## 2 Materials and Methods  
### Vehicle Selection and Driving Modes  
Various passenger cars, vans, and SUVs using gasoline, the liquefied petroleum gas (LPG), and diesel were selected for the study, as listed in Table 1. Gasoline vehicles with multi-point injection (MPI) technology, in which a mixture of fuel and air is injected into a cylinder, and gasoline direct injection (GDI) vehicles, in which the fuel is directly injected into a cylinder, were employed for the experiment. In addition, GDI vehicles were measured separately before and after the application of the PM regulation (0.004 g km\({}^{-1}\)). This standard applies only to GDI vehicles of the model year after 2014 in gasoline. MPI vehicles manufactured between 2001 and 2005 (G#7) and between 2009 and 2012 (G#8) were selected for evaluating the BC emissions based on the degree of vehicle aging. LPG vehicles with liquified petroleum injection (LPI) combustion system were conducted as manufactured 2014 (L#1, 2), 2015 (L#3), and 2008 (L#4). For gasoline and LPG vehicles, passenger cars installed with a three-way catalyst (TWC) as the aftertreatment device were used. Diesel vehicles were selected according to the European regulation standards (EURO 3-6). EURO 6 vehicles are equipped with aftertreatment devices such as a diesel oxidation catalyst (DOC), DPF, and lean NOx trap (LNT) or selective catalyst reduction (SCR). However, EURO 5 vehicles have DOC and DPF, and EURO 3 vehicles only have DOC. PM regulation for diesel vehicles in Korea can be briefly explained as follows: EURO 3 allowed the highest level of PM at 0.11 g km\({}^{-1}\), and as the regulation became stricter, EURO 4, 5, and 6 allow a maximum of 0.06, 0.005, and 0.0045 g km\({}^{-1}\), respectively. The driving speed over time in the modes used in the study are shown in Figure 1, and were conducted about two times for each mode. NIER modes were selected to estimate the air pollutant emissions of on-road mobile source air pollution. These NIER modes were developed by the National Institute of Environmental Research according to the road conditions of Korea. In these modes, the driving pattern of low speed to high speed at city centers in Korea can be reproduced on the chassis dynamometer, and they consist of 13 types of modes in total. Among these modes, in this study, NIER-01 (avg. 4.7 km h\({}^{-1}\)), NIER-05 (avg. 17.3 km h\({}^{-1}\)), NIER-09 (avg. 34.1 km h\({}^{-1}\)), NIER-12 (avg. 65.4 km h\({}^{-1}\)), and NIER-14 (avg. 97.3 km h\({}^{-1}\)) modes were used to measure BC emissions based on low to high driving speeds (Figure 1) [16]. Prior to driving in all of these NIER modes, to prepare the conditions of driving in a heated state, the vehicle was driven at a speed of 70 km h\({}^{-1}\) until the coolant temperature stabilized, and the speed was maintained for an additional 4 min to measure the emission from the vehicle after accounting for preheating. In addition, during measurement, to eliminate the impact of BC emitted when the vehicle engine is started, the driving mode started with the vehicle's engine turned on after the preheating. \begin{table}
\begin{tabular}{r c c c c c c} \hline \hline
**No.** & **Vehicle** & **Type** & **Displacement (cc)** & **Fuel** & **After-Treatment** & **Engine and Regulation** & **Mode** \\ \hline  
an & 2400 & Diesel & DOC, DPF, SCR & EURO 6 & NEDC \\ \hline \multicolumn{7}{c}{Gasoline: regular gasoline is fuel with octane number of 91–94. TWC: Three-Way Catalyst, DOC: Diesel Oxidation Catalyst, DPF: Diesel Particulate Filter. LNT: Lean NOx trap, SCR: Selective Catalytic Reduction. GDI: Gasoline Direct Injection, MPI: Multi-Port Injection; LPI: Liquified Petroleum Injection. \({}^{\text{(a)}}\) GDI Vehicle before PM regulation, \({}^{\text{(b)}}\) GDI Vehicle after PM regulation. \({}^{\text{(c)}}\) MPI Vehicle made between 2001 and 2005, \({}^{\text{(d)}}\) MPI Vehicle made between 2009 and 2012.} \\ \end{tabular}
\end{table} 
Table 1: Information on test vehicles measured using chassis dynamometer (Nos.