Non-Targeted Quantitative Profiling of the Molecular Composition and Relative Distribution of Water-Soluble Organic Carbon from Biomass Pyrolysis Smoke Using GC×GC-TOF-MS

Biomass pyrolysis produces abundant water-soluble organic carbons (WSOC) that influence the environmental behavior and utilization potential of pyrolysis products. However, the molecular-level formation mechanisms and physicochemical fractionation processes of pyrolytic WSOC remain poorly understood. This study systematically characterized the molecular composition, redox properties, aromaticity and volatility distribution of WSOC generated during biomass pyrolysis to elucidate its formation pathways and aqueous-phase partitioning behavior. The results showed that among the 274 chromatographic peaks detected, 158 were tentatively assigned, with aromatic/phenolic compounds contributing the largest relative peak area (46.5%), followed by hydrocarbons (26.4%) and esters (16.9%). Aromatic/phenolic compounds were dominant, highlighting the important contribution of lignin-derived products, while the occurrence of diverse oxygenated compounds reflects the thermal transformation of cellulose and hemicellulose. Most WSOC molecules exhibited moderate molecular size and unsaturation, with carbon oxidation states (OS-C) ranging from -2 to 0, indicating predominantly reduced characteristics. Volatility analysis revealed a negative relationship between molecular weight and volatility, with volatility-dependent fractionation controlling WSOC enrichment in the aqueous phase. Highly volatile low-molecular-weight compounds were preferentially released into the gas phase, whereas intermediate-volatility polar compounds containing hydroxyl, carbonyl, and ester functionalities were efficiently condensed and retained in the aqueous phase. This study provides molecular-level insights into the coupling between pyrolysis pathways, molecular properties, and aqueous partitioning of WSOC, contributing to improved understanding of biomass pyrolysis-derived soluble organic matter and its potential toxicity and environmental implications.