Intercomparison of Long-term Trends of Key Greenhouse Source Gases
in the Troposphere, Determined Remotely and In Situ from
Ground Validation of Related Records from Space-based Sensors

A contribution to ACCENT-TROPOSAT-2, Task Group 3

Emmanuel Mahieu

University of Liège – Institute of Astrophysics and Geophysics
17, Allée du 6-Août, 4000 Liège, Belgium
Tel.:  +32-4-3669786
Fax:  +32-4-3669747

The long-term evolution of the chemical composition of the Earth’s troposphere is a key element in understanding the climate- and the ozone layer changes, and in assessing the adherence and compliance to international Conventions (i.e. Vienna, Rio) and the adequacy of related Protocols (i.e. Montreal, Kyoto) to warrant a durable and sustainable environment for mankind.

During the five-year time span of the AT-2 program, the GIRPAS (Groupe Infra-rouge de Physique Atmosphérique et Solaire) of the University of Liège (ULg) envisages to:

1.       expand the long-term solar observations performed with FTIR (Fourier-transform infra-red) spectrometers at the Jungfraujoch station (Switzerland) to retrieve total and in most cases partial (tropospheric- versus stratospheric-) column abundances of source gases affecting the climate and/or the stratospheric ozone layer. Key target source gases include species with large global warming- and/or ozone depletion potentials (e.g. CO2, CH4, N2O, CFC-11, CFC-12, CCl4, HCFC-22, SF6), as well as others affecting the oxidizing capacity of the troposphere and the atmospheric aerosol layer, or reflecting the occurrence of forest fires (e.g. CO, C2H6, C2H2, OCS, HCN, HCOH, HOCOH).

2.       analyse these databases to derive related temporal changes (both short- and long-term) in the tropospheric loadings and compare the latter with similar findings available from other ground-based sites, preferably within the context of both remote and in situ network-type activities (such as the NDSC, AGAGE, NOAA/CMDL,...); maintain interactions with spectroscopy groups, in order to gain guidance in the selection of the most accurate spectroscopic parameters needed in the remote sensing retrieval processes.

3.       establish rationales to compare above data sets with measurements derived from observations by space-based sensors (e.g. MOPITT, MIPAS, SCIAMACHY, ACE, AURA, IASI,...); a particular AT-2 validation effort will deal with the study of tropospheric ozone (O3) and formaldehyde (HCOH) in support of the AURA-OMI experiment.

4.       ensure synergy with modelling activities (e.g. at U. of Leeds, U. of Oslo, MPIC-Mainz), in order to assess consistency between observations and predictions and to identify species-specific processes at work in the troposphere; also to perform some global assimilation of ground- and space-based ensembles of measurements, and to update predictive scenarios.

Time schedule

All above activities are expected to proceed during the full period (2004-2008) of the project.

Approximate manpower needed to support the participation to AT2







Personnel (man-year)






Yearly cost (kEUR)






Likely funding sources

Belgian Federal Science Policy Office; ESA-Prodex; EC-Research Directorate.

Some proposed activities are part of the overall research work performed by ULg-GIRPAS within the frame of national and international programs (among which are the Belgian Global Change, and the EC-SOGE and -UFTIR projects) and collaborations; related contributions to AT-2 will depend on the levels of funding received.


Christian Servais;                     

GIRPAS, Institute of Astrophysics and Geophysics,
Univ. of Liege, Belgium

Philippe Demoulin;                   

GIRPAS, Institute of Astrophysics and Geophysics,
Univ. of Liege, Belgium

C.P. Rinsland                           
NASA Langley Research Center,
Hampton, VA, USA




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