Abstract
<jats:p>Abstract. New particle formation (NPF) is a major source of atmospheric particulates and cloud condensation nuclei (CCN), yet conventional sulfuric acid (SA)–ammonia (NH3) nucleation cannot fully explain the observed NPF and CCN generation. While recent CLOUD studies have shown that nitric acid can enhance SA–NH3 nucleation in the cold upper troposphere [Nature, 605, 483-489, 2022], this mechanism can only explain particle formation under certain cold atmospheric environments. Here, we use trifluoroacetic acid (TFA) as a model perfluorocarboxylic acid (PFCA) to investigate the stabilizing effect of PFCAs on SA–NH3 clusters, given their atmospheric nucleation relevance, long lifetime, and widespread distribution. Using quantum chemical calculations with Atmospheric Cluster Dynamics Code simulations, we find that TFA forms stable cage-like SA–NH3–TFA clusters via strong hydrogen bonds and proton transfer. At 220 K (favourable cold conditions), TFA enhances the SA–NH3 nucleation rate by up to 950-fold and contributes up to 93 % of the main simulated growth flux at low SA. TFA assisted stabilization represents a potentially efficient pathway for SA–NH3 nucleation in cold atmospheres. This mechanism is most directly relevant to the cold boundary layer environments where TFA has been measured. In the upper troposphere, its role serves as a critical low-temperature mechanistic insight, pending direct observations of gas-phase TFA aloft. This study provides a molecular-level foundation for understanding general PFCA-enhanced nucleation mechanisms in cold atmospheric environments.</jats:p>