Application of stable isotope analysis for improved understanding of the methane budget: comparison of TROICA measurements with TM3 model simulations

Abstract

Presented is a detailed comparison of CH 4 and δ 13 C-CH 4 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 (δ 13 C) 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 13 C(CH 4 ) 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,

Arctic methane sources: Isotopic evidence for atmospheric inputs

“…The results imply the dominant Arctic summer CH 4 source in 2008 and 2009 was biogenic, from wetland. This is consistent with evidence from Siberia of the importance of wetland CH 4 [ Tarasova et al , 2009]. In winter, gas emissions dominate the CH 4 input.…”

Measurements of δ13C in CH4 and using particle dispersion modeling to characterize sources of Arctic methane within an air mass

“…[] report −69.8‰ for the Plotnikovo region. It is clear that the Russian wetland regions are a major atmospheric source of CH 4 , with model simulations suggesting that the Siberian wetland CH 4 contribution to the Arctic may be considerably underestimated [ Tarasova et al ., ] compared to areas such as Finland. With CH 4 mixing ratios of 2000 ppb commonly recorded north of 59°N during the daytime [ Tarasova et al ., ], it is easy to see how air parcels from Russia could provide large volumes of isotopically depleted CH 4 to the Arctic troposphere.…”

Train-Based Platform for Observations of the Atmosphere Composition (TROICA Project)

“…Accumulated data have proven to have a high potential to be further used for models (Tarasova et al, 2009) and satellite observations validation as well as provided better understanding of the atmosphere composition features over substantial part of the Russian territory.…”