Investigation of Ultrafine Particle Number Measurements from a Clean Diesel Truck Using the European PMP Protocol

The sampling protocol proposed by the international PMP program for determination of particle emissions from clean light-duty vehicles was applied to the emissions from a California heavy-duty trap-equipped diesel truck. CARB is interested in developing opinions about the potential of this new European approach for emission determination and in exploring its utility for use in California. In this exercise, the use of various commercially available instruments for counting and sizing particles in the context of the PMP recommendations are explored. A single vehicle on a chassis dynamometer was exercised over steady-state and transient cycles. Multiple measurements of gaseous, mass, and particle emissions were collected in order to determine statistical significance.

The PMP approach yielded particle emission measurements with higher precision and accuracy than the reference mass-based emission measurement. While commercially available fast multichannel electrometers are a significant advancement for convenient determination of the particle size distribution, they are not always appropriate for determining total particle counts. The thermally conditioned sample per the PMP protocol still contained a significant number of sub-20 nm solid particles, which can be counted without loss of accuracy with current instrumentation. Tunnel storage and release can lead to unexpected nucleation events even in the case where ULSD fuel is used. The use of aftertreatment devises to remove volatile material otherwise prevented the formation of a measurable nucleation mode. This work allows CARB to continue to explore issues related to the nature of the particles post PMP sampling, the toxicity of volatile, sub-20 nm particles, and the improved statistics of particle counting relative to mass weighing.