A method of affecting soot particulate size in an internal combustion engine exhaust by selectively providing a phosphorous based additive to the engine during combustion. Soot particulate size can be increased or decreased depending on the particular additive provided. Also disclosed in a conditioning effect experienced by using a phosphorous based additive for a period of time. A conditioned engine can also have its exhaust properties affected during the life of its conditioned state. Manipulating particle size during engine operation can employ an oligomeric phosphorous compound. Engine conditioning can employ a monomeric phosphorous containing compound, an oligomeric phosphorous containing compound, a polymeric phosphorous containing compound, or combinations thereof.