Abstract
Volatile particles cannot be detected at the engine exhaust by an aerosol detector. They are
formed when the exhaust is mixed with ambient air downstream. Lack of a precise definition of
volatile engine particles has been an impediment to engine manufacturers and regulatory agencies
involved in the development of an effective control strategy. It is beyond doubt that volatile
particles from combustion sources contribute to the atmospheric particulate burden, and the effect
of that contribution is a critical issue in the ongoing research in the areas of air quality and
climate change. A new instrument, called volatile particle separator (VPS), has been developed.
It utilizes a proprietary microporous metallic membrane to separate particles from vapors. VPS
data were 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 that for large engine particles. The VPS instrument
provides a means beyond just being a volatile particle remover; it enables a numerical definition
to characterize volatile engine particles.
