Infrared quantitative spectroscopy and atmospheric satellite measurements

Transcription

1 Infrared quantitative spectroscopy and atmospheric satellite measurements Jean-Marie Flaud Laboratoire Interuniversitaire des Systèmes Atmosphériques CNRS, Universités Paris Est Créteil et Paris Diderot

2 OUTLINE THE MIPAS EXPERIMENT Phosgene (COCl 2 ), H 14 NO 3, Questions/Comments

3 MIPAS The MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) instrument is a Fourier transform spectrometer that measures earthlimb emissions in the cm 1 range with an unapodized resolution of cm 1, and with high sensitivity, The spectral resolution of the instrument permits to obtain the atmospheric spectra with an unprecedented accuracy. Day and night

4 A MIPAS SPECTRUM (J.-M. Flaud and H. Oelhaf, Infrared spectroscopy and the terrestrial atmosphere, C. R. Physique 5 (2004) )

5 Phosgene (COCl 2 ) in the UTLS: vertical distribution from MIPAS observations using new spectroscopic data at 11.65µm

6 Phosgene in the UTLS region Why to study phosgene? It is absorbing in the same spectral region as CFC11! Phosgene (COCl 2 ) in the 20th century was mainly used by chemical industry in the preparation of insecticides, pharmaceuticals and herbicides.

7 Previous studies First study about atmospheric phosgene: Singh (1976) studied the surface distribution of phosgene using data from six stations in California. Wilson et al. (1988) measured phosgene at various altitudes during an aircraft flight over Germany. Toon et al. (2001) used the Jet Propulsion Laboratory - MkIV Interferometer, onboard stratospheric balloons, to retrieve different VMR profiles of phosgene from 1992 to First satellite measurements of stratospheric phosgene: Fu et al. (2007) used ACE-FTS measurements to make the first analysis of the global distribution of phosgene. Using data acquired by the same experiment, Brown et al. (2011) focused their work on the study of phosgene inter-annual variations. But these studies were not using high resolution spectra

8 Cross sections from PNNL are not sufficient because not covering the atmoshere temperatue range High resolution spectra of the ν 5 bands of CO 35 Cl 37 Cl, CO 35 Cl 37 Cl and CO 37 Cl 37 Cl were recorded and analysed

9 Estimation of the abundances of the various isotopic species of phosgene Abundance Abundance 35 Cl CO 35 Cl 35 Cl Cl CO 35 Cl 37 Cl CO 37 Cl 37 Cl

10 High resolution analysis of the ν 1 and ν 5 bands of phosgene 35 Cl 2 CO and 35 Cl 37 ClCO FTS spectra of phosgene have been recorded in the μm and 5.47 μm spectral regions at a resolution of ~ cm -1 leading to the observation of the ν 5 and ν 1 bands of the three isotopologues 35 Cl 2 CO, 35 Cl 37 ClCO and 37 Cl 2 CO. The upper state ro-vibrational levels were fit to within the experimental accuracy i.e. ~0.17 x10-3 cm -1. using Hamiltonians accounting for resonance effects when necessary and in this way it proved possible to simulate the observed spectra to within experimental accuracy.

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12 Hot bands

13 Phosgene low resolution spectrum [PNNL] around 11.65µm

14 ISOTOPIC SPECIES Bands calculated to model the absorption cross sections of Phosgene at 11.65µm VIBRATION AL BAND INTENSITY (cm-1 / molecule.cm-2) Number of lines GROUND Cl2 >V D Cl2 V3-->V3+V D Cl2 V6-->V5+V D Cl2 V2-->V2+V D GROUND Cl2 >V D Cl2 V3-->V3+V D Cl2 V6-->V5+V D Cl2 GROUND-- >V D (The intensities account for the isotopic abundances)

15 Observed (red) and calculated (green) X- sections at 5 C Missing hot band

16 Summary and conclusions We studied the phosgene global distribution using: the new phosgene spectroscopic database, the new MTR functionality of the ORM (COCl 2 and CFC-11 joint retrieval), more than profiles retrieved from MIPAS in the 2008 year. MIPAS allowed to highlight the seasonal and latitudinal variations: largest values in the tropical regions, less peaked vertical distributions in the mid-latitude and polar regions, no seasonal variability in the UTLS apart for a weak seasonality in the polar regions, the lowest average values occur in the South Polar Winter (JJA).

