Abstract
Volatile particles cannot be detected at the engine exhaust by an aerosol detector, as they are formed when the exhaust is mixed downstream with the ambient air. The lack of a precise definition of volatile engine particles has been an impediment to engine manufacturers and regulatory agencies involved in the development of effective control strategies. Volatile particles from combustion sources contribute to the atmospheric particulate burden, and this is a critical issue in ongoing research in the areas of air quality and climate change. A new instrument, called a volatile particle separator (VPS), is developed in this work. It utilizes a proprietary microporous metallic membrane to separate particles from vapors. VPS data are used in the development of a two-parameter function to quantitatively classify, for the first time, the volatilization behavior of engine particles. The value of parameter “A” describes the volatilization potential of an aerosol. A nonvolatile particle has a larger A-value than a volatile one. The value of parameter “k,” an effective evaporation energy barrier, is found to be much smaller for small engine particles than for large engine ones. The VPS instrument is not simply a volatile particle remover, as it makes possible the characterization of volatile engine particles in numerical terms.
Highlights
Particles emitted by combustion engines are composed of a highly complex mixture of organic and inorganic matter
The thermal behavior of the conventional diesel combustion (CDC) exhaust particles was investigated using monodisperse samples extracted by DMA1 (see Figs. 6(a), (b), and (c))
Previous volatile particle separator (VPS) data from the synthetic particle tests (Cheng and Allman, 2011) indicated that the peak number concentration decreased as the heating temperature increased, but the peak size or location would not change significantly for nonvolatile particles
Summary
Particles emitted by combustion engines are composed of a highly complex mixture of organic and inorganic matter They vary in size, chemical composition, morphology and microstructure. The engine particles are generally ultrafine (Cheng et al, 2008, 2009); i.e., their size is generally smaller than 100 nm, making them more toxic than the larger ones (Donaldson et al, 1998). This is because their large surface area per unit mass enhances their transport capacity for toxic substances such as polyaromatic hydrocarbons. The small size promotes translocation and penetration once they are inhaled into a human lung (Oberdörster and Utell, 2002)
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