The hydroxyl radical (OH) plays a central role in the chemistry of the atmosphere. In addition to controlling the lifetimes of many trace gases important to issues of global climate change and stratospheric ozone depletion, the OH radical initiates the oxidation of carbon monoxide and volatile organic compounds which in the presence of nitrogen oxides can lead to the production of ground-level ozone and secondary organic aerosols, the primary components of photochemical smog. Accurate measurements of OH radical concentrations in the atmosphere can provide critical tests of our understanding of atmospheric chemistry and ground-level ozone production in urban and rural areas. Because of its high reactivity, mixing ratios of OH in the atmosphere are extremely low (typically less than 0.1 parts per trillion) and its chemical lifetime very short (less than 1 second). As a result, measurements of OH present a serious analytical challenge, especially on the timescale necessary to test our understanding of the fast photochemistry of the atmosphere. This presentation will describe the Indiana University laser-induced fluorescence instrument for the sensitive detection of OH radicals in the atmosphere, including recent results from several measurement campaigns in both urban and rural environments.

We report experimental measurements and theoretical calculations for He-broadened Lorentz half-width coefficients and He- pressure-shift coefficients of 45 carbon monoxide transitions in the 1-0 band. The high-resolution spectra analyzed in this study were recorded over a range of sample temperatures between 296 and 80 K. The He-broadened line parameters and their temperature dependences were retrieved using a multispectrum nonlinear least squares analysis program. A previous analysis of these spectraA. W. Mantz et al., J. Molec. Structure 742 (2005) 99-110.sed only the Voigt line shape. In the present study four line shape models were compared including Voigt, speed dependent Voigt, Rautian (to take into account confinement narrowing) and Rautian with speed dependence. The line mixing coefficients have been calculated using the Exponential Power Gap scaling law. We were unable to retrieve the temperature dependence of the line mixing coefficients. The current measurements and theoretical results are compared with other published results, where appropriate.

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A. W. Mantz et al., J. Molec. Structure 742 (2005) 99-110.u

In this study we have re-analyzed high-resolution spectra of pure CO and CO broadened by hydrogen recorded in the spectral range of the first overtone band.V. Malathy Devi et al., J. Mol. Spectrosc. 228 (2004) 580-592.e have used four different line shapes in the multispectrum analysis (Voigt, speed dependent Voigt, Rautian, and Rautian with speed dependence) and compared the resulting line shape parameters. The line mixing coefficients have been calculated using the Exponential Power Gap and the Energy Corrected Sudden scaling laws. A classical approach was applied to calculate CO line widths in CO-H₂ and CO-CO collisions. The formulas of classical impact theoryR. G. Gordon, J. Chem. Phys. 44 (1966) 3083-3089; ibid., 45 (1966) 1649-1655.re used for calculation of dipole absorption half-widths along with exact 3D Hamilton equations for simulation of molecular motion. The calculations utilize Monte Carlo averaging over collision parameters and simple interaction potential (Tipping-Herman + electrostatic).J.-P. Bouanich and A. Predoi-Cross, J. Molec. Structure 742 (2005) 183-190.A. Predoi-Cross, J.-P. Bouanich, D. Chris Benner, A. D. May, and J. R. Drummond, J. Chem. Phys. 113 (2000) 158-168. Molecules are treated as rigid rotors. The dependences of CO half-widths on rotational quantum number J ≤ 24 are computed and compared with measured data at room temperature.

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V. Malathy Devi et al., J. Mol. Spectrosc. 228 (2004) 580-592.W R. G. Gordon, J. Chem. Phys. 44 (1966) 3083-3089; ibid., 45 (1966) 1649-1655.a J.-P. Bouanich and A. Predoi-Cross, J. Molec. Structure 742 (2005) 183-190.

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Retrievals of atmospheric composition from near-infrared measurements require measurements of airmass to better than the desired precision of the composition. The oxygen bands are obvious choices to quantify airmass since the mixing ratio of oxygen is fixed over the full range of atmospheric conditions. The OCO-2 mission is currently retrieving carbon dioxide concentration using the oxygen A-band for airmass normalization. The 0.25% accuracy desired for the carbon dioxide concentration has pushed the required state-of-the-art for oxygen spectroscopy. To measure O₂ A-band cross-sections with such accuracy through the full range of atmospheric pressure requires a sophisticated line-shape model (Rautian or Speed-Dependent Voigt) with line mixing (LM) and collision induced absorption (CIA). Models of each of these phenomena exist, however, this work presents an integrated self-consistent model developed to ensure the best accuracy. It is also important to consider multiple sources of spectroscopic data for such a study in order to improve the dynamic range of the model and to minimize effects of instrumentation and associated systematic errors. The techniques of Fourier Transform Spectroscopy (FTS) and Cavity Ring-Down Spectroscopy (CRDS) allow complimentary information for such an analysis. We utilize multispectrum fitting software to generate a comprehensive new database with improved accuracy based on these datasets. The extensive information will be made available as a multi-dimensional cross-section (ABSCO) table and the parameterization will be offered for inclusion in the HITRANonline database.

