Explicit particle kinetics simulations of reactive diffusion at air-water interfaces

Area of Science:

• Atmospheric Chemistry and Physics
• Aerosol Science
• Chemical Kinetics

Background:

• Reactive uptake of trace gases by aqueous aerosols is crucial for atmospheric chemistry.
• Distinguishing between interfacial and bulk contributions to this uptake is methodologically challenging.
• Existing models often struggle to resolve the interplay between diffusion and reaction dynamics at the air-water interface.

Purpose of the Study:

• To develop and present an explicit particle-based reactive diffusion framework.
• To quantitatively simulate stochastic transport and chemical reactions at air-water interfaces.
• To resolve and differentiate interfacial versus bulk reactivity in aqueous aerosols.

Main Methods:

• Developed an explicit particle-based reactive diffusion framework.
• Simulated stochastic transport and reactions at air-water interfaces.
• Utilized ozone-nitrite (O3-NO2-) chemistry as a model system for validation.

Main Results:

• The framework successfully reproduced concentration profiles consistent with reacto-diffusive theory.
• Quantitative extraction of the characteristic reacto-diffusive length was achieved.
• Demonstrated that interfacial chemistry dominates when droplet radii are near or below the reacto-diffusive length.

Conclusions:

• The developed framework rigorously connects microscopic kinetics with macroscopic uptake in multiphase systems.
• Highlights the critical importance of resolving nanometer-scale interfacial regions for accurate aerosol modeling.
• Emphasizes the transition from diffusion-limited to reaction-limited behavior and the elevated role of interfacial chemistry in small aerosols.