As a major source of cloud condensation nuclei, atmospheric new particle formation (NPF) events exert significant influences on the global climate. Among the various nucleation mechanisms that have been identified in diverse environments, sulfuric acid-amine nucleation is unique for its high efficiency to form stable clusters and drive intense nucleation. Despite the fact that this nucleation mechanism could explain observed NPF events at a number of megacity sites in China, its applicability to a larger regional scale remains unclear. Here, we analyzed characteristics of NPF events and influencing factors at three suburban sites in the eastern region of China based on measured and theoretically predicted particle formation rates and cluster concentrations. Results show that sulfuric acid-dimethylamine is a predominant nucleation mechanism at these sites, while atmospheric conditions including precursor concentrations and temperature causes the differences in NPF characteristics among different sites. This indicates the significance of the sulfuric acid-amine nucleation mechanism over a large spatial scale in the urban agglomerations in the eastern region of China. We also find that oxygenated organic molecules are likely involved in the formation of 1.7-nm new particles at these sites by contributing the initial growth of stable sulfuric acid clusters.