Effective Mass Accommodation Model for Surface and Bulk Reactions in Particles.

Mass accommodation is a critical process, controlling uptake coefficients of gaseous species in aerosols and clouds. The effective mass accommodation coefficient (αeff) was developed to account for kinetic limitations of bulk diffusion and reactions with a simple analytical equation. In this work, αeff is extended by including surface reactions and bulk accommodation. Systematic simulations over a wide range of kinetic parameters demonstrate excellent agreement between the αeff method and a benchmark kinetic multilayer model once quasi-equilibrium is achieved in the effective penetration depth. The αeff method can quantify the contributions of surface and bulk processes to overall uptake. Comparisons with two other models (Wilson et al., 2022; Prophet and Wilson, 2025) show that the αeff method more accurately predicts uptake coefficients when uptake is limited by bulk diffusion of volatile species or when surface reactions dominate under high surface coverage conditions. The developed method provides a useful tool for analyzing experimental measurements and developing uptake parametrizations for large-scale models.