NASA’s Orbiting Carbon Observatory missions require spectroscopic parameterization of the Oxygen A-Band absorption (757-775 nm) with unprecedented detail to meet the objective of delivering space-based column CO2 measurements with an accuracy of better than 1 ppm, and spectroscopic parameters with accuracies at the 0.1% level. To achieve this it is necessary for line shape models to include deviations from the Voigt line shape, including the collisional effects of speed-dependence, line mixing (LM), and collision-induced absorption (CIA). LM and CIA have been difficult to quantify in FTIR and CRDS spectra which have been limited to lower pressure measurements. A photoacoustic spectrometer has been designed to study the pressure- dependence of the spectral line shape up to pressures of 5 atm, where LM and CIA contribute significantly to the A-Band absorption. This spectrometer has a high signal-to-noise (S/N) of about 10,000 and frequency accuracy of 2 MHz. In addition, temperature-dependent effects on the line shape are studied using PID-controlled cooled nitrogen flow/ heater system. The latest acquired spectra and analysis are reported here.

The physico-chemistry of the Earth's atmosphere has been one of the main subjects of studies over last years. In particular, the composition of the atmosphere is indeed very important to understand chemical processes linked to depletion of stratospheric ozone and greenhouse effect. The vertical concentration profiles of atmospheric gases can be provided by remote sensing measurements, but they require the accurate knowledge of the parameters involved: line positions, transition intensities, pressure-broadened half-widths, pressure-induced frequency shifts and their temperature dependence. In particular, the collisional broadening parameters have a crucial influence on the accuracy of spectra calculations and on reduction of remote sensing data. Rotational spectroscopy, thanks to its intrinsic high resolution, is a powerful tool for providing most of the information mentioned above: accurate or even very accurate rotational transition frequencies, accurate spectroscopic as well as hyperfine parameters, accurate pressure-broadening coefficients and their temperature dependence. With respect to collisional phenomena and line shape analysis studies, by applying the source frequency modulation technique it has been found that rotational spectroscopy may provide very good results: not only this technique does not produce uncontrollable instrumental distortions or broadenings, but also, having an high sensitivity, it is particularly suitable for this kind of investigations. A number of examples will be presented to illustrate the work carried out at the Laboratory of Millimeter/submillimeter-wave Spectroscopy of Bologna in the field of atmospheric studies.

Sulfur dioxide is a molecule that have a great interest in different domains: for atmospheric and planetology chemistry, it is also ubiquitous and abundant in interstellar medium. If the ¹⁶O species were extensively studied, this is not the case of the ¹⁸O isotopologues. The aim of this study is first to complete the rotational spectra of the ground state with these new measurements up to 1.5 THz, previous measurements are up to 1050 GHz for the ³²S¹⁶O¹⁸O speciesBelov, S. P.; et al., 1998, J. Mol. Spectrosc. 191, 17 and 145 GHz concerning the ³²S¹⁸O₂ speciesLindermayer, J.; et al., 1985, J. Mol. Spectrosc. 110, 357 The second part is making a global fit of the rotational and vibrational transitions for the excited vibrational states. For the v₂ band, we will complete the recent I.R. analysisGueye, F.; et al. Mol. Phys. in press About the triad (v₁, 2v₂, v₃): ³²S¹⁸O₂ species was studiedUlenikov, O. N.; et al., 2015, JQSRT 166, 13 but not the ³²S¹⁶O¹⁸O one.
The FT-IR spectra were recorded on the AILES Beamline at Synchrotron SOLEIL using the Synchrotron light source, coupled to the Bruker IFS125HR Fourier transform spectrometerBrubach, J.; et al., 2010, AIP Conf. Proc. 1214, 81 The THz spectra were obtained from 150 to 1500 GHz using the Lille's solid state spectrometerZakharenko, O.; et al., 2015, J. Mol. Spectrosc. 317, 41 The analysis is in progress, the latest results will be presented.
Support from the French Laboratoire d'Excellence CaPPA (Chemical and Physical Properties of the Atmosphere) through contract ANR-10-LABX-0005 of the Programme d'Investissements d'Avenir is acknowledged

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Belov, S. P.; et al., 1998, J. Mol. Spectrosc. 191, 17, Lindermayer, J.; et al., 1985, J. Mol. Spectrosc. 110, 357. Gueye, F.; et al. Mol. Phys. in press. Ulenikov, O. N.; et al., 2015, JQSRT 166, 13, Brubach, J.; et al., 2010, AIP Conf. Proc. 1214, 81. Zakharenko, O.; et al., 2015, J. Mol. Spectrosc. 317, 41.

Ozone (O₃) is crucial for studies of air quality, human and crop health, and radiative forcing. Spectroscopic remote sensing techniques have been extensively employed to investigate ozone globally and regionally. Infrared intensities of ≤ 1% accuracy are desired by the remote sensing community. The accuracy of the current state-of-the-art infrared ozone intensities is on the order of 4-10%, resulting in ad hoc intensity scaling factors for consistent atmospheric retrievals. The large uncertainties on the infrared ozone intensities arise from the fact that pure ozone is very difficult to generate and sustain in the laboratory. Best estimates have employed IR/UV cross beam experiments to determine the accurate O₃ volume mixing ratio of the sample through its standard cross section value at 254 nm.
This presentation reports our effort to improve the absolute accuracy of ozone intensities in the 9-11 μm region via a transfer of the precision of the rotational dipole moment onto the infrared measurement (MW/IR). Our approach was to use MW/IR cross beam experiments and determine the O₃ mixing ratio through alternately measuring pure rotation ozone lines from 692 to 779 GHz. The uncertainty of these pure rotation line intensities is better than 0.1%. The sample cell was a slow flow cross cell and the total pressure inside the sample cell was maintained constant through a proportional–integral–derivative (PID) flow control. Five infrared O₃ spectra were obtained, with a path length of 3.74 m, pressures ranging from 30 to 120 mTorr, and mixing ratio ranging from 0.5 to 0.9. A multi spectrum fitting technique was employed to fit all the FTS spectra simultaneously. The results show that we can determine intensities of the 9.6μm band with absolute accuracy better than 4%.

Phosgene (COCl₂) is relatively more abundant in the stratosphere, but is also present in the troposphere in spite of a shorter lifetime (seventy days). Monitoring its concentration by remote sounding of the upper atmosphere is of importance, since some of its strong infrared absorptions, occurring in the important 8-12 μm atmospheric window, hinder the correct retrieval of Freon-11 concentration profilesG. Toon, J.F. Blavier, B. Sen and B.J. Drouin, Geophys. Res. Lett., 28/14 (2001) 2835. Indeed, the infrared absorptions used to retrieve this ozone depleting compound occur in the same spectral region. Phosgene, presents two fundamental bands in the 250 - 480 cm⁻¹spectral region, with the lowest (ν₃) near 285 cm⁻¹. These are responsible for hot bands, not yet analysed but of great importance for accurate modeling of the 5.47 μm (ν₁) and 11.75 μm (ν₅) spectral regions and consequently the correct retrieval of Freon-11 atmospheric absorption profiles. High-resolution absorption spectra of phosgene have been recorded at 0.00102 cm⁻¹resolution in the 250–480 cm⁻¹region by Fourier transform spectroscopy at synchrotron SOLEIL. Due to the spectral congestion, the spectra have been recorded at low temperature (197 K) using a 93.15 m optical path length cryogenic cellF. Kwabia Tchana, F. Willaert, X. Landsheere, J.-M. Flaud, L. Lago, M. Chapuis, P. Roy and L. Manceron, Rev. Sci. Inst., 84 (2013) 093101. This enables the first detailed far-infrared analyzes of the ν₃ and ν₆ bands of the ³⁵Cl₂CO and ³⁵Cl³⁷ClCO isotopologues of phosgene. Using a Watson-type Hamiltonian, it was possible to reproduce the upper state rovibrational infrared energy levels to within the experimental accuracy. The results will be presented in this talk.

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G. Toon, J.F. Blavier, B. Sen and B.J. Drouin, Geophys. Res. Lett., 28/14 (2001) 2835.. F. Kwabia Tchana, F. Willaert, X. Landsheere, J.-M. Flaud, L. Lago, M. Chapuis, P. Roy and L. Manceron, Rev. Sci. Inst., 84 (2013) 093101..