Multiple sulfur and oxygen isotope compositions in Beijing aerosol

Multiple sulfur isotopes (³²S, ³³S, ³⁴S, ³⁶S) and oxygen isotopes (¹⁶O, ¹⁸O) in Beijing aerosols were measured with MAT-253 isotope mass spectrometer. The δ ³⁴S values of Beijing aerosol samples range from 1.68‰ to 12.57‰ with an average value of 5.86‰, indicating that the major sulfur source is from direct emission during coal combustion. The δ ¹⁸O values vary from ?5.29‰ to 9.02‰ with an average value of 5.17‰, revealing that the sulfate in Beijing aerosols is mainly composed of the secondary sulfate. The main heterogeneous oxidation of SO₂ in atmosphere is related to H₂O₂ in July and August, whereas H₂O₂ oxidation and Fe³⁺ catalytic oxidation with SO₂ exist simultaneously in September and October. Remarkable sulfur isotope mass-independent fractionation effect is found in Beijing aerosols, which is commonly attributed to the photochemical oxidation of SO₂ in the stratosphere. In addition, thermochemical reactions of sulfur-bearing compounds might be also a source of sulfur isotope anomalies based on the correlation between Δ³³S and CAPE.