Singlet oxygen and triplet state production from primary biomass burning organic aerosol from different fuels: Role of solvent-dependent extraction

Biomass burning organic aerosol (BBOA) is a significant source of brown carbon (BrC), a class of light-absorbing organic compounds that influence climate and atmospheric oxidation chemistry. Certain BrC chromophores act as photosensitizers, producing reactive oxidants such as singlet oxygen (SO) and triplet excited states (TP) upon solar irradiation. However, most studies rely on water extractions, potentially overlooking water-insoluble chromophores that contribute to this photochemistry. In this work, we developed a new organic-solvent extraction method to probe water insoluble chromophores and their ability to sensitize SO and TP, and to understand the ability of multi-phase aerosols to produce these in situ oxidants. Primary organic aerosol (POA) filters from the combustion of beechwood, cow dung, straw, and plastic, collected during the BAMBE campaign, were extracted. We analyzed them using a two-probe photochemical method with furfuryl alcohol (FFA) and syringol as probes to quantify SO and TP steady-state concentrations and quantum yields, respectively, under UVA irradiation. Acetonitrile extraction captured a broader range of chromophores than water, leading to both higher absorbance and enhanced reactive oxidants production. Solvent ratios modulated SO deactivation, with higher acetonitrile content increasing steady-state concentrations through reduced quenching, showing up to 6-fold increase in SO concentrations. Fuel type significantly influenced oxidant yields; beechwood and plastic extracts showed the highest SO and TP production, up to 4.9+/-0.1% for SO and 4.2+/-0.2% for TP. These trends were not solely explained by combustion efficiency, indicating that BrC chemical composition plays a dominant role. Our findings underscore the importance of solvent selection and fuel source in assessing BrC photochemical activity and offer new insight into the oxidative potential of BBOA in atmospheric multiphase environments.