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Updated: Sep 14, 2025

Production and Measurement of Organic Particulate Matter in the Harvard Environmental Chamber
Published on: November 18, 2018
Ionic Strength Inhibits the Multiphase Reaction Rate between Dissolved SO2 and HCHO in Aqueous Aerosols: Implications
Chen Yu1,2, Tengyu Liu1,2,3, Xuguang Chi1,2
1Joint International Research Laboratory of Atmospheric and Earth System Sciences, School of Atmospheric Sciences, Nanjing University, Nanjing 210023, China.
Abstract:
Hydroxymethanesulfonate (HMS) is an important reservoir of particulate sulfur, especially during winter haze episodes. However, the kinetics and mechanisms of HMS formation in aqueous aerosols remain poorly understood. In this study, we investigated the kinetics of the multiphase reaction between sulfur dioxide (SO2) and formaldehyde (HCHO) in aqueous ammonium nitrate aerosol particles buffered by gas-phase NH3 at pH of 4.6 to 5.1 via well-controlled flow tube experiments. We found that high ionic strength inhibits the HMS formation rate in aqueous aerosol particles by up to a factor of 10 compared to that in dilute bulk solutions. Using the new kinetic parameters predicts a negligible formation rate of HMS in aerosol water relative to that in cloud/fog water for typical winter haze conditions in the North China Plain. Our results suggest that atmospheric models should consider the effects of ionic strength on the HMS formation rate in aqueous aerosol particles to better describe the HMS chemistry and evaluate its impact on air quality.
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