Spatial distribution of Delta super(14)CO sub(2) across Eurasia: measurements from the TROICA-8 expedition

• Published in: Atmospheric chemistry and physics discussions 2008-08, Vol.8 (4), p.15207-15238
• Main Authors: Turnbull, J C, Miller, J B, Lehman, S J, Hurst, D, Tans, P P, Southon, J, Montzka, S, Elkins, J, Mondeel, D J, Romashkin, P A, Elansky, N, Skorokhod, A
• Format: Article
• Language: English
• ISSN: 1680-7367; 1680-7375

Because fossil fuel derived CO sub(2) is the only source of atmospheric CO sub(2) that is devoid of super(14)C, atmospheric measurements of Delta super(14)CO sub(2) can be used to constrain fossil fuel emissions at local and regional scales. However, at the continental scale, atmospheric transport and other sources of variability in Delta super(14)CO sub(2) may influence the fossil fuel detection capability. We present a set of Delta super(14)CO sub(2) observations from the train-based TROICA-8 expedition across Eurasia in March-April 2004. Local perturbations in Delta super(14)CO sub(2) are caused by easily identifiable sources from nuclear reactors and localized pollution events. The remaining data show an increase in Delta super(14)CO sub(2) from Western Russia (40 degree E) to Eastern Siberia (120 degree E), consistent with depletion in super(14)CO sub(2) caused by fossil fuel CO sub(2) emissions in heavily populated Europe, and gradual dispersion of the fossil fuel plume across Northern Asia. Other tracer gas species which may be correlated with fossil fuel CO sub(2) emissions, including carbon monoxide, sulphur hexafluoride, and perchloroethylene, were also measured and the results compared with the Delta super(14)CO sub(2) measurements. The sulphur hexafluoride longitudinal gradient is not significant relative to the measurement uncertainty. Carbon monoxide and perchloroethylene show large-scale trends of enriched values in Western Russia and decreasing values in Eastern Siberia, consistent with fossil fuel emissions, but exhibit significant spatial variability, especially near their primary sources in Western Russia. The clean air Delta super(14)CO sub(2) observations are compared with simulated spatial gradients from the TM5 atmospheric transport model. We show that the change in Delta super(14)CO sub(2) across the TROICA transect is due almost entirely to emissions of fossil fuel CO sub(2), but that the magnitude of this Delta super(14)CO sub(2) gradient is relatively insensitive to modest uncertainties in the fossil fuel flux. In contrast, the Delta super(14)CO sub(2) gradient is strongly sensitive to the modeled representation of vertical mixing, suggesting that Delta super(14)CO sub(2) may be a useful tracer for training mixing in atmospheric transport models.