Analyses on ASF distribution showed that heavy tails of oligomers can be formed via radical polymerization at the colder section of the column with the presence of oxygen, due to the larger elongation probability of the peroxyl propagation chain. We analyzed the simulation using rate of production analyses, and found that oxygen chemistry predominantly impacts liquid-phase radical polymerization and film growth in the colder section of the column. This is because the O 2 rises in the column and has a very low concentration in the hotter trays. We also found that the dominating film growth pathways can change at early and later fouling stages because thick films limit diffusion. These results suggest different antifouling additives are needed in different trays and perhaps at different times.