12 Sep 2023
 | 12 Sep 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

pH regulates the formation of organosulfates and inorganic sulfate from organic peroxides reaction with dissolved SO2 in aquatic media

Lin Du, Xiaofan Lv, Makroni Lily, Kun Li, and Narcisse Tsona Tchinda

Abstract. Organic peroxides (OPs) are an important component of dissolved organic matter (DOM), detected in various aquatic media. Despite their unique functions as redox agents in water ecosystems, the complete mechanisms and factors controlling their transformation are not explicitly established. Here, we evaluate the pH effect on the aqueous-phase reaction of three selected OPs (methyl hydroperoxide (MHP), peracetic acid (PAA) and benzoyl peroxide (BZP)) with dissolved SO2. Results show that due to the presence of hydroperoxyl group in their structures, MHP and PAA preferably form inorganic sulfate and organosulfate (methyl sulfate for MHP and acetyl sulfate for PAA) depending on the pH, while BZP exclusively forms organosulfate (benzoyl sulfate) in the pH range investigated. Moreover, it is seen that the ability for PAA to form inorganic sulfate relative to organosulfate is more pronounced, which is supported by a previous experimental observation. The effective rate constants of the transformation of these peroxides within pH 1 – 10 and 240 K – 340 K ranges exhibit positive pH and temperature dependencies, and BZP is seen to degrade more effectively than MHP and PAA. In addition to the pH impact, it is highlighted that the formation of organic and/or inorganic sulfate strongly depends on the nature of the substituents on the peroxy function. Namely, PAA and BZP are more reactive than MHP, which may be attributed to the electron-withdrawing effects of -C(O)R (R = -CH3 and -C6H5 for PAA and BZP, respectively) substituents that activate the peroxy function. The results further indicate that the aqueous-phase degradation of OPs can adequately drive the change in the chemical composition of DOM, both in terms of organic and inorganic sulfate mass fractions.

Lin Du et al.

Status: open (until 24 Oct 2023)

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  • RC1: 'Comment on egusphere-2023-2044', Anonymous Referee #1, 03 Oct 2023 reply

Lin Du et al.


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Short summary
This study explores the pH effect on the reaction of dissolved SO2 with selected organic peroxides. Results show that formation of organic and/or inorganic sulfate from these peroxides strongly depends on their electronic structures, and they are likely to affect the chemical composition of dissolved organic matter in different ways. The rate constants of these reactions exhibit positive pH and temperature dependencies within pH 1 – 10 and 240 K – 340 K ranges.