Measurement of nucleation and soot mode particle emission from a diesel passenger car in real world and laboratory in situ dilution

Uncertainties still remain in the size and number emission of nucleation and soot mode particles from diesel vehicles and understanding of the nucleation process under different ambient conditions. Particle emission measurements were carried out with a EURO-3 certified European diesel passenger car running on low (<10 ppm S) and high (310 ppm S) sulfur fuel. A newly developed in situ diluter which sampled exhaust continuously from the tailpipe and diluted in two steps by a factor of 500–6000 was employed to study nucleation particle formation under well-controlled temperature and humidity conditions. Particle emission measurements were also carried out with a mobile laboratory chasing the exhaust plume of the same vehicle in summer (19–25 °C) and winter (9 °C), with no significant difference of the nucleation or soot mode particle emission found. The particle size distributions compared well with those measured in the laboratory with the same vehicle under identical driving conditions. Simple nucleation and coagulation calculations were compared with the atmospheric and laboratory measurements. It was shown that the primary dilution step had the largest impact on the nucleation mode formation, while the model overpredicted the influence of temperature and humidity. No nucleation mode particles were observed running the diesel vehicle on low (<10 ppm S) fuel.