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Ouf F.X.,Institute for Radiological Protection and Nuclear Safety | Yon J.,INSA Rouen | Ausset P.,Laboratoire Interuniversitaire des Systemes Atmospheriques | Coppalle A.,INSA Rouen | Maille M.,Laboratoire Interuniversitaire des Systemes Atmospheriques
Aerosol Science and Technology | Year: 2010

The aim of this work was to compare the fractal characteristics, Df and kf, the primary particle diameter, Dpp, the gyration diameter of aggregates, Dg, and the overlap coefficient, Cov, of carbon nanoparticle aggregates produced by an ethylene diffusion flame and sampled by means of four commonly used techniques. The first method involves a thermophoretic piston probe (TPP) which inserts a TEM grid into the flame. Three other methods were applied at the outlet of a dilution device, also inserted in the flame. The first of these used a nuclepore filtration sampler (NFS), and is based on filtration of particles onto a polycarbonate membrane. The second, post dilution method, the insertion particle sampler (IPS), inserts a TEM grid, perpendicular to the aerosol flow. Similar to TPP, the last method is a thermophoretic particle sampler (TPS) sampling directly onto a TEM grid. After collection, the samples are stored in the dark either, (1) in a nitrogen filled cell at low humidity or, (2) in ambient air for studying atmospheric ageing. Good agreement was observed between TPP, TPS, and IPS indicating that the dilution induced for TPS and IPS does not significantly change the morphology of soot. On the other hand, the NFS protocol tended to overestimate the overlap coefficient and the size of primary particles and aggregates. Finally, with regard to the aging effect, we found that k f and D pp evolve slowly during storage in the atmosphere while D f, was insensitive to the storage conditions. However, the overlap coefficient increased and the gyration diameter decreased as a function of storage duration, while storage under nitrogen tended to reduce these changes. © 2010 American Association for Aerosol Research.


Pierre C.,Geosciences Environnement Toulouse | Pierre C.,Laboratoire Interuniversitaire des Systemes Atmospheriques | Bergametti G.,Laboratoire Interuniversitaire des Systemes Atmospheriques | Marticorena B.,Laboratoire Interuniversitaire des Systemes Atmospheriques | And 3 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2012

To address the challenging issue of estimating mineral dust emissions from the semi-arid Sahel, a modeling approach is developed by combining two specific models: one dedicated to the simulation of the seasonal herbaceous layer in the Sahel (STEP) and the other to the estimation of dust emissions (MB). The area of interest is the Sahelian belt (12°N-20°N, 20°W-35°E) and the simulations were performed at a 0.25° spatial resolution over a 4-year period (2004-2007). The rainfall forcing is provided by a TRMM (Tropical Rainfall Measuring Mission) satellite-derived product; the other meteorological data are ECMWF products. An empirical parameterization is used to estimate the surface roughness and its temporal dynamics according to the characteristics of the simulated vegetation in terms of surface cover and height. Where no vegetation grows, the surface properties are considered as constant in time and are derived from the POLDER-1 satellite measurements. Simulations are constrained step by step by comparisons with observations. Simulated annual dust fluxes emitted from the whole area range from approximately 100 Mt to 400 Mt depending on the year, in good agreement with previous works dealing with Saharan dust emissions. For the fringe where herbaceous vegetation can affect dust emissions, the annual dust emission fluxes range between 0.5 Mt and 20 Mt depending on the year. Inhibition of dust emissions due to the seasonal dynamics of vegetation and surface soil moisture over this fringe varies between 20% and 35%. © 2012 by the American Geophysical Union.


Bertrand M.,CNRS Center for Molecular Biophysics | Chabin A.,CNRS Center for Molecular Biophysics | Brack A.,CNRS Center for Molecular Biophysics | Cottin H.,Laboratoire Interuniversitaire des Systemes Atmospheriques | And 2 more authors.
Astrobiology | Year: 2012

To understand the chemical behavior of organic molecules in the space environment, amino acids and a dipeptide in pure form and embedded in meteorite powder were exposed in the PROCESS experiment in the EXPOSE-E facility mounted on the European Technology Exposure Facility (EuTEF) platform on board the International Space Station (ISS). After exposure to space conditions for 18 months, the samples were returned to Earth and analyzed in the laboratory for reactions caused by solar UV and cosmic radiation. Chemical degradation and possible racemization and oligomerization, the main reactions caused by photochemistry in the vacuum ultraviolet domain (VUV, wavelength range 100-200nm for photon energy from 6.2 to 12.4eV) were examined in particular. The molecules were extracted and derivatized by silylation and analyzed by gas chromatograph coupled to a mass spectrometer (GC-MS) to quantify the rate of the degradation of the compounds. Laboratory exposure in several wavelength ranges from UV to VUV was carried out in parallel in the Cologne Deutsches Zentrum für Luft- und Raumfahrt (DLR) Center and Centre de biophysique moléculaire (CBM) laboratories. The results show that resistance to irradiation is a function of the chemical nature of the exposed molecules and the wavelengths of the UV light. The most altered compounds were the dipeptide, aspartic acid, and aminobutyric acid. The most resistant were alanine, valine, glycine, and aminoisobutyric acid. Our results also demonstrate the protective effect of meteorite powder, which reemphasizes the importance of exogenic contribution to the inventory of prebiotic organics on early Earth. Key Words: Irradiation-Photochemistry-VUV-Amino acid-International Space Station-GC-MS analysis-low-Earth orbit. Astrobiology 12, 426-435. © Mary Ann Liebert, Inc.


