American Chemical Society
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Multiphase Reactions between Secondary Organic Aerosol and Sulfur Dioxide: Kinetics and Contributions to Sulfate Formation and Aerosol Aging

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journal contribution
posted on 2019-12-02, 18:33 authored by Min Yao, Yue Zhao, Minghao Hu, Dandan Huang, Yuchen Wang, Jian Zhen Yu, Naiqiang Yan
As two of the most important components of atmospheric fine particulate matter (PM2.5), secondary organic aerosol (SOA) and sulfate are tightly coupled in terms of their formation and evolution, yet our knowledge of the kinetics and mechanisms of such coupling remains incomplete. Here we show that the multiphase reaction between α-pinene-derived SOA and sulfur dioxide (SO2) results in efficient production of inorganic sulfate (85–90%) and organosulfates (10–15%) and chemical evolution of SOA. The reactive uptake coefficient of SO2SO2) on α-pinene SOA was determined to be ∼10–4–10–3, depending markedly on the organic peroxide content (implicating an important role of particle-phase peroxides in SO2 oxidation) and also being strongly affected by the aerosol liquid water content. We estimate an aqueous-phase reaction rate constant (kII) of 154–1545 M s–1 for S­(IV) with α-pinene-derived peroxides under weakly acidic conditions (pH ∼ 4–5). These kII values range between those for commercially available cumene hydroperoxide and 2-tert-butyl hydroperoxide and those for the smallest peroxides such as hydrogen peroxide and methylhydroperoxides. A quantitative analysis based on our estimated kII values indicates that the multiphase reaction between SOA and SO2 is an important pathway for sulfate formation and SOA aging that needs to be considered in the modeling of aerosol budgets and impacts on air quality and climate.