Rapid spontaneous generation of organosulfur from inorganic sulfur in atmospheric microdroplets

Organosulfur compounds are important constituents of atmospheric aerosols and have been extensively investigated through field observations, laboratory experiments, and atmospheric modeling. However, the mechanisms underlying their formation and atmospheric abundance remain incompletely understood. Ubiquitous in the atmosphere, micrometer-sized droplets provide unique interfacial reaction environments that may facilitate organosulfur formation. Here, we show that sulfite-derived inorganic sulfur species react with oxygenated volatile organic compounds in microdroplets to generate organosulfur compounds under catalyst-free conditions without external energy input. Theoretical calculations suggest that interfacial electric fields facilitate organosulfur formation by lowering reaction activation barriers. Furthermore, several organosulfur species identified in laboratory experiments were also detected in ambient aerosols collected from an urban site and a high-altitude mountain station, supporting the potential atmospheric relevance of this pathway. Our findings provide insights into the role of microdroplet interface in organosulfur formation and their potential contribution to atmospheric aerosol chemistry.