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Understanding the catalytic role of oxalic acid in SO3 hydration to form H2SO4 in the atmosphere

Abstract. The hydration of SO3 plays an important role in atmospheric
sulfuric acid formation. Some atmospheric species can be involved in and
facilitate the reaction. In this work, using quantum chemical calculations,
we show that oxalic acid, the most common dicarboxylic acid in the
atmosphere, can effectively catalyze the hydration of SO3. The
energy barrier of the SO3 hydration reaction catalyzed by oxalic acid
(cTt, tTt, tCt and cCt conformers) is a little higher or less than
1 kcal mol−1, which is lower than the energy barrier of
5.17 kcal mol−1 for water-catalyzed SO3 hydration. Compared
with the rates of the SO3 hydration reaction catalyzed by oxalic acid
and water, it can be found that in the upper troposphere the OA-catalyzed SO3 hydration can play an important role in
promoting SO3 hydration. It leads us to conclude that the
involvement of oxalic acid in SO3 hydration to form
H2SO4 is significant in the atmosphere.
