Sulfur chemistry in laser-simulated impact vapor clouds: implications for the K/T impact event

One of the most promising mechanisms for the mass extinction at the K/T boundary event is blockage of sunlight by sulfuric acid aerosol, which is induced by impact vaporization of sulfate in evaporite deposits around the K/T impact site. One of the advantages of this hypotheses is that it may cause an impact winter much longer than that by silicate dust and soot due to a global wildfire. However, the residence time of sulfuric acid aerosol in the stratosphere depends strongly on the ratio of SO2/SO3 in the K/T impact vapor. If SO3 was dominant, the blockage of sunlight by the sulfuric acid aerosol would not last longer than that by silicate dust and soot. The chemical reaction of sulfur oxides in an impact vapor cloud has not been studied extensively before. This study carries out chemical equilibrium calculations, kinetic model calculations, and laser irradiation experiments with a quadrupole mass spectrometer to estimate the SO2/SO3 ratio in the K/T impact vapor cloud. The results strongly suggest that most of sulfur oxides in the K/T impact vapor cloud may have been SO3, not SO2. The sulfuric acid aerosol may not have been able to block the sunlight for a long time.