Enhanced oxidation of SO2 by H2O2 during haze events: constraints from sulfur isotopes
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Sulfate aerosols play a critical role in atmospheric chemistry and climate change. However, the mechanism of sulfate formation during haze events remains highly uncertain. In this work, sulfur isotopic compositions of SO<sub>2</sub> and sulfate in PM<sub>2.5</sub> samples collected in Tianjin, China as well as a Rayleigh distillation model are used to constrain SO<sub>2</sub> oxidation pathways. Here, we show the sulfur isotopic compositions of SO<sub>2</sub> and sulfate as well as concentrations of major ions in PM2.5. Our results show that a large sulfur isotope fractionation between SO<sub>2</sub> and sulfate observed in the first stage of haze events may be attributed to an enhanced oxidation of SO<sub>2</sub> by H<sub>2</sub>O<sub>2</sub>. This study highlights the important role of SO<sub>2</sub> oxidation by H<sub>2</sub>O<sub>2</sub> during the haze events. In addition, it is particularly important to note that the sulfur isotopic fractionation factors during haze events dispaly a distinct trend to other periods, indicating that this isotopic approach is useful in understanding the sulfate formation during haze events.
