Enhancement of Formic Acid on New Particle Formation Involving Methanesulfonic Acid and Ethanolamine

Abstract Methanesulfonic acid (MSA), an acid molecule with properties similar to that of sulfuric acid (SA), has attracted increasing attention for its role in driving atmospheric new particle formation (NPF). Currently, ethanolamine (MEA) is recognized as the most promising atmospheric organic amine for promoting the formation of MSA‐based clusters. Given the complexity of multi‐component aerosol nucleation mechanisms, it is essential to explore the potential of other gaseous substances participating in the MSA‐MEA‐driven NPF. Formic acid (FA), the most abundant organic acid in both the atmospheric gas phase and particulate phase, warrants urgent investigation regarding its potential role in aerosol nucleation. Herein, we investigate the enhancement potential of FA on MSA‐MEA‐driven NPF within the troposphere. The results indicate that the enhancing effect of FA emerges in the lower troposphere ( T ≤ 278.15 K) when [FA] ≥ 10 10 cm −3 . The enhancement strength, R FA , increases with decreasing temperature and increasing FA concentration, reaching a factor of up to 21.54 at 258.15 K, and is most significant in regions with high MEA emissions. At 258.15 K, when [FA] ≥ 10 11 cm −3 , FA can directly promote the MSA‐MEA‐FA growth pathway, rather than merely acting as a catalyst for the MSA‐MEA pathway. Consequently, the ternary MSA‐MEA‐FA nucleation mechanism may play a crucial role in the NPF processes in cities with severe Industrial pollution, forested areas, industrial zones rich in volatile compounds, cold oceans, and polar regions.