Gas bubbles bursting at the sea surface produce drops, which contribute to marine aerosols. The contamination or enrichment of water by surface-active agents, of biological or anthropogenic origin, has long been recognized as affecting the bubble bursting processes and the spray composition. However, despite an improved understanding of the physics of a single bursting event, a quantitative understanding of the role of the physico-chemical conditions on assemblies of bursting bubbles remains elusive. We present experiments on the drop production by millimetric, collective bursting bubbles, under varying surfactant concentration and bubble density. We demonstrate that the production of supermicron droplets (with radius larger than 35 μm) is nonmonotonic as the surfactant concentration increases. The bursting efficiency is optimal for short-lived, sparsely distributed and non-coalescing bubbles. We identify the combined role of contamination on the surface bubble arrangement and the modification of the jet drop production process in the bursting efficiency. Plain Language Summary Understanding the production of primary ocean spray aerosol and its dependence on meteorological and environmental variables is critical for modeling potentially health-adverse effects from dispersants used to break down oil spills, as well as radiative processes and cloud microphysical properties. We demonstrate experimentally that the coupling between the chemical properties of contaminated water and the physical mechanism of droplet production when a bubble bursts controls the efficiency of aerosols production during collective bubble bursting, and reveals an optimal production regime at intermediate contamination. This fundamental study paves the way to improved predictions of aerosol production in contaminated water. NÉEL ET AL.