Droplet surface spontaneous oxidation as a dominant formation pathway of organosulfates in the marine atmosphere.

Organosulfates (OSs) have been widely detected in marine aerosols and have various potential formation pathways in the atmosphere. However, the key formation mechanism of OSs in the marine environment remains unclear. Here, by combining field measurements, laboratory experiments, and model calculations, we suggest that the surface spontaneous oxidation of sea spray aerosol (SSA) particles produces OSs rapidly and is the dominant formation pathway of OSs in the marine atmosphere. SSA microdroplets provide a large surface area for the spontaneous formation of OH radicals, inducing the oxidization of dimethyl sulfide into sulfate (SO42-), sulfuric acid, and organic acids, thereby acidifying the droplets. Subsequently, SO42- reacts with dissolved alcohols under such acidic conditions to produce OSs. This process is fast enough to be a major source of detected OSs in the aerosol samples collected in the marine atmosphere. This pathway contributes to a global OS production of 13.96 ± 10.99 Tg yr-1, comparable to global isoprene-derived OS production. This study reveals that rapid secondary processes are the main source of OSs in the marine atmosphere and highlights the important role of the droplet surface spontaneous oxidation process in atmospheric chemistry over the ocean.