# Analysis of Four Years of Global XCO\({}_{2}\) Anomalies as
## 4 Results
### Modeling Results  
We analyze the XCO\({}_{2}\) enhancements related to fossil fuel combustion and biospheric fluxes corresponding to the OCO-2 sounding footprints using the Lagrangian FLEXPART model. This allows us to account for the effect of the OCO-2 sampling as well as the transport by the wind.  
Figure 7 illustrates the modeled XCO\({}_{2}\) enhancements for the year 2015. We illustrate the contribution from the ODIAC fossil fuel fluxes alone (Figure 7, upper panel) and together with the biospheric contribution (Figure 7, lower panel). The anthropogenic component shows spatial patterns similar to those observed from the XCO\({}_{2}\) anomalies in Figure 3, with high positive enhancements in eastern USA, Europe, India, Middle East and China. In the Southern Hemisphere, the Highveld region in South Africa shows the strongest anthropogenic signal, together with the area around Sidney in Australia. When adding the biospheric component, we also find negative values in the northern mid-latitudes and in the Southern Cone in South America, as observed from the anomalies in Figure 3. In Europe, the large anthropogenic XCO\({}_{2}\) enhancements are drawn down by the biospheric sink (Figure 7, lower panel). The largest differences between the patterns in the FLEXPART simulations and the OCO-2 anomalies are in the tropical region, where the OCO-2 XCO\({}_{2}\) anomalies show large positive values while the FLEXPART enhancements are close to zero. Part of the reason is that the FLEXPART simulations do not include the biomass burning contribution, but also the biospheric contribution is lower.  
Figure 6: Seasonal biospheric (BIO) and biomass burning (FIRE) fluxes from NOAA’s CarbonTracker CT2017 from September 2014 to August 2015.  
Figure 8 illustrates the results of the FLEXPART seasonal simulations. We find that the Highveld region is clearly visible during SON and JJA, while it is not detectable during DJF due to effect of the biospheric sink. The same feature is also visible in the seasonal anomalies in Figure 4. In addition, while OCO-2 shows negative XCO\({}_{2}\) anomalies over central North America and South Central Asia during the fall (SON) and winter (DJF), the FLEXPART enhancements over both regions are positive.  
Four local \"case studies\" for both FLEXPART enhancements and OCO-2 anomalies are illustrated in Figure 9. The first one is the Iberian peninsula, where OCO-2 XCO\({}_{2}\) retrievals are available consistently throughout the year. Here, OCO-2 measurements indicate larger XCO\({}_{2}\) anomalies over coastal cities than the model results. The second area is the Highveld industrial region in South Africa. In this case, the anthropogenic signatures seem more localized in the FLEXPART simulations than in the OCO-2 anomaly maps, although positive anomalies are clearly visible over the area as well. The third case study is over India, where we can see a clear positive signal in both OCO-2 and FLEXPART data, but the OCO-2 results indicate more discrete and localized anthropogenic emissions than the model results. The last case is Mexico City, where we also see strong anthropogenic signatures (i.e., positive enhancements and anomalies), related to the emissions from the city as well as the power plants in the area, with some differences in the locations of the positive enhancements. These differences may reflect uncertainties in the the emission source intensities or locations or significant local wind data errors at low wind conditions while using wind data from global reanalysis.  
Figure 7: FLEXPART simulation results for the year 2015 with contribution from fossil fuel combustion (FF) only and also with biospheric component (FF + BIO).  
Figure 8: FLEXPART seasonal XCO\({}_{2}\) enhancement simulations from September 2014 to August 2015, including fossil fuel and biospheric contribution (FF + BIO).