## 2 Challenges Posed by the Upcoming Emission Legislation  
Figure 2 shows an overview of the development of emissions legislation in Europe since 2015. The standards take into account technical trends and further developments that enable more non-critical emissions behavior while at the same time allowing for justifiable additional effort on the part of manufacturers and consumers. Forecasts and future scenarios are particularly important for OEM, as the development cycles of new hardware are in some cases longer than the current revision intervals of emissions legislation in Europe [8]. The overall objective of the regular revision of emission legislation is an improvement in air quality. In particular, zero-emission mobility in urban environments is focused since many years. The sometimes considerable discrepancies between emission results determined in the laboratory and PEMS measurement results on the road [9; 10; 11; 12] have led to public discussions, juristic conflicts and consequently to local bans on vehicles of older construction years [7; 13]. With the introduction of the \"Worldwide harmonized Light duty vehicle Test Procedure\" (WLTP), RDE tests were integrated into the vehicle homologation procedure in addition to chassis dyno tests in the laboratory environment. Currently, a debate is taking place about the elimination of laboratory tests as main criterion for the evaluation of pollutant emissions for the period after EU6 [14]. The Clove Consortium states that so far \"non-regulated pollutants (gaseous and particles) [shall] be included in the regulations and measured on board the vehicle with PEMS\" [14]. Laboratory tests should then only be necessary, for example, to evaluate new pollutants for which an appropriate mobile measuring technology is not yet available. Additionally \"for CO\({}_{2}\) emission measurement and check of compliance with the fleet-based CO\({}_{2}\) emission targets\" [15], the WLTP chassis dynamometer tests could still be applied  
Figure 2: FEV scenario for European emission legislation roadmap with focus on RDE. according to this reference. However, the actual \"[pollutant] emission certification [will probably be]-based (solely) on RDE and PEMS testing\" [15]. A further adjustment of the specifications is planned in the form of fuel and technology neutrality of emission standards [15; 16]. Thus, there will probably be uniform limit values for petrol, diesel, and any hybrid applications. At the same time, it is likely that all fuels available on the market can be used for test purposes. Examples for the influence of the fuel on the particulate number (PN) emission result are given in [17; 18; 19; 20; 21; 22; 23]. The oxygen content in the fuel has a strong influence; increasing oxygen content in the fuel (e.g., in ethanol or methanol) causes a decrease in the total PN concentration and in the concentration of nucleation mode PN [24; 25; 26]. The importance of RDE will increase significantly as a result of these changes. Especially as the acceptance in society for emission results from measurements in real road traffic is higher than for the testing approach on chassis dynos used so far. However, the current legally defined boundary conditions for e.g., longitudinal vehicle dynamics or road topography still lead to discrepancies between compliant RDE test results and reality. The current conditions and limitations are highlighted in Figure 3.  
With a clear differentiation of the drive profile into the urban, rural and motorway phases, the possible shares of speed ranges are clearly defined. On top of the speed itself, restrictions for allowed driving dynamics ranges are given by providing a maximum limitation for v-apos95 (95 th percentile of the products of velocity and positive acceleration for each phase) and a minimum limitation for RPA (relative positive acceleration).