## 2 Materials and Methods
### Measurement Equipment  
The laboratory tests were conducted at the one-axis roller dynamometer Vehicle Emissions Laboratory (VELA 1) of the JRC in Italy (Figure 2). The exhaust gas was connected to the full dilution tunnel with a <3 m tube. A flow rate of 9 m\({}^{3}\)/min was used at the full dilution tunnel, with Constant Volume Sampling (CVS). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Technology** & **Vehicle 1 (SI)** & **Vehicle 2 (CI)** \\ \hline Displacement (L) & 1.4 & 1.6 \\ Power (kW) & 57 & 90 \\ Transmission/gearbox & Manual/5 & Manual/6 \\ Vehicle mass (kg) & 1130 & 1360 \\ Exhaust after treatment & TWC & DOC + DPF + NS \\ Fuel & Gasoline & Diesel \\ Fuel system & MPFI & Common rail \\ Emission standard & Euro 6 & Euro 6 \\ \hline \hline \end{tabular}  
* DOC—diesel oxidation catalytic converter; DPF—diesel particulate filter; TWC—three-way catalytic converter; NS—NO\({}_{x}\) Storage system; MPFI—multi point fuel injection; SI—spark-ignition; CI—compression-ignition.  
\end{table} 
Table 1: Characteristics of the vehicles. Figure 1: A Worldwide harmonized Light vehicle Test Cycle (WLTC) Class 3 divided in four phases (low, medium, high, and extra high), and a pre-recorded real driving emissions (RDE) cycle under laboratory conditions (lab-RDE) cycle divided in three phases (urban, rural, and motorway). As required by the regulation, for the WLTC, the sampling bags were filled with the diluted exhaust and were analyzed at the end of the test. As a result of the long duration of the lab-RDE cycle, no bag measurements were taken, but the emissions were calculated using the integrated real time data of the analyzer connected to the CVS (diluted gas). One analyzer (AMA i60 from AVL) was used to measure the diluted gas in real time (lab-RDE) or the bags filled with diluted exhaust at the end of the test (WLTC). The bag and/or diluted measurements were considered as the reference values. Another analyzer (AMA i60) was used to measure the raw exhaust from the tailpipe of the vehicle, after the two PEMS (technical specifications in Table 2). PEMS #1 (OBS-ONE, Horiba, Kyoto, Japan) and PEMS #2 (M.O.V.E., AVL, Graz, Austria) were tested with the SI gasoline vehicle, while PEMS #2 and PEMS #3 (M.O.V.E. and AVL) were tested with the CI diesel vehicle (technical specifications in Table 2). Each PEMS was connected to its own exhaust flow meter (EFM). Attention was given to leave enough tube diameters length (>four diameters) before and after the EFMs to ensure their proper operation, and additionally, not to cause any significant pressure drop by reducing the tailpipe inner diameter. For this reason, bigger flow meters were used for the CI vehicle, which has higher flow rates. The zero and span calibration of the analyzers was conducted before each test. The zero and span drift of the PEMS was checked only after the RDE tests. All of the results were well within the regulation requirements (NOx zero drift <5 ppm, NOx span drift <2%) and there was no systematic drift (positive or negative), thus, all of the presented results include the contribution of the drift (if any). \begin{table}
\begin{tabular}{c c c c c} \hline
**Technology** & **PEMS \#1** & **PEMS \#2, \#3** & **Tailpipe** & **Diluted/Bags** \\ \hline Manufacturer & Horiba & AVL & AVL & AVL \\ Model & OBS-ONE & M.O.V.E. & AMA i60 & AMA i60 \\ Principle CO2 & Heated NDIR & NDIR & NDIR & NDIR \\ Range CO2 & 20\% & 20\% & 1\%, 20\% & 1\%, 6\% \\ Principle NOx & Heated CLD & NDUV & CLD & CLD \\ Range NOx (ppm) & 3000 & 5000 & 100, 1000, 10,000 & 10, 100, 1000 \\ EFM & Pitot 2\({}^{\prime}\) & Pitot 2\(\&\)2.5\({}^{\prime}\) & CO2 tracer & - \\ \hline \end{tabular} NDIR—on-dispersive infrared detection; CLD—chemiluminescence detection, NDUV—non-dispersive ultraviolet; EFM—exhaust flow meter; PEMS—portable emissions measurement systems.  
\end{table} 
Table 2: Characteristics of the equipment. Figure 2: Vehicle Emissions Laboratory (VELA 1) experimental setup (spark-ignition [SI] vehicle).