Mechanistic insights into marine boundary layer nucleation: synergistic interactions of typical sulfur, iodine, and nitrogen precursors

Abstract. Marine new particles significantly impact the global atmosphere, yet the key nucleation process underlying their formation remains unclear. Sulfur-, nitrogen-, and iodine-containing species are expected to coexist in the marine atmosphere, including the canonical precursors methanesulfonic acid (MSA), iodic acid (IA), and dimethylamine (DMA). To elucidate how they interact to drive NPF, we performed high-level quantum chemical calculations and cluster dynamics simulations to investigate their synergistic nucleation mechanism at the molecular level. The results show that IA, MSA, and DMA form stable pre-nucleation clusters via intermolecular hydrogen and halogen bonding, with acid-base reactions during clustering, forming ion pairs. The proposed IA–MSA–DMA ternary nucleation is thermodynamically more favorable in regions rich in sulfur and nitrogen but poor in iodine. Its cluster formation rate is notably higher than that of any corresponding binary nucleation, showing a synergistic enhancement of 4–8 orders of magnitude. Moreover, this rate even exceeds that of the well-established efficient iodine oxoacids nucleation under sulfur-rich conditions. In polar coastal regions such as Marambio, the inclusion of the IA–MSA–DMA nucleation pathway brings simulated nucleation rates closer to field measurements than considering the established IA–DMA nucleation alone, identifying it as a critical mechanism in these environments. Accordingly, the proposed IA–MSA–DMA nucleation mechanism is expected to be important in the marine boundary layer, helping to explain the missing sources of marine particles, especially in cold polar marine regions. Incorporating this mechanism into atmospheric modelling can potentially improve aerosol formation simulations and refine climate predictions.