Multiple sulfur and oxygen isotope compositions in Beijing aerosol

Multiple sulfur isotopes (S-32, S-33, S-34, S-36) and oxygen isotopes (O-16, O-18) in Beijing aerosols were measured with MAT-253 isotope mass spectrometer. The delta S-34 values of Beijing aerosol samples range from 1.68aEuro degrees to 12.57aEuro degrees with an average value of 5.86aEuro degrees, indicating that the major sulfur source is from direct emission during coal combustion. The delta O-18 values vary from -5.29aEuro degrees to 9.02aEuro degrees with an average value of 5.17aEuro degrees, 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 Delta S-33 and CAPE.