Retrieval of ethane from ground-based FTIR solar spectra using improved spectroscopy: Recent burden increase above Jungfraujoch. (July 2015)

• Record Type: Journal Article
• Authors: Franco, B.; Bader, W.; Toon, G.C.; Bray, C.; Perrin, A.; Fischer, E.V.; Sudo, K.; Boone, C.D.; Bovy, B.; Lejeune, B.; Servais, C.; Mahieu, E.
• Is Part Of: Journal of quantitative spectroscopy & radiative transfer. Volume 160(2015:Oct.)
• Page Start: 36
• Page End: 49
• Publication Date: 2015-07
• Subjects: Ethane -- FTIR -- Jungfraujoch -- Pseudo-lines -- Trend -- Shale gas; Spectrum analysis -- Periodicals; Radiation -- Periodicals; Analyse spectrale -- Périodiques; Rayonnement -- Périodiques; Radiation; Spectrum analysis; Periodicals; 543.0858
• DOI: 10.1016/j.jqsrt.2015.03.017
• Languages: English
• ISSNs: 0022-4073

Abstract

Abstract: An improved spectroscopy is used to implement and optimize the retrieval strategy of ethane (C2 H6 ) from ground-based Fourier Transform Infrared (FTIR) solar spectra recorded at the high-altitude station of Jungfraujoch (Swiss Alps, 46.5°N, 8.0°E, 3580 m a.s.l.). The improved spectroscopic parameters include C2 H6 pseudo-lines in the 2720–3100 cm −1 range and updated line parameters for methyl chloride and ozone. These improved spectroscopic parameters allow for substantial reduction of the fitting residuals as well as enhanced information content. They also contribute to limiting oscillations responsible for ungeophysical negative mixing ratio profiles. This strategy has been successfully applied to the Jungfraujoch solar spectra available from 1994 onwards. The resulting time series is compared with C2 H6 total columns simulated by the state-of-the-art chemical transport model GEOS-Chem. Despite very consistent seasonal cycles between both data sets, a negative systematic bias relative to the FTIR observations suggests that C2 H6 emissions are underestimated in the current inventories implemented in GEOS-Chem. Finally, C2 H6 trends are derived from the FTIR time series, revealing a statistically-significant sharp increase of the C2 H6 burden in the remote atmosphere above Jungfraujoch since 2009. Evaluating cause of this change in the C2 H6 burden, which may be related to the recent massive growth of shale gas exploitation in North America, is of primary importance for atmospheric composition and air quality in the Northern Hemisphere. Abstract : Highlights: 20-year time series of C2 H6 is retrieved from ground-based FTIR solar spectra. Improved spectroscopy reduces fitting residuals and enhances information content. Negative bias to FTIR suggests underestimated C2 H6 emissions in the GEOS-Chem model. Trend analysis reveals a sharp increase of C2 H6 burden since 2009. C2 H6 upturn may be related to growth of shale gas exploitation in North America.