Early-Stage Aerosol Nucleation Mapping via Post-Electrospray Ionization Cluster Growth

Abstract To elucidate the early nucleation pathways of multicomponent atmospheric aerosols, this study proposes a novel post- Electrospray Ionization (ESI) cluster growth approach operating at ambient pressure. By decoupling the generation and growth of seed clusters in space and time, the method enables molecular-level interrogation of ionic cluster growth under ambient-pressure conditions, providing clues relevant to atmospheric new particle formation (NPF). In this setup, seed clusters are produced via ESI, and reactant vapors are introduced before vacuum entry, allowing cluster growth at ambient pressure. A key advantage lies in the independent tunability of the ESI and growth sources, which permits flexible pairing of precursor systems. Moreover, performing reactions at ambient pressure minimize mass spectrometer contamination, extending the method’s applicability across diverse chemical systems. Using this method, we mapped the growth pathways of iodic acid (IA)-sulfuric acid (SA)-dimethylamine (DMA) clusters and found that IA-SA nucleation followed by DMA addition is a particularly favorable route. Furthermore, integrating isotopic labeling and collision induced dissociation (CID), we investigated cluster growth in the citric acid (CA)-DMA-SA system and clarified the role of each component. Results indicate that although DMA and SA are key initial precursors, CA plays a critical role later by stabilizing small clusters and suppressing component volatilization during growth. This post-ESI strategy provides mechanistic insights into early atmospheric aerosol nucleation.