## Appendix A  
The statistical analysis determined the (experimental) repeatability (\(S_{r}\)) and reproducibility (\(S_{R}\)) of pollutants with various methods based on the standard ISO 5725-2 (ISO, 1994). In order to capture the situation as it is today and due to the limited number of laboratories, no variance (Cochran test) or average (Grubbs test) outliers tests were applied. For each methodology (Bags, Golden PEMS, Lab PEMS) and pollutant (CO\({}_{2}\), CO, NOx, PN), the overall reproducibility variance was calculated using the following formula:  
\[S_{R}^{2}=S_{r}^{2}+S_{L}^{2}\]  
where \({S_{L}}^{2}\) stands for the between-laboratories variance and \({S_{r}}^{2}\) for the overall repeatability variance:  
\[S_{r}^{2}=\frac{\sum_{i=1}^{p}(n_{i}-1)S_{i}^{2}}{\sum_{i=1}^{p}(n_{i}-1)}\]  
\[S_{L}^{2}=\frac{[1/(p-1)]\sum_{i=1}^{p}\Bigl{[}n_{i}(x_{i}-\overline{x})^{2} \Bigr{]}-S_{r}^{2}}{\overline{n}}\]  
where \(n_{i}\) stands for the number of measurement achieved by laboratory \(i\), \(S_{i}\) the standard deviation of laboratory \(i\), \(p\) the number of laboratories available (without any outlier removal), \(\overline{x}\) stands for the average of the means of the non-outlier laboratories, and \(\overline{n}\) defined as:  
\[\overline{n}=\frac{1}{p-1}\left[\sum_{i=1}^{p}n_{i}-\frac{\sum_{i=1}^{p}n_{i}^ {2}}{\overline{n}_{i}^{p}=n_{i}}\right]\]  
* RDE4 2018 2018. _Commission Regulation (EU) (Voted 3 rd of May 2018)__Amending Directive 2007/46/EC,__Commission Regulation (EC) No 692/2008__and Commission Regulation (EU) 2017/1151__for the Purpose of Improving the Emission Type Approval Tests and Procedures for Light Passenger and Commercial Vehicles, Including Those for In-Service Conformity and Real-Driving Emissions and Introducing Devices for Monitoring the Consumption of Fuel and Electric Energy,_ Ares (2018)1297632; European Commission: Brussels, Belgium, 2018. * CEN/TC 2018. _Road Vehicles.__Portable Emission Measuring Systems (PEMS)__Performance Assessment_; Proposal for European Standard; European Committee for Standardization: Brussels, Belgium, 2018. * ISO/IEC 17025:2017. _General Requirements for the Competence of Testing and Calibration Laboratories_; International Organization for Standardization: Geneva, Switzerland, 2017; Available online: [[https://www.iso.org/standard/66912.html](https://www.iso.org/standard/66912.html)]([https://www.iso.org/standard/66912.html](https://www.iso.org/standard/66912.html)) (accessed on 16 November 2018). * ISO/IEC 17020:2012. _Conformity Assessment--Requirements for the Operation of Various Types of Bodies Performing Inspection_; International Organization for Standardization: Geneva, Switzerland, 2012; Available online: [[https://www.iso.org/standard/52994.html](https://www.iso.org/standard/52994.html)]([https://www.iso.org/standard/52994.html](https://www.iso.org/standard/52994.html)) (accessed on 16 November 2018). * ISO/IEC 17043:2010. _Conformity Assessment--General Requirements for Proficiency Testing_; International Organization for Standardization: Geneva, Switzerland, 2010; Available online: [[https://www.iso.org/standard/29366.html](https://www.iso.org/standard/29366.html)]([https://www.iso.org/standard/29366.html](https://www.iso.org/standard/29366.html)) (accessed on 16 November 2018). * [PERSON] et al. 2004 [PERSON]; [PERSON]; [PERSON] Comparability of particle emission measurements between vehicle testing laboratories: A long way to go. _Meas. Sci. Technol._**2004**, _15_, 1855-1866. [CrossRef]
* [PERSON] et al. 2005 [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON] Inter-laboratory test of exhaust PM using ELPI. _Aerosol Sci. Technol._**2005**, _39_, 333-346. [CrossRef]
* [PERSON] et al. 2006 [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON]; [PERSON], [PERSON]; [PERSON] [PERSON]; [PERSON], [PERSON] Inter-laboratory study of the exhaust gas particle number measurements using the condensation particle counter (CPC).