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Air quality is a growing concern worldwide because of its impacts on both the environment and the human health. The road transport sector is a major contributor to this poor air quality. To reduce the emission of particulate matter, all diesel passenger cars were equipped with diesel particulate filters since the EURO5b emission standard. Unfortunately, these filters can be damaged or intentionally removed during the lifetime of a vehicle. This work presents the particle number emission factors for EURO5 and EURO6 diesel passenger cars, based on the measurements of 757 vehicles. These measurements were performed at low idle, which shows a high correlation to particle number emission factors obtained during homologation cycles or real-driving emission measurements. The results show that the average Particle Number (PN) emission factors are highly impacted by high emitters present in the fleet and that the mileage has a significant impact on the PN emission factors. Finally, the estimated PN emission factors based on low idle measurements were higher by a factor 5.6 for EURO5a, 2.5 for EURO5b and 5.5 for EURO6, compared to their respective HBEFA (Handbook Emission Factors for Road Transport) emission factors. many places over the world. In Europe, air quality limit val-2 ues have been defined for PM 2.5 and PM 10 (particulate mat-3 ter with a diameter smaller than 2.5 and 10 µm, respectively): 4 the PM 2.5 yearly average must not exceed 25 µg∕m 3 while 5 PM 10 values must respect a yearly average of 40 µg∕m 3 and 6 a 24-hour average of 50 µg∕m 3 (this 24-hour average can be 7 exceeded 35 times per year). In 2016, the yearly PM 2.5 limit 8 was not respected at 5% of the European reporting stations 9 while the PM 10 daily limit was exceeded at 19% of these 10 stations. Also in 2016, long-term exposure to PM 2.5 caused 11 422 000 premature deaths in Europe [9]. 12 Additionnally to these EU limits, the World Health Or-13 ganization (WHO) defined Air Quality Guidelines (AQG) 14 which are more strict than the current EU limits. These 15 guidelines recommend that PM 2.5 remains below 10 µg∕m 3 16 for the annual average and below 25 µg∕m 3 for the 24-hour 196 on a large set of vehicles. The linear regression was obtained 197 by considering only the measurements that have PN values 198 at low idle above 10 000 #/cm 3 because of the low accuracy 199 of the diffusion charging measurement devices for very low 200 concentrations (see Figure 3). This linear regression is thus

Increasing the biodiesel content of diesel fuels is encouraged because of its reduced carbon footprint. Pure rapeseed methyl ester (RME)and used cooking oil methyl ester (UCOME) are characterised by well-to-tank greenhouse gas (GHG) reductions of 54% and 88% compared to pure B0 petrodiesel, respectively. Captive fleets such as public transport buses could benefit from these GHG reductions by increasing the biodiesel content of their fuel because they have a consequent yearly fuel consumption. The aim of this paper is to compare on-road tailpipe emissions of a diesel bus when increasing the biodiesel concentration in the fuel. The tests were carried out on a standard city bus belonging to the Euro V EEV emission standard that was equipped with a portable emission measurement system measuring NO, NO2, PN, CO and CO2 at the tailpipe. The bus followed the SORT which is representative of urban bus driving. The heavy urban on-road measurements indicated increased NOx emissions (24–26%), decreased PN emissions (43–45%) and slightly decreasing CO emissions for B30 RME and UCOME compared to B7. A measurement uncertainty analysis showed that the CO emissions were less reliable. Similar conclusions were drawn for the easy urban on-road bus emission measurements with smaller differences between B7 and B30 RME and UCOME.