Identification and Quantification of Isoprene‐Derived Organosulfates in Atmospheric PM _2.5 Based on Synthetic Chemicals

ABSTRACT Rationale Isoprene is the volatile precursor contributing the most to global secondary organic aerosols (SOA). 2‐Methyltetrols organosulfates (2‐MT‐OS) and 2‐methylglyceric acid organosulfates (2‐MG‐OS) are two common organic sulfate species formed from photochemical reactions of isoprene. Accurate measurement of isoprene‐derived OSs is the basis for determining the formation mechanisms of isoprene‐derived SOA and significant for PM 2.5 prediction and pollution mitigation. Methods In this work, 2‐MT‐OS and 2‐MG‐OS were synthesized. The structure of isomers of 2‐MT‐OS and 2‐MG‐OS in ambient aerosols was confirmed based on the spectra analyzed by various instruments. The concentrations of 2‐MT‐OS and 2‐MG‐OS in ambient PM 2.5 aerosols were measured with ultra‐high performance liquid chromatography/electrospray ionization/tandem mass spectrometry (UPLC/ESI/MS/MS). Results The major isomers of 2‐MT‐OS are 3‐methyl‐1, 3, 4‐trihydroxy‐2‐sulfate and 2‐methyl‐1, 3, 4‐trihydroxy‐2‐sulfate. Meanwhile, the major isomer of 2‐MG‐OS is 2‐methyl‐2‐hydroxypropionic acid‐1‐sulfate. The concentrations of 2‐MT‐OS and 2‐MG‐OS in Wenjiang (Chengdu, China) PM 2.5 samples exhibit a strong seasonal variation, reaching their peaks in summer and far higher than in other seasons. The application of synthetic chemicals greatly reduces the analytical errors. The error of the entire analysis process is estimated to be ±14.1%. Conclusions Standard substances are crucial for the quantification of OSs. Enabling the precise measurement of OSs in aerosols provides a critical tool for improving atmospheric models and developing effective strategies to mitigate pollution.