## 2 Materials and Methods
### Chassis Dynamometer System and Exhaust Gas Analysis  
In this study, a chassis dynamometer system was employed to replicate actual road conditions by controlling the load applied to the vehicle. The chassis dynamometer simulates the driving process of repeated stoppage, acceleration, constant speed, and deceleration that occurs on real roads. Specifically, a dynamometer designed for small passenger vehicles and trucks with a total vehicle weight of less than 3.5 tons was utilized. Figure 1 depicts the chassis dynamometer system employed in this study, comprising an exhaust gas analyzer, a sampling device, a dilution tunnel, PM measurement equipment, an exhaust gas heat exchanger, and auxiliary operation devices (such as a driver's aid and weather station). The exhaust gas analyzer was utilized to analyze the composition of exhaust gases emitted through the vehicle's exhaust pipe. Furthermore, a dilution tunnel was incorporated to achieve a clean gas-to-exhaust gas dilution ratio of 100:1. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Parameters**} & \multicolumn{4}{c}{**Driving Mode**} \\ \cline{2-5}  & **CVS-75** & **NEDC** & **WLTC** & **US06** \\ \hline Driving time (second) & 1874 & 1180 & 1800 & 600 \\ Driving distance (km) & 17.84 & 11 & 23.26 & 12.9 \\ Average speed (km/h) & 34.1 & 33.6 & 46.3 & 77.9 \\ Maximum speed (km/h) & 91.2 & 120 & 131.6 & 128 \\ \hline \end{tabular}
\end{table} 
Table 2: Driving mode conditions using a chassis dynamometer to test vehicles. The exhaust gas emitted from the vehicle's exhaust pipe during each mode of operation on the chassis dynamometer was diluted with a specific volume of air using a Constant Volume Sampler (Figure 2a). The diluted exhaust gas was then collected in a sampling bag for subsequent quantitative analysis. A MEXA-7200H (HORIBA) instrument capable of analyzing CO, HC, NOx, CO\({}_{2}\), and CH\({}_{4}\) was used to measure the exhaust gas composition (Figure 2b). CO and CO\({}_{2}\) were analyzed using the Non-Dispersive InfraRed (NDIR) method, HC was measured using the Heated Flame Ionization Detection (HFID) technique, NOx was determined using Chemiluminescence Detection (CLD), and CH\({}_{4}\) was analyzed via Gas Chromatography-Flame Ionization Detection (GC-FID) [17; 35]. The real-time instrument performs a background value and calibration before each measurement. The collection of PM\({}_{2.5}\) involved diluting the exhaust gas with air at a predetermined ratio while the vehicle was driven on the chassis dynamometer, and the particulate matter was collected on a filter (Figure 2c). Samples were collected using quartz filters (Pallflex, 2500 QATUP, Pall Corp., USA) for PM and organic marker analysis. Prior to sampling, the quartz filters were baked at 450 \({}^{\circ}\)C for 6 h to remove impurities and minimize the presence of carbonaceous components in the blank samples. The PM\({}_{2.5}\) emissions were calculated by measuring the weight difference of the filter before and after collection. Vehicle NH\({}_{3}\) emissions were analyzed using an Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) instrument (Los Gatos Research (LGR), ABB Inc., Quebec, Canada) based on Laser Diode Spectrometry. Figure 2d shows the equipment used in this study. This method utilizes the Lambert-Beer law, which calculates absorbance based on the variation in laser intensity before and after transmission through the sample. In addition, measurements of gas temperature, pressure, wavelength travel distance, and wavelength after passing through the sample were taken to calculate the NH\({}_{3}\) concentration. The NH\({}_{3}\) meter used in this study was calibrated by a diluter treated with electrolytic polishing (EP) before measurement. All instruments were calibrated before and after major measurements using a chassis dynamometer. Figure 1: Schematic diagram of the chassis dynamometer system.