Coupling Effect\nof Elemental Carbon and Organic Carbon\non the Changes of Optical Properties and Oxidative Potential of Soot\nParticles under Visible Light

Soot particles, coming from the incomplete combustion\nof fossil\nor biomass fuels, feature a core–shell structure with inner\nelemental carbon (EC) and outer organic carbon (OC). Both EC and OC\nare known to be photoactive under solar radiation. However, research\non their coupling effect during photochemical aging remains limited.\nThis study examines how the optical properties and oxidative potential\n(OP) of wood, coal, and diesel soot particles with varying EC and\nOC levels are affected by exposure to visible light. Wood soot, which\nhas the highest OC content, showed the most significant changes in\nboth optical properties and OP, indicating its highest sensitivity\nto visible light aging. Molecular composition analysis revealed that\nthe reduction of polycyclic aromatic hydrocarbons (PAHs) and methyl-PAHs\nprimarily affects the optical properties, while oxygenated PAHs play\na major role in OP. Combined with the results from reactive oxygen\nspecies detection, it is suggested that EC initiates photoreactions\nby generating superoxide anions, while OC undergoes compositional\nchanges that result in subsequent atmospheric effects. These findings\nenhance our understanding of the photochemical aging process of soot\nparticles and their implications for climate and health.