Abstract Surface growth of soot was examined in several premixed flat flames. The fuel was a mixture of toluene and ethylene, with more than half of the carbon supplied by the toluene. We found: (I) Acetylene in the burned gases supplied most of the mass for surface growth, and the growth mechanism in toluene/ethylene flames was the same as in the ethylene flames that we examined previously; i.e., the rate constants that we found in the earlier work predicted the surface growth rates in these flames. (2) In comparing ethylene and toluene/ethylene flames, the fluorescence intensity from polycyclic aromatic hydrocarbons (PAH) was very different for flames with the same C/O ratios but similar for flames with the same soot volume fraction. (3) For a given C/O ratio the amount of soot produced in the particle inception stage in the toluene/ethylene flames was much higher than in the ethylene flames. However, because the acetylene concentrations were higher in the ethylene flames, the rate of surface growth per...