Sampling System for Solid and Volatile Exhaust Particle Size, Number, and Mass Emissions

A solid particle sampling system (SPSS) that is equipped with a heated oxidation catalyst, micro-dilution tunnels, filter holders and sampling probes, was designed and developed to collect filter-based solid and total (solid plus volatile) particles from the exhaust of internal combustion engines, and to facilitate the measurement of solid and total particles when equipped with particle measuring instruments for size, number, mass, and other particle characteristics. The SPSS was characterized with laboratory aerosol and showed a very low solid particle loss of less than 5 percent using sodium chloride particles, very high volatile particle removal of better than 98 percent using oil droplets, and no formation of sulfuric acid particles when using ammonium sulfate particles. The SPSS is a useful tool for researchers interested in characterizing the solid and volatile fraction of particles emitted from combustion sources. The SPSS technique can also be used for any future solid particle number-based regulation similar to that proposed in Switzerland and currently considered in Europe and Japan.

The SPSS together with a TSI scanning mobility particle sizer (SMPS) were used to characterize PM emissions from a heavy-duty diesel engine. The size distribution data revealed the presence of solid nuclei in the core of volatile particles. The solid nuclei were below 20 nm in diameter and their upward trend suggests the presence of solid particles below 10 nm, the low-end detection limit of the particle instrument used. Previous work suggested that the source of such nuclei could be metallic ash in lube oil. The presence of the solid nuclei is important to obtaining a better understanding of the origin, control, and potential environmental impact of nanoparticles (diameter < 50 nm). It may be also of interest to health researchers studying the impact of PM emission characteristics on human health.