Molecular-Level Exploration of Pyrogenic Dissolved Organic Matter in Charcoal and Soot Produced Simultaneously by the Combustion of Rice Straw

Biomass burning is a substantial source of pyrogenic dissolved organic matter (PyDOM), yet the molecular-level differences between PyDOM derived from charcoal and soot remain poorly constrained. This study systematically compared the molecular characteristics of PyDOM from charcoal and soot coproduced by the combustion of rice straw under different temperatures and oxygen levels via ultrahigh-resolution mass spectrometry. The molecular composition of charcoal PyDOM showed significant temperature-dependent variations, whereas soot PyDOM exhibited negligible alterations with different temperatures. Moreover, common molecules shared by both PyDOM types were consistently dominated by lignin-like features, indicating a fuel-inherited emission profile that dominated overall composition. By contrast, unique molecules for each PyDOM type retained signatures related to their formation pathways and combustion conditions. PyDOM derived from charcoal showed a strong response to combustion temperature, with the enrichment of more condensed formulas under harsher conditions. PyDOM derived from soot remained relatively stable, featuring highly oxygenated CHO and CHON compounds and a strong presence of lignin- and carbohydrate-like groups. Furthermore, CHOS compounds were consistently more abundant in charcoal than in soot, suggesting charcoal preferentially retains sulfur. This study provides the first molecular-level features for distinguishing PyDOM in coproduced charcoal and soot, offering insights for assessing its environmental effect and behavior.