Reaction of Criegee Intermediates with SO2─A Possible Route for Sulfurous Acid Formation in the Atmosphere

The reaction of a Criegee intermediate (CI) with SO2 is of significant interest due to its negative impact on the environment and ecosystem. In the present work, the formation of H2SO3 through the reaction of the CIs CH2OO, syn-CH3CHOO, and (CH3)2COO with SO2 is studied by using high-level electronic structure calculations. The reaction of CIs with SO2 is a stepwise process; in the first step an O atom from a CI is transferred to the S atom of SO2, which results in the formation of SO3 through a heterozonide (HOZ) formation in a barrierless reaction, and in the next step, the two hydrogen atoms of a CI are transferred to SO3, resulting in the formation of H2SO3 and other carbon-containing compounds. The calculated thermochemical parameters associated with the formation of intermediates and products show the spontaneity of the reactions. The rate constant calculated for the studied reactions shows that the formation of sulfurous acid through the reaction of CH2OO with SO2 is faster than the reaction of syn-CH3CHOO or (CH3)2COO with SO2. Our results show that the reaction of CIs with SO2 is one of the significant processes in the atmosphere and is responsible for the formation of H2SO3, carbon monoxide, ketene, cyclopropanone, 2-oxopropyl hydrogen sulfite, and other sulfur-containing compounds in the atmosphere.