This work has focused on the development and evaluation of an experimental setup to measure in real time and with on-board equipments the particle emissions of diesel vehicle minimizing the uncertainties associated to dilution ratio, the length of the transfer line and the sampling point in the engine exhaust pipe. Its suitability has been verified by ensuring the repeatability of the results in dynamometer tests reproducing standard circuits, as well as in closed circuits and in real urban traffic in Madrid, Spain. The experience derived from this work has been very useful, contributing to the advance in the measurement of particle number and size distribution in real time using on-board equipment and bringing us closer to understanding the relationship between the physical characteristics of the particles emitted by a diesel engine and its operation in real urban traffic conditions. The proposed on-board system has provided very satisfactory results.

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A novel on-board system was tested to characterize size-resolved particle number emission patterns under real-world driving conditions, running in a EURO4 diesel vehicle and in a typical urban circuit in Madrid (Spain). Emission profiles were determined as a function of driving conditions. Source apportionment by Positive Matrix Factorization (PMF) was carried out to interpret the real-world driving conditions. Three emission patterns were identified: (F1) cruise conditions, with medium-high speeds, contributing in this circuit with 60% of total particle number and a particle size distribution dominated by particles >52 nm and around 60 nm; (F2) transient conditions, stop-and-go conditions at medium-high speed, contributing with 25% of the particle number and mainly emitting particles in the nucleation mode; and (F3) creep-idle conditions, representing traffic congestion and frequent idling periods, contributing with 14% to the total particle number and with particles in the nucleation mode (<29.4 nm) and around 98 nm. We suggest potential approaches to reduce particle number emissions depending on particle size and driving conditions. Differences between real-world emission patterns and regulatory cycles (NEDC) are also presented, which evidence that detecting particle number emissions <40 nm is only possible under real-world driving conditions.