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| Titel |
Evolution of methanol (CH3OH) above the Jungfraujoch station (46.5Ë N): variability, seasonal modulation and long-term trend |
| VerfasserIn |
Whitney Bader, Emmanuel Mahieu, Benoît Bovy, Bernard Lejeune, Philippe Demoulin, Christian Servais, Jeremy J. Harrison |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250072897
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| Zusammenfassung |
| Methanol (CH3OH) is the second most abundant organic compound in the Earth’s
atmosphere with concentrations close to a few ppbv, after methane, despite a short lifetime of
a few days (Jacob et al., 2005). Natural sources of CH3OH include plant growth, oceans,
decomposition of plant matter, oxidation of methane and other VOCs,-¦ while anthropogenic
sources are from vehicles, industry,-¦ biomass burning completes the emission budget. The
main sink is the oxidation by hydroxyl radical, leading to the formation of carbon monoxide
(CO) and formaldehyde (H2CO).
The retrieval of methanol is very challenging due to the presence of strong absorption of
ozone and its isotopologues in addition to water vapour and carbon dioxide in the
region of the selected strong nu8 band of CH3OH. First retrievals from satellite
observations using the Atmospheric Chemistry Experiment infrared Fourier Transform
Spectrometer (ACE-FTS) on board the SCISAT satellite have been performed by
Dufour et al. (2007 and references therein) using a spectral interval going from
995.5 to 1008.3 cm-1. In 2009, first retrievals from a ground-based FTS, using
spectra recorded at Kitt Peak (31.9Ë N) and a window going from 992 to 999 cm-1
have been reported by Rinsland et al. (2009), followed by Vigouroux et al. (2012
and references therein) who used yet another spectral interval going from 1029 to
1037cm-1.
From those former retrieval strategies and also considering the Mahieu et al. (2012)
contribution, we redefined our spectral intervals to maximize the information content. Indeed,
our first window, starting from 992 to 1008.3 cm-1, is issued from the merge of Rinsland et
al. and Dufour et al. windows while our second, going from 1029 to 1037 cm-1, is the one
used by Vigouroux et al. With this new combination of windows, we were able to enlarge the
range of zenith angles providing robust results while maintaining good correlation between
our two windows; this also resulted in an improvement of the fitting residuals and of the
information content.
We used the 2008 HITRAN compilation (Rothman et al., 2009) for spectroscopic
parameters. However, systematic residuals still remain in the 1033 cm-1 region which are
attributed to unsatisfactory line parameters for methanol. New cross sections recorded at the
Molecular Spectroscopy Facility of the Rutherford Appleton Laboratory (Harrison et al.
2012) and calibrated in intensity by using the reference spectra from the Pacific Northwest
National Laboratory (PNNL) IR database will be tested as soon as converted into
pseudolines.
In this work, we will present the first long-term time series of methanol total columns,
resulting from the implementation of our new retrieval strategy. All retrievals have been
performed with the SFIT2 algorithm (v 3.91) (Rinsland et al., 1998) using a series of about 7
000 spectra recorded between 1995 and 2012, with zenith angles between 60 and 85Ë . These
solar absorption observations have been recorded with a high-resolution FTIR Bruker 120HR
instrument, at the high altitude 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).
References
Dufour, G., et al. (2007), The influence of biogenic emissions on upper-tropospheric
methanol as revealed from space, Atmospheric Chemistry and Physics, 7, 6119.
Harrison, J.J., et al. (2012), Infrared cross sections for methanol, Journal of Quantitative
Spectroscopy and Radiative Transfer, 113, 2189.
Jacob, D. J., et al. (2005), Global budget of methanol: Constraints from atmospheric
observations, Journal of Geophysical Research, 110, D08303.
Mahieu, E., et al. (2012), Seeking for the optimum retrieval strategy of methanol
(CH3OH) from ground-based high-resolution FTIR solar observations recorded at the
high-altitude Jungfraujoch station (46.5ºN) , poster presentation at the “EGU General
Assembly”, 22–27 April 2013, Vienna, Austria, 2012.
Rinsland, C.P., et al. (1998), Northern and southern hemisphere ground-based infrared
spectroscopic measurements of tropospheric carbon monoxide and ethane, Journal of
Geophysical Research, 103 (D21), 28197.
Rinsland, C. P., et al. (2009), First ground-based infrared solar absorption measurements
of free tropospheric methanol (CH3OH)Â : Multidecade time series from Kitt Peak (31.9Ë N
111Ë W): Trend, seasonal cycle, and comparison with previous measurements, Journal of
Geophysical Research, 114, D04309.
Rothman, L. S., et al. (2009), The HITRAN 2008 molecular spectroscopic database,
Journal of Quantitative Spectroscopy and Radiative Transfer, 110, 533.
Vigouroux, C., et al. (2012), FTIR time-series of biomass burning products (HCN, C2H6,
C2H2, CH3OH, and HCOOH) at Reunion Island (21Ë S, 55Ë E) and comparisons with
model data, Atmospheric Chemistry and Physics, 12, 10367.
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 FRS-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. |
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