Due to the uneven distribution of organics, D was evaluated for water molecules enclosed within unique volumes defined by spherical shells, similar to the geometric delineations given in Figure . In this way, we were able to correlate the location of long-lived organic clusters to molecular diffusion of water. Generally, D is the lowest within 10 nm of the particle center and increases nearer to the surface. One unique exception is System A2 (See Figure for snapshots) in which the core region has a diffusion coefficient similar to the system average. This exception may be due in part to the fact that this replicate has fewer FAs situated in the core than other systems. Whereas A1 and A3 have a large FA agglomerate in the center, A2 has more FAs distributed near the surface. FAs may thus impede the diffusion of water by confining the water to smaller volumetric regions inside the particle, imposing physical membrane-like barriers throughout the aerosol. In larger SSA systems, FAs and other surfactants may take the form of vesicles and micelles, trapping internal water molecules and slowing diffusion. The most complex systems (C) had the lowest apparent rates of diffusion. In C systems the saccharides slow the diffusion of water through various intermolecular interactions. Highly soluble glucose monomers dispersed throughout the aqueous phase slow water diffusion via hydrogen bonding. Additionally, C3 contains laminarin which, as seen in SI M5, interacts with neighboring LPS and BCL molecules to form a molecular aggregate. The aggregates slow water diffusion by creating physical barriers to movement, and also by integrating into hydrogen bonding networks and increasing ion-water interactions, leading to the lowest D of all systems studied. LPS and divalent cations alone are known to form rigid gel-like structures through non-covalent ion bridging, preventing diffusion of small molecules. 122 However, our B systems do not show a decrease in diffusion due to LPS and divalent cations alone. Instead, only when coupled with additional mono-and oligosaccharides do we see a decrease in D. While the sugars in LPS are linear, laminarin is highly branched which may allow for it to better interlink between the various organics and could help explain the difference between LPS alone (B systems) and with additional laminarin (C3). This shows that the type of organics, their organization, and their interactions in the aqueous phase can all modulate mass transport throughout SSAs. Furthermore, divalent cations are expected to reduce the diffusion coefficient of water in solution relative to monovalent cations due to stronger ion-water interactions, which leads to co-diffusion of the solvation shell of water molecules along with each cation. We would thus expect to see a corresponding decrease in D for systems B and C with addition of Ca 2+ and Mg 2+ to the aqueous phase. However, this addition of cation complexity in our simulations did not always lead to a reduced D. We attribute this to the heterogeneous distribution of organics, whereby one diffusion coefficient is insufficient to describe the full complexity of molecular transport throughout aerosol particles.