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Decreasing emissions of NOx relative to CO2 in East Asia inferred from satellite observations


At present, global CO2 emission inventories are mainly based on bottom-up estimates that rely, for example, on reported fossil fuel consumptions and fuel types1,2. The associated uncertainties propagate into the CO2-to-NOx emission ratios that are used in pollution prediction and monitoring3, as well as into biospheric carbon fluxes derived by inverse models4. Here we analyse simultaneous and co-located satellite retrievals from SCIAMACHY (ref. 5; SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY) of the column-average dry-air mole fraction of CO2 (refs 6, 7) and NO2 (refs 8, 9, 10) for the years 2003–2011 to provide a top-down estimate of trends in emissions and in the ratio between CO2 and NOx emissions. Our analysis shows that the CO2-to-NOx emission ratio has increased by 4.2 ± 1.7% yr−1 in East Asia. In this region, we find a large positive trend of CO2 emissions (9.8 ± 1.7% yr−1), which we largely attribute to the growing Chinese economy. This trend exceeds the positive trend of NOx emissions (5.8 ± 0.9% yr−1). Our findings suggest that the recently installed and renewed technology in East Asia, such as power plants, transportation and so on, is cleaner in terms of NOx emissions than the old infrastructure, and roughly matches relative emission levels in North America and Europe.

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Figure 1: Expected XCO2 enhancement from nearby anthropogenic emissions (XCO2e) and corresponding NO2 levels.
Figure 2: Data-period-averaged regional weekday anomaly of ΔXCO2 (green) and ΔNO2 (red) for the regions North America/Europe (solid) and East Asia (dashed).
Figure 3: Trends of the CO2-to-NOx emission ratio (that is, conversion factor F), tropospheric NO2, XCO2e and EDGAR CO2 emissions.

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This work was in part funded by ESA/ESRIN (GHG-CCI), EU FP7 (MACC-II), DLR (SADOS), and the State and the University of Bremen. We acknowledge the use of data from the Emission Database for Global Atmospheric Research (EDGAR), BP’s statistical review of world energy, the Regional Emission inventory in ASia (REAS), the Global Carbon Project (GPC), and the CARMA (CARbon Monitoring for Action) database. Thanks also to the ECMWF for providing the meteorological reanalysis data.

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Authors and Affiliations



M.R.: experimental set-up, data analysis, interpretation, design and operation of the XCO2 satellite retrieval, writing the paper. M.B., M.H., J.H., O.S., H.B., J.P.B.: experimental set-up, interpretation, design of the XCO2 satellite retrieval, improving the paper. A.H., A.R.: experimental set-up, interpretation, design and operation of the NO2 satellite retrieval, improving the paper.

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Correspondence to M. Reuter.

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The authors declare no competing financial interests.

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Reuter, M., Buchwitz, M., Hilboll, A. et al. Decreasing emissions of NOx relative to CO2 in East Asia inferred from satellite observations. Nature Geosci 7, 792–795 (2014).

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