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

Phenyl sulfate (PhOSO₃ H), 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 PhOSO₃ H formation via reactions between phenol (PhOH) and SO₃ , catalyzed by prevalent atmospheric species (H₂ O, H₂ SO₄ , NH₃ , HCOOH, HNO₃ , and CH₃ NH₂ ), through ab initio calculations and kinetic analysis. Our results reveal that these atmospheric constituents enhance PhOSO₃ H production, with alkaline molecules (NH₃ and CH₃ NH₂ ) exhibiting exceptional catalytic efficiency by rendering the reaction nearly barrierless. Importantly, NH₃ and CH₃ NH₂ further stabilize PhOSO₃ H to form clusters through hydrogen bonding and π–π, CH−π, and NH−π interactions, facilitating further nucleation. Moreover, we found that PhOSO₃ H–CH₃ NH₂ nucleation proceeds without barriers under low-temperature conditions of 248.15 K. The nucleation rate enhanced by CH₃ NH₂ exceeds that of NH₃ by 5 orders of magnitude, though NH₃ ’s abundance (up to ppbv levels) in the atmosphere necessitates consideration of both CH₃ NH₂ - and NH₃ -enhanced PhOSO₃ H formation and nucleation. In the upper free troposphere, PhOSO₃ H–NH₃ nucleation dominates due to CH₃ NH₂ scarcity. This study provides mechanistic insights into PhOSO₃ H formation and its role in particle nucleation, advancing our knowledge of organosulfates in atmospheric chemistry and environmental impacts.