Direct Measurements of Covalently Bonded Sulfuric Anhydrides from Gas-Phase Reactions of SO with Acids under Ambient Conditions.

Sulfur trioxide (SO) is an important oxide of sulfur and a key intermediate in the formation of sulfuric acid (HSO, SA) in the Earth's atmosphere. This conversion to SA occurs rapidly due to the reaction of SO with a water dimer. However, gas-phase SO has been measured directly at concentrations that are comparable to that of SA under polluted mega-city conditions, indicating gaps in our current understanding of the sources and fates of SO.