Compared with gasoline, ethanol yielded considerably less PM emissions due to a significantly lower soot formation resulting from its oxygen content and higher volatility.
Faster oxidation of ethanol–generated soot due to internal burning in the engine cylinder possibly is another reason for its low PM emissions,which requires further investigation. PN emissions from ethanol were higher than those from gasoline. This is because,unlike gasoline, most of unburnt HC from ethanol formed the nanoparticles in the nucleation mode, whilst only a small fraction of unburnt HC is attached or adsorbed on the limited soot.