Unlocking the Hidden Source of Phenyl Sulfate and Role in the Atmosphere: Alkali-Catalyzed Barrierless Formation Mechanism and Impact on Aerosol Nucleation

Phenyl sulfate (PhOSO₃H), a key organosulfate in atmospheric particles, exerts significant impacts on air quality and human health, yet its formation mechanisms and role in aerosol nucleation remain unclear. Herein, we identify a novel pathway for PhOSO₃H formation via reactions between phenol (PhOH) and SO₃, catalyzed by prevalent atmospheric species (H₂O, H₂SO₄, NH₃, HCOOH, HNO₃, and CH₃NH₂), through <i>ab initio</i> calculations and kinetic analysis. Our results reveal that these atmospheric constituents enhance PhOSO₃H production, with alkaline molecules (NH₃ and CH₃NH₂) exhibiting exceptional catalytic efficiency by rendering the reaction nearly barrierless. Importantly, NH₃ and CH₃NH₂ further stabilize PhOSO₃H to form clusters through hydrogen bonding and π-π, CH-π, and NH-π interactions, facilitating further nucleation. Moreover, we found that PhOSO₃H-CH₃NH₂ nucleation proceeds without barriers under low-temperature conditions of 248.15 K. The nucleation rate enhanced by CH₃NH₂ exceeds that of NH₃ by 5 orders of magnitude, though NH₃'s abundance (up to ppbv levels) in the atmosphere necessitates consideration of both CH₃NH₂- and NH₃-enhanced PhOSO₃H formation and nucleation. In the upper free troposphere, PhOSO₃H-NH₃ nucleation dominates due to CH₃NH₂ scarcity. This study provides mechanistic insights into PhOSO₃H formation and its role in particle nucleation, advancing our knowledge of organosulfates in atmospheric chemistry and environmental impacts.