Doctoral thesis (Dissertations and theses)
Long-term study of methane and two of its derivatives from solar observations recorded at the Jungfraujoch station
Bader, Whitney
2015
 

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Abstract :
[en] A long-term study of methane and two of its derivatives, i.e. ethane and methanol from ground-based FTIR solar observations recorded at the high alpine International Scientific Station of the Jungfraujoch (3580 m a.s.l.) is reported. Those three gases act as tropospheric ozone precursors through their removal pathway and therefore have an impact on air quality. In the stratosphere, methane influences the content of ozone and in the production of water vapor. Moreover, both methane and ethane impact the greenhouse radiative forcing. While the latter is an indirect greenhouse gas because of its sinks, the former is the second most important anthropogenic greenhouse gas after CO2. The primary challenge of this work is the development and optimization of retrieval strategies for the three studied gases from FTIR spectra recorded at the Jungfraujoch station, in the framework of the Network for Detection of Atmospheric Composition Change (NDACC), in order to assess their concentrations in the atmosphere and to study their long-term trend and recent changes as well as their seasonal variations. The development and optimization of a retrieval strategy, based on the selection of the best combination of parameters, aims to limit interferences, minimize residuals, and maximize information content. To this end, the best retrieval strategy has been selected from a great number of available combinations thanks to a method for error analysis developed through this work. A 17-year time series of methanol is presented thanks to the combination of spectral windows for the first time for ground-based observations resulting in the improvement of the information content. We therefore present the first long-term time series of methanol total, lower tropospheric and upper tropospheric–lower stratospheric partial columns. We found no significant long-term trend of methanol but its seasonal cycle shows a high peak-to-peak amplitude of ̴103 % for total columns characterized by minimum values in winter and maximum values during summertime. The presented time series provides a valuable tool for model and satellite validation and complement the few NDACC measurements at northern mid-latitudes. Regarding ethane, we have for the first time included a combination of improved spectroscopic parameters as well as an improved a priori state that substantially reduce fitting residuals and enhance information content. Analysis of the long-term trend of ethane covering 20 years of observations revealed a strong positive trend of ethane from 2009 onwards of ̴5 %/year. We hypothesize that this recent ethane upturn may be the result of a large increase in fugitive emissions from the massive exploitation of shale gas and tight oil reservoirs on the North American continent. Finally, we quantified the changes of methane since 2005 from 10 ground-based NDACC sites, with a mean global increase of 0.30 %/year. Investigations into the source(s) responsible for this re-increase are performed with a GEOS-Chem tagged simulation that provides the contribution of each emission source and one sink to the total methane simulated. From the analysis of the GEOS-Chem tracers on both the local and global scales, we determined that the increasing anthropogenic emissions such as coal mining, gas and oil transport and exploitation, have played a major role in the increase of atmospheric methane observed since 2005 while they are secondary contributors to the total methane budget.
Disciplines :
Earth sciences & physical geography
Author, co-author :
Bader, Whitney ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Groupe infra-rouge de phys. atmosph. et solaire (GIRPAS)
Language :
English
Title :
Long-term study of methane and two of its derivatives from solar observations recorded at the Jungfraujoch station
Defense date :
30 November 2015
Institution :
ULiège - Université de Liège
Degree :
Doctor of Philosophy in Sciences
Promotor :
Mahieu, Emmanuel  ;  Université de Liège - ULiège > Sphères
President :
Magain, Pierre  ;  Université de Liège - ULiège > Unités de recherche interfacultaires > Space sciences, Technologies and Astrophysics Research (STAR)
Secretary :
François, Louis  ;  Université de Liège - ULiège > Sphères
Jury member :
Erpicum, Michel ;  Université de Liège - ULiège > Département de géographie
Perrin, Agnes
Muller, Jean-François
Available on ORBi :
since 05 January 2016

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