Organosulfates are tracers for secondary organic aerosol (SOA) formation. We propose a new mechanism of organosulfur product formation in the atmosphere, in which sulfur dioxide (SO2) reacts directly with alkenes. The experiments were conducted at the gas-liquid interface with a coated-wall flow tube reactor. It was shown, for the first time, that SO2 reacts efficiently with the unsaturated bond in oleic acid under atmospheric conditions (without ozone), leading to the formation of C-9 and C-18 organosulfur products. The associated uptake coefficients were in excess of 10(-6), decreasing with initial SO2 concentration and increasing with humidity. These results might explain a fraction of organosulfur products detected in atmospheric particles. This work tends to elucidate the role of organosulfates' interfacial chemistry as a potentially unrecognized pathway for their contribution to SOA formation; however, it remains to be determined how significant this pathway is to the overall organosulfate abundances measured in ambient aerosol.