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| Titel |
Retrievals of ethane from ground-based high-resolution FTIR solar observations with updated line parameters: determination of the optimum strategy for the Jungfraujoch station. |
| VerfasserIn |
W. Bader, A. Perrin, D. Jacquemart, K. Sudo, H. Yashiro, M. Gauss, P. Demoulin, C. Servais, E. Mahieu |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250066844
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| Zusammenfassung |
| Ethane (C2H6) is the most abundant Non-Methane HydroCarbon (NMHC) in the Earth’s
atmosphere, with a lifetime of approximately 2 months. C2H6 has both anthropogenic and
natural emission sources such as biomass burning, natural gas loss and biofuel
consumption. Oxidation by the hydroxyl radical is by far the major C2H6 sink as
the seasonally changing OH concentration controls the strong modulation of the
ethane abundance throughout the year. Ethane lowers Cl atom concentrations in the
lower stratosphere and is a major source of peroxyacetyl nitrate (PAN) and carbon
monoxide (by reaction with OH). Involved in the formation of tropospheric ozone
and in the destruction of atmospheric methane through changes in OH, C2H6 is a
non-direct greenhouse gas with a net-global warming potential (100-yr horizon) of
5.5.
The retrieval of ethane from ground-based infrared (IR) spectra is challenging. Indeed,
the fitting of the ethane features is complicated by numerous interferences by strong
water vapor, ozone and methane absorptions. Moreover, ethane has a complicated
spectrum with many interacting vibrational modes and the current state of ethane
parameters in HITRAN (e.g. : Rothman et al., 2009, see http://www.hitran.com)
was rather unsatisfactory in the 3Â μm region. In fact, PQ branches outside the
2973–3001 cm-1 range are not included in HITRAN, and most P and R structures are
missing.
New ethane absorption cross sections recorded at the Molecular Spectroscopy Facility of
the Rutherford Appleton Laboratory (Harrison et al., 2010) are used in our retrievals. They
were calibrated in intensity by using reference low-resolution spectra from the Pacific
Northwest National Laboratory (PNNL) IR database. Pseudoline parameters fitted to these
ethane spectra have been combined with HITRAN 2004 line parameters (including all the
2006 updates) for all other species encompassed in the selected microwindows. Also, the
improvement brought by the update of the line positions and intensities of methyl chloride
(CH3Cl) in the 3.4 μm region (Bray et al., 2011) will be quantified. The ethane a
priori volume mixing ratio (VMR) profile and associated covariance are based
on synthetic data from the chemical transport model (CTM) of the University of
Oslo.
In this contribution, we will present updated ethane total and tropospheric column
retrievals, using the SFIT-2 algorithm (v3.91) and high-resolution Fourier Transform Infrared
(FTIR) solar absorption observations recorded with a Bruker 120HR instrument, at the high
altitude research station of the Jungfraujoch (46.5Ë N, 8Ë E, 3580 m asl), within the
framework of the Network for the Detection of Atmospheric Composition Change (NDACC,
visit http://www.ndacc.org).
We will characterize three microwindows encompassing the strongest ethane features
after careful selection of a priori VMR profiles, spectroscopic parameters, accounting at best
for all interfering species. We will then present the retrieval strategy representative of the best
combination of those three characterized micro-windows in order to minimize the
fitting residuals while maximizing the information content, the precision and the
reliability of the retrieved product. The long-term C2H6 column time series will
be produced using the Jungfraujoch observational database. Comparisons with
synthetic data produced by two chemical transport model (CHASER and the one of the
University of Oslo) will also be presented and analyzed, aiming at the determination and
interpretation of long-term trends and interannual variations of ethane at Northern
mid-latitudes.
Acknowledgments
The University of Liège involvement has primarily been supported by the PRODEX
program funded by the Belgian Federal Science Policy Office, Brussels and by the Swiss
GAW-CH program. E. Mahieu is Research Associate with the F.R.S. – FNRS. The
FRS-FNRS and the Fédération Wallonie-Bruxelles are further acknowledged for
observational activities support. We thank the International Foundation High Altitude
Research Stations Jungfraujoch and Gornergrat (HFSJG, Bern) for supporting the
facilities needed to perform the observations. We further acknowledge the vital
contribution from all the Belgian colleagues in performing the Jungfraujoch observations
used here. We further thank G.C. Toon (NASA-JPL, Pasadena) for the conversion
of the ethane cross sections into pseudolines which can be used by our retrieval
algorithm.
References
Bray, C., A. Perrin, D. Jacquemart et al., The ν1, ν4 and 3 ν6 bands of methyl chloride in
the 3.4-μm region: Line positions and intensities, J. Quant. Spectrosc. Radiat. Transfer, 112,
2446–2462, 2011.
Harrison, J.J., N.D.C. Allen, and P.F. Bernath, Infrared absorption cross sections for
ethane (C2H6) in the 3 μm region, J. Quant. Spectrosc. Radiat. Transfer, 111, 357-363,
2010.
Rothman, L.S., D. Jacquemart, A. Barbe et al., The HITRAN 2009 molecular
spectroscopic database, J. Quant. Spectrosc. Radiat. Transfer, 110, 533-572, 2005. |
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