## 2 Materials and Methods  
### Test Vehicle Selection  
The present study aimed to investigate the chemical characteristics of ER using a chassis dynamometer for eight different vehicles. The specifications of the selected vehicles in this study are presented in Tables 1 and 2, as shown in Appendix A. Initially, two gasoline vehicles employing Gasoline Direct Injection (GDI), which is the most recent  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Fuel Type** & **Vehicle** & \begin{tabular}{c} **PM** \\ **(mg/km)** \\ \end{tabular} & \begin{tabular}{c} **NOx** \\ **(mg/km)** \\ \end{tabular} & \
\begin{tabular}{c} **CO** \\ **(mg/km)** \\ \end{tabular} &
\begin{tabular}{c} **CO\({}_{2}\)** \\ **(g/km)** \\ \end{tabular} & **Reference** \\ \hline \hline \multirow{2}{*}{Diesel} & Euro4 & 27.10 & & & & [9] \\  & Euro5 DPF & 0.63 & & & [9] \\  & Light-duty & & 1735 & 1395 & & [10] \\  & Light-duty & & 1907 & 1138 & & [10] \\  & Light-duty & 98.00 & 1173 & 980 & 281.6 & [11] \\  & Light-duty & 85.00 & 1128 & 1685 & 283.9 & [11] \\  & Light-duty & 233.00 & 1001 & 1208 & 311.7 & [11] \\  & Light-duty & 243.00 & 3983 & 2650 & 442.4 & [11] \\  & Light-duty & 52.00 & 1642 & 671 & 377.2 & [11] \\  & Light-duty & 315.00 & 1480 & 1178 & 407.8 & [11] \\  & EURO5 & & 0.01–0.65 & 209–770 & & [12] \\  & DPF & & & & [12] \\  & EURO5 & & 0–0.32 & 158–900 & & [12] \\  & DPF & & & & [12] \\  & EURO4 & & & & & [12] \\  & DIF & & & & [12] \\  & EURO5 & & 0–0.18 & 311–747 & & [12] \\  & EURO5 1 & & 212–763 & 14–572 & 89–172 & [13] \\  & EURO5 2 & & 162–910 & 17–185 & 87–169 & [13] \\  & EURO41 & & & & [13] \\  & EURO5 & & & & [13] \\  & EURO5 & & & & [14] \\  & Light truck & 13 & 371 & 115 & & [14] \\  & Heavy & & & & [14] \\  & truck & & & & [14] \\  & truck & & & & [14] \\ \hline \hline \multirow{2}{*}{Gasoline} & EURO3 & 2.41 & & & & [9] \\  & EURO1 & 72.10 & & & & [9] \\  & EURO4 & 0.04–18.38 & 10–125 & & & [12] \\  & EURO5 & 2.67–29.44 & 5–214 & & & [12] \\  & EURO4 & & 11–122 & 21–954 & 113–205 & [13] \\  & EURO5 & & 128–128 & 32–32 & 233 & [13] \\  & EURO6b & & 3–15 & 32–27 & 91–174 & [13] \\  & Sedan & 1.25 & 20 & 256 & & [14] \\  & Sedan & 1.10 & 84 & 714 & & [14] \\  & SUV & 3.28 & 32 & 2340 & & [14] \\  & Light truck & 0.64 & 39.1 & 1000 & & [14] \\ \hline \hline \multirow{2}{*}{LPG} & EURO4 & & 35 & 3000 & 233 & [15] \\  & EURO4 & & 31 & 947 & 184 & [15] \\  & EURO4 & & 92 & 1949 & 230 & [15] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Results of previous studies on emission rate of diesel and gasoline vehicles.  
fuel supply method, were chosen. A 2.0 L class vehicle and a 1.6 L class vehicle were selected to diversify vehicle displacement and technology. The 2.0 L class vehicle featured a turbocharger, while the 1.6 L class vehicle was a naturally aspirated model. Both vehicles were equipped with TWC converters designed to reduce CO, NOx, and HC emissions. For the LPG vehicles, two vehicles in the 2.0 L class equipped with TWC were selected. However, the impact of fuel injection technology on air pollutant emissions was assessed by including an LPLi vehicle that injects LPG in a liquid phase and an LPGi vehicle that injects LPG in a gaseous phase. Regarding the diesel vehicles, two vehicles complying with EURO4 regulations and two vehicles complying with EURO6 regulations were chosen. EURO4 vehicles utilized Exhaust Gas Recirculation (EGR) and a Diesel Oxidation Catalyst (DOC). The DOC served to reduce concentrations of CO, HC, and PM by utilizing an oxidation catalytic converter. EURO6 vehicles employed EGR, DOC, Selective Catalyst Reduction (SCR), and a diesel particulate filter (DPF). EGR and SCR were employed to mitigate NOx emissions, while the DPF served as an aftertreatment device for particulate matter reduction. In addition, vehicles with displacements of 2.0 L and 1.6 L were selected for each regulation to evaluate the impact of displacement on diesel vehicle emissions.