Development and Characterization of Aerosol Conditioning Devices for Solid Ultrafine Particle Measurement from Diesel Engines: A Review

Emission regulations mandate the measurement of solid particles of size greater than 23 nm according to UNECE informal working group particle measurement protocol (PMP). The volatile particles from the engine exhaust are removed by heating and dilution in a device according to the UNECE PMP program. The analysis of solid particles from diesel engines requires aerosol conditioning systems, which can effectively remove volatile particles/species with minimum solid particle losses. Currently, the regulations only allow using an evaporation tube for the measurement of solid particles. Different laboratories have also demonstrated other alternatives such as thermodenuder and catalytic stripper for measuring the solid ultrafine particles emitted from the diesel engine. This paper reviews the recent literature related to the thermodenuder and catalytic striper’s design and operating characteristics. The performance parameters, such as penetration efficiency and volatile removal efficiency, are discussed. Further, theoretical calculation using the empirical equations of the particle losses in these aerosol conditioning system is also described. The merit and demerit of sampling diesel aerosols from the thermodenuder and catalytic striper are discussed. Finally, the performance based on engine particle size distributions and the effect of engine operating conditions on nonvolatile emissions sampled with a catalytic stripper and thermo-denuder is presented and discussed.