Density functional theory and ab initio molecular orbital methods were used to study molecular species and chemical reactions involved in the production of sulfuric acid and sulfate-based aerosols from sulfur dioxide (SO2) in the atmosphere. A new reaction mechanism was proposed following the initial reaction of SO2 with OH radical.  The resulting intermediate HOSO2 was proposed to react with molecular oxygen and water to produce sulfuric acid (H2SO4) and hydroperoxyl radical (HO2), rather than forming sulfur trioxide (SO3) before the production of sulfuric acid as proposed in several recent studies. Equilibrium structures and the corresponding molecular properties were determined for the reaction complexes, intermediates, and transition states at several theoretical levels including B3LYP, MP2, and QCISD with the 6-31+G* and aug-cc-pVDZ basis sets.  Single-point energy calculations were also performed at CCSD(T) level with the aug-cc-pVDZ basis set. The results show that our new mechanism is thermodynamically and kinetically favorable. Atmospheric implications of the study were discussed.

Theoretical mechanisms of atmospheric production of sulfuric acid and sulfate aerosols from sulfur dioxide

243rd National Meeting (2012)

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