Compositions and photoactivities of pyrogenic dissolved organic matter in char residues and smoke aerosols during open-air burning of rice straw.

Abstract

Biomass burning produces extensive pyrogenic dissolved organic matter (PyDOM), but the differences in compositions and photoactivities between PyDOM from char residues and smoke aerosols (referred to as PyDOM_char and PyDOM_aerosol) remain poorly understood. Here, we systematically compared the composition and photoactivity of PyDOM_char and PyDOM_aerosol coproduced by open-air burning of rice straw. At the bulk level, PyDOM_aerosol exhibited lower ultraviolet-visible absorption but higher fluorescence intensity than PyDOM_char. Additionally, PyDOM_aerosol had a lower weight-averaged molecular weight (1940 Da) than PyDOM_char (2601 Da). At the molecular level, 3594 and 2734 molecular formulae were identified for PyDOM_aerosol and PyDOM_char, indicating greater chemical diversity of PyDOM_aerosol. PyDOM_aerosol was enriched in aromatic compounds (19.1% vs. 15.8%), aliphatic compounds (12.3% vs. 5.3%), carbohydrate-like compounds (3.9% vs. 0.02%), and N/S-containing molecules (43.9% vs. 20.6%) compared to PyDOM_char. Accordingly, PyDOM_aerosol more effectively promoted ³DOM* and ¹O₂ formation under simulated sunlight. Our findings revealed structural and photoactivity differences between PyDOM_char and PyDOM_aerosol, informing their environmental effects.