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Many researchers have reported the measurement of high numbers of emitted particles from gasoline vehicles operating at high speed. To date, in the absence of standard test protocols or analytical techniques, these measurements have all been made from a dilution tunnel set up according to regulatory procedures. Currently, there is great uncertainty relating to the use of the dilution tunnel as a suitable tool for the measurement of automotive particle size and number distribution and also the relevance of the procedure to ambient measurement of the same parameters. Gasoline particle number emissions, as measured on a dilution tunnel, are low at speeds under 120km/h. Beyond this speed, high numbers of very small particles have been measured. There is some evidence to show that these particles may be formed as an artefact within the sampling system, either from the desorption of deposited material or from the pyrolysis of other material in the sampling system itself.

Particle emissions from vehicles are currently under close scrutiny with respect to their contribution to ambient air quality relative to other sources. Small particles, less than 10 μm, referred to as PM10, have been linked to various health issues. In this study, tests have been performed on European diesel light duty vehicles using a range of production diesel fuels. Tests were also performed on two gasoline passenger cars for comparison. Measurements were made of exhaust particle size distribution and number, as well as mass emissions using the legislated filter paper method. The results showed that most of the particles emitted were very small, with median size of the order 100 nanometres (nm). The median particle size was insensitive to changes in fuel, vehicle or operating condition. Measurements of particle number broadly correlated with particle mass emissions, and ranked fuels and vehicle types in the same order.