnt gas from a combustion of a hydrogen-air mixture in an enclosure. Initial measurements were performed in the visible range, in the 0.8 µm band of water with a grating spectrometer and a CCD detector

LINE STRENGTH MEASUREMENTS IN THE ν2\nu_2 BAND OF \mbox{H}_2{^{18}\mbox{O}}

Toth, {\em J.\ Molec.\ Spectrosc.Toth, {\em J.\ Opt.\ Soc.\ Am.\ BCoudert, Wagner, Birk, Baranov, Lafferty, and Flaud, {\em J.\ Molec.\ Spectrosc.Author Institution: Institute of Experimental Meteorology, Lenina 82; Obninsk, Kaluga region 249020, Russia; LISA, CNRS/Universites Paris 12 et 7, 61 Avenue du; General de Gaulle, 94010 Creteil, FranceSpectra of an \mbox{H}_2{^{18}\mbox{O}} enriched sample of water vapor were recorded from 1780 to 4500~cm$^{-1}$, at room temperature, with a Bruker IFS-125 instrument and a liquid nitrogen cooled InSb detector. A single path, 24~cm long, glass cell with ZnSe windows was filled with \mbox{H}_2{^{18}\mbox{O}} water vapor at 97.1\% purity from CDN Isotopes. For the various spectra, pressures ranging from 4.3 to 18.4~Torr were measured with two different MKS Baratron gauges having 10 and 100~Torr pressure limits. The unapodized spectral resolution was 0.002~cm$^{-1}$. Line strengths were retrieved from these spectra for transitions belonging to the $\nu_2$ band with the help of a computer program determining simultaneously line positions, strengths, and linewidths by nonlinear least-squares fitting. The new line strength values were analyzed with those already available for rotational transitions within the ground vibrational state~{\bf 190} (1998) 379.} and for $\nu_2$ band~{\bf 9} (1992) 462.} transitions. In order to account for the anomalous centrifugal distortion displayed by water, this line intensity analysis was performed using the Bending-Rotation Hamiltonian approach.~{\bf 251} (2008) 339.

FOURIER-TRANSFORM SPECTROSCOPY OF 14^{14}NH3_3 AND 15^{15}NH3_3 IN THE NEAR-INFRARED

Author Institution: Laboratoire Interuniversitaire des Systemes Atmospheriques (LISA), CNRS and Universites Paris-7 et -12, Creteil, France; Laboratorio de Espectroscopia e Laser, Instituto de Fisica, Universidade Federal Fluminense, Niteroi, Rio de Janeiro, BrazilThe near-infrared absorption spectrum of NH$_3$ is an interesting opportunity for atmospheric {\it in-situ} measurements of this species using tuneable diode-lasers. For this purpose, accurate line positions and intensities are indispensable. In the past, several studies of the absorption spectrum of $^{14}$NH$_3$ in the near-infrared were carried out, using Fourier-transform$^{1}$ and tuneable diode-laser spectroscopy.$^{2-4}$ More recently, high-resolution diode-laser spectra of $^{15}$NH$_3$ were analyzed for the first time.$^{5}$ The lines of $^{14}$NH$_3$ in this region are also useful for wavenumber calibration of absorption spectra obtained with tuneable lasers. In our group, we have recently investigated the possibility to detect atmospheric NH$_3$ using photoacoustic laser spectroscopy in the 1.5 $\mu$m region, and observed several discrepancies between individual line positions and intensities observed in our and previous studies$^{1,4}$, as already noticed by other groups.$^{2,5}$ In order to solve this problem we have measured new absorption spectra of $^{14}$NH$_3$ (and also of $^{15}$NH$_3$) in the 6300-7500 cm$^{-1}$ region using a Bruker IFS 120-HR Fourier-transform spectrometer. The length of the absorption cell was 30 cm. The NH$_3$ pressures employed were around 30 mbar, and the spectral resolution used was 0.02 cm$^{-1}$, leading to linewidths (Full-Width at Half-Maximum) of about 0.03 cm$^{-1}$. Based on these spectra, we have produced a list of individual line positions and line intensities at 296 K. Comparisons with the previous studies$^{1-5}$ will be presented. }, {\bf 162}, 230-245 (1993).} }, {\bf 40}, 2031-2042 (2004).} }, {\bf 45}, 31-45 (2004).} }, {\bf 28}, 59-66 (2004).} }, in press (2006).

Measurements and modeling of absorption by CO 2 + H 2 O mixtures in the spectral region beyond the CO 2 ν 3 -band head

International audienceIn this work, we measured the absorption by CO 2 + H 2 O mixtures from 2400 to 2600 cm −1 which corresponds to the spectral region beyond the ν 3 band head of CO 2. Transmission spectra of CO 2 mixed with water vapor were recorded with a high-resolution Fourier-transform spectrometer for various pressure, temperature and concentration conditions. The continuum absorption by CO 2 due to the presence of water vapor was determined by subtracting from measured spectra the contribution of local lines of both species, that of the continuum of pure CO 2 as well as of the self-and CO 2-continua of water vapor induced by the H 2 O-H 2 O and H 2 O-CO 2 interactions. The obtained results are in very good agreement with the unique previous measurement (in a narrower spectral range). They confirm that the H 2 O-continuum of CO 2 is significantly larger than that observed for pure CO 2. This continuum thus must be taken into account in radiative transfer calculations for media involving CO 2 + H 2 O mixture. An empirical model, using sub-Lorentzian line shapes based on some temperature-dependent correction factors χ is proposed which enables an accurate description of the experimental results

ABSOLUTE LINE INTENSITIES OF HONO AND DONO IN THE FAR INFRARED AND REDETERMINATION OF THE ENERGY DIFFERENCE BETWEEN THE TRANS AND CIS SPECIES OF NITROUS ACID

Author Institution: Laboratoire Interuniversitaire des Systemes Atmospheriques, CNRS et Universites Paris 7 et Paris 12, 61 av. General de Gaulle, 94010, Creteil, France; Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, GermanyNitrous acid is an important species in the atmosphere of the Earth since it is a significant daytime source of OH radicals, known to play an important role in tropospheric ozone formation. It is also a molecule of interest for molecular dynamics and \emph{ab-initio} calculations. In this work, relative line intensities of \emph{trans-} and \emph{cis-}HONO and ??DONO have been measured using absorption spectra in the far-infrared previously recorded by high-resolution Fourier-transform spectroscopy . These relative line intensities measurements were fitted in a least-squared procedure leading to the determination of the b-component of the permanent dipole moments for those species and their rotational corrections. Scaling those values to the absolute values derived from Stark effect measurements allowed us to re-determine the energy difference between the two isomers ($\Delta E_{HONO}$) to be 107$\pm$26 cm$^{-1}$. This value is in good agreement with previous experimental studies calculations and with recent high-level \emph{ab-initio} calculations