Theoretical study on the bases-enhanced formic sulfuric anhydride nucleation: A new insight from the mechanism,...

The formation of formic sulfuric anhydride (FSA) through gas-phase reactions between sulfur trioxide and formic acid represents a potentially important pathway in atmospheric aerosol nucleation processes. However, the nucleation mechanisms and roles of FSA are not fully understood. The formation mechanism and kinetics of FSA with common atmospheric base precursors, including ammonia, methylamine, dimethylamine, urea clusters, and their hydration clusters were investigated in this study. Quantum chemistry calculations reveal that FSA clusters exhibit greater thermodynamic stability than sulfuric acid due to their increased hydrogen bonding sites and proton transfer capabilities, with water molecules further enhancing nucleation. Cluster dynamics simulations indicate that the nucleation effect of FSA surpasses that of sulfuric acid under similar concentrations, suggesting the significant role of FSA in regions with low sulfuric acid concentrations. Temperature, pressure, altitude, and humidity influence FSA and hydration cluster properties, with clusters favoring formation under low-temperature, high-pressure conditions. This research provides new insights into the role of FSA in atmospheric aerosols, potentially enhancing understanding of nucleation processes.