First, the CHARMM36 force field was used for all simulations, and care was taken to ensure that only molecules that had been sufficiently parameterized and characterized with the force field were investigated. All ions and their concentrations were kept within the force field accuracy limitations. The latest NBFixes (2019) to the CHARMM36 parameter set for Na + and Ca 2+ were applied. Secondly, 30-50 nm diameter aerosols are the most difficult to study experimentally due to their small size yet correspond to computationally large systems containing multiple millions of atoms, which require leadership-class computing facilities. We were thus limited by computational resources and had to compromise on complexity and size such that the simulation length scales would ensure proper sampling and still give statistically rigorous results. Finally, the largest limitation was capturing the vast chemical complexity of nascent SSA. There is broad agreement on the major classes of organic compounds but narrowing down our selection of molecular components to include the most chemically relevant species was non-trivial. We ultimately chose to build three 40-nm diameter aerosol systems to be run in triplicate (9 total simulations), with each system representing a step up in chemical complexity, i.e., with each new set of models, we added a new molecular component to the organic mass fraction while keeping the organic mass fraction as a whole constant. A more detailed discussion of the force field parameters, inclusion or omission of particular molecular species, and experimental validation is outlined in the Supporting Information.