| 摘 要： |
Sulfate aerosol is a major fraction of haze, playing an important role in aerosol formation and aging processes. To understand the mechanism of sulfate formations, the characteristics of sulfur isotope composition were determined during different heterogeneous oxidation reactions of sulfur dioxide on the surface of alpha-Fe2O3. Although NH3 was more beneficial to the formation of sulfate, compared with NOX and O-3, S-34 tended to enrich the lighter sulfur isotopes in the presence of NH3. Furthermore, in consideration of the potential competitive effects of NOX, O-3, and NH3 in the heterogeneous oxidation processes, the contributions of each gas were evaluated via Rayleigh distillation model. Notably, the oxidation by NOX contributed 67.5 +/- 10 % of the whole sulfate production, which is higher than that of O-3 (13.3 +/- 10 %) and NH3 (19.2 +/- 10 %) on the basic of the average fractionation factor. The observed delta S-34 values of sulfate aerosols were negatively correlated with sulfur oxidation ratios, owing to the sulfur isotopic fractionations during the sulfate formation processes. Given the isotope mass balance, the overall delta S-34(sulfate) approached the delta S-34(emission) as oxidation of SO2 progressed, suggesting that NOX played a major rather than a sole role in the different heterogeneous oxidation processes of SO2 on the mineral dust surface. |
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