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

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 PyDOMchar and PyDOMaerosol) remain poorly understood. Here, we systematically compared the composition and photoactivity of PyDOMchar and PyDOMaerosol coproduced by open-air burning of rice straw. At the bulk level, PyDOMaerosol exhibited lower ultraviolet-visible absorption but higher fluorescence intensity than PyDOMchar. Additionally, PyDOMaerosol had a lower weight-averaged molecular weight (1940 Da) than PyDOMchar (2601 Da). At the molecular level, 3594 and 2734 molecular formulae were identified for PyDOMaerosol and PyDOMchar, indicating greater chemical diversity of PyDOMaerosol. PyDOMaerosol 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 PyDOMchar. Accordingly, PyDOMaerosol more effectively promoted 3DOM* and 1O2 formation under simulated sunlight. Our findings revealed structural and photoactivity differences between PyDOMchar and PyDOMaerosol, informing their environmental effects.