Using the clustering data extracted from the simulations, we identified the FA clusters that formed at the surfaces and estimated their total surface coverage (See Supporting Information for calculation details). Figure shows the percentage of surface area covered by FA monolayers compared to the total surface area of the final ellipsoid. As expected, systems with a more complex organic fraction had less FA surface coverage. The more complex systems have fewer total FAs, as they make up a smaller percentage of the overall organic mass fraction (A:93%, B:80%, C:63%). For all systems, the percentage of the surface found to be saturated with FAs was lower than expected based on the total FA count. Because the percentage of fatty acids varies with each system, it is more pragmatic to evaluate the "surface excess" to better understand the extent to which chemical complexity impacts how the surface saturates with FAs. Here we define "surface excess" as the percentage of FAs covering the surface with respect to how many are available. We estimated how much of the surface should have theoretically been covered by lipids should all the lipids available to the system have saturated the surface (Figure ). A value of one indicates that there are exactly the same number of lipids as there are available "sites" at the surface, where every surface site is occupied by a lipid. A value >1 indicates that there are more lipids than surface sites available (surplus), and vice versa for values <1, i.e., a deficit means that there are less lipids than sites available for occupation at the surface. In the all A systems, there are more lipids available than can fit at the surface, and we should expect 100% surface saturation. However, we observe that in each replicate, there are available sites at the surface that are unoccupied by lipids. Even for the most complex systems (C), in which there is a lipid deficit for all replicates, less surfactants are present at the surface than would be expected. This result can be attributed to the sequestering and stabilization of FAs in the core of the particle by other organics (Figure ). As a consequence, space at the surface is either left empty, exposing water directly to the atmosphere, or is occupied by other macromolecular species in the system such as BCL or LPS. While FAs spontaneously aggregate into aqueous structures, these structures are stabilized in solution by interacting with proteins and saccharides. BCL and LPS may be acting co-surfactants or emulsifying agents, 123-125 enabling the system to maintain incomplete phase separation. Additionally, due to their amphiphilic nature, they also occupy space at the air/water interface, contributing to the observed lipid deficit and increasing interfacial heterogeneity.