Karras G.,Laboratory Interdisciplinaire Carnot de Bourgogne | Hertz E.,Laboratory Interdisciplinaire Carnot de Bourgogne | Billard F.,Laboratory Interdisciplinaire Carnot de Bourgogne | Lavorel B.,Laboratory Interdisciplinaire Carnot de Bourgogne | And 2 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

Field-free molecular alignment has been used in order to track the collisional relaxation occurring in a molecular gas. CO2 molecules were initially irradiated by a short linearly polarized laser pulse resulting in the increase of their rotational energy. The evolution of the subsequent ultrafast relaxation process was optically probed after irradiating the sample with a second, weaker, short pulse leading to the alignment of the preheated molecules. Using classical molecular dynamic simulations, we were able to quantitatively reproduce the experimental shapes and amplitudes of the recorded revival transients for a time interval extending from 25 to 500 ps until thermalization of the gas sample is reached. © 2014 American Physical Society.


Perrin A.,Laboratoire Interuniversitaire des Systemes Atmospheriques | Floresantognini A.,National University of Tucuman | Zeng X.,Soochow University of China | Beckers H.,University of Wuppertal | And 2 more authors.
Chemistry - A European Journal | Year: 2014

Gas-phase FTIR spectra of the ν6 (B-type) and the ν4 (C-type) fundamental bands of S2N2 (D2h) were recorded with a resolution of ≤0.004cm-1 and the vibrational spectrum of S2N2 (D2h) in solid Ar has been revisited. All IR-active fundamentals and four combination bands were assigned in excellent agreement with calculated values from anharmonic VPT2 and VCI theory based on (explicitly correlated) coupled-cluster surfaces. Accurate experimental vibrational ground- and excited-state rotational constants of 32S214N2 are obtained from a rovibrational analysis of the ν6 and ν4 fundamental bands, and precise zero-point average rz (R z(SN)=1.647694(95)Å, αz(NSN)=91.1125(33)) and semi-experimental equilibrium structures (Re(SN)=1.64182(33)Å, αe(NSN)=91.0716(93)) of S2N2 have been established. These are compared to the solid-state structure of S 2N2 and structural properties of related sulfur nitrogen compounds and to results of ab initio structure calculations. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Bussery-Honvault B.,Laboratory Interdisciplinaire Carnot de Bourgogne | Hartmann J.-M.,Laboratoire Interuniversitaire des Systemes Atmospheriques
Journal of Chemical Physics | Year: 2014

We present (far-infrared) Collision Induced Absorption (CIA) spectra calculations for pure gaseous N2 made for the first time, from first-principles. They were carried out using classical molecular dynamics simulations based on ab initio predictions of both the intermolecular potential and the induced-dipole moment. These calculations reproduce satisfactory well the experimental values (intensity and band profile) with agreement within 3% at 149 K. With respect to results obtained with only the long range (asymptotic) dipole moment (DM), including the short range overlap contribution improves the band intensity and profile at 149 K, but it deteriorates them at 296 K. The results show that the relative contribution of the short range DM to the band intensity is typically around 10%. We have also examined the sensitivity of the calculated CIA to the intermolecular potential anisotropy, providing a test of the so-called isotropic approximation used up to now in all N2 CIA calculations. As all these effects interfere simultaneously with quantitatively similar influences (around 10%), it is rather difficult to assert which one could explain remaining deviations with the experimental results. Furthermore, the rather large uncertainties and sometimes inconsistencies of the available measurements forbid any definitive conclusion, stressing the need for new experiments. © 2014 AIP Publishing LLC.