17 Results Polar bands The average profiles do not exceed 30 pptv with maxima at around 100 hpa. Only in the polar regions we observe a weak seasonality.

18 MIPAS database Goal: Retrieve HNO3 using simultaneously the 11 and 7.6 µm regions New H 14 NO 3 line parameters at 7.6 µm derived from MIPAS satellite measurements and laboratory intensity measurements

19 MIPAS MW & n 9 {n 5,2n 9 ) {n 4,n 3 } n cm cm , 896cm , 1326cm cm - Far-IR 22µm 11µm 7.6µm Enables a simultaneous measurement of HNO 3 both at 11 µm & 7.6 µm using MIPAS spectra

20 Process The 11 µm band line parameters were kept as they are in HITRAN or GEISA As a starting point, we use the 2013 list of line positions and relative line intensities at 7.6 µm The new 7.6 µm parameters (line positions and relative intensities) were improved relatively to those at 11 µm.

21 Strategy for improving the 7.6 µm region (H 14 NO 3 ) We used and combined three sets of experimental data MIPAS spectra (orbit from 24 january 2003) A list of laboratory experimental (individual) line positions and intensities measured in the 7.6 µm region using FTS spectra recorded in 2004 at Giessen. The Pacific Northwest Laboratory (PNNL) cross sections

22 Hamiltonian matrix

23 Old database at 7.6 µm

24 New database at 7.6 µm

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27 About 350 line intensities were measured using an FTS spectrum recorded in the 7.6 µm region (P?) Ratio R=MIPAS-new/ Measured line intensities

28 The Pacific Northwest Laboratory cross sections ( HITRAN-2012 HITRAN-2012

29 Conclusion Atmospheric spectra can be used to improve spectroscopic databases

30 What are the problems? 1 The possibility of the retrievals is directly linked to the availablity of the spectroscopic parameters 2 The quality of the retrievals is directly linked to the quality of the spectroscopic parameters 3 Many species( O 3, HCHO, H 2 O,C 2 H 6, ) are measured in various spectral regions with different instruments How to perform really meaningful comparisons of concentration profiles obtained by spectrometric measurements in various spectral regions How to perform simultaneous retrievals in different spectral regions if the corresponding the line parameters are not consistent

31 SEED QUESTIONS What are the spectroscopic needs? Where are recognised weaknesses? Which new species are relevant and why? Together with other groups! What about line shapes, continuum absorption How is the consistency between different wavelength ranges (e.g. UV, SWIR, TIR)? Auxiliary data: what/how/why? (e.g. microwindows, climatology)

32 Spectroscopy for infrared limb/nadir sounders Some comments: Only a small amount of the MIPAS data is used in the level 2 analysis Is redundant and new information properly used? Independent set of (micro)windows in level 2 can be used to assess data product uncertainty including spectroscopy Status of IR spectroscopic databases Still missing quantified uncertainties ( Especially for air broadening and temperature dependences, and air pressure shifts and temperature dependences). Line narrowing almost entirely missing In case of absorption cross sections: often insufficient spectral resolution, missing air pressure and temperature dependences, errors due to temperature inhomogeneity Some molecules like CO2, H2O, CO, HCl, HF, N2O and O3 seems to be in reasonable shape

33 Spectroscopy for infrared limb/nadir sounders Error propagation into level 2 Global scalar error for trace gas profiles (contributing errors are scalar line intensity errors): this error is not fully critical since, in principle, it can be removed by validation. However accuracies of 1-10% are extremely difficult to reach Need to use laboratory and/or atmospheric spectra Spectroscopic errors with contributions varying with pressure and temperature and thus height, geolocation, time of year, day night are extremely difficult to estimate. Question: Can rigorous retrieval simulations for the MIPAS data products regarding these issues give an answer? How can the microwindow selection tackle these issues?

34 Spectroscopy for infrared limb/nadir sounders Some ideas to improve the spectroscopic databases: Identify species where specific scientific issues require an improved data quality and consistency Test the impact of spectroscopic error by doing retrievals with different microwindow sets, however this does not unambiguously point out to spectroscopic errors Perform the right spectroscopic studies

35 I WOULD LIKE TO THANK: Phosgene M. Valeri, M. Carlotti, P. Raspollini, M. Ridolfi, B. M. Dinelli H 14 NO 3 A. Perrin, M. Ridolfi, J. Vander-Auwera, M. Carlotti THANK YOU FOR YOU ATTENTION