Authors: Yixin Li*, Bianca Aridjis-Olivos, Veronica Kowalewski, and Renyi Zhang
The poster abstract by Yixin Li was presented at the American Geophysical Union (AGU) 2025 Annual Meeting in New Oreleans, LA, showing that sulfate forms far faster at aerosol surfaces than in bulk solutions, with interfacial properties—rather than acidity—driving this accelerated chemistry and revealing new insights into atmospheric sulfate formation.
Heterogeneous oxidation of SO2 by NO2 is an important pathway for atmospheric sulfate formation, with profound implication for air quality, human health and climate. It is shown that this reaction is >3 orders of magnitude faster on aerosols than in dilute bulk solutions, indicating a significant interfacial effect. However, the chemical mechanisms and kinetics of this multiphase reaction remain elusive, and previous studies have been interpreting this process with bulk phase properties and equilibrium parameters such as pH and Henry’s law constant.
In this study, we used an aerosol flow reactor to investigate mechanism and kinetics of heterogenous oxidation of SO2 by NO2 with a focus on the influence of aerosol interfacial effects. Mono-dispersed deliquescent seed particles with distinct interfacial properties and acidity including NH4HSO4, (NH4)2SO4, NaCl, sucrose, NH4NO3, Na2SO4, glycolic acid, and oxalic acid were exposed to SO₂, NO₂, and NH₃ vapors. Particle size growth and particle phase composition were continuously monitored using a scanning mobility particle sizer and a thermal desorption–ion drift–chemical ionization mass spectrometer. By comparing the particle growth and sulfate production on different seed particles, we showed that the interfacial properties such as surface charge rather than particle acidity determines the rate of sulfate formation. New mechanistic insights were gained by simultaneously tracking particle phase sulfate, sulfite, nitrate, and nitrite formation. Furthermore, the kinetics of this multiphase reaction was systematically studied and interpreted by a synergetic reactive uptake mechanism.
Dr. Renyi Zhang's Group 