Exptl. data on the probability distribution of the N. (no. of primary particles per soot aggregate) in a nonpremixed laminar flame is obtained. The distribution of N of soot aggregates thermophoretically sampled from a laminar ethylene/air diffusion flame is studied and thousands of aggregates in TEM images are analyzed. The distribution of N is poorly fit by a lognormal distribution model, and the double lognormal model can represent the statistical results of the aggregate size distribution more precisely. [on SciFinder(R)]