Effects of volatility, viscosity, and non-ideality on particle–particle mixing timescales of secondary organic aerosols

Different populations of aerosol are constantly mixed throughout the atmosphere. Large-scale models often assume no particle–particle mixing or fast among populations, so that they stay externally instantaneously form internal mixtures. We apply kinetic multilayer model gas–particle interactions (KM-GAP) to simulate evaporation semi-volatile species from one particle population and partitioning into another with various phase states nonideal conditions. find timescale (τmix) is prolonged when transport a in which it miscible, as more mass must be transported. Extremes volatility prolong τmix, low-volatility evaporate slowly, while high-volatility condense slowly. When bulk diffusivities two greater than 10−15 cm2 s−1, mix rapidly; otherwise, τmix can beyond 1 h. KM-GAP experiments H-toluene SOA D-toluene limonene SOA, showing toluene highly viscous, initial gas rapid because low viscosity SOA. Simulations β-caryophyllene indicate apparent discrepancy limited under conditions where both predicted have explained by miscibility components. Our study demonstrates timescales affected complex interplay volatility, diffusion limitations, non-ideal miscibility.