Abstract: To explore and optimize the technology and process of photolytic removal of endogenous polycyclic aromatic hydrocarbons（PAHs） in biochar, this study focused on corn stover biochar. Biochar with different particle sizes （>1.0 mm, 0.5~1.0 mm, 0.001~0.5 mm） was prepared, and TiO₂-photocatalytic degradation experiments were conducted to systematically analyze the characteristics of the biochar and the efficacy of degrading and removing endogenous PAHs with different particle sizes. The results showed that the endogenous PAHs content in corn stover biochar was 76.1 mg/kg, predominantly comprising 4-ring and 5-ring PAHs, significantly exceeding the limit value for basic biochar PAHs （20 mg/kg） set by the International Biochar Initiative （IBI）. TiO₂-photocatalysis could significantly reduce the content of endogenous PAHs in biochar. After photocatalytic degradation, the endogenous PAHs content in the three particle sizes of biochar ranged from 3.3 to 14.9 mg/kg, with degradation rates for total PAHs ranging from 55.2% to 95.6%. The maximum degradation rate for high-ring PAHs reached 97.1%, while low-ring PAHs reached 62.0%. The 0.001~0.5 mm particle size biochar exhibited the highest degradation rate of 95.6% after 40 minutes of light exposure, and the toxicity equivalent value decreased from 9.096 mg/kg to 0.088 mg/kg, significantly below the thresholds set by the European Biochar Certification（4 mg/kg） and the International Biochar Initiative（6 mg/kg）. The study demonstrated that TiO₂-photocatalysis effectively degraded endogenous PAHs in biochar of different particle sizes, ensuring the safety of biochar and its products for application in agricultural fields.

Key words: biochar, particle size, polycyclic aromatic hydrocarbons, photocatalytic degradation, equivalent toxicity