Optical characterization of nano-sized organic carbon particles emitted from a small gasoline engine

The nano-sized organic carbon (NOC) particles emitted from a small gasoline engine were characterized using various ex situ optical techniques to assess their hazardous impact. The exhaust gas was sampled iso-kinetically by a quartz probe and passed through de-ionized water to gather the hydrophilic carbonaceous particulates as hydrosol. The hydrodynamic diameter of the particles ranged between 1.7 and 3.6 nm at no load, with a mean diameter of 2.4 nm. The particle size in the engine exhaust was found to increase at higher loads, which is attributed to coagulation of the particles. The chemical structure of the particles was analyzed using UV–vis and infra-red spectroscopy. Both the band gap energy and oscillator strength data evaluated from the UV–vis absorbance showed that the NOC particles contained polyaromatic hydrocarbon structures with three to five aromatic rings. Infra-red spectroscopy analysis further confirmed the presence of aliphatic and carbonyl functionalities in the aromatic structures of the particles. The fine size of the particles, their high number concentration for the type of the engine under study and their structural features, make the particles extremely hazardous for environment and health.

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► Nano-sized particles emitted from gasoline engine were characterized by optical techniques.
► Particle size and chemical structure were determined at different engine loads.
► Bonding structures in the particles were explained.
► Origin of the particles and reason of particle growth at higher load were justified.