Molecular characteristics and formation pathways of organosulfates in atmospheric fine particles: A case study in steel industrial city during winter heating period

Air pollution is a critical global issue, posing serious threats to both the environment and human health. Organosulfates play a significant role in haze formation, yet research on their molecular characteristics, pollution dynamics, and atmospheric transformation processes remains relatively limited. In this study, 25 PM_2.5 samples were collected from a steel industrial city during the winter heating period and subjected to comprehensive chemical characterization employing Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). A total of 6348 sulfur-containing compounds were identified, encompassing CHOS₁, CHOS₂, CHON₁S₁, CHON₁S₂, CHON₂S₁, and CHON₂S₂. Analysis showed 42.0–95.2 % of these compounds had O/(4S+3 N)≥ 1, indicating a high prevalence of organosulfates (OSs) and nitrooxy-organosulfates (NOSs) in the samples. OSs and NOSs derived from different precursors showed the following relative proportions: long-chain alkanes (24.9 %), monoterpenes (22.0 %), sesquiterpenes (14.5 %), diterpenes (5.1 %), and naphthalenes (2.5 %). Further analysis of the FT-ICR MS dataset reveals that temperature, O₃, metal ions, relative humidity, and NO₂ were key factors in driving the formation of OSs and NOSs. These results highlight the critical role of acid-catalyzed epoxide ring-opening reactions, esterification processes, and reactions involving sulfate radicals or liquid-phase mechanisms in the formation pathways of OSs and NOSs.