Abstract
Abstract. We assess the large-scale, top-down constraints on regional fossil fuel emissions provided by observations of atmospheric total column CO2, XCO2. Using an atmospheric general circulation model (GCM) with underlying fossil emissions, we determine the influence of regional fossil fuel emissions on global XCO2 fields. We quantify the regional contrasts between source and upwind regions and probe the sensitivity of atmospheric XCO2 to changes in fossil fuel emissions. Regional fossil fuel XCO2 contrasts can exceed 0.7 ppm based on 2007 emission estimates, but have large seasonal variations due to biospheric fluxes. Contamination by clouds reduces the discernible fossil signatures. Nevertheless, our simulations show that atmospheric fossil XCO2 can be tied to its source region and that changes in the regional XCO2 contrasts scale linearly with emissions. We test the GCM results against XCO2 data from the GOSAT satellite. Regional XCO2 contrasts in GOSAT data generally scale with the predictions from the GCM, but the comparison is limited by the moderate precision of and relatively few observations from the satellite. We discuss how this approach may be useful as a policy tool to verify national fossil emissions, as it provides an independent, observational constraint.
Highlights
The atmospheric mixing ratio of CO2 has increased from a preindustrial value of 280 ppm to over 390 ppm in 2011
Ground-based measurements of XCO2 are obtained by spectrometers in the Total Carbon Column Observing Network (TCCON) (Wunch et al, 2011)
We primarily present results using ACOS-GOSAT v 2.9 retrievals, we have analyzed preliminary ACOS-GOSAT v 2.10 retrievals to test the sensitivity of our results to the retrieval
Summary
The atmospheric mixing ratio of CO2 has increased from a preindustrial value of 280 ppm to over 390 ppm in 2011. Results from Los Angeles suggest that fossil fuel enhancements over a megacity are large enough (around 3 ppm) to be observed in the total column (the vertically integrated mass of CO2 in the atmosphere above a given location) via satellite observations (Wunch et al, 2009; Newman et al, 2012; Kort et al, 2012). Observations over megacities, urban areas, and large power plants are likely to show large enhancements in CO2 and provide improved processlevel constraints on emissions from various sources and sectors (Duren and Miller, 2012). They do not completely bridge the gap between bottom-up inventories and the top-down observational constraints on the spatial scale necessary for complete verification of national level emissions. We attempt to explore the signature of fossil fuel emissions on regional scales
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