## 3 Results
### Emission Rate of Organic Molecular Markers  
According to [PERSON] et al. [45], a significant proportion of pollutants emitted from vehicles consists of organic components. In this study, exhaust gas samples were collected and analyzed during driving in the US06 and CVS-75 modes to determine the ER of OC and EC based on the fuel type. OC and EC emissions were quantified using quartz filters for gas collection, and the results are presented in Table 6.  
Diesel engines are extensively utilized in various applications such as vehicles, ships, and construction machinery due to their high thermal efficiency, cost-effectiveness, and durability [1; 45]. However, the widespread use of diesel engines also contributes to significant environmental pollution issues [32]. To mitigate PM emissions, the installation of DPF in diesel vehicles has become crucial for effective exhaust gas emission control, considering the substantial role of diesel vehicles as a major source of PM production [1]. Nevertheless, despite the oxidation and combustion of most PM during vehicle operation, non-volatile substances such as elemental carbon, ash, and soot persist [7; 32; 45]. Hence, this study focused on analyzing the carbon content by capturing exhaust gas during DPF regeneration (DPFre) using EURO6 vehicles (EURO6 DPFre). Regarding the CVS-75 mode, all vehicles except for gasoline vehicles exhibit minimal emissions of OC and EC. Therefore, the carbon components generated in the US06 mode were analyzed for LPG and diesel vehicles. Among the vehicles, EURO4 vehicles emit the highest levels of OC and EC. On the other hand, EURO6 vehicles show the lowest emissions of OC and EC. During DPF regeneration, OC and EC emissions increased to 0.03 and 0.04 mg/km, respectively, which were 2.2 and 3.3 times higher than normal levels. These findings indicate that while DPFs effectively remove significant amounts of PM from exhaust gases, they also contribute to the generation and emission of another air pollutant, carbonaceous material. Furthermore, this study analyzed the presence of organic molecular markers in the samples collected from the quartz filters, categorized by fuel type. The analyzed OC data were normalized, and Table 7 presents the quantities of specific organic markers such as PAHs, Hopanes, Cycloalkanes, Alkanes, Alkanoic acids, Benzo carboxylic acids, and Di-carboxylic acids per unit of OC. The results revealed variations in emission rates depending on the fuel type. EURO4 vehicles, which exhibit the highest OC emissions among all vehicles, also show the highest emissions of organic marker substances overall. Notably, PAHs, Hopanes, Cycloalkanes, and Alkanes exhibit higher values compared with the other vehicles. With the exception of EURO4, EURO6 vehicles exhibit the highest values for Cycloalkanes, Alkanes, and Benzo carboxylic acids, while gasoline vehicle G1 shows the highest values for PAHs, Alkanoic acids, and Di-carboxylic acids. These findings provide significant data for distinguishing between the emission characteristics of EURO regulations and diesel vehicles based on air-soluble organic markers. In addition, the lower PAH emissions observed in EURO6 vehicles compared with gasoline vehicles indicate the relatively superior exhaust gas component reduction function of EURO6. Notably, EURO6 DPFre exhibits much higher PAH emissions at 49.3 ng/km, approximately 114 times higher than EURO6. Moreover, EURO6 vehicles do not emit Cycloalkanes, whereas EURO6 DPFre emits 47.7 ng/km of Cycloalkanes, indicating a distinct difference. As emissions during DPF operation exceeded general emissions, further studies are necessary to investigate the organic molecular markers generated during the operation of aftertreatment devices.