Impact of Sulfur-Containing Groups on Aqueous-Phase OH Radical Oxidation – Atmospheric Implications for Small Organosulfur Compounds
DONGER LAI, Thomas Schaefer, Yimu Zhang, Yong Jie Li, Sinan Xing, Hartmut Herrmann, Man Nin Chan, The Chinese University of Hong Kong
Abstract Number: 76
Working Group: Aerosols, Clouds and Climate
Abstract
Organosulfur compounds are known to be important components of atmospheric aerosols and cloud droplets, which have major implications on human health, environment, and climate. The presence of hydrophilic moiety within their molecular structures contributes to their low volatility and significant relevance in atmospheric aqueous-phase chemistry. To date, while their formation mechanisms have become better understood, the transformation pathways, particularly concerning aqueous-phase OH radical oxidation, have remained largely unexplored. In this study, we used laser flash photolysis-long path absorption setup together with competition kinetics methods to investigate the reaction rate constants and temperature effects on aqueous-phase OH radical oxidation of five small organosulfur compounds. Moreover, we also examined the importance of considering the sulfur-containing functional groups (sulfate and sulfite functional groups) on the kinetics by extending the structure-activity relationship (SAR) model to organosulfur compounds. The measured rate constants, ranging from 106 to 108 L mol–1 s–1, and showed a positive temperature dependence across temperature range of 278 to 318 K. Our results also revealed that two sulfur-containing functional groups exhibit a strong deactivating effect on the two adjacent carbon atoms. Specifically, the sulfate group displayed a F value (α-neighboring effect) of 0.22, while the sulfite group exhibited an F value of 0.05. Furthermore, the G parameters (β-neighboring effect) were determined to be 0.44 for the sulfate group and 0.32 for the sulfite group. These values infer that the presence of two sulfur-containing functional groups will lower the hydrogen abstraction rates upon OH radical oxidation and this behavior could be explained by their strong electron-withdrawing natures. Overall, the experimentally determined rate constants obtained bridge a crucial gap in model assessments, and the observed deactivating effect of sulfur-containing functional groups enhance our understanding and predictive capabilities regarding the lifetimes of other organosulfur compounds in the atmosphere.