## 3 Results and Discussion  
In this study, the CO\({}_{2}\) emissions (kg/100 km) of CV (fueled by gasoline) and EV of different countries/regions from year 2018 to 2040 were predicted. Figure 8 presents the CO\({}_{2}\) emission from CV and EV of different countries under NEDC. It was chosen for comparing different countries' CO\({}_{2}\) emission because it is considered to have the least degradation in performance. It should be noted that the emission of CV is universal across the globe in this study, as it was calculated based vehicle fuel consumption. It can be seen in Figure 8 that, from year 2018 to 2040, CV has higher CO\({}_{2}\) emission than EV. For all the countries studied, China has the highest CO\({}_{2}\) emission for EV, around 50% of that from CV in Year 2018 and 66% of that from CV in Year 2040. However, carbon emission of EV from the EU remains at the lowest level (around 7 kg/100 km) in this time frame. Meanwhile, CO\({}_{2}\) emission of EV from Japan and the world average is in between that from China and the EU, and their differences are completely determined by the CO\({}_{2}\) emission of electricity (shown in Figure 2). Figure 9 presents the simulated results under eight different driving cycles. Since EV emission of different countries follow the exact same trend with their electricity emissions (shown in Figure 2), the following figures only show the trend for China and the EU as the two extreme representatives. Although the results are dependent on driving cycles (road conditions), there are some common trends for all types of driving cycles studied--(1) The CO\({}_{2}\) emission decreases over the years for both CVs and EVs, due to the increased engine efficiency and increased fraction of renewable energy in the power grid, respectively; (2) For all countries/regions, CV has higher CO\({}_{2}\) emission than EV from year 2018 to 2040; (3) China has the highest CO\({}_{2}\) emission for EVs, attributed to its higher CO\({}_{2}\) emission of electricity, followed by Japan, the world average and the EU. Comparing Figure 9a,b with the other subfigures, it can be observed that the CO\({}_{2}\) emissions of CV (red curve) under China-fast and HWFET cycle are significantly lower, and closer to the emission of EV than other driving cycles. Specifically, under China Fast condition, the CO\({}_{2}\) emission of CV  
Figure 8: CO\({}_{2}\) emission of CV and EV under New European Driving Cycle for different countries from year 2018 to 2040. The EV model has electricity regeneration during braking. is about 23% and 17% higher than that of China EV with no electricity regeneration during braking (ebraking) in year 2018 and 2040, respectively. For HWFET, the CO2 emission of CV is 16% higher than that of China EV with no ebraking in 2018, and this figure decreases to 9% by 2040. As described in the previous section, HWFET represents relatively stable highway operating conditions in the US, while China-fast represents the driving conditions in expressways with no traffic lights in China. Under these conditions, the engine operates at high speed, medium load (torque), where the brake specific fuel consumption is the lowest (engine efficiency highest), as shown in Figure 6a. This explains the lower CO2 emission of CV under highway than other conditions. In contrast, in Figure 9c-g, the CO2 emission of CV is a lot higher than that of EV. Among them, the most significant difference was observed in NYCC and UDDS cycle. For NYCC, the emission of  
Figure 9: CO2 emission from conventional vehicles fueled by gasoline and electric vehicles from China and the EU, predicted through 2040 under different driving conditions, including (**a**) China Fast cycle; (**b**) HWFET; (**c**) JC08; (**d**) China Common cycle; (**e**) NYCC; (**f**) UDDS; (**g**) FTP75 and (**h**) NEDC. ebraking means electricity regeneration during braking. CV is 59% higher than that of China EV with no ebraking in 2018, and this difference is only slightly reduced to 56% in 2040, while that, for the UDDS cycle is 56% and 52%, respectively.