To understand the specific impacts of chemical complexity on submicron SSA, we chose to both increase the cation complexity as well as the complexity of the organic species. In the subsequent two steps (Systems B and C), the aqueous phase contained approximately 110 mM Mg 2+ , 25 mM Ca 2+ , and 20 mM K + , in addition to the existing NaCl concentration. When considering the components of the organic fraction, we focused on systems that had been studied before both computationally and experimentally so that our simulations could ultimately be validated by laboratory experiments. For the first step (System B, Figure ), we added lipopolysaccharides (LPS), which are components of bacterial cell membranes that are often found in SSA due to cellular breakdown. We expected that this addition would be a valuable perturbation to the simple system in two major ways. First, it has been observed that LPS-containing particles readily uptake and react with nitric acid in the atmosphere and are thus chemically significant. Second, based on previous studies, we expected that the interaction between LPS and divalent cations such as Ca 2+ would cause a meaningful phase change within the particle that could be explored computationally. Finally, it is estimated that at least 2-10% of the organic carbon mass in submicron SSA is made up of poly-and oligosaccharides, as well as free saccharides, the most abundant monomer of which is glucose. Based on this data, for the final system (System C, Figure ), we added a combination of free glucose and laminarin, a neutral glucose oligosaccharide. Recently, Richards et al. demonstrated that some monosaccharides in sufficiently high concentrations and in the presence of divalent cations-typical conditions within atmospheric aerosols-form supramolecular ion-bridging interactions that can induce phase transitions to a rigid gel. This unique phase behavior had been observed for macromolecular systems (such as those containing LPS described above) but not yet with small molecules. This final step up in complexity allows us to explore the impacts of neutral saccharides within the overall mixture and computationally explore any non-covalent bridging interactions that could lead to phase changes. Figure outlines all three systems and the compositions of their respective organic mass fractions.