Use of a Catalytic Stripper as an Alternative to the Original PMP Measurement Protocol

The Particle Measurement Programme (PMP) developed an exhaust particle number measurement protocol that has been adopted by current light duty vehicle emission regulations in Europe. This includes thermal treatment of the exhaust aerosol to isolate solid particles only and a number counting device with a lower cutpoint of 23 nm to avoid measurement of smaller particles that may affect the repeatability of the measurement. In this paper, we examine a potential alternative to the PMP system, where the thermal treatment is replaced by a catalytic stripper (CS). This offers oxidation and not just evaporation of the volatile components. Alternative sampling systems, either fulfilling the PMP recommendations or utilizing a CS, have been explored in terms of their volatile particle removal efficiency. Tests have been conducted on diesel exhaust, diesel equipped with DPF and gasoline direct injection emissions. The results showed that the CS offers similar performance characteristics to the PMP when tested on diesel exhaust. In tests with the gasoline vehicle, the CS has been shown of leading to lower particle concentrations than the PMP, indicating that a larger number of particles can be removed as volatiles. Moreover, steady speed tests at 120 kph revealed that the PMP protocol was not sufficient in removing particles below 10 nm, which were completely eliminated when the CS was positioned downstream of an evaporation tube. The results of the study once more confirm the robustness of the PMP protocol for diesel exhaust sampling but also suggest that more analysis is needed before extending the protocol to other vehicle types and/or particle sizes.