## 2 Materials and Methods  
The experimental setup is given in Figure 1. The light-duty vehicles tested were respecting the Euro 6 emission standard [34] and the two-wheelers (L-category) the recently introduced Euro 4 [35]. They were all registered in 2017-2018 with one exception (2014). The fleet consisted of vehicles with diesel, gasoline, and CNG fueled engines; see Table 2. Market fuels were used during the campaign: diesel B7, gasoline E10, and CNG (\(>\)87% methane). The vehicles were tested with the recently introduced Worldwide harmonized Light-duty vehicle Test Cycle (WLTC) for type approval in EU. For two-wheelers, the recently introduced Worldwide harmonized Motorcycle Test Cycle (WMTC) was used. Extra cold and hot NEDC (New European Driving Cycle) and WLTC tests were done with the Gasoline Direct Injection (G-DI) and constant speed tests with the Gasoline Port Fuel Injection (G-PFI) #2 vehicles. The motorcycles were tested at the one axle roller dynamometer Vehicle Emissions Laboratory (VELA 1) of the European Commission-Joint Research Centre in Italy. The light-duty tests were conducted at the two axis roller dynamometer Vehicle Emissions Laboratory (VELA 2). G-PFI #1 \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **PEMS A** & **PEMS B** & **Lab 1** & **Lab 2** & **FTIR** \\ \hline Manufacturer & Horiba & AVL & AVL & Horiba & AVL \\ Model & OBS-ONE & M.O.V.E. & AMA i60 & MEXA 7100 & Sesam \\ Principle CO\({}_{2}\) & Heated NDIR & NDIR & NDIR & NDIR & FTIR \\ Measurement & wet & dry & dry & dry & wet \\ Max CO\({}_{2}\) & 20\% & 20\% & 20\% & 20\% & 20\% \\ Calibration gas & 15\% & 15\% & 15\% & 15\% & - \\ Sampling line & 90 \({}^{\circ}\)C & 90 \({}^{\circ}\)C & 190 \({}^{\circ}\)C & 190 \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristics of the equipment. Figure 1: Experimental setup. The tests were conducted with various vehicles (Table 2) at two laboratories with different equipment (Table 1). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Code** & **Euro** & **MY** & **Fuel** & **Mass** & **Power** & **Displ.** & **Aftertreatment** \\  & **(-)** & **(-)** & **(-)** & **(kg)** & **(kW)** & **(l)** & **(-)** \\ \hline Diesel \#1 & 6b & 2017 & B7 & 1360 & 90 & 1.6 & DOC + DPF \\ Diesel \#2 & 6d-temp & 2018 & B7 & 1180 & 96 & 1.5 & DOC + DPF + SCR \\ CNC \#1 & 6c & 2018 & CNG & 1360 & 80 & 1.0 & TWC \\ CNG \#2 & 6b & 2018 & CNG & 2310 & 100 & 3.0 & TWC \\ G-PFI \#1 & 6b & 2014 & E10 & 1130 & 57 & 1.4 & TWC \\ G-PFI \#2 & 6d-temp & 2018 & E10 & 1200 & 60 & 1.2 & TWC \\ G-DI \#1 & 6c & 2017 & E10 & 1390 & 110 & 1.5 & TWC \\ Motorcycle & 4 & 2018 & E10 & 150 & 16 & 0.28 & TWC \\ Moped & 4 & 2018 & E10 & 95 & 2.5 & 0.05 & TWC \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Characteristics of the vehicles. was additionally tested at the one-axis roller dynamometer (VELA 1). In all cases laboratory grade analyzers were sampling from the tailpipe in parallel with PEMS or FTIR. The characteristics of the equipment are summarized in Table 1. All systems used heated lines \(>\)90 \({}^{\circ}\)C in order to avoid any condensation in their sampling lines. PEMS A [36] and FTIR measure chemical concentrations on a wet basis, thus they do not apply any dry-wet correction on the original signal. PEMS B and the laboratory grade analyzers of laboratory 1 and 2 measure on a dry basis: PEMS B compensates for the water interference and for Lab1 and Lab2 the dry-wet correction is applied in post-processing. NDIR analyzers are composed of an infrared source lamp, a sample chamber, and a reference parallel chamber through which the split IR beam is focused, an optical filter to select the wavelength that the molecules absorbs, and a detector. FTIR is composed of an infrared source lamp, a Michelson interferometer as dispersive element, a sample chamber, and a detector.