Aerosols produced by combustion processes have a relevant impact
on the chemistry and physics of the atmosphere and on human health.
Soot particles are one of the main constituents of the elemental
carbon present in the atmosphere, but the role of combustion
processes in the formation of organic carbon, which is more
abundant than the elemental one in the atmosphere, is less well
characterized.
Nanoparticles of Organic Carbon (NOC) have been detected in
laminar flames employing a variety of experimental diagnostics and
some of their chemical and physical properties have been
characterized.
NOC are not easily detected at the exhausts of practical
combustion devices like vehicles equipped with spark ignition or
diesel engines because the current available instrumentations do
not allow detection of nanoparticles smaller than 3 nm. Also, the
number concentration of nanoparticles smaller than 10 nm is
strongly variable with temperatures and flow rates of the exhaust
products.
The purpose of this paper is to review the characteristics of
NOC and to show that these particles are also emitted from
commercial combustion devices. Different measurement techniques are
used to analyze the size and mass concentrations of particulates
including UV-visible absorption spectroscopy and Atomic Force
Microscopy. These techniques have been applied in laboratory flames
and at the exhausts of vehicles equipped with a common-rail diesel
engine and a fuel port injection S.I. engine.
On the basis of the results obtained, we advance some hypothesis
on the role of NOC on the nucleation burst in polluted
atmosphere.