## 2 Materials and Methods
### Measurement Method and Calculation Formula for Emission Estimation  
A schematic of the BC emission measurement method is shown in Figure 3. BC concentrations was continuously measured at 1 min interval using an Aethalometer (AE33, Magee Scientific) which incorporated the patented Dual-Spot technology and a seven wavelength (370, 470, 520, 590, 660, 880, 950 nm) [17]. The flow rate of emissions into the equipment was set at 2 LPM and had been tested during the cycles, the deviation of the flow rate was found within 5%. Simultaneously, the leakage test of the filter was performed and was also under \(<\)10% the appropriate range provided by the manufacturer. To determine the BC concentrations, the mass absorption cross-section (MAC) 7.77 m\({}^{2}\) g\({}^{-1}\) at 880 nm was used [17]. Two sampling systems were conducted for measuring BC. The constant volume sampler (CVS) tunnel system first diluted the raw exhaust from vehicles using the CVS tunnel, and then, moisture was controlled from the diluted emission using a diffusion dryer; finally, particles with a maximum size of 2.5 \(\upmu\)m were captured using a URG cyclone. Tail-pipe system used direct sucking from the exhaust of the vehicles, and the subsequent measurement method was the same as that of the CVS tunnel system. The PM weight was measured using the PM sampler in all driving modes from the CVS tunnel. However, the PM concentration in the NIER modes, which included only the driving modes in the heated state, was too low to be measured using a balance. Therefore, in this study, only PM values measured in CVS-75 and NEDC modes were used.  
Figure 2: Regulation modes used in measurement. CVS-75 mode used in gasoline, LPG, and diesel vehicles for EURO 3. NEDC mode used in diesel vehicles after EURO 4.  
For NIER modes, Equation (1) was used for calculating the emission factor. If the concentration of the sample is below the minimum detection limit of the equipment, a diffusion dryer was used in the vehicle's exhaust pipe without dilution. The sample with moisture removed was directly measured using the tail-pipe sampling formula shown in Equation (2). The calculation result is represented in the emission unit considering the dilution factor [16].  
\[\text{Emissionfactor}\left(g\;km^{-1}\right)\text{\emph{of}}\;CVS\;\text{\emph{ tunnel}}\;\text{\emph{in}}\;\text{\emph{NIER}}\;\text{\emph{Mode}}=\;\frac{BC\;\times\;V_{mix}}{d} \tag{1}\]  
\[\text{\emph{Emission}}\;\text{\emph{factor}}\left(g\;km^{-1}\right)\text{\emph{of }}\;\text{\emph{tailpipe}}\;\text{\emph{in}}\;\text{\emph{NIER}}\;\text{ \emph{Mode}}=\;\frac{BC\;\times\;V_{mix}}{d\;\times\;DF} \tag{2}\]  
where \(BC\) is the measured \(BC\) concentration (mg m\({}^{-3}\)), \(V_{mix}\) is the total volume of sample from CVS tunnel (m\({}^{3}\)), d is the distance that the test vehicle has run (km), and DF is the dilution factor of the sample that has been measured from CVS tunnel.  
During CVS-75 and NEDC driving, the results were calculated using Equations (3) and (4) [18]. In the CVS-75 mode, weights were applied to all three phases (0.43 and 0.57) to meet the same conditions as the existing PM emission calculation formula. The p1, p2, and p3 represent data from phases 1, 2, and 3, respectively, in the following equations.  
\[\begin{split}&\text{\emph{Emission}}\;\text{\emph{factor}}\left(g  
measured at 370 nm and 880 nm, and \(\lambda_{1}\) and \(\lambda_{2}\) are wavelengths used for each absorption coefficient, respectively [21].  
\[\mathrm{AEE}=-\frac{\mathrm{ln}(\mathrm{p_{abs1,370 nm}/\mathrm{b_{abs2,880 nm}}})}{ \mathrm{ln}(\lambda_{1,370 nm}/\lambda_{2,880 nm})} \tag{5}\]  
In this section, in order the comparison with various emission source, the experiments of the biomass burning (oak wood) using the stove, coal burning from the power plant stack in addition to the results of the NIER modes were conducted. The set-up systems were the same as the measurement of the tailpipe sampling by chassis-dynamometer tests.