Particle measurement programme (PMP) light-duty inter-laboratory exercise: Repeatability and reproducibility of the particle number method

A Euro 4 Light-Duty Diesel vehicle equipped with a diesel particulate filter (DPF) was circulated to 9 labs where repetitions of the current regulatory New European Drive Cycle (NEDC) were conducted. Regulated gaseous and improved (with cyclone, filter temperature 47 +/- 5 degrees C, constant filter face velocity, high precision balance at all labs) particulate mass (PM) measurements were also conducted. A reference particle number (PN) measurement system measuring non-volatile particles was circulated along with the test vehicle. Labs also tested their own PN systems built to comply with the reference system's performance specifications. The mean PN emissions level of the vehicle was below 1 x 10(11) particles/km. The intra-lab variability (repeatability) was similar to 40% and the inter-lab variation was similar to 25%. The study showed that the new PN method had similar variability to other gaseous pollutants such as carbon monoxide and hydrocarbons and better than the PM (intra-lab variability similar to 55% and inter-lab similar to 35%). Even with the improved PM method the emissions of the vehicle were similar to the background level (similar to 0.4 mg/km) and the method was subject to volatile artifact. The PN method showed greater sensitivity than the PM method as it could distinguish the DPF fill state or different preconditioning states of the vehicle. However, the PN emission level of the vehicle estimated by the reference system were on average 15% higher than any given lab's own system, indicating that the procedures and calibration designed for the standardization of performance should be precisely defined and followed.