## 3 Results
### Emission Rate of Organic Molecular Markers
Among the analyzed PAHs, EURO4 vehicles exhibited the highest ER, with notable increases in Phenanthrene, Fluoranthene, and Pyrene emissions compared with other vehicles in Table 8. These findings serve as important indicators for identifying EURO4-specific emission sources, as the aforementioned three components show significantly higher emission rates compared with other vehicles. Most of the PAHs emitted from EURO6 are below the detection limit. Similarly, in the analysis of 16 Hopane types in Table 9, \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Vehicles** & **Mode** & **OC** & **EC** & **OC/EC** \\ \hline LPG & US06 & 0.04 & 0.01 & 4.0 \\ Gasoline (G1) & US06, CVS-75 & 0.10 & 0.03 & 0.3 \\ Gasoline (G2) & US06, CVS-75 & 0.02 & 0.02 & 1.2 \\ Diesel EURO4 & US06 & 1.44 & 10.38 & 0.1 \\ Diesel EURO6 & US06 & 0.01 & 0.01 & 0.9 \\ Diesel EURO6 & & & & \\ during DPF & US06 & 0.03 & 0.04 & 0.6 \\ regeneration & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Emission Rate of OC and EC by test mode (mg/km). EURO4 vehicles exhibit the highest emissions overall. Emissions of 22S-Trishomboapane, 22R-Trishomboapane, AAA-20S-C27-Cholestane, ABB-20R-C27-Cholestane, and AAA-20R-27-cholestane are exclusively observed in EURO4 vehicles. Among the Alkane series, n-Tetradecane and n-Hexadecane exhibit the highest emissions. EURO4 vehicles also emit the highest levels of the Cycloalkane series, whereas EURO6 vehicles emit negligible amounts, indicating contrasting emission patterns between EURO4 and EURO6. Regarding the Alkane series, EURO4 vehicles show the highest emissions of Phytane, while EURO6 vehicles display the highest emissions of n-Tetradecane. Notably, EURO6 DPFe vehicles show the highest emissions of n-Heneicosane. Components such as n-Tridecane, n-Pentadecane, Norpristane, Pristane, and Phytane are exclusively emitted by EURO4 vehicles, making them potential representative emission components in future studies. However, components after n-Hexacosane exhibited characteristics of being unanalyzed. Particularly, among the polar components, all components of Benzene carboxylic acid (i.e., Phthalic Acid, Isophthalic Acid, Terephthalalic Acid, 1,2,4-Benzenetricarboxylic Acid, 1,2,3-Benzenetricarboxylic Acid, 1,3,5-Benzenetricarboxylic Acid, 1,2,4,5-Benzenetetracarboxylic Acid, and Methylphthalic Acid) display elevated levels in EURO4 vehicles, indicating their high emission rates in Table 10. \begin{table}
\begin{tabular}{c c c c c c c} \hline  & **LPG** & **Gasoline** & **Gasoline** & **Diesel** & **Diesel** & **Diesel (DPFe)** \\  & & & & **EURO4** & **EURO6** & **EURO6** \\ \hline
**Compounds** & **L2 + L1** & **G1** & **G2** & **D4-1 + D4-2** & **D6-1 + D6-2** & **D6-1 + D6-2** \\ \hline PAHs & 17.30 & 1482.09 & 90.44 & 62,997.68 & 0.43 & 49.28 \\ Hopanes & 1.83 & 10.44 & 4.60 & 854.52 & 0.53 & 5.31 \\ Cycloalkanes & 5.14 & 28.30 & 16.89 & 1208.50 & - & 47.68 \\ n-Alkanes & 211.13 & 717.99 & 355.88 & 85,290.67 & 171.17 & 1177.62 \\ Alkanoic acids & 1444.59 & 3836.63 & 1693.68 & 47,426.31 & 1913.94 & 2697.11 \\ Benzene carboxylic acids & 21.49 & 111.09 & 17.16 & 35,419.15 & 38.76 & 60.52 \\ Di-carboxylic acids & 193.07 & 1315.33 & 212.12 & 7430.16 & 72.65 & 228.02 \\ \hline \end{tabular}
\end{table} 
Table 7: Emission Rate of Organic Molecular Markers (ng/km).