Application of stable isotope analysis for improved understanding of the methane budget: comparison of TROICA measurements with TM3 model simulations |
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| Authors: | Oksana A Tarasova Sander Houweling Nikolai Elansky Carl A M Brenninkmeijer |
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| Institution: | (1) Atmospheric Environment Research Division, WMO, Geneva, Switzerland;(2) SRON Netherlands Institute for Space Research, Utrecht, the Netherlands;(3) Institute for Marine and Atmospheric Research Utrecht, Utrecht, the Netherlands;(4) Obukhov Institute of Atmosphere Physics RAS, Moscow, Russia;(5) Max Planck Institute for Chemistry, Mainz, Germany |
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| Abstract: | Presented is a detailed comparison of CH4 and δ13C–CH4 measurements with simulations of the global transport model TM3. Experimental data were obtained during campaigns along the
Trans-Siberian railroad in the framework of the TROICA project. Two summer (1999 and 2001) and one spring (2003) expeditions
are evaluated. Model simulations include sensitivity tests to further investigate the isotopic composition of natural gas
and emissions from Siberian wetlands. Comparison of the average mixing ratio of methane and its isotopic composition (δ13C) has been performed for different geographic zones, including the European part of Russia, Western Siberia and Central Siberia.
Simulations are in reasonable agreement with the measurements for the European part of Russia and confirm a high contribution
of natural gas to the observed methane levels. An increase of emission from bogs shifts the simulated methane isotopic composition
closer to the observations. The relative importance of the Western Siberia emissions in current inventories is underestimated
in comparison with other wetland regions in the former USSR. Simulated average mixing ratios are in a good agreement with
the observations in Central Siberia, while 13C(CH4) values tend to be higher than measured in all considered scenarios. These results point to a bias in the modeled source
mixture over Russia, which could be repaired by shifting emissions from isotopically heavy methane sources (e.g. coal, oil
or biomass burning) to light sources (e.g. wetlands, ruminants, waste treatment). Alternatively, the average isotopic signature
of Siberian wetlands may be lighter than expected. |
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