Modelling component diffusion in aerosol particles using Maxwell-Stefan's laws and the implications for cloud particle formation .

Until now, non-reactive mixing through secondary organic aerosols has been modelled using the Fickian laws of diffusion (Shiraiwa, 2013). Atmospheric aerosols are comprised of components with varying physical and chemical properties, including solubility. This is confirmed by virtue of the fact that liquid-liquid phase separations can exist within individual aerosol particles (Bertram, 2011). This spectrum of solubility means that modelling diffusion according to the Fickian definition is subject to unknown errors.In this study, we introduce a new framework of diffusion through aerosol particles based on Maxwell-Stefan's law. This framework uses a gradient in chemical potential to drive mixing through individual particles, for which we use the UNIFAC model. Including non-ideal effects of diffusion allows mixing to occur against the concentration gradient and liquid-liquid phase separations to be treated alongside any changes in viscosity of the mixture. Results from this framework give new insights on the interplay between thermodynamic factors and phase state changes on aerosol-cloud interactions. We further confirm that understanding the composition of aerosol particles is essential to better model their interactions in cloud systems.