## 4 Conclusions  
In this study, BC emissions from domestic vehicles in South Korea were measured. The emissions were categorized according to fuel type and the vehicles were categorized by the engine technology used and the regulator standards applied. Various vehicle speeds were also considered. In all types of vehicles, BC emission was reduced with driving speeds from low to high, but beyond a certain threshold (65.4 km h\({}^{-1}\) or 97.3 km h\({}^{-1}\)), the emission increased again. In terms of fuel oil type, in NIER modes with preheating, the emission of GDI vehicles were 0.0032-0.27 mg km\({}^{-1}\), and the highest value of 0.16 mg km\({}^{-1}\) was observed in the regulation mode that included the cold start section. Diesel vehicles with DPF and LPG vehicles showed low levels of emissions at 0.01 mg km\({}^{-1}\) or less in NIER modes, and at 0.045 mg km\({}^{-1}\) and 0.0009 mg km\({}^{-1}\) in regulation modes, respectively.  
Among gasoline vehicles, GDI vehicles showed BC emissions of 2.8-5 times higher than that of MPI vehicles. With the tightening of regulations, MPI vehicles showed reduced PM emissions other than BC. Among diesel vehicles, EURO 3 vehicles without DPF showed emissions of 6.21-66 mg km\({}^{-1}\), which is estimated to be at least 1500 times higher than regulated vehicles with DPF. This confirms that DPF reduces BC emissions. With the application and tightening of PM regulations, both gasoline and diesel vehicles exhibited reduced BC emissions as well as PM emissions. However, for gasoline vehicles, many GDI vehicles were manufactured before the application of the PM regulation, and diesel vehicles without DPF are still in operation in Korea. The AAE values of 2.88 for biomass burning (oak wood), 1.56 for coal combustion (power plant stack), and 0.64-1.29 for automobile emissions by NIER modes could be obtained, confirming the possibility of tracking BC sources using AE33 measurement data.  
Conceptualization, G.P. and T.L.; methodology, K.K. and T.L.; formal analysis, T.P., S.K. ([PERSON]), J.B., D.-G.Y., and J.-H.W.; investigation, S.K. ([PERSON]) and S.C.; resources, S.L., Y.L., S.K. ([PERSON]), and J.L.; data curation, G.P. and T.L.; writing--original draft preparation, G.P. and T.L.; writing--review and editing, G.P., K.K., and T.L., supervision, T.L. All authors have read and agreed to the published version of the manuscript.  
This work was supported by a grant from the National Institute of Environment Research (NIER), founded by the Ministry of Environment (MOE) of the Republic of Korea (NIER-2019-04-02-018). Additional data analysis was supported by Korea Environment Industry & Technology Institute (KEITI) through Public Technology Program based on Environmental Policy Program, funded by Korea Ministry of Environment (MOE) (2019000160007).  
The authors thank the research scientists at the Transportation Pollution Research Center in the National Institute of Environmental Research (NIER) for their contribution to the success of the project.  
The authors declare no conflict of interest.  
Figure 10: Calculated AAE values in this study. \(\alpha_{\text{tb}}\): AAE of biomass burning, \(\alpha_{\text{ff}}\): AAE of fossil fuel burning for the average results of the NIER modes [33; 34; 35].