## 3 Problem Analysis and Consequences of Potential Legislative Amendments for Calibration
### \"New Pollutants\"--Is Measurement Technology up to the Task? State-of-the-art PEMS are equipped with sensors for concentration measurement of nitrogen oxides (NO\({}_{\chi}\)), carbon monoxide (CO) and carbon dioxide (CO\({}_{2}\)) as well as for counting PN (with diameters >23 nm: PN\({}_{23}\)). In addition, the PEMS setup includes an exhaust gas mass flow measurement (EFM) system, a Global Positioning System (GPS) and an energy source. Each additional analyzer requires further installation space in the already very compact PEMS design [39]. The compact design causes compromises in measurement accuracy (currently the law allows 50% deviation for PN and 43% for NO\({}_{\chi}\)) [4]. Since PEMS are operated under strongly varying environmental conditions (temperature, humidity) and  
Figure 4: Development of vehicle emission test system market size [38]. are subject to strong accelerations and shaking, they are designed simpler than laboratory devices in order to increase robustness. This is another reason for the higher measurement uncertainty compared to the laboratory grade equipment [40; 41]. Mobile measuring systems are already available on the market for some of the potentially future regulated gaseous pollutants. Some of those new pollutants can be measured quite satisfactorily with such systems [37]. In contrast to the gaseous emissions, the results for the measurement of ultrafine particles (PN\({}_{10}\)) are subject to high inaccuracies. [PERSON] et al. show that PN\({}_{10}\) can account for up to 50% of the total PN result when a vehicle is operated dynamically on a chassis dynamometer [42]. For these investigations, a selection of gasoline vehicles with state-of-the-art aftertreatment systems including a gasoline particulate filter (GPF) have been used. Figure 5 shows measurement results of PN\({}_{10}\) and PN\({}_{23}\) and their respective share of the total PN emission result. The investigation points out how critical a deviation of only 50% in PN\({}_{10}\) can be for the overall result. The diagram shows the PN results in a WLTC for a J-, S- and A-class vehicle, each equipped with a state-of-the-art emission aftertreatment system including a GPF. These were measured on the emission chassis dynamometer with a Cambustion DMS500 [43] and a condensation particle counter (CPC--[44; 45; 46]). On the other hand, measurement results of selected stationary operating points (measured upstream and downstream of the GPF) of the S-class vehicle are shown. For this purpose the DMS500 was set up on the engine test bench. The significant share of PN\({}_{10}\) on the total PN results is also confirmed by the results of another study on the \"Laboratory and On-Road Evaluation of a GPF-Equipped Gasoline Vehicle\", which shows proportions between 20% and 50% [47]. PEMS for PN\({}_{10}\) are part of different studies that show large scattering measurement results [48; 49]. Particularly in direct comparison with laboratory equipment, clear deviations are detected. The \"Assessment of 10-nm Particle Number (PN) PEMS\" [40] summarizes that the most accurate system shows \(\pm\)25% deviations. However, depending on the measuring principle, deviations between 25% and 100% can be observed:  
* CPC systems had 25% to 50% differences compared to the reference systems
* diffusion charger systems had 50% to 100% differences [40]  
The use of the current PN\({}_{10}\) mobile emission measurement technology would therefore in some cases falsely generate results that exceed the legal limit. If the legislator provides a sufficiently high Conformity Factor (CF), this is acceptable for individual homolog  
Figure 5: Share of ultrafine particles in the overall PN result for transient and stationary measurements. tests, but not for development purposes where high measurement accuracy is required for system optimization. On top of challenges regarding the robustness and availability of measurement devices for the new pollutants, the impact of adjusted boundary conditions needs to be considered for PEMS devices.