Ammonia Synergistic Effects and Stability Evolution in Sulfuric Acid-Dimethylamine Clusters up to 10 Molecules

Abstract

Sulfuric acid-dimethylamine (SA-DMA) cluster formation drives new particle formation in polluted atmospheres, but growth mechanisms for large-size SA-DMA clusters (>8 molecules) remain unclear. In this study, we systematically investigated neutral SA-DMA and SA-DMA-ammonia (AM) clusters up to 10 molecules and found that the dominant stability-regulating mechanism shifted from acid–base interactions in small-size clusters to synergistic structural and acid–base effects in large-size ones, with growing stabilization by van der Waals forces. AM lowered the critical size of encapsulated configurations and significantly increased nucleation rate for clusters with ≥4 acid–base pairs. At larger sizes, the thermodynamic stability gap between binary and ternary clusters narrowed, with kinetic concentration effect dominating further growth. This work filled the critical gap in large-size cluster evolution research and provided theoretical support for multiprecursor synergistic nucleation.