High Particle Number Emissions Determined with Robust Regression Plume Analysis (RRPA) from Hundreds of Vehicle Chases.

Particle number emission factors were determined for hundreds of individual diesel and gasoline vehicles in their real operation on Finnish highways and regional roads in 2020 with one-by-one chase measurements and Robust Regression Plume Analysis (RRPA). RRPA is a rapid way to analyze data from a large number of vehicle chases automatically. The particle number emission factors were determined for four ranges of particle diameters (>1.3, > 2.5, > 10, and >23 nm). The emission factors for most of the measured vehicles were observed to significantly exceed the non-volatile particle number limits used in the most recent European emission regulation levels, for both light-duty and heavy-duty vehicles. Additionally, most of the newest vehicles (covering regulation levels up to Euro 6), for which the particle number emission regulations (non-volatile >23 nm particles) apply, showed emission factors of the >23 nm particles clearly above the regulation limits. Although the experiments included measurements of real-world plume particles (mixture of non-volatile and semi-volatile particles) and not only the non-volatile regulated particles, it is important to note that the emissions of regulated particles were also estimated to exceed the limits, based on non-volatile >23 nm particle fraction from curbside studies. Moreover, the emission factors of the >1.3 nm particles were mostly about an order of magnitude higher compared to the >23 nm particles.