Deciphering <sup>13</sup>C and <sup>34</sup>S Isotopes of Organosulfates in Urban Aerosols by FT-ICR Mass Spectrometry
Qiaorong Xie, Sihui Su, Yuqing Dai, Wei Hu, Siyao Yue, Dong Cao, Guibin Jiang, Pingqing Fu
Abstract
Organosulfates (OSs) are some of the important components of secondary organic aerosols in ambient air. However, little is known about the stable carbon and sulfur isotopic compositions of OSs. Here, we identified the isotopic pair 12Cn/13C12Cn–1 and 32Sn/34S32Sn–1 formulas in urban aerosols using ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry. Family series of 694–1649 13C32S OSs and 40–144 12C34S OSs with completely coherent carbon chains were detected, accounting for 37–52% and 2.2–4.5%, respectively, of the observed 12C32S OSs. OSs with detected isotopic peaks have relatively high levels of saturation and high volatilities, especially those containing 34S isotopes with H/C > 1.5. Moreover, the δ13C and δ34S values of OSs were estimated with mean values ranging from −22‰ to −0.87‰ and from −1‰ to 26‰, respectively. Notably, unsaturated OSs might be more enriched with 34S than aliphatic ones. Furthermore, all detected 12C34S OSs are in the low-O/C corridor with a low carbon oxidation state, which are mostly volatile and low-volatile organic compounds with high volatility, implying that they are generated by gas-phase oxidation. These findings represent a first step toward identifying the individual molecules of 13C and 34S isotopic OSs in atmospheric aerosols.