Picquet-Varrault B.,Laboratoire Interuniversitaire des Systemes Atmospheriques | Scarfogliero M.,Laboratoire Interuniversitaire des Systemes Atmospheriques | Doussin J.-F.,Laboratoire Interuniversitaire des Systemes Atmospheriques
Environmental Science and Technology | Year: 2010

Vinyl acetate is widely used in industry. It has been classified as a high-production volume (HPV) chemical in the United States. To evaluate its impact on the environment and air quality, its atmospheric reactivity toward the three main tropospheric oxidants (OH, NO3, and O3) has been investigated. Kinetic and mechanistic experiments have been conducted at room temperature and atmospheric pressure using an indoor Pyrex simulation chamber coupled to Fourier transform infrared (FTIR) and UV-visible spectrometers. Rate constants for the reactions of vinyl acetate with OH, NO3, and O3 were equal to (2.3 ± 0.3) - 10 11, (7.3 ± 1.8) - 1015, and (3.0 ± 0.4) - 1018 cm3 molecule-1 s-1, respectively. From these data, tropospheric lifetimes of vinyl acetate have been estimated as follows: τOH = 6 h, τNO3 = 6 days, and τO3 = 5 days. This demonstrates that reaction with OH radicals is the main tropospheric loss process of this compound. From the mechanistic experiments, main oxidation products have been identified and quantified and oxidation schemes have been proposed for each studied reaction. © 2010 American Chemical Society.


Flaud J.-M.,Laboratoire Interuniversitaire des Systemes Atmospheriques | Lafferty W.J.,U.S. National Institute of Standards and Technology | Kwabia Tchana F.,Laboratoire Interuniversitaire des Systemes Atmospheriques | Perrin A.,Laboratoire Interuniversitaire des Systemes Atmospheriques | Landsheere X.,Laboratoire Interuniversitaire des Systemes Atmospheriques
Journal of Molecular Spectroscopy | Year: 2012

Fourier transform spectra of oxirane (ethylene oxide, c-C 2H 4O) 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. © 2011 Elsevier Inc. All rights reserved.


Lafferty W.J.,U.S. National Institute of Standards and Technology | Flaud J.-M.,Laboratoire Interuniversitaire des Systemes Atmospheriques | Tchana F.K.,Laboratoire Interuniversitaire des Systemes Atmospheriques
Molecular Physics | Year: 2011

Fourier transform spectra of ethylene (C 2H 4) have been recorded in the 1800-2350cm -1 (4.3-5.6μm) spectral region using a Bruker IFS125HR spectrometer at a resolution of 0.004cm -1 leading to the observation of six vibrational bands, v 7+v 8,v 4+v 8,v 6+v 10, v 6+v 7,v 4+v 6 and v 3+v 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 {8 110 1,7 18 1,4 18 1,8 112 1,6 110 1,6 17 1,4 16 1,3 110 1,3 17 1} of which three (8 110 1, 8 112 1 and 3 17 1) 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: v 0(v 7+v 8)=1888. 9783(20)cm -1, v 0(v 4+v 8)=1958. 2850(20)cm -1, v 0(v 6+v 10)=2047. 7589(20)cm -1, v 0(v 6+v 8)=2178.011(60) cm -1, v 0(v 4+v 6)=2252.8026(24)cm -1 and v 0(v 3+v 10)=2171.2397(20) cm -1. Finally, a synthetic spectrum that could be useful for ethylene detection in planetary atmospheres was generated. Copyright © 2011 Taylor and Francis Group, LLC.


Saiagh K.,Laboratoire Interuniversitaire des Systemes Atmospheriques | Cloix M.,Laboratoire Interuniversitaire des Systemes Atmospheriques | Fray N.,Laboratoire Interuniversitaire des Systemes Atmospheriques | Cottin H.,Laboratoire Interuniversitaire des Systemes Atmospheriques
Planetary and Space Science | Year: 2014

The photochemistry of an organic compound in extraterrestrial environments is related to its photoabsorption cross sections in the VUV/UV range (<300 nm). Such data, especially in the VUV range (<200 nm) are quite scarce in the literature. This paper presents an experimental setup and associated methodology to measure VUV/UV spectra of thin films of organic molecules. The case of adenine is extensively discussed as an example study. The absorption cross sections spectrum of adenine between 115 and 300 nm is measured from transmission measurements and accurate calculation of the thickness of our samples set thanks to interferometry techniques and infrared spectrometry. From these data, the infrared integrated band strength of solid adenine between 3600 and 1970 cm-1 has also been measured and is equal to 7.9×10-16±4% cm molecule-1. The use of the VUV/UV spectrum to estimate the photolysis rate constant is discussed and compared to direct kinetic measurements available in the literature for low Earth orbit experiments. However the lack of measurements of the photodissociation quantum yield as a function of the wavelength prevents a precise calculation. VUV/UV cross section spectrum is yet a necessity to conduct either proper kinetic studies on optically thin samples (less than 2 nm in the VUV for adenine) or an appropriate modeling for optically thick samples. © 2013 Elsevier Ltd.

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