| Soot with different mean particle size shows different EC/OC ratio. The larger the soot particles are, the higher is their EC portion in soot. The explanation therefore comes from the understanding of the combustion process: Within a flame or in a combustion process smaller particles are generated in the following cases: 1. when the combustion is quenched or stopped by other influencing factors in a earlier phase of the soot formation, and PAHs that are formed before as intermediate products of soot formation remain on the soot particles. 2. when soot particles are oxidized and become smaller. This reaction runs in the opposite direction of the soot formation and a part of soot particles are reduced to liquid PAHs. These are of real processes which can be found in combustion engines as well. | 
