Understanding the catalytic role of oxalic acid in the SO<sub>3</sub> hydration to form H<sub>2</sub>SO<sub>4</sub> in the atmosphere

Abstract

The hydration of SO 3 plays an important role in atmospheric sulfuric acid formation. Some atmospheric species can involve 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 SO 3 . The energy barrier of SO 3 hydration reaction catalyzed by oxalic acid (cTt, tTt, tCt and cCt conformers) is about or below 1 kcal mol -1 , which is lower 15 than the energy barrier of 5.73 kcal mol -1 for water-catalyzed SO 3 hydration. By comparing the rate of SO 3 hydration reaction catalyzed by oxalic acid and water, it can be found that the oxalic acid-catalyzed SO 3 hydration can compete with water-catalyzed SO 3 hydration in the upper troposphere. This leads us to conclude that the involvement of oxalic acid in SO 3 hydration to form H 2 SO 4 is significant in the atmosphere. 20

Pyruvic acid, an efficient catalyst in SO<sub>3</sub> hydrolysis and effective clustering agent in sulfuric-acid-based new particle formation

“…As shown on the energy surface in Fig. 1, though the formation of These energies are respectively within 0.17-1.81 and 0.47-1.06 kcal mol −1 , similar to previously reported values for the same reaction (Hazra and Sinha, 2011;Torrent-Sucarrat et al, 2012;Long et al, 2013;Lv et al, 2019). The slight observed differences likely result from the differences in the computational approaches used in these studies.…”

“…The slight observed differences likely result from the differences in the computational approaches used in these studies. This intermediate overcomes an electronic energy barrier of 5.47 kcal mol −1 to form H 2 SO 4 and Sinha, 2011;Long et al, 2013;Lv et al, 2019). The underlying mechanism is similar to those previously reported for the same reaction and is characterized by two hydrogen atom transfers to and from the second water molecule that acts as the catalyst.…”

“…Despite the demonstrated catalytic effect of water on SO 3 hydrolysis, comparison of previous studies demonstrates that as many as four water molecules could be needed to achieve similar results to those obtained when a single molecule of other species is used as catalyst (Hazra and Sinha, 2011;Torrent-Sucarrat et al, 2012;Long et al, 2013;Lv et al, 2019;Daub et al, 2020;Larson et al, 2000). Some of these species include carboxylic acids, sulfuric acid and nitric acid.…”

“…It should be noted that the prereactive intermediate can also form from the formation of the binary complex between the catalyst and water, followed by its interaction with SO 3 . Recent studies showed that no matter the order in which the binary complex and the pre-reactive intermediate are formed and regardless of the specific reactants involved in the formation of the binary complex, the interactions between SO 3 , H 2 O and the catalyst lead to the formation of sulfuric acid plus catalyst (Weber et al, 2001;Jayne et al, 1997;Torrent-Sucarrat et al, 2012;Hazra and Sinha, 2011;Lv et al, 2019). Assuming equilibrium between the reactants and the complex, and steady-state approximation of the pre-reactive intermediate, the overall rate of Reaction (R2) with catalyst X is…”

“…This reaction is considered as the major loss pathway for SO 3 in the atmosphere. Beside a second water molecule, a number of studies have shown that the SO 3 + H 2 O → H 2 SO 4 reaction can be facilitated by organic and inorganic species including sulfuric acid, formic acid, nitric acid and oxalic acid (Torrent-Sucarrat et al, 2012;Hazra and Sinha, 2011;Daub et al, 2020;Long et al, 2013;Lv et al, 2019). In the presence of these species, the SO 3 + H 2 O reaction can effectively proceed in a near barrierless mechanism, where they also act as bridge for hydrogen atom transfer